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.

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.

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.

Natural Convection From Protruding Heat Sources in a Channel

2003 ◽  
Author(s):  
Tunc Icoz ◽  
Qinghua Wang ◽  
Yogesh Jaluria
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Natural Convection ◽  
Rayleigh Scattering ◽  
Convection Heat Transfer ◽  
Separation Distance ◽  
Natural Convection Heat Transfer ◽  
Temperature Profiles ◽  
Heat Sources ◽  
Convection Heat

Natural convection has important implications in many applications like cooling of electronic equipment due to its low cost and easy maintenance. In the present study, two-dimensional natural convection heat transfer to air from multiple identical protruding heat sources, which simulate electronic components, located in a horizontal channel has been studied numerically. The fluid flow and temperature profiles, above the heating elements placed between an adiabatic lower plate and an isothermal upper plate, are obtained using numerical simulation. The effects of source temperatures, channel dimensions, openings, boundary conditions, and source locations on the heat transfer from and flow above the protruding sources are investigated. Different configurations of channel dimensions and separation distances of heat sources are considered and their effects on natural convection heat transfer characteristics are studied. The results show that the channel dimensions have a significant effect on fluid flow. However, their effects on heat transfer are found to be small. The separation distance is found to be an important parameter affecting the heat transfer rate. The numerical results of temperature profiles are compared with the experimental measurements performed using Filtered Rayleigh Scattering (FRS) technique in an earlier study, indicating good agreement. It is observed that adiabatic upper plate assumption leads to better temperature predictions than isothermal plate assumption.

Numerical Study of Deteriorated Convection Heat Transfer of Supercritical Fluid Flowing Through Vertical Mini Tube at Relatively Low Reynolds Numbers

2018 ◽  
Author(s):  
Chen-Ru Zhao ◽  
Zhen Zhang ◽  
Qian-Feng Liu ◽  
Han-Liang Bo ◽  
Pei-Xue Jiang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Convection Heat Transfer ◽  
Turbulence Models ◽  
Convection Heat ◽  
Flow Acceleration ◽  
Heat Transfer Deterioration ◽  
Low Reynolds

Numerical investigations are performed on the convection heat transfer of supercritical pressure fluid flowing through vertical mini tube with inner diameter of 0.27 mm and inlet Reynolds number of 1900 under various heat fluxes conditions using low Reynolds number k-ε turbulence models due to LB (Lam and Bremhorst), LS (Launder and Sharma) and V2F (v2-f). The predictions are compared with the corresponding experimentally measured values. The prediction ability of various low Reynolds number k-ε turbulence models under deteriorated heat transfer conditions induced by combinations of buoyancy and flow acceleration effects are evaluated. Results show that all the three models give fairly good predictions of local wall temperature variations in conditions with relatively high inlet Reynolds number. For cases with relatively low inlet Reynolds number, V2F model is able to capture the general trends of deteriorated heat transfer when the heat flux is relatively low. However, the LS and V2F models exaggerate the flow acceleration effect when the heat flux increases, while the LB model produces qualitative predictions, but further improvements are still needed for quantitative prediction. Based on the detailed flow and heat transfer information generated by simulation, a better understanding of the mechanism of heat transfer deterioration is obtained. Results show that the redistribution of flow field induced by the buoyancy and flow acceleration effects are main factors leading to the heat transfer deterioration.

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