Investigation On Heat Transfer Performance Of Three-phase Closed Thermosyphon

Gravity-assisted heat pipe which is an efficient device used for transferring heat has been widely concerned and used in recent years due to its simple structure and high heat transfer efficiency.The technology of fluidized bed heat exchange for fouling prevention and energy saving which is used for destroying boundary layer to enhance heat transfer and prolonging induction period of scaling has been also used in various fields.A three-phase closed thermosyphon(THPCT),combining the two-phase closed thermosyphon(TPCT)and fluidized bed heat transfer technology,is designed and constructed.Selecting an appropriate kind of solid particles is particularly important.After comprehensive consideration,glass beads particles are chosen as main solid working medium for its stable chemical property and low cost.Convective heat transfer coefficients and overall thermal resistance are considered to evaluate the effect of various operating parameters including the input power(500–2000 W),filling ratio(40%–60%),cooling water flow rate(60–120 L/h),type and size of solid particles and solid holdup(5%–35%)on the heat transfer performance on the system.Experiments are operated under vacuum condition,the actual pressure is about 5–17 k Pa and the operating temperature ranges from 30℃to 60℃.The results show that the thermal performance of the system is enhanced with the addition of solid particles.Atε_s=10%,FR=40%and an input power of 500 W and cooling water flow rate of 60 L/h,the maximum rate of reduction on overall thermal resistance is 16.1%and the maximum rate of increment on evaporation and condensation convective heat transfer coefficients are 10.9%and 29.6%,correspondingly.The experimental results of the effects of different operating parameters on the heat transfer performance of the system show that the thermal performance is enhanced with the increase of the input power and cooling water flow rate and decrease of filling ratio.Among all solid particles considered in this paper,glass beads with a diameter of 0.6 mm most effectively enhance heat transfer performance of the system.The thermal performance of THPCT fluctuates with the increase of the solid holdup.Different solid particles lead to different trend of the fluctuation due to different characteristics of particles and particle bed.