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AUTOMOBILE AIR CONDITIONER BY UTILIZING WASTE HEAT RECOVERY 1

TABLE OF CONTENTS

Table of Contents

01

List of Figures

02

Acknowledgement

03

Abstract

 

04

Chapters:

 

 

1.

Introduction

05

2.

Related Papers

06

3.

Automobile Waste Heat Recovery

07

 

3.1. System Layout

07

 

3.2. Component Descriptions and Functions

07

 

3.3. Adsorption (Solid–Vapor) Cooling

09

4.

Advantages

11

5.

Disadvantages

13

6.

Applications

14

7.

Conclusion

16

8.

Bibliography

17

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LIST OF FIGURES

Fig 1.Layout of the exhaust-powered automotive adsorption heat pump

07

Fig 2: Schematic diagram of the exhaust-powered

08

Fig. 3Thermodynamic cycle for adsorption

10

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ACKNOWLEDGEMENT

The satisfaction that accompanies the successful completion of any work would be incomplete without the mentioning of the personalities whose ceaseless cooperation made it possible. Their constant guidance and encouragement crown all efforts with successes.

I am grateful to my seminar guide Mr.Manikandan, Assistant Professor, Department of Aeronautical engineering, Jawaharlal College of Engineering and Technology, for his sincere guidance and extending a helping hand at the crucial times during seminar period.

It will be incomplete without thanking my friends and staffs of Aeronautical department of both IIT and JCET who helped me with extreme pleasure at the time of necessity. I thank God for his constant blessing which ultimately made this work possible.

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ABSTRACT

Large quantity of hot flue gases is generated from boilers, kilns, ovens, furnaces and automobile engine exhausts. If some of this waste heat could be recovered, a considerable amount of primary fuel could be saved. The energy lost in waste gases cannot be fully recovered. However, much of the heat could be recovered and loss can be minimized. This paper focus on the recovery of waste heat gases for the air conditioning in automobiles. The significant power used by the mechanical compressor of an automobile can be eliminated by powering the air conditioner with wasted exhaust heat. This method of indirect heating and cooling achieves the required coefficient of performance(COP), permits optimum placement of components in the vehicle, and allows the use of phase-change material (e.g. wax) to store exhaust heat, shortening the time needed to recharge the refrigerant reservoir which provides immediate cooling after start-up of a cold engine. The strategy of how to recover this heat depends in part on the temperature of the waste heat gases and the economics involved.

Keywords: adsorption heat pump, automotive air conditioning, waste heat recovery

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1. INTRODUCTION

Waste heat is heat, which is generated in a process by way of fuel combustion or chemical reaction, and then “dumped” into the environment even though it could still be reused for some useful and economic purpose. The essential quality of heat is not the amount but rather its “value”. The strategy of how to recover this heat depends in part on the temperature of the waste heat gases and the economics involved.

Large quantity of hot flue gases is generated from Boilers, Kilns, Ovens, Furnaces and engine exhausts. If some of this waste heat could be recovered, a considerable amount of primary fuel could be saved. The energy lost in waste gases cannot be fully recovered. However, much of the heat could be recovered and loss can be minimized.

A waste heat recovery unit (WHRU) is an energy recovery heat exchanger that recovers heat from hot streams with potential high energy content, such as hot flue gases from a diesel generator or steam from cooling towers or even waste water from different cooling processes such as in steel cooling

There are three potential uses for waste heat in a vehicle: cabin heating, cabin cooling, and electricity generation, the last of which could be used for heating and cooling. Heating is already performed efficiently, compactly, and economically by routing engine coolant through a small finned tube heat exchanger (HEX) in the cabin air duct. The only drawback is the long delay (5 min or more) during frigid weather between engine start-up and effective cabin heating and defrosting.

A thermoelectric generator directly powered by exhaust heat could conceivably replace the alternator and power motors connected to the water pump, power steering pump, and compressor. The average of the power drawn by the compressor during a typical20 min commute is 1.6–2.3 kW equal to or greater than that for all other ancillary equipment combined (1.0 kW by the alternator plus 0.7 kW by the water and power steering pumps). Therefore, eliminating the compressor provides the greatest boost to efficiency. Using a thermoelectric generator to power a motor driving a compressor is only one method of eliminating its parasitic power drain. There are a number of thermal effect devices that can convert wasted exhaust heat directly into cabin cooling without having to go through the intermediate step of producing electricity with the attendant losses in efficiency.

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2.RELATED PAPERS

1.R.Z.Wang and R.G.Oliveiria [1]: This paper presents the achievements in solid sorption refrigeration prototypes. The prototypes presented were designed to use waste heat or solar energy as the main heat sources. Despite their advantages, solid sorption systems present some drawbacks such as low specific cooling power and COP.

