Water temperature sensor in a brazed plate heat exchanger

Abstract

To continue operating a compression refrigerant system even while the system's brazed plate heat exchanger contains, in localized areas, water at or below its atmospheric subfreezing water temperature, a penetrating temperature probe senses the water temperature at a strategic intermediate point between the heat exchanger's water inlet and outlet. The brazed plate heat exchanger comprises a series of corrugated plates stacked and brazed together to create an alternating arrangement of water and refrigerant passages in heat transfer relationship with each other. In some examples, the idea is to take advantage of the principle that water has a lower freezing temperature at relatively high pressure and that the relatively small micro-channel passages of intermediate water passages within the brazed plate heat exchanger can withstand appreciably higher pressure than other areas within the heat exchanger, such as the areas at the heat exchanger's water inlet and water outlet.

Claims

1. A control method involving a temperature sensor disposed within a heat exchanger that conveys a refrigerant and water, the water having an atmospheric freezing point temperature at atmospheric pressure, the control method comprising: defining a lower temperature limit that is below the atmospheric freezing point temperature; sensing the temperature of the water within the heat exchanger using the temperature sensor, the temperature sensor extending into at least one passage within the heat exchanger, the temperature sensor being positioned at a target point, wherein the water at the target point is colder than the water at an inlet of the heat exchanger, the target point having a lower flow rate of water than the water inlet; providing a feedback signal from the temperature sensor that is responsive to the temperature of the water; conveying the feedback signal to a controller; and in response to the feedback signal, the controller distinguishing between an acceptable operation and an unacceptable operation, the unacceptable operation being the temperature of the water being below the lower temperature limit, the acceptable operation being the temperature of the water being above the lower temperature limit.

2. A control method involving a temperature sensor disposed within a heat exchanger that conveys a refrigerant and water, the heat exchanger having a water outlet, the water having an atmospheric freezing point temperature at atmospheric pressure, the control method comprising: defining a lower temperature limit; sensing the temperature of the water within the heat exchanger using the temperature sensor, the temperature sensor extending into at least one passage within the heat exchanger, the temperature sensor being positioned at a target point, wherein the water at the target point is colder than the water at an inlet of the heat exchanger, the target point having a lower flow rate of water than the water inlet; providing a feedback signal from the temperature sensor that is responsive to the temperature of the water; conveying the feedback signal to a controller; and in response to the feedback signal, the controller distinguishing between an acceptable operation and an unacceptable operation, the unacceptable operation being the water temperature falling below the lower temperature limit a predetermined number of times, the predetermined number of times being greater than one, the acceptable operation being the water temperature falling below the lower temperature limit less than the predetermined number of times.

3. The control method of claim 2, wherein the lower temperature limit is less than the atmospheric freezing point temperature of the water.

4. The control method of claim 2, wherein the lower temperature limit is less than a temperature at which the water would freeze at the water outlet.

5. A control method involving a temperature sensor disposed within a heat exchanger that conveys a refrigerant and water, the heat exchanger defining a water outlet, the water having an atmospheric freezing point temperature at atmospheric pressure, the control method comprising: defining a lower temperature limit; sensing the temperature of the water within the heat exchanger using the temperature sensor, the temperature sensor extending into at least one passage within the heat exchanger, the temperature sensor being positioned at a target point, wherein the water at the target point is colder than the water at an inlet of the heat exchanger, the target point having a lower flow rate of water than the water inlet; providing a feedback signal from the temperature sensor that is responsive to the temperature of the water; conveying the feedback signal to a controller; and in response to the feedback signal, the controller distinguishing between an acceptable operation and an unacceptable operation, the unacceptable operation being the water temperature being below the lower temperature limit longer than a predetermined period, the acceptable operation being the water temperature being not lower than the lower temperature limit for less than the predetermined period.

6. The control method of claim 5, wherein the lower temperature limit is less than the atmospheric freezing point temperature of the water.

7. The control method of claim 5, wherein the lower temperature limit is less than a temperature at which the water would freeze at the water outlet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an exploded view of an example brazed plate heat exchanger.

(2) FIG. 2 is a perspective view of the brazed plate heat exchanger illustrating various examples of temperature probe positions.

