EP2848180A1 - Dishwasher with cooled tub wall - Google Patents

Abstract

In a dishwasher, at least one wall (4) of the tub (1) is cooled in the drying phase in order to accelerate the condensation of water out of the process air. This ensures that the temperature of the wall (4) is at most 10 ° C below the center temperature of the tub (1). In this way, extensive mist formation, which may affect the drying process, can be avoided.

Description

Field of the invention

The invention relates to a dishwasher with a tub for receiving dishes, with a cooling device for cooling at least one wall of the tub and with a controller for controlling the cleaning process. The invention also relates to a method for operating such a dishwasher.

background

In dishwashers of this type, the cleaning process comprises an actual cleaning phase in which the dishes are cleaned in one or (usually) several washing cycles with process water, partly with the addition of cleaning agents. Furthermore, the cleaning process comprises a drying phase in which the dishes are dried.

Before the drying phase, the controller heats up the tub and in particular the washware contained therein, usually by the process water is heated in the rinse cycle to a relatively high temperature, for example 50-60 ° C. Then begins the drying phase, in which a cooling device, for example in the form of a blower is activated to at least one wall of the tub or an exchange surface with the tub air to cool. This creates a drying effect by the hot process air in the tub first absorbs moisture from the dishes and then passes, for example by convection or diffusion to the cooled wall, where it gives off the moisture.

Presentation of the invention

It is an object of the present invention to provide a dishwasher and a method of the type mentioned above with improved drying efficiency.

This object is solved by the subject matter of the independent claims.

Accordingly, the control of the dishwasher is configured to control the cooling device in the drying phase such that the center temperature of the tub is between 3 ° and 10 ° C above the temperature of the cooled wall.

The term "center temperature of the tub" is to be understood as the temperature which the process air in the middle of the tub assumes.

The invention is based on the finding that in conventional processes at least over part of the drying process mist is formed in the region of the cooled wall, ie the air spontaneously condenses into suspended droplets. This mist formation represents a less efficient drying process than the direct condensation on the tub wall, along which the water can flow. In addition, the mist can rewet the dishes and thus counteract the drying process. Furthermore, condensed droplets significantly hinder the exchange process caused by diffusion or convection. It can be seen that the formation of mist can be at least largely avoided if the temperature difference between the middle of the Vat and the wall is limited to about 10 °. However, the temperature difference should be at least 1 °, otherwise the drying rate drops.

It turns out that particularly good drying results are achieved when the temperature difference is between 2 and 6 ° C.

Since the temperature usually drops during the drying phase, the control for maintaining the desired temperature difference is preferably configured to increase the cooling performance of the cooling device in several steps or continuously during the drying phase.

In an advantageous embodiment, the cooling device has a control loop to control the temperature of the wall to a desired value. This control loop may be at least partially implemented in the software of the controller. Further, the controller is configured to lower the setpoint in the drying phase in several steps or continuously. In this way, regardless of the efficiency of the cooling device (which may be dependent on the ambient temperature, for example), it can be well ensured that the temperature difference remains within the desired range.

The invention is particularly suitable for dishwashers in which no means for actively circulating air in the tub are provided. Under active circulation is thereby a circulation by mechanical means, such. Fans and blowers, as opposed to a passive circulation due to convection effects. The problem of fog formation is particularly prominent in devices in which the air is passively circulated and thus the moisture transport in the air based on free convection and diffusion.

The invention also relates to a method for operating a dishwasher with a tub for receiving dishes and with a cooling device for cooling at least one wall of the tub. In the context of this Method is a cleaning process comprising a cleaning phase and a drying phase, wherein in the drying phase, the wall of the tub is cooled with the cooling device. In this case, in the drying phase, the cooling device is controlled such that the center temperature of the tub is between 1 ° and 10 °, in particular 2 ° - 6 ° C, above the temperature of the wall.

Brief description of the drawings

• Fig. 1 einen schematischen Schnitt durch einen Geschirrspüler,
• Fig. 2 den Verlauf der Temperaturen und der Kühlerleistung und
• Fig. 3 ein Mollier-Diagramm von mit Wasser befrachteter Luft.

