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Electronic Resource
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NASA CR 812; Report; June 1967.
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Library's review
ABSTRACT:
The purpose of this paper is to define and present the wicking material properties that are considered to be important to the operation of a vapor-chamber fin or a heat pipe.
Three classes of wicking materials are studied: sintered metal screens, sintered metal powders, and sintered metal
Two characteristics of the wicking material are considered to limit the operation of the heat pipe, 1) the capillary pumping characteristics of a wick, and 2) the evaporative heat transfer characteristics of a liquid-saturated wick.
To evaluate the effect of capillary pumping characteristics, a simplified analysis of a planar-wick heat pipe is made. The result of this analysis gives the maximum operating length of a planar-wick model in terms of the external boundary conditions, the heat pipe fluid properties, and the capillary pump characteristics of the wicking material. The capillary pump characteristics are found to be proportional to the equilibrium height to which the heat pipe liquid will rise in the wicking material, divided by the wicking material friction factor, when net body forces are zero. The latter is the reciprocal of the permeability for the wicking material. When gravity effects cannot be neglected, then the equilibrium height to which the heat pipe liquid will rise in the wicking material becomes another distinct factor.
The results of wick equilibrium height experiments and wick permeability experiments run on the three classes of wicking materials are presented. Both water and Freon 113 are used as working fluids in these experiments. These results are combined to yield the capillary pumping characteristics of wicking materials.
The purpose of this paper is to define and present the wicking material properties that are considered to be important to the operation of a vapor-chamber fin or a heat pipe.
Three classes of wicking materials are studied: sintered metal screens, sintered metal powders, and sintered metal
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fibers. The porosity of these sintered materials ranges from 47.7 to 91.8 percent.Two characteristics of the wicking material are considered to limit the operation of the heat pipe, 1) the capillary pumping characteristics of a wick, and 2) the evaporative heat transfer characteristics of a liquid-saturated wick.
To evaluate the effect of capillary pumping characteristics, a simplified analysis of a planar-wick heat pipe is made. The result of this analysis gives the maximum operating length of a planar-wick model in terms of the external boundary conditions, the heat pipe fluid properties, and the capillary pump characteristics of the wicking material. The capillary pump characteristics are found to be proportional to the equilibrium height to which the heat pipe liquid will rise in the wicking material, divided by the wicking material friction factor, when net body forces are zero. The latter is the reciprocal of the permeability for the wicking material. When gravity effects cannot be neglected, then the equilibrium height to which the heat pipe liquid will rise in the wicking material becomes another distinct factor.
The results of wick equilibrium height experiments and wick permeability experiments run on the three classes of wicking materials are presented. Both water and Freon 113 are used as working fluids in these experiments. These results are combined to yield the capillary pumping characteristics of wicking materials.
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