Pradip Majumdar

Heat and mass transfer in composite desiccant pore structures for dehumidification

A composite desiccant dehumidifier made of mixed inert and desiccant materials is investigated. A heat and mass transfer model that incorporates the composite nature of the structure is discussed. The model includes both gas-side and solid-side resistances for heat and mass transport. The solid-side resistance for the mass transport includes gas-phase diffusion and surface diffusion. The effectiveness for moisture removal and heat transfer during adsorption and desorption processes in such a dehumidifier during single blow operation is investigated. Results are presented for composite structures made of silica gel and inert materials of different compositions and thermophysical properties.

COMPUTATIONAL MODEL FOR HIGH-ENERGY LASER-CUTTING PROCESS

A computational model for the simulation of a laser-cutting process has been developed using a finite element method. A transient heat transfer model is considered that deals with the material-cutting process using a Gaussian continuous wave laser beam. Numerical experimentation is carried out for mesh refinements and the rate of convergence in terms of groove shape and temperature. Results are also presented for the prediction of groove depth with different moving speeds.

COMPUTATIONAL ANALYSIS OF TURBULENT FLUID FLOW AND HEAT TRANSFER OVER AN ARRAY OF HEATED MODULES USING TURBULENCE MODELS

A computational analysis is carried out using the standard k - l model and two low Reynolds number turbulence models as applied to developing turbulent fluid flow and heat transfer in a channel with surface-mounted heat-generating modules. The channel is assumed to be formed between two adjacent circuit boards with surface-mounted heat-generating modules mounted on a single side of each board. A detailed discussion of the computational model and the solution algorithm is given. Numerical experimentation is carried out with respect to mesh size and other mesh parameters. Calculation is performed for a Reynolds number range 2,000-7,000, and a Prandtl number of 0.7. The predictions of both pressure drop and heat transfer coefficient over the modules are compared with selected experimental data. The comparison showed that the low Reynolds number model based on Jones and Launder gives good predictions in a Reynolds number range of 2,000-5,000. At higher Reynolds numbers such as at Re=7,000, the standard k - l results in better predictions.

Heat, moisture transport, and induced stresses in porous materials under rapid heating

High temperatures and other severe thermal conditions cause release of significant amounts of water in porous materials, and induce pore pressure and temperature gradients under which water is transported through pores. A mathematical model that simulates the coupled heat and mass transfer in heated porous media as well as the resulting stress are discussed. A finite element analysis for the solution of such a model is developed and used to study the temperature and pore pressure distribution and the resulting stresses. A comparison of predicted temperature distribution with experimental data is made, and sensitivity of the coefficient of shrinkage on the induced stress is investigated.

Numerical Simulation of Phase Change Heat Transfer in PCM-Encapsulated Heat Sinks

An enthalpy-based computational model is developed for analyzing PCM-encapsulated heat sinks for electronics chips. Solution is obtained by developing a control volume-based finite difference code and results are validated by comparing results with an analytical solution for a limiting case problem. Results based on a parametric study indicate that the two-dimensional code developed for this study can be used in evaluating PCM, and selecting geometrical dimensions of the PCM encapsulated heat sink

Numerical simulation of phase change heat transfer in PCM-encapsulated heat sinks

The enthalpy-based computational model is developed for analysing PCM-encapsulated heat sinks for electronics chips. Solution is obtained by developing a control volume-based finite difference code and results are validated by comparing results with that given by analytical solution available for a limiting case problem. Preliminary results based on a parametric study indicate the two-dimensional code developed for this study can be used in evaluating PCM, and selecting geometrical dimensions of the PCM encapsulated heat sink.

