Refrigeration system and method of operating a refrigeration system

Abstract

A refrigeration system including an evaporator 100 is disclosed, as well as a method of operating a refrigeration system. The evaporator 100 includes a first fluid volume 110 upstream of a second fluid volume 120, and a plurality of passages 130 fluidly connecting the first fluid volume 110 and the second fluid volume 120. The system further includes a flow restrictor 150 arranged to prevent fluid flow through at least a first passage of the plurality of passages 130 in response to a pressure differential between the first fluid volume 100 and the second fluid volume 120 being less than a predetermined threshold, and to permit fluid flow through the first passage in response to the pressure differential being greater than the predetermined threshold.

Description

Technical Field

[0001] This invention relates to a refrigeration system including an evaporator, and to a method of operating the refrigeration system. Background Technology

[0002] Refrigeration systems are used for a wide variety of heating, cooling, and environmental conditioning needs, including comfort and industrial applications. Different systems can be suited to different purposes, where the system's components are designed to provide desired or predetermined functions and operate within specific parameter ranges or serve specific conditions, such as a specific temperature range. For example, a refrigeration system used for ice making may not be suitable for air conditioning a space.

[0003] Some systems use liquid coolants and operate under negative-temperature brine conditions, for example, by using a working fluid (e.g., water) containing additives that allow the working fluid to operate below its freezing point without freezing (thus, the temperature is negative relative to the Celsius (°C) scale). Refrigeration systems operating under negative-temperature brine conditions typically use suitable heat exchangers, such as copper plate heat exchangers (BPHE) or direct expansion (DX) evaporators. However, they can alternatively use evaporators with heat exchange tube bundles of predetermined cross-sections (e.g., flooded evaporators) to facilitate the desired fluid velocity required to maintain sufficient turbulence for the desired heat transfer. However, the use of tube bundles of predetermined size limits the functionality of the refrigeration system because the higher flow rates required for conditions such as positive-temperature brine are not possible without generating too large a pressure drop across the evaporator. Summary of the Invention

[0004] According to a first aspect of the invention, a refrigeration system including an evaporator is provided, the evaporator comprising: a first fluid volume upstream of a second fluid volume, and a plurality of channels fluidly connecting the first fluid volume and the second fluid volume; the system further comprising a flow restrictor arranged to prevent fluid from flowing through at least a first channel of the plurality of channels in response to a pressure difference between the first fluid volume and the second fluid volume being less than a predetermined threshold, and to allow fluid to flow through the first channel in response to the pressure difference being greater than the predetermined threshold.

[0005] Therefore, the refrigeration system can operate in two different modes, one with a lower total flow cross-section through the evaporator and the other with a higher total flow cross-section through the evaporator.

[0006] A flow restrictor can be arranged to move or switch between a first configuration where the first channel is closed and a second configuration where the first channel is open. Therefore, the flow restrictor is operable to control the flow between a first fluid volume and a second fluid volume by closing and / or opening the first channel. Thus, the flow restrictor is operable to increase the fluid velocity in the open channel to maintain sufficient turbulence for the desired heat transfer, for example, when the fluid viscosity increases due to lower brine temperature conditions. The flow restrictor can be arranged to reduce the total flow cross-section through the evaporator in a first mode and increase the total flow cross-section through the evaporator in a second mode. The flow restrictor can be arranged to ensure that the flow cross-section outside the first fluid volume is the same as the flow cross-section entering the second fluid volume (e.g., in a multi-pass evaporator). The flow restrictor can be arranged to maintain the fluid velocity in the multiple channels within a predetermined range. The flow restrictor can be arranged to reduce the total flow cross-section in response to the total flow volume through the evaporator being less than a total fluid flow volume threshold, thereby maintaining the fluid velocity in the multiple channels above the fluid velocity threshold. A flow restrictor can be arranged to increase the total flow cross-section in response to the total flow volume through the evaporator exceeding a total fluid flow volume threshold, thereby maintaining the fluid velocity in multiple channels above the fluid velocity threshold while keeping the pressure difference below a desired or predetermined level. The pressure difference can be a function of the fluid flow rate, temperature, and other system conditions and parameters. Therefore, the fluid flow volume threshold can vary as a function of temperature, etc. The predetermined threshold for the pressure difference can be a function of system conditions. The pressure difference can be a function of the flow rate. The thresholds discussed herein can be for a given (e.g., fixed) system condition (e.g., for a given temperature, ethylene glycol percentage, etc.). The thresholds can differ for different system conditions or applications.