Further embodiments, advantages and applications of the invention will become apparent from the dependent claims and from the following description with reference to FIGS. Showing:

• Fig. 1 a schematic section through a dishwasher,
• Fig. 2 the course of the temperatures and the cooler performance and
• Fig. 3 a Mollier diagram of water-laden air.

Ways to carry out the invention Unit design:

The dishwasher according to Fig. 1 has a tub 1 for receiving the dishes. In the tub 1 crockery baskets, spray arms and other means for receiving and cleaning the dishes are provided in a conventional manner. These components are not central in the present context and therefore not shown in the figure.

Front side of the tub 1 is closed by a door 2. The apparatus further has a cooling device 3 for cooling at least one wall of the tub 1, in the present example for cooling the door 2 opposite the rear wall 4. The cooling device is configured in the present example as a fan that sucks ambient air from the base portion of the front of the device. The air thus conveyed passes along the rear wall 4 and is then blown out through the front of the appliance via the tub. Thus, the fan is configured to cool the wall 4 by means of ambient air.

Further, a controller 5 is provided, which controls the operation of the components of the device according to user inputs. The controller 5 is a process controller which is designed to carry out the process steps described here.

The device continues to have (in Fig. 1 not shown) in a conventional manner, a water-carrying system comprising a fresh water supply for supplying fresh water, a water circulation system to convey water from the sump of the tub in the spray devices, and a system for discharging spent water into the sewer. Heating means are attached to the water circulation system and / or the tub to heat the process water. A detergent addition allows the controlled, process-controlled addition of washing reagents, such as dishwashing or Glanzspüler.

In the execution after Fig. 1 two further (optional) temperature sensors are shown. A wall temperature sensor 6 is used to measure the temperature of the rear wall 4. A control temperature sensor 7 is spaced from the wall 4, preferably at a distance of at least 10 cm, and also measures the temperature at or in the tub 1. The objects of these sensors will be discussed below described in more detail.

Business:

In operation, the controller 5 controls the components of the device according to a user-selected cleaning program. At least one of the selectable cleaning programs is designed to carry out a cleaning process in accordance with the procedure described below.

In a first phase of the cleaning process, referred to herein as the cleaning phase, the controller 5 supplies process water to the tub 1 to clean the dishes. This phase may include several process water cycles, e.g. a pre-wash without dishwashing detergent and a main wash with the addition of dishwashing detergent. There may also be provided further process water cycles with or without the addition of dishwashing detergent. In some of the process water cycles, the process water can optionally be heated, typically at temperatures between 40 and 50 ° C. Between process water cycles, the process water is partially or completely discharged and replaced with new water.

During the cleaning phase, the cooling device 3 preferably remains switched off.

The end of the cleaning phase is formed by a rinse cycle, in which the tub 1 fresh process water and rinse aid are supplied. The water is heated to a relatively high temperature of about 50-60 ° C so as to supply heat to the tub 1 and in particular the dishes. Thereafter, the water is drained.

Now, the cooling device is activated at a time t0. This is on Fig. 2 which shows in the upper diagram the course of the center temperature (solid line) and the wall temperature (dotted line), and in the lower diagram the cooler performance (ie, the electric power supplied to the cooling device).

The cooling device 3 can (optionally) initially be operated with a relatively high cooling capacity, to rapidly lower the temperature of the wall 4 by 1-10 ° C below the center temperature. Then, the cooling device is operated in the drying phase from time t1 so that the wall temperature is set in the range of 1 - 10 ° C below the center temperature. Since during the drying phase, the center temperature in the tub continuously decreases, the cooling of the wall 4 must be increasingly strong, as shown in the lower diagram of Fig. 2 is shown to maintain the desired temperature difference.

In Fig. 2 is shown a continuous increase in the cooling capacity from time t1. However, this increase can also take place in several discontinuous steps.

"Cooling power" is to be understood as the power averaged over a period of a few minutes, in particular of at most 5 minutes, which power is supplied to the cooling device 3. In other words, the cooling may be e.g. also in the form of short "cooling pulses" of e.g. for a few seconds, increasing the intensity or length of the cooling pulses over time.

In addition, it is conceivable that especially at the beginning (as in Fig. 2 shown) or towards the end of the radiator performance deviates from the described rising course. As the drying phase in the sense of the claims is the in Fig. 2 between t1 and t2, in which the cooling capacity increases in several steps or continuously and the temperature of the wall is lower than the center temperature by the said difference. The length of this drying phase is at least 10 minutes, in particular at least 20 minutes.

