19-02-2013, 04:44 PM
A Proposed Model for Utilizing Exhaust Heat to run Automobile Air-conditioner
A Proposed Model for Utilizing.pdf (Size: 148.79 KB / Downloads: 151)
Abstract:
In these paper three fluid vapor absorption systems is used for air conditioning of four strokes, four cylinders passenger
car. The capacity of air conditioner is one ton. The exhaust of car is used to heat the ammonia solution in the generator. The
temperature of exhaust heat is measured at different engine speed under 1/4th and half opening of throttle valve. The analysis shows
that the maximum amount of useful heat available in the exhaust gas is about 6 KJ/sec. In this study it is found that the amount of heat
required for generator is 3.02 KJ/sec. However the heat present in the exhaust is more than this amount. Therefore, the required heat
to run the one-ton air conditioner that is needed to convert ammonia solution into ammonia vapor is sufficient
INTRODUCTION
Like other air conditioner systems, the automobile air conditioner must provide adequate comfort cooling to the passenger in the
conditioned space under a wide variety of ambient conditions. In automobile air conditioning load factors are constantly and rapidly
changing as the automobile moves over highways at different speeds and through all kinds of surroundings. As the car moves faster
there is greater amount of infiltration into the car and the heat transfer between the outdoor air and the car surface is increased. The
sun baking down on a black top road will raise its temperature to 500C – 600C approximately and thus increases the amount of heat
transmitted into car. When driving through a grassy terrain, much less radiant heat is experienced than when passing through sandy
flats or rocky hills. Therefore, the car is subjected to varying amounts of heat load when its orientation changes during the journey.
An automobile engine utilizes only about 35% of available energy and rests are lost to cooling and exhaust system. If one is
adding conventional air conditioning system to automobile, it further utilizes about 5% of the total energy. Therefore automobile
becomes costlier, uneconomical and less efficient. Additional of conventional air conditioner in car also decreases the life of engine
and increases the fuel consumption. For very small cars compressor needs 3 to 4 bhp, a significant ratio of the power output.
DESCRIPTION OF PROPOSED MODEL
The proposed model is based on three fluid vapor absorption systems. It consists of basic components needed for vapor absorption
system as shown in Fig. 1. The three fluid used in this system are ammonia, water and hydrogen. Although ammonia is toxic, but due
to absence of any moving part there is a little chance for the leakage. The hydrogen gas is used to increase the rate of evaporation of
the liquid ammonia passing through the system. The water is used because it has the ability to absorb ammonia readily.
The exhaust gas is used to heat the ammonia solution in the generator. A rectifier is used before condenser, which removes water
from ammonia vapor. The ammonia vapor is condensed and flows under gravity to the evaporator where it meets the hydrogen gas.
The hydrogen of gas, which is being feed to the evaporator, permits the liquid ammonia to evaporate at low pressure and temperature.
During the process evaporation the ammonia absorbs the latent heat from refrigerated space and produces cooling effect. The mixture
of ammonia vapor and hydrogen is passed to the absorber where ammonia is absorbed while hydrogen raises the top and flows back
to the evaporator.
The arrangement of various components of this proposed air conditioning system is also a challenge because of the fix size of cars.
In the proposed model condenser and evaporator are arranged same as the conventional unit. However, absorber is fitted immediately
below radiator and extends to one of the fenders. The dephlegmator is fitted against to the condenser as the latter has been so
designed to make place for both the other units. The generator is mounted as close to the exhaust manifold as possible to save on heat
losses from the gases before they are routed through the generator heat exchangers. Since the generator is actually a fairly large size
unit. It can only be placed below the engine and slightly to the rare dynamo.
MEASURED DATA AND HEAT LOAD CALCULATION
To generate base line data, the engine is allowed to run at different throttle position (one-fourth and half) considering engine speed
as running parameter. The mass flow rate of air, mass flow rate of fuel and temperature of exhaust gas is measured as given in Table
1.0. For measuring the required data plenum chamber (1 m3) with circular orifice of 32 mm diameter, inclined tube manometer,
burette for petrol measurement and thermocouple for exhaust temperature measurement in installed on engine.
The determination of actual load becomes very difficult in car air conditioning because of the variation of the load in the climatic
conditions when the car is exposed during the course of long journey.
The cooling load of a typical automobile is also considered at steady state conditions. The cooling capacity is affected by outdoor
infiltration into car and heat gain through panels, roofs, floors etc. The cooling load considered in this analysis is given in Table 2.0
The table shows that heat load inside the car is 2.2 kW. Therefore, one ton air conditioning unit is sufficient to fulfill the cooling
requirement.
CONCLUSION
In the proposed analysis it is shown that useful heat available in the exhaust gas is sufficient to generate ammonia vapor from
ammonia solution for one ton air conditioning unit. Since this system does not use direct energy of engine, therefore, it does not
affect fuel consumption, life and efficiency of the engine.