Radiation and Convection Heat Transfer in a Porous Bed

1968 ◽  
Vol 90 (1) ◽  
pp. 51-54 ◽  
Author(s):  
W. A. Beckman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Collection Efficiency ◽  
Convection Heat Transfer ◽  
Heat Fluxes ◽  
Fluid Temperature ◽  
Radiation Heat ◽  
Radiation Heat Flux ◽  
Flowing Fluid ◽  
Porous Bed

The one-dimensional steady-state temperature distribution within an isotropic porous bed subjected to a collimated and/or diffuse radiation heat flux and a transparent flowing fluid has been determined by numerical methods. The porous bed was assumed to be nonscattering and to have a constant absorption coefficient. Part of the radiation absorbed by the porous bed is reradiated and the remainder is transferred to the fluid by convection. Due to the assumed finite volumetric heat transfer coefficient, the bed and fluid have different temperatures. A bed with an optical depth of six and with a normal incident collimated radiation heat flux was investigated in detail. The radiation incident on the bed at the fluid exit was assumed to originate from a black surface at the fluid exit temperature. The investigation covered the range of incident diffuse and collimated radiation heat fluxes expected in a nonconcentrating solar energy collector. The results are presented in terms of a bed collection efficiency from which the fluid temperature rise can be calculated.

Study of Heat Transfer and Fluid Flow in Transitional Regime Inside a Channel With Offset Plates Heated by Radiation for Photovoltaic/Thermal System

2010 ◽  
Author(s):  
Ahmed Hamza H. Ali ◽  
M. S. Youssef ◽  
Mahmoud Ahmed
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Convection Heat Transfer ◽  
Incident Radiation ◽  
Convection Heat ◽  
Radiation Heat ◽  
Radiation Heat Flux ◽  
Transitional Regime ◽  
Air Heater

This study investigates experimentally and theoretically both the effects of operating and configuration parameters on convection heat transfer process and fluid flow characteristics for air flowing in transitional regime through parallel plate channel with offset plate segments heated by a radiation heat flux. This configuration is intended to be applied into air heater solar collectors and/or a combined photovoltaic and air heater solar collector system (PV/T). In the experimental measurements, the operating parameters tested were Re values ranging from 2580 to 4650 with combination of incident radiation heat flux (qinc) values of 400, 700, and 1000 W/m2, respectively. The experimental results show that the local Nusselt number (Nux) is not unique function in the axial distance. In addition, a linear relationship between Re and apparent friction factor is observed. Moreover, in case of Re = 2600, increasing the incident radiation flux values by 175% and 250% leads to an increase in Nux values by 20% and 35%, respectively. The theoretical results indicate that, combinations of Re values inside the channel falling within the laminar regime with selections of both the plate’s length and thickness can lead to the convection heat transfer enhancement with avoiding of additional pumping power penalty when the channel flow falls in transitional regime.

scholarly journals Convection Heat Transfer Analysis with Flow Resistance for Mini-Helically Coiled Tubes at Supercritical Pressures Experimentally

2021 ◽  
Vol 39 (3) ◽  
pp. 817-824
Author(s):  
Ameer Abed Jaddoa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Mass Flux ◽  
Flow Resistance ◽  
Convection Heat Transfer ◽  
Heat Fluxes ◽  
Exergy Destruction ◽  
Convection Heat

