Freeze-off limits in transient liquid-phase infiltration

Abstract

Transient liquid-phase infiltration (TLI) involves a powder-metal skeleton and an infiltrant with similar composition containing a melting-point depressant (MPD). Upon infiltration, the MPD diffuses into the skeleton, causing isothermal solidification and allowing a homogeneous final-part composition. Diffusional solidification of the infiltrant can restrict liquid flow and result in premature freeze-off if the liquid solidifies before filling the entire part. A capillary-driven fluid-flow model was developed to predict the infiltration rate and freeze-off limit using a variable skeleton permeability. Diffusional solidification was measured via quenching experiments, compared to theory, and used to define the change in permeability of the skeleton. The infiltration rate was measured via mass increase and compared to the flow model for various skeletons with powder sizes ranging from 60 to 300 m. The predicted horizontal infiltration freeze-off limits were proportional to the square root of d 3 ␥/D␤ 2 , where d is the average powder diameter, ␥ and are the infiltrant surface tension and viscosity, respectively, D is the solid diffusivity, and ␤ is a function of the solidus and liquidus concentrations. These relations can be used for selection of processing parameters and for evaluation of new material systems.

Effects of Particle Size and Particle Size Distribution on Heat Dissipation of Heat Pipes with Sintered Porous Wicks

“…[1][2][3]5,6] This equation indicates that the permeability increases as the particle size and porosity increase. It also suggests that a coarse powder with a low tap density or packing density would be ideal for heat pipe applications.…”

“…[1,3,4] The capillary pressure (P) can be derived based on the energy balance between the work done by the liquid over a given volume (DV) and the surface energy reduction due to the coverage of the solid by a liquid (DA). [6] PDV % c sv À c sl ð Þ DA ½2…”

“…Equation [6] indicates that the capillary pressure is inversely proportional to the particle diameter. A small particle size will thus be favorable to draw water to the evaporator section of the heat pipe.…”

“…Equations [1] and [6] indicate that the permeability and capillary pressure are influenced by the porosity and particle size in an opposite way. A large powder that yields large pore size generates an increased permeability through Eq.…”

Effects of Powder Shape and Processing Parameters on Heat Dissipation of Heat Pipes with Sintered Porous Wicks

“…These requirements can be assessed by the permeability, capillary pressure, and capillary speed, which can be described by the following equations. [1][2][3][4][5][6] …”