A liquid heat-conducting circulating temperature control system for laboratory
By integrating cold and heat source temperature control equipment into laboratory temperature control devices, adopting a parallel structure of plate heat exchangers and heaters, and combining the regulation of proportional valves and branch valves, the problems of limited temperature range and slow response speed of existing temperature control equipment are solved, realizing wide temperature range and high-precision temperature control to meet the diverse temperature needs of laboratories.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- JIUTAI ENERGY INNER MONGOLIA
- Filing Date
- 2025-08-26
- Publication Date
- 2026-06-16
AI Technical Summary
Existing laboratory temperature control equipment uses only one method and has a limited temperature range, which cannot meet the needs of large or small temperature changes during experiments. In addition, the response speed is slow and cannot meet the requirements of experimental cycle and accuracy.
Design a liquid heat conduction circulation temperature control system that integrates cold and heat source temperature control equipment. Through the series and parallel structure of plate heat exchangers and heaters, combined with the regulation of proportional valves and branch valves, a closed-loop temperature control of the circulating liquid is achieved, covering a wide temperature range and high-precision control.
It achieves wide-range temperature control with high precision and fast response, adapting to diverse temperature requirements in laboratories and improving experimental efficiency and equipment usability.
Smart Images
Figure CN224366356U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of experimental instrument and equipment technology, and specifically relates to a liquid heat conduction circulation temperature control system for laboratory use. Background Technology
[0002] Currently, high and low temperature constant temperature equipment is generally required in laboratory research to achieve precise control of the temperature environment. For example, in the organic and inorganic reaction processes of chemical synthesis, accurate temperature control of the reaction environment is required to avoid the generation of by-products caused by temperature fluctuations. In biological experiments, it is necessary to ensure the stability of the experimental environment temperature and strictly control the temperature to prevent the loss of biological activity. Furthermore, in the process of material testing, such as the thermal stability analysis of polymer materials and the preparation of nanomaterials, accurate and stable environmental temperature control is required. However, existing laboratory temperature control equipment is generally a single heat source or cold source device, meaning it can only perform independent heating and cooling functions. Examples include commonly used high-temperature water baths or oil baths, as well as cooling water circulators or cold trap cooling platforms. This limited temperature control method and poor ease of use significantly impacts experimental cycles. Furthermore, traditional cold or heat source temperature control equipment has a limited temperature control range, failing to meet the environmental temperature requirements of some experiments. For instance, the temperature control range of commonly used high-temperature water baths is generally between room temperature and 200°C, while cold source temperature control equipment relies on the chosen cooling medium; for example, the temperature control range of cooling water circulators is typically slightly above ambient temperature up to -20°C. In addition, with increasing demands for process stability and experimental repeatability across industries, temperature control in some experiments requires varying degrees of change, such as large or small temperature increases and decreases, and there are specific requirements for the speed of temperature transitions. Existing traditional heat and cold source temperature control equipment clearly cannot meet these temperature control needs.
[0003] Therefore, it is necessary to design a laboratory liquid thermal conductivity circulation temperature control system that can at least solve some of the above problems and defects. Summary of the Invention
[0004] To address the above technical problems, this invention proposes a laboratory liquid heat conduction circulation temperature control system. It integrates cold and heat source temperature control equipment to perform closed-loop circulation temperature regulation of circulating liquids such as heat conduction oil. This ensures the overall stability and reliability of the system while achieving a wide temperature range coverage, high temperature control accuracy, and fast response speed. It is highly practical and easy to promote and use on a large scale.
[0005] The technical solution of this utility model is:
[0006] This utility model proposes a laboratory liquid heat conduction circulation temperature control system, including a heat conduction circulation pipeline with a circulating liquid inlet and a circulating liquid outlet, and a circulation pump, a plate heat exchanger and a heater arranged in series on the heat conduction circulation pipeline. The circulation pump is arranged near the circulating liquid inlet, and the heater is arranged near the circulating liquid outlet.
[0007] The plate heat exchanger is provided with a heating branch connected in parallel. The output end of the heating branch is located between the heater and the plate heat exchanger. The heating branch is provided with a first proportional valve. The heat conduction circulation pipeline is provided with a second proportional valve. The second proportional valve is located between the input end of the heating branch and the input end of the plate heat exchanger.
