An Improved Steady-State Model of Loop Heat Pipes Based on Experimental and Theoretical Analyses

Open Access
Author:
Chuang, Po-Ya Abel
Graduate Program:
Mechanical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
November 04, 2003
Committee Members:
  • John Michael Cimbala, Committee Chair
  • Jack Brenizer Jr., Committee Chair
  • Ralph Webb, Committee Member
  • Fan Bill B Cheung, Committee Member
  • Triem T Hoang, Committee Member
Keywords:
  • loop heat pipe
  • heat pipe
  • capillary pumped loop
  • two-phase heat transfer
  • two-phase fluid flow
  • heat tranfer
  • thermal management
Abstract:
A loop heat pipe (LHP), a two-phase heat transfer device, was studied both analytically and experimentally. Thermocouples were used to measure temperatures along the loop, and neutron radiography was employed as a visualization tool to see-through the metal shell. A new gravity-assisted operating theory was formulated based on these experimental measurements and observations. Trends of steady-state operating temperature are presented and explained at adverse, zero, and positive elevations. An improved 1-D steady-state model was developed, based on the newly formulated operating theory at various elevations. The effects of sink temperature, ambient temperature, elevation, external thermal conductance of the condenser, two-phase heat transfer and pressure drop correlations, heat leak, and insulation, on the performance of a LHP were studied in detail. Experimental results of the measured temperatures when the LHP was operated at 2-inch adverse, zero, 1-inch, 3-inch, and 5-inch positive elevations, are presented and discussed. Temperature hysteresis and low-power start-up problems were observed and are also discussed. The measured temperatures are also compared to the results predicted by the steady-state model when the LHP was operated at 3 ½-inch adverse, zero, and 3 ½-inch positive elevations. In all cases, there is excellent agreement between the experimental data and the predicted results. The most significant result of this study is the discovery, development, and modeling of the operating theory at gravity-assisted conditions. The operating characteristics when the LHP is operating at these conditions are unique and have never been studied before. In this study, the gravity-assisted operating theory is explained thoroughly and the LHP performance can be predicted analytically.