Air Conditioner Using Engine Exhaust Heat

Air Conditioner Using Engine Exhaust fomenting energy energyThis paper describes the development possible in the field of vehicle standard military press instruct based on vapour absorption cooling. The cooling assemble is produced by waste genus Oestrus energy recovered from engine exculpate. The advantages of such a system are drastic reduction of fuel over consumption and emissions associated with vehicle air conditioner usage. The current air teach system used in automobile is based on vapour compression cycle which ineluctably consists of a compressor driven by engine output and thus increases fuel consumption rate and defilement proportion. The introduction of vehicle air condition using vapour absorption cycle eliminates the exigency for compressor here compressor is replaced by generator and absorber unit. Engine waste heat from acquit gases is used as heat stemma for generator of vapour absorption system. This paper describes the development possible in the field of vehicle air conditioning based on vapour absorption cooling. Some limitations are outlined and suggestions for future good are pointed out.Keywords Vapour Absorption Refrigeration Cycle, Vapour Compression Refrigeration Cycle. invention Motivating factors for the pattern this system is continuous optimization of the surgery of internal combustion engines and the increasing utilization of air conditioning in vehicles, as it reaches the status of essential need for modern life. Internal combustion engines are strength energy sources for absorption refrigeration systems, as about one third of the energy availability in the combustion processes wasted through the circumvent gas. Thus, use of the exhaust gas in an absorption refrigeration system give the bounce increase the overall system efficiency.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 aut omobile, it further utilizes about 5% of the total energy. Therefore automobile becomes costlier, uneconomical and little efficient. It likewise decreases the life of engine and increases the fuel consumption. For very small cars compressor needs 3 to 4 bhp, a portentous ratio of the power output. Keeping these problems in mind, a car air conditioning system is proposed from convalescence of engine waste heat using engine exhaust as source of generator for VARS.Introduction to VARS Figure 1 Schematics of Ammonia Water Absorption Refrigeration SystemFig. 1 shows a ceremonious of the basic aqua- ammonium hydroxide refrigeration cycle. High pressure ammonium hydroxide water vapor enters the capacitor, where it transfers heat to the neighborhood. Liquid ammonia leaves the condenser and passes through an expansion valve, reaching the evaporator pressure. The refrigerating then enters the evaporator, where it receives heat from the cold source, turning into low pressure vapor. In the sequence, ammonia vapor enters the absorber, where a weak resolvent of water and low concentration ammonia absorbs the refrigerating and, at the same time, transfers heat to the neighborhood. The solution has now a high ammonia concentration, and is pump to the vapor generator, where it receives heat from an external source. The ammonia in the solution then evaporates, separating from water and consorting to the condenser to start a new cycle. A weak water-ammonia solution leaves the vapor generator and enters the absorber to absorb ammonia vapor from the evaporator. A heat ex shiftr between the absorber and the vapor generator transfers heat from the weak solution leaving the vapor generator to the high ammonia concentration solution going into the vapor generator.The coefficient of performance ( get word) of the absorption system is usually much lower in magnitude then the compression system. just now this low rank of the former is not of much importance since it uses th e waste heat such as engine exhaust heat. The most important thing about VARS is even if the evaporator temperature falls, the same COP empennage be maintained by elevating the generator temperature .Hence the message of the system remains almost the same.Design single-valued spot of heat tearion device Since VARS is heat operated cycle we need heat extraction device to extract heat from high temperature source and to deliver this heat to the generator of system. In order to enhance the performance of the refrigeration cycle we need to optimize the design of the vex Extraction device. Because of its simplicity in operation, less installation as well as maintenance cost, we select Heat money changer as heat extraction device.CUsersLENOVODesktopA4heatex.jpgFigure2- Schematic of Heat ExchangerIn order to find the dimensions of the Heat Exchanger we begin to assume veritable cooling capacity of the cooling system. Lets assume it as 2.5 kW that is Qref = 2.5 kW. countings for He at Extraction Device that is in our case a Heat Exchanger are as follows computing for Ammonia site computation of mass flow rateQref = *cp*(Tg Te ) (1) Where , cp specific heat capacityTg Temperature of the generatorTe Temperature of evaporator Mass flow rateFrom this compare we can determine mass flow rate of refrigerant. computer science of velocity=A*v* (2)Where, = density of the refrigerant ( coinn from design data book)A Flow Area for Refrigerant AmmoniaIn order to find A we accept to take diameter of the tube according to availability in the market. v is the velocity of the refrigerant .Calculation of Reynolds patternRe = (*v*D)/ (3)Where D = diameter of the refrigerant tube = dynamic viscosity of refrigerant at mean temperature (taken from design data book)Calculation of Prandtl numberPr = (*Cp)/ k (4)Where, Cp = specific heat of the refrigerantk = thermal conductivity of the refrigerantCalculation of Nusselt numberCalculation of the Nusselt number is based on the co- tattles and the selection of the co-relation is based on the magnitude of the Re ,Pr , and the nature of the heat transfer surface. In our peculiar(a) condition we select