K. Ramamurthi

Bio: K. Ramamurthi is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Thermal contact conductance & Surface roughness. The author has an hindex of 5, co-authored 7 publications receiving 88 citations.

Prediction of Thermal Contact Conductance in Vacuum Using Monte Carlo Simulation

Abstract: Predictions of thermal contact conductance between two conforming e at surfaces in vacuum are carried out. Theprediction model considersheate owthrough thecontactzonesof asperitiesonthesurfacesby conduction.The probability of occurrence of contact between the surface asperities is evaluated using a Monte Carlo simulation. A Gaussian distribution of asperity heights on the surfaces, which has been validated earlier, is assumed. The distribution of these contact spots and their respective contact areas are determined in the model and used for evaluating the thermal contact conductance. Predictions are carried out for different materials at varying contact pressures in a vacuum environment. A wide range of surface characteristics is considered. The predictions show excellent agreement with the measured values of thermal contact conductance.

Influence of Flatness and Waviness of Rough Surfaces on Surface Contact Conductance

Abstract: The effect of surface roughness, waviness and flatness deviations on thermal contact conductance is predicted. Threshold values of the surface parameters which do not adversely influence thermal contact conductance are determined. Flatness deviations less than ten times the average roughness and waviness less than about four times the average roughness do not significantly affect the contact conductance. A correlation is developed for contact conductance in terms of the surface parameters, the material properties and the contact pressure at the joint. Experiments are conducted in vacuum with rough, non-flat and wavy surfaces

Thermal contact conductance for cylindrical and spherical contacts

Abstract: A prediction methodology based on Monte-Carlo simulation model, developed for flat conforming surfaces in contact, is modified and extended to predict contact conductance between curvilinear surfaces like cylinders and spheres. Experiments are also conducted in vacuum for the measurement of contact conductance between stainless steel and aluminium cylindrical contacts and stainless steel spherical contacts over a range of contact pressures. The contact conductance between cylindrical and spherical bodies is, in general, about an order of magnitude lower than for flat surfaces in contact. Increase of surface roughness and decrease in contact pressure lowers the contact conductance. However, the influence of these parameters is larger than those obtained for flat surfaces. The prediction for different parametric conditions agree closely with those measured in the experiments.

Prediction of air blast mitigation in an array of rigid obstacles using smoothed particle hydrodynamics

Abstract: The mitigation of blast waves propagating in air and interacting with rigid barriers and obstacles is numerically investigated using the mesh-free smoothed particle hydrodynamics method. A novel virtual boundary particle procedure with a skewed gradient wall boundary treatment is applied at the interfaces between air and rigid bodies. This procedure is validated with closed-form solutions for strong and weak shock reflection from rigid surfaces, supersonic flows over a wedge, formation of reflected, transverse, and Mach stem shocks, and also earlier experiments on interaction of a blast wave with concrete blocks. The mitigation of the overpressure and impulse transmitted to the protected structure due to an array of rigid obstacles of different shapes placed in the path of the blast wave is thereafter determined and discussed in the context of the existing experimental and numerical studies. It is shown that blockages having the shape of a right facing triangle or square placed in tandem or staggered provide better mitigation. The influence of the distance between the blockage array and protected structure is assessed, and the incorporation of a gap in the blockages is shown to improve the mitigation. The mechanisms responsible for the attenuation of air blast are identified through the simulations.

Fundamental study of thermal conduction in dry soils

Abstract: The thermal conductivity of the different soil components—mineral, liquids and air—varies across two or- ders of magnitude. Two studies are implemented to explore the role of contacts in heat conduction in dry granular mate- rials. The first set of experiments is designed to elucidate heat transfer at contacts, and it is complemented with a numeri- cally based inversion analysis for different local and boun- dary conditions to extract proper material parameters. Then, the thermal conductivity of dry soils is measured at different packing densities to address the relevance of coordination number and particle shape effects. Together, both studies confirm the prevailing effect of contact quality and number of contacts per unite volume on heat conduction in granular materials. Interparticle contacts and the presence of liquids in pores play a critical role in heat transfer, and determine the ordered sequence of typical thermal conductivity values: kair < kdry-soil < kwater < ksaturated-soil < kmineral.

Microscopic and macroscopic thermal contact resistances of pressed mechanical contacts

Abstract: Contact heat transfer at mechanical pressed contacts between two materials is very important in many applications. There are two types of thermal contact resistance at the interface of two solids. One of them is due to the constriction of heat flow lines at the interface, commonly known as thermal contact resistance, and the engineering literature has extensively dealt with this macroscopic phenomenon. The other type of constriction resistance is instead microscopic in nature. If the characteristic dimension of the constriction becomes comparable to the mean free path of the heat carriers (i.e., electrons and phonons), then there is a ballistic component to the constriction resistance. For different materials on the two sides, thermal boundary resistance due to phonon acoustic mismatch and to electron-phonon interaction in the case of metals becomes important. Here a unified model is developed which bridges the gap between the macroscopic constriction resistance and the microscopic contact resistance for ...

Literature Survey of Numerical Heat Transfer (2000–2009): Part II

Abstract: A comprehensive survey of the literature in the area of numerical heat transfer (NHT) published between 2000 and 2009 has been conducted Due to the immenseness of the literature volume, the survey