[0007] The system can operate in two different modes, for example, a first negative brine temperature low flow mode that prevents flow through the first channel, and a second positive brine temperature high flow mode that allows flow through the first channel. Therefore, the present invention can provide a refrigeration system capable of having dual modes, for example, for negative temperature cooling water and positive temperature cooling water. The flow restrictor can automatically adjust the flow through the evaporator in response to changes in the pressure difference (e.g., pressure drop across the evaporator) between the first and second fluid volumes. Such changes may be caused, for example, by a user changing desired settings, such as increasing the pump rate for a positive temperature by delivering more cooling capacity or a decrease in temperature (thus increasing the viscosity of the working fluid, and subsequently increasing the pressure drop for a given flow rate). Changes in the pressure difference may be caused by any suitable system or environmental changes.

[0008] Flow restrictors can be arranged to prevent or permit fluid flow through multiple of a plurality of channels. Typically, an evaporator will have a tube bundle providing multiple channels between a first fluid volume and a second fluid volume, and the flow restrictor can be arranged to prevent or permit fluid flow through multiple of the multiple channels (i.e., not only through the first fluid channel). A flow restrictor can be arranged to prevent or permit fluid flow through multiple (but not all) of the multiple channels. A flow restrictor can be arranged to prevent fluid flow through only some (e.g., a subset) of the multiple channels. A flow restrictor may not be able to prevent fluid flow through all fluid channels. A flow restrictor can be arranged not to prevent or permit fluid flow through some of the multiple channels. Therefore, a flow restrictor can be arranged to prevent or permit fluid flow through the first channel (or through multiple of the multiple channels) and always permit fluid flow through the other channels. In both modes, some flow through the evaporator may exist, for example, during operation, there may always be flow through the evaporator.

[0009] Flow restrictors can be arranged to control (i.e., prevent or permit) fluid flow through approximately one-quarter, one-third, half, or three-quarters of multiple channels. Therefore, flow restrictors can have a significant effect on the flow through the evaporator. Flow restrictors can also be arranged to control more than one-quarter, more than half, or more than three-quarters of the flow through multiple channels.

[0010] The plurality of channels may be heat exchange channels (e.g., pipes), and therefore may be arranged to allow heat exchange between a fluid flowing therein (e.g., from a first fluid volume to a second fluid volume) and another fluid outside the channels. Thus, a flow restrictor may be arranged to increase or decrease heat exchange by increasing or decreasing the fluid flow between the first and second fluid volumes as needed. The system may be arranged such that the first and second fluid volumes receive a coolant fluid (e.g., water and antifreeze additives, brine, etc.) during use. The system may be arranged such that, during use, the refrigerant is outside the first and second fluid volumes and outside the plurality of channels. The system may be arranged such that, during use, the coolant fluid exchanges heat with the refrigerant. The system may include a liquid coolant cycle, and the first and second fluid volumes and the plurality of channels may form part of the liquid coolant cycle. An evaporator and a flow restrictor may be part of the liquid coolant cycle. The system may be arranged such that the fluid in the liquid coolant cycle is always a liquid during use. The system may be arranged such that, during use, the refrigerant undergoes a vapor compression cycle, and its state changes to liquid and from liquid, for example, within the evaporator. The system can be arranged such that the coolant fluid circulating through the evaporator remains liquid (e.g., water or an aqueous mixture) during use. That is, the system can be arranged such that the working fluid (e.g., coolant fluid) in the first and second fluid volumes of the evaporator remains liquid during use and throughout its circulation. Therefore, the invention can relate to systems that rely on liquid coolants (and not simply direct expansion systems using, for example, refrigerant fluid and air).

[0011] The second fluid volume can be downstream of the first fluid volume and can therefore be arranged to receive fluid flow from the first fluid volume. All fluid flow from the first fluid volume to the second fluid volume can be via multiple channels. The first channel can carry only a portion of the fluid flow between the first and second fluid volumes. In the case where a flow restrictor controls the flow through multiple of the multiple fluid channels, the multiple channels can carry only a portion of the flow between the first and second fluid volumes (when they are open).

[0012] The evaporator can be any suitable evaporator. The evaporator can be an overflow evaporator. The evaporator can be any suitable wet evaporator. The evaporator can be a falling film evaporator, etc. The evaporator can be any shell-and-tube heat exchanger that uses a coolant (e.g., water or any other coolant fluid) inside the tubes and a refrigerant outside the tubes in the shell. The system can be arranged such that the evaporator receives 100% liquid coolant in the first and second fluid volumes, and that the coolant remains liquid throughout the circulation including the first and second fluid volumes. The evaporator can be a liquid cooler, or it can be a heat pump that uses a liquid coolant as a heat source.

[0013] The refrigeration system can be any suitable heat cycle system, such as a refrigeration system, heat pump, etc. The refrigeration system can be a liquid cooling system. The refrigeration system can be any system that relies on a liquid coolant. The refrigeration system may use not only refrigerant fluid and air. The refrigeration system can be operated to heat and / or cool, for example, depending on the operating mode. For example, the system can be arranged to cool when the flow restrictor is in a first configuration, and can be operated to cool less (or heat) when the flow restrictor is in a second configuration. The system can be a heating, ventilation, and air conditioning (HVAC) system. The system can be a heating, ventilation, air conditioning, and cooling (HVACR) system. The system can be a heating, air conditioning, and cooling (HACR) system. The refrigeration system can be a heating and cooling system.