During the drying phase, the cooling capacity is preferably increased by at least 50% in order to take account of the cooling of the bottom temperature.

The effect of the drying phase can be seen from the Mollier diagram of Fig. 3 in which the amount of water per air quantity along the horizontal axis and the enthalpy are plotted along the vertical axis, the latter corresponds approximately to the temperature of the air. The curve "φ = 100%" shows the locations with a relative humidity of 100%. All points above this curve correspond to conditions with a relative humidity of less than 100%. All points below this curve correspond to unstable, supercooled states where water begins to condense in the air (fogging), with the tendency for misting to increase with increasing distance from the curve "φ = 100%".

If the temperature difference between the center temperature of the tub and the wall temperature is very high, the air will reach a relative humidity of 100% relatively early on its approach to the wall 4 caused by the convective movement, resulting in mist formation at a considerable distance from the wall 4 can lead. These fog droplets generated in this way usually do not reach the wall 4, but are transported by the air flow into the warmer areas of the tub, where they evaporate again or precipitate on the items to be washed, so that the drying loses efficiency.

If, on the other hand, the temperature difference between the center temperature of the tub and the wall temperature is low, condensation only takes place shortly before or on the wall 4, and the chance of water droplets condensed into air due to their movement striking the wall is high. In this way, most of the condensed moisture settles on the wall and can flow from there into the sump of the device, so that it can be excreted. The drying effect is therefore higher.

Remarks:

From a physical point of view, the invention is based on the idea that the air on the cooled wall 4 is not too supersaturated. Expressed in numerical terms, this means that the quantity φ, which corresponds to the ratio between the partial pressure of water vapor in the gas and the vapor pressure at a given temperature, is preferably between 1.04 and 1.05, which (depending on the absolute temperature and as described above) as a certain temperature difference between wall and center temperature can be expressed.

Preferably, as shown in Fig. 6, a wall temperature sensor 6 is provided, by means of which the temperature of the wall 4 can be controlled. For this purpose, the cooling device 3, the controller 5 and the temperature sensor 6 form a control loop, with which the temperature of the wall 4 is adjusted to a desired value. The controller 5 is designed to lower this setpoint in the drying phase continuously or in several steps. About the drying phase, the setpoint is preferably reduced by at least 10 ° C, in particular at least 20 ° C, so as to take into account the corresponding reduction of the center temperature, which is also at least 10 ° C, in particular at least 20 ° C.

Further, as mentioned, a control temperature sensor 7 may be provided with which the temperature at or in the tub 1 at a distance from the cooled wall can be measured. The signal of such a sensor is a measure of the center temperature of the tub 1, so that it can be pulled up for better control of the cooling device 3 zoom. The lower the temperature at the control temperature sensor 7, the higher the radiator performance is to be selected. In particular, the controller 5 may be configured to control the radiator output depending on the difference of the temperatures on the wall 4 and the control temperature sensor 7 - the smaller this temperature difference is, the bigger the cooler performance has to be.

In a particularly simple embodiment, however, it is also possible to dispense with the control temperature sensor 7. In this case, the setpoint temperature for the wall 4 is reduced in the drying phase according to a determined by the device manufacturer target profile. This desired course is e.g. determined in the manufacturer's experiments so that the desired temperature difference for conventional loads and process parameters is maintained.

In an even simpler embodiment, in principle, the wall temperature sensor 6 can be dispensed with. In this case, in the drying phase, the cooling capacity is increased stepwise or continuously in accordance with a desired course determined by the device manufacturer. This nominal course is also used e.g. determined in the manufacturer's experiments so that the desired temperature difference for conventional loads and process parameters is maintained.

• Zum Kühlen kann ein Wasserbehälter vorgesehen sein, der im thermischen Kontakt mit der Wand 4 steht. Über ein Ventil kann Frischwasser in den Wasserbehälter eingeleitet werden, um die Wand zu kühlen.
• Zum Kühlen kann mindestens ein Peltier-Element verwendet werden, das im thermischen Kontakt mit der Wand steht.
• Zum Kühlen kann eine Wärmepumpe vorgesehen sein, deren Verdampfer im thermischen Kontakt mit der Wand steht.

