Patent Application
20230034594
The present invention is directed at a thermal expansion valve for a residential refrigeration application, comprising a valve body with a high pressure inlet, a low pressure outlet, a first suction gas port and a second suction gas port. The valve further comprises a superheat defining mechanism with a diaphragm, a pushpin and a charge.
The presently described thermal expansion valve (TXV) is a block type valve. However, the invention may also pertain to different types of valves.
Block type or similar TXV's without a separate sensor bulb are challenging to apply to systems requiring long valve time constants due to the nature of their design. The close vicinity of the charge (above the diaphragm) to the superheated suction gas causes very fast temperature and pressure changes of the charge. This can lead to unstable super heat control on larger refrigeration systems where the dynamics of the system causes the valve to “hunt” the superheat (SH), constantly opening and closing the valve in periods of seconds or minutes.
One way to avoid this “hunting” is to increase the time constant of the valve. The time constant defines the time it takes the valve to reach 63% of a new setpoint. E.g., if the SH increases by 4K, the time constant is defined by the time it takes for the valve to change the opening equivalent to 63% of a 4K SH increase.
The time constant can be affected in several ways, e.g. by changing the thermal resistance between the superheated gas and the charge and/or by changing other material properties and/or geometries of the valve or similar solutions.
However, when valve systems are designed for obtaining very high time constants, of e.g. 60-300 seconds or more, these solutions lead to systems, which are very sensitive to the tolerances of their components. In particular, the gaps between said components and the contact areas between the components influence conductive heat transfer significantly and are dependent on precise tolerances. Also, these solutions are strongly influenced by the effects of ambient temperature on the charge.
The aim of the present invention is to overcome these problems by providing a cheaper and more robust valve. This aim is reached by a thermal expansion valve according to claim 1. Preferable embodiments of the invention are subject of the dependent claims.
According to the invention, a thermal expansion valve for a residential refrigeration application is provided. The valve comprises a valve body with a high pressure inlet, a low pressure outlet, a first suction gas port and a second suction gas port. The suction gas ports may be bidirectional, i.e. they may function as an inlet or an outlet, depending on the direction of the fluid flow. The valve further comprises a superheat defining mechanism with a diaphragm, a pushpin and a charge. The superheat defining mechanism typically provides some mechanical feedback between the gas flowing through the valve and the position of the valve. The valve may be set by the superheat defining mechanism such that gas leaving the refrigeration application is maintained at or near superheat conditions.
According to the invention, the amount of charge is selected such that a part of the charge is in a liquid state at typical operation conditions of the refrigeration application. The charge may be selected such that at least some of the charge or rather the corresponding fluid is in liquid phase at all operation conditions of the refrigeration application. In other words, the charge is never fully in a gaseous state in normal operation conditions of the refrigeration application.
The typical operation conditions of the refrigeration application may correspond to internal temperature ranges of the refrigeration application, which the refrigeration application is designed for and/or external temperature ranges, in which the refrigeration application may typically be used.
The invention makes it possible to increase the heat transfer between the SH gas and the charge, and to control the time constant by adding ballast material to the charge, thereby achieving a robust, energy efficient design that is not significantly affected by production tolerances or ambient temperature. The charge may be understood to comprise only a fluid or a fluid and the corresponding ballast material.
Examples of designs for varying the heat transfer between the SH gas and the charge include the selections of the diameter and the material of the pushpin of the valve. Changing its diameter from 1.5 to 6 mm increases its cross-sectional area and thereby its heat transfer capacity by 16 times. Also, a material change from stainless steel to aluminum increases the thermal conductivity by 17 times. By combining these two factors, the thermal resistance of a 10 mm pushpin can be varied between 0.0015 and 0.4042K/W, i.e. by a factor of approximately 270
Alternatively or additionally, a passage or gap for the SH gas can be provided to the underside of the diaphragm, thereby increasing the effective heat transfer to the charge and reducing the time constant of the valve.
