US20130269912A1

US20130269912A1 - Gas-to-water heat exchanger

Info

Publication number: US20130269912A1
Application number: US13/831,902
Authority: US
Inventors: Dumitru Fetcu
Original assignee: Econotherm UK Ltd
Current assignee: Econotherm UK Ltd
Priority date: 2012-03-17
Filing date: 2013-03-15
Publication date: 2013-10-17

Abstract

A heat exchanger is disclosed for cooling a gas from a first temperature to a second temperature. The exchanger comprises a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber. The first heat exchanging chamber comprises an inlet for receiving a coolant into the chamber and an outlet through which the coolant can exit the first chamber, the coolant being arranged to pass over the portion of the heat pipes which extend within the first chamber. The second heat exchanging chamber comprises an inlet for receiving the gas at a first temperature into the chamber and an outlet through which the gas can exit the second chamber at a second temperature. The gas is arranged to pass along the second chamber between the inlet and the outlet, along a path comprising a substantially constant cross-sectional area to minimize the pressure drop between the inlet and the outlet.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims the benefit of provisional application No. 61/612,251 filed on Mar. 17, 2012, entitled “Gas-to-Water Heat Exchanger”, including Appendix A, which application and appendix are incorporated herein in their entirety by this reference.

BACKGROUND

The present invention relates to a heat exchanger and particularly, but not exclusively to a heat exchanger comprising heat pipes.
A heat pipe is a hermetically sealed evacuated tube typically comprising a mesh or sintered powder wick and a working fluid in both the liquid and vapour phase. When one end of the tube is heated the liquid turns to vapour upon absorbing the latent heat of vaporization. The hot vapour subsequently passes to the cooler end of the tube where it condenses and gives out the latent heat to the tube. The condensed liquid then flows back to the hot end of the tube and the vaporization-condensation cycle repeats. Since the latent heat of vaporization is usually very large, considerable quantities of heat can be transported along the tube and a substantially uniform temperature distribution can be achieved along the heat pipe.
It is known to utilize a heat exchanger comprising separated chambers and a plurality of heat pipes which extend between the chambers, such that heat can become transferred from one chamber to the other. In this respect, by passing a heated fluid through one chamber, the heat pipes can transfer the heat absorbed from the heated fluid to the other chamber wherein a cooled fluid may pass to subsequently absorb the heat from the heat pipes.
However, when passing a fluid through a chamber of the heat exchanger it is found that the pressure drop between an inlet and an outlet of the respective chamber can be significant. This is found to reduce the heat transfer efficiency between the fluid and the heat pipes within the chamber with the result that the heat can rapidly increase to dangerous levels within the chamber.