2.M A Lambert and B J Jones [2]: In this work the conceptual and embodiment design of an exhaust-powered adsorption (desiccant–vapor) air conditioner are traced. The design is preceded by detailed discussion of automotive cooling requirements and the typical driving scenario on which the design is based. Adsorption cooling is then compared with other thermally powered cooling technologies [Sterling, absorption (liquid–vapor), and thermoelectric (i.e. Peltier)], demonstrating that adsorption is the best alternative in terms of size and mass.

3.Monika Gwadera and Krzysztof Kupiec [3]: The principle of operation of adsorption cooling systems, a review of adsorbent- adsorbate working pairs as well as basic information on modeling and methods for improvement of their efficiency are presented. Possible applications and perspectives for developments of adsorption cooling devices are also analyzed.

4.K. Smith and M. Thornton [4]: A combined vehicle model and engine waste heat model were used to compare various accessory electrification scenarios for four different conventional vehicle platforms: a midsize car, a midsize sport utility vehicle, a Class 4 truck, and a Class 8 truck. The Class 8 truck—which has a large amount of waste heat, low mass sensitivity, and a high number of miles traveled per year—was found to be most attractive for early market penetration of a TE waste heat recovery system.

5.R.E.Critoph [5]: This paper describes a mathematical model including each part of a system, i.e. an adsorber, condenser and evaporator. The model describes heat transfer between these devices and mass transfer inside the adsorber. The condenser and the evaporator are described by the heat balance. Due to he fact that mass transfer rate must be implemented in the balance equations, it is necessary to determine the kinetics model describing the rate of refrigerant transfer between the gas phase and the surface of the adsorbent.

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3.AUTOMOBILE WASTE HEAT RECOVERY

3.1.System layout

The adsorption cooling system is depicted as integrated into an automobile. The system comprises three circuits; an HTF loop, an NH3 (or CH3OH) adsorption loop entirely exterior to the passenger cabin, and an R-134a refrigerant loop transferring heat from the cabin to the exterior NH3 (or CH3OH) loop. The R-134a loop could be eliminated by pumping NH3 or CH3OH directly through the evaporator inside the dash. Safety valves installed in the refrigerant tubing would close automatically in the event of a leak to prevent NH3 or CH3OH from entering the cabin.

3.2. Component descriptions and functions

Adsorbers: These contain powdered or granulated adsorbent and are heated and cooled cyclically and asynchronously by hot and cold HTF to pump refrigerant to the condenser and suck it from the evaporator. Three adsorbers are shown, rather than two. This allows for more effective heating and cooling, as shown.

Fig 1.Layout of the exhaust-powered automotive adsorption heat pump

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Heat transfer fluid heater: This is a counter flow heat exchanger in which catalyzed exhaust heats HTF. It resembles an enclosed radiator with multiple serpentine tube banks. As in a typical HTF tubes are oval shaped with thin corrugated fins between them. This design exerts low backpressure on the exhaust.

Thermal reservoirs: Two thermal reservoirs store exhaust heat in PCM (e.g. wax, zinc, or lithium) for drying all adsorbers after the engine is shut off in order to fill the refrigerant reservoir. The reservoirs are thin-walled steel boxes measuring approximately40 cm×10 cm×3 cm and are brazed to the outboard surfaces of the HTF heater manifolds.

Fig 2: Schematic diagram of the exhaust-powered

Heat transfer fluid cooler: This is a radiator that dissipates excess heat from the HTF to cool it near to ambient before it is pumped into the adsorbers being cooled.

Heat transfer fluid pump, tubing, and expansion tank: The small, low-power HTF pump comes after the HTF cooler in the circuit, allowing for an inexpensive OEM fuel pump or engine oil pump for a very small engine. The HTF tubes are insulated. The expansion tank has an internal volume of about0.6 l. It is almost empty when the HTF is cold and nearly full when the heat pump is operating to make allowance for ~12 per cent expansion of the HTF automotive adsorption heat pump from ambient to a mean operating temperature of~160–170 °C.

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Exhaust bypass pipe and control valves: Exhaust exiting the catalytic converter ranges from 400 °C at idle to 450–500 °C at city and highway cruise, to as high as 600 °C for sustained operation at full throttle under heavy load (e.g. uphill towing). Excess exhaust heat beyond that needed to operate the heat pump could overheat the HTF. The bypass pipe allows .When the heat pump is on, a servo motor controlled butterfly valve in the bypass branch opens enough automotive adsorption heat pumps to tap off any excess exhaust. Therefore, although exhaust may reach 600 °C in extreme cases, only a small flow rate of such very hot exhaust would be allowed through the HTF. When the heat pump is off and the HTF is stagnant, the bypass valve is wide open and another solenoid- controlled butterfly valve in the HTF heater branch is closed, preventing overheating. The bypass branch also ensures that excessive backpressure will not result from trying to force all exhaust through the HTF heater at or near full throttle.