[0014] The evaporator can be, for example, a single-pass evaporator, such that the first fluid volume and the second fluid volume are located at opposite ends of the evaporator. Alternatively, the evaporator can be a multi-pass evaporator. The evaporator can be, for example, a two-pass evaporator, such that the first fluid volume and the second fluid volume are on the same side of the evaporator.

[0015] A flow restrictor can be part of the evaporator or part of the refrigeration system. A flow restrictor can be mechanically coupled to the evaporator. A flow restrictor may not control fluid flow outside the evaporator.

[0016] The first and second fluid volumes can be mutually exclusive; for example, they may not overlap. The first and second fluid volumes can be entirely within the evaporator. All fluid entering the second fluid volume can originate from the first fluid volume (e.g., via multiple channels).

[0017] The flow restrictor can be an electronic device. It may include, for example, one or more pressure sensors arranged to detect pressure in a first fluid volume and a second fluid volume, and may be configured to switch the flow restrictor between different modes in response to measurements from the sensors. The electronic flow restrictor may include electronically powered actuators, etc. The electronic flow restrictor is operable to control fluid flow through at least a first fluid channel upon command from a user of, for example, a refrigeration system. The flow restrictor may be operated by an electronic controller or command circuitry (e.g., a system controller, etc.), which may also be arranged to control other components of the refrigeration system. The electronic flow restrictor may change its configuration in response to commands (e.g., signals) from the controller. The electronic flow restrictor may be (at least partially) located outside the evaporator. The flow restrictor is operable to control flow through the first fluid channel to benefit, for example, from a larger heat transfer surface when the system is operating under turbulence-compatible conditions.

[0018] Flow restrictors can be mechanical. A flow restrictor can be entirely mechanical and can operate in response to a pressure difference between a first fluid volume and a second fluid volume. A flow restrictor can be pressure-actuated and can change its configuration in response to changes in the pressure difference. Therefore, it is possible to avoid, for example, using externally powered actuators and / or electronic controllers or command circuits to control the flow restrictor.

[0019] Therefore, the flow restrictor can automatically adjust the total flow cross-section through the evaporator, and thus can automatically adjust the fluid flow velocity in multiple channels. Therefore, the flow restrictor can automatically adjust turbulence in multiple channels, and thus can automatically adjust heat exchange efficiency. Therefore, the flow restrictor can operate solely in response to pressure differential and, for example, cannot be controlled by any other means. Alternatively, the flow restrictor may include a manual overrun control to allow or prevent fluid flow through the first fluid channel regardless of the pressure differential.

[0020] The flow restrictor may include a piston movable between a first position and a second position, and may include a biasing mechanism arranged to push the piston to the first position. The flow restrictor may be arranged such that when the pressure difference between a first fluid volume and a second fluid volume is less than a predetermined threshold, the piston is pushed to the first position by the biasing mechanism, and such that when the pressure difference is greater than the predetermined threshold, the piston resists the action of the biasing mechanism and moves to the second position. Therefore, the biasing mechanism can determine a predetermined threshold at which the flow restrictor changes its configuration between its first and second configurations. Thus, the biasing mechanism can be selected such that the flow restrictor changes its configuration (and therefore its operating mode) at the predetermined threshold.

[0021] The biasing mechanism can be any suitable mechanical device, and can be, for example, a spring, a disc spring, a leaf spring, an elastic member, a predetermined counterweight, etc.

[0022] The flow restrictor may include an actuable flap arranged to allow or prevent fluid flow through a first channel. The actuable flap may be actuated by movement of a piston, which may be actuated by a pressure difference between a first fluid volume and a second fluid volume.

[0023] For example, when the pressure differential increases beyond a predetermined threshold (e.g., when the refrigeration system switches to a higher total flow mode, such as high-flow-rate operation at a positive brine temperature), the pressure differential (i.e., the pressure drop across the evaporator) may increase due to the higher flow rate, and thus may cause the piston to move from its first position to its second position against the action of the biasing mechanism. The piston's movement may cause (e.g., via a mechanical coupling) an actuable flapper to move (e.g., open), thereby allowing fluid to flow through the first channel.

[0024] When the pressure difference decreases to less than a predetermined threshold (e.g., when the system switches to a lower total flow mode, such as low-flow operation at a negative brine temperature), the biasing mechanism can overcome the force caused by the pressure difference and cause the piston to move from its second position to its first position. The movement of the piston to its first position can cause (e.g., via a mechanical coupling) an actuable flapper to move (e.g., close), thereby preventing fluid from flowing through the first channel.

