Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/31610
Title: Pore Size Effect on Heat Transfer through Porous Medium
Authors: CHRISTIAN SURYONO SANJAYA
Keywords: pore size, modified Rayleigh number, porous medium, cryogenic temperature, guarded-hot-plate apparatus, regression analysis estimation
Issue Date: 25-Jul-2011
Source: CHRISTIAN SURYONO SANJAYA (2011-07-25). Pore Size Effect on Heat Transfer through Porous Medium. ScholarBank@NUS Repository.
Abstract: The inclusion of air pores to reduce the thermal conductivity of insulations is a common practice. Air has very low thermal conductivity and therefore its inclusion will reduce the overall thermal conductivity. However, this is not always the case as convection can also set-in in pores, under some conducive boundary conditions, and increase the rate of heat transfer, and ultimately increase the overall thermal conductivity. As pore size, amongst other factors, governs the onset of convection in an air pore, this thesis aims to study the effect of pore size on the heat transfer through porous medium. The boundary conditions that cause convection to take place in air pores of various sizes were first numerically determined using computational fluid dynamics. Comparing the results against Rayleigh number that provides the boundary conditions for convection to take place in an arbitrary air gap, a modified Rayleigh number was derived to predict more accurately the boundary conditions for convection to take place in an air pore. With the modified Rayleigh number, the minimum pore size that is required to suppress convection from taking place in a given boundary condition can be determined. This information is useful in designing insulation with air pores, particularly in the application at cryogenic condition where convection can set-in even at very small pore size. To experimentally verify the veracity of the modified Rayleigh number, a new experimental method was devised using the Guarded Hot Plate (GHP) equipment. Using the new method, the additional rate of heat flow due to convection in air pores was able to be measured. Cement mortar test specimens with prescribed arrays and sizes of air pores were then produced in the laboratory and tested using the GHP equipment with the new method. The experimental results verified the validity of the modified Rayleigh number.
URI: http://scholarbank.nus.edu.sg/handle/10635/31610
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