(3) FIG. 3 is an exploded view of the brazed plate heat exchanger showing an example temperature probe position.

(4) FIG. 4 is a cross-sectional view taken generally along line 4-4 of FIG. 5 showing an example temperature probe position relative to an example brazed plate heat exchanger.

(5) FIG. 5 is a schematic view of the example brazed plate heat exchanger connected to a refrigerant system its controller.

(6) FIG. 6 is a block diagram showing an algorithm and control method.

(7) FIG. 7 is a block diagram showing another algorithm and control method.

(8) FIG. 8 is a block diagram showing yet another algorithm and control method.

(9) FIG. 9 is a graph showing the relationship between the freezing point of pure water and water pressure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(10) FIGS. 1-5 show an example of a brazed plate heat exchanger 10 that uses a refrigerant 12 to cool a current of water 14. Examples of the term, water include pure water and mixtures containing at least some water. A water temperature probe 16 is strategically positioned within heat exchanger 10 to help achieve and monitor operation at water temperatures that are almost at or even slightly below the temperature at which water at atmospheric pressure normally freezes. In some examples, a temperature sensor 18 at a tip 20 (FIG. 2) of probe 16 senses water 14 at a target point (e.g., at target points 22a, 22b, 22c or 22d) where water 14 is colder than it is at a chilled water outlet 24 of heat exchanger 10. Temperature sensor 18 is schematically illustrated to represent any temperature responsive device examples of which include, but are not limited to, a temperature transducer, a bi-metallic switch, PTC thermistor, NTC thermistor, thermocouple, resistance temperature detector, etc.

(11) To make use of the sensed temperature, probe 16 includes a pair of wires 26 (two or more wires) that convey a water temperature feedback signal 28 to a controller 50 (FIG. 5) associated with heat exchanger 10. Controller 50 is schematically illustrated to represent any electrical circuit that provides one or more outputs in response to one or more inputs. Examples of controller 50 include, but are not limited to, a computer, microprocessor, integrated circuit(s), programmable logic controller (PLC), electromechanical relays, and various combinations thereof.

(12) In the illustrated example, heat exchanger 10 comprises a plurality of corrugated plates 30 and 32 disposed along substantially parallel planes (e.g., plurality of first and second planes) and being stacked in an alternating arrangement. In some examples, plates 30 and 32 are made of stainless steel sheet metal clad or otherwise coated with a thin layer of braze material 34 (e.g., copper or copper alloy) that provides a joining interface of braze material 34 at contact points between adjacent plates 30 and 32. For assembly, plates 30 and 32 are temporarily clamped together and heated to permanently braze plates 30 and 32 together to create alternating layers of a plurality of refrigerant passages 36 and a plurality of water passages 38 between adjacent plates 30 and 32. The brazing operation hermetically isolates water passages 38 from refrigerant passages 36 and hermetically seals an outer peripheral edge 40 of plates 30 and 32.

(13) The actual design of plates 30 and 32 may vary to provide an infinite number of heat exchanger configurations with any number of passes and flow patterns. For clear illustration, heat exchanger 10 is shown having one each of a water inlet 42, water outlet 24, a refrigerant inlet 44 and a refrigerant outlet 46. Each plate 32 includes a refrigerant supply opening 44a, a refrigerant return opening 46a, a water supply opening 42a and a water return opening 24a. Likewise, each plate 30 includes a refrigerant supply opening 44b, a refrigerant return opening 46b, a water supply opening 42b and a water return opening 24b.

(14) In use, relatively cold refrigerant 36 enters heat exchanger 10 through refrigerant inlet 44 and flows through refrigerant supply openings 44a and 44b. In some examples, the cold refrigerant 36 is from a conventional refrigerant compression system 48 (e.g., an air conditioner, a heat pump, etc.) of which heat exchanger 10 functions as an evaporator. Openings 44a of heat exchanger 10 deliver refrigerant 36 to refrigerant passages 36, which convey the refrigerant in a zigzag and/or otherwise convoluted pattern between adjacent plates 30 and 32 to refrigerant return openings 46a. Openings 46a and 46b then direct the refrigerant to outlet 46 to recycle refrigerant 36 through system 48.