[0025] The flapper can be mechanically coupled to the piston and moved via the coupling. For example, a rod can connect the piston to the flapper. The flapper can be actuated by the piston via any suitable coupling or connection.

[0026] The flap can be closed, for example, by covering the inlet or outlet of the first channel. For example, the flap can close the inlet from the first fluid volume to the first channel, or it can close the outlet of the first channel into the second fluid volume.

[0027] The flow restrictor may include multiple flaps. For example, the flow restrictor may include two flaps, which can simultaneously prevent flow from a first fluid volume into a first channel and prevent flow from exiting a second channel into a second fluid volume. The two flaps can always move synchronously, so that the cross-section of the flow through the multiple channels is always uniform along its length.

[0028] The first and second fluid volumes can be adjacent to each other in the header of an evaporator, for example, the evaporator can be a two-pass evaporator. The evaporator may include separators or partitions (e.g., walls) in the header to separate the first fluid volume from the second fluid volume. The plurality of channels can flow back and forth through the evaporator. The plurality of channels can retrace their course (e.g., make a U-turn). The evaporator may include another second header on the side of the evaporator opposite to the first header, and the plurality of channels may include a first tube bundle (e.g., one pass through the evaporator) for supplying flow from the first fluid volume to the second header, and a second tube bundle (e.g., another pass through the evaporator) for supplying fluid flow from the second header to the second fluid volume. The flow through the second tube bundle can be parallel and opposite to the flow through the first tube bundle. The second header can be downstream of the first fluid volume. All fluid flow leaving the first fluid volume can be transferred to the second header via the first tube bundle. The second header can be upstream of the second fluid volume. All fluid flow leaving the second header can be transferred to the second fluid volume via the second tube bundle. All fluid flows entering the second manifold can originate from the first fluid volume, and all fluid flows entering the second fluid volume can originate from the second manifold. Therefore, the second manifold can fluidly connect the first tube bundle to the second tube bundle.

[0029] The flow restrictor may be located within the manifold. The flow restrictor may be entirely within the manifold. Therefore, the flow restrictor may be part of the evaporator. The flow restrictor may be housed within a separator (e.g., a wall) that separates the first and second fluid volumes. Therefore, the flow restrictor may be within the first and second fluid volumes and / or between the first and second fluid volumes. The flow restrictor may be partially within the first fluid volume and partially within the second fluid volume. By positioning the flow restrictor between the first and second fluid volumes, the flow restrictor can be simply exposed to the pressure within the first and second fluid volumes, and therefore, the flow through the evaporator can be automatically adjusted as described herein.

[0030] The flow restrictor can be located outside the first and second fluid volumes. Therefore, the evaporator can be a single-pass or multi-pass evaporator. Each of the first and second fluid volumes can be divided into a main fluid volume and an auxiliary fluid volume. The system may include an auxiliary inlet into the auxiliary fluid volume of the first fluid volume and an auxiliary outlet from the auxiliary fluid volume of the second fluid volume. The flow restrictor can be arranged to allow or prevent flow through the auxiliary inlet and / or auxiliary outlet, thereby allowing or preventing fluid flow through the first channel. A flapper can be disposed within the auxiliary inlet and / or auxiliary outlet.

[0031] The system may include a first pressure conduit leading to a flow restrictor and a second pressure conduit leading to a flow restrictor. The first and second pressure conduits may be arranged to actuate the flow restrictor (e.g., a piston) based on the pressure difference between the main volume of a first fluid volume and the main volume of a second fluid volume.

[0032] A flow restrictor can be configured to automatically limit the pressure drop between a first fluid volume and a second fluid volume, for example, by changing its mode in response to changes in pressure difference. Therefore, the flow restrictor can automatically adjust the fluid velocity through multiple channels, and thus automatically adjust the turbulence therein (since turbulence depends on fluid velocity). Consequently, the flow restrictor can ensure sufficient turbulence in multiple channels for efficient heat exchange over a wider range of operating parameters than is possible without a flow restrictor. Therefore, the flow restrictor can be configured to guarantee the required Reynolds number for the heat exchange fluid flow.

[0033] According to a second aspect of the invention, a method is provided for operating a refrigeration system to switch from a first operating mode to a second operating mode, the refrigeration system including an evaporator, the evaporator including a first fluid volume upstream of a second fluid volume and a plurality of channels fluidly connecting the first fluid volume and the second fluid volume; the method includes allowing or preventing fluid flow through a first channel of the plurality of channels based on a pressure difference between the first fluid volume and the second fluid volume.

[0034] The method may include allowing fluid to flow through the first channel in response to the pressure difference exceeding a predetermined threshold (e.g., using a flow restrictor). The method may include increasing the total flow cross-section through the evaporator when the pressure difference exceeds the predetermined threshold. The method may include preventing the pressure drop across the evaporator from exceeding a predetermined amount.

