GB2471452A

GB2471452A - Exhaust gas to liquid heat pipe heat exchanger

Info

Publication number: GB2471452A
Application number: GB0911101A
Authority: GB
Inventors: Dumitru Fetcu
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-06-29
Filing date: 2009-06-29
Publication date: 2011-01-05
Also published as: GB2471562B; GB201010887D0; GB0911101D0; GB2471562A

Abstract

An exhaust gas to liquid heat exchanger comprises a circular arrangement of heat pipes 1 located inside a housing 3, and passing exhaust gases through the housing 3 over the heat pipes 1 by one or more baffles 2. Gas and liquid are separated by a wall 4. Liquid is passed over a portion of the heat pipes 1 protruding through the wall 4 in a circular path formed by baffles 12. An exhaust inlet 16 and outlet 9 are coaxial. A butterfly valve 14 may manually or automatically direct the exhaust gases over the heat pipes 1. A removable lid 8 on the liquid side may permit the heat pipes 1 to be installed or uninstalled. The heat pipes 1 may be installed in the separation wall 4 by a threaded nut (18, fig 8) screwed down onto a washer (20) and o-ring (17) in a threaded hole. Hinged walls / doors (fig 4) or removable arched panels (figs 5 and 6) may enable cleaning surfaces of the heat pipes 1. The heat exchanger is used for heat recovery from exhaust flues coming from boilers or industrial processes and used to preheat water or other kinds of liquid.

Description

Gas to liquid heat pipe heat exchanger The present invention solves the problem of the existing gas to hquid heat exchangers that usually require significant pressure head on exhaust side and at the same time offer limited cleaning possibilities of the heat transfer area.

The theoretical basis of this invention derives from developments in the area of heat pipe technology. A heat pipe is a hermetically sealed evacuated tube normally containing 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 absorbing the latent heat of vaporization. The hot vapor flows to the colder end of the tube where it condenses and gives out the latent heat. The recondensed liquid then flows back through the wick to the hot end of the tube. Since the latent heat of evaporation is usually very arge, considerable quantities of heat can be transported with a very small temperature difference from one end to the other. The vapor pressure drop between the evaporator and the condenser is very small. Therefore, the boiling -condensing cycle is essentially an isothermal process. Furthermore, the temperature losses between the heat source and the vapor and between the vapor and the heat sink can be diminished by means of apropriate design. Therefore, one feature of the heat pipe is that it can be designed to transport heat between the heat source and the heat sink with very small temperature losses. The amount of heat that can be transported as latent heat of vaporization is usually several orders of magnitude larger than can be transported as sensible heat in a conventional convective system with an equivalent temperature difference. Therefore, a second feature of the heat pipe is that arge amounts of heat can be transported with the help of small lightweight structures.

An object of the present invention is to produce a gas to liquid heat pipe heat exchanger having a low pressure drop and high overall heat transfer coefficient on exhaust side and to make possible installing it on existing boilers or industrial processes which almost always have limited pressure drop available.

Another object is to produce a gas to liquid heat pipe heat exchanger with high overall heat transfer coefficient on liquid side.

A further object is to produce a gas to liquid heat pipe heat exchanger where the amount of recovered heat can be controlled.

A further object is to produce a gas to liquid heat pipe heat exchanger that offers better installation possibilities directly on exhaust stack, particularly in very limited spaces.

A further object is to produce a gas to liquid heat pipe heat exchanger where the heat pipes can be easily installed/uninstalled.

A further object is to produce a gas to quid heat pipe heat exchanger with better cleaning possibffities of the heat transfer area on exhaust side.

A further object is to produce a gas to liquid heat pipe heat exchanger which is easier and cheaper to manufacture.

