Investigation On Heat Transfer And Flow Resistance Of Non-Newtonian Nanofluids In The Shell Side Of A Helical Baffle Heat Exchanger With Enhanced Tubes

Since the 18 th century, energy has played an important role in the human and economic development. However, the demand of human for energy has been continuously growing and it seems hard to satisfy people’s need. Moreover, the severe environment and sustainable development problems come along with the growing demand. Thus, it is a general trend to improve the energy and production utilization in order to achieve energy conservation and emissions reduction. Non-Newtonian fluid are widely used in many industries such as food, petrochemical, pharmaceutical industries, etc. Nevertheless, most of the non-Newtonian fluids applied in production departments will encounter heat transfer problems like larger viscosity and lower Reynolds number, so it is necessary to carry out researches about the enhanced heat transfer of non-Newtonian fluids. As we all known, 55-70% of the heat exchangers using in production are shell and tube heat exchangers(STHEs). Though the researches and developments for STHEs are published for years, it is few reports about enhanced heat transfer of non-Newtonian fluids in efficient STHEs.In this paper, Xanthan Gum aqueous solution(XG) with mass concentration 0.2% was chosen as base fluid. Then the nanofluids with mass concentration 0.2%, 0.5% and 1.0% were respectively created after dispersing Multi-Walled Carbon Nanotubes(MWCNTs) into base fluid. Through rheological properties analysis, it is found that the base fluid and nanofluids have the shear-thinning rheological behavior, which means that they are pseudoplastic fluid, one of non-Newtonian fluids. According to the tests of thermal conductivity of base fluid and nanofluids, it is suggested that nanofluids have outstanding thermal property compared with the base fluid.Experiments were carry out to investigate the heat transfer and flow resistance of the base fluid and MWCNTs/XG non-Newtonian nanofluids with mass concentration 0.2%, 0.5% and 1.0% in helical baffle heat exchanger with low-finned tubes(HEFT) and helical baffle heat exchanger with elliptical tubes(HEET). Experimental results show that compared with base fluid, when the test fluids flowed in the shell side of HEFT, the the overall heat transfer coefficients of MWCNTs/XG with mass concentration 0.2%, 0.5% and 1.0% increase by 4.6%, 13.8% and 19.0% on average, while the shell-side heat transfer coefficients increase by 4.7%, 13.2% and 24.3% with the shell-side Nusselt number increasing by 6.2%, 13.9% and 23.9% and the shell-side friction coefficient increasing by 2.8%, 4.5% and 8.5%, and when the test fluids flowed in the shell side of HEET, the overall heat transfer coefficients of MWCNTs/XG with mass concentration 0.2%, 0.5% and 1.0% increase by 6.0%, 14.0% and 22.0% on average, while the shell-side heat transfer coefficients increase by 9.0%, 39.1% and 50.5% with the shell-side Nusselt number increasing by 11.0%, 21.0% and 35.0% and the shell-side friction coefficient increasing by 7.1%, 19.4% and 31.2%. All of the comprehensive thermal performance factors in the experiments are larger than 1.For the sake of further study, some mathematical models of non-Newtonian nanofluid flowing in the shell side of HEFT and HEET were proposed based on datum from heat transfer experiments. All deviations between experimental data and calculated data are less than ±10%.