Showing papers by "S.V. Prabhu published in 2015"
TL;DR: In this article, the influence of curvature and Reynolds number on local heat transfer coefficient in a helical coil with water as the working medium was studied. And the experimental results of friction factor and overall averaged total Nusselt number were compared with the available correlations in the literature.
100 citations
TL;DR: In this article, the heat transfer and friction factor characteristics of air flow inside twisted square ducts are studied experimentally and through three-dimensional numerical simulations for both laminar and turbulent flow regimes.
81 citations
TL;DR: In this article, heat transfer and friction factor characteristics of air flow in an annulus formed by an inner twisted square duct and an outer circular pipe are studied experimentally for Reynolds number range of 400-60,000.
57 citations
TL;DR: In this paper, the effect of pitch and curvature of helically coiled capillary tube on the pressure drop was studied experimentally and numerically with R134a as the working fluid.
33 citations
TL;DR: In this article, the inverse heat conduction (IHCP) technique was used to estimate the heat flux of perforated plate burner flame impinging on a flat plate.
32 citations
TL;DR: In this article, the effect of swirl on flame jet impingement heat transfer characteristics was studied and four twisted tapes of twist ratios 2, 3.2, 4.5 and 7.5 were used to obtain the swirling flame jet and it was found that swirl enhances the heat flux distribution by 40-140% at low Reynolds number.
29 citations
TL;DR: In this article, three circular tube burners arranged in a staggered pattern with inter tube spacing (S/d) of 2 to 6 are considered, and the ratio of distance from tube burner tip to the impingement plate (z/d), while the Reynolds number is varied from 400 to 1000.
25 citations
TL;DR: In this article, a circular burner of 13.5mm is used for impingement on a quartz plate of 3mm thickness, and the heat flux distribution is estimated using an inverse heat conduction (IHCP) technique.
22 citations
TL;DR: In this article, the spanwise correlation of a circular cylinder and a trapezoidal bluff body placed inside a circular pipe in fully developed turbulent regime is studied using hotwire anemometer.
9 citations
TL;DR: In this article, the authors presented experimental and three-dimensional numerical study of early onset of separation with rarefied gas flow through a tube with single sharp 90° bend. But they only used three conventional size tubes, and the flow was dynamically similar to gas flow in a microchannel as the Knudsen number range (0.0003).
9 citations
TL;DR: In this article, the velocity is estimated by applying stagnation pressure correction proposed by earlier researchers, as the Bernoulli equation cannot be applied in gas flow for Rep < 30, and the velocity within ±8% with reference to the analytical solution is obtained.
TL;DR: In this article, the problem of fluid flow and heat transfer inside twisted duct of square cross-section was studied for steady fully developed laminar flow and for uniform wall heat flux boundary conditions using commercially available software.
Abstract: The problem of fluid flow and heat transfer was studied for flow inside twisted duct of square cross-section. Three-dimensional numerical solutions were obtained for steady fully developed laminar flow and for uniform wall heat flux boundary conditions using commercially available software. Reynolds number range considered was 100–3000. Twist ratio used are 2.5, 5, 10 and 20. Fluids considered are in Prandtl number range of 0.7–20. Product of friction factor and Reynolds number is found to be a function of Reynolds number and maximum values are observed for a twist ratio of 2.5 and Reynolds number of 3000. Maximum Nusselt number is observed for the same values along with Prandtl number of 20. Correlations for friction factor and Nusselt number are developed involving swirl parameter. Local distribution of friction factor ratio and Nusselt number across a cross-section is presented. Based on constant pumping power criteria, enhancement factor is defined to compare twisted ducts with straight ducts. Selection of twisted square duct is presented in terms of enhancement factor. It is found that twisted duct performs well in the laminar region for range of parameters studied. Heat transfer enhancement for Reynolds number of 3000 and Prandtl number of 0.7 for twist ratio of 2.5, 5, 10, and 20 is 20%, 17.8%, 16.1% and 13.7%, respectively. The results are significant because it will contribute to development of energy efficient compact size heat exchangers.
