CN110872775A

CN110872775A - Laundry dryer comprising a heat pump system

Info

Publication number: CN110872775A
Application number: CN201910815713.6A
Authority: CN
Inventors: 弗朗切斯科·卡瓦雷塔; 法比奥·甘巴罗; 詹尼·戈博
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2018-08-30
Filing date: 2019-08-30
Publication date: 2020-03-10
Anticipated expiration: 2039-08-30
Also published as: PL3617392T3; AU2019208187A1; EP3617392A1; EP3617392B1; CN110872775B

Abstract

The present invention relates to a dryer, including: a treatment chamber in which the articles are introduced for treatment with a flow of treatment air; a heat pump system having a refrigerant circuit through which a refrigerant can flow, the circuit comprising: a first heat exchanger that heats a refrigerant; a second heat exchanger that cools the refrigerant; a compressor that pressurizes a refrigerant and circulates the refrigerant through the circuit; and pressure reducing means, the first and/or second heat exchanger facilitating heat exchange between a refrigerant flowing in the circuit and the process air, the refrigerant being a flammable refrigerant, each of the first and second heat exchangers: is a finned tube heat exchanger comprising a tube having a plurality of sections one above the other and a plurality of fins; the method comprises the following three parts: a central portion, a plurality of sections of the tube in contact with the plurality of fins; the first and second end portions, the tubes not in contact with the plurality of fins, the ratio between the total external volume of all the sections of the second and first heat exchangers, including the tubes in contact with the plurality of fins in the central portion, has a value greater than 0.98.

Description

Laundry dryer comprising a heat pump system

Technical Field

The present invention relates to a laundry dryer comprising a heat pump system, wherein the refrigerant of the heat pump circuit comprises a combustible refrigerant.

Background

Currently, heat pump technology in laundry dryers is the most efficient way to dry laundry in terms of energy consumption. In a heat pump system of a laundry dryer, a process air stream flows in a closed process air stream circuit. Furthermore, the heat pump system comprises a closed refrigerant circuit. The process air flow is moved through the laundry chamber by means of the main fan and removes moisture from the wet laundry in the laundry chamber, wherein the laundry chamber is preferably formed as a rotatable laundry drum. The process air flow is then cooled and dehumidified in an evaporator, heated in a condenser and re-entered into the laundry drum again.

The refrigerant is compressed by a compressor, condensed in a condenser, expanded in an expansion device, and then evaporated in an evaporator.

The condenser and the evaporator are thus parts of the process air flow circuit and the refrigerant circuit. The condenser and the evaporator are heat exchangers between the process air flow circuit and the refrigerant circuit.

Typically, the components of the heat pump system are placed in the base of the laundry dryer. The base of the laundry dryer is a part of a casing which, in addition to the base, comprises walls, such as a front wall and a rear wall, and side walls, supported substantially vertically from the base. A drum into which laundry is introduced to dry the laundry is rotatably supported in the housing. In particular, a compressor, an evaporator and a condenser are arranged in the base below the laundry drum.

Typical refrigerants used in heat pumps are Hydrofluorocarbons (HFCs), such as R134a and R407C. However, the use of these refrigerants may have a detrimental effect on global warming because they have a higher Global Warming Potential (GWP), which is a relative measure of the amount of heat trapped in the atmosphere by such refrigerants (in gaseous form) compared to the amount of heat trapped in the atmosphere by a similar mass of carbon dioxide.

Particularly in the past few years, the global warming problem has become more and more serious, and thus alternative refrigerants have been widely researched and used.

As also disclosed by document EP 3066406B 1, hydrocarbon refrigerants such as propane (R-290) and propylene (R-1270) have proven to be good replacements for the above-mentioned high GWP refrigerants in heat pump dryers and laundry dryer electrical appliances. In addition to having negligible GWP, these natural fluids have desirable thermal and physical properties. However, since these alternative refrigerants are flammable and explosive, current regulations currently limit the maximum charge of refrigerant in the wash to prevent problems that may arise due to leakage in the refrigerant circuit.

Disclosure of Invention

The applicant has thus realised that in addition to the choice of refrigerant, the design of the heat exchangers, i.e. the evaporator and the condenser, can also seriously affect the energy consumption, drying efficiency and time consuming performance. The proper configuration of the heat exchanger allows several benefits to be achieved, such as maximizing the heat exchange between the refrigerant and the process air, reducing the pressure drop in both the refrigerant and process air circuits, and reducing the amount of refrigerant required for proper operation of the heat pump. All these benefits allow to save energy, to improve drying efficiency and, together with the choice of refrigerants with low GWP as a whole, to achieve a more "environmentally friendly" dryer.

It is therefore an object of the present invention to provide a dryer with a heat pump system having an improved design aimed at maximizing the proportion of refrigerant charge that effectively participates in heat exchange.

It is another object of the present invention to provide a dryer with a heat pump system having a good performance in terms of efficiency while having a negligible effect on global warming.

According to one aspect, the present invention relates to a dryer, comprising:

a treatment chamber into which the articles are introduced and which is treated with a flow of treatment air;

a heat pump system having a refrigerant circuit in which a refrigerant is flowable, the refrigerant circuit comprising: a first heat exchanger in which the refrigerant is heated; a second heat exchanger in which the refrigerant is cooled; a compressor that pressurizes and circulates a refrigerant through a refrigerant circuit; and a pressure reducing device, said first heat exchanger and/or said second heat exchanger facilitating heat exchange between said refrigerant flowing in said refrigerant circuit and said process air, the refrigerant being a flammable refrigerant,

wherein each of the first and second heat exchangers:

is a finned tube heat exchanger comprising a tube and a plurality of fins, the tube having a plurality of sections one above the other;

the method is divided into the following three parts: a central portion, wherein the plurality of sections of the tube are in contact with the plurality of fins; and a first end portion and a second end portion, wherein the tube is not in contact with the plurality of fins,

and wherein the ratio between the total external volume (TEV2) of all sections of the second heat exchanger, including tubes in contact with the plurality of fins in the central portion, and the total external volume (TEV1) of all sections of the first heat exchanger, including tubes in contact with the plurality of fins in the central portion, has a value greater than 0.98.

