Evaluating the Effect of Number of Spans on Heat Transfer in Greenhouses

2019 ◽  
Author(s):  
S. Kruger ◽  
L. Pretorius
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Fluid Dynamic ◽  
Cfd Model ◽  
Transfer Velocity ◽  
Nusselt Number Distribution ◽  
Convective Cells ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

Abstract The present study concerns convective flows in the empty volume above the plant canopy in a confined greenhouse. The purpose of this paper is to numerically investigate the effect of the number of spans on the convective heat transfer in closed greenhouses. The initial greenhouse CFD model cavity is validated against experimental results found in the literature. Thermal convection is induced by heating the bottom of the cavity. The numerical model is then modified to represent two-l greenhouse cavities with different numbers of spans. The computational fluid dynamic (CFD) software is then used to analyze mainly the natural convective heat transfer, velocity and temperature distributions for the single span greenhouse, as well as multi-span greenhouses (containing two and three spans). The greenhouse CFD model floor is heated, and the walls are adiabatic, corresponding to Rayleigh-Bénard convection. A mesh sensitivity analysis was conducted to determine a suitable size for the mesh. Results show that adding additional spans to the initial single-span cavity has a pronounced effect on the Nusselt-number distribution on the floor of the cavity. The temperature and velocity distributions were also significantly influenced. The four-span cavity showed three convective cells instead of four as for the lowest Rayleigh number.

Numerical and Experimental Study of Heat Transfer in a BIPV-Thermal System

2007 ◽  
Vol 129 (4) ◽  
pp. 423-430 ◽  
Author(s):  
L. Liao ◽  
A. K. Athienitis ◽  
L. Candanedo ◽  
K.-W. Park ◽  
Y. Poissant ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Wave Radiation ◽  
Measured Temperature ◽  
Cfd Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients ◽  
T System

This paper presents a computational fluid dynamics (CFD) study of a building-integrated photovoltaic thermal (BIPV∕T) system, which generates both electricity and thermal energy. The heat transfer in the BIPV∕T system cavity is studied with a two-dimensional CFD model. The realizable k‐ε model is used to simulate the turbulent flow and convective heat transfer in the cavity, including buoyancy effect and long-wave radiation between boundary surfaces is also modeled. A particle image velocimetry (PIV) system is employed to study the fluid flow in the BIPV∕T cavity and provide partial validation for the CFD model. Average and local convective heat transfer coefficients are generated with the CFD model using measured temperature profile as boundary condition. Cavity temperature profiles are calculated and compared to the experimental data for different conditions and good agreement is obtained. Correlations of convective heat transfer coefficients are generated for the cavity surfaces; these coefficients are necessary for the design and analysis of BIPV∕T systems with lumped parameter models. Local heat transfer coefficients, such as those presented, are necessary for prediction of temperature distributions in BIPV panels.

Convective Heat Transfer and Fluid Dynamic Characteristics of SiO2 Ethylene Glycol/Water Nanofluid

2008 ◽  
Vol 29 (12) ◽  
pp. 1027-1035 ◽  
Author(s):  
Devdatta P. Kulkarni ◽  
Praveen K. Namburu ◽  
H. Ed Bargar ◽  
Debendra K. Das
Keyword(s):  
Heat Transfer ◽  
Ethylene Glycol ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Dynamic Characteristics ◽  
Fluid Dynamic

Numerical Study of Conjugate Heat Transfer in a BIPV-Thermal System

Solar Energy ◽  
2005 ◽  
Author(s):  
Liang Liao ◽  
Andreas Athienitis ◽  
Kwang-Wook Park ◽  
Michael Collins ◽  
Yves Poissant
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Conjugate Heat Transfer ◽  
Numerical Study ◽  
Test Facility ◽  
Cfd Model ◽  
Transfer Coefficients ◽  
Model Average ◽  
T System

This paper presents a computational fluid dynamics (CFD) study of a building-integrated photovoltaic thermal (BIPV/T) system, which generates both electricity and thermal energy. The conjugate heat transfer in the BIPV/T system cavity is studied with a 2-D CFD model. The k-ε model is used to simulate the turbulent flow and convective heat transfer in the cavity, in addition to buoyancy effect. Longwave radiation between boundary surfaces is also modeled. Experimental measurements taken in a full scale outdoor test facility at Concordia University are generally in good agreement with the CFD model. Average and local convective heat transfer coefficients are generated and PV panel average temperature and local cell temperatures are calculated and compared with the experimental data.

Convective Heat Transfer in a Rectangular Channel Filled With Sintered Bronze Beads and Periodically Spaced Heated Blocks

2005 ◽  
Vol 128 (5) ◽  
pp. 453-464 ◽  
Author(s):  
Sheng Chung Tzeng
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Average Nusselt Number ◽  
Rectangular Channel ◽  
Block Height ◽  
Nusselt Number Distribution ◽  
Sintered Bronze ◽  
Block Width

This work numerically investigated the steady state fluid flow and heat transfer behaviors associated with a sintered porous channel that contains periodically spaced heated blocks. Some typical cases are experimentally examined in this study. The relevant varied parameters were the average bead diameter (d), the relative block height (h∕H), the relative block width (w∕H), the relative block spacing (s∕H), and the Reynolds number (Re). The numerical results revealed a lack of global recirculation in regions between the blocks, where the forced convective heat transfer was low, but the heat in those regions was transferred to the metallic block by conduction through porous media, before being dissipated into the fluid that passed over the zone above the heated block. Additionally, the relevant parameters considerably affect the local Nusselt number distribution along the periphery of the block surface. The average Nusselt number for each block decreased along the direction of the flow until it reached its fully developed value. The Nusselt number increased with h∕H or Re in the fully developed region. The effect of h∕H on the fully developed Nusselt number became stronger as Re increased and w∕H decreased. The effects of s∕H and d on the fully developed Nusselt number were insignificant over the ranges of parameters considered herein (d=0.7 and 1.16mm, h∕H=0.12-0.59, w∕H=0.24-0.47, s∕H=0.24-0.7, and Re=1019-5059). Finally, this study summarized the average Nusselt number for different configurations of the heated blocks with various d, h∕H, w∕H, s∕H, and Re.

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