| With the development of the economy,the demand of energy resources for human activities is increasing,and the problem of energy shortage is becoming more and more serious.Therefore,it is necessary to improve the efficiency of energy resources utilization.In industrial production,heat exchangers and other equipment consume a lot of energy,so improving the heat exchanger and enhancing the heat exchange efficiency are important for saving energy and reducing industrial production cost.This paper mainly improves the double-tube heat exchangers from two aspects.Firstly,for the tube structure,a smooth tube is replaced by a corrugated tube that can simultaneously disturb the shell-side and tube-side fluids.Secondly,for the heat transfer working medium,this paper replaces the traditional heat transfer working medium with a new heat transfer working fluid-nanofluids with higher thermal conductivity.In order to investigate the effects of the use of corrugated tube and nanofluids on the heat transfer and flow in double-tube heat exchangers,this paper explores the flow and heat transfer characteristics of TiO2-H2 O nanofluids in double-tube heat exchangers by experimental and numerical simulation methods respectively.The main research work and the results of this paper are as follows:?1?Three kinds of TiO2-H2O nanofluids with different mass fractions??=0.1wt%,0.3wt% and 0.5wt%?are prepared by a two-step method,and the stability of nanofluids is studied by sedimentation method.And their physical parameters are got at the same time.?2?A corrugated double-tube heat exchanger experimental system is set up,and an experimental study is carried out when the shell-side is filled with hot fluid and the tube-side is filled with nanofluids,also,the experimental results are compared with that of a smooth double-tube heat exchanger with the same size.The results show that the use of corrugated tube and nanofluids can effectively enhance the overall heat transfer effect of the double-tube heat exchanger,which is mainly shown in the improvement of the number of heat transfer unit and effectiveness.However,based on the comprehensive evaluation of nanofluids in the tube-side,it is found that the comprehensive performance of nanofluids flowing in the corrugated tube is worse than that of nanofluids flowing in the smooth tube.?3?Based on the experimental results,a numerical model is developed to conduct a numerical simulation when the shell-side is filled with hot fluid and the tube-side is filled with nanofluids.The changes of temperature field,velocity field and flow field in the heat exchanger under above condition are analyzed,and the heat transfer enhancement characteristics of nanofluids and corrugated tube are further revealed.?4?An experimental study is carried out when the shell-side is filled with nanofluids and the tube-side is filled with hot fluid.The results show that the overall heat transfer effect of the heat exchanger is improved,but the enhanced heat transfer effect of the nanofluids is slightly weaker than the first case.At the same time,based on the comprehensive evaluation of the nanofluids,it is found that the comprehensive performance of nanofluids flowing in shell-side of corrugated double-tube heat exchanger is better than that of smooth double-tube heat exchanger under the same conditions.?5?A numerical simulation study is carried out when the tube-side is filled with hot fluid and the shell-side is filled with nanofluids,and the temperature field,velocity field and flow field in this case are further analyzed to reveal the heat transfer and flow inside the heat exchanger under above condition. |
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