Hereinafter, the term "dryer" refers to both a dryer that performs only drying and a combined washing and drying machine. In particular, it also refers to a washing and drying machine for washing, spinning/centrifuging, and finally tumble drying laundry.

Dryers comprise "treatment chambers", such as washing and/or drying chambers (commonly called drums) in which the laundry can be located for washing and/or drying; the chamber may be rotatable about a chamber axis during washing and/or drying operations. Furthermore, the dryer may be a front-loading dryer, meaning that the axis of rotation of the treatment chamber is positioned in a horizontal manner or slightly inclined with respect to the horizontal, or a top-loading laundry dryer, in which the axis of the treatment chamber is substantially vertical.

In a preferred embodiment, the dryer is a front loading laundry dryer.

The dryer preferably comprises a housing, preferably comprising a front wall, a rear wall, side walls, a top wall and a base section or base. The front or top wall may include a user panel to command the operation of the dryer by a user. The housing defines a boundary between an interior volume of the dryer and an exterior of the dryer. Furthermore, preferably, the casing comprises a door that can be opened to introduce the laundry into the laundry chamber, the door being hinged to the casing itself, for example: in the case of front loading dryers, the door is hinged to the front wall; alternatively, in the case of a top loading dryer, the door may be hinged to the top wall.

The base has the function of housing, among other things, several components of the dryer, such as a portion of the drying air duct, a heat exchanger, a motor for rotating the chamber, a fan, etc. Furthermore, the base also has the function of supporting some of the walls of the housing.

The base may be implemented with any material; preferably, it is realized in a plastic material. Furthermore, the walls of the housing may also be realized in any material.

The base is usually located on the ground on which it rests when the machine is in a standard operating condition.

For example, the base may be divided into an upper case and a lower case. The upper and lower shells define the outer boundary of the base, separating the "interior" volume of the base from the "exterior" of the base.

In heat pump dryers, the process chamber is part of a process air circuit, in particular a closed loop air circuit, for example in the case of a condensation dryer; or, in the case of a vented dryer, an open circuit, which in both cases includes an air duct for directing a flow of air to dry the load. Two opposite ends of the process air circuit are connected to the process chamber. The hot dehumidified air is fed into the treatment chamber, flows over the laundry, and the resulting humid cool air is exhausted from the treatment chamber. The humid air stream rich in water vapour is then fed into the evaporator of the heat pump, where the moist hot process air cools and the moisture present in the process air condenses. The resulting cold dehumidified air is then either vented outside of the appliance in its environment or the air continues to travel in a closed loop circuit. In the second case, the dehumidified air in the process air circuit is then heated by means of the condenser of the heat pump before re-entering the drying chamber, and repeatedly passes through the entire circuit until the end of the drying cycle. Alternatively, ambient air enters into the drum from the surroundings via an inlet duct and is heated by the condenser of the heat pump before entering the drying chamber. In the case of laundry dryers, different circuits are known in the art.

The heat pump of the dryer includes a refrigerant circuit in which a refrigerant can flow, and a first heat exchanger or evaporator, a second heat exchanger or condenser, a compressor and a pressure reducing device are connected via piping. The refrigerant is pressurized by the compressor and circulated through the system. On the discharge side of the compressor, the hot high-pressure steam is cooled in a condenser until it condenses into a high-pressure, medium-temperature liquid, which heats the process air before it is introduced into the drying chamber. The condensed refrigerant then passes through a pressure reduction device such as an expansion device, e.g., a choke, a valve, or a capillary tube. The low-pressure liquid refrigerant then enters an evaporator, where the fluid absorbs heat and evaporates due to the heat exchange with the heat-treated air leaving the drying chamber. The refrigerant then returns to the compressor and the cycle repeats.

For compressing the refrigerant, the compressor comprises an electric motor, which is usually powered by an electric current, for example from the mains.

The first heat exchanger and the second heat exchanger are located within the process air circuit for heat exchange with the process air. The process air circuit defines a bottom portion or bottom section. The second heat exchanger abuts a bottom part or bottom section of the process air circuit. Hereinafter, the "horizontal plane" used as the reference plane is defined as follows. The second heat exchanger is in contact with the bottom section of the process air duct at least at three points. These three points define a plane which is the horizontal plane of the frame of reference of the present description. If there are more than three points of abutment between the second heat exchanger and the bottom section/portion of the process air duct, the horizontal plane is a plane comprising most of the connection points.

This plane is generally "horizontal" in the general sense, that is, it is parallel to the floor on which the dryer is placed, which is generally considered "horizontal".

However, there are situations where the plane defined above is not horizontal in the general meaning of the term, e.g. it is inclined with respect to the floor on which the dryer is located (i.e. it forms an angle). This may occur, for example, because the floor is uneven and the dryer must be adjusted, for example, using "height adjustable legs" provided by standards to stabilize on uneven floors. Alternatively, the heat exchanger may indeed be positioned obliquely with respect to the ground.

Preferably, the first heat exchanger and/or the second heat exchanger are located in a base of the dryer.

In the present invention, the refrigerant used in the heat pump circuit is a flammable refrigerant and preferably a hydrocarbon refrigerant. While maximum charge limits are specified by current regulations for flammable refrigerants, these refrigerants have desirable thermal and physical properties for heat exchangers, and most importantly, they have low GWP, which means that the impact on global warming is negligible.

The first and second heat exchangers of the present invention are finned tube heat exchangers comprising a tube having a plurality of sections one above the other and a plurality of fins. The total length of the first and second heat exchangers is defined along the length direction. The total length of the first heat exchanger may be equal to or different from the total length of the second heat exchanger.

Finned tube heat exchangers are the most common type of heat exchanger used to transfer heat between a fluid (refrigerant flowing inside the tubes) and air (drying process air flowing over the fins and outside the tubes).

Such heat exchangers typically comprise a continuous curved tube having straight portions connected by U-shaped bent sections, along which fins are mounted transversely. The fins are provided with holes or apertures of suitable shape and size to allow assembly transversely along the continuous curved tube. Furthermore, the fins are suitably designed so that a contact with a suitable interference is ensured between the tubes and the holes of the fins. The contact between the portions of the tubes and the fins may be random and/or dispersed, as the installation process may vary the mechanical tolerances and the relative positioning of the tubes and the fins mounted thereon.

