S.V. Prabhu

Bio: S.V. Prabhu is an academic researcher from Indian Institute of Technology Bombay. The author has contributed to research in topics: Heat transfer & Nusselt number. The author has an hindex of 31, co-authored 168 publications receiving 3766 citations. Previous affiliations of S.V. Prabhu include Nokia & Indian Institutes of Technology.

Heat Transfer of a Metal Foamed Flat Plate Impinged by Multiple Jets

Abstract: The present study focuses on the measurement of the local heat transfer distribution of a smooth flat plate, a flat plate with attached metal foam, and detached metal foam under an inline array of multiple jets using thermal imaging and the thin metal foil technique. After impingement, jet flow exits from all directions. The range of the Reynolds numbers covered in the study is 2500 to 15,000. The impinging distance of [Formula: see text] to [Formula: see text] is studied. A 4-mm-thick aluminum metal foam having 92% porosity and 20-pore-per-inch pore density is used. The contribution of the convection and conduction heat for a flat plate with metal foam is studied using a flat plate with a detached foam configuration. The effect of the impinging distance and Reynolds number on the local, spanwise-averaged, and overall averaged Nusselt numbers is studied. The presence of the 4 mm metal foam enhances the local heat transfer in comparison with a smooth flat plate due to conduction heat transfer without the addition of extra hydraulic resistance to the jet flow. The enhancement of the heat transfer due to the presence of the metal foam is quantified by the enhancement factor [Formula: see text], and it is found to be around 1.6.

A Comprehensive Compendium on Passive Augmentation Techniques for Enhancement of Single-Phase Heat Transfer Coefficients in Heat Exchanger Tubes under Laminar and Turbulent Flow Conditions

Abstract: Abstract Several passive techniques can substantially improve the heat transfer performance of conventional heat exchangers. Passive methods persistently use heat transfer augmentation inside tubular sections, which tackle dominant thermal resistance. The thermal resistance in turbulent flow is primarily due to a thin viscous sublayer near the tube wall. This proliferates into the cross-section of the conduit in the case of laminar flows due to the existence of a relatively thicker boundary layer. This urges disturbance in the entire fluid throughout the cross-section in laminar flows, whereas augmentation devices are usually located close to the wall for turbulent flows. Most of these methods yield increased fluid residence time within the system by inducing swirling motion. The form of disturbance in the flow field is the characteristic of the passive technique used to prolong the fluid residence time and is exhibited differently in both flow regimes. The present article showcases a comprehensive review of heat transfer enhancement through thermo hydraulic performance assessment of these methods reported in the literature. The comparison is based on ratios of Nusselt numbers, first at the same Reynolds numbers, and then, at equal pumping power with constant heat transfer area.

Gas flow in ultra-tight shale strata

Abstract: We study the gas flow processes in ultra-tight porous media in which the matrix pore network is composed of nanometre- to micrometre-size pores. We formulate a pressure-dependent permeability function, referred to as the apparent permeability function (APF), assuming that Knudsen diffusion and slip flow (the Klinkenberg effect) are the main contributors to the overall flow in porous media. The APF predicts that in nanometre-size pores, gas permeability values are as much as 10 times greater than results obtained by continuum hydrodynamics predictions, and with increasing pore size (i.e. of the order of the micrometre), gas permeability converges to continuum hydrodynamics values. In addition, the APF predicts that an increase in the fractal dimension of the pore surface leads to a decrease in Knudsen diffusion. Using the homogenization method, a rigorous analysis is performed to examine whether the APF is preserved throughout the process of upscaling from local scale to large scale. We use the well-known pulse-decay experiment to estimate the main parameter of the APF, which is Darcy permeability. Our newly derived late-transient analytical solution and the late-transient numerical solution consistently match the pressure decay data and yield approximately the same estimated value for Darcy permeability at the typical core-sample initial pressure range and pressure difference. Other parameters of the APF may be determined from independent laboratory experiments; however, a pulse-decay experiment can be used to estimate the unknown parameters of the APF if multiple tests are performed and/or the parameters are strictly constrained by upper and lower bounds.

A review on small scale wind turbines

Abstract: Meeting future world energy needs while addressing climatic changes has led to greater strain on conventional power sources. One of the viable sustainable energy sources is wind. But the installation large scale wind farms has a potential impact on the climatic conditions, hence a decentralized small scale wind turbines is a sustainable option. This paper presents review of on different types of small scale wind turbines i.e., horizontal axis and vertical axis wind turbines. The performance, blade design, control and manufacturing of horizontal axis wind turbines were reviewed. Vertical axis wind turbines were categorized based on experimental and numerical studies. Also, the positioning of wind turbines and aero-acoustic aspects were presented. Additionally, lessons learnt from various studies/countries on actual installation of small wind turbines were presented.

A review on the performance of Savonius wind turbines

Abstract: This paper presents a review on the performance of Savonius wind turbines. This type of turbine is unusual and its application for obtaining useful energy from air stream is an alternative to the use of conventional wind turbines. Simple construction, high start up and full operation moment, wind acceptance from any direction, low noise and angular velocity in operation, reducing wear on moving parts, are some advantages of using this type of machine. Over the years, numerous adaptations for this device were proposed. The variety of possible configurations of the rotor is another advantage in using such machine. Each different arrangement of Savonius rotor affects its performance. Savonius rotor performance is affected by operational conditions, geometric and air flow parameters. The range of reported values for maximum averaged power coefficient includes values around 0.05–0.30 for most settings. Performance gains of up to 50% for tip speed ratio of maximum averaged power coefficient are also reported with the use of stators. Present article aims to gather relevant information about Savonius turbines, bringing a discussion about their performance. It is intended to provide useful knowledge for future studies.

Infrared thermography for convective heat transfer measurements

Abstract: This paper deals with the evolution of infrared (IR) thermography into a powerful optical tool that can be used in complex fluid flows to either evaluate wall convective heat fluxes or investigate the surface flow field behavior. Measurement of convective heat fluxes must be performed by means of a thermal sensor, where temperatures have to be measured with proper transducers. By correctly choosing the thermal sensor, IR thermography can be successfully exploited to resolve convective heat flux distributions with both steady and transient techniques. When comparing it to standard transducers, the IR camera appears very valuable because it is non-intrusive, it has a high sensitivity (down to 20 mK), it has a low response time (down to 20 μs), it is fully two dimensional (from 80 k up to 1 M pixels, at 50 Hz) and, therefore, it allows for better evaluation of errors due to tangential conduction within the sensor. This paper analyses the capability of IR thermography to perform convective heat transfer measurements and surface visualizations in complex fluid flows. In particular, it includes the following: the necessary radiation theory background, a review of the main IR camera features, a description of the pertinent heat flux sensors, an analysis of the IR image processing methods and a report on some applications to complex fluid flows, ranging from natural convection to hypersonic regime.