SUMMARY

We have now devised an improved heat exchanger which alleviates the above-mentioned problem.
In accordance with the present invention, there is provided a heat exchanger for cooling a gas from a first temperature to a second temperature, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber;
the first heat exchanging chamber comprising an inlet for receiving a coolant into the chamber and an outlet through which the coolant can exit the first chamber, the coolant being arranged to pass over the portion of the heat pipes which extend within the first chamber;
the second heat exchanging chamber comprising an inlet for receiving the gas at a first temperature into the chamber and an outlet through which the gas can exit the second chamber at a second temperature; wherein,
the gas is arranged to pass along the second chamber between the inlet and the outlet along a path comprising a substantially constant cross-sectional area to minimize the pressure drop between the inlet and the outlet.
The provision of a substantially uniform cross-sectional area for the gas flow reduces regions of significant pressure gradients within the chamber. The heat exchanger of the present invention thus ensures a minimal pressure drop and thus a substantially uniform transfer of heat between the gas and the heat pipes at all positions within the chamber.
Preferably, the second heat exchanging chamber further comprises a deflection plate which is arranged to deflect the passage of gas across the heat pipes in passing between the inlet and the outlet of the second chamber. The deflection plate is arranged to cause the gas to pass predominantly across the heat pipes as opposed to along the heat pipes to increase the thermal transfer between the heat pipes and the gas and thus the thermal transfer between the first and second chambers.
The deflection plate preferably extends substantially radially of the second chamber and comprises an outer periphery which is spaced from a side wall of the second chamber. The gas is thus arranged to pass through an annular aperture defined between the outer periphery of the deflection plate and the side wall of the chamber, in passing between the inlet and the outlet of the second chamber.
The inlet and outlet of the second chamber are preferably disposed on a longitudinal axis of the heat exchanger.
Preferably, the deflection plate comprises a gate disposed therein which is arranged to open and close a central region of the deflection plate. The gate serves as a valve to control the passage of gas direct from the inlet to the outlet of the second chamber, through the plate. The gate preferably comprises a butterfly valve.
The outlet of the first chamber preferably comprises a sensor for sensing the temperature of the liquid exiting the first chamber. The gate is preferably arranged to open and close in dependence on the sensed temperature of the liquid exiting the first chamber.
Preferably, the array of heat pipes comprises heat pipes arranged in substantially concentric circular rows. The heat pipes are preferably orientated substantially parallel to each other.
The rows of heat pipes preferably comprise a plurality of flow disturbers disposed at separated positions along the rows and which serve to create a turbulent flow of liquid within the row. The flow disturbers preferably comprise a plurality of rods which extend along the length of the first chamber substantially parallel to the heat pipes. Successive rods along each row are preferably disposed at opposite sides of the row to redirect the flow of liquid along the row.
The first and second heat exchanging chambers are preferably separated by a separation plate, through which the heat pipes extend. Preferably, the heat pipes extend in sealing relation with the separation plate via sealing means. Preferably, the sealing means comprises a collar separately disposed around each heat pipe which is arranged to compress a sealing ring against the separation plate.
The first chamber preferably further comprises a compression plate disposed above the heat pipes, which is arranged to abut the upper region of the heat pipes at one side thereof and comprises a plurality of compression springs disposed on the other side thereof.
The compression springs are preferably arranged to extend against a lid of the first chamber and act to urge the compression plate against the heat pipes and thus the heat pipes within the separation plate. During operation of the heat exchanger the temperature of the heat pipes will increase and it is found that this temperature increase causes a small expansion of the heat pipes. The compression plate and springs enable the heat pipes to freely expand while maintaining a bias of the heat pipes toward the separation plate.
Note that the various features of the present invention described above may be practiced alone or in combination. These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be more clearly ascertained, some embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of a heat exchanger according to an embodiment of the present invention;

FIG. 2 is a transverse sectional view of the heat exchanger of FIG. 1 taken across line A-A;

FIG. 3 is a transverse sectional view of the heat exchanger of FIG. 1 taken along line B-B;

FIG. 4 is a plan view of the baffle disposed within the second chamber;

FIG. 5 is a magnified longitudinal sectional view of a heat pipe disposed within a separation plate, illustrating the sealing means;

FIG. 6 is a magnified view of a spring disposed upon the compression plate; and

FIG. 7 is a transverse sectional view of the heat exchanger of FIG. 1 taken across line B-B, with side walls of the heat exchanger opened.

