Heat Transfer Coefficient for a Packed Bed of Shredded Materials

2003 ◽  
Author(s):  
Mohammad S. Saidi ◽  
Firooz Rasouli ◽  
Mohammad R. Hajaligol
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Distribution ◽  
Packed Bed ◽  
Spherical Particles ◽  
Channeling Effect ◽  
Nusselt Number Correlation ◽  
Good Agreement

Heat transfer coefficient of packed beds of shredded materials such as biomass fuels at low Peclet numbers is of interest. Due to the dependence of flow distribution on particle shape, the application of the Nusselt number correlation of packed bed of spherical particles overestimates the rate of heat transfer. This discrepancy is even more pronounced due to channeling effect at low Peclet numbers. Here, based on applying a pore submodel and combining the numerical simulation and experimental results of a cylindrical packed bed, a new correlation is derived for apparent Nusselt number of the packed bed of shredded materials. The correlation is approximated by a power law formulation for Pecelt < 25. The Nusselt number calculated from this correlation is in a good agreement with other experimental data.

Non-Intrusive Heat Transfer Coefficient Determination in a Packed Bed of Spheres

2010 ◽  
Author(s):  
David J. Geb ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Generation ◽  
Packed Bed ◽  
Computational Procedure ◽  
Spherical Particles ◽  
Average Heat Transfer Coefficient ◽  
Heat Generation Rate ◽  
Average Heat

Non-intrusive measurements of the internal average heat transfer coefficient [1] in a randomly packed bed of spherical particles are made. It is desired to establish accurate results for this simple geometry so that the method used can then be extended to determine the heat transfer characteristics in any porous medium, such as a compact heat exchanger. Under steady, one-dimensional flow the spherical particles are subjected to a step change in volumetric heat generation rate via induction heating. The fluid temperature response is measured. The average heat transfer coefficient is determined by comparing the results of a numerical simulation based on volume averaging theory with the experimental results. More specifically, the average heat transfer coefficient is adjusted within the computational procedure until the predicted values of the fluid outlet temperature match the experimental values. The only information needed is the basic material properties, the flow rate, and the experimental data. The computational procedure alleviates the need for solid and fluid phase temperature measurements, which are difficult to make and can disturb the solid-fluid interaction. Moreover, a simple analysis allows us to proceed without knowledge of the heat generation rate, which is difficult to determine due to challenges associated with calibrating an inductively-coupled, sample specific, heat generation system. The average heat transfer coefficient was determined, and expressed in terms of the Nusselt number, over a Reynolds number range of 20–600. The results compared favorably to the work of Whitaker [2] and Kays and London [3]. The success of this method, in determining the average heat transfer coefficient in a randomly packed bed of spheres, suggests that it can be used to determine the average heat transfer coefficient in other porous media.

scholarly journals Internal Heat Transfer Coefficient Determination in a Packed Bed From the Transient Response Due to Solid Phase Induction Heating

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
David Geb ◽  
Feng Zhou ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Internal Heat ◽  
Temperature Response ◽  
Packed Bed ◽  
Spherical Particles ◽  
Fluid Temperature ◽  
The Core ◽  
Internal Heat Transfer

Nonintrusive measurements of the internal heat transfer coefficient in the core of a randomly packed bed of uniform spherical particles are made. Under steady, fully-developed flow the spherical particles are subjected to a step-change in volumetric heat generation rate via induction heating. The fluid temperature response is measured. The internal heat transfer coefficient is determined by comparing the results of a numerical simulation based on volume averaging theory (VAT) with the experimental results. The only information needed is the basic material and geometric properties, the flow rate, and the fluid temperature response data. The computational procedure alleviates the need for solid and fluid phase temperature measurements within the porous medium. The internal heat transfer coefficient is determined in the core of a packed bed, and expressed in terms of the Nusselt number, over a Reynolds number range of 20 to 500. The Nusselt number and Reynolds number are based on the VAT scale hydraulic diameter, dh=4ɛ/S. The results compare favorably to those of other researchers and are seen to be independent of particle diameter. The success of this method, in determining the internal heat transfer coefficient in the core of a randomly packed bed of uniform spheres, suggests that it can be used to determine the internal heat transfer coefficient in other porous media.