[0008] Preferably, the heat transfer circulation pipeline is provided with a cooling branch connected in parallel with the plate heat exchanger and the heater, and the input end of the cooling branch is arranged close to the output end of the circulation pump;
[0009] The cooling branch is equipped with a cooler and a branch valve connected in series, and the branch valve is located near the input end of the cooling branch.
[0010] Preferably, the heat conduction circulation pipeline is provided with a main valve located near the output end of the heater, and the main valve is located between the output end of the heater and the output end of the cooling branch.
[0011] Preferably, the heat conduction circulation pipeline is provided with a liquid recovery pipeline connected in parallel, the liquid recovery pipeline is provided with a liquid storage container, the input end of the liquid storage container is connected to the steam outlet of the heater, and the output end of the liquid storage container is connected to the input end of the circulation pump.
[0012] Preferably, the liquid recovery pipeline is further provided with a first capillary tube and a check valve connected in series with the liquid storage container. The first capillary tube is arranged near the input end of the liquid storage container, and the check valve is arranged near the output end of the liquid storage container.
[0013] Preferably, the liquid storage container is equipped with a level gauge for monitoring the liquid level in its inner cavity and a filling port connected to its inner cavity. The filling port is also equipped with an air vent that connects the inner cavity of the liquid storage container to the external atmospheric environment.
[0014] Preferably, the plate heat exchanger is provided with a refrigerant circulation pipeline connected thereto, and the refrigerant circulation pipeline is provided with an expansion valve, a compressor, a condenser, a dryer filter and a second capillary tube connected in series.
[0015] The expansion valve is positioned near the input end of the refrigerant circulation pipeline, and the second capillary tube is positioned near the output end of the refrigerant circulation pipeline.
[0016] Preferably, the refrigerant circulation pipeline is further provided with a low-pressure needle valve and a high-pressure needle valve arranged on both sides of the compressor. The low-pressure needle valve is located on the input side of the compressor, and the high-pressure needle valve is located on the output side of the compressor.
[0017] Preferably, the heat-conducting circulation pipeline is provided with an input valve located near the end of the circulating liquid inlet and an output valve located near the end of the circulating liquid outlet.
[0018] This utility model has the following advantages and effects compared with the prior art:
[0019] (1) A plate heat exchanger and heater connected in series to the heat transfer circulation pipeline are adopted to integrate the heat source temperature control function and the cold source temperature control function, so as to perform closed-loop circulation temperature regulation of the circulating liquid such as heat transfer oil in the heat transfer circulation pipeline, so that the temperature range of the temperature control system is large, for example, it can support temperature range regulation from -15℃ to 200℃, and the overall structure is reasonable and compact, which improves practicality and adaptability.
[0020] (2) A heating branch is used in parallel with the plate heat exchanger, and the heating branch is equipped with a first proportional valve and the heat conduction circulation pipeline is equipped with a second proportional valve. The flow ratio of the circulating liquid through the heating branch and the heat conduction circulation pipeline is adjusted by the first proportional valve and the second proportional valve respectively, thereby adjusting the different ratios of the circulating liquid flowing through the heating passage and the cooling passage, and thus achieving precise control of the circulating liquid temperature.
[0021] (3) A cooling branch is adopted in parallel with the plate heat exchanger and the heater, and the cooling branch is equipped with a branch valve. The proportion of the circulating liquid flowing through different pipeline passages is adjusted by the branch valve in conjunction with the first proportional valve and the second proportional valve mentioned above, thereby further improving the accuracy of temperature control and increasing the precision of temperature control. Attached Figure Description
[0022] Figure 1 This is a schematic diagram of the laboratory liquid heat conduction circulation temperature control system in Embodiment 1 of this utility model;
[0023] Figure 2 This is a schematic diagram of the laboratory liquid heat conduction circulation temperature control system in Embodiment 2 of this utility model.
