Study On Characteristics Of Passive Enhanced Heat Transfer Of Self-Exciting Mode Oscillating-Flow Heat Pipe

With the development of modern new high-technology, higher and higher thermal requirement per unit on many devices is demanded because of the miniaturization or microminiaturization of cooling or heat exchanging equipments in the high heat load situation. Traditional heat pipe is facing the challenge for the micro-sized devices, and the application of self-exciting mode oscillating-flow heat pipe is expected to solve this technical problem.In this paper, experiment is performed to investigate the characteristics of heat transfer and Self-Exciting enhanced heat transfer of the looped uniform SEMOS HP. The heat transfer characteristics were analyzed by comparing the wall temperatures of the SEMOS Heat Pipe with uniform structure, non-uniform structure, and the pipe with Cu-H2O nano-fluids as thermal exchanging medium. Then, by using theoretical analysis, it simplifies the physical process of SEMOS HP and builds the internal flow and heat transfer mathematical model, and then qualitative research also has been done on heat transfer and Self-Exciting enhanced heat transfer characteristics by calculating and comparing analysis.In the experiment, the material of self-excited oscillation flow heat pipe was brass, the total vertical height was 480mm, and the condensation section was 150mm, heating and insulation section were 330mm in all, the total numbers of elbows is 8, and heat pipe inclination is 55°. Non-uniform cross-section structure is based on the uniform cross-section heat pipe with 3mm internal diameter, the heating and insulation section is changed into vertical segment staggered layout, the cross-section was oval-shaped structure, the working fluid inside the heat pipe was high-purity distilled water, filling rate of working fluids was 42%. For the non-uniform heat pipe, the main part diameter is 3mm also, the central tube sections is changed into lmm diameter. The length of the non-uniform section was 220mm; the working fluid was high-purity distilled water, filled rate 74.5%. For the Cu-H2O nano-fluid heat pipe, the inner diameter of 2mm, Cu-H2O fluid-filled nano-fluid rates is 40%,43%,58%, 60%,67%, the volume fraction of Cu were 1.0%,0.50%,0.30%,0.10%,0.05%, respectively.The main conclusions of experimental research: (1) Self-excited oscillation flow heat pipe using non-uniform cross-section structure can achieve the purpose of enhancement of heat transfer, but the heating power must be high enough, so that the circulation power can overcome the flow resistance caused by the non-uniform cross-section.(2) The non-uniform structure self-excited oscillation flow heat pipe can enhance heat transfer performance, this effect is much better on medium heat requirement and especially the heat source is located in non-uniform structure section.(3) Cu-H2O nano-fluid as self-excited oscillation heat pipe working fluid can also help to enhance heat transfer, but complementary, the key factor to determine its heat transfer performance should be the filling rate.The target of this theoretical analysis is to investigate the working fluid stress, heat transfer and the performance oscillation influenced by diameter, the rate of fluid-filled, temperature difference between the hot and cold-side and so on. The emphasis is the calculation and analysis of heat transfer characteristics of heating section. For passive enhanced heat transfer, the studies focus on calculation and analysis for the non-uniform section. Through comparative analysis theoretical calculation results tallied basically with the corresponding experimental conclusion.Combined with the next step researches, the applications of self-excited oscillation flow heat pipe on solar thermal technology, electronic components heat transfer and low temperature waste heat recovery are discussed.