US20130233512A1

US20130233512A1 - Heat exchanger

Info

Publication number: US20130233512A1
Application number: US13/772,219
Authority: US
Inventors: Dumitru Fetcu
Original assignee: Econotherm UK Ltd
Current assignee: Econotherm UK Ltd
Priority date: 2012-02-21
Filing date: 2013-02-20
Publication date: 2013-09-12

Abstract

A heat exchanger is disclosed for exchanging heat between a first gas and a second gas. The heat exchanger comprises a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend between the first and second heat exchanging chambers. The first heat exchanging chamber comprising an inlet for receiving the first gas into the chamber and an outlet through which the first gas can exit the first chamber, the flow of first gas being substantially along the array of heat pipes. The second heat exchanging chamber comprising an inlet for receiving a second gas into the chamber and an outlet through which the second gas can exit the second chamber, the flow of second gas being substantially across the array of heat pipes. The flow of second gas is split into two subsidiary flow paths, with each subsidiary flow path comprising a substantially identical array of heat pipes. This ensures that each heat pipe receives a similar rate of heat exchange.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims the benefit of provisional application No. 61/601,544 filed on Feb. 21, 2012, entitled “Heat Exchanger”, which application is incorporated herein in its entirety by this reference.

BACKGROUND

The present invention relates to a heat exchanger.
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 vapor phase. When one end of the tube is heated the liquid turns to vapor upon absorbing the latent heat of vaporization. The hot vapor 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.
Heat can both enter and leave heat pipes of a heat exchanger by convection. The amount of heat transferred is dependent upon the convection heat transfer coefficient, which is dominated primarily by the average velocities of the hot gas passing over the heat pipe at the vaporization end and cold gas passing over the heat pipe at the condensation end. The working temperature of the heat pipe, namely the temperature at which the pipe settles during use, adjusts automatically according to the amount of heat absorbed from the hot gas on the vaporization section and the amount of heat given off and thus absorbed by the cold gas, at the condensation section. When there is an unequal volume flow rate between the hot and cold gas at the vaporization and condensation sections respectively, the working temperature of the heat pipes can depart significantly from the desired value. Moreover, it is found that the flow of gas over an array of heat pipes at the condensation and vaporization section, can vary from one heat pipe to the next and so there can be a variation in the working temperature of the heat pipes within a heat exchanger. This can result in the generation of incondensable gases within the pipe due to a decomposition of the working fluid, which can severely restrict the performance of the heat pipe.