This paper analyzes the effect of fluid flow characteristics on the convection heat transfer for mini-helically coiled tubes (HCT) using supercritical carbon dioxide (CO2) as a natural refrigerant. Two experimental cases have studied in this work for mini-helically coiled tubes at different diameters with different coil pitches for analyzing the convection heat transfer with flow resistance. In the first case, the inner tube diameter, coil diameter and coil pitch were 5 mm, 200 mm and 10 mm respectively, while 10 mm, 100 mm and 5 mm were for the second case. Moreover, this work has also investigated the influence of frictional pressure drop, heat flux, friction factor and mass flux on dimensionless exergy destruction. The work environments were 300-500 K as an inlet temperatures range, 200-2000 Kg / (m2. s) as a mass heat fluxes range, 50,000-500,000 as a Reynolds number (Re) range and 50-200 Kw/m2 as an inner heat fluxes range. As a result, a large effect has been observed for dimensionless exergy destruction compared with the flow friction of CO2 which induced by heat transfer irreversibility. On the other point of view, a good sensitivity of optimal Re with the tube dimeter and mass flux also noticed compared with the heat flux. At a suitable range for Re, smallest and best exergy destruction also noticed for the tube diameters. A correlation has for the optimal Reynolds number as function of main dimensionless parameters related to wall heat flux, mass flux, fluid properties and geometric dimensions is proposed. Characteristics of the fluid flow had influenced significantly by mass and heat fluxes. In the future, the collected experimental data can be employed in order to design and improve the refrigeration conditioning performance for exchangers and other systems such as heat pumps.

scholarly journals Radiation Heat Transfer in a Complex Geometry Containing Anisotropically-Scattering Mie Particles

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3986 ◽  
Author(s):  
Ali Ettaleb ◽  
Mohamed Abbassi ◽  
Habib Farhat ◽  
Kamel Guedri ◽  
Ahmed Omri ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fly Ash ◽  
Complex Geometry ◽  
Radiation Heat Transfer ◽  
Solid Particles ◽  
Isotropic Scattering ◽  
Isotropic Case ◽  
Radiation Heat ◽  
Radiation Heat Flux

This study aims to numerically investigate the radiation heat transfer in a complex, 3-D biomass pyrolysis reactor which is consisted of two pyrolysis chambers and a heat recuperator. The medium assumes to be gray, absorbs, emits, and Mie-anisotropically scatters the radiation energy. The finite volume method (FVM) is applied to solve the radiation transfer equation (RTE) using the step scheme. To treat the complex geometry, the blocked-off-region procedure is employed. Mie equations (ME) are applied to evaluate the scattering phase function and analyze the angular distribution of the anisotropically scattered radiation by particles. In this study, three different states are considered to test the anisotropic scattering impacts on the temperature and radiation heat flux distribution. These states are as: (i) Isotropic scattering, (ii) forward and backward scattering and (iii) scattering with solid particles of different coals and fly ash. The outcomes demonstrate that the radiation heat flux enhances by an increment of the albedo and absorption coefficients for the coals and fly ash, unlike the isotropic case and the forward and backward scattering functions. Moreover, the particle size parameter does not have an important influence on the radiation heat flux, when the medium is thin optical. Its effect is more noticeable for higher extinction coefficients.

Numerical analysis of radiative heat transfer in an inhomogeneous and non-isothermal combustion system considering H2O/CO2/CO and soot

2017 ◽  
Vol 27 (9) ◽  
pp. 1967-1985 ◽  
Author(s):  
Zhenhua Wang ◽  
Shikui Dong ◽  
Zhihong He ◽  
Lei Wang ◽  
Weihua Yang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Radiative Properties ◽  
Combustion System ◽  
Radiation Heat ◽  
Radiation Heat Flux ◽  
Participating Media ◽  
Content Type