[0035] The method may include preventing fluid from flowing through the first channel in response to the pressure difference falling below the predetermined threshold (e.g., using a flow restrictor). The method may also include reducing the total flow cross-section through the evaporator when the pressure difference is less than the predetermined threshold.

[0036] The method may include altering the flow cross-section through the evaporator in response to a change in the pressure difference between a first fluid volume and a second fluid volume. Thus, the method may include, for example, maintaining the fluid velocity in multiple channels within a predetermined range for the desired heat transfer.

[0037] The first mode can be a negative brine temperature and low flow rate mode. The second mode can be a positive brine temperature and high flow rate mode. The method may include switching the evaporator from a positive brine temperature and high flow rate mode to a negative brine temperature and low flow rate mode, and may further include switching the evaporator from a negative brine temperature mode to a positive brine temperature mode.

[0038] The method may include automatically allowing flow through the first channel in response to the pressure difference exceeding the predetermined threshold; and / or automatically preventing flow through the first channel in response to the pressure difference falling below the predetermined threshold. That is, no additional input may be required besides changes in the pressure difference.

[0039] The method may include automatically adjusting the flow through said plurality of channels by, for example, using a flow limiter to close and / or open at least a first channel of a plurality of channels. The method may also include adjusting the flow by, for example, using a flow limiter to close and / or open multiple channels of a plurality of channels.

[0040] The method may include adjusting the fluid velocity within the plurality of channels by increasing and / or decreasing the number of channels through which fluid flows. The method may also include automatically adjusting the fluid velocity within the plurality of channels by increasing and / or decreasing the number of channels through which fluid flows (e.g., by opening and / or closing channels using flow restrictors).

[0041] The method may include maintaining turbulence in the plurality of channels within a predetermined range. The method may include reducing the total flow cross-section by closing a first channel, thereby increasing the fluid velocity through the open channels of the plurality of channels to maintain turbulence. The method may also include increasing the total flow cross-section by opening the first channel.

[0042] The method may include limiting the pressure drop across the evaporator by allowing fluid to flow through a first channel. The method may include automatically limiting the pressure drop. The method may include configuring a flow restrictor to automatically limit the pressure drop between a first fluid volume and a second fluid volume by opening the first channel and allowing fluid to flow through it. The method may include accordingly selecting a biasing mechanism for the flow restrictor.

[0043] The method may include preventing or allowing flow through multiple of a plurality of channels. It may include always allowing flow through at least one of the plurality of channels.

[0044] The method may include controlling the pressure drop between a first fluid volume and a second fluid volume, and thus may include controlling the fluid velocity through the channels, and thus may include controlling turbulence in the plurality of fluid channels. Therefore, the method may include controlling turbulence in the plurality of channels to ensure sufficient heat exchange. The method may include ensuring that the heat exchange efficiency does not drop below a predetermined level.

[0045] The method may include using a refrigeration system as described herein with reference to a first aspect of the invention. The refrigeration system as described herein with reference to a first aspect of the invention may be configured to implement the method as described herein with reference to a second aspect of the invention.

[0046] According to another aspect of the invention, a system is provided comprising a heat exchanger including a plurality of channels and a flow restrictor operable to open and close some of the plurality of channels. The heat exchanger may be an evaporator. The heat exchanger forms part of a liquid coolant cycle. The system may include any of the features described herein with reference to a first aspect of the invention, and / or may be configured to implement the methods described herein with reference to a second aspect of the invention. Attached Figure Description

[0047] Some preferred embodiments of the invention will be described below by way of example only and with reference to the accompanying drawings, wherein:

[0048] Figure 1 A schematic diagram of a portion of the evaporator is shown with the flow restrictor in its first configuration.

[0049] Figure 2 This shows the case where the flow limiter is in the second configuration. Figure 1 The portion of the evaporator;

[0050] Figure 3 A schematic diagram of a portion of the evaporator is shown with the flow restrictor in its first configuration; and

[0051] Figure 4 This shows the case where the flow limiter is in the second configuration. Figure 3 The portion of the evaporator. Detailed Implementation

[0052] Figure 1A schematic diagram showing a portion of a multi-pass heat exchanger, specifically a two-pass overflow evaporator 100 of a refrigeration system, is shown. The overflow evaporator includes a first fluid volume 110 and a second fluid volume 120. A plurality of channels 130, in the form of a tube bundle, fluidly connect the first fluid volume 110 to the second fluid volume 120, such that all fluid flow from the first fluid volume 110 to the second fluid volume 120 passes through the plurality of channels 130. The arrangement of the channels 130 consists only of… Figure 1 The arrow on the left side is shown schematically.

