Numerial Simulation Analysis Of Wasted Flue Gas Heat Recovery For Double Heat Exchange Tube Wiht Spiral Coil Inserted

Under the background of developing the efficient recovery technology of wasted heat from flue gas in China,the heat exchange pipes,as a kind of important part in thermal equipment,are set as the research object.On the basis of heat-transferring principle of gas-solid-liquid flow,a new equipment of the wasted heat recovery for the flue gas was modeled,which is named the double pipe heat-exchange tube with spiral coil inserted.According to the basic researches of flow and heat-exchange characteristics of the tubes,results of numerical simulation were calculated and analyzed.The following conclusions are obtained through the simulation calculation:(1)When compared with the ordinary double pipe heat exchange tube,the fluctuation of flue gas pressure of the double pipe heat-exchange tube with spiral coil inserted is more obvious and there exists serious stratification of flue gas temperature.Besides,low temperature fold zone was observed near the inner tube surface,where the gas is in a rotating flow state.(2)Under the given conditions,the differential pressure between inlet and outlet is increasing,while the Nusselt number and heat transfer coefficient of the inner wall grow with the augment of inlet flue gas velocity.Compared with the regular ones,the bigest differential pressure of the double pipe heat-exchange tube with spiral coil inserted is 11.4 times larger,and the maximum variation of Nusselt number reaches to 22.54%.(3)Under the given velocity of flue gas,with the shrink of the gaps of spiral coils inserted,the fluctuation of flue gas pressure and the outlet velocity of flue gas is more obvious,the differential pressure between inlet and outlet is larger.Meanwhile,the value of Nusselt number and the coefficient of heat transfer are also increasing,the differential pressure and Nusselt number have the biggest change,when the gaps of spiral coils is 50mm;Increasing the thickness of inserted spiral coils will leads to an increase of the differential pressure and the outlet velocity of flue gas,and a larger vortex occuring between the inner surface of tubes and the center.At the same time,stronger rotation of gas,larger Nusselt number,more efficient heat transfer and obvious variation were also observed,the differential pressure and Nusselt number have the biggest change,when the thickness of inserted spiral coils is 4.0mm;Increasing the length of inserted spiral coils will also results in an increase of the differential pressure and the outlet velocity of flue gas,and the value of Nusselt number,the differential pressure and Nusselt number have the biggest change,when the length of inserted spiral coils is 980 mm.(4)When Re<35000,the structural parameters of the double pipe heat-exchange tube with spiral coil inserted are 200-4.0-980 can enhance the effect of wasted heat recovery from flue gas extremely.while Re >35000,the structural parameters of the double pipe heat-exchange tube with spiral coil inserted are 50-4.0-980 has the best effect of heat transfer in the whole rang of Re number simulated.