TL;DR: In this paper, a correlation using the experimental data is developed incorporating the fluid-to-fluid modeling parameters for the prediction of critical heat flux in horizontal channels under low-pressure, low-flow (LPLF) conditions.
Abstract: Experimental investigations on critical heat flux (CHF) are mostly on vertical channels involving high mass fluxes and high system pressures. Reported studies on CHF in horizontal flow channels under low-pressure, low-flow (LPLF) conditions are limited. Understanding CHF is essential in the design and operation of heat exchangers and heat-generating devices including fuel channels of nuclear reactors. The present work investigates CHF in horizontal tubes for low steady flow at atmospheric pressure conditions. Appearance of a “red hot” spot on the test section is considered to be the occurrence of critical heat flux condition in this study. Present data could not be predicted using the reported method of applying a correction factor for the vertical lookup table data. A correlation using the experimental data is developed incorporating the fluid-to-fluid modeling parameters for the prediction of CHF in horizontal channels under LPLF conditions. Numerical study using thermal hydraulic system code RELAP5 sug...
TL;DR: In this paper, a simple model that divides the heat flux to the bodies engulfed in a diffusion flame into different components, namely radiation and convection, was proposed to compute the thermal energy absorbed by the lumped body.
Abstract: A simple model that divides the heat flux to the bodies engulfed in a diffusion flame into different components, namely radiation and convection is studied. Different sizes of brass and stainless steel (SS 304L) rods varying from 25.4 mm to 50.8 mm in length and 25.4 mm in diameter are used as specimens in this study. Experiments are conducted with each body inside a diesel pool fire of different diameters, namely 0.5 m, 0.7 m and 1.0 m. The temperature history of the body engulfed in a pool fire is measured to compute the thermal energy absorbed by the lumped body. Using an energy balance, the total energy is divided into three different components. The gas velocity in the flame is measured to be 1.53 m/s to 1.79 m/s for the diesel pool fires of 0.5 m to 1.0 m in diameter. The dominant mode of heat transfer in this study is radiative in nature. This simple model is reasonably able to predict the heat flux incident on to the lumped bodies engulfed by diesel pool fires using the measured temperature history. A three dimensional formulation for an axi-symmetric pool fire of a measured flame shape, flame temperature and a gray flame absorption coefficient is employed to predict the temperature of the body engulfed in pool fires. This formulation has to be modified to capture the absolute temperature values of the flame.
01 Jan 2015
TL;DR: In this paper, an experimental and three-dimensional numerical study of early onset of separation with rarefied gas flow through a tube with single sharp 90 bend was conducted for nitrogen gas flowing at low pressures in three conventional size tubes and the static pressure measurement indicates adverse pressure gradient near the bend along the inner and outer walls of the tube at much lower value of Reynolds number as compared to conventional flow.
Abstract: This paper presents experimental and three-dimensional numerical study of early onset of separation with rarefied gas flow through a tube with single sharp 90 bend. Experiments are conducted for nitrogen gas flowing at low pressures in three conventional size tubes. The flow is dynamically similar to gas flow in a microchannel as the Knudsen number range (0.0003 < Kn < 0.0385) covers part of the continuum and the slip flow regime while maintaining the Reynolds number between 0.27 and 418.5. The static pressures along the inner, outer and top walls are measured for different mass flow rates and analyzed to understand the flow behavior. The static pressure measurement indicates adverse pressure gradient near the bend along the inner and outer walls of the tube at much lower value of Reynolds number as compared to conventional flow. The numerical solution of the Navier–Stokes equations with the Maxwell’s slip boundary condition shows good agreement with experimental data and helps bring out the complex flow behavior near the bend. The adverse pressure gradient, velocity profile, flow streamlines and velocity vectors in the bend plane clearly indicates secondary flows near the bend at as low a Reynolds number as unity. The flow acceleration and the presence of secondary flows near the bend causes a larger pressure drop as compared with a straight tube. Empirical correlations for Poiseuille number and additional pressure drop coefficient are proposed as part of this work. It is noted that limited experimental data exists in the literature for such flows; these results should therefore help enhance the fundamental understanding of gas flow in microchannels with bend.