Alternatively, such a heat exchanger may comprise individual straight tubes inserted in circular holes or bores of transverse fins, which tubes are then expanded to provide suitable contact with interference between the tubes and the circular holes of the fins. Then, the ends of the straight tubes are connected in pairs by means of short U-shaped bent sections, thereby ensuring the continuity of the refrigerant circuit. The U-bend section is typically welded or soldered to a straight tube.

In any case, there are multiple pipe sections, all of which are portions of the same pipe or different individual pipes. For the sake of simplicity, a single "tube" is used below to denote a continuous curved tube and an assembly of tubes comprising a plurality of straight tubes stacked one above the other and stacked substantially parallel to each other and connected at their ends by suitable connecting sections, such as the above-mentioned U-shaped bending sections welded or soldered to the ends of the straight tubes.

Preferably, the tube sections are all parallel to each other. These tube sections may correspond to "straight" portions of the tube that extend generally in a single direction without bending or kinking. Preferably, the sections of the tubes are horizontal, that is to say they are parallel to the horizontal plane.

In both of the above-described configurations, such finned tube heat exchangers typically include a central portion that, for example, generally corresponds to the length of the straight tube sections. The central portion is the portion through which the process air flows, and thus heat exchange takes place at the central section between the refrigerant flowing in the sections of tubes and the process air. Furthermore, finned tube exchangers comprise lateral portions on two opposite sides of a central portion, comprising U-shaped bent tube sections connecting the straight tube portions and not participating in (or participating minimally in) heat exchange, since the process air is not intended to flow or only minimally flows through them.

Although such lateral portions are not useful in terms of heat exchange, they are necessary for constructional reasons, since the straight tube sections of the central portion must be connected to ensure continuity of the refrigerant circuit.

The minimum length of the lateral portions depends on the minimum bend radius of the tube, which in turn depends on the size and flexibility of the tube material, and on the space required to weld or solder the U-bend when using a plurality of individual straight tubes. According to standard techniques, for heat exchangers, the length of the lateral portions (sum of the two lengths) is between 40mm and 60 mm. This length is taken along the length direction, which is better defined hereinafter.

In use, the entire heat exchanger is filled with refrigerant. Therefore, when referring to finned tube heat exchangers, it is necessary to consider the portion of the refrigerant that does not participate in heat exchange, i.e., the portion of the refrigerant that flows in the lateral portions. This is of particular concern when flammable and explosive refrigerants such as the hydrocarbons described above are used, as their maximum charge is limited. The maximum filling can be set, for example, in a specification.

This maximum charge limit, in turn, may affect the drying performance of the clothes dryer, since the best performance of conventional clothes dryers is typically observed for higher refrigerant charges.

The reference to the horizontal plane defined above allows to define two orthogonal directions: length direction and thickness direction. Both directions are horizontal, that is to say they are parallel to the horizontal and form an angle of approximately 90 ° with one another.

Hereinafter, "length direction" refers to a horizontal direction substantially parallel to a plane containing at least two of a plurality of pipe sections stacked one on top of the other. The plane is preferably a vertical plane, i.e. a plane perpendicular to the horizontal plane. Thus, hereinafter, "length" means a measurement taken along the length direction.

The first heat exchanger and the second heat exchanger of the present invention are divided into three sections: a central portion, wherein the plurality of sections of tube are in contact with the fins; and a first end portion and a second end portion, wherein the tube is not in contact with the fin.

Furthermore, the external volume of all the sections of the tube included in the central portion in contact with the fins of the first or second heat exchanger (in short, the total external volume or TEV) can also be defined.

TEV＝π*(De/2)^2*Nt*Le；

Where Nt is the number of segments;

le — the length of the section of tube in the central region;

de-the outer diameter of the section of tube.

In the case where the diameters of all tubes or sections are not the same, the sum of the individual volumes is given by the sections of tubes having different diameters. The same applies if the lengths of all tube sections differ.

Preferably, the outer diameter De is comprised between 4mm and 10 mm.

The length of a section of the tube is calculated as the length along its extension. Typically, the sections of the tube are straight, so that their length is equal to the extension of the tube from one end to the other. If the section of tube is substantially horizontal (if the section of tube extends horizontally), this may correspond to the length of the central portion in the length direction.

If the section of the tube has a circular cross section, the above-mentioned volume is calculated in this way. If the cross-section of the tube is not circular, the volume is:

TEV (cross section of the pipe section) Nt Le.

Preferably, the number of segments is comprised between 20 and 70.

Preferably, the length Le of the section is comprised between 200mm and 450mm, more preferably between 200mm and 300 mm. Preferably, the length of the section of tube (length in the central part of the tube) is equal to: le >280mm, preferably Le >300mm, more preferably Le >320mm, even more preferably Le >350 mm.

Preferably, the thickness of the tube (i.e. of the outer wall of the tube) is comprised between 0.2mm and 0.8 mm.

The TEV can be defined in the same way for the evaporator (called TEV1) and for the condenser (TEV 2). According to the invention, the ratio TEV2/TEV1 is > 0.98. Preferably TEV2/TEV1>1.1, more preferably TEV2/TEV1>1.3, even more preferably TEV2/TEV1> 1.5. However, TEV2/TEV1<2.5 is preferred.

Inside the heat pump circuit, when the compressor is on, the majority of the refrigerant charge is located inside the condenser, since in this heat exchanger the refrigerant is at high pressure and, for a part of it that is in its liquid state, it has a higher density level than the gaseous phase present in the evaporator.

Conversely, the evaporator operates at low pressure and in which the refrigerant is in a liquid-vapor mixture, the superheated vapor being in the relevant part of the heat exchanger and therefore having a low density level.

In view of the charge limitations of flammable refrigerants, it is important to limit the volume occupied by the refrigerant within the heat exchanger.

Possible solutions for reducing the volume occupied by refrigerant in the heat exchanger are as follows. A first solution is to reduce the number of sections of tubes present in the heat exchanger. Alternatively, the length of the section of the tube may be reduced. As a third possibility, the inner diameter of the section of the tube may be reduced.

