Experimental And Numerical Investigation On Heat Transfer Enhancement Of Non-newtonian In The Shell Side Of Helical Baffled Heat Exchanger With Elliptic Tubes

Non-Newtonian fluids are widely used in the industries of food,oil and medicine,involving many processes of heating and cooling.With high viscosity and low thermal conductivity,the heat transfer coefficient of non-Newtonian fluid is considerably low,which limits the applications of non-Newtonian fluids.Therefore,in this paper,we try to apply high-efficiency heat exchanger with continuous helical baffles and elliptic tubes to enhance the heat transfer process of non-Newtonian fluids.Moreover,the multi-walled carbon nanotubes(MWCNTs)were added into non-Newtonian base fluid to improve the thermal conductivity.The flow and heat transfer process of carboxymethocel(CMC)solution flowing in shell-and-tube heat exchanger with elliptic and circular tubes was experimentally and numerically investigated.Results shows that,the simulation data from commercial software Fluent fits very well with experimental data.Errors of shell-side heat transfer coefficient and pressure drop between numerical and experimental data are 1.02-9.83% and 0.73-7.16%,respectively.Compared with circular tubes heat exchanger,the shellside Nusselt number and comprehensive performance of elliptic tubes heat exchanger are 11.4-16.6% and 30-35% higher while the friction factor is 29.2-36.9% lower,proving that the elliptic tubes can enhance the flow and heat transfer process of nonNewtonian fluids.Moreover,the effects of the elliptic aspect ratio(2.0-5.0)and helical angle(20°-60°)on heat exchanger performances were numerically investigated.According to the simulation results,when the elliptic aspect ratio and helical angle are 2.5-3.0 and 40°,the comprehensive performance of the heat exchanger reaches the best.In this paper,the flow and heat transfer performance of non-Newtonian nanofluids in helical baffled heat exchanger with elliptic tubes was experimentally and numerically studied.The MWCNTs were added into xanthan gum solution to form non-Newtonian nanofluid.The shell-side heat transfer coefficients of MWCNTs/XG with mass concentration 1.0%,0.5% and 0.20% increase by 22%,14% and 6%,while the shell-side pressure drop increase by 33%,21% and 5% and the comprehensive performance increase by 24-26%,15-17% and 3-5%.Based on experimental data,correlations for predicting shell-side Nusselt number and friction factor of non-Newtonian fluids and nanofluids flowing helical baffled heat exchanger with elliptic tubes were obtained.Errors between predicted values and experimental results are less than ±10%.