By variating the diameter of the pushpin and the size of the gap, the area of the passage can be variated significantly. For example, by variating the diameter of the pushpin from 1.5 to 6 mm and the size of the gap from 0.02 to 1 mm, the area of the gap varies from 0.1 to 18.8 mm2, i.e. a factor of ca. 200
Alternatively or additionally, a guide element or flow restrictor can be placed between the pushpin and the valve body or valve house to guide the pushpin and optionally restrict the flow of gas along the pushpin and towards the diaphragm.
The internal structure of the valve may hence be designed in such a way that the heat transfer between the suction gas and the charge is very high. Accordingly, the time constant associated only with the immediate heat transfer between the suction gas and the charge will be very low. However, in the charge volume, an anti-hunt or ballast may be provided, increasing the time constant significantly. By having this design, the time constant is defined in the relationships between the charge volume, the amount/weight of charge (mg), the phase distribution of the charge or rather the fluid component of the charge, the distribution of the liquid phase of the fluid between a portion absorbed by the ballast material and a non-absorbed or free flowing portion, and/or the amount of ballast material.
These factors can be precisely controlled during the manufacturing of the valve. They will not be significantly affected by part tolerances. At the same time, due to the high heat transfer from the suction gas to the charge, the valve will be less sensitive to disturbances from ambient temperature. It can therefore provide better energy efficiency (i.e. operation at low SH conditions) and protect the compressor from e.g. flooding in all operation conditions.
In a preferred embodiment of the invention, the charge comprises ballast material and/or the charge comprises a refrigerant other than CO2 and/or the time constant of the valve is a function of at least the dimensions and materials of the superheat defining mechanism, wherein the superheat defining mechanism is designed for providing a time constant of greater than 30 seconds, in particular greater than 60 seconds, and wherein the charge is designed such that it determines the value of the time constant for the most part and/or that the superheat defining mechanism comprises a superheat setting screw. The time constant without consideration of the charge may be in the order of several seconds or less. However, the charge may increase the time constant to several tens or hundreds of seconds.
The ballast material or anti-hunt can consist of different materials and/or of a mixture of different materials. It may be provided in different shapes.
The charge may comprise or consist of different medias. Typical refrigerants such as HFC (R410A, R32, R134a), HCFC's (R22, R142b), HFO (R1234yf, R1234ze) or natural refrigerants (R290, R744), either with a single media or as a blend of multiple medias may be chosen. Additionally, the charge may be pressurized with an inert gas such as Nitrogen.
The amount of charge can vary depending on application, system type and amount of ballast used, but will typically range from 50-500 mg/cm3 available volume. This is much higher than the typical charge for a block type valve, where the charge typically will be 5-20 mg/cm3 available volume.
In another preferred embodiment of the invention, a protection member is provided between the diaphragm and the ballast material of the charge or the ballast material of the charge is in direct contact with the diaphragm and/or the charge density is 30 to 350 mg/cm3, preferably 60 mg/cm3 to 100 mg/cm3 if ballast material is provided and 50-400 mg/cm3 if no ballast material is provided.
Since the ballast material is in close vicinity to the diaphragm, a protection member may be required between the diaphragm and the ballast material, blocking the filter elements, or particles hereof, from damaging the diaphragm. This element can take many forms, like solid perforated, flat mesh, porous filter or like.
In another preferred embodiment of the invention, the superheat defining mechanism comprises a diaphragm top, a diaphragm bottom and/or a diaphragm support, wherein the diaphragm support comprises a perforated plate and/or a ring and/or a non-rotational-symmetric plate.
The diaphragm support may be used in particular in combination with a cylindrical or largely cylindrical diaphragm top. The diaphragm support may connect the diaphragm top to the diaphragm bottom and/or provide support for the diaphragm.
In another preferred embodiment of the invention, a connection element is provided for connecting the pushpin and/or the diaphragm bottom 29 to the valve body 1.
In another preferred embodiment of the invention, the diaphragm top is shaped at least partially cylindrically. The cylindrical or partially cylindrical shape of the diaphragm top may advantageously increase the volume of the charge provided between the diaphragm top and the diaphragm.
In another preferred embodiment of the invention, ballast material of the charge comprises diatomite, a molecular sieve and/or marinite and/or is provided in cylindrical, cubic, conical, spherical and/or toroidal form.