Gnielinski co-relation, since it involves less uncertainty (6%) so mathematical result leave alone be to a greater extent accurate.Nu = ((/2)* (Re 1000)*Pr)/ (1+12.7* (/2)1/2*((Pr)2/3 1)) (5)Where, = friction factor its value depends on the Re= 0.079(Re)-0.25 4*103=0.046(Re)-0.2 3*104Calculation of convective heat transfer co-efficientNu = (hr*D)/k (8)Where, hr = Convective heat transfer co-efficientk = Thermal conductivity of the ammoniaSimilar way we can find out these parameters for exhaust gases by by-line the same procedure.Calculation of Log Mean Temperature Difference (LMTD)Tm = (T1-T2) / ln(T1/T2) (9)Where, T1 = Temperature difference between the exhaust inlet temperature and refrigerant leave alone temperatureT2 = Temperature difference between exhaust outlet temperature and refrigerant i nlet temperatureCalculation of Total Thermal foemanQref =U*A *Tm (10)Since Tm / Qref is the total thermal resistance we will get the value of 1/ U*ACalculation of the length of heat money changerRtotal = Rconv.+Rcond.+Rconv. (11)1/(U*A)= 1/(he*A) + (ln( ro/ri)) /(2*L*k) + 1/(href*A) (12)Where, he = Convective heat transfer coefficient of the exhaust gasseshref = Convective heat transfer coefficient of the refrigerantA = Heat Transfer AreaFrom equation (12) we can easily calculate optimum value of the length of heat exchanger.Now Effectiveness of Heat Exchanger changes as Inlet Temperature Difference between hot exhaust gases and cool refrigerant varies. Effectiveness of Heat exchanger can be calculated by following procedure.Calculation of the efficaciousness of the heat exchangerIn case of the counter flow the authorization is apt(p) by = (1-EXP((-1+C)*NTU) /(1- C* EXP( (-1-C)*NTU)) (13)Where, NTU = Number of Transfer UnitNTU = (U*A)/( * CP)min. (14)C = Capacity RatioC = ( * CP)min / ( * CP)max (15)Calculation of amount of heat transfer to the generator = (actual heat transfer / maximum heat transfer) (16)Maximum heat transfer Qmax = *CP*Tmax (17)Where, Tmax = Maximum temperature difference between hot exhaust gases and cold refrigerantUsing Equations (14) (15) we can calculate actual heat transferred to the generator of the VARS.Calculation of Coefficient of Performance (COP) of VARSCOP= (Cooling Effect Produced / Heat brawn Input to Generator) (18)Since COP is the function of temperature we can calculate the COP by using following relation also,COP= (Te*(Tg-Ta))/ (Tg*(Ta-Te)) (19) Where Te = Temperature of the evaporatorTg = Temperature of the generatorTa = Temperature of absorberResults and Discussion For optimization of design of heat extraction device, we need to determine and piddle some parameters. Assume desired heat transfer to be 3 kW. as well we need to find out the specific temperature or temperature range of VARS generator so as to produce optimum COP.Graph 1 Generator Temperature Vs COP of VARSFrom graphical record 1, it is clear that VARS system will have maximum COP in the generator temperature range of 118c (391 K) to 127c (400 K). Now we can fix the refrigerant outlet temperature. Furthermore we cannot reduce the exhaust gas temperature below certain level. Sudden sack in exhaust temperature will cause the exhaust gas to slow down. The drop in exhaust temperature can be accommodated by reducing the exhaust pipe diameter.After fixture the generator temperature i.e. , refrigerant outlet temperature, exhaust gas outlet temperature and refrigerant inlet temperature, the only parameter remaining is exhaust gas inlet temperature. Exhaust temperature varies with load conditions (no load to full load conditions) and driving conditions (idling to power mode). This results in to change in LMTD, due to which the overall heat transferred to refrigerant changes.As a result of change in exhaust gas inlet tempe rature the strong point of heat exchanger changes. As exhaust temperature increases exitive heat transfer area required decreases as well as strength of heat exchanger reduces. Optimum heat transfer area and effectiveness of heat exchanger is represented by graph 2.Graph 2 Optimum Heat Transfer Area, Effectiveness Vs Inlet Temperature DifferenceEffectiveness is the function of temperature difference between hot exhaust gases and cold refrigerant at inlet. As this temperature difference increases, effectiveness of heat exchanger decreases. Effectiveness of heat exchanger is not of prime concern. We can maintain the effectiveness to certain level by varying refrigerant inlet temperature by some means, for example, electric heating. It will maintain the temperature difference between two fluids at inlet. Small amount of energy will be utilized to elevate the refrigerant temperature. Prime concern of the study is to obtain desired cooling effect by utilizing exhaust waste heat. So ef fectiveness of heat exchanger can be compromised to certain level.Practically, COP of system will be much lower as compared to mathematically obtained values nevertheless sufficient to produce desired cooling effect efficiently. Graph 1 represents the theoretical values of COP obtained by equation (19). We have used these values to determine optimum generator temperature. After fixing the parameters of heat extraction device (Heat Exchanger), the practical values of COP are obtained by using equation (18). Graph 3 represents the practical values of COP. It is clear from graph 3 that as generator temperature rises from 118c to 127c, COP values drops to 73% and cooling effect obtained at a point is 2.8 kW and effectiveness of heat exchanger is about 50%.Graph 3 Generator Temperature Vs COPConclusionFrom the higher up results we can say that it is possible to extract waste heat of the engine exhaust using heat exchanger. In order to increase the performance of VARS we have to operate heat exchanger at the optimum condition mentions in results. Some precaution we have to take care such as at the initial stages of engine operation performance of VARS is low, hence to get the same cooling effect we have heat ammonia generator using heating coil.