Permeability measurements of the flow of interdendritic liquid in equiaxed aluminum-silicon alloys
- PDF / 182,214 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 30 Downloads / 219 Views
RODUCTON
THE permeability, which is a measure of the ease of fluid flow through a porous medium, is a parameter defined by Darcy’s law as ⫽
KS dp dx
[1]
where KS is the specific permeability of the porous medium, and are the viscosity and superficial flow velocity of the liquid, and dp/dx is the pressure gradient in the direction of the flow. It has been determined that the permeability is related to the shapes of the flow channels in the porous medium, i.e., the morphology of solid.[1] For fluid flow through granular beds, the Kozeny–Carman equation,[2] KS ⫽
3 kCS 2V
[2]
where is the void fraction, SV is the surface area of the solid per unit volume of sample, and kC is a constant that takes on various values depending on the characteristics of the porous medium, has been widely used for relating permeability with the morphology of the solid. When the Kozeny–Carman equation is applied to the mushy zones of solidifying alloys, is replaced by gL , the volumetric liquid fraction. Although several efforts have been made to measure the liquid permeability in the mushy zones of alloys and to correlate the permeability with the microstructure of the solidifying alloy,[1,3–8] there has been some uncertainty in the accuracy of the measurements due to the large scatter in the data. The scatter in the data is partly due to the practice of reporting the average permeability during the test. In fact, permeability changes constantly during the test as SV decreases due to microstructural coarsening, and gL
Q. HAN, Research Staff Member, and S. VISWANATHAN, Senior Research Staff Member, are with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6083. Contact e-mail: [email protected] A.J. DUNCAN, formerly Postdoctoral Fellow, Metals and Ceramics Division, Oak Ridge National Laboratory, is Research Staff Member, Westinghouse Savannah River Company, Aiken, SC 29808. Manuscript submitted September 10, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
decreases as a result of back diffusion of solute into the solid. Recently, the authors of this article measured the liquid permeability in the mushy zones of aluminum-copper alloys.[9] The measurements in aluminum-copper alloys showed that the permeability data exhibited a good fit with the Kozeny–Carman equation, when instantaneous values of KS , SV , and gL were used, and when kC was taken to be equal to 5. Based on the initial success, the method was used to measure the permeability in the mushy zones of aluminumsilicon alloys, in which surface oxidation and channeling are more severe. Experiments were also carried out using glass beads, because measurements could be made in the absence of microstructural coarsening. II. EXPERIMENTAL PROCEDURE Typical procedures for measuring liquid permeability in the mushy zone can be found in the literature.[7,9,10] The details of the experimental procedure used in this study are provided in Reference 9. The experimental setup is illustrated in Figure 1. An aluminum-silicon alloy sample was placed
Data Loading...