[0053] The evaporator 100 also includes a manifold 140 (or tank) within which a first fluid volume 110 and a second fluid volume 120 are defined. The manifold 140 can be of any suitable shape. A partition or wall 142 within the manifold 140 separates the first fluid volume 110 from the second fluid volume 120. An evaporator inlet 112 is immediately upstream of the first fluid volume 110 and supplies fluid flow to it in use, and an evaporator outlet 122 is immediately downstream of the second fluid volume 120 and receives fluid flow from it in use. Thus, in use, fluid flows from the evaporator inlet 112 to the evaporator outlet 122 via the first fluid volume 110, the plurality of channels 130, and then via the second fluid volume 120.

[0054] exist Figure 1 The diagram shows inlets 132 of a plurality of channels 130 that receive fluid flow from a first fluid volume 110. Fluid thus enters the plurality of channels 130 via inlets 132 adjacent to the first fluid volume 110. Outlets 134 of the plurality of channels 130 are also shown, providing flow to a second fluid volume 120. Inlets 132 and outlets 134 may be defined by tubes, etc. Thus, inlet 132 may be the inlet 132 of a first bundle of channels 130 (e.g., flow from right to left in the diagram), and outlet 134 may be the outlet 134 of a second bundle of channels 130 (e.g., flow from left to right in the diagram). Each bundle may be one stroke of an evaporator.

[0055] Although multiple channels 130 are shown schematically, they can have any suitable geometry between inlet 132 and outlet 134. Furthermore, although not shown, the overflow evaporator 100 may include a second manifold (e.g., replacing the leftmost vertical arrow in the figure) on the side of the evaporator 100 opposite to manifold 140. This second manifold can receive fluid flow from inlet 132 and corresponding channels of the multiple channels 130 (e.g., from the first tube bundle), and can supply fluid flow to outlet 134 via corresponding channels of the multiple channels 130 (e.g., the second tube bundle). That is, fluid flow between inlet 132 and outlet 134 can be via the second manifold.

[0056] The plurality of fluid channels 130 are fluidly isolated from each other except at the first fluid volume 110 and the second fluid volume 120 (and at the second manifold where the second manifold is located). That is, fluid can flow between each of the plurality of channels 130 only in the manifold 140 (and in the second manifold where it is used). Therefore, fluid cannot flow directly between the channels in the plurality of channels 130.

[0057] Flow restrictor 150 is located within wall 142 and is thus partially disposed within the first fluid volume 110 and partially disposed within the second fluid volume 120. Therefore, flow restrictor 150 is subjected to a pressure difference 170 between the first fluid volume 110 and the second fluid volume 120 (depending on the pressure drop across the evaporator). Flow restrictor 150 includes a piston 152 and a spring 154. Piston 152 is movable between a first position where spring 154 is fully extended and a second position where spring 154 is compressed. Therefore, spring 154 is arranged, for example, to bias piston 152 to the first position against forces from the pressure difference 170.

[0058] The flow restrictor 150 includes a mechanical coupling or rod 156 coupled to an opposite end of the piston 152. An actuable flap 160 is coupled to a corresponding end of the rod 156 opposite the piston 152. Each actuable flap 160 is pivotally coupled to a strip defining an inlet 132 and an outlet 134 of a plurality of channels 130. The flaps 160 are arranged to cover some of the inlets 132 and some of the outlets 134. Therefore, the flaps are arranged to reduce the number of inlets 132 receiving flow from the first fluid volume 110 and to reduce the number of outlets 134 allowing fluid to flow into the second fluid volume 120.

[0059] Figure 1 The diagram illustrates the arrangement of an overflow evaporator 100 and a flow restrictor 150 in a first configuration during operation at a negative brine temperature in a refrigeration system. In this configuration, a lower fluid flow rate is required, but it is necessary to promote the fluid velocity through the evaporator and channel 130 in order to ensure sufficient turbulence for efficient heat transfer.

[0060] exist Figure 1 In this configuration, the pressure difference 170 between the first fluid volume 110 and the second fluid volume 120 is less than a predetermined threshold required to move the piston 152 against the biasing action of the spring 154. Accordingly, the actuated flap 160 in the first fluid volume is in the closed position, thereby covering some (but not all) inlets 132 of the plurality of channels 130 and thus preventing fluid from flowing through the corresponding channels in the channels 130. The actuated flap 160 in the second fluid volume 120 is also in the closed position, thereby covering some (but not all) outlets 134 of the plurality of channels 130 and thus preventing fluid from flowing through the corresponding channels in the channels 130.

[0061] Because the flow restrictor 150 prevents fluid from flowing through multiple of the multiple channels 130, and thus allows fluid to flow through only some of the multiple channels 130, the total flow cross-section through the evaporator 100 is reduced, and the fluid velocity of the flow increases. In this way, turbulence is maintained at a sufficient level to ensure efficient heat transfer.

[0062] Figure 2 This shows the second configuration during operation at the positive brine temperature of the refrigeration system. Figure 1 An overflow evaporator 100. Under such conditions, a higher flow rate is required, but an increase in pressure drop across the evaporator 100 is not desirable.