[0024] Reference numerals: 1. Heat transfer circulation pipeline; 11. Circulating liquid inlet; 12. Circulating liquid outlet; 13. Circulating pump; 14. Plate heat exchanger; 15. Heater; 151. Steam outlet; 16. Second proportional valve; 17. Main valve; 18. Inlet valve; 19. Outlet valve; 2. Heating branch; 21. First proportional valve; 3. Cooling branch; 31. Cooler; 32. Branch valve; 4. Liquid recovery pipeline; 41. Liquid storage container; 411. Filling port; 42. First capillary tube; 43. Check valve; 5. Refrigerant circulation pipeline; 51. Expansion valve; 52. Compressor; 53. Condenser; 54. Dryer filter; 55. Second capillary tube; 56. Low-pressure needle valve; 57. High-pressure needle valve. Detailed Implementation
[0025] To enable those skilled in the art to better understand this utility model, it will now be further described in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this utility model.
[0026] Example 1:
[0027] like Figure 1 As shown, this utility model provides a laboratory liquid heat conduction circulation temperature control system, which includes a heat conduction circulation pipeline 1 with a circulating liquid inlet 11 and a circulating liquid outlet 12, and a circulation pump 13, a plate heat exchanger 14, and a heater 15 arranged in series on the heat conduction circulation pipeline 1. The heat conduction circulation pipeline 1 is provided with an input valve 18 arranged near the end of the circulating liquid inlet 11 and an output valve 19 arranged near the end of the circulating liquid outlet 12. The circulation pump 13 is arranged near the end of the circulating liquid inlet 11, and the heater 15 is arranged near the end of the circulating liquid outlet 12.
[0028] Furthermore, the plate heat exchanger 14 is provided with a heating branch 2 connected in parallel. The output end of the heating branch 2 is located between the heater 15 and the plate heat exchanger 14. The heating branch 2 is provided with a first proportional valve 21. The heat conduction circulation pipeline 1 is provided with a second proportional valve 16 arranged near the input end of the plate heat exchanger 14. The second proportional valve 16 is located between the input end of the heating branch 2 and the input end of the plate heat exchanger 14.
[0029] The heater 15 is equipped with a heating unit (such as a heating tube, heating wire, etc., not shown in the figure) and a temperature sensing unit (such as a high-precision temperature measuring resistance thermometer, etc., not shown in the figure) to heat the circulating liquid flowing through the heater 15. It should be noted that, since the heating unit and the temperature sensing unit are both mature existing technologies in this field, their specific structures and principles will not be described in detail here.
[0030] refer to Figure 1As shown, the heat transfer circulation pipeline 1 is also provided with a cooling branch 3 connected in parallel with the plate heat exchanger 14 and the heater 15. The input end of the cooling branch 3 is arranged near the output end of the circulation pump 13. The cooling branch 3 is provided with a cooler 31 and a branch valve 32 connected in series. The branch valve 32 is arranged near the input end of the cooling branch 3. The heat transfer circulation pipeline 1 is provided with a main valve 17 arranged near the output end of the heater 15. The main valve 17 is located between the output end of the heater 15 and the output end of the cooling branch 3. That is, the output end of the cooling branch 3 is located between the main valve 17 and the output valve 19.
[0031] Optionally, in some embodiments, the branch valve 32 is specifically a proportional valve, so as to adjust the proportion of the circulating liquid flow through the cooling branch 3.
[0032] Furthermore, in combination Figure 1 As shown, the heat transfer circulation pipeline 1 is also provided with a liquid recovery pipeline 4 connected in parallel. A liquid storage container 41 is provided on the liquid recovery pipeline 4. The input end of the liquid storage container 41 is connected to the steam outlet 151 of the heater 15 through a pipeline, and the output end of the liquid storage container 41 is connected to the input end of the circulation pump 13 through a pipeline. Specifically, in this embodiment, the liquid recovery pipeline 4 is also provided with a first capillary tube 42 and a check valve 43 connected in series with the liquid storage container 41. The first capillary tube 42 is arranged near the input end of the liquid storage container 41, and the check valve 43 is arranged near the output end of the liquid storage container 41. That is, the liquid recovery pipeline 4 is also provided with a first capillary tube 42 connected in series between the liquid storage container 41 and the heater 15 and a check valve 43 connected in series between the liquid storage container 41 and the circulation pump 13. The first capillary tube 42 allows the circulating liquid vapor flowing out of the steam outlet 151 of the heater 15 to be liquefied and stored in the liquid storage container 41, while the check valve 43 ensures that the circulating liquid stored in the liquid storage container 41 flows unidirectionally into the heat transfer circulation pipeline 1 to replenish the circulating liquid. It should be noted that the circulating liquid (such as heat transfer oil) in the liquid storage container 41 does not participate in the circulation movement in the heat transfer circulation pipeline 1. It is in an independent and adiabatic state with the circulating liquid in the heat transfer circulation pipeline 1, and the temperature of the circulating liquid stored in the liquid storage container 41 is not affected.