Refrigerant reservoir: This contains sufficient refrigerant to provide immediate ‘surge cooling’ during the initial 10 min interval after start-up of a cold engine, while the HTF is being heated in order to start thermally cycling the adsorbers and pumping refrigerant.

Condenser: This is identical in size and shape to current units, since likely adsorption refrigerants (e.g. NH3 or CH3OH) have much better thermal properties than R-134a.

Evaporator: This is identical to current units, since it also utilizes R-134a.

Interloop heat exchanger: This device can be omitted if it is decided to use a single refrigerant loop (e.g. NH3 or CH3OH). It is a standard shell and tube HEX resembling the refrigerant reservoir in size and shape. This HEX is relatively small, since it employs two-phase heat transfer for both refrigerants (boiling NH3 or CH3OH, condensing R 134a). A small, very low-power pump circulates R-134a through the nearly isobaric internal loop.

3.3. Adsorption (solid–vapor) cooling

Solid–vapor adsorption is similar to liquid–vapor absorption, except that the refrigerant is adsorbed onto a solid desiccant (freeze dried) rather than absorbed into a liquid (dissolved). The adsorption cycle is illustrated in Fig. 3 and proceeds as follows.

1. At state 1, a cool canister, or adsorber, contains adsorbent saturated with a large fraction of, refrigerant at slightly below Pevap. The cool adsorber is heated and desorbs refrigerant vapor isosterically (i.e. at constant total mass in the adsorber), thereby pressurizing it to state 2, slightly above Pcond. At this point, vapor starts being forced out of the hot adsorber through a one-way ‘check’ valve to the condenser.

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Fig. 3Thermodynamic cycle for adsorption

.

2.Isobaric heating desorbs more refrigerant, forcing it into the condenser until state 3 is attained, where the adsorber is nearly devoid of refrigerant.

3.The hot adsorber is then cooled isosterically (at constant total mass), causing adsorption and depressurization, until the pressure drops below Pevap (state 4), opening another check valve to allow vapor to enter the adsorber from the evaporator.

4.Isobaric cooling to state 1 saturates the adsorbent completing the cycle.

Thus, the mechanical compressor can be replaced with one or more adsorbers. Cyclically and asynchronously heating and cooling two or more adsorbers results in continuous cooling.

.

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4. ADVANTAGES

Manufacturing methods are all cost effective and yield durable products.

1.No ‘exotic’ or uncommon, usually expensive, fabrication operations are involved.

2.Nearly all operations lend themselves to automation, and most tasks can be performed by semi-skilled labor. For example, components can be mass produced on common lathes and vertical mills (three-axis: x–y bed with a z direction tool head) or CNC milling machines.

3.All tolerances are relatively loose. For example, the length of heat exchanger tubing inside the adsorbers need only be within •+ or -2 mm of the nominal, and holes in the end plates for accepting these tubes need be drilled only within•+ or - 0.25 mm.

4.‘As-received’ finishes (e.g. machined, drawn, extruded) are suitable for all components, fore going secondary operations such as grinding, lapping, and honing, which add cost.

5.Pressure vessel joints can be brazed in lieu of more expensive welding by skilled labor, although automated (robotic) arc welding of seams on adsorber shells may be more cost effective for high-volume production.

Materials and parts are all commonly available, being produced in great numbers or bulk, and are inexpensive.

1.Adsorbents (zeolite, activated carbon, or silica gel) can be used in as-received, powdered, or granulated form and require no special processing, such as consolidation into pellets or bricks, which sacrifices vapor permeability for higher thermal conductivity, trading one problem for another. Simple vibratory compaction to the desired porosity will suffice.

2.Heat exchanger tubing and shells can be constructed from inexpensive carbon steel or modestly more expensive low-alloy steel or ferrite stainless steel. Austenitic stainless steel, at somewhat greater expense, is an option if higher corrosion resistance is required

3.Medium- to coarse grade metal wool for enhancing conductance is inexpensive.

4.Simple, inexpensive, rugged ball check valves are used to regulate flow of refrigerant.

5.The HTF pump is a low-pressure (<400 kPa medium-capacity (5 l/min) oil pump.

6.The R-134a pump is of even lower pressure and capacity than the HTF pump

Direct Benefits:

Recovery of waste heat has a direct effect on the efficiency of the process. This is reflected by reduction in the utility consumption & costs, and process cost.

