Research paper Experimental study of effective thermal conductivity of stainless steel fiber felt W.Q. Li, Z.G. Qu * State Key Laboratory of Multiphase Flow in Power Engineering, Energy and Power Engineering School, Xi'an Jiaotong University, Xi'an 710049, China highlights  Matrix conduction, radiation and air convection were in the same order of magnitude.  Air natural convection was suppressed by reducing operating pressure.  Intensity of air convection was more sensitive to fiber diameter than porosity.  Surface area and permeability was comparable in air convection as fiber diameter fixed.  Interfacial area exerted dominant role in radiation and air convection as porosity fixed. article info Article history: Received 5 September 2014 Accepted 9 April 2015 Available online 23 April 2015 Keywords: Stainless steel fiber felt Effective thermal conductivity Natural convection Thermal radiation abstract An experimental apparatus was designed to measure the effective thermal conductivity of porous stainless steel fiber felt under different operating pressures. The total effective thermal conductivity was studied by analyzing matrix heat conduction, air natural convection, and matrix thermal radiation at ambient pressure. The contribution of air natural convection was experimentally obtained by changing the ambient pressure to vacuum condition and the solid matrix heat conduction was evaluated using a theoretical model. The ratios of the three mechanisms to the total effective thermal conductivity were approximately 40%, 37.9%, and 22.1%, respectively. In addition, the effects of fiber diameter and porosity on the three mechanisms and on the total effective thermal conductivity were studied. The air natural convection was found to gradually intensify when the operating pressure increases from vacuum con- dition (15 Pa) to ambient pressure (1.0  10 5 Pa). With an increase in fiber diameter under fixed porosity, the solid matrix heat conduction remained unchanged, and air natural convection and thermal radiation decreased, thereby resulting in reduced effective thermal conductivity. With an increase in porosity under fixed fiber diameter, the air natural convection was almost unchanged, and solid matrix heat conduction and thermal radiation were reduced, thereby resulting in reduced effective thermal conductivity. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Porous metallic materials have attracted attention recently in the fields of aerospace transportation system, enhanced heat transfer, infiltration, and energy conservation because of several advantages, including light weight, high thermal conductivity, high mobility of inside fluid, and large interfacial area. A number of experimental, numerical, and theoretical studies have been con- ducted to characterize the heat transfer mechanisms of the porous material. Lee and Cunnington [1] briefly reviewed the heat transfer of the porous medium and developed the theoretical model for the conduction behavior of solids and gases in fibrous porous material. Phanikumar and Mahaja [2] conducted a numerical and experi- mental study to present the buoyancy-induced natural convection in metallic foam by adopting the BrinkmaneForchheimer extended flow model and the non-equilibrium energy model. Calmidi and Mahajan [3] explored the forced convection in metal foam within a range of porosities and pore densities. Thermal transport in compact porous media is considered as a complex process because of the inner-connected solid ligaments and multiple heat transfer mechanisms inside the structure. Zhao [4] summarized the thermal transport in high-porosity cellular foam. The terms of effective * Corresponding author. Tel./fax: þ86 029 82668036. E-mail address: zgqu@mail.xjtu.edu.cn (Z.G. Qu). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng http://dx.doi.org/10.1016/j.applthermaleng.2015.04.024 1359-4311/© 2015 Elsevier Ltd. All rights reserved. Applied Thermal Engineering 86 (2015) 119e126