DETAILED DESCRIPTION

The present invention will now be described in detail with reference to several embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, to one skilled in the art, that embodiments may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. The features and advantages of embodiments may be better understood with reference to the drawings and discussions that follow.
Referring to FIGS. 1 to 3 of the drawings, there is illustrated a heat exchanger according to an embodiment of the present invention. The heat exchanger 10 comprises a first heat exchanging chamber 11 and a second heat exchanging chamber 12. Each chamber 11, 12 comprises a substantially cylindrical housing 13, 14, which are mounted one on top of the other such that a longitudinal axis of the first chamber 11 extends in a substantially collinear relationship with a longitudinal axis of the second chamber 12 and thus the heat exchanger 10.
The first chamber 11 of the heat exchanger 10 is disposed above the second chamber 12 and comprises an inlet 15 and an outlet 16 which are disposed within an arcuate side wall of the housing 13. The inlet and outlet 15, 16 of the first chamber 11 are arranged to enable a liquid coolant such as water, to pass into and out from the chamber 11, respectively. The first chamber 11 further comprises a passage 17 which extends along the first chamber 11 substantially along the longitudinal axis thereof. The passage 17 is defined by a substantially cylindrical wall 18 which seals the interior of the first chamber 11 from the passage 17, and extends between an opening 19 disposed in an upper end wall 20 of the first chamber 11 to an upper region of a separation plate 21.
Referring to FIG. 4 of the drawings, the separation plate 21 comprises a first aperture 22 disposed substantially at the centre thereof which is arranged to align with the cylindrical wall 18 defining the passage 17, such that the wall 18 extends substantially around a periphery of the first aperture 22. The second chamber 12 is secured to the underside of the separation plate 21 and thus the first chamber 11, and comprises an inlet 23 disposed substantially upon the longitudinal axis of the chamber 12, within a lower end wall 24 thereof. The first aperture 22 disposed within the separation plate 21 and the passage 17 serve as an outlet of the second chamber 12, such that the gas to be cooled for example, is arranged to pass into the second chamber 12 through the inlet 23 disposed in the lower end wall 24 of the second chamber 11 and out of the second chamber through the first aperture 22 and along the passage 17.
The heat exchanger 10 further comprises a plurality of substantially linear heat pipes 25 which extend from within the first chamber 11, through an array of second apertures 26 disposed within the separation plate 21 around the first aperture 22, and terminate in the second chamber 12 so as to enable heat to be transferred between the chambers 11, 12. The heat pipes 25 extend substantially parallel to the longitudinal axis of the first and second chambers 11, 12 and are configured in a substantially concentric arrangement of rows of heat pipes 25, as illustrated in FIGS. 2 and 3 of the drawings, centered substantially on the longitudinal axis. In this manner each chamber 11, 12 comprises a plurality of arcuate rows of heat pipes 25, having different radii of curvature.
Adjacent circular rows of heat pipes 25 within the first chamber 11 are separated by a wall 26 which extends along the length of the first chamber 11 and defines a channel 27 along which the liquid can flow. Adjacent walls 26 comprise an aperture 28 disposed at opposite ends thereof such that the liquid is cause to flow in a clockwise direction, for example, within the channel 27 in passing across one row of heat pipes 25 substantially around the chamber 11, before passing radially of the chamber 11 to the adjacent row of heat pipes 25, and subsequently in a counter-clockwise direction in passing across the heat pipes 25 in the adjacent row.
The channel 27 disposed in the first chamber 11 further comprises a plurality of rods 29 which extend substantially parallel to each other and the longitudinal axis of the heat exchanger 10. The rods 29 are disposed along the channel 27 between the heat pipes 25, and successive rods 29 along the channel 27 are disposed at opposite sides of the channel 27 to prevent the liquid from simply passing around a side of the channel 27 without significantly extracting the heat from the heat pipes 25. The rods 27 act to create a turbulent flow within the channel 27 and thus encourage the interaction of the liquid with the heat pipes 25 to maximize the transfer of heat between the heat pipes 25 and the liquid.
The second chamber 12 comprises a deflection plate or baffle 30 which extends across the chamber 12, substantially transverse the longitudinal axis of the chamber 12, between the inlet 23 and the outlet region defined by the first aperture 17 in the separation plate 21. The baffle 30 extends substantially radially of the second chamber 12 from a central region thereof, and comprises an outer periphery which is spaced from the housing 14 of the second chamber 12 to define an annular passage 31. The heat pipes 25 are arranged to extend through apertures 30 a in the baffle 30 in sealing relation therewith, such that the gas is arranged to pass across the heat pipes 25, through the annular passage 31, and back across the heat pipes 25, in moving from the inlet 23 to the outlet region of the second chamber 12.