SUMMARY

The main object of the present invention is to provide an improved heat pipe heat exchanger for heat recovery from exhaust flues from boilers or industrial processes and to utilize the heat to preheat air or other kind of gas when there is an unequal volume flow rate between the hot and cold gas at the vaporization and condensation sections, respectively. It is a further object of the present invention to provide an arrangement of heat pipes for a heat exchanger, so that the flow of gas over the arrangement provides a similar rate of heat exchange for each pipe.
A further object of the present invention is to provide a heat pipe heat exchanger having a low pressure drop and high overall heat transfer coefficient on a hot side of the heat exchanger. It is a further object to provide a heat exchanger which can be retro-fitted to existing boilers or within industrial processes, which almost always have limited pressure drop available.
A further object of the present invention is to provide a heat pipe heat exchanger with an improved overall heat transfer coefficient and low pressure drop on the cold air side of the heat exchanger.
A further object of the present invention is to provide a heat pipe heat exchanger where the amount of recovered heat can be controlled.
A further object of the present invention is to provide a heat pipe heat exchanger that offers better installation possibilities directly on an exhaust stack of an industrial process, for example, particularly in very limited spaces.
A further object of the present invention is to provide a heat pipe heat exchanger where the heat pipes can be easily installed and uninstalled.
A further object of the present invention is to provide a heat pipe heat exchanger with better cleaning possibilities of the heat transfer area particularly on the hot side of the heat exchanger.
A further object of the present invention is to produce a heat pipe heat exchanger which is easier and cheaper to manufacture.
In accordance with a first aspect of the present invention, there is provided a heat exchanger for exchanging heat between a first gas and a second gas, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend between the first and second heat exchanging chambers;
the first heat exchanging chamber comprising an inlet for receiving the first gas into the chamber and an outlet through which the first gas can exit the first chamber, the flow of first gas being substantially along the array of heat pipes;
the second heat exchanging chamber comprising an inlet for receiving a second gas into the chamber and an outlet through which the second gas can exit the second chamber, the flow of second gas being substantially across the array of heat pipes; wherein,
the flow of second gas is split into two subsidiary flow paths, with each subsidiary flow path comprising a substantially identical array of heat pipes.
The heat exchanger of the present invention thus ensures that the flow of second gas is uniformly distributed across each heat pipe to ensure that each heat pipe of the array receives a similar rate of heat exchange for optimal performance.
Preferably, the flow of second gas is split into the two subsidiary flow paths by the outlet of the first heat exchanging chamber. The inlet and outlet of the first heat exchanging chamber are preferably disposed on a longitudinal axis of the heat exchanger.
The cross-sectional area, through which the subsidiary flows of second gas pass, is reduced by the outlet of the first heat exchanging chamber thereby causing the second gas to flow with an increased average velocity.
Preferably, the flow of first gas is arranged to move across the array of heat pipes, in passing along the first chamber, by at least one baffle, which extends across the first chamber substantially transverse to the longitudinal axis of the heat exchanger. The baffle preferably comprises a valve, which can be selectively opened and closed to enable the rate of flow of gas along the first chamber to be controlled. When the valve is closed all of the first gas is arranged to pass across the array of heat pipes to increase the transfer of heat between the first gas and the heat pipes within the first chamber. The amount of heat transferred between the first gas and the heat pipes is preferably controlled by selectively opening the valve to effect the flow of gas across the array of heat pipes.
Preferably, the first and second heat exchanging chambers comprise a substantially cylindrical housing. The first heat exchanging chamber preferably further comprises an internal wall arrangement which is arranged to substantially conform to an outer periphery of the array of heat pipes. Preferably, the wall arrangement comprises a first and second pair of walls which extend along the length of the first chamber. Preferably, the walls of each pair separately converge from the housing of the first chamber to an apex positioned proximate a longitudinal axis of the first chamber. The first and second pair of walls are preferably positioned diametrically opposite each other within the first chamber, such that the apex of each wall extend within a common plane which also comprises the longitudinal axis.
The housing of the first and/or second chambers preferably comprise at least one panel which is removably coupled to the respective housing.
The heat pipes are preferably configured to an array of arcuate rows. Preferably, each arcuate row of the array of heat pipes comprises a radius of curvature that is centered on the longitudinal axis of the heat exchanger. The arcuate disposition of the heat pipes and the first and second pair of walls increase the surface area of the heat pipes encountered by the first flow of gas and further provide for a minimal pressure drop of the first gas between the inlet and outlet of the first chamber. The is because the first gas flows along the first chamber while making one or more passes across the arcuate rows of heat pipes and as such, the gas passes through a large number of heat pipes per arcuate row than the second gas.
The second gas flows across the first chamber and thus the heat pipes, and therefore passes across fewer heat pipes per row than the first gas (the flow of second gas in the second chamber is across an approximate linear arrangement of rows). In order to prevent the working temperature of the heat pipes rising above a preferred value, the heat absorbed by the second gas and thus the mass rate of second gas across the second chamber must be greater than the mass rate of gas along the first chamber. This is achieved by splitting the flow of second gas along the two flow paths, namely one either side of the outlet of the first chamber to increase the flow velocity of second gas along each flow path compared to the flow of first gas along the first chamber.
The arcuate arrangement of heat pipes further provides for a similar rate of heat exchange for each pipe within a particular row. Preferably, the flow of gas along a particular arcuate row within the first and second chambers is substantially uniform so that each heat pipe in the particular arcuate row provides a similar rate of heat exchange. This is achieved by ensuring the gas flows with the substantially same velocity at all positions along a given row; there will be a different velocity in different rows, but it is necessary for the gas flow velocity to be substantially the same at all positions along a given row.
Preferably, the first gas is hotter that the second gas.
Preferably, the second heat exchanging chamber comprises a cover that is removably coupled thereto, to provide access to the heat pipes for maintenance and or replacement etc.
In accordance with a second aspect of the present invention there is provided a gas processing system, the processing system comprising the heat exchanger of the first aspect.
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 sectional view along the length of the heat exchanger according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view across the first chamber of the heat exchanger of FIG. 1;

FIG. 3 is a cross-sectional view across the second chamber of the heat exchanger of FIG. 1;

FIG. 4 is a sectional view along the length of the heat exchanger of FIG. 1, as viewed in the direction of the inlet of the second chamber;

FIG. 5 is a cross-sectional view across the first heat exchanging chamber illustrating the removable panels;

FIG. 6 is a cross-sectional view across the second heat exchanging chamber illustrating the removable panels; and

FIG. 7 is a plan view of the heat exchanger of FIG. 1.