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Indirect Benefits:

a)Reduction in pollution: A number of toxic combustible wastes such as carbon monoxide gas, sour gas, carbon black off gases, oil sludge, Acrylonitrile and other plastic chemicals etc, releasing to atmosphere if/when utilized serves dual purpose i.e. recovers heat and reduces the environmental pollution levels.

b)Reduction in equipment sizes: Waste heat recovery reduces the fuel consumption, which leads to reduction in the flue gas produced. This results in reduction in equipment sizes of all flue gas handling equipments.

c)Reduction in auxiliary energy consumption: Reduction in equipment sizes gives additional benefits in the form of reduction in auxiliary energy consumption like electricity for fans, pumps etc.

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5. DISADVANTAGES

The disadvantages of adsorption cooling systems include

1.Lack of continuity of operation

2.High design requirements for the maintenance of high vacuum

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6. APPLICATIONS

The heat pipes are used in following industrial applications:

a.Process to Space Heating: The heat pipe heat exchanger transfers the thermal energy from process exhaust for building heating. The preheated air can be blended if required. The requirement of additional heating equipment to deliver heated make up air is drastically reduced or eliminated.

b.Process to Process: The heat pipe heat exchangers recover waste thermal energy from the process exhaust and transfer this energy to the incoming process air. The incoming air thus become warm and can be used for the same process/other processes and reduces process energy consumption.

c.HVAC Applications:

Cooling: Heat pipe heat exchanger pre cools the building make up air in summer and thus reduces the total tons of refrigeration, apart from the operational saving of the cooling system. Thermal energy is supply recovered from the cool exhaust and transferred to the hot supply make up air.

Heating: The above process is reversed during winter to preheat the makeup air.

The other applications in industries are:

•Preheating of boiler combustion air

•Recovery of Waste heat from furnaces

•Reheating of fresh air for hot air driers

•Recovery of waste heat from catalytic deodorizing equipment

•Reuse of Furnace waste heat as heat source for other oven

•Cooling of closed rooms with outside air

•Preheating of boiler feed water with waste heat recovery from flue gases in the heat pipe economizers.

•Drying, curing and baking ovens

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•Waste steam reclamation

•Brick kilns (secondary recovery)

•Reverberatory furnaces (secondary recovery) and for Heating, ventilating and air- conditioning systems



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7. CONCLUSION

Using otherwise wasted exhaust heat to power automotive air conditioners would virtually eliminate the substantial power consumption of mechanical compressors. Of available thermally powered cooling technologies, adsorption (solid–vapor) heat pumps are smaller and lighter than absorption (liquid–vapor), reversed Sterling, and Peltier coolers, the last two of which would require bulky thermoelectric generators.

Thus an adsorption heat pump is quite feasible for the following reasons:

1. It can potentially reduce fuel consumption, 12–17 per cent when in use (for a 50/50 mix of city and highway driving for mid-size, compact and subcompact cars), or 4–6 per cent annually if the air conditioner is used 4 months of the year. Internal combustion engine waste heat potential for an automotive absorption system of air condition- This improvement will be somewhat diluted by expected increased mass of the adsorption heat pump as compared with a mechanical compressor.

2.The volume and shape of all components are such that they may fit within the available spaces in a passenger vehicle. The adsorbers will be under driver seat in an indentation in the floor pan, and the HTF heater will be under the front passenger seat in another indentation in the floor pan. The HTF cooler will be next to the condenser in front of the radiator. The Interloop heat exchanger will replace the accumulator, and the refrigerant reservoir will be located at any convenient place forward of the firewall.

3.Innovations for improved performance employ con- cost effective and proven components, materials, and manufacturing techniques in a manner heretofore untried, and no exotic technologies or materials are used.

4.Its performance can match that of mechanical vapor compression devices. For instance, a refrigerant reservoir can provide immediate cooling after start-up of a cold engine, as is so for a mechanical compressor.

5.A refrigerant reservoir is especially useful for hybrid vehicles in which the engine is turned off during idling. A mechanical compressor would require a 2.4–3.4 kW motor which would add mass and drain battery charge, the latter of which is at a premium.

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8. BIBLIOGRAPHY

[1] R.Z.Wang and R.G.Oliveiria, Adsorption Refrigeration – An Efficient Way to Make Good Use Of Waste Heat And Solar Energy

[2] M A Lambert and B J Jones, Automotive adsorption air conditioner powered by exhaust heat. Part 1: conceptual and embodiment design

[3].Monika Gwadera and Krzysztof Kupiec, Adsorption Cooling As an Effective Method of Waste Heat Utilization

[4].K. Smith and M. Thornton, Feasibility of Thermoelectric for Waste Heat Recovery in Conventional Vehicles

[5].R.E.Critoph, Evaluation of Alternative Refrigerant –Adsorbent Pairs for Refrigeration Cycles

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