Such a solution effectively reduces the volume available for refrigerant, but may compromise the performance of the heat pump due to insufficient heat exchange.

For example, a reduction in either the outside or inside diameter of the tube reduces the internal volume of the tube, which is desirable, but it also reduces the surface of the section of the tube that comes into contact with the process air to provide heat exchange. This can be compensated by adding more fins, but the heat exchange efficiency between the refrigerant and the fins is lower than the heat exchange efficiency with the tube portions. The inner and outer diameters of the tube are related to each other: the tubes in a standard heat exchanger typically have a "standard" thickness, which is constant and depends on the material from which the tubes are formed.

Furthermore, in a standard dryer, the process air leaving the drum is filtered before entering the evaporator. The process air may include fluff and/or other undesirable material that inadvertently detaches from the laundry during drying. To filter the air to remove undesired materials, a filter is typically positioned before the evaporator. More than one filter may also be used. However, these filters are not able to remove all the undesired material from the process air and it is not uncommon that some fluff may remain in the process air stream. For this reason, too many fins may exacerbate the air pressure reduction and the space between the fins, especially at the evaporator, cannot be reduced too much due to the risk of clogging by fluff not captured by the air filter.

Therefore, a tradeoff between design constraints due to charging limitations and good heat exchange is desirable.

Generally, the amount of refrigerant in the condenser is 60% to 80% of the total amount, and the amount of refrigerant in the evaporator is 10% to 30% of the total amount. Thus, although the majority of the refrigerant is mainly in the condenser, the share in the evaporator is also not negligible, especially when the maximum amount of available refrigerant is limited. Furthermore, the condenser cannot have a too small volume, since otherwise the liquid refrigerant cannot be properly heat exchanged with the process air.

Considering that the efficiency or efficiency of a heat exchanger increases with its size (but also the need for charging), and considering that the condenser has a higher impact on the compressor consumption than the evaporator due to a larger refrigerant charge, the present invention consists in satisfying the need for a sufficiently large condenser to provide a proper heat exchange between the drying air and the condenser, wherein the size of the evaporator is "small" without unduly affecting their heat exchange performance due to the limitation of the total refrigerant charge circulating in the heat pump circuit.

Therefore, due to the ratio defined in the present invention, the total volume of the condenser is greater than the total volume of the evaporator, while still ensuring a suitable heat exchange efficiency between the drying air and the refrigerant in both heat exchangers.

Preferably, the first heat exchanger and/or the second heat exchanger are coil heat exchangers and wherein the tubes in the end portion comprise bends. In this embodiment, the end portion is specifically shaped as a U-bend section.

Preferably, the external diameter of the tubes of the first and/or second heat exchanger is comprised between 4 and 10 mm. More preferably, it is comprised between 5mm and 8 mm. When low refrigerator charging is involved, the upper limit value of this size interval is advantageously chosen to limit the internal volume of the tubes of the second heat exchanger, so that for the same amount of refrigerant, a higher density of refrigerant circulating in the tubes is obtained, which in turn increases the cooling capacity of the second heat exchanger and reduces the occurrence of pressure losses. In another aspect, a lower limit is provided to ensure a minimum acceptable cooling capacity of the heat exchanger. The internal volume of the tube is referred to below. The volume concerned is only the volume comprised in the central portion of the second heat exchanger (i.e. the sum of the internal volumes of all portions of the tubes comprised in the central portion of the second heat exchanger). The internal volume can be measured as:

inner volume (volume occupied by the outer wall of the TEV tube)

Preferably, the dryer comprises a process air circuit comprising said process chamber and a base on which said heat pump is located, the process air circuit comprising a base portion comprising a process air duct in which the first and second heat exchangers are located, wherein said central portion of said first and/or second heat exchanger is completely housed in said base process air duct. Thereby, the entire central part of the condenser is used for heat exchange, so that the maximum available heat exchange surface is used.

Preferably, the flammable refrigerant comprises propane or propylene. Propane and propylene are highly efficient natural refrigerants with minimal levels of harmful emissions.

Preferably, the first and/or second heat exchanger defines an overall length in a length direction, the end portions being located at opposite sides of the central portion in the length direction, the length direction being substantially perpendicular to a main flow direction of the process air as it passes through the first and/or second heat exchanger. Thus, in this embodiment, the first heat exchanger and/or the second heat exchanger have a so-called "cross-flow configuration", which is particularly suitable for low pressure applications such as laundry dryers, and is generally suitable when large volume steam flows are involved and a low pressure drop is required. Moreover, this configuration allows the size of the heat exchanger to be reduced.

Preferably, the first heat exchanger and/or the second heat exchanger define a thickness in the thickness direction, and wherein the thickness is comprised between 40mm and 150 mm. After reaching a certain thickness, the overall efficiency of the heat pump is not significantly improved, as the pressure drop becomes significant. The range chosen is therefore a compromise between a "small" heat exchanger, thus using less refrigerant, and a good heat exchange.

Preferably, the first and/or second heat exchangers define an overall length along the length direction, the end portions being located at opposite sides of the central portion along the length direction, the overall length being less than 550 mm. The total length Lt is the sum of the central length Le plus the two lateral lengths Lc. Dryers are usually of standard acceptable size and this maximum length is optimal for using all available space. For example, the standard maximum dimensions of a dryer are 60cm x 60cm (length x thickness) in europe, whereas the base of a dryer is typically a few centimeters short.

Preferably, the base comprises an upper shell and a lower shell, the base process air duct being formed by the upper shell and the lower shell. A simple assembly of the machine is achieved.

Preferably, the high pressure of the refrigerant in the steady state phase of the heat pump cycle is comprised between 19 bar and 38 bar.

Preferably, the low pressure of the refrigerant in the steady-state phase of the heat pump cycle is comprised between 7 bar and 17 bar.

Further, the larger the exchange area of the condenser, the lower the condensation pressure of the refrigerant. Thus, increasing the size of the condenser, the same air flow at the same temperature at the outlet of the condenser can be obtained at a lower refrigerant condensation pressure. This is useful to improve performance.

