Analysis Of Internal Flow Mechanism And Structural Enhancement Of Biomass Fuel Spiral Tube Heat Exchanger

With the depletion of fossil energy sources and the increasingly serious environmental problems,the development of clean energy is imminent.Biomass energy,as an important part of clean energy,has received widespread attention due to its large resource reserves,renewable nature and superior environmental performance.In recent years,biomass fuel development technology has also been rapidly developed,of which shell and tube heat exchanger is the core equipment of biomass fuel development and utilization,and its comprehensive heat exchange performance directly affects the exchange and utilization of heat.At present,there are few studies on shell and tube heat exchangers for biomass fuels.Therefore,this paper uses spiral tube heat exchangers to build a heat transfer test bench for biomass fuels,constructs a threedimensional model of spiral tube heat exchangers,and uses a combination of numerical calculations and experiments to analyse the heat transfer performance of heat exchangers and to optimise the structural parameters.The main research results include:(1)By comparing and analysing the test and numerical calculation results,the relative error of cold fluid outlet temperature is 3.06%,the error of air outlet velocity is 4.27%,the error of pressure is 3.03% and the error of heat transfer is 1.08%;the data errors are all less than 5%,which are within the maximum error tolerance and provide a basis for the accuracy of the subsequent heat transfer characteristics analysis.(2)Gravity has basically no effect on the heat transfer performance of the spiral tube and shell heat exchanger.As the air inlet velocity increases,the convective heat transfer coefficient,PEC index and Nussle number of the heat exchanger increase,while the resistance coefficient decreases.When the air inlet velocity increased from 12 m/s to 18 m/s,the air heating effect of the spiral tube and shell heat exchanger was obvious,and the maximum air outlet temperature was 304.122 K.When the air inlet velocity increased to 20 m/s,the heat exchanger outlet temperature was 273.1 K lower than that at 18 m/s.In the shell process of the biomass-fuelled shell and tube spiral heat exchanger,the shell and tube process between The air temperature distribution is not uniform and there are more low temperature regions.(3)The spiral diameter,pitch and tube pass diameter of the spiral tube have a significant effect on the heat transfer performance of the heat exchanger.The PEC index of the spiral tube heat exchanger increases by 6.7% when the spiral diameter is increased from 400 mm to 500 mm,and decreases by 5.55% when it is increased from 500 mm to 600 mm.Due to the higher air velocity,the excessive spiral diameter leads to the formation of a jet of air in the heat exchanger,which reduces the overall heat transfer performance of the heat exchanger;the increase in pitch reduces the degree of turbulence and convective heat transfer coefficient decreases,the resistance coefficient increases,resulting in an increase in pressure drop and a weakening of the heat transfer effect,which reduces the comprehensive performance of the heat exchanger;as the diameter of the pipe course increases,the comprehensive heat transfer performance of the heat exchanger also increases.(4)Orthogonal tests were used to optimise the structural parameters of the spiral tube biomass fuel heat exchanger.The PEC index of the heat exchanger,and the resistance coefficient were compared and analysed to determine the optimum heat exchanger performance.The optimum ratio was 500 mm spiral diameter,100 mm tube length diameter and 180 mm pitch,which acted as a disturbance and vortex generator in the heat exchanger,transforming the laminar flow into turbulent flow and increasing the overall heat transfer performance of the heat exchanger.The degree of priority of each factor varies for different evaluation indicators.(5)The optimized spiral tube heat exchanger heat flow solid coupling simulation calculations found that the high temperature of the flue gas will produce a large equivalent force in the heat transfer process,the stress concentration in the connection position between the tube process and the shell process,the maximum equivalent force of 169.75 MPa to meet its yield strength,indicating better safety,stability and reasonable design.