Date of Award

12-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Ochterbeck, Jay M

Committee Member

Zumbrunnen , David A

Committee Member

Tong , Chenning

Abstract

Heat transport in capillary wick structures is an important parameter in loop heat pipe (LHP) design. The purpose of this study was to investigate the conductive heat leak in operating capillary wick structures. The heat leak is the portion of applied heat load conducted through the wick in spite of the convection of working fluid. Four sintered 316 stainless steel wicks were tested for porosity, effective thermal conductivity, pore size, and heat leak. Pore sizes were found to correlate well with the nominal pore size and pores were very narrowly distributed within a size range of approximately 1-10μm. Effective thermal conductivity was found to vary linearly with temperature over the range of 300-400K for all samples within the range of 0.7 W/m-K to 3.7 W/m-K in vacuum. Using a correlation for truncated packed spheres, the conductivity of the samples saturated in methanol was determined. These values ranged from 1.1 W/m-K to 4.1 W/m-K. Other models in the literature predicted the effective thermal conductivity to within an order of magnitude for all samples; however, the models did not capture the temperature dependence of conductivity and errors of 100% or more were found in some cases. The samples were tested in a vertical orientation for heat leak in operation as a capillary wick with methanol as a working fluid. Evaporative heat fluxes between 5,000 and 65,000 W/m2 were measured. Heat leak was found to vary linearly with the power dissipated by evaporation. The heat leak fraction of the total dissipated power decreased monotonically in a power-law relationship with total dissipated power. For each sample, this fractional heat leak approached a limit proportional to the sample effective conductivity. This limit was on the order of 1% of the total dissipated power.

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