The mentioned pressures are measured in this way:

when the cycle of the heat pump is in steady state, the low pressure of the refrigerant at the inlet of the compressor is measured between the evaporator and the compressor.

When the cycle of the heat pump is in steady state, the high pressure of the refrigerant at the outlet of the compressor is measured between the compressor and the condenser.

In the case of propane as refrigerant fluid:

preferably, the high pressure in the steady state phase of the cycle is comprised between 19 and 32 bar, preferably from 21 to 29 bar.

Preferably, the low pressure in the steady-state phase of the cycle is comprised between 7 and 14 bar, preferably from 9 to 12 bar.

In the case of propylene as the refrigerant fluid:

preferably, the high pressure of the steady-state phase of the cycle is comprised between 23 and 38 bar, preferably from 25 to 35 bar.

Preferably, the low pressure in the steady-state phase of the cycle is comprised between 8 and 17 bar, preferably from 11 to 15 bar.

The steady state phase is defined as follows. The entire heat pump cycle can be divided into a first transient phase and a steady-state phase. The first transient phase starts at the beginning of the heat pump cycle and may last up to 60% of the total duration of the cycle, preferably up to 45% of the total duration of the cycle, more preferably up to 30%. During the transient phase, the pressure gradually increases (a single pressure measurement may still fluctuate, but the general trend of the pressure is an increasing trend). During the steady state phase, the pressure is substantially constant (in this case, a single measurement will also fluctuate, but the overall trend is a substantially constant pressure value). The steady state phase begins at the end of the transient phase and may continue until the end of the heat pump cycle. The steady state phase satisfies the following conditions for its duration.

The first condition is that the steady state phase contains the highest pressure of the entire phase.

The second condition relates to its "constant". The pressure is measured at a given frequency, and therefore the pressure curve during the heat pump cycle includes a plurality of points, one point for each sampling time. These pressure values are represented by X_iN, where N depends on the length of the cycle.

During the steady-state phase of the heat pump cycle, the average of all Xi during the steady-state phase is taken and called the average X_averAll points X in the steady-state phase_iIs such that at least 90% of:

|X_aver-X_i|<7bar

preferably, the first and second electrodes are formed of a metal,

|X_aver-X_i|<5bar

more preferably still, the first and second liquid crystal compositions are,

|X_aver-X_i|<2bar

the steady state phase is defined as above, and then it is verified whether:

when it becomes high pressure (measured at the compressor outlet, between compressor and condenser)

23bar<X_aver<38bar，

When it becomes low (measured at the compressor inlet, between evaporator and compressor)

8bar<X_aver<17bar。

Preferably, the amount of flammable refrigerant contained in the heat pump refrigerant circuit is comprised between 80g and 300 g. More preferably, the amount of flammable refrigerant is comprised between 100g and 250 g. More preferably, the amount is comprised between 120g and 200 g.

The amount of flammable refrigerant may be set by law or may depend on the country. This amount is relatively "low" to minimize the risk of combustion.

Preferably, the tube is realized in copper, aluminum or a combination of both. These materials have good thermal expansion, internal pressure resistance, corrosion resistance and fatigue strength in addition to excellent thermal conductivity. Preferably, the tube is realized in one of aluminum, or alloys thereof. The wall thickness of the Al tube is larger than that of the Cu tube, since the mechanical properties of Cu and Al ensure similar mechanical resistance. This means that if the outer diameters of the Cu pipe and the Al pipe are the same, the inner diameter of the Al pipe is smaller than that of the Cu pipe. In view of the cost of raw materials, the use of Al tubes instead of Cu tube heat exchangers has economic advantages despite the large amount of material. The small inner diameter means that the inner volume of the heat exchanger is small, which is particularly useful in the case where the charge amount of flammable refrigerant is limited.

The reduction of the inner diameter, thus maintaining the same number of tube sections and length of the heat exchanger, can be achieved not only by increasing the thickness of the wall, but also by reducing the outer diameter of the tubes. However, the large outer diameter of the tubes increases the turbulence of the air flowing through the exchanger. This high turbulence increases the heat exchange coefficient of the air and thus increases the heat exchanged by the exchanger.

Therefore, given an outer diameter, it is preferable to use an Al tube to reduce the overall internal volume.

Preferably, the compressor is a rotary compressor.

Preferably, the module of the temperature difference between the temperature of the process air at the outlet of the second heat exchanger and the condensation temperature is lower than 10 ℃. More preferably, it is less than 7 deg.C, even more preferably less than 5 deg.C. This means that the temperature of the process air at the outlet of the condenser, called Tpc, and the condensation temperature Tcond of the refrigerant satisfy the following equation:

|T_pc-T_cond|<10℃

more preferably still, the first and second liquid crystal compositions are,

|T_pc-T_cond|<5℃

the larger the exchange area of the condenser, the smaller the temperature difference between the air at the outlet of the condenser and the condensing temperature of the refrigerant. Thus, increasing the size of the condenser, the same air flow at the same temperature at the outlet of the condenser can be obtained at a lower condensation temperature of the refrigerant. This is useful to improve performance.

The temperature was measured at the outlet of the condenser. The following are possible: consider a plane parallel to the elevation of the condenser from which the process air exits. The distance of the plane from the facade is comprised between 0cm and 10 cm. In the "standard" parallelepiped shape of the heat exchanger, the median line of the two sides of the condenser defining the vertical plane is taken on this plane. The measurement can be made at the intersection (center) or at a plurality of points (at least 4) along the midline, which are less than 10cm from the intersection of the two midlines.

Drawings

Other advantages of the invention will be better understood by reference, without limitation, to the accompanying drawings, in which:

figure 1 is a perspective view of a laundry dryer realized according to the present invention;

fig. 2 is a perspective view of the laundry dryer of fig. 1, with elements of the casing removed to show some internal components;

figure 3 is a perspective view of an exploded configuration of the base of the dryer of figure 1 or 2;

figure 4 is a perspective view of the base of figure 3, with all the elements housed in the base removed;

figure 5 is a top view of the base of figure 3;

figure 6 is a perspective view of a heat exchanger, an element of the dryer of figure 3;

figure 7 is a front view of the heat exchanger of figure 6;

figure 8 is a top view of the heat exchanger of figures 6 and 7;

figure 9 is a side view of the heat exchanger of figures 6 to 8;

figure 10 is a simplified view of figure 9; and

figure 11 is a graph showing the high pressure (upper curve) and low pressure (lower curve) measurements of the time and pressure of the refrigerant in the heat pump cycle.

