Heat exchange device
The invention concerns a heat exchange device intended for systems which require heat exchange between two different agents circulating in two different circuits, in particular when a heating agent circulates in one of the circuits, and a cooling agent undergoing change of state circulates in the other circuit. In particular, the device can be used as a condenser In hydraulic heat pump modules, heating systems, or cooling systems.
Known are many different heat exchange devices and installations which include heat exchangers of various structures aligned to the specific designation and the desired heat exchange parameters, and to the agents which flow in them. There are several condenser categories known among the heat exchangers which are used as condensers, especially in heat pump systems. These may be plate condensers consisting of plates which form separate spaces where the agents exchanging heat with the plates flow. Also known are coat and tube condensers where the tubes run between strips of metal sheet. Another category groups condensers consisting of two coaxial tubes (outer and inner), coiled into spirals. Known, too, are devices having a tank filled with one heat exchange agent and a spiral tube coil filled with the other heat exchange agent placed inside the tank.
Known from patent publication EP1103775 is a heat exchanger to be used in water heating systems. The exchanger has a central inner flow duct delimited by the first wall, and an outer flow duct delimited by the second wall, and is designated for the flow of two media. The two flow ducts form a spiral designated especially for being placed inside a hot water tank. Disclosed in the publication are different shapes of the walls delimiting the flow ducts, intended to maximise the speed of heat transfer from the outer flow duct to the area around it and to intensify heat exchange between the flow ducts.
Disclosed in the publication of international patent application WO2015/107970 is a tube structure which enables the heat exchanger to have a compact construction. It consists of an outer tube and multiple inner tubes inserted through the outer tube so that the axes of the inner tubes are arranged with an equal distance one to the other in a cross section perpendicularto the axes. The outer tube is fitted with the first coil fixed on its inner circumferential surface, and the multiple inner tubes are fitted with other coils fixed on their inner circumferential surfaces. The first flow duct is defined by the inside of the outer tube and the outsides of the inner tubes, and the second flow duct is defined by the total area of the cross sections of the inner tubes. The ratio of the area of cross sections of the first and second flow ducts falls within the range between 1:2 and 2:1.
Known from patent description EP 1965164 is an installation incorporating a heat exchange device provided with a tank containing a heating agent, where the tank has an agent inlet In its bottom part and an agent outlet In its top part, and where there Is an exchanger in the tank in the form of two coaxial tubes immersed in the heating agent. The bottom end of the inner tube designated to accommodate the heating agent is connected to the heating agent Inlet, and the other end of the tube opens into the tank in its middle part. The inlet and outlet of the outer tube is connected to the circuit in which the cooling agent circulates. The solution envisages different variants of the number of coaxial exchangers in the tank, their connections, and the positions of the tube Inlets and outlets. Also known from European patent description EP 2080975 is a modified device disclosed in publication EP 1965164 in which the Inner tube, in its length between the Inlet of the heating agent to the tank and the coaxial tube exchanger, is uncovered by the outer tube in which at least one outlet opening is arranged. The size of the opening is adjusted so as to ensure that the flow rate of the heating agent flowing out of the tank falls within the range of 20-60% of the flow rate of the heating agent supplied through the Inlet. The publication discloses preferable dimensions of the inner tube and the outflow opening. .
Disclosed in the international patent application published under No. WO2007/090861 is a heat exchange device comprising a coil consisting of two coaxial tubes and placed in a tank having an outlet and an inlet. The outer tube is designated for the first heat exchange fluid, and the inner tube for the second heat exchange fluid which fills also the tank. The outlet of the tank from which the second fluid is collected Is coupled directly to one end of the inner tube, and its inlet for the second fluid opens freely into the tank. The inlet and outlet of the outer tube are connected to the circuit of the first fluid. The publication discloses different variants of positioning the inlets and outlets of the tank and the inner tube, the shape of the coil, the directions of the flow of the two fluids in the tubes and the tank, and the shapes of the tubes and connection stub pipes.
The heat exchange device according to the invention, having a coil heat exchanger with inlets and outlets for the heat exchanging agents and a tank for one of the agents, where the tank is provided with an inlet and outlet stub pipes is characterized in that the coll heat exchanger consists of at least one coil wound spirally around the tank on Its outside. The coil takes the form of three coaxial tubes, where the outer and inner tubes serve as the first flow ducts for the first agent, and the central tube serves as the second flow duct for the second agent. At the first end of the coil its outer and inner tubes are connected by way of the first collector to the inlet stub pipe for the supply of the first agent, and the central tube is connected by way of the second collector to the outlet of the second agent, while at the other end of the coll its outer tube and inner tube are connected with the inside of the tank by way of the third collector and a supply
stub pipe, and the central tube is connected to the inlet of the second agent by way of the fourth collector and a supply tube.
