Investigation On The Thermal Performance Of A Three-phase Closed Thermosyphon With Variable Evaporation Section

Combining the fluidized bed heat transfer technology with closed thermosyphon,the three-phase closed thermosyphon can obviously enhance heat transfer with simple operation.A three-phase closed thermosyphon with variable evaporation sections is designed and built to investigate the heat transfer performance in this paper.The effects of evaporation section length and heating position on the heat transfer performance of the closed thermosyphon are analyzed by varying heat power,solid holdup and particle size.The empirical correlations of the total thermal resistance,the convective heat transfer coefficients of evaporation and condensation sections are constructed.The operating pressure and start-up time of the three-phase closed thermosyphon under different evaporation section settings are preliminarily discussed.Results show that the addition of the glass bead particles can enhance the heat transfer of the closed thermosyphon under different evaporation section settings at certain conditions.And the heat transfer effect is not only affected by the operation parameters such as solid holdup and heat power,but also closely related to the evaporation section setting.The maximum reduction rates of the total thermal resistance are 16.5%,25.4%,13.5% and 27.7% for four different evaporation section settings in the experiments,respectively.The total thermal resistances of both two-phase and three-phase closed thermosyphon decrease with the increase in evaporation section length.At a certain heating area of evaporation section,the upward shifting of the heating position is beneficial to reduce the total thermal resistance of the two-phase closed thermosyphon and the three-phase closed thermosyphon with small size of particles,but increases that of the three-phase closed thermosyphon with large size of particles in most cases.The variation trends of the total thermal resistance with particle size under different evaporation section lengths are different,depending on solid holdup and heat power.From the point of view of heat transfer enhancement,the evaporation section length of the three-phase closed thermosyphon should be moderate,and the size of glass beads used should not be too small.The variation trend of the operation pressure of the three-phase closed thermosyphon with solid holdup is similar to that of the convection heat transfer coefficient of the condensation section,which can reflect the enhancement effect of the convection heat transfer in the condensation section to a certain extent.The start-up times of the two-phase and three-phase closed thermosyphons are generally shortened with the increase in heat power.The initial start-up time of the three phase closed thermosyphon is lower than that of the two-phase one when the length of evaporation section is short but higher than that of the two-phase one when the heating position is shifted upward.The empirical correlation constructed in this paper is in good agreement with the experimental results.The research results are helpful to promote the industrial application of the three-phase closed thermosyphon.