In the embodiment shown so far is shown as a cooling device 3, a fan which cools the wall 4 by means of ambient air. Alternatively or additionally, the cooling device may also have at least one of the following components:

• For cooling, a water tank may be provided, which is in thermal contact with the wall 4. Via a valve fresh water can be introduced into the water tank to cool the wall.
• For cooling, at least one Peltier element which is in thermal contact with the wall can be used.
• For cooling, a heat pump may be provided, the evaporator is in thermal contact with the wall.

In the execution after Fig. 1 the rear wall of the tub 1 is cooled. However, it is also conceivable that another wall, eg one of the side walls, is cooled, or that several walls are cooled.

Thanks to the embodiment of the device described here, the drying time and / or the temperature of the rinse cycle can be reduced compared to conventional devices with a constant drying result.

While preferred embodiments of the invention are described in the present application, it is to be understood that the invention is not limited thereto and may be embodied otherwise within the scope of the following claims.

Claims (14)

A dishwasher with a tub (1) for receiving dishes, with a cooling device (3) for cooling at least one wall (4) of the tub (1) and with a controller (5) for controlling a cleaning process comprising a cleaning phase and a drying phase the controller (5) is designed to heat the tub (1) to dry the dishes and to cool the wall (4) of the tub (1) with the cooling device (3) in the drying phase, characterized in that the control (5 ) is configured to control the cooling device (3) in the drying phase such that a center temperature of the tub (1) is between 1 ° and 10 ° C., in particular 2 ° -6 ° C., above a temperature of the wall (4) , Dishwasher according to claim 1, wherein the controller (5) is adapted to increase a cooling capacity of the cooling device (3) during the drying phase in several steps or continuously. Dishwasher according to one of the preceding claims, wherein the cooling device (3) comprises a fan which is adapted to cool the wall (4) from the outside by means of ambient air. Dishwasher according to one of the preceding claims, wherein the cooling device (3) comprises a water tank in thermal contact with the wall (4), and a valve for introducing fresh water into the water tank, and / or wherein the cooling device (3) is a heat pump or a Peltier element has. A dishwasher according to any one of the preceding claims, wherein the dishwasher comprises a control circuit (3, 5, 6) for controlling the temperature of the wall (4) to a desired value, and wherein the controller (5) is adapted to set the desired value in the drying phase in several steps or continuously lower, in particular by at least 10 ° C, preferably by at least 20 ° C. Dishwasher according to one of the preceding claims, further comprising a control temperature sensor (7), with which a temperature at or in the tub (1) at a distance from the cooled wall (4) is measurable, wherein the controller (5) is designed to control the cooling device (3) in response to a signal from the control temperature sensor (7). A dishwasher according to claim 6, wherein the controller (5) is adapted to control the cooling device (3) depending on a difference in the temperatures of the wall (4) and the control temperature sensor (7). Dishwasher according to one of the preceding claims, wherein no means for actively circulating air in the tub (1) are provided. Dishwasher according to one of the preceding claims, wherein a length of the drying phase is at least 10 minutes, in particular at least 20 minutes. Dishwasher according to one of the preceding claims, wherein the controller (5) is adapted to increase the cooler performance by at least 50% in the drying phase. A method of operating a dishwasher with a tub (1) for holding dishes and with a cooling device (3) for cooling at least one wall (4) of the tub (1), wherein a cleaning process comprising a cleaning phase and a drying phase is performed is cooled in the drying phase, the wall (4) of the tub (1) with the cooling device (3), characterized in that in the drying phase, the cooling device (3) is controlled such that a center temperature of the tub (1) between 1 ° and 10 °, in particular 2 ° - 6 ° C, above a temperature of the wall (4). The method of claim 11, wherein a cooling performance of the cooling device (3) during the drying phase is increased in several steps or continuously. A method according to any one of claims 11 to 12, wherein the temperature of the wall (4) is controlled to a desired value which is lowered in the drying phase in several steps or continuously, in particular by at least 10 ° C, preferably by at least 20 ° C , Method according to one of claims 11 to 13, wherein in the drying phase, the center temperature is lowered continuously, in particular by at least 10 ° C, preferably by at least 20 ° C.

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