Design And Optimization Of Heat Pipe Heat Exchanger Used For Exhaust Heat Grain Drying On Harvester

To solve the constraints of climate and field after grain harvest,achieve timely and efficient grain drying and improve thermal efficiency of diesel engine for combine harvester,this paper based on the exhaust performance of combine harvester and the analysis of grain drying to research the design and optimization of heat pipe heat exchanger(HPHE)for hot-air grain drying by exhaust heat.Firstly,this paper built the experiment bench of 4C6-100U32 diesel engine used for combine harvester and carried out the performance experiment.The exhaust energy variation law of engine was obtained by experiment and the waste heat recovery potential was calculated.A carbon steel-water gravity HPHE was designed by empirical method,which combined the exhaust temperature,exhaust flow and air temperature and air velocity required for hot-air grain drying.Secondly,the numerical analysis model of fixed heat flux of HPHE was established and verified by heat transfer performance experiment of HPHE.The results of numerical simulation and heat transfer performance experiment show that HPHE could recover about25.1%of exhaust waste heat and maintain the output hot-air temperature between 50 to60~oC with the little change of exhaust pressure drop,meet the requirements of grain hot-air drying.At the same time,the verified numerical analysis model was used to obtain the influence law of the working condition of engine,air flow of exchanger’s cold side and heat pipe structural parameters including diameter,bundle spacing,fin thickness and fin spacing on the waste heat recovery efficiency,exhaust pipe pressure drop,and outlet air temperature to provide the theory support for optimization design.Finally,the orthogonal optimization research with 5 factors and 5 levels was carried out.The heat pipe diameter,pipe spacing,fin thickness,fin spacing and air flow of cold side were defined as factors and waste heat recovery quantity,exhaust pipe pressure drop and air temperature under the common working condition of diesel engine were defined as experiment indexs.The results showed that the heat pipe spacing,fin spacing and air flow of cold side have significant effect on waste heat recovery quantity;The outer diameter of heat pipe and fin spacing had significant effect on the pressure drop of exhaust pipe.The fin spacing and air flow on the cold side have significant effects on the hot-air temperature difference.In comparison to previous empirical design,the waste heat recovery quantity of the optimized HPHE is increased by 13.6%,the pressure drop of the exhaust pipe of the heat exchanger is only increased by 3.2%and the hot-air temperature is 55~oC while having less impact on the performance of diesel engine,and the moderate hot air temperature is more suitable for the occasional fluctuations of combine harvester’s working condition.