Detailed Description

With reference first to fig. 1 and 2, a laundry dryer realized according to the present invention is generally indicated with 1.

The dryer 1 includes: an outer box or casing 2, preferably, but not necessarily, parallelepiped in shape; and a drying chamber, such as a drum 3, for example having the shape of a hollow cylinder, to contain the laundry to be dried, typically clothes and apparel. The drum 3 is preferably rotatably fixed to the housing 2 such that the drum 3 can rotate about a preferably horizontal axis R (in an alternative embodiment, the axis of rotation may be inclined). Access to the drum 3 is obtained, for example, by means of a door 4, the door 4 preferably being hinged to the casing 2, the door 4 being able to open and close an opening 4a realised on the casing itself.

In more detail, the casing 2 generally comprises a front wall 20, a rear wall 21 and two side walls 25, all mounted on a base 24. Preferably, the base 24 is made of a plastic material. Preferably, the base 24 is molded by an injection molding process. Preferably, the door 4 is hinged on the front wall 20 to access the drum. The casing defines by its

walls

20, 21, 25 the volume of the laundry dryer 1. Advantageously, the base 24 comprises an upper shell portion 24a and a lower shell portion 24b (visible in figures 3 to 5 detailed below).

Dryer 1, and in particular base 24, is typically located on the floor.

Laundry dryer 1 also preferably comprises an electric motor assembly 50 for rotating drum 3 on command along its axis inside cabinet 2. The motor 50 includes a shaft 51, the shaft 51 defining a motor rotation axis M.

Furthermore, laundry dryer 1 may comprise an electronic central control unit (not shown) which controls electric motor assembly 50 and other components of dryer 1 so as to carry out on command one of the user-selectable drying cycles, preferably stored in the same central control unit. The program and other parameters of laundry dryer 1 or alarm and warning functions may be set and/or visualized in control panel 11, control panel 11 preferably being implemented in the top part of dryer 1, such as above door 4.

With reference to fig. 2, the rotatable drum 3 comprises a hood 3c, preferably having a substantially cylindrical tubular body, preferably made of metal material and arranged inside the casing 2 and apt to rotate about a general rotation axis R. The hood 3c defines a first end 3a and a second end 3b, and the drum 3 is arranged so that the first end 3a of the hood 3c faces the laundry loading/unloading opening and the door 4 realized on the front wall 20 of the casing 2, while the second end 3b faces the rear wall 21.

The drum 3 may be an open drum, i.e. both the first end 3a and the second end 3b are open; alternatively, the drum 3 may comprise a rear wall (not shown in the drawings) fixedly connected to the hood and rotating together with the hood.

For rotation, a support element for rotation of the drum is also provided in the laundry dryer of the present invention. Such support elements may comprise rollers at the front and/or rear of the drum and, or alternatively, a drum shaft (the shaft not being shown in the drawings) connected to the rear end of the drum. For example, in fig. 2, a roller 10 connected to the base via a bracket 101a and a roller 10 connected to the rear wall 21 via a boss 101 are depicted. Any support element for the rotation of the drum about the axis R is included in the present invention.

Additionally, the dryer 1 comprises a process air circuit comprising the drum 3 and a process air duct 18, the process air duct 18 being depicted as a plurality of arrows showing the path flow of the process air flow through the dryer 1 (see fig. 3 and 4). In the base 24, a part of the process air duct 18 is formed by the connection of the upper case 24a and the lower case 24 b. The process air duct 18 is preferably connected with its opposite ends to two opposite sides of the drum 3, namely a first end 3a and a second, rear end 3b of the hood 3 c. The process air circuit also includes a fan or blower 12 (partially shown in fig. 5).

The dryer 1 of the present invention additionally comprises a heat pump system 30, which heat pump system 30 comprises a second heat exchanger (also called condenser) 31 and a first heat exchanger (also called evaporator) 32 (see fig. 3). The heat pump 30 further comprises a closed refrigerant circuit (partially shown) in which a refrigerant fluid flows, cools, and may condense, release heat in correspondence with the condenser 31, and heat up, absorb heat in correspondence with the evaporator 32, when the dryer 1 is in operation. The compressor 33 receives gaseous refrigerant from the evaporator 32 and feeds the condenser 31, closing the refrigerant cycle. Hereinafter, the heat exchangers are referred to as an evaporator and a condenser, or a first heat exchanger and a second heat exchanger, respectively. In more detail, the heat pump circuit connects the evaporator 32 to the condenser 31 via a compressor 33 by means of a line 35 (see fig. 3). The outlet of the condenser 31 is connected to the inlet of the evaporator 32 via an expansion device (not visible) such as a choke, a valve or a capillary tube.

The refrigerant present in the closed refrigerant circuit of the heat pump 30 is propane in the preferred embodiment.

Preferably, in correspondence of the evaporator 32, the laundry dryer 1 of the present invention may comprise a condensation water container (also not visible) which collects condensation water generated inside the evaporator 32 by condensation of excess moisture in the flow of process air coming from the drying chamber (i.e. the drum) 3 when the dryer 1 is in operation. The container is located at the bottom of the evaporator 32. Preferably, the collected water is fed into a reservoir located in correspondence of the highest portion of dryer 1 through a connection pipe and a pump (not shown in the drawings) to facilitate comfortable manual drainage of the water by the user of dryer 1.

The condenser 31 and the evaporator 32 of the heat pump 30 are positioned in correspondence with the process air duct 18 formed in the base 24 (see fig. 3).

In the case of a condensing dryer as depicted in the drawing, in which the process air circuit is a closed loop, the condenser 31 is located downstream of the evaporator 32. The air leaving the drum 3 enters the duct 18 and reaches the evaporator 32, which evaporator 32 cools and dehumidifies the process air. The dry cold process air continues to flow through the duct 18 until it enters the condenser 31, in which condenser 31 the dry cold process air is heated by the heat pump 30 before re-entering the drum 3.