scholarly journals Computational analysis of convective heat transfer across a vertical tube

2021 ◽  
Vol 49 (4) ◽  
pp. 932-940
Author(s):  
Jashanpreet Singh ◽  
Chanpreet Singh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Computational Analysis ◽  
Numerical Data ◽  
Vertical Tube ◽  
Steady State Condition ◽  
Convective Mode ◽  
Good Agreement

This paper deals with the numerical investigation of the convective mode of heat transfer across a vertical tube. Experiments were carried out using air as a fluid in a closed room by achieving a steady-state condition. Implicit scheme of finite difference method was adopted to numerically simulate the free convection phenomenon across vertical tube using LINUX based UBUNTU package. Numerical data were collected in the form of velocity, temperature profiles, boundary layer thickness, Nusselt number (Nu), Rayleigh's number (Ra), and heat transfer coefficient. The results of the Nusselt number showed a good agreement with the previous studies. Results data of heat transfer coefficient indicate that there were some minor heat losses due to radiation of brass tube and curvature of the tube.

Algal Biomass Harvesting Using Low-Grade Waste Heat: Evaluation of Overall Heat Transfer Coefficient in a Heat Exchanger

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Temesgen Garoma ◽  
Ramin E. Yazdi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Waste Heat ◽  
Low Grade ◽  
Cfd Analysis ◽  
Overall Heat Transfer Coefficient ◽  
Nusselt Number Correlation

Abstract This study is part of a broader study on a novel method for harvesting algae by evaporation, and it investigated the feasibility of heating algal biomass using low-grade waste heat in a heat exchanger. Computational fluid dynamic (CFD) analysis was performed with ansysfluent, and the results were verified with experiments. The results of CFD analysis showed the overall heat transfer coefficient increased by 4, 13, and 100% as inlet gas temperature increased from 150 to 245 °C, liquid mass flow rate increased from 1.82 to 9.1 g/s, and gas mass flow increased from 2.2 to 13.2 g/s, respectively. It was also observed the overall heat transfer coefficient was not significantly affected with variations of properties of the liquid (thermal conductivity, density, and viscosity), thermal conductivity of the tube wall, and thickness of the tube banks, but it was sensitive to thermal conductivity of the gas. The experimental data were analyzed with logarithmic mean temperature difference (LMTD), number of transfer units (NTU), and Nusselt number correlation methods. There was an excellent agreement between the overall heat transfer coefficient calculated with the LMTD and NTU methods. The coefficients calculated with the LMTD method and Nusselt number correlation exhibited slight variations. This is likely because the LMTD is a theoretical method covering all experimental conditions and material properties, but Nusselt number correlation is an empirical approach based on correlations. The overall heat transfer coefficient calculated by CFD was slightly overestimated because the CFD analysis assumed complete insulation.

scholarly journals Experimental Estimation of Temporal and Spatial Resolution of Coefficient of Heat Transfer in a Channel Using Inverse Heat Transfer Method

2019 ◽  
Author(s):  
Majid Karami ◽  
Somayeh Davoodabadi Farahani ◽  
Farshad Kowsary ◽  
Amir Mosavi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Spatial Resolution ◽  
Time History ◽  
Inverse Technique ◽  
Inverse Heat Transfer ◽  
Temporal And Spatial ◽  
Transfer Method

In this research, a novel method to investigation the transient heat transfer coefficient in a channel is suggested experimentally, in which the water flow, itself, is considered both just liquid phase and liquid-vapor phase. The experiments were designed to predict the temporal and spatial resolution of Nusselt number. The inverse technique method is non-intrusive, in which time history of temperature is measured, using some thermocouples within the wall to provide input data for the inverse algorithm. The conjugate gradient method is used mostly as an inverse method. The temporal and spatial changes of heat flux, Nusselt number, vapor quality, convection number, and boiling number have all been estimated, showing that the estimated local Nusselt numbers of flow for without and with phase change are close to those predicted from the correlations of Churchill and Ozoe (1973) and Kandlikar (1990), respectively. This study suggests that the extended inverse technique can be successfully utilized to calculate the local time-dependent heat transfer coefficient of boiling flow.