[0033] Furthermore, the liquid storage container 41 is equipped with a level gauge for monitoring the liquid level of the recovered liquid inside the container and a filling port 411 connected to its inner cavity. The filling port 411 is equipped with an air vent that connects the inner cavity of the liquid storage container 41 to the external atmospheric environment, so as to discharge the air gas in the liquid recovery pipeline 4 and the heat conduction circulation pipeline 1 as well as the water vapor in the circulating liquid.
[0034] Optionally, in some embodiments, the above-mentioned laboratory liquid heat conduction circulation temperature control system further includes a controller electrically connected to the circulation pump 13, heater 15, and plate heat exchanger 14. The controller is equipped with a programmable unit to achieve precise temperature regulation of the circulating liquid by controlling the start and stop of the circulation pump 13, heater 15, and plate heat exchanger 14.
[0035] Furthermore, in this embodiment, the input valve 18, output valve 19, check valve 43, branch valve 32, main valve 17, first proportional valve 21, and second proportional valve 16 are all solenoid valves, and all of the above solenoid valves are electrically connected to the controller so that the controller can control the opening and closing of the above solenoid valves to adjust and switch the circulating liquid to different pipeline paths, thereby meeting the temperature regulation requirements of precise temperature control and rapid response.
[0036] The working principle of the laboratory liquid heat conduction circulation temperature control system provided in this embodiment will be explained below in conjunction with specific usage scenarios. It should also be noted that heat conduction oil is used as the specific circulating liquid in the following explanation:
[0037] Connect the heat transfer oil outlet of the energy-consuming equipment to the circulating liquid inlet 11 of the heat transfer circulation pipeline 1, and connect the heat transfer oil inlet of the energy-consuming equipment to the circulating liquid outlet 12 of the heat transfer circulation pipeline 1 to form a closed liquid heat transfer circulation system; open the filling port 411 of the liquid storage container 41 and add an appropriate amount of heat transfer oil, start the circulation pump 13 to fill the pipeline of the entire heat transfer circulation system with heat transfer oil, and the air in the pipeline is discharged into the liquid storage container 41 through the first capillary tube 42 and finally discharged through the air outlet of the filling port 411. After normal circulation operation, keep the liquid level of heat transfer oil in the liquid storage container 41 at the upper middle position.
[0038] The heat transfer oil flows into the input end of the circulating pump 13 through the circulating liquid inlet 11 and the input valve 18, and flows out through the output end under the action of the circulating pump 13. When the heat transfer oil needs to be cooled, the first proportional valve 21 of the heating branch 2 is closed, and the heat transfer oil completes heat exchange and cooling through the cooler 31 and / or plate heat exchanger 14 of the cooling branch 3. During this process, the heater 15 is closed and will not heat the heat transfer oil flowing through the heater 15. Since the cooling effect of the cooler 31 is worse than that of the plate heat exchanger 14, the flow rate of the heat transfer oil flowing through the cooler 31 and the plate heat exchanger 14 can be adjusted according to the specific required cooling temperature of the heat transfer oil. For example, if the required cooling temperature of the heat transfer oil is close to room temperature, the flow rate of the heat transfer oil flowing through the cooler 31 can be increased. If the required cooling temperature of the heat transfer oil is low, the flow rate of the heat transfer oil flowing through the plate heat exchanger 14 can be increased. When the heat transfer oil needs to be heated, the second proportional valve 16 and branch valve 32 are both closed, while the first proportional valve 21 and main valve 17 are open. The heat transfer oil flows into the heater 15 through the first proportional valve 21 of the heating branch 2 for heating, and the heating temperature of the heat transfer oil is adjusted by the temperature control of the heater 15. When the oil is in a cooling state but needs to be heated: if a small temperature increase is required, the first proportional valve 21 is opened, and the flow rate of the heat transfer oil flowing through the plate heat exchanger 14 is controlled by adjusting the opening of the first proportional valve 21 and the second proportional valve 16 to achieve the set small temperature increase value; if the temperature increase is large, the first proportional valve 21 is not opened, the heater 15 is opened, and the heater 15 is closed after the heat transfer oil approaches the set temperature increase value. Then the first proportional valve 21 is opened, and the set temperature increase value is achieved by adjusting the opening of the first proportional valve 21 and the second proportional valve 16. When the system is heating up but cooling down is required: If a small temperature drop is needed, the first proportional valve 21, the second proportional valve 16, the main valve 17, and the heater 15 are all closed, while the branch valve 32 of the cooling branch 3 is opened. The heat transfer oil flows through the cooler 31 of the cooling branch 3 and reaches the set temperature after cooling. If the temperature drop is large, the main valve 17, the second proportional valve 16, and the plate heat exchanger 14 are opened, while the first proportional valve 21, the branch valve 32, and the heater 15 are closed. The first proportional valve 21 is opened when the temperature approaches the set value, and the set temperature value is reached by adjusting the opening of the first proportional valve 21 and the second proportional valve 16.