Purpose H2O, CO2 and CO are three main species in combustion systems which have high volume fractions. In addition, soot has strong absorption in the infrared band. Thus, H2O, CO2, CO and soot may take important roles in radiative heat transfer. To provide calculations with high accuracy, all of the participating media should be considered non-gray media. Thus, the purpose of this paper is to study the effect of non-gray participating gases and soot on radiative heat transfer in an inhomogeneous and non-isothermal system. Design/methodology/approach To solve the radiative heat transfer, the fluid flow as well as the pressure, temperature and species distributions were first computed by FLUENT. The radiative properties of the participating media are calculated by the Statistical Narrow Band correlated K-distribution (SNBCK), which is based on the database of EM2C. The calculation of soot properties is based on the Mie scattering theory and Rayleigh theory. The radiative heat transfer is calculated by the discrete ordinate method (DOM). Findings Using SNBCK to calculate the radiative properties and DOM to calculate the radiative heat transfer, the influence of H2O, CO2, CO and soot on radiation heat flux to the wall in combustion system was studied. The results show that the global contribution of CO to the radiation heat flux on the wall in the kerosene furnace was about 2 per cent, but that it can reach up to 15 per cent in a solid fuel gasifier. The global contribution of soot to the radiation heat flux on the wall was 32 per cent. However, the scattering of soot has a tiny influence on radiation heat flux to the wall. Originality/value This is the first time H2O, CO2, CO and the scattering of soot were all considered simultaneously to study the radiation heat flux in combustion systems.

Assisting and Opposing Combined Convective Heat Transfer and Nanofluids Flows Over a Vertical Forward Facing Step

2014 ◽  
Vol 5 (1) ◽  
Author(s):  
H. A. Mohammed ◽  
Omar A. Hussein
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Volume Fraction ◽  
Convection Heat Transfer ◽  
Vertical Channel ◽  
Heat Fluxes ◽  
Recirculation Region ◽  
Fluid Temperature ◽  
Laminar Mixed Convection ◽  
Forward Facing Step

Numerical simulations of two-dimensional (2D) laminar mixed convection heat transfer and nanofluids flows over forward facing step (FFS) in a vertical channel are numerically carried out. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The wall downstream of the step was maintained at a uniform wall heat flux, while the straight wall that forms the other side of the channel was maintained at constant temperature equivalent to the inlet fluid temperature. The upstream walls for the FFS were considered as adiabatic surfaces. The buoyancy assisting and buoyancy opposing flow conditions are investigated. Four different types of nanoparticles, Al2O3, CuO, SiO2, and ZnO with different volumes' fractions in the range of 1–4% and different nanoparticle diameters in the range of 25–80 nm, are dispersed in the base fluid (water) are used. In this study, several parameters, such as different Reynolds numbers in the range of 100 < Re < 900, and different heat fluxes in the range of 500 ≤ qw ≤ 4500 W/m2, and different step heights in the range of 3 ≤ S ≤ 5.8 mm, are investigated to identify their effects on the heat transfer and fluid flow characteristics. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number compared with other nanofluids. The recirculation region and the Nusselt number increase as the step height, Reynolds number, and the volume fraction increase, and it decreases as the nanoparticle diameter increases. This study has revealed that the assisting flow has higher Nusselt number than opposing flow.

Effect of Aspect Ratio and Tube Orientation on Free Convection Heat Transfer to Water and Mercury in Enclosed Circular Tubes

1961 ◽  
Vol 83 (1) ◽  
pp. 87-93 ◽  
Author(s):  
Floyd W. Larsen ◽  
James P. Hartnett
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Convection Heat Transfer ◽  
Temperature Fluctuations ◽  
Heat Fluxes ◽  
Radius Ratio ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Convection Heat ◽  
Free Convection Heat

Free convection heat transfer to water and to mercury in a circular tube closed at the bottom end, open to a cooled reservoir at the top, and heated through the wall with a uniform heat flux, has been investigated with emphasis on the effect of length-to-radius ratio and tube inclination. Dimensionless wall and fluid temperatures are presented for several tube inclinations over a range of imposed dimensionless heat fluxes to a tube of length-to-radius ratio 14.6; these results are compared to earlier measurements in a tube of length-to-radius ratio 21.0. Over the range of the investigation the flow was apparently in fully mixed turbulent motion, as evidenced by the large fluid temperature fluctuations recorded during the tests. Inclination of the tube was found to result in a considerable decrease in temperature fluctuations and a corresponding increase in heat transfer above that observed with the tube axis vertical.

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