(15) Water 14 to be cooled enters heat exchanger 10 through inlet 42 and flows through water supply openings 42a and 42b. Openings 42b of heat exchanger 10 deliver water 14 to water passages 38, which convey the water in a zigzag and/or otherwise convoluted pattern between other adjacent plates 30 and 32 to water return openings 24b. As water 14 flows through water passages 38, refrigerant 12 in adjacent passages 36 cool the water. After refrigerant 12 cools water 14, openings 24a and 24b direct the chilled water 14 to water outlet 24, which delivers the chilled water 14 to wherever it may be needed.

(16) In some examples, due to the convoluted interrelated flow patterns created by passages 36 and 38, water 14 reaches its lowest temperature at some point downstream of water inlet 42 and upstream of water outlet 24. Referring to FIG. 3, the plurality of water passages 38 between adjacent plates 30 and 32 include a plurality of upstream water passages 38a, a plurality of downstream water passages 38c, and a plurality of intermediate water passages 38b therebetween. Thus, water 14 flows sequentially from water inlet 42, through water supply opening 42b, through upstream water passages 38a, through intermediate water passages 38b, through downstream water passages 38c, through water return opening 24b, and through water outlet 24. In the example of FIG. 3, water 14 reaches its lowest temperature at target point 22d within intermediate water passages 38b, so sensor 18 of probe 16 is positioned at this point 22d. Water 14 at target point 22d is colder there than at water inlet 42, at upstream water passages 38a, at downstream water passages 38c, and at water outlet 24. Also, the current of water 14 at water inlet 42 is warmer than the current of water 14 at water outlet 24, and the current of water 14 at water outlet 24 is warmer than at least some of the current of water 14 flowing through the plurality of intermediate water passages 38b. In some cases, the location of target point 22d is a function of where the two phase refrigerant is at its lowest temperature (lowest pressure when no glide is present) and the lowest flow rate of the water.

(17) In some examples, to position sensor 18 at target point 22d, probe 16 penetrates at least one corrugated plate 30, as shown in FIGS. 3 and 4. In other examples, as shown in FIG. 2, probe 16 passes through water inlet 42 to position sensor 18 at target point 22a, passes through water outlet 24 to position sensor 18 at target point 22c, penetrates outer peripheral edge 40 to position sensor 18 at target points 22b or 22d, and/or probe 16 penetrates interface of braze material 34 (e.g., to access points 22b and/or 22d). In one or more of the foregoing examples, wires 26 convey temperature feedback signal 28 to controller 50, as shown in FIG. 5.

(18) Various examples of controller 50 operate with temperature sensor 18 according to the control schemes 52, 54 and 56, as illustrated in FIGS. 6, 7 and 8 respectively. In control scheme 52 of FIG. 6, probe 16 monitors the water temperature at a target point (e.g., points 22a, 22b, 22c or 22d) within an intermediate water passage 38b to determine whether the water temperature is at or above an acceptable subfreezing temperature at that point. The term, subfreezing means a temperature that is below a fluid's freezing temperature at atmospheric pressure. In some examples, the idea is to take advantage of the principle that water has a lower freezing temperature at relatively high pressure (see FIG. 9), and that the relatively small micro-channel passages of intermediate water passages 38b can withstand appreciably higher pressure than other areas of heat exchanger 10, such as the areas at water inlet 42 and water outlet 24.

(19) In control scheme 52 specifically, block 58 of FIG. 6 represents controller 50 defining a lower temperature limit (e.g., a subfreezing temperature of 31.5 degrees Fahrenheit) that is below the atmospheric freezing point temperature of water 14 (e.g., 32 degrees Fahrenheit). Block 60 represents temperature sensor 18 sensing the temperature of water 14 within heat exchanger 10, providing feedback signal 28 in response to sensing the temperature of water 14, and conveying feedback signal 28 to controller 50. Blocks 62, 64 and 66 represent controller 50 distinguishing between an acceptable operation (block 68) and an unacceptable operation (block 70), wherein the unacceptable operation (block 70) is the temperature of water 14 being below the lower temperature limit (e.g., 31.5 degrees Fahrenheit), and the acceptable operation (block 68) is the temperature of water 14 being above the lower temperature limit. The acceptable operation (block 68) includes the temperature of water 14 being between the atmospheric freezing point temperature (e.g., 32 degrees Fahrenheit) and the lower temperature limit (e.g., 31.5 degrees Fahrenheit). Upon determining acceptable operation, in some examples, controller 50 activates a first indicator 72 (e.g., a green light) that indicates normal operation and/or controls system 48 in some acceptable predetermined manner. Upon determining unacceptable operation, in some examples, controller 50 activates a second indicator 74 (e.g., a red light) and deactivates or otherwise disables system 48. In some examples, upon determining unacceptable operation, controller 50 initiates some predetermined corrective action such as, for example, increasing water flow through heat exchanger 10.

