Investigation Of Pulsating Heat Pipe With Partial Horizontal Structure

High integration and high density have been the development trend of electronic components in recent years.So it puts forward higher request in solve the cooling problem.Pulsating heat pipe(PHP),with simple structure and excellent heat transfer efficiency,has drawn considerable attention in the research field of heat radiator.To further improve the practicability and heat transfer performance,numerous schemes have been implemented through experimental or theoretical investigation.To solve the heat transfer between two planes in practical engineering application,a novel closed loop pulsating heat pipe(CLPHP)with partial horizontal structure(horizontal evaporator and condenser)is proposed and numerically investigated in present work.The critical dimensionless vertical start-up height and thermal resistance of proposed CLPHP are researched by analyzing vapor volume fraction variation and temperature fluctuation characteristics under the condition of varying input power ranged 10 W to 40 W and filling ratio ranged 30% to 60%.In addition,three non-uniform heating ways are carried out to explore the effect of that on the thermal performance of PHP: asymmetric set(geometric center line of evaporator section is the axis of symmetry),incremental set(heating power increasing gradually from the evaporator to adiabatic section)and decreasing set(heating power decreasing gradually from the evaporator to adiabatic section).The conclusion has been made by comparing the temperature and thermal resistance results of non-uniform heating with that of uniform heating.In the present investigations,the consistency on the thermal performance and flow pattern between the simulation and reference results demonstrates that numerical method adopted in this work is correct and reliable.According to the temperature oscillation curve of PHP with partial horizontal structure,the PHP fails to start-up if the temperature of two parts of adiabatic section is nearly the same.But when the temperature of one part of adiabatic section is obviously greater than that of another,it proves the PHP start up successfully.The growth of bubbles and long vapor slugs during heating process,and the changes from long vapor slug to short vapor slug in condenser are all shown in vapor volume fraction variation.It's found that the critical dimensionless vertical start-up height under the conditions of filling ratio 50% at 10 W,20W and 30 W heating power are 0.283,0.200 and 0.069,respectively.Meanwhile,the PHP wouldn't start up if the dimensionless vertical height is less than 0.069.The performance of PHP with higher dimensionless vertical height is generally superior to that of PHP with lower higher dimensionless vertical height.The dry-out occurs easily at low filling ratio and high input power,which worsen the heat transfer performance of PHP.Furthermore,the thermal performance of present PHP can be improved effectively when asymmetric or incremental way is employed,and the thermal resistance can be reduced up to 13.26% when the asymmetric heating way is applied.In conclusion,the numerical results of proposed PHP in this research are hoped to provide a reliable reference to solve the heat transfer between two planes in engineering application.Moreover,asymmetric heating set is expected to provide an optimum way in improving the performance of PHP.