[0039] Example 2:
[0040] In Embodiment 2 of this utility model, using Figure 2 The following description will be provided. Furthermore, descriptions of parts that are no different from those in Embodiment 1 will be omitted, and the same reference numerals will be used instead.
[0041] like Figure 2As shown, the laboratory liquid heat conduction circulation temperature control system of this utility model includes a plate heat exchanger 14 connected to a refrigerant circulation pipeline 5. The refrigerant circulation pipeline 5 includes an expansion valve 51, a compressor 52, a condenser 53, a dryer filter 54, and a second capillary tube 55 connected in series. The expansion valve 51 is positioned near the input end of the refrigerant circulation pipeline 5, and the second capillary tube 55 is positioned near the output end of the refrigerant circulation pipeline 5. The input and output ends of the refrigerant circulation pipeline 5 are connected to the refrigerant output port and refrigerant input port of the plate heat exchanger 14, respectively. It should be noted that the temperature sensing component of the expansion valve 51 is located at the refrigerant input port of the plate heat exchanger 14, i.e., at the output end of the refrigerant circulation pipeline 5.
[0042] Furthermore, the refrigerant circulation pipeline 5 is also equipped with a low-pressure side needle valve 56 and a high-pressure side needle valve 57 arranged on both sides of the compressor 52. The low-pressure side needle valve 56 is arranged near the refrigerant outlet of the plate heat exchanger 14, that is, the low-pressure side needle valve is located on the input side of the compressor 52. The high-pressure side needle valve 57 is located between the compressor 52 and the condenser 53, that is, the high-pressure side needle valve 57 is located on the output side of the compressor 52. The needle valves on both sides are connected to the refrigerant circulation pipeline 5, which facilitates detection and diagnosis, as well as charging and recovery of refrigerant, and ensures the normal and stable operation of the refrigerant circulation pipeline 5.
[0043] It should be noted that in this embodiment, the expansion valve 51, compressor 52, and condenser 53 are all electrically connected to the controller to ensure the normal circulation of refrigerant in the refrigerant circulation pipeline 5, thereby enabling the circulating refrigerant to complete heat exchange and temperature regulation of the circulating liquid in the plate heat exchanger 14.
[0044] In practical use, the refrigerant forms a circulation path between the refrigerant circulation pipeline 5 and the plate heat exchanger 14. The refrigerant flows to the compressor 52 through the refrigerant outlet of the plate heat exchanger 14. After being compressed by the compressor 52, it is discharged from the outlet end of the compressor 52 to the condenser 53. The condenser 53 cools and condenses the compressed refrigerant, and then dries it through the dryer filter 54. The dried refrigerant is depressurized through the second capillary tube 55 to form a low-temperature, low-pressure liquid. Finally, it enters the plate heat exchanger 14 through the refrigerant inlet for heat exchange. The above steps are repeated to complete the refrigerant heat exchange cycle.
[0045] In summary, the laboratory liquid heat conduction circulation temperature control system provided by this utility model integrates cold and heat source temperature control equipment to perform closed-loop circulation temperature regulation of circulating liquids such as heat conduction oil. While ensuring the overall stability and reliability of the system, it also achieves a wide temperature range coverage, high temperature control accuracy, and fast response speed. It is highly practical and easy to promote and use on a large scale.