(20) In the example of control scheme 54, of FIG. 7, controller 50 identifies unacceptable operation as being the water temperature at a target point (e.g., point 22a, 22b, 22c or 22d) falling below a lower temperature limit (e.g., 29 degrees Fahrenheit, 32 degrees Fahrenheit, 35 degrees Fahrenheit, etc.) a predetermined number of times (e.g., once, twice, . . . , etc.) within a predetermined length of time (e.g., within 5 seconds, within 5 minutes, . . . etc.). In some examples, block 76 of FIG. 7 represents controller 50 defining a lower temperature limit (e.g., a subfreezing temperature of 31.5 degrees Fahrenheit) that is below the atmospheric freezing point temperature of water 14 (e.g., 32 degrees Fahrenheit). Block 78 represents temperature sensor 18 sensing the temperature of water 14 within heat exchanger 10, providing feedback signal 28 in response to sensing the temperature of water 14, and conveying feedback signal 28 to controller 50. Blocks 80, 82 and 84 represent controller 50 distinguishing between an acceptable operation (block 82) and an unacceptable operation (block 84), wherein the unacceptable operation (block 84) is the temperature of water 14 falling below the lower temperature limit a predetermined number of times (represented by the letter N) within a predetermined length of time, and the acceptable operation (block 82) is the temperature of water 14 not falling below the lower temperature limit the predetermined number of times. Upon determining acceptable operation, in some examples, controller 50 activates first indicator 72 and/or controls system 48 in some acceptable predetermined manner. Upon determining unacceptable operation, in some examples, controller 50 activates second indicator 74 and/or deactivates or otherwise disables system 48.

(21) In the example of control scheme 56, of FIG. 8, controller 50 identifies unacceptable operation as being the water temperature at a target point (e.g., point 22a, 22b, 22c or 22d) being below a lower temperature limit (e.g., 29 degrees Fahrenheit, 32 degrees Fahrenheit, 35 degrees Fahrenheit, etc.) for a predetermined length of time (e.g., for 5 seconds, for 5 minutes, . . . etc.). In some examples, block 86 of FIG. 8 represents controller 50 defining a lower temperature limit (e.g., a subfreezing temperature of 31.5 degrees Fahrenheit) that is below the atmospheric freezing point temperature of water 14 (e.g., 32 degrees Fahrenheit). Block 88 represents temperature sensor 18 sensing the temperature of water 14 within heat exchanger 10, providing feedback signal 28 in response to sensing the temperature of water 14, and conveying feedback signal 28 to controller 50. Blocks 90, 92 and 94 represent controller 50 distinguishing between an acceptable operation (block 92) and an unacceptable operation (block 94), wherein the unacceptable operation (block 94) is the temperature of water 14 being below the lower temperature limit for a predetermined length of time, and the acceptable operation (block 92) is the temperature of water 14 not being below the lower temperature limit for the predetermined length of time. Upon determining acceptable operation, in some examples, controller 50 activates first indicator 72 and/or controls system 48 in some acceptable predetermined manner. Upon determining unacceptable operation, in some examples, controller 50 activates second indicator 74 and/or deactivates or otherwise disables system 48.

(22) It should be noted that, the term, predetermined length of time is equivalent to the terms, predetermined time span, predetermined period, and predetermined duration. The term, water outlet means an exit through which water 14 leaves heat exchanger 10 and does not necessarily mean that the water must escape to atmosphere. The term, penetrate and derivatives thereof means extending through, protruding through, etc.

(23) Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. The scope of the invention, therefore, is to be determined by reference to the following claims: