WO1993002328A1

WO1993002328A1 - Refrigeration and air conditioning system for vehicles

Info

Publication number: WO1993002328A1
Application number: PCT/US1992/006018
Authority: WO
Inventors: Uri Rapoport; Avigdor Zur; Itzhak Shechtman
Original assignee: Uri Rapoport
Priority date: 1991-07-23
Filing date: 1992-07-20
Publication date: 1993-02-04
Also published as: ZA925541B; IL98938A; IL98938A0

Abstract

A refrigeration and air conditioning system for use in vehicles (2) that is an absorption-refrigeration system in which the refrigerant-absorbent mixture is heated through heat pipes (12a) by the waste heat of exhaust gases from the vehicle (2) which has a fuel-driven internal combustion engine (3). The absorption-refrigeration system is based on the principle of evaporation at relatively low pressure and temperature followed by absorption of refrigerant vapor by the absorbent at relatively low pressure and then evaporation of the refrigerant from the absorbent when heated by an external heat source.

Description

DESCRIPTION

REFRIGERATION AND AIR CONDITIONING SYSTEM FOR VEHICLES

TECHNICAL FIELD

The present invention relates to a refrigeration and air conditioning system for use in vehicles and, in particular, to a so-called absorption-refrigeration system based on the principle of evaporation at relatively low pressure and temperature followed by absorption of refrigerant vapor by the absorbent at relatively low pressure and then evaporation of the refrigerant from the absorbent when heated by an external heat source.

The present invention relates moreover to an absorption-refrigeration system in which the refrigerant-absorbent mixture is heated through heat pipes by the waste heat of exhaust gases from the vehicle which has a fuel-driven internal combustion engine. This method of energizing an absorption refrigeration system in a car by means of a heat pipe, has never been done before.

Background Art

Air-conditioning and refrigeration systems in general and their use in vehicles in particular are well known. Their description can be found in many engineering textbooks and monographs, for example Refrigeration and Air Conditioning by . F. Stoecker, McGraw-Hill, 1958.

These systems can be divided into two main groups according to their principle of operation: systems based on the compression of refrigerant vapor, and systems based on the absorption of refrigerant vapor. The first group is the most common and its main components are evaporator, compressor, condenser and expansion valve. In the operation of such a system refrigeration is produced by the repeated process of ⁵ compression, condensation, expansion and evaporation of the refrigerant, which is a liquid with a relatively high vapor pressure.

For operation of compression systems two principal conditions ought to be satisfied: 10 1) energy should be supplied for compressor operation; 2) separate cooling should be provided for condenser operation. These conditions are the reason for several •L5 serious disadvantages of a compression refrigeration system in vehicles.

Part of the vehicle engine power usually serves as the energy source for the compressor thus reducing the available useful power and increasing fuel consumption. 20 This drawback restricts application of the compression system mostly to relatively high-powered cars and industrial vehicles such as lorries. Besides there is reduced refrigeration effect when operating at low revolutions and no refrigeration at all when the engine ⁵ stops.

The condenser is cooled by engine cooling water or by a fan. However, use of engine cooling water may reduce engine efficiency and overload the engine cooling system. 0 The refrigerants used in compression systems are usually freons which are environmentally harmful. Despite the above mentioned drawbacks inherent to refrigeration systems based on compression, these systems are rather common both in general use and in vehicles in particular, because their coefficient of performance (ratio between the "cold" produced and the energy consumed) is high and construction is relatively simple. The second type of refrigeration system is the absorption-separation (henceforth absorption) system. Absorption systems have been known for a long time, their first use probably dating back to the time of the Civil War in the United States.

The operation principle of the absorption system is similar to that of the compression system and its main components also include an evaporator and a condenser. Instead of a compressor, which is a mechanical means for increasing pressure difference between evaporator and condenser the absorption system utilizes a generator filled with a mixture of at least two intermiscible substances (refrigerant and absorbent) and an absorber, in which absorption of the refrigerant in the absorbent takes place. The refrigerant and absorbent should have sufficiently different vapor pressures, so that when the generator is heated the vapor of the more volatile refrigerant is produced and then condensed in the condenser.

The absorption system usually includes a pump to deliver the liquid from the absorber back to the generator. The vapor from the generator passes to the condenser, where it condenses into a liquid and then proceeds via a pressure reducing valve into the evaporator where it again turns into vapor with the accompanying cooling effect due to the absorption of its latent heat of vaporization. The absorption system also includes fanned air or cooling liquid which cool the absorber and condenser. The main advantage of this system is the small* amount of mechanical work required for its operation. Instead of a large quantity of mechanical energy demanded by the compressor only a negligible amount is needed for operation of pump and cooling means. Furthermore, the f ct that the energy received by the system is in the form of heat which is supplied to the generator, is the reason that its coefficient of performance is much lower than in compression systems.

These systems are used in applications where power supply is not sufficient but heat is available.

There is also a certain limitation imposed by the required properties of the refrigerant-absorbent pair (volatility, solubility, viscosity, latent heat of vaporization, etc.), the common choices being water-ammonia and water-lithium bromide.

Nevertheless despite the above mentioned drawbacks there are several known attempts to use absorption systems for refrigeration and air conditioning in vehicles because of the very attractive possibility of utilizing the waste heat of exhaust gases as an external heat source for the generator. As an example of such attempts one can mention the systems described in US patents 3661200 and 4924676, British application 1368911, or European patent 350764. The main disadvantages of the above mentioned systems are associated with the problem of optimization of conditions for heat transfer from the exhaust gases to the generator. For example in US patent 3661200 is described refrigeration absorption system which includes a generator installed in a casing which extends along and over the exhaust conduit of the engine. The waste gases usually enter the exhaust pipe at a temperature of between 600 and 800 degrees C and a pressure of a few inches of Hg; they move along the exhaust pipe at velocities of 60-100 m/sec. Effective extraction of heat from the exhaust pipe and its transfer at these conditions to a generator designed as per above patent requires a very large heat transfer area, which means excessively long exhaust pipe and generator resulting in pumping and pressure drops. It should be pointed out that specification for this patent mentions above problem without providing specific suggestions for its solution.

Another disadvantage of the absorption system described in this patent is that it requires an exhaust pipe with thick walls in order to withstand the relatively high pressure needed for its effective operation.

The systems described in other patents relate to an alternative solution where the generator is placed inside the exhaust pipe to ensure direct contact with the hot waste gases. The presence of a generator in the exhaust pipe causes back pressure on the engine outlet ports and reduces its efficiency.

As an inevitable consequence of the above considerations the known refrigeration and air-conditioning systems for vehicles based on the absorption principle become complicated, bulky and inefficient. This may explain why a practical, efficient and economical absorption system based on utilization of waste heat from exhaust gases without adversely affecting the engine performance is still unavailable. Disclosure of the invention

The object of the present invention is to provide an absorption refrigeration and air-conditioning system for use in a vehicle in which the above mentioned drawbacks are reduced or eliminated while the inherent advantages of the absorption principle still remain.

In particular, the first object of the present invention is to provide a simple absorption system for use in vehicles which efficiently extracts the heat of waste gases passing through the exhaust conduit without necessity of a large exhaust conduit and generator, without increasing the wall thickness of the exhaust pipe and without causing back pressure on the engine.

The second object of the present invention is to provide an efficient absorption system in which the heat transfer from the exhaust gases to the generator system ensures achieving and maintaining a maximum cooling effect independently of the speed of the engine.

Another object of the present invention is to provide an efficient absorption system which utilizes heat of the engine waste gases with a minimum pressure drop of exhaust gases and minimum temperature gradient, thus improving the engine efficiency.

Another object of the present invention is to provide an improved and compact absorption system which includes heat exchanger and can be installed in the motor compartment of any car without reducing engine performance and without increasing fuel consumption.

Still another object of the present invention is providing an efficient absorption system, in which a small fan cools absorber and condenser demanding only little power from the engine. Above mentioned objects of the present invention can be achieved with the inclusion of the following components: a generator heated by the heat of waste gases passing through the main branch of the exhaust conduit, while said generator is filled with a mixture of at least two intermiscible substances having different volatilities, while the vapor of more volatile component evolved during the heating of said generator serves as a refrigerant and the remaining solution of less volatile component with the refrigerant serves as an absorbent for said vapor, an absorber in which said refrigerant vapor after passing through the condenser and evaporator will be absorbed by the absorbent coming from the bottom of the generator, a condenser for liquifying of said refrigerant vapor coming from the generator, an evaporator connected to said condenser via an expansion valve which serves for expansion of said condensed refrigerant into vapor thus providing a cooling effect, a pump for transferring the absorbent from the absorber back to the generator, a means for supplying the external air for cooling of said absorber and a means for supplying the cooled and conditioned air to the passenger compartment after utilizing the cooling effect which is provided in said evaporator and after mixing (if needed) with the air heated in said absorber, and a means for controlling the refrigerant vapor pressure inside the evaporator, the level of the refrigerant-absorbent mixture inside the generator and the amount of waste gases passing through the exhaust conduit c h a r a c t e r i z e d i n t h a t said generator is connected with the internal part of said exhaust conduit via intermediate means whereas said intermediate means is carried out as a plurality of heat pipes connecting said generator with the exhaust conduit.

By virtue of system construction in accordance with the present invention extraction of heat and its adiabatic transfer from exhaust gases to said generator is provided with a maximum heat flux density and with a minimum temperature gradient along the intermediate means between the exhaust conduit and the generator.

In a preferred embodiment of the invention said exhaust conduit is provided with a receiving portion for connection to the heat pipes. The pipes are oriented in such a manner that waste gases passing through the exhaust conduit flow over the evaporator section of each heat pipe inserted into said receiving portion. The condenser section of each heat pipe is inserted into the generator and makes contact with the mixture of the refrigerant and absorbent.

The present invention in its various aspects has only been summarized briefly. For a better understanding of the present invention and its objects and advantages reference should now be made to the following description of its preferred embodiment taken in conjunction with the accompanying drawings. Brief description of the drawings

Fig. 1 is a schematic view of the system according to the present invention including its main components and installed in the engine compartment of a vehicle.

Fig. 2 shows the connection of the intermediate means with the generator and with the receiving portion of the exhaust conduit when said receiving portion is located in the main branch of the conduit. Fig. 3 shows connection of the intermediate means with the generator and the receiving portion of the exhaust conduit when said portion is located in the bypass of the conduit.

Fig. 4 shows the plurality of the heat pipes inserted in the receiving portion of the exhaust conduit.

Fig. 5 shows the exploded view of the heat pipe with its division into evaporator, adiabatic and condenser section.

Fig. 6 shows section A-A of Fig. 4.

Best Mode for Carrying out the Invention

Fig. 1 presents an absorption system for refrigeration and air conditioning of passenger compartment 1 of the vehicle provided with a fuel driven internal combustion engine. The system is installed in a vehicle engine compartment 2 and utilizes the heat of waste gases entering the exhaust conduit 4 from the engine outlet ports 3.

The main components of the system are: generator 5, absorber 6, condenser 7, evaporator 8, expansion valve 7a, pump 9 and heat exchanger 10. The generator 5 is filled with a mixture of at least two intermiscible substances having different volatilities. In most cases this mixture is presented by a liquid solution of two liquids but it can be a solution of a solid in the liquid as well. The substance with higher volatility serves as a refrigerant and the substance with lower volatility together with the remaining portion of the more volatile component as an absorbent. In the preferred embodiment of the present invention ammonia is used as the refrigerant and NaSCN as the absorbent. It should be understood that alternative choices are possible for the refrigerant-absorbent combination for example the combination H,0 and LiBr, NH₃ and LiN0₃. The generator 5 is heated by the heat extracted from waste gases passing through the main branch 4a and entering the receiving portion 11 of the exhaust conduit. This heat is transferred directly to the generator 5 via intermediate means 12 which connects the receiving portion 11 with the generator 5. A more elaborate description of the intermediate means 12 will be presented later.

When the generator is heated the pressure and temperature inside it builds up and the vapor of the more volatile substance concentrates at the top of the generator, passes to the condenser 7 and condenses. The pressure of the liquid refrigerant coming out at the bottom of the condenser is reduced when it flows through the expansion valve 7a, where part of the liquid evaporates.

Evaporation of the rest of the refrigerant takes place in the evaporator 8 at reduced pressure and is accompanied by cooling due to extraction of heat from the surroundings in accordance with the latent heat of evaporation of the refrigerant. The vapor produced in the evaporator flows back to the absorber where it is absorbed by a stream of absorbent coming from the bottom of the generator. The solution of the absorbent being enriched by the refrigerant component is pumped back to the generator by means of pump 9 via heat exchanger 10.

The hot solution of the absorbent from the bottom of the generator passes through the heat exchanger and transfers part of its heat to the stream of absorbent enriched by the refrigerant returning to the generator from the absorber and thereby heating it while itself cooling down.

The fan 16 supplies ambient air to the evaporator 8 for cooling before it enters the passenger compartment.

The amount of air to be cooled and supplied as a cooling media to the passenger compartment can be adjusted with a batterfly valve 18 installed in the outlet 18a located between the fan 16 and the evaporator 8. The fan 17 supplies ambient air for cooling the absorber and condenser where this air is heated by the heat released upon absorption and condensation. It should be understood that separate fans may be provided for the absorber and condenser. The heated air is pushed by the fan 17 via duct 13 to the passenger compartment for heating it, or for conditioning by preliminary mixing with the cold air which passed the evaporator. The amount of hot air passing through the duct 13 can be adjusted with two batterfly valves 14 and 15 installed in duct 13 and with outlet 15a opened to the atmosphere.

For operation of both fans and the pump only a small amount of power is needed which can be supplied by the vehicle battery. Now the intermediate means 12 which serves to extract heat from the waste gases and transfer it to heat the generator will be explained with reference to figs. 4 and 5. This means comprises a plurality of small devices 12a known in the art as heat pipes. These heat pipes connect the generator and receiving portion 11 of the exhaust conduit.

The heat pipe construction as shown in fig. 5 consists of a tubular container 121 containing a hollow wick 122 made of a fibrous or porous material and filled with a volatile liquid. The heat input at the evaporator section 124 of the heat pipe causes the liquid in the wick to vaporize while its vapor moves inside the hollow section 127 of the wick towards condenser section 126. In this section condensation of the vapor back to a liquid takes place with accompanying heat output into the surroundings and thus providing the heating effect. The liquid after condensation moves due to the capillarity of the wick material back to the evaporator section. The intermediate means 12 is carried out as a plurality of heat pipes oriented in such a manner that evaporator section 124 of each heat pipe is inserted into receiving section 11 of the exhaust conduit while condenser section 126 is inserted into generator 5. Hot waste gases passing through the exhaust conduit flow over the evaporator sections while the condenser sections are in close contact with the refrigerant-absorbent mixture.

The above design of the intermediate means ensures extraction of heat from the waste gases and its adiabatic transfer to the vehicle absorption system for subsequent obtaining of cooling effect with a minimum temperature gradient along the intermediate means. The amount of the waste gases entering the receiving portion and flowing over the evaporator section of each heat pipe can be adjusted with the batterfly valve 19a placed in the main branch adjacent to the receiving section.

It will now be explained how additional advantages due to the absorption system according to the present invention can be achieved.

Fig. 1 and 2 show the location of the receiving portion 11 in the main branch 4a of the conduit, while fig. 3 shows how this receiving portion can be located in the bypass 4b of the exhaust conduit. This embodiment ensures extraction of the heat from the waste gases without causing back pressure on the engine outlet port, which could reduce engine efficiency.

Another embodiment of the present invention is presented in fig. 6. This figure shows that the heat pipes 12a of the intermediate means 12 are provided with longitudinally extending fins 128 protruding through their outside surfaces. Transverse fins may also be used.

These fins extending along evaporator sections of the heat pipes inside receiving portion 11 of the exhaust conduit serve as a labyrinth for gases moving through the conduit and thus provide a silencing effect in addition to dedicated silencers 20, 22.

It should be understood that providing of an additional silencing effect can be achieved also if only part of the heat pipes is provided with these fins.

Different control means some of which are shown in fig. 1 contribute to the reliable functioning of the system according to the present invention. The pressostat 20 governs the pressure and thus the temperature in the evaporator 8; the level device 30 controls the level of refrigerant-absorbent mixture in the generator and changes the flow of absorbent from the generator to the absorber; the thermostat 40 controls the position of the batterfly valve 19a and the amount of heat transferred from waste gases to the generator 5 via intermediate device 12.

It is not shown in particular in the drawings but should be understood by a person skilled in the art that the amount of cooled air entering the passenger compartment via evaporator 8 depends on rotational speed of the fan 16 which, in turn, may be controlled by the same thermostat 40.

Although several preferred embodiments have been disclosed and described in details herein it should be understood that this invention is not limited thereby. In particular, the absorption system according to the present invention may include more than one of each of its main components and more than one pair of absorbent-refrigerant, the particular type of substances chosen as absorbent and refrigerant in each pair may differ from those mentioned above, the intermediate means can be provided with fins extending both longitudinally or transversall .

The scope of the invention is to be determined by the appended claims.

Claims

Claims 1. A system for refrigeration and air conditioning in a vehicle passenger compartment comprising: at least one generator heated by waste gases passing through the main branch of an exhaust conduit, while said generator is filled with a mixture of at least two intermiscible substances having different volatilities, while the vapor of the more volatile component produced by the heating of said generator serves as a refrigerant and the less volatile component serves as an absorbent for said vapor, at least one absorber connected to the generator and serving to absorb said refrigerant vapor by the absorbent, at least one condenser for liquifying said refrigerant vapor and being connected with said generator, at least one evaporator connected with said condenser via pressure reducing means which serves to expand said refrigerant and thus provide a cooling effect, a means for transferring the absorbent-refrigerant mixture from the absorber back to the generator, a means for supplying the external air for cooling of said absorber and condenser, a means for supplying the cooled and conditioned air to the passenger compartment after utilizing the cooling effect provided in said evaporator c h a r a c t e r i z e d i n t h a t said generator is connected with the internal part of said exhaust conduit via intermediate means whereas said intermediate means ensures extraction of heat and its transfer from exhaust gases to said generator and with a maximum heat flux density and minimum temperature gradient along the intermediate means between the internal part of the exhaust conduit and the generator.

2. A system according to claim 1. c h a r a c t e r i z e d i n t h a t said exhaust conduit is provided with a receiving portion for connection with said intermediate means and said intermediate connecting means is carried out as at least one heat pipe connecting said generator with receiving portion of the exhaust conduit, while said heat pipe is oriented in such a manner that its evaporator section is inserted into said receiving portion of the exhaust conduit over which flow the waste gases passing through the exhaust conduit whereas condenser section of said heat pipe is inserted into the generator to be in contact with a mixture of the refrigerant and absorbent.

3. A system according to the preceding claims c h a r a c t e r i z e d i n t h a t said receiving portion of the exhaust conduit is located in its main branch.

4. A system according to claims 1-2 c h a r a c t e r i z e d i n t h a t said exhaust conduit is provided with a bypass and said receiving portion is located in the bypass.

5. A system according to one of the preceding claims c h a r a c t e r i z e d i n t h a t at least some of said heat pipes are provided with extending fins protruding around the outside surfaces of the pipes and extending along the evaporator sections of said heat pipes inserted into the receiving portion of the exhaust conduit.

6. A system according to one of the preceding claims c h a r a c t e r i z e d i n t h a t said means for supplying the cooled and conditioned air to the passenger compartment comprises a fan for supplying the outside air to said evaporator and a valve for controlling the flow of the external air passing via said evaporator whereas said means for supplying the external air for cooling of said absorber and condenser includes a fan for supplying external air over the absorber and condenser and valves for respectively controlling the flow of hot air released to the atmosphere and the flow of hot air supplied for mixing with the cold air passing over the evaporator.

7. A system according to one of the preceding claims c h a r a c t e r i z e d i n t h a t a heat exchanger is installed between said generator and said absorber.

8. A system according to one of the preceding claims f u r t h e r c o m p r i s i n g means for controlling the amount of waste gases passing through the exhaust conduit over the evaporator section of said heat pipe. The controlling means including a butterfly valve installed inside the exhaust conduit before said receiving portion.

9. A system as hereinbefore described and with reference to accompanying drawings.