The Experts below are selected from a list of 125364 Experts worldwide ranked by ideXlab platform
Massimo Cimmino - One of the best experts on this subject based on the ideXlab platform.
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Fluid and borehole Wall Temperature profiles in vertical geothermal boreholes with multiple U-tubes
Renewable Energy, 2016Co-Authors: Massimo CimminoAbstract:An analytical model for the calculation of fluid Temperature profiles in geothermal boreholes with multiple U-tubes is presented. A linear system of first order differential equations is built based on a steady-state thermal resistances approach to the heat transfer between the U-tube pipes and the borehole Wall. Analytical expressions for fluid Temperature profiles are provided for boreholes with arbitrary borehole Wall Temperature profiles as well as piece-wise uniform and uniform borehole Wall Temperature for different U-tube configurations: independent, parallel and series. The analytical model is coupled to a finite line source model of the heat transfer between the borehole and the ground. Fluid and borehole Wall Temperature profiles are solved simultaneously using numerical Laplace transforms to consider the time variation of the Temperatures and heat extraction rates. Results are verified against a finite difference model of the borehole. Differences between the fluid Temperatures calculated with the numerical and analytical models are smaller than 0.003 °C.
Sudarshan Kumar - One of the best experts on this subject based on the ideXlab platform.
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dynamics of premixed methane air mixtures in a heated microchannel with different Wall Temperature gradients
RSC Advances, 2017Co-Authors: Ratna V Kishore, S S Minaev, Mohammad Akram, Sudarshan KumarAbstract:The observation of various flame propagation modes for externally heated tubes has led to many fundamental studies aimed at understanding flame propagation in microtubes. During these studies, it has been observed that for moderately low flow velocities, flames with repetitive extinction and ignition (FREI) have been observed to exist in various experimental, theoretical and numerical studies. The formation of these FREI flame modes depends on various parameters such as channel dimensions, Wall Temperature gradient, flow rates and mixture type. In the present work, an effort has been made to understand the effect of the Wall Temperature gradient on the FREI phenomenon through a 1 mm diameter circular tube using 2D numerical studies with detailed GRI Mech3.0 for premixed methane/air mixtures. The different Wall Temperature gradients analyzed are varied from 33.3–1 K mm−1, with an upper range corresponding to experimental conditions. Five different phases of flame propagation have been observed during the FREI flame propagation mode. The entire fuel gets consumed during the cycle and a significant amount of unburned CO remains during the weak reaction phase, towards the extinction of FREI mode. The effect of the Wall Temperature gradient on the FREI ignition phenomenon has been investigated to understand the development of ignition kernels. It is observed that the ignition happens at the axis and not at the Wall of the channel. This happens due to a boundary-layer phenomenon discouraging ignition at the Wall. It has been observed that a decrease in the Temperature gradient results in movement of the ignition point towards the low-Temperature region. The peak CO value increases with a decrease in the Wall Temperature gradient.
Nawaf H Saeid - One of the best experts on this subject based on the ideXlab platform.
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Natural Convection in a Square Cavity with Spatial Side-Wall Temperature Variation
Numerical Heat Transfer Part A: Applications, 2006Co-Authors: Nawaf H Saeid, Yusli YaacobAbstract:ABSTRACT Laminar natural convection in a two-dimensional square cavity filled with a pure air (Pr = 0.71) is studied numerically in the present article with nonuniform side-Wall Temperature. The heated vertical Wall is assumed to have spatial sinusoidal Temperature variations about a constant mean value, which is higher than the cold side-Wall Temperature, while the top and the bottom Walls are adiabatic. A finite-volume method is used to solve numerically the nondimensional governing equations in the vorticity–stream function formulation. The effects of the amplitude and the wave number of the heated side-Wall Temperature variation on the natural convection in the cavity are investigated. It is found that the average Nusselt number varies based on the hot-Wall Temperature. It increases with an increase in the amplitude, while the maximum average Nusselt number occurs at the wave number of k = 0.7 for Rayleigh number range 103 ≤ Ra ≤ 106. It is found that the values of maximum fluid circulation occur at a...
