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Thermal energy storage can be achieved in the form of sensible heat of a solid orliquid medium, latent heat of a phase change substance or by a chemical reaction.The choice of storage media depends on the amount of energy to be stored in unit

volume or weight of the medium and the temperature range which is required for agiven application.

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The experimental setup consists of a six cylinders Ashok Leyland engine, heatrecovery heat exchanger and thermal storage system. Fig shows a schematicdiagram of the experimental setup.

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SCHEMATIC OF EXPERIMENTAL SETUP

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The engine used for this work is a four stroke, water cooled, six cylinder Dieselengines. The rating of the engine is 82 hp at 1500rpm. The engine is mounted onthe bed with suitable connections for fuel and cooling water supply. The engine iscoupled with a generator to vary the load on the engine.

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It consists of a vertical cylindrical shape heater core made of mild steel, with acircumference of 0.3m and an active length of 0.45m. A copper tube of size 0.01m iswound over this heater core at gradual intervals across its length. The copper tubeis connected into the thermal storage tank that is filled with water and phasechange material, and is made in the shape of a coil, inside the tank. The above saidsetup is fitted in the exhaust pipe of the engine to extract the waste heat fromengine exhaust gas, using water as heat transfer fluid. The water inside the coppertube flows with natural Circulation. Fig shows the schematic diagram of the heatrecovery heat exchanger.

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The storage tank is a stainless steel vessel of diameter 0.25m and height 0.3m. Itcontains water as the sensible heat material and paraffin as the latent heatmaterial. Hence it is called combined sensible and latent heat storage system. Thewater also acts as the heat transfer fluid to extract the heat from the flue gas. The

tank is filled with 40 spherical containers made of low density polyethylene(LDPE)having diameter 0.05m and each spherical container contains approximately 100grams of paraffin. The thermal storage tank is well insulated by using fibre coir toprevent heat radiation to the surroundings.

In this paper, the experimental results are enumerated in the form of

various graphs of exhaust gas temperature variation. Variations of temperature ofthe storage and other performance parameters under various loads on the engineare studied. Based on these graph interferences are given for various observations

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It is already seen that as the load increases the exhaust temperature also increases.Hence, when the load on the engine is increases, the exhaust temperatureincreases. However, initially for some period of time, the engine and auxiliaries willabsorb part of the incremental heat till the system attains steady state. Thereafterthe temperature of exhaust gas coming from the engine will be approximately at aconstant temperature.

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The heat in the exhaust gas is extracted in the HRHE by circulatingwater from the storage tank.

The time required to attain 65C at the outlet of the storage tank is 240minutes at no load condition and 180 minutes at 40 amps and 140minutes at 60 amps load condition respectively. This is due to theincreased heat extraction rate at higher loads.

It is also evident from the graphs that at all load conditions the rate ofincrease in temperature is appreciable up to a temperature of60degreeC to 65degreeC. It is due to the fact that when the temperaturereaches 60degreeC, the paraffin in the storage tank start changes itsphase and for the phase large amount of heat is taken from the waterand this reduces the rate of increase in temperature of water.

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Fig shows the temperature variation of the water in the storage tank at the selectedthermocouple locations. The temperature measurements are taken at 6 differentlocations (i.e., at three different heights and two radial locations at each height) inthe storage tank. It is seen from the graphs that at any time, there is smalldifference in temperature between the top and bottom thermocouples. This is dueto stratification caused by the density difference of the hot and cold water.

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The fuel consumed by the engine is noted in order to calculate the heat carriedaway by the exhaust gas. It is seen that the fuel consumption is increases as the loadon the engine increases. The fuel consumed is 8 lit/hr at no load and 11lit/hr at 40amps load and 13lit/hrat 60 amps load.

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VARIATION OF HEAT CARRIED AWAY BY EXHAUST GAS

FOR DIFFERENT LOADS ON THE ENGINE

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VARAITION OF TEMPERATURE IN C WITH TIME IN

MINUTES FOR DIFFERENT LOADS ON THE ENGINE

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VARIATION OF CHARGING RATE FOR DIFFERENT LOADS

ON THE ENGINE

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VARIATION OF CHARGING EFFICIENCY FOR DIFFERENT

LOADS ON THE ENGINE

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Based on the results obtained, the following conclusions are drawn.

Approximately 0.2% of the energy in the fuel or 6 to 7% of the energy in theexhaust waste heat can be recovered using such a HRHE system can be stored in

the storage tank depending on the load on the engine.The percentage of heat recovered can be increased further by increasing thesurface area of the HRHE.

The charging efficiency of the storage tank and the percentage energy saved can beimproved further with proper insulation.

A combined storage system overcomes the main drawback of sensible storagesystem by exhibiting isothermal behavior.

The higher heat capacity of the combined system reduces the size and spacerequirements compared to conventional storage.

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