Effect of incident flow conditions on convective heat transfer from the inclined windward roof of a low-rise building with application to photovoltaic-thermal systems

2012 ◽  
Vol 104-106 ◽  
pp. 428-438 ◽  
Author(s):  
Panagiota Karava ◽  
Chowdhury Mohammad Jubayer ◽  
Eric Savory ◽  
Siwei Li
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flow Conditions ◽  
Incident Flow ◽  
Thermal Systems

scholarly journals Effect of corrugated minichannel variable width on entropy generation for convective heat transfer of alpha-Alumina-water nanofluid

2021 ◽  
Vol 2053 (1) ◽  
pp. 012016
Author(s):  
N M Muhammad ◽  
N A C Sidik ◽  
A Saat ◽  
Y Asako ◽  
W M A A Japar ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Entropy Production ◽  
Convective Heat ◽  
Entropy Generation ◽  
Entropy Generation Rate ◽  
Thermal Systems ◽  
Volume Fractions ◽  
Thermal Entropy ◽  
Alpha Alumina

Abstract Energy management and sustainability in thermal systems require maximum utilization of resources with minimal losses. However, it is rarely unattainable due to the ever-increasing need for a high-performance system combined with device size reduction. The numerical study examined convective heat transfer of an alpha-Alumina-water nanofluid in variable-width corrugated minichannel heat sinks. The objective is to study the impact of nanoparticle volume fractions and flow area variation on the entropy generation rate. The determining variables are 0.005 – 0.02 volume fractions, the fluid velocity 3 – 5.5 m/s and heat flux of 85 W/cm2. The numerical results show an acceptable correlation with the experiment results. The results indicate the thermal entropy production drop with an increase in nanoparticles volume fraction. Contrastingly, the frictional resistance entropy suggests the opposite trend due to the turbulence effect on the fluid viscosity. The induction of Alumina-Water nanofluid with enhanced thermal conductivity declined the entropy generation rate compared to water alone. The increase in width ratio by 16% between the cases translates to at least a 9% increase in thermal entropy production. The outcome of this study can provide designers and operators of thermal systems more insight into entropy management in corrugated heatsinks.

A Numerical Study of Assisting and Opposing Mixed Convective Heat Transfer From a Horizontal Isothermal High Aspect Ratio Rectangular Cylinder

2012 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Boussinesq Approximation ◽  
Forced Flow ◽  
Width Ratio ◽  
Flow Conditions ◽  
Rectangular Cylinder

Mixed convective heat transfer from an isothermal cylinder with a rectangular cross-section and a relatively large height-to-width ratio has been numerically studied. The axis of the cylinder is horizontal with the longer sides of the rectangular cylinder being vertical. There is a vertical forced flow over the cylinder. The flow conditions considered are such that in general mixed forced and natural convective flow exists. Both the case where the buoyancy forces act in the same direction as the forced flow (assisting flow) and the case where they act in the opposite direction to the forced flow (opposing flow) have been considered. The flow has been assumed to be two-dimensional and the Boussinesq approximation has been adopted. Attention has been restricted to the flow of air and results have therefore been obtained for a Prandtl number of 0.74. The flow conditions considered are such that laminar or turbulent flow can exist. The main attention is this work has been directed at determining the effect of the flow parameters on the mean heat transfer rate from the cylinder and on determining the conditions under which the flow can be assumed to be forced convective and under which it can be assumed to be natural convective.

Heat Transfer Coefficient in Helical Heat Exchangers under Turbulent Flow Conditions

2008 ◽  
Vol 4 (1) ◽  
Author(s):  
Pablo Coronel ◽  
K.P. Sandeep
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Exchangers ◽  
Convective Heat Transfer Coefficient ◽  
Flow Conditions ◽  
Overall Heat Transfer Coefficient ◽  
Turbulent Flow Conditions

This study involved the determination of convective heat transfer coefficient in both helical and straight tubular heat exchangers under turbulent flow conditions. The experiments were conducted in helical heat exchangers, with coils of two different curvature ratios (d/D = 0.114 and 0.078), and in straight tubular heat exchangers at various flow rates (1.89 x 10-4 - 6.31 x 10-4 m3/s) and for different end-point temperatures (92 - 149 °C). The results show that the overall heat transfer coefficient (U) in the helical heat exchanger is much higher than that in straight tubular heat exchangers. In addition, U was found to be larger in the coil of larger curvature ratio (d/D = 0.114) than in the coil of smaller curvature ratio (d/D = 0.078). The inside (hi) and outside (ho) convective heat transfer coefficients were determined based on the overall heat transfer coefficient and a correlation to compute the inside convective heat transfer coefficient (hi) as a function of NRe, NPr, and d/D was developed.

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