DEVELOPING FLOW AND HEAT TRANSFER IN A RECTANGULAR DUCT WITH A MOVING WALL

Abstract Flow and heat transfer are studied numerically in a duct of rectangular cross section with a moving wall. The temperature of the moving wall is assumed to be constant while the other three walls are insulated. This boundary condition has important applications in the design of oil-cooled friction pairs. Results are presented for wall Reynolds numbers of 0, 100, 500, and 2500; Prandtl numbers of 0.7, 10, 50, and 100; and cross-sectional aspect ratios of 0.5 and 1. It is found that flow and heat transfer are strongly affected by an interaction between the boundary layer on the moving wall and a recirculation zone set up by that wall. In particular, the Nusselt number shows an interesting maximum before fully developed conditions are established. This maximum is believed to result from the enhancing effect of the widening recirculation zone as fully developed conditions are approached. Hydrody-namic and thermal entrance lengths are drastically reduced with increasing wall Reynolds number. This behav...

Far-Field Noise Prediction of Wind Turbines at Different Receivers and Wind Speeds: A Computational Study

Far-field noise propagation from wind turbines propel development of wind farms to an issue for public acceptance. Airstream contains pressure fluctuations as a result of instability, giving a regular eddy pattern or an irregular turbulent motion which are responsible for the sound produced by wind turbine blades. Aeroacoustic noise emanated from a wind turbine is mainly generated by the interactions of tip and trailing edge of wind turbine blades with the mechanics in wake region such as inflow turbulence structures, boundary layer separation and vortex shedding. Hence, there is a strong necessity for an analytical investigation for noise reducing design and development of the technology in order to further expand wind farms. The objectives of this study are to analyze the far-field aeroacoustics of wind turbines with the purpose of predicting far-field sound pressure levels at different receivers and monitoring total acoustic power captured within wind turbine performance for various wind speeds. Blades are modeled based on NREL S825 airfoil since it has high maximum lift and low profile drag. With the purpose of predicting far-field noise, the Ffowcs Williams-Hawkings (FW-H) acoustics model is the preferred method in order to compute the far-field sound signal which is released from near-field flow. As the key attribute of the research, detached eddy simulation (DES) provides accurate results for the desired simulation since it is a hybrid modeling approach that combines features of Reynolds-averaged Navier-Stokes (RANS) simulation in boundary layers and irrotational flow regions, and large-eddy simulation (LES) in unsteady separation regions. In addition, SST K-Omega detached eddy turbulence model is used due to its good compromise between robustness, computational cost and accuracy. Aerodynamic and aeroacoustic analysis of a wind turbine is performed using a three-dimensional model and a commercial CFD Software, STAR-CCM+. In order to predict far-field sound pressure levels and acoustic powers on different locations, five point receivers are defined downstream of the wind turbine model. Receivers are placed one diameter, D, over the wind turbine rotor blades with 1D, 2D, 5D, 10D and 15D away from the wind turbine that represent receivers 1 to 5. Higher acoustic powers are delivered at closer receivers. It means that acoustic power fades out with larger distances. It is observed that there is a fractional variation of 61%, 17%, 6% and 3% as compared to the receiver 1 for receivers 2, 3, 4 and 5 respectively. Moreover, the results show that variation in total acoustic power is non-linear and higher acoustic powers will be captured for higher velocities. This comparison is done between wind speeds of 10m/s and 15m/s.Copyright

Boundary element method in evaporative laser cutting

A computational model for the simulation of a laser-cutting process has been developed using a boundary element method. A steady heat transfer model is considered that deals with the material-cutting process using a Gaussian continuous wave laser beam. The geometric nonlinearity due to the melting region is handled by an iterative scheme. Numerical analyses are carried out for mesh refinements and the rate of convergence in terms of groove shape and temperature. Boundary element method (BEM) results are compared with finite element method (FEM) results.

A COMPUTATIONAL MODEL FOR FORCED CONVECTION COOLING IN ELECTRONIC COMPONENTS

This study deals with simulation and modeling of forced convection cooling in electronic components. A computational model is developed for two-dimensional laminar fluid flow and heat transfer in cooling channels formed by stacked printed circuit boards with electronic blocks. The computational procedure involves solving two-dimensional continuity, momentum and energy equations with the assumption of periodic fully developed velocity and temperature conditions in the flow direction. A parametric study is carried out to present results for the local and average Nusselt number, and friction factor with varying Reynolds number and geometric parameters.