[0063] exist Figure 2 In this process, the pressure difference 170 between the first fluid volume 110 and the second fluid volume 120 has increased beyond a predetermined threshold, and therefore the piston 152 has moved to its second position against the biasing action of the spring 154 by the pressure difference 170. Consequently, the rod 156 has also moved the actuable flap 160 to its open position, so that the covered inlets 132 and outlets 134 of the plurality of channels 130 are no longer covered. Thus, the movement of the flap 160 allows fluid flow through the corresponding channels 130.

[0064] Because the flow restrictor 150 allows fluid to flow through all the multiple channels 130, the total flow cross-section through the evaporator is increased. Therefore, a higher flow rate through the evaporator is achieved, and the pressure drop can be controlled.

[0065] Therefore, the overflow evaporator 100 and the flow restrictor 150 enable the refrigeration system to operate in two modes, each requiring substantially different flow characteristics through the evaporator 100. In a first mode (e.g., negative temperature brine mode) where less fluid needs to flow through the evaporator 100, the flow restrictor 150 is arranged to prevent flow through some of the multiple channels 130, thereby reducing the total flow cross-section through the evaporator 100. A reduced heat transfer surface is acceptable during this mode (i.e., fewer channels 130 carry fluid for heat transfer) because less cooling capacity is delivered from the refrigeration cycle at lower temperatures. The reduced cross-section allows the fluid flow velocity to remain sufficiently high to maintain the desired turbulence in the channels 130, and thus maintain efficient heat transfer. In a second mode (e.g., positive temperature brine mode) where more fluid needs to flow through the evaporator 100, the flow restrictor 150 is arranged to allow flow through multiple channels (e.g., through all of the multiple channels 130), thereby increasing the total flow cross-section through the evaporator 150. In this mode, an increased heat transfer surface is required due to the higher cooling capacity delivered by the refrigeration cycle (i.e., more channels 130 carry the fluid used for heat transfer). The increased cross-section allows for an increased total fluid flow rate without causing too large a pressure drop across the evaporator.

[0066] Furthermore, the flow restrictor 150 automatically switches between different configurations in response to the pressure difference 170 between the first fluid volume 110 and the second fluid volume 120. Therefore, it is operable to automatically limit the pressure drop between the first fluid volume 110 and the second fluid volume 120, thereby ensuring efficient operation of the refrigeration system. The spring 154 can be configured (e.g., during assembly) to provide mode switching at desired times, for example, based on system parameters (e.g., fluid physics, heating / cooling requirements, etc.).

[0067] Figure 3 An alternative overflow evaporator 100 and flow restrictor 150 are shown. A first fluid volume 110 is divided into a main fluid volume 114 and an auxiliary fluid volume 116. The main fluid volume 114 receives fluid flow from the evaporator inlet 112 regardless of the configuration of the flow restrictor 150 (e.g., always receiving flow from the evaporator inlet 112 during operation). The auxiliary fluid volume 116 receives fluid flow from the evaporator inlet 112 only when the flow restrictor 150 permits this flow. Inlets 132 of a plurality of channels 130 are divided between the main fluid volume 114 and the auxiliary fluid volume 116, and therefore receive fluid from only one or the other.

[0068] The second fluid volume 120 also includes a main fluid volume 124 and an auxiliary fluid volume 126. The outlets 134 of the plurality of channels 130 are divided between the main fluid volume 124 and the auxiliary fluid volume 126. Therefore, the main fluid volumes 114, 124 are fluidly isolated from their corresponding auxiliary fluid volumes 116, 126 within the manifold 140.

[0069] The flow restrictor 150 also includes a first pressure conduit 180 fluidly connecting one side of the piston 152 to the pressure at the evaporator inlet 112, and a second pressure conduit 182 fluidly connecting the other side of the piston 152 to the pressure at the evaporator outlet 122. Thus, the first pressure conduit 180 and the second pressure conduit 182 ensure that the piston 152 responds to the pressure difference 170 between the main fluid volume 114 of the first fluid volume 110 and the main fluid volume 124 of the second fluid volume 120. The flow restrictor 150 includes an actuable flap 160 operable to open and close the auxiliary inlet 118 and the auxiliary outlet 128, thereby allowing or preventing fluid flow through some of the plurality of channels 130 communicating with the auxiliary fluid volumes 116, 126. The auxiliary inlet 118 provides fluid flow to the auxiliary fluid volume 116, and the auxiliary outlet 128 receives fluid flow from the auxiliary fluid volume 126.

[0070] Therefore, with Figure 1 and Figure 2 The evaporator 100 and flow restrictor 150 are similar. Figure 3 The evaporator 100 and flow restrictor 150 enable the refrigeration system to operate in two different modes. Figure 3 In the first mode shown, the pressure 170 between the evaporator inlet 112 and the evaporator outlet 122 is below a predetermined threshold, and the refrigeration system is in a first mode (e.g., a negative brine temperature mode). Fluid flow through some (but not all) of the plurality of channels 130 is prevented by actuating the flap 160 in its closed position, thereby preventing fluid flow through the auxiliary inlet 118 and auxiliary outlet 128, and thus preventing flow through the associated channels of the plurality of channels 130.

