J.L. Bhagoria

Numerical investigation of flow through an artificially roughened solar air heater

A numerical investigation is conducted to analyse the heat transfer and flow friction characteristics in an artificially roughened solar air heater having square-sectioned transverse ribs considered at underside of the top wall, where constant heat flux condition is applied. The effect of relative roughness pitch on average Nusselt number, average friction factor, and thermo-hydraulic performance parameter (THPP) has been investigated. This investigation covers relative roughness pitch in the range of 7.14≤P/e≤17.86 and relevant Reynolds numbers in the range of 3800≤Re≤18, 000. The two-dimensional steady, turbulent flow, and heat transfer governing equations are solved using the finite volume method with the semi-implicit method for pressure-linked equations algorithm. The THPP under the same pumping power constraint is calculated in order to examine the overall effect of the relative roughness pitch. For the present range investigated, the maximum THPP of 1.82 is achieved by the use of the ribs with P/e of 10.71.

A Numerical Investigation of Turbulent Flows through an Artificially Roughened Solar Air Heater

A numerical investigation of turbulent flows through a solar air heater roughened with semicircular sectioned transverse rib roughness has been executed. The physical problem is represented mathematically by a set of governing equations, and the transport equations are solved using the finite element method. The numerical results show that the flow-field, average Nusselt number, and average friction factor are strongly dependent on the relative roughness height. The thermohydraulic performance parameter is found to be the maximum for the relative roughness height of 0.042. Comparisons with previously published work are performed and were found to be in excellent agreement.

Modeling and simulation of turbulent flows through a solar air heater having square-sectioned transverse rib roughness on the absorber plate.

Solar air heater is a type of heat exchanger which transforms solar radiation into heat energy. The thermal performance of conventional solar air heater has been found to be poor because of the low convective heat transfer coefficient from the absorber plate to the air. Use of artificial roughness on a surface is an effective technique to enhance the rate of heat transfer. A CFD-based investigation of turbulent flow through a solar air heater roughened with square-sectioned transverse rib roughness has been performed. Three different values of rib-pitch (P) and rib-height (e) have been taken such that the relative roughness pitch (P/e = 14.29) remains constant. The relative roughness height, e/D, varies from 0.021 to 0.06, and the Reynolds number, Re, varies from 3800 to 18,000. The results predicted by CFD show that the average heat transfer, average flow friction, and thermohydraulic performance parameter are strongly dependent on the relative roughness height. A maximum value of thermohydraulic performance parameter has been found to be 1.8 for the range of parameters investigated. Comparisons with previously published work have been performed and found to be in excellent agreement.

Performance Measurement and Data Analysis of Material Removal Rate for Wire Cut Electro Discharge Machining Process

In this paper, statistical and regression analysis of material removal rate using design of experiments is proposed for WEDM operations. Experimentation was planned as per Taguchi’s mixed orthogonal array. Each experiment has been performed under different cutting conditions of gap voltage, pulse ON time, pulse OFF time, wire feed and dielectric flushing pressure. Stainless Steel grade 304L was selected as a work material to conduct the experiments. From experimental results, the material removal rate was determined for each machining performance criteria. Analysis of variance (ANOVA) technique was used to find out the variables affecting the material removal rate. Assumptions of ANOVA were discussed and carefully examined using analysis of residuals. Variation of the material removal rate with machining parameters was mathematically modeled by using the regression analysis method. The developed model was validated with a set of experimental data and appeared to be satisfactory. Signal to noise ratio was applied to measure the performance characteristics deviating from the actual value. Finally, experimental confirmation was carried out to identify the effectiveness of this proposed method.