The baffle 30 comprises a gate or valve 32, such as a butterfly valve, which can be configured between a fully open state in which the gas is arranged to pass direct from the inlet 23 to the outlet region without substantially passing through the annular passage 31, a closed state in which the majority of the gas is arranged to pass through the annular passage 31 in passing from the inlet 23 to the outlet region of the second chamber 12, and various intermediate states in which a portion of the gas is arranged to pass through the valve 32 and a portion of the gas is arranged to pass through the annular passage 31. The cross-sectional area of the annular passage 31 is substantially matched to the cross-sectional area of the inlet 23 and outlet region of the second chamber 12 to minimize the pressure drop of the gas between the inlet 23 and outlet region of the second chamber 12.
Referring to FIG. 5 of the drawings, the heat pipes 25 are supported within the heat exchanger 10 by the separation plate 21 via a series of collars 33 disposed upon the heat pipes 25. The collars 33 are arranged to extend within each of the second apertures 26 and serve to seal the heat pipes 25 to the separation plate 21, such that the interior of the first and second chambers 11, 12 remain isolated from each other.
The second apertures 26 comprise an internal flange 34 which extends into the respective second aperture 26 to reduce the diameter of the second aperture 26 at the side of the plate 21 adjacent the second chamber 12. The flanges 34 separately act as a seat for a sealing ring 35, such as an O-ring, such that the collars 33 separately disposed upon the heat pipes 25 are arranged to extend into the respective aperture 26 from within the first chamber 11 and compress the sealing ring 35 against the flange 34 and the heat pipe 25, to seal the heat pipe 25 within the separation plate 21.
The longitudinal ends of the heat pipes 25 disposed within the second chamber 12 are uncoupled and separated from the lower end wall 24 of the second chamber 12, whereas the longitudinal end of the heat pipes 25 disposed within the first chamber are arranged to abut the underside of a compression plate 36. The compression plate 36 is substantially annular in shape, and is sized to extend between the cylindrical wall 18 defining the passage 17 and the arcuate side walls 13 of the first chamber 11.
The upper side of the compression plate 36 comprises a plurality of compression springs 37 which are arranged to abut the upper wall 20 of the first chamber 11, as illustrated in FIG. 6 of the drawings. When the upper wall 20 is secured upon the first chamber 11 to seal the first chamber 11, the springs 37 are arranged to partially compress to urge the compression plate 36 upon the upper ends of the heat pipes 25 and thus bias the heat pipes 25 into the second apertures 26 to maintain the seal between the heat pipes 25 and the separation plate 21. During use it is found the increase in temperature of the heat pipes 25 causes the heat pipes 25 to expand which can cause thermal stresses to develop within the heat exchanger 10. The compression plate 36 and springs 37 enable the heat pipes to expand to relieve any stresses which develop, while maintaining an intimate seal of the heat pipes within the second apertures of the separation plate 21.
In use, the gas to be cooled is arranged to pass into the second chamber 12 via the inlet 23 and subsequently pass radially outwardly across the heat pipes 25 due to the baffle 30, through the annular passage 31. The gas is then caused to pass radially inwardly of the second chamber 12, back across the heat pipes 25 toward the outlet region. As the gas passes across the heat pipes 25, the heat associated with the gas becomes transferred to the heat pipes 25, causing the gas to become cooled. The heat transferred to the heat pipes 25 is then communicated along the heat pipes 25 to the first chamber and becomes extracted therefrom by the flow of liquid, for example water, within the channel 27. The outlet 16 of the first chamber comprises a sensor (not shown), for example a thermocouple sensor, for sensing the temperature of the liquid exiting the chamber 11. If the monitored temperature of the liquid rises above a threshold value, then in order to control the amount of heat recovered from the gas, the valve 32 on the baffle 30 is opened accordingly to vent a portion of the gas direct to the outlet region and thus reduce the amount of heat transferred between the gas and the heat pipes 25.
Referring to FIG. 7 of the drawings, the arcuate walls 14 of the second chamber 12 may be hinged or otherwise removable from the heat exchanger to provide for access into the chamber 12 for cleaning and maintenance. The skilled reader will recognize however, that the arcuate side walls 13 of the first chamber 11 may also be hinged or removable for cleaning and maintenance.
For further details of the present invention, please see attached Appendix A.
While this invention has been described in terms of several embodiments, there are alterations, modifications, permutations, and substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and substitute equivalents as fall within the true spirit and scope of the present invention.

