Heat Transfer Characteristics and Performance Limit of Two-Phase Closed Thermosyphons

1986 Fiscal Year Final Research Report Summary

• Project/Area Number: 60550162
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: Thermal engineering
• Research Institution: Kogakuin University
• Principal Investigator: UEDA Tatsuhiro Dept. of Mechanical Engineering, Kogakuin Univ., Professor, 工学部, 教授 (60010584)
• Co-Investigator(Kenkyū-buntansha): MIYASHITA Tooru Dept. of Mechanical Engineering, Kogakuin Univ., Assistant, 機械工学科, 助手 (00100371)
• Project Period (FY): 1985 – 1986
• Keywords: Two-phase closed thermosyphon / Heat transfer characteristics / Boiling heat transfer / Condensation heat transfer / Flooding / フラッディング / 熱輸送限界

Research Abstract

Heat transfer rate and performance limit are investigated of two-phase closed thermosyphons. The thermosyphon is a botton heatin type arranged vertically and consists of an evaporator, a condenser both made of copper block and a glass tube adiabatic section. Experiments are performed with three test sections of 15, 10 and 6 mm in I.D., the working fluids used are R113, methanol and water.
The results derived from this study are as follows:
1. Non-dimensional expressions relating the heat transfer rate of thermosyphon with the temperature difference between evaporator and condenser are derived.
2. Boiling heat transfer in the evaporator shows the same characteristic with the well-known one of pool boiling. Condensation heat transfer in the condenser shows a similar trend for its temperature difference to the laminar film condensation theory by Nusselt, however, the values of heat transfer coefficient reveal to decrease considerably with increasing vapor velocity flowing upwards in the tube as in the cases of methanol and water. Comparison with the analytical results on the condensate film flow suggests that the discrepancy is caused by the effects of upward momentum of condensing vapor and droplet mass flow rate entrained with vapor flow.
3. The performance limit i.e. the maximum heat transfer condition appears in the process to increase the heat input to the evaporator. The flow state observation through the glass adiabatic section indicates that the condition is reached under which the condensate returning to the evaporator is flooded by the upward vapor flow. The experimental results are compared with the empirical equations presented so far.
The paper is now under arrangement to present a meeting of JSME, and a further study on the performance limit is scheduled to perform continuously in our laboratory.