In another preferred embodiment of the invention, the charge is pressurized with an inert gas such as nitrogen.
In another preferred embodiment of the invention, the high pressure inlet is provided between the low pressure outlet on the one side and the first suction gas port and/or second suction gas port on the other side with respect to an axial direction of the valve body.
In another preferred embodiment of the invention, the connection between the diaphragm and the valve body comprises a knife edge seal and/or an O-ring and/or a weld. The connection between the diaphragm and the valve body may include further components such that the valve body and the diaphragm are not necessarily in direct contact with each other.
In another preferred embodiment of the invention, the valve comprises a check valve. The check valve may simplify the use of the valve as a bidirectional valve.
Further advantages and details of the invention are described with reference to the following figures, the figures showing:
Inside a sealed portion of the superheat defining mechanism 2, the amount of charge 22 is selected such that a part of the charge 22 is in a liquid state at typical operation conditions of the refrigeration application. The charge may comprise or consist of different medias. Typical refrigerants such as HFC (R410A, R32, R134a), HCFC's (R22, R142b), HFO (R1234yf, R1234ze) or natural refrigerants (R290, R744), either with a single media or as a blend of multiple medias may be chosen. Additionally, the charge may be pressurized with an inert gas such as nitrogen. The charge 22 may comprise a refrigerant other than CO2.
The superheat defining mechanism 2 comprises a diaphragm top 28, a diaphragm bottom 29 and/or a diaphragm support 30, wherein the diaphragm support 30 is shown in
A connection element 15 is provided for connecting superheat defining mechanism (2), particularly the diaphragm bottom 29, to the valve body 1. More details on the connection element 15 will be shown with reference to
The high pressure inlet 11 is provided between the low pressure outlet 12 on the one side and the first suction gas port 13 and/or second suction gas port 14 on the other side with respect to an axial direction of the valve body 1. The axial direction of the valve body 1 corresponds to the vertical direction in
Usually, the expansion direction in block valves occur from a lower high pressure inlet to an upper low pressure outlet, i.e. in the opposite direction it occurs at the shown embodiments. One reason to do this is to avoid the need of a piston seal 34 on the pushpin 23 and/or cone. In the shown embodiments, a corresponding seal 34 is present and the expansion direction is from the upper high pressure inlet 11 to the lower low pressure outlet 12. In other embodiments of the invention, the expansion direction could be inverted.
The diaphragm assembly of
In all embodiments, the charge 22 may comprise ballast material, which functions as a thermal-transfer-delay means. The ballast material is indicated by spherical objects between the diaphragm 21 and the diaphragm top 28. The ballast material of the charge 22 may comprise diatomite, a molecular sieve and/or marinite and/or may be provided in cylindrical, cubic, conical, spherical and/or toroidal form.
The time constant of the valve is a function of the dimensions and materials of the superheat defining mechanism 2 as well as its charge 22. The superheat defining mechanism 2 is designed for providing a time constant of greater than 30 seconds, in particular greater than 60 seconds. The charge 22 may be chosen such that it determines the value of the time constant for the most part.
The embodiments of
The embodiments of
According to the embodiment of
An additional diaphragm support 30 is shown in
A known way of fixing and sealing the diaphragm assembly is by means of a thread and an O-ring 25. The embodiment of
Alternatively or additionally, laser welding, soldering and/or laser brazing may be applied to the interfacing elements, such as the connection element 15 and the valve body 1. An aluminium interface element or connection element 15 could be brazed to the stainless steel lower capsule, diaphragm bottom 29 and/or valve body prior to the laser welding.
A gap 33 is shown radially inwards of the connection element 15. The gap 33 may be located between the connection element 15 and the pushpin 23 for providing a fluid passage between the first and second suction gas ports 13, 14 and the diaphragm 21. The diaphragm 21 is not shown in
Features not shown in the figures may include an additional check valve provided at the thermal expansion valve. The check valve may be an internal check valve, allowing the valve to be used in reversible systems, where the expansion function/orifice 36 shown in
While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.