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 FIG. 1 of the drawings, there is illustrated a sectional view through a heat exchanger 10 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 comprising a substantially cylindrical housing. The chambers 11, 12 comprise substantially the same diameter and are mounted on top of each other so that a longitudinal axis of the first chamber 11 is substantially collinear with a longitudinal axis of the second chamber 12.
The first chamber 11 of the heat exchanger is disposed below the second chamber 12 and comprises an inlet 13, which is disposed at the underside of the first chamber 11, for receiving a first gas into the chamber 11. The first chamber 11 further comprises an outlet 14, which extends from an upper region of the first chamber, from which gas can leave the chamber 11. The inlet 13 and outlet 14 are centered on the longitudinal axis of the first chamber 11, so that the flow of first gas is substantially along the longitudinal axis of the chamber 11.
The second chamber 12 comprises an inlet 15 for receiving a second gas into the second chamber 12, which extends through the arcuate side wall of the housing, and an outlet 16 also disposed in the arcuate side wall, from which the second gas can leave the chamber 12. The inlet 15 and outlet 16 of the second chamber 12 are disposed substantially diametrically opposite each other so that the flow of second gas within the chamber 12 is substantially across, namely substantially transverse to the longitudinal axis of the chamber 12.
The first and second chambers are separated from each other by a plate 17, so that the first and second gas flows remain separated. The outlet of the first chamber 11 however comprises a duct 18 which extends from an upper region of the first chamber 11 through the second chamber 12. The duct 18 extends substantially along the longitudinal axis of the second chamber and terminates at an upper region of the second chamber 12.
The heat exchanger further comprises a plurality of substantially linear heat pipes 19 which extend from within the first chamber, through the plate 17 and terminate in the second chamber 12 so as to enable heat to be transferred between the chambers 11, 12. The heat pipes 19 extends substantially parallel to the longitudinal axis of the first and second chambers 11, 12 and are configured in a substantially arcuate arrangement of rows of heat pipes (as illustrated in FIGS. 2 and 3), the radius of curvature of each arcuate row being centered substantially on the longitudinal axis. In this manner each chamber 11, 12 comprises a plurality of arcuate rows of heat pipes 19, having different radii of curvature.
The first chamber 11 of the heat exchanger 10 further comprises a plurality of baffles 20 (only one of which is illustrated in FIG. 4) which extend across the first chamber 11. Each baffle 20 comprises a plate 20 a having a valve 21 disposed therein, which can be selectively opened and closed to alter the flow path and thus the rate of flow of first gas along the first chamber 11. The first chamber 11 further comprises an internal wall arrangement 22 that extends between opposite longitudinal ends of the first chamber 11. The wall arrangement 22 comprises a first and second pair of walls 22 a, 22 b, which extend from diametrically opposite positions on the cylindrical housing of the first chamber 11. The walls of each pair 22 a, 22 b separately converge toward each other and meet at an apex positioned proximate to the longitudinal axis of the first chamber 11. The wall arrangement 22 is arranged to substantially conform to the outer periphery of the array of heat pipes 19 so as to remove any pocket regions within the chamber 11 which could otherwise provide a flow path for gas along the chamber 11 without encountering a heat pipe 19.
The housing of each chamber 11, 12 of the heat exchanger 10 is supported by a plurality of pillars 23 which extend between opposite longitudinal ends of each chamber 11, 12. The housing of each chamber 11, 12 further comprises a series of panels 24 (as illustrated in FIGS. 5 and 6) which may be removably coupled thereto using nuts and bolts (not shown), for example, so that the panels 24 can be removed to provide access to the interior of the respective chamber for cleaning and maintenance of the heat pipes. In addition, the heat exchanger 10 further comprises a removable cover 25 (as illustrated in FIG. 7) which extends over the upper region of the second chamber 12 so that access can be gained to the heat pipes to enable them to be removed and replaced if necessary.
In use, hot gas from an industrial process for example, is passed into the inlet 13 of the first chamber 11. The baffle 20 causes the hot gas to move across the heat pipes 19 in moving along the first chamber 11 to the outlet 14. As the hot gas passes across the heat pipes 19, it gives up the heat associated therewith to the heat pipes 19 thereby causing the temperature of the heat pipes 19 to rise. The hot gas thus becomes cooled in moving along the first chamber 11 between the inlet 13 and the outlet 14.
In order to reduce the amount of heat transferred to the heat pipes 19, the valve 21 on the baffle 20 may be opened, so that the hot gas can also pass along the longitudinal axis of the chamber 11 without passing across the pipes 19. When fully opened, very little heat transfer to the heat pipes 19 takes place since the hot gas can pass direct from the inlet 13 to the outlet 14, and so the working temperature of the pipes 19 remains relatively low. However, upon fully closing the valve 21, all the hot gas is forced to pass across the heat pipes to encourage maximum heat transfer. Accordingly, by controlling the extent of the opening of the valve 21, the working temperature of the heat pipes 19 can be controlled.
The heat pipes 19 subsequently transfer the heat to the second chamber 12 which receives cold air from an air conditioning system, for example, through the inlet 15 disposed on the arcuate housing wall. The cold air flow is split by the duct 18 of the outlet 14 of the first chamber 11 into two flow paths which extend around opposite sides of the duct 18. Each flow path encounters an identical array of heat pipes 19 so that each flow path provides a uniform exchange of heat with the heat pipes 19. The cold air absorbs the heat from the heat pipes 19 and thus becomes warmed as it flows between the inlet 15 and the outlet 16 of the second chamber 12. Each of the two flow paths presents a reduced cross-sectional area to the flow of gas, in view of the obstruction provided by the duct 18 forming the outlet 14 of the first chamber 11, thereby causing the average velocity of the flow of cold gas along each path to increase.
From the foregoing therefore, it is evident that the heat exchanger of the present invention provides for an improved control over the working temperature of the heat pipes and provides an array of heat pipes each of which receives a similar rate of heat exchange.
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 exchanging heat between a first gas and a second gas, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend between the first and second heat exchanging chambers;