[0071] Figure 4 This shows the refrigeration system operating in its second mode (e.g., positive brine temperature mode). Figure 3 The evaporator 100 and flow restrictor 150. In the depicted case, the pressure difference 170 exceeds a predetermined threshold and actuates the flapper 160 to move to its open position, thereby allowing fluid to flow through the auxiliary inlet 118 and the auxiliary outlet 128, thereby allowing fluid to flow through the corresponding channels in the plurality of channels 130.

[0072] The proportion of channels 130 controlled by the flow restrictor 150 can be selected as needed. Furthermore, the strength of the spring 154 can be selected as needed, allowing the evaporator to change mode under predetermined conditions. Moreover, since the flow restrictor 150 is external to the manifold 140, a manual overrun control (not shown) can be provided to the user to manually control the actuated vane 160, for example, manually opening it after increasing the system's pump speed or manually closing it after decreasing the system's pump speed.

[0073] Although Figure 3 and Figure 4 The evaporator in this device is a two-pass evaporator, but since the flow restrictor 150 is outside the manifold 140, it can also be used with a single-pass heat exchanger or any multi-pass heat exchanger.

[0074] The flow restrictor 150 can be arranged such that it controls the same number of inlets 132 as outlet 134, thereby helping to homogenize the fluid velocity in the multiple channels 130 through which the fluid flows. Alternatively, the number of channels 130 controlled by the flow restrictor 150 in each tube bundle can be selected based on the temperature difference between each pass of the evaporator 100.

[0075] Although Figure 3 and Figure 4 Mechanical flow restrictor 150 is shown, but electronic flow restrictors can be used alternatively. For example, pressure lines 180 and 182 can be replaced by pressure transducers, and actuable flapper 160 can be replaced by a solenoid valve or a motor-driven valve. An electronic controller can then be provided to open and close the valve in response to pressure measured by the pressure transducer. If desired, the pressure transducer can also be overridden by the electronic controller.

Claims

1. A refrigeration system including an evaporator, said evaporator comprising: The first fluid volume upstream of the second fluid volume The second fluid volume, and Multiple channels fluidly connect the first fluid volume and the second fluid volume; The system further includes a flow restrictor arranged to prevent fluid from flowing through at least a first channel of the plurality of channels in response to a pressure difference between the first fluid volume and the second fluid volume being less than a predetermined threshold, and to allow fluid to flow through the first channel in response to a pressure difference being greater than the predetermined threshold. The flow restrictor includes an actuable flap arranged to allow or prevent fluid from flowing through the first channel.

2. The refrigeration system according to claim 1, wherein, The flow restrictor is mechanical.

3. The refrigeration system according to claim 1 or 2, wherein, The flow restrictor includes a piston movable between a first position and a second position, and a biasing mechanism arranged to push the piston to the first position.

4. The refrigeration system according to any of the preceding claims, wherein, The first and second fluid volumes are adjacent to each other in the manifold of the evaporator.

5. The refrigeration system according to claim 4, wherein, The flow restrictor is located within the manifold.

6. The refrigeration system according to any one of claims 1 to 4, wherein, The flow restrictor is located outside the first fluid volume and the second fluid volume.

7. The refrigeration system according to any of the preceding claims, wherein, The flow restrictor is configured to automatically limit the pressure drop between the first fluid volume and the second fluid volume.

8. A method of operating a refrigeration system to switch from a first operating mode to a second operating mode, the refrigeration system including an evaporator, the evaporator including a first fluid volume upstream of a second fluid volume, a second fluid volume, and a plurality of channels fluidly connecting the first fluid volume and the second fluid volume; the method including using an actuable flapper to allow or prevent fluid flow through a first channel of the plurality of channels based on a pressure difference between the first fluid volume and the second fluid volume.

9. The method of claim 8, further comprising allowing fluid to flow through the first channel in response to the pressure difference exceeding a predetermined threshold.

10. The method of claim 8 or 9, further comprising preventing fluid from flowing through the first channel in response to the pressure differential falling below a predetermined threshold.

11. The method according to claim 8, 9 or 10, further comprising adjusting the fluid velocity within the plurality of channels by increasing and / or decreasing the number of channels through which the fluid flows.

12. The method according to any one of claims 8 to 11, comprising maintaining turbulence in the plurality of channels within a predetermined range.

13. The method according to any one of claims 8 to 12, further comprising limiting the pressure drop across the evaporator by allowing fluid to flow through the first channel.

14. The method according to any one of claims 8 to 13, comprising using the refrigeration system according to any one of claims 1 to 7.

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