It should be understood that in the dryer 1 of the present invention, an air heater such as an electric heater may be present in addition to the heat pump 30. In this case, the heat pump 30 and the heater may also work together to speed up the heating process (thereby reducing the drying cycle time). In the latter case, the condenser 31 of the heat pump 30 is preferably located upstream of the heater. Appropriate measures should be provided to avoid the electric heater from melting the plastic parts of the dryer 1.

Further, referring now to fig. 4 and 5, in the base, the process air duct 18 comprises a duct formed by an upper shell 24a and a lower shell 24b, having an inlet 19in which process air is received from the drum 3 and an outlet 19 which leads process air out of the base 24. Preferably, the duct is formed as two single pieces joined together and belonging to the upper and lower shells 24a, 24b between the inlet 19in and the outlet 19, and comprises a first portion 29 and a second portion 28. Seats for positioning the first heat exchanger 32 and the second heat exchanger 31 are formed in the first portion 29 of the duct. Preferably, the heat exchangers 31, 32 are placed one after the other, the second heat exchanger 31 being located downstream of the first heat exchanger 32 in the flow direction of the process air. Furthermore, the second portion 28 directs the process air exiting from the second heat exchanger 31 towards the outlet 19 of the base.

Thus, a heat exchanger, in particular a condenser 31, is positioned in the first portion 29 of the base 24. The condenser 31 is in contact with the lower shell 24b of the base 24, which forms a flat portion 29a for abutting against the condenser. The point of contact between the base conduit 18 and the condenser defines a plane designated P in figure 5. The plane P is considered a horizontal reference plane. In this case, considering dryer 1 and flat portion 29a of the base, which are located on a flat ground, horizontal plane P is parallel to the ground and defined by standard (X, Y) coordinates. However, the plane P may be inclined with respect to the ground.

Given the P plane, a vertical Z direction may be defined, so that a vertical plane, e.g. plane V of fig. 4, may also be defined as a plane perpendicular to plane P.

A detailed illustration of the heat exchanger 31 or 32 is given in fig. 6 to 8. The heat exchangers 31, 32 comprise a tube or pipe 40 having an inlet 40a and an outlet 40b and comprising straight parallel sections, all indicated 41, and bends, all indicated 42, connecting the straight parallel sections 41 to each other. The sections 41 are one above the other, that is to say some of the sections 41 lie on the same vertical plane. The heat exchangers 31, 32 thus define vertical planes, one parallel to the other or others, which connect different groups of sections 41. In the same way, several sections may be located on the same horizontal plane, i.e. a group of sections is located on a plane parallel to the P-plane. The heat exchangers 31, 32 thus define horizontal planes parallel to one another, said horizontal planes connecting different groups of sections 41. The distance between two nearest neighboring sections 41 belonging to the same horizontal plane is referred to as the row pitch of the sections in the same horizontal plane. The distance between two nearest adjacent sections belonging to the same vertical plane is referred to as the pitch of the sections in the same vertical plane. This is schematically depicted in fig. 10.

Preferably, the tube or pipe 40 is realized in aluminum. Preferably, the outer diameter of the tube or pipe 40 is comprised between 4mm and 10 mm.

The coordinate system may be defined by a plane P, wherein the straight section 41 extends along the X-direction. This direction is also referred to as the "length" direction. The Y direction defines the "thickness" direction.

The bend 42 may be welded to connect different sections 41 in different planes.

The section 41 is surrounded by fins 50. The fins 50 are positioned perpendicular to the straight sections 41, that is, the fins 50 extend in the Y direction. The fins 50 also define the following spacing: i.e., the distance between two nearest neighboring fins, is referred to as the fin pitch.

Preferably, the pitch of the fins of the evaporator is comprised between 1.8mm and 3.3 mm. Preferably, the pitch of the fins of the condenser is comprised between 1.4mm and 3.3 mm.

Preferably, the spacing of the tubes of the first heat exchanger and/or of the second heat exchanger is comprised between 15mm and 30 mm. Preferably, the row pitch of the tubes of the first heat exchanger and/or the second heat exchanger is comprised between 10mm and 30 mm.

The fins have holes 51 to receive the sections 41 of the tubes 40. A view of the holes is given in the side view of fig. 9. The fins 50 are then in contact with the sections 41. There need not be a connection between each fin 50 and each segment 41.

As shown in detail in fig. 6 to 8, each heat exchanger is therefore divided into three parts: a central portion 60 in which the fins 50 are present and the tube 40 has a straight section 41; and two

lateral portions

61, 62 at two lateral ends of the central portion 60, the two

lateral portions

61, 62 being free of fins and comprising the bend 42.

The central portion 60 has a generally parallelepipedal form with a front surface 70, which is generally a vertical surface on which the process air impinges, and an outlet surface 71, which is also vertical 71, from which outlet surface 71 the air exits. These

surfaces

70, 71 are preferably perpendicular to the main flow of process air (see e.g. fig. 10). The

surfaces

70, 71 are preferably rectangular.

As can be seen in fig. 3, only the central section 60 is located within the process air duct formed in the base 24, more precisely in the portion 29 thereof. The

lateral portions

61, 62 are located outside the duct and are only slightly surrounded by process air.

In the defined frame of reference, the total length of the condenser 31, i.e. the total length of the condenser 31 in the length direction or X direction, is referred to as Lt. This length is equal to the length of the central portion (which is generally equal to the length 41 of each segment) Le plus the length of the two lateral portions Lc. Assuming that the length of the two lateral portions is the same, then:

Lt＝Le+2x Lc

for the condenser 31 and evaporator, it is preferred that Lt <550 mm.

Furthermore, in the Y direction, the heat exchangers 31, 32 define a thickness t that is substantially the extension of the fins 50 along the Y direction (assuming that all fins have the same extension).

For condensers and evaporators preferably 40mm < t <150 mm.

The external volume of the central portion 60 can be calculated for both the condenser and the evaporator. For the evaporator, this external volume is referred to as TEV 1; for the condenser, this external volume is referred to as TEV 2. In the present embodiment, the tube 40 is substantially a cylindrical body, and therefore its volume is calculated by multiplying the circumferential area by the length of the cylindrical body.

