Pradip Dutta

Studies on Optimum Distribution of Fins in Heat Sinks Filled With Phase Change Materials

This paper deals with phase change material (PCM), used in conjunction with thermal conductivity enhancer (TCE), as a means of thermal management of electronic systems. Eicosane is used as PCM, while aluminium pin or plate fins are used as TCE. The test section considered in all cases is a 42 \times 42

THERMAL MODELING OF GAS TUNGSTEN ARC WELDING PROCESS WITH NONAXISYMMETRIC BOUNDARY CONDITIONS

mm^2

Modelling of transport phenomena in laser surface alloying with distributed species mass source

base with a TCE height of 25 mm. An electrical heater at the heat sink base is used to simulate the heat generation in electronic chips. Various volumetric fractions of TCE in the conglomerate of PCM and TCE are considered. The case with 8% TCE volume fraction was found to have the best thermal performance. With this volume fraction of TCE, the effects of fin dimension and fin shape are also investigated. It is found that a large number of small cross-sectional area fins is preferable. A numerical model is also developed to enable an interpretation of experimental results.

Modelling of transport phenomena in laser welding of dissimilar metals

A numerical study of three-dimensional heat transfer and fluid flow in a moving gas tungsten arc welding (GTAW) process is performed by considering nonaxisymmetric boundary conditions. The current density distribution and the resulting Lorentz force field are evaluated by numerically solving Maxwells equations in the domain of the workpiece. The numerical modeling of the melting/solidification process is done by appropriately applying the enthalpy-porosity approach to the GTAW process. Numerical computations of the heat transfer and flow characteristics are carried out by including the effects of buoyancy, surface tension, and electromagnetic forces. The weld-pool dynamics is found to be strongly dependent on the relative locations of the clamp and electrode.

Thermodynamic formalism of minimum heat source temperature for driving advanced adsorption cooling device

In this paper, a three-dimensional transient macroscopic numerical model is developed for the description of transport phenomena during laser surface alloying. In order to make accurate estimates for the species composition distribution during the process, the addition of alloying elements is formulated by devising a species generation term for the solute transport equation. By employing a particle-tracking algorithm and a simultaneous particle-melting consideration, the species source term is estimated by the amount of fusion of a spherical particle as it passes through a particular control volume. Numerical simulations are performed for two cases. The first case corresponds to aluminium as alloying element on a nickel substrate, while the second case is for alloying nickel on aluminium substrate. It is observed for the latter case that the melting of the alloying element is not instantaneous, and hence it cannot be modelled as a species mass flux boundary condition at the top surface. The predicted results are compared with experiments, and the agreement is found to be good.

Determination of gas tungsten arc welding efficiencies

The transport phenomena (heat transfer, fluid flow and species distribution) are numerically modelled for the case of laser welding of dissimilar metals. The model involves convection in the weld pool along with melting and mixing. The associated metallurgical phenomenon is an extremely complex one, and the present work is a preliminary attempt to model the process after making suitable assumptions. The numerical study is performed using a pressure based finite volume technique after making appropriate modifications to the algorithm to include the associated phase change processes and dissimilarity in the metal properties. The phase change process is modelled using an enthalpy‐porosity technique, while the dissimilar metal properties are handled using appropriate mixture theories. As a case study, we have used dissimilar couples of copper‐nickel. It is observed that the weld pool shape becomes asymmetric even when the heat source is symmetrically applied on the two metals forming the couple. As the weld p...

Effect of packing density and adsorption parameters on the throughput of a thermal compressor

This letter presents a thermodynamic formulation to calculate the minimum driving heat source temperature of an advanced solid sorption cooling device, and it is validated with experimental data. This formalism has been developed from the rigor of the Boltzmann distribution function and the condensation approximation of adsorptive molecules. An interesting and useful finding has been established from this formalism that it is possible to construct a solid sorption refrigeration device that operates in a cycle transferring heat from a low temperature source to a heat sink with a driving heat source at a temperature close to but above ambient.

THREE-DIMENSIONAL MODELING OF TURBULENT WELD POOL CONVECTION IN GTAW PROCESSES

A combined experimental/computational technique for the estimation of gas tungsten arc welding (GTAW) efficiencies under quasi-steady conditions is presented. The instantaneous measurements of the weld pool length ahead of and behind the electrode are obtained from digitized free surface images, using a pulsed laser vision system. Measurements of the width and depth of the pool are obtained from weld sections using optical microscopy. Based on these measurements of the actual fusion boundary created by weldpool convection and other effects, a three-dimensional model outside the molten zone in the solid material is used to determine welding efficiency. Measurements and calculations are performed for a range of power inputs and torch speeds for both grooved and ungrooved, high-yield strength steel samples. Computed efficiencies are compared with those available in the literature.

Numerical simulation of solidification of liquid aluminum alloy flowing on cooling slope

Vapour adsorption refrigeration systems (VAdS) have the advantage of scalability over a wide range of capacities ranging from a few watts to several kilowatts. In the first instance, the design of a system requires the characteristics of the adsorbate-adsorbent pair. Invariably, the void volume in the adsorbent reduces the throughput of the thermal compressor in a manner similar to the clearance volume in a reciprocating compressor. This paper presents a study of the activated carbon +HFC-134a (1,1,1,2-tetrafluoroethane) system as a possible pair for a typical refrigeration application. The aim of this study is to unfold the nexus between the adsorption parameters, achievable packing densities of charcoal and throughput of a thermal compressor. It is shown that for a thermal compressor, the adsorbent should not only have a high surface area, but should also be able to provide a high packing density. Given the adsorption characteristics of an adsorbent-adsorbate pair and the operating conditions, this paper discloses a method for the calculation of the minimum packing density necessary for an effective throughput of a thermal compressor

Studies on Thermal Stratification Phenomenon in

Three-dimensional turbulent weld pool convection in a gas tungsten are welding (GTAW) pool is simulated using a high Reynolds number k–ϵ model. The k–ϵ model is suitably modified to account for the morphology of the solid–liquid interface. Melting and solidification occurring during the welding process are modeled using a modified enthalpy– porosity technique. Key issues regarding turbulent transport in a GTAW process are highlighted by comparing the results from the turbulence modeling with the corresponding ones from a laminar model, keeping all process parameters unaltered. A scaling analysis is also performed to obtain order-of-magnitude estimates of certain key features of a turbulent weld pool. The scale analysis predictions show good agreement with the numerical results.