The above objects are obtained by a gas to liquid heat pipe heat exchanger made by a circu'ar arrangement of heat pipes inside a cy'indrical housing designed to be placed on an industrial or domestic exhaust where the gases pass through the circular arrangement of heat pipes being forced by one or more baffles. The gas and liquid are separated by a wall. Cooling liquid is passed through a portion of the heat pipes that protrudes through the wall, wherein baffles are arranged to force the liquid through the greatest possible surface area of the heat pipes, by forcing the liquid into circular paths starting at an entry point and leaving at an exit point.

In order to achieve the lowest pressure drop possible and the highest overall heat transfer coefficient on hot gas side, the heat pipes are arranged in circular rows thus letting the exhaust to flow through a far larger number of heat pipes than in existing heat pipe heat exchangers.

In order to achieve high overall heat transfer coefficient on iquid side, liquid is determined to flow through the greatest possible surface area by means of the circular baffles.

In order to achieve controlling the amount of recovered heat, a butterfly valve is installed on a baffle on the hot gas side. When the butterfly valve is closed all the exhaust will pass through the circular bundle of heat pipes. Thus a maximum recovered heat is received from exhaust and transferred to liquid. By opening the butterfly valve, it is only the desired rate of exhaust that will pass through the heat pipe bundle thus controlling the amount of heat received by the liquid. The butterfly valve can be manual or can be actuated automatically to maintain the desired temperature of the liquid.

In order to achieve a gas to liquid heat pipe heat exchanger offering better possibilities to be easily installed directly on exhaust stack, particularly in very limited spaces, an overall circular shape has been chosen with exhaust inlet/outlet connections placed on the same vertical axis.

In order to achieve the possibility of easy installing or uninstalling the heat pipes a special system is provided for instaling the heat pipes in the separation pate.

Installing or uninstalling the heat pipes is made through a removable lid.

In order to achieve better cleaning possibilities of the heat transfer area on exhaust side hinged wals or removable arching panels can be provided on the exhaust side cyinder.

In order to achieve a heat pipe heat exchanger which is easier and cheaper to manufacture, the overaU cylindrical shape has been chosen. Thus the unit is mainly made of welded cylinders and flanges. This reduces a the material stress and distortions associated with welding significant'y. The manufacturing process is also significantly eased since it only involves dealing with cylinders and flanges.

The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows a vertical cutaway of the gas to liquid heat pipe heat exchanger, Figure 2 shows a horizontal cutaway on exhaust side of gas to liquid the heat pipe heat exchanger Figure 3 shows a horizontal cutaway on liquid side of the gas to liquid heat pipe heat exchanger Figure 4 shows a horizontal cutaway on gas side of the gas to liquid heat pipe heat exchanger having hinged walls Figure 5 shows a horizontal cutaway on gas side of the gas to liquid heat pipe heat exchanger having removable arching panels in version 1 Figure 6 shows a horizontal cutaway on gas side of the gas to liquid heat pipe heat exchanger having removable arching panels in version 2 Figure 7 shows the view of the baffle on exhaust side of the gas to liquid heat pipe heat exchanger Figure 8 shows a vertical cutaway of the installing system of the heat pipes in the separation plate.

In figure 1, a gas to liquid heat exchanger, designed to be placed on an industrial or domestic exhaust, is made by an arrangement of circular rows of heat pipes 1 inside a cylindrical housing 3 on exhaust side and a cylindrical housing 5 on liquid side. The hot gas and cold liquid are separated by a waU 4 (separation plate). The exhaust, entering through connection 16, installed on the bottom lid 15 is forced to flow radial'y through the bund'e of heat pipes by the baffle 2 and has the possibility to be controlled by a butterfly va've 14. The baffle 2 is fixed in the proper place by several independent brackets 13.

Each heat pipe 1 draws in a quantity of exhaust heat and transfers it to the other side of the separation plate to be released to the liquid. When the butterfly valve 14 is closed the whole mass of exhaust is forced to flow radially through the circular bundle of heat pipes and a maximum heat transfer is obtained. When the butterfly valve is partially open a certain amount of exhaust goes directly to stack without flowing through the heat pipe bundle and thus the overaU heat transfer is diminished.

