V. Vasudeva Rao

Instrumentation to measure thermal contact resistance

Instrumentation was developed to measure the thermal contact resistance across metallic contacts by varying the contact pressure in different environments. Experiments were conducted on oxygen free, high conductivity (OFHC) copper cylindrical flat contacts and the measured thermal contact resistance is in good agreement with the theoretical models reported in the literature. The thermal conductivity of OFHC copper and stainless steel was measured at different temperatures and these values are in good agreement with the literature values.

Recent developments in Micro Friction Stir Welding: A review

The advent of friction stir welding (FSW) in 1991 has been evolutionary in the joining of metals and related materials. Friction stir welding has enabled the joining of metals that could not be joined by other welding processes. Research has shown that dissimilar materials with very different properties, plastics, composites and even wood can be joined by FSW. Recent activities in the application of FSW has seen the development of micro friction stir welding (μFSW), which is the FSW of very thin sections of thickness 1000 μm (1 mm) or less. Micro friction stir welding further extends the applications of FSW to areas such as copper electrical contacts, tailor-welded blanks, wood. Though μFSW is relatively new development significant work has been done to date with interesting research findings being reported. This paper aims to review developments in μFSW to date. The focus of the paper will be on problems peculiar to μFSW due to downscaling to the micro scale and other practical considerations.

Thermal Conductivity and Thermal Contact Conductance Studies on Al12%Si10wt.%SiCp Metal Matrix Composites

Al12%Si10wt.%SiCp is a metal matrix composite (MMC) which is replacing the traditional metals in automobile industry. This paper describes the detailed investigations carried out for the first time on thermal contact resistance across this MMC contacts and also across the contacts between this MMC and other engineering materials like stainless steel, aluminum and copper, in vacuum at different contact pressures. The experimental results are compared with the theoretical models available in the literature for metal contacts. It is found that MMC contacts also show a behavior of metallic contacts in respect of thermal contact conductance i.e., the contact conductance increases as a function of contact pressure and number of load cycles. The thermal conductivity of the MMC is measured at different temperatures and is found to be invariant with temperature up to 100 C.

Thermal conductivity and stability of nanosize carbon-black-filled PDMS: fuel cell perspective

Carbon black filled polydimethylsiloxane (PDMS) was considered as a prospective bipolar plate material candidate for a fuel cell. In this perspective, thermal conductivity and stability of the composites were investigated. Samples with filler weight fractions from 10% to 25% were prepared. The Thermal Gravimetric Analysis (TGA) study under oxygen atmosphere has shown good thermal stability of the composite up to 300°C. Thermal conductivity as a function of temperature and filler fraction was measured. Results have shown excellent improvement in the PDMS thermal conductivity with carbon black fillers (an order of magnitude, when compared with the pure PDMS). We found that PDMS?CB composites with lesser CB loading (10 wt%) achieve thermal conductivity on par with the reported values in the literature of epoxy resin?CB composites (with 70wt% loading).

STUDIES ON THE PERFORMANCE OF ALUMINIUM FOILS IN THE INTERFACE THERMAL CONTROL

The thermal joint conductance between the two contacting surfaces must be increased in order to improve the overall thermal efficiency of a system that involves heat transfer across a joint. An experimental test facility to determine the thermal joint conductance is designed and developed successfully. An experimental investigation has been conducted on bare joints of stainless steel-304 (SS-304) specimens and with commercial grade aluminum foil of 20 µm thickness as an interstitial material. A set of 56 data points were obtained, analyzed and reported in this paper. The improvement in thermal joint conductance, using thermal control material (interstitial material) in the joint is much better when compared to the bare contacts under the same test conditions. The conductance improvement factor (CIF), which is defined as the ratio of joint conductance with foil to with out foil is found to vary from 0.34 to a maximum of 8.85. In the present work, applied pressure has been varied in the range of 0.1 MPa to 10 MPa, for the contacting surfaces with RMS surface roughness between 1.20µm to 13.40µm. The results are presented graphically.