Design And Investigation Of Multi-layer/Gradient Porous Material With Its Sound Absorption And Enhanced Heat Transfer Properties

Porous materials (porous medium) have large-surface-area, light-weight, and other excellent features, which have important applications in the fields of energy, mechanical and environment engineering. In the field of porous materials, mul-ti-layer/gradient porous material is one of the research hot spots in recent years. In this work, one of the goals is to fabricate multi-layer porous structure with good acoustic performance. The concept of multi-layer MCF porous materials was pro-posed and verified. The effects of structural parameters of MCF on the sound-absorbing performance were investigated. The other goal is to design porous heat-transfer equipments with excellent enchanced performance. Therefore, the inniti-ative of gradient-porous heat transfer equipments was put forward and studied nu-merically. The fluid flow and heat transfer performances were comprehensively in-vestigated in equipments filled with gradient-porous materials.Based on its constituting parallel micro-capillaries, the sound absorption be-hav-ior of multi-layer plastic micro-capillary films(MCFs) structures has been inves-tigated. The effects of micro-capillary diameter, perforation rate and perforation di-ameter on the sound absorption performance of the multi-layer MCF porous structures were studied using the standing wave tube method. It was demonstrated that the mul-ti-layer MCFs had good sound absorption especially at low frequencies around the first resonant frequency. The mechanical property of porous MCF samples was meas-ured by strength tester and results demonstrated this sound absorption structures have stable mechanical properties. Compared to other traditional two sound absorption materials (perforated panel and porous materials), the sound absorption coefficients of MCF samples are comparable and competitive to them. Therefore the novel mul-ti-layer porous MCFs, which are easy-to-manufacture and cost-effective, have prom-ising applications in the field of sound absorption.An innovative design of a GPM-filled pipe structure was proposed to improve the heat transfer and reduce pressure drop of fluid flowing through the pipes filled with gradient porous materials. The pore-size gradient and porosity gradient were studied for both partially and fully filled configurations. The effects of GPMs on the fluid flow and heat transfer in the pipes were investigated and compared with the those under the conditions of non-porous materials and homogeneous porous materi-als (HPMs) serving as controls. Typical GPM configurations were studied with Rp=0.6, Rp=0.8 and Rp=1.0, showing an enhanced heat transfer and a relatively low friction factor can be reached in comparison with the controls. An attempt was made to illustrate the mechanism of heat transfer enhancement with the field synergy theory. Velocity-based average pore-size was introduced to explain the reduction in friction factors in GPM configurations. A tradeoff analysis between pressure drop and heat transfer enhancement was made based on performance evaluation criteria (PEC).The innitiative of gradient-porous heat sink (GPHS) was proposed and nu-meri-cally studied in this work. Computational simulation was carried out to analyze the effects of gradient porous material (GPM) configuration on the hydraulic and thermal performances of heat sinks in comparison of homogeneous-porous heat sink (HPHS) serving as the control. Both gradient pore-size (dp) in the flow direction and the direction normal to flow direction were studied. It was found that, compared with conventional HPHS, GPHS can effectively improve the hydraulic and thermal per-formances simultaneously. Both the friction factor and overall thermal resistance of heat sinks with GPM configurations are considerably lowered. The Nusselt numbers of GPHS with gradient in flow direction are larger than those of homogeneous porous material (HPM) configurations. GPHS is also featured with the capabilities of effec-tively suppressing the bottom wall temperature and enhancing the convection perfor-mance.