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Motor Cooling
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
There are several types of thermal interface materials [11.34]: Thermal greases typically offer the best thermal performance to serve as the most popular thermal interface materials. Thermal greases are made by dispersing thermally conductive fillers in viscous silicone or hydrocarbon oils. The use of thermal greases can effectively eliminate the interstitial air in voids or gaps and thus provide a low thermal resistance across the contacted surfaces. Thermal greases tend to wet the matching surfaces well while allowing retention of the high-thermal-conductivity asperity microcontacts. The conductivity of thermal greases is about 0.3 W/(m·K) [11.35], which is about ten times higher than that of air.The characteristics of five greases were studied by Tonapi et al. [11.36]. The thermal performance of these greases was measured using the laser flash thermal diffusivity method. The primary filler in these greases is spherical boron nitride (BN) with an average filler size of 60 μm. The testing results are summarized in Table 11.2. The results show that the increase in thermal conductivity is mainly due to the increase in filler loading for all five greases under different pressures. It also shows a significant reduction in thermal resistance with increasing pressure due to a combination of reduced bondline thickness and interfacial thermal resistance. Conductive-particle-filled silicone- or acrylic-based thermal tapes and pads offer high thermal conductivity, ranging from 0.7 to 7.3 W/(m·K), and low thermal resistance, ranging from 0.11 to 1.0°C/W, depending on the material and its thickness.As indicated by their name, phase-change materials can change their phase when the temperature changes. At room temperature, the material is a film. As the temperature increases to a certain value, the viscosity of the materials becomes very small, allowing them to freely flow throughout the joint and fill the voids/gaps.Soft metal foils have been developed for years as compressible metallic shims in many applications, especially power devices. Soft metal foils are very thermally conductive, reliable, and easily adopted.Thermally conductive elastomers are silicone elastomer pads filled with conductive ceramic particles.Thermal adhesives, such as thermal adhesive pads, thermal adhesive tapes, and thermal adhesive films, provide low thermal impedance with long-term reliability.
Effect of metal foam thickness on the conduction and convection heat transfer for a flat plate with metal foam impinged by multiple jets
Published in Experimental Heat Transfer, 2022
Ketan Yogi, Shankar Krishnan, S.V. Prabhu
Figure 2 shows the schematic drawing of the targeted plate assembly. A stainless steel foil which is act as a heater is sandwiched (approx 5 mm) between two copper bus bars and stretched from both ends with the help of a stretching screw. The thickness of the stainless steel foil is 0.06 mm. The whole heater assembly is supported by a thick bakelite plate. A metal foam sample is pasted on stretched stainless steel foil on the impinging side using thermal adhesive paste. An inline array of 27 jets (9 in streamwise direction and 3 in spanwise direction) of 3 mm diameter introduced from the jet plate is made to impinge on a targeted plate. Katti and Prabhu et al. [27, 28] extensively studied the effect of streamwise and spanwise pitch on the local heat transfer of a smooth flat plate impinged by multiple jet for two side exit scheme (intermediate cross flow) and reported that the streamwise and spanwise pitch of 4d is the best configuration. Hence, in the present study, the streamwise and spanwise pitch is selected to be same as 4d following the logic of intermediate cross flow scheme reported in literature. An imprint of the jets is shown in Figure 2 for understanding purposes.