TEV1,2＝π*(De/2)^2*Nt*Le

Wherein Nt is the number of tubes;

le is the length of the section of tube in the central region;

de-the outer diameter of the section of tube.

According to the invention, TEV2/TEV1>0.98, which means that the external volume of the evaporator is typically smaller than the external volume of the condenser. In the drawings, this difference is not visible due to the tubes having a smaller diameter in the evaporator than in the condenser (tubes 40 are covered by fins in fig. 3).

In normal operation, when the dryer 1 is turned on, the compressor is started and the heat pump 30 starts its cycle. Both the Low Pressure (LP) and the High Pressure (HP) of the refrigerant (at the inlet and outlet of the compressor 33, respectively) start to increase. The increase in pressure occurs during the so-called "transient phase" of the heat pump cycle. This operating condition is shown in fig. 11 (the upper curve is relative to the pressure measurement at the compressor outlet and the lower curve is relative to the pressure measurement at the compressor inlet). At the end of the transient phase, the steady state phase begins. In the steady-state phase, the pressure is substantially constant or increases/decreases only slightly. The measured values fluctuate substantially around a substantially constant average value. In fig. 11, in particular, the steady state phase terminates at the end of the heat pump cycle.

Considering the average value Xaver of the pressure values at the inlet/outlet of the compressor 33, these values are preferably included in the following ranges:

7bar<X_aver(Low)<17bar；

19bar<X_aver(high)<38bar.

Claims

1. A dryer (1) comprising:

-a treatment chamber (3) into which the articles are introduced (3) and treated with a flow of treatment air;

-a heat pump system (30), the heat pump system (30) having a refrigerant circuit in which a refrigerant is flowable, the refrigerant circuit comprising: a first heat exchanger (32) in which the refrigerant is heated (32); a second heat exchanger (31) in which the refrigerant is cooled in the second heat exchanger (31); a compressor (33), the compressor (33) pressurizing the refrigerant and circulating the refrigerant through the refrigerant circuit; and a pressure reduction device, wherein the first heat exchanger (32) and/or the second heat exchanger (31) facilitate heat exchange between the refrigerant flowing in the refrigerant circuit, which is a flammable refrigerant, and the process air,

wherein each of the first heat exchanger (32) and the second heat exchanger (31) is:

-is a finned tube heat exchanger comprising a tube (40) and a plurality of fins (50), said tube (40) having a plurality of sections (41) one above the other;

omicron is divided into the following three parts: a central portion (60), wherein the plurality of sections (41) of the tube are in contact with the plurality of fins (50); and a first end portion (61) and a second end portion (62), wherein the tube (40) is not in contact with the plurality of fins (50);

and wherein the ratio between the total external volume (TEV2) of all the sections of the tubes of the second heat exchanger (31) included in the central portion (60) in contact with the plurality of fins and the total external volume (TEV1) of all the sections of the tubes of the first heat exchanger (32) included in the central portion (60) in contact with the plurality of fins has a value greater than 0.98.

2. Dryer (1) according to any of the preceding claims, wherein the total external volume (TEV2) of all the sections of the second heat exchanger (31) including the tubes in the central portion is comprised between 200cc and 600 cc.

3. Dryer (1) according to any of the preceding claims, wherein the total external volume (TEV1) of all the sections of the first heat exchanger (32) including the tubes in the central portion is comprised between 250cc and 600 cc.

4. Dryer (1) according to any of the preceding claims, wherein said first heat exchanger (32) and/or said second heat exchanger (31) is a coil heat exchanger and wherein said tube (40) comprises a bend in said end portions (61, 62).

5. Dryer (1) according to any of the previous claims, wherein said tubes of said first heat exchanger (32) and/or of said second heat exchanger (31) have an outer diameter (De) comprised between 4mm and 10 mm.

6. Dryer (1) according to any one of the preceding claims, comprising a process air circuit comprising said process chamber (3) and a base (24), said heat pump (30) being located at said base (24), said process air circuit comprising a base portion comprising a process air duct at which said first heat exchanger (32) and said second heat exchanger (31) are positioned, wherein said central portion (60) of said first heat exchanger (32) and/or said second heat exchanger (31) is completely housed in said base process air duct.

7. Dryer (1) according to any of the preceding claims, wherein said combustible refrigerant comprises propane or propylene.

8. Dryer (1) according to any one of the preceding claims, wherein said first heat exchanger (32) and/or said second heat exchanger (31) define a total length (Lt) along a length direction (X), said end portions (61, 62) being located at opposite sides of said central portion (60) along said length direction, said length direction being substantially perpendicular to a main flow direction of said process air when passing through said first heat exchanger and/or said second heat exchanger.

9. Dryer (1) according to any of the previous claims, wherein said first heat exchanger (32) and/or said second heat exchanger (31) define a thickness along a thickness direction (Y), and wherein said thickness is comprised between 40mm and 150 mm.

10. Dryer (1) according to any one of the preceding claims, wherein said first heat exchanger (32) and/or said second heat exchanger (31) define an overall length (Lt) along a length direction (X), said end portions being located at opposite sides of said central portion along said length direction, said overall length being less than 550 mm.

11. Dryer (1) according to any one of the preceding claims when depending on claim 6, wherein said base (24) comprises an upper shell (24a) and a lower shell (24b), said base process air duct being formed by said upper and lower shells.

12. Dryer (1) according to any of the previous claims, wherein in a steady state phase of the heat pump cycle, the high pressure of said refrigerant is comprised between 19 and 38 bar.

13. Dryer (1) according to any of the preceding claims, wherein in a steady state phase of the heat pump cycle, the low pressure of the refrigerant is comprised between 7 and 17 bar.

14. Dryer (1) according to any of the previous claims, wherein the amount of flammable refrigerant contained in said heat pump refrigerant circuit is comprised between 80 and 300 g.

15. Dryer (1) according to any of the preceding claims, wherein the modulus of the temperature difference between the temperature of the process air at the outlet of the second heat exchanger and the condensation temperature is lower than 10 ℃.