[0046] The above are merely preferred embodiments of the present utility model and do not limit the patent scope of the present utility model. All equivalent changes and modifications made within the scope of the present utility model shall still fall within the scope of the present utility model.
Claims
1. A laboratory liquid thermal conductivity circulating temperature control system, characterized in that: It includes a heat-conducting circulation pipeline (1) with a circulating liquid inlet (11) and a circulating liquid outlet (12), and a circulation pump (13), a plate heat exchanger (14) and a heater (15) arranged in series on the heat-conducting circulation pipeline (1). The circulation pump (13) is arranged near the circulating liquid inlet (11), and the heater (15) is arranged near the circulating liquid outlet (12). The plate heat exchanger (14) is provided with a heating branch (2) connected in parallel. The output end of the heating branch (2) is located between the heater (15) and the plate heat exchanger (14). The heating branch (2) is provided with a first proportional valve (21). The heat conduction circulation pipeline (1) is provided with a second proportional valve (16). The second proportional valve (16) is located between the input end of the heating branch (2) and the input end of the plate heat exchanger (14).
2. The laboratory liquid thermal conductivity circulating temperature control system according to claim 1, characterized in that: The heat-conducting circulation pipeline (1) is provided with a cooling branch (3) connected in parallel with the plate heat exchanger (14) and the heater (15). The input end of the cooling branch (3) is arranged close to the output end of the circulation pump (13). The cooling branch (3) is equipped with a cooler (31) and a branch valve (32) connected in series, and the branch valve (32) is arranged near the input end of the cooling branch (3).
3. The laboratory liquid thermal conductivity circulating temperature control system according to claim 2, characterized in that: The heat conduction circulation pipeline (1) is provided with a main valve (17) located near the output end of the heater (15), and the main valve (17) is located between the output end of the heater (15) and the output end of the cooling branch (3).
4. The laboratory liquid thermal conductivity circulating temperature control system according to claim 1, characterized in that: The heat conduction circulation pipeline (1) is provided with a liquid recovery pipeline (4) connected in parallel. The liquid recovery pipeline (4) is provided with a liquid storage container (41). The input end of the liquid storage container (41) is connected to the steam outlet (151) of the heater (15), and the output end of the liquid storage container (41) is connected to the input end of the circulation pump (13).
5. The laboratory liquid thermal conductivity circulating temperature control system according to claim 4, characterized in that: The liquid recovery pipeline (4) is also provided with a first capillary tube (42) and a check valve (43) connected in series with the liquid storage container (41). The first capillary tube (42) is arranged near the input end of the liquid storage container (41), and the check valve (43) is arranged near the output end of the liquid storage container (41).
6. The laboratory liquid thermal conductivity circulating temperature control system according to claim 4, characterized in that: The liquid storage container (41) is equipped with a level gauge for monitoring the liquid level in its inner cavity and a filling port (411) connected to its inner cavity. The filling port (411) is equipped with an air outlet that connects the inner cavity of the liquid storage container (41) to the external atmospheric environment.
7. The laboratory liquid thermal conductivity circulating temperature control system according to claim 1, characterized in that: The plate heat exchanger (14) is provided with a refrigerant circulation pipeline (5) connected thereto. The refrigerant circulation pipeline (5) is provided with an expansion valve (51), a compressor (52), a condenser (53), a dryer filter (54) and a second capillary tube (55) connected in series. The expansion valve (51) is located near the input end of the refrigerant circulation pipeline (5), and the second capillary tube (55) is located near the output end of the refrigerant circulation pipeline (5).
8. The laboratory liquid thermal conductivity circulating temperature control system according to claim 7, characterized in that: The refrigerant circulation pipeline (5) is also provided with a low-pressure needle valve (56) and a high-pressure needle valve (57) arranged on both sides of the compressor (52). The low-pressure needle valve (56) is located on the input side of the compressor (52), and the high-pressure needle valve (57) is located on the output side of the compressor (52).
9. The laboratory liquid thermal conductivity circulating temperature control system according to claim 1, characterized in that: The heat-conducting circulation pipeline (1) is provided with an input valve (18) located near the end of the circulating liquid inlet (11) and an output valve (19) located near the end of the circulating liquid outlet (12).