Research On Optimization Of Heat Pipe Heat Exchanger For Waste Heat Recovery Of Kitchen Exhaust In Commercial Buildings

Today,our country attaches great importance to energy shortage and environmental pollution,and advocates energy saving and emission reduction in all walks of life.In the field of construction,since exhaust and supplementary air in the kitchens of commercial buildings will cause a large amount of heat waste,it is of great significance to save energy by recovering the waste heat of the exhaust air and then heating the supplementary air in the commercial building kitchens.Due to the small temperature difference between the exhaust air and supplementary air,and the small convection heat transfer coefficient of the exhaust air and supplemental air,the conventional heat exchangers cannot meet the requirements of waste heat recovery.The heat pipe heat exchanger has the characteristics of low flow resistance,high heat exchange efficiency,and convenient disassembly.Therefore,the heat pipe heat exchanger is suitable for the recovery of waste heat from the exhaust air of the commercial building kitchen.Based on a shopping mall in Xi’an,this paper will design and optimize the gas-gas heat pipe heat exchanger used for the recovery of waste heat from the exhaust air of the commercial building kitchen.Firstly,this paper focuses on the theoretical basis of gravity heat pipes and heat pipe heat exchangers,and elaborates on the waste heat recovery system in this paper.Subsequently,based on the actual project,this paper uses the conventional gas-gas heat pipe heat exchangers "wall-type" design method and empirical formula to conduct a preliminary design and obtains the preliminary design values of heat pipe heat exchanger parameters such as the total heat exchange amount,flow resistance,structural size,the number of heat pipes and the number of heat pipe rows.Next,this paper uses Matlab to write the design program of gas-gas heat pipe heat exchanger used for the recovery of waste heat from the exhaust air of the commercial building kitchen.Then,based on the gas-gas heat pipe heat exchanger discrete calculation model and efficiency(ε)-number of heat transfer unit(NTU)method,a numerical calculation simulation program of the heat pipe heat exchanger was written by using Matlab.Through the program calculation,the numerical calculation simulation of the temperature field and flow field in the gas-gas heat pipe heat exchanger used for the recovery of waste heat from the exhaust air of the commercial building kitchen are realized.Through design calculation and theoretical analysis,when a heat pipe heat exchanger unit module is designed with fixed working condition and heat pipe structure parameters,the factors that affect the total heat transfer coefficient of the heat pipe and the total pressure loss of the heat pipe heat exchanger unit module are:(1)the horizontal pipe spacing S1;(2)the number of heat pipes in the first row N1.the average total heat transfer coefficient of the heat pipes decreases with the increase of the number of heat pipes in the first row N1 and the horizontal pipe spacing S1,and the decreasing trend gradually slows down.According to economic analysis,the structural optimization model with the shortest recovery time of the initial investment is: the number of heat pipes in the first row is 2,the horizontal pipe spacing is 52 mm,and the longitudinal pipe spacing is 45 mm,the number of heat pipe rows is 19,the shortest recovery time is: 4.437 years.Afterwards,the two-factor analysis of variance proved that S1 and N1 had a very significant effect on the initial investment recovery time of the heat pipe heat exchanger unit module,thus proving the rationality of variable selection.Finally,according to comprehensive analysis of energy efficiency,when the number of heat pipe rows is 39,the energy efficiency reaches the maximum.