Claims

What is claimed is:

1. A heat exchanger for cooling a gas from a first temperature to a second temperature, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber;

the first heat exchanging chamber comprising an inlet for receiving a coolant into the chamber and an outlet through which the coolant can exit the first chamber, the coolant being arranged to pass over the portion of the heat pipes which extend within the first chamber;

the second heat exchanging chamber comprising an inlet for receiving the gas at a first temperature into the chamber and an outlet through which the gas can exit the second chamber at a second temperature; wherein,

the gas is arranged to pass along the second chamber between the inlet and the outlet along a path comprising a substantially constant cross-sectional area to minimize the pressure drop between the inlet and the outlet.

2. A heat exchanger according to claim 1, further comprising a deflection plate which is arranged to deflect the passage of gas across the heat pipes in passing between the inlet and the outlet of the second chamber.

3. A heat exchanger according to claim 2, wherein the deflection plate is arranged to cause the gas to pass predominantly across the heat pipes as opposed to along the heat pipes.

4. A heat exchanger according to claim 2, wherein the deflection plate extends substantially radially of the second chamber and comprises an outer periphery which is spaced from a side wall of the second chamber.

5. A heat exchanger according to claim 2, wherein the deflection plate comprises a gate disposed therein which is arranged to open and close a central region of the deflection plate.

6. A heat exchanger according to claim 5, wherein the outlet of the first chamber comprises a sensor for sensing the temperature of the liquid exiting the first chamber.

7. A heat exchanger according to claim 6, wherein the gate is arranged to open and close in dependence on the sensed temperature of the liquid exiting the first chamber.

8. A heat exchanger according to claim 1, wherein the inlet and outlet of the second chamber are disposed on a longitudinal axis of the heat exchanger.

9. A heat exchanger according to claim 1, wherein the array of heat pipes comprises heat pipes arranged in substantially concentric circular rows.

10. A heat exchanger according to claim 1, wherein the heat pipes are orientated substantially parallel to each other.

11. A heat exchanger according to claim 1, wherein the rows of heat pipes comprise a plurality of flow disturbers disposed at separated positions along the rows and which serve to create a turbulent flow of liquid within the row.

12. A heat exchanger according to claim 11, wherein the flow disturbers comprise a plurality of rods which extend along the length of the first chamber substantially parallel to the heat pipes.

13. A heat exchanger according to claim 12, wherein successive rods along each row are disposed at opposite sides of the row to redirect the flow of liquid along the row.

14. A heat exchanger according claim 1, wherein the first and second heat exchanging chambers are separated by a separation plate, through which the heat pipes extend.

15. A heat exchanger according to claim 14, wherein the heat pipes extend in sealing relation with the separation plate via sealing means.

16. A heat exchanger according to claim 15, wherein the sealing means comprises a collar separately disposed around each heat pipe which is arranged to compress a sealing ring against the separation plate.

17. A heat exchanger according to claim 1, wherein the first chamber further comprises a compression plate disposed above the heat pipes, which is arranged to abut the upper region of the heat pipes at one side thereof and comprises a plurality of compression springs disposed on the other side thereof.

18. A heat exchanger according to claim 17, wherein the compression springs are arranged to extend against a lid of the first chamber and act to urge the compression plate against the heat pipes and thus the heat pipes within the separation plate.