The first end of the coil with the first and second collectors, the inlet stub pipe for the supply of the first agent and outlet of the second agent are placed in the bottom part of the tank, and the second end of the coll with the third and fourth collectors and the supply stub pipe are placed in the top part of the tank.
Preferably, the second collector is placed inside the first collector, and the fourth collector Is placed inside the third collector.
The second agent inlet is located in the bottom part of the tank, and the supply pipe runs vertically along the outer wall of the tank.
Preferably, at the inlet to the fourth collector the supply pipe ends with an elbow in the shape of reversed letter U.
In one of the variants of the device there are at least two coils wound around the tank on its outside, where the subsequent turns of the coils are arranged alternatingly and the ends of all coils are inserted in the shared collectors: the first, second, or third collector, respectively.
in a preferable embodiment variant, the subsequent turns of the coils contact one another tightly, without any free space left in between.
The coaxial tubes of the exchanger are fitted with distancing elements.
In one of the variants the outer tube and central tube have indentations on their outer surfaces, where the depth of the indentations ensures the required distance between the tubes.
In another variant the outer tube and the central tube have spiral notches on their outside surfaces, where the depth of the notches ensures the required distance between the tubes.
In another variant of the device the inner tube and the central tube are provided with distancing wires wound spirally around them on the outside, where the diameter of the wires ensures the required distance between the tubes.
Most preferably the ratio between the diameters of the coaxial tubes of the coil falls within the range from 1:1.05:1.1 to 1:3:6.
The solution according to the invention ensures higher efficiency and effectiveness of heat transfer between two different agents circulating in two circuits in a heat exchange device without enlarging the device Itself.
An exemplary embodiment of the heat exchange device is shown on a drawing where Fig. 1 depicts the device in partial section, Fig. 2 presents a diagram of the agents' flow in the tubes of the exchanger, and Fig. 3 a, b, c shows schematically three variants of achieving the distance between the tubes.
The heat exchange device in the exemplary embodiment shown on Fig. 1 is in particular intended to work as a condenser, in e.g. heat pump systems, and serves heat
exchange between the first agent and second agent circulating in the first and second circuits, respectively, where water Is used as the first agent, and a Freon refrigerant as the second agent. The device consists of a closed vertical tank 1 with a spiral heat exchanger coiled around it on the outside, where the exchanger consists of two identical coils 2A and 2B. The subsequent turns of coils 2A, 2B are arranged alternating^ and contact one another tightly without any free space left in between. The first ends of the two colls are placed in the bottom part of the tank 1, and their opposite ends in the top part of the tank 1. Each of the coils 2A, 2B is formed of three coaxial tubes inserted one into another with some distance left between their walls. The outer tube 3 and inner tube 4 in each coil are intended for the flow of the first heat exchange agent, i.e. water serving as the heating agent accumulated in the tank 1 and collected from the tank to be supplied to the heating devices, while the central tube 5 of each coil serves as the flow duct for the other heat exchange agent, i.e. Freon refrigerant. The bottom ends of the outer tubes 3 and Inner tubes 4 in both coils are inserted in the first shared collector 6 connected to the inlet stub pipe 7 through which the water which needs to be heated flows Into the device. The bottom ends of the central tubes 5 of both coils are inserted In the second shared collector 8 connected to the outlet 9 of the second agent, i.e. the refrigerant, where the second collector 8 is placed inside the first collector 6. The top ends of the outer tubes 3 and inner tubes 4 of both coils are inserted in the third shared collector 10 which is connected with the inside of the tank 1 via the supply stub pipe 11. The top ends of the central tubes 5 of both coils are inserted in the fourth collector 12 which is placed inside the third collector 10. The inside of the fourth collector 12 is connected with the inlet 14 of the second agent via the supply pipe 13, where the inlet 14 is positioned below the tank 1. The supply pipe 13 runs vertically inside the tank 1, and in its top section Is shaped into reversed letter U to form an elbow 15 above the inlet to the fourth collector 12. In its bottom part, the tank 1 is fitted with the outlet stub pipe 16 through which the heated water is drawn from the tank 1 and supplied to the outer circuit feeding the heating devices. In addition, the tank 1 may be fitted with an electric heating coil 17. So as to ensure an appropriate distance between the three coaxial tubes in the process of coiling them to form spirals it is preferable to use appropriate distancing elements. In the first variant, presented on Fig. 3a, there are indentations 18 formed on the outside of the outer tube 3 and the inner tube 4, where the depth of the indentations ensures the required distance between the tubes in the bending process. In the second variant, there are wires 19 wound spirally around the inner tube 4 and the central tube 5, as shown on Fig.3c, where the diameter of the wires ensures the appropriate distance between the tubes in the bending process. The third variant, shown on Fig. 3b, envisages spiral notches 20 made on the outer tube 3 and the central tube 5, where the depth of the notches is determined by the desired distance between the tubes.
The first agent, i.e. water, which transferred its heat in the outer heating devices, is supplied to the first collector 6 through the inlet stub pipe 7, from where it is distributed to the outer and inner tubes 3, 4 of both coils 2A, 2B and then flows up the exchanger in the first two flow ducts Kl In each of the coils, i.e. between the walls of the outer tube 3 and the central tube 5, as well as inside the inner tubes 4. While flowing, the water takes heat from the second agent, the Freon refrigerant, which is supplied in the form of gas from the inlet 14, via the vertical supply pipe 13 with the elbow 15, up to the fourth collector 12 at the top of the tank 1, from where It Is distributed to the central tubes 5 of the two coils 2A, 2B, Inside which it flows down In the second flow ducts K2 In the direction opposite to the direction in which the first agent, i.e. water, flows, as shown schematically on Fig. 2. When the water is receiving heat, the Freon refrigerant changes its state from gas to liquid, i.e. gets condensed, and flows down the two coils to the second collector 8, from where it is discharged to the outlet 9. The water heated when flowing up inside the outer and Inner tubes 3,4 of the two coils 2A, 2B flows into the third shared collector 10, from where it flows into the tank 1 via the supply stub pipe 11, and from the tank it is drawn via the outlet stub pipe 16. The elbow 15 which ends the vertical supply pipe 13 prevents any undesired oil impurities from getting to the fourth collector 12 and the exchanger tubes from the circuit of the second agent - the impurities flow down and can then be discharged.
In its different embodiments, the device is preferably made of stainless steel, the capacity of the tank ranges from 20 to 500 litres, and the ratio between the tube diameters preferably falls within the range between 1:1.05:1.1 and 1:3:6. In the exemplary embodiment the diameter of the outer tube 3 is 25 mm, its wall 1 mm thick, the diameter of the central tube 5 Is 18 mm, the wall 1 mm thick, and the diameter of the inner tube 4 is 12 mm, the wall 0.6 mm thick.
The solution according to the invention ensures more effective heat exchange than in the solutions known to date, in both heat exchangers in the form of a coil, and heat exchange devices incorporating spiral heat exchangers placed in a tank, because the heat is transferred between the first and second agents through the two walls of the second flow duct K2 of the second agent, Freon refrigerant in particular, i.e. through the wall of the inner tube 4 and the wall of the central tube 5, on both sides of which the first agent, water in particular, flows in the first flow ducts Kl in forced countercurrent.
In the devices of the type it is necessary to force the flow, especially with a compressor, which may lead to mixing of oil and gas used as the coolant, as well as undesirable transfer of the mixture into the exchanger tubes. The shape of the elbow element and the point where the tube supplying the Freon refrigerant is connected to the spiral exchanger, as used in the solution, prevents the phenomenon by facilitating the discharge of undesired oil which cannot get into the exchanger through the elbow. In addition, placing the spiral exchanger outside the tank and the inlet and outlet stub
pipes of both agents at the bottom of the tank facilitates its assembly and maintenance in the systems in which it is Installed.
The presented exemplary embodiment does not exhaust the possible structural variants of the device. The number of coils optimal for different working conditions, tank dimensions, and the desired total efficiency of the device is determined based on the tests and efficiency calculations for a single coil with the predetermined diameters, thickness of tube walls, tube lengths, the agents flowing inside, the temperatures at inlet and outlet, and other additional requirements. When appropriate heat exchange agents are used and the direction of their flow is externally forced, the device according to the invention can work as both a condenser, and an evaporator.