Investigation Of Improved Single Loop Pulsating Heat Pipe

Pulsating heat pipe(PHP)is a new kind of passive heat transfer device with simple design,compact structure,and excellent heat transfer performance.It has drawn considerable attention since been invented on the background of increasing demand for the heat transfer device with higher efficiency in engineering application such as electronic cooling.Recently,a growing number of experimental and theoretical investigations have been made in purpose improving and optimizing the heat transfer characteristics of PHPs,so that the thermal efficiency of pulsating heat pipe is hoped to be enhanced.A single loop pulsating heat pipe with improved measures on the ratio of heating/cooling lengths and specific structures respectively is numerically and experimentally investigated in present work.The investigation is carried out under the condition of varying the input power ranged 10 W to 40 W and filling ratio ranged30% to 60%.The present work focuses on the effect on the start-up and thermal performance of a single loop PHP with different length ratio of heating and cooling section and with corrugated structure in different sections.Temperature fluctuation characteristics of pulsating heat pipe under different conditions are analyzed.The influence of the filling ratio and the input heating power on pulsating heat pipe is also studied.The paper discusses the effect on the start-up characteristic and thermal performance of a single loop CLPHP with different heating/cooling length ratios.The effect on the start-up characteristic and thermal performance of a single loop CLPHP with different corrugated configuration is compared.In the present investigations,the agreement on the temperature fluctuation trend,flow pattern distribution and thermal resistance between the simulation and experimental results indicates that present numerical method is enough reliable to simulate the liquid-vapor two-phase flow of the pulsating heat pipe.The running process of pulsating heat pipe includes the start-up stage firstly and the stable operation stage finally.And the analysis on the characteristics of temperature oscillation curve can reveal the start-up time of single loop PHP.It is found that the type of start-up varies from temperature sudden increase to temperature smooth increase when the input power augments.It is found that the optimum filling ratio for the shortest start-up time is 50% under present conditions in this paper.The result shows that the start-up time of single loop PHP is reduced by 16.92% at most when the length ratio of heating/cooling section is increasing.Meanwhile,the thermal resistance is reduced by 8.58% at most as the length ratio of heating/cooling section increased under higher filling ratios.It should be noted that the “dry-out” occurredeasier at low filling ratio with the lager length ratio of heating/cooling section.In addition,the present result indicates that pulsating heat pipe with corrugated configuration also could improve the performance of the pulsating heat pipe.The results show that the pulsating heat pipe with corrugated configuration in evaporation section is helpful to accelerate the start-up,which can reduce by 28.96% at most.And the thermal resistance is reduced by 23.43% to the biggest under certain conditions.The present research results are hoped to provide more data for numerical simulation and experimental investigation.In additional,it is expected to provide an improved operation and an optimum design of structure of pulsating heat pipe in engineering applications.