scholarly journals Evaluation of Alternative Designs for a High Temperature Particle-to-sCO2 Heat Exchanger

2019 ◽  
Vol 141 (2) ◽  
Author(s):  
Clifford K. Ho ◽  
Matthew Carlson ◽  
Kevin J. Albrecht ◽  
Zhiwen Ma ◽  
Sheldon Jeter ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
High Temperature ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Fluidized Bed ◽  
Structural Reliability ◽  
Packed Bed ◽  
Heat Losses ◽  
Transient Operation

This paper presents an evaluation of alternative particle heat-exchanger designs, including moving packed-bed and fluidized-bed designs, for high-temperature heating of a solar-driven supercritical CO2 (sCO2) Brayton power cycle. The design requirements for high pressure (≥20 MPa) and high temperature (≥700 °C) operation associated with sCO2 posed several challenges requiring high-strength materials for piping and/or diffusion bonding for plates. Designs from several vendors for a 100 kW-thermal particle-to-sCO2 heat exchanger were evaluated as part of this project. Cost, heat-transfer coefficient, structural reliability, manufacturability, parasitics and heat losses, scalability, compatibility, erosion and corrosion, transient operation, and inspection ease were considered in the evaluation. An analytic hierarchy process was used to weight and compare the criteria for the different design options. The fluidized-bed design fared the best on heat transfer coefficient, structural reliability, scalability, and inspection ease, while the moving packed-bed designs fared the best on cost, parasitics and heat losses, manufacturability, compatibility, erosion and corrosion, and transient operation. A 100 kWt shell-and-plate design was ultimately selected for construction and integration with Sandia's falling particle receiver system.

Convective Heat Transfer Coefficient and Pressure Drop of Al2O3-Water Nanofluid in a Single-Phase Microchannel for Cooling of High Heat Output Devices

2008 ◽  
Author(s):  
Guillermo E. Valencia ◽  
Miguel A. Ramos ◽  
Antono J. Bula
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Heat Output ◽  
Flux Boundary Condition

The paper describes an experimental procedure performed to obtain the convective heat transfer coefficient of Al2O3 nanofluid working as cooling fluid under turbulent regimen through arrays of aluminum microchannel heat sink having a diameter of 1.2 mm. Experimental Nusselt number correlation as a function of the volume fractions, Reynolds, Peclet and Prandtl numbers for a constant heat flux boundary condition is presented. The correlation for Nusselt number has a good agreement with experimental data and can be used to predict heat transfer coefficient for this specific nanofluid, water/Al2O3. Furthermore, the pressure drop is also analyzed considering the different nanoparticles concentration.

Heat Transfer Experiments in a Confined Jet Impingement Configuration Using Transient Techniques

2010 ◽  
Author(s):  
Florian Hoefler ◽  
Nils Dietrich ◽  
Jens von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Direction ◽  
Jet Impingement ◽  
Thermochromic Liquid Crystal ◽  
Transient Techniques ◽  
Nusselt Numbers ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

A confined jet impingement configuration has been investigated in which the matter of interest is the convective heat transfer from the airflow to the passage walls. The geometry is similar to gas turbine applications. The setup is distinct from usual cooling passages by the fact that no crossflow and no bulk flow direction are present. The flow exhausts through two staggered rows of holes opposing the impingement wall. Hence, a complex 3-D vortex system arises, which entails a complex heat transfer situation. The transient Thermochromic Liquid Crystal (TLC) method was used to measure the heat transfer on the passage walls. Due to the nature of the experiment, the fluid as well as the wall temperature vary with location and time. As a prerequisite of the transient TLC technique, the heat transfer coefficient is assumed to be constant over the transient experiment. Therefore, additional measures were taken to qualify this assumption. The linear relation between heat flux and temperature difference could be verified for all measurement sites. This validates the assumption of a constant heat transfer coefficient which was made for the transient TLC experiments. Nusselt number evaluations from all techniques show a good agreement, considering the respective uncertainty ranges. For all sites the Nusselt numbers range within ±9% of the values gained from the TLC measurement.

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