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natural convection in porous cavity with sinusoidal bottom Wall Temperature variation
International Communications in Heat and Mass Transfer, 2005Co-Authors: Nawaf H SaeidAbstract:Abstract Numerical study of natural convection in a porous cavity is carried out in the present paper. Natural convection is induced when the bottom Wall is heated and the top Wall is cooled while the vertical Walls are adiabatic. The heated Wall is assumed to have spatial sinusoidal Temperature variation about a constant mean value which is higher than the cold top Wall Temperature. The non-dimensional governing equations are derived based on the Darcy model. The effects of the amplitude of the bottom Wall Temperature variation and the heat source length on the natural convection in the cavity are investigated for Rayleigh number range 20–500. It is found that the average Nusselt number increases when the length of the heat source or the amplitude of the Temperature variation increases. It is observed that the heat transfer per unit area of the heat source decreases by increasing the length of the heated segment.
Iztok Golobic - One of the best experts on this subject based on the ideXlab platform.
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analysis of heater Wall Temperature distributions during the saturated pool boiling of water
Experimental Thermal and Fluid Science, 2019Co-Authors: Jure Voglar, Matevž Zupancic, Aljosa Peperko, Patrick Birbarah, Nenad Miljkovic, Iztok GolobicAbstract:Abstract This paper investigates transient Temperature fields of thin metal foil heaters recorded with high-speed infra-red thermography during saturated pool boiling of water at atmospheric pressure. Three different thin heaters were tested: stainless steel (SS316), titanium (Ti) and copper with oxidized superhydrophilic surface (CuO). Experimentally acquired Temperature fields were analysed using statistical approach. Samples with lower values of Wall-Temperature standard deviation and skewness and high values of kurtosis are found to perform better during nucleate boiling regime by providing higher heat transfer coefficient. The same samples had narrower heater-Wall Temperature distributions with higher peaks. The stainless steel sample exhibited bimodal Temperature distributions, which resulted from occurrence of bubbles with relatively large contact diameters and long growth times. In addition to that, it was confirmed that Wall Temperature distributions are effective tool to distinguish between active nucleation sites and non-active single-phase convection area and also to qualify different bubble evolution cycles.
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experimental determination of transient Wall Temperature distributions close to growing vapor bubbles
Heat and Mass Transfer, 2009Co-Authors: Iztok Golobic, J Petkovsek, Matej Baselj, A Papez, David B R KenningAbstract:Experiments were performed to study the spatio-temporal Temperature variation underneath growing bubbles on a thin platinum heating foil in saturated and subcooled nucleate pool boiling of water at atmospheric pressure. The transient Wall Temperature distributions were recorded with spatial resolution of 40 μm by a high-speed infrared camera at intervals of 1 ms, synchronised with a high-speed video camera to record bubble motion. Examples are presented of the transient distributions of Wall Temperature, heat flux and heat transfer coefficient underneath bubbles growing with the fast and slow bubble detachment mechanisms in saturated and subcooled pool boiling. Comments are made on the evidence for and against particular mechanisms of heat transfer.
J. Krishnaiah - One of the best experts on this subject based on the ideXlab platform.
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Artificial Neural Networks model for predicting Wall Temperature of supercritical boilers
Applied Thermal Engineering, 2015Co-Authors: R. Dhanuskodi, R. Kaliappan, S. Suresh, N. Anantharaman, Appusamy Arunagiri, J. KrishnaiahAbstract:Abstract Prediction of Wall Temperature for the range of operating conditions and selecting appropriate material for water-Wall tubes, cooled by turbulent water/steam with drastic changes in property, is important in boiler design. An analytical route of predicting the Wall Temperature for such flow conditions is not reliable. Empirical correlations of non-dimensional numbers, based on experimental data, are used for predicting Wall Temperatures of turbulent flow with abrupt changes in fluid properties. BHEL has conducted many experiments with supercritical water/steam and developed Artificial Neural Network (ANN) based Wall Temperature prediction model. This model predicts Wall Temperature using the given inputs of fluid pressure, fluid Temperature, product of mass flux and diameter, and heat flux. The model has prediction accuracy of 100% for the experimental data and 81.94% for the literature data at a deviation level of ±7 °C. This ANN model is useful for predicting Wall Temperatures of supercritical boilers operating in the tested range of parameters.