the first heat exchanging chamber comprising an inlet for receiving the first gas into the chamber and an outlet through which the first gas can exit the first chamber, the flow of first gas being substantially along the array of heat pipes;

the second heat exchanging chamber comprising an inlet for receiving a second gas into the chamber and an outlet through which the second gas can exit the second chamber, the flow of second gas being substantially across the array of heat pipes; wherein,

the flow of second gas is split into two subsidiary flow paths, with each subsidiary flow path comprising a substantially identical array of heat pipes.

2. A heat exchanger according to claim 1, wherein the flow of second gas is split into the two subsidiary flow paths by the outlet of the first heat exchanging chamber.

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

4. A heat exchanger according to claim 3, wherein the flow of first gas is arranged to pass substantially across the array of heat pipes in moving along the first chamber, by at least one baffle which extends across the first chamber substantially transverse to the longitudinal axis of the heat exchanger.

5. A heat exchanger according to claim 4, wherein the baffle comprises a valve, can be selectively opened and closed to enable the rate of flow of gas along the first chamber to be controlled.

6. A heat exchanger according to claim 1, wherein the first and second heat exchanging chambers comprise a substantially cylindrical housing.

7. A heat exchanger according to claim 6, wherein the first heat exchanging chamber comprises an internal wall arrangement which is arranged to substantially conform to an outer periphery of the array of heat pipes.

8. A heat exchanger according to claim 7, wherein the wall arrangement comprises a first and second pair of walls which extend along the length of the first chamber.

9. A heat exchanger according to claim 8, wherein the walls of the first and second pair of walls separately converge from the housing of the first chamber to an apex positioned proximate a longitudinal axis of the first chamber.

10. A heat exchanger according to claim 9, wherein the first and second pair of walls are positioned diametrically opposite each other within the first chamber, such that the apex of each wall extends within a common plane which also comprises the longitudinal axis.

11. A heat exchanger according to claim 6, wherein the housing of the first and/or second chambers comprise at least one panel which is removably coupled to the respective housing.

12. A heat exchanger according to claim 1, wherein the heat pipes are configured to an array of arcuate rows.

13. A heat exchanger according to claim 12, wherein the flow of gas along a particular arcuate row within the first and second chambers is substantially uniform so that each heat pipe in the particular arcuate row provides a similar rate of heat exchange.

14. A heat exchanger according to claim 1, wherein the first gas is hotter that the second gas.

15. A heat exchanger according to claim 1, wherein the second heat exchanging chamber comprises a cover that is removably coupled thereto.

16. A gas processing system, the processing system comprising the heat exchanger according to claim 1.