The butterfly valve can be manual or automaticay actuated by a thermocouple placed on the liquid side (liquid outlet temperature).

The liquid side of the heat exchanger is made by cylindrical walls 5 and 10, separation plate 4 and the removable upper lid 8. The liquid, entering through the flange 7 and nozzle 6 and leaving through 11, is forced to flow (19 Figure 3) through the greatest possible surface area by the circular baffles 12 thus the liquid being forced through the greatest possible surface area of the heat pipes.

The hot gas goes out of the heat exchanger through the connection 9 placed in the middle of the removable upper lid 8. Both connection 9 and 16 are on the same vertical axis of the heat exchanger so that it is very easy to install the unit directly on a hot gas stack.

Figure 2 shows a horizontal cutaway on gas side in which the concept of circular arrangement of heat pipes 1 is presented together with the position of the baffle 2, the four independent brackets 13, the cylindrical housing 3, the bottom lid 15, and the buterfly valve 14 installed in the baffle 2. Figure 2 shows also the suporting structure of the heat pipe bundle made by a polar array of pillars 21.

Figure 3 shows a horizontal cutaway on liquid side in which the concept of circular arrangement of heat pipes 1 is also presented together with the concept of circular baffles 12, installed to force the liquid flow through the greatest possible surface area of the heat pipes.

Figures 4, 5 and 6 show a horizontal cutaway on gas side in which the concepts of hinged walls 3 and removable arching panels are presented. The easy cleaning of exhaust side heat transfer area is a feature of great importance made possible by the arrangement of circular rows of heat pipes 1 inside a cylindrical housing 3.

Figure 7 shows the shape of the baffle 2 on exhaust side of the heat pipe heat exchanger together with the position of butterfly valve 14 and the baffle supporting brackets 13.

Figure 8 shows the vertical cutaway of the installation system of the heat pipes in the separation plate which consists of a threaded hole in the separation plate, a threaded nut 18 designed to compress an 0-ring 17 by a washer 20. By screwing in the threaded nut, a water tight separation between gas side and liquid side is realized allowing, at the same time, an easy installing or uninstalling of heat pipes.

This installation system becomes very important when the heat exchanger has very large dimensions and weight, because allows installing the heat pipes one by one on site after installing the casing.

Claims

SClaims 1. A gas to liquid heat exchanger designed to be placed on an industrial or domestic exhaust, made by an arrangement of circular rows of heat pipes inside a cylindrical housing where the gases pass through the circular arrangement of heat pipes being forced by one or more baffles, thus letting the exhaust to flow through a large number of heat pipes.
2. A gas to liquid heat exchanger according to claim 1, in which the cooling liquid is passed through a portion of the heat pipes that protrudes through the separation wall, wherein baffles are arranged in a certain way to force the liquid through the greatest possible surface area of the heat pipes, by forcing the liquid into circular paths starting at an entry point and leaving at an exit point.
3. A gas to liquid heat exchanger according to claim 1, in which the exhaust inlet/outlet connections are placed on the same vertical axis.
4. A gas to liquid heat exchanger according to claim 1, in which a butterfly valve is installed on a baffle on the hot gas side thus controlling, manually or automatically, the amount of heat received by the liquid.
5. A gas to liquid heat exchanger according to claim 1, in which the baffle is fitted by independent brackets to avoid thermal stress distortions.
6. A gas to liquid heat exchanger according to claim 1, in which a removable lid is provided on liquid side so that the heat pipes can be easily installed or uninstalled.
7. A gas to liquid heat exchanger according to claim 1, in which the heat pipes are installed in the separation wall by a system comprising a threaded hole, a threaded nut, a washer and an 0-ring.
8. A gas to liquid heat exchanger according to claim 1, in which hinged walls or removable arching panels can be provided on the exhaust side cylinder in order to allow easy heat transfer surface cleaning.
9. A gas to liquid heat exchanger according to claim 1, in which the supporting structure is formed by the separation plate which acts as a horizontal beam and a polar array of pillars.