Thermal Design of Uniformly Heated Vertical Convergent Channels in Natural Convection in Air

Volume 1 ◽  
2004 ◽  
Author(s):  
Nicola Bianco ◽  
Luigi Langellotto ◽  
Oronzio Manca ◽  
Sergio Nardini
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Numerical Procedure ◽  
Thermal Design ◽  
Uniform Heat Flux ◽  
Geometrical Parameters ◽  
Surface Emissivity ◽  
Convergent Channel ◽  
Design Charts ◽  
Parameter Ranges

In this paper, design charts for the evaluation of thermal parameters for natural convection in air in a vertical convergent channel are proposed. In the thermal analysis of natural convection in a convergent channel, the parameters that play an important role are: the heat flux, maximum wall temperatures and geometrical parameters such as the length of the heated walls, the minimum and maximum channel sections. A simple numerical procedure to obtain the thermal design charts is presented. Results are carried out for symmetrically heated channels with walls at uniform heat flux. Some simple examples are given to show the use of the charts. The proposed charts are obtained from data resulting from numerical investigation in the following parameter ranges: angles of convergence not greater than 10 deg, surface emissivity between 0.10 and 0.90, 30 ≤ (qc + qr)≤ 220 W/m2, 2.0 ≤ L/bmax ≤ 60 and 0.030 ≤ bmin/bmax ≤ 1.0.

Mixed Convection in Air in an Open Ended Cavity With a Moving Plate Parallel to the Cavity Open Surface

2005 ◽  
Author(s):  
Assunta Andreozzi ◽  
Nicola Bianco ◽  
Vincenzo Naso ◽  
Oronzio Manca
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Mixed Convection ◽  
Plate Motion ◽  
Uniform Heat Flux ◽  
Geometrical Parameters ◽  
Heated Plate ◽  
Open Surface ◽  
Moving Plate ◽  
Plate Temperature

In this study, a numerical investigation of mixed convection in air in an open ended cavity, with a moving plate parallel to the cavity open surface, is carried out. The moving plate has a constant velocity, whereas a vertical plate of the open cavity is heated at uniform heat flux. All the other walls are adiabatic. The numerical analysis is obtained by means of the commercial code FLUENT. Two configurations, assisting and opposing, are analyzed. In the assisting configuration, natural convection is supported by the plate motion, whereas, in the opposing configuration, natural convection and plate motion have opposing effects. The effect of different geometrical parameters, heat flux and moving plate velocity are analyzed. Results in terms of heated plate and moving plate temperature profiles are presented and simple monomial correlation equations for both the configurations are proposed between the terms Nu/Re0.6 and Ri.

Experimental Investigation of Natural Convection in an Asymmetrically Heated Vertical Channel with an Asymmetric Chimney

2005 ◽  
Vol 127 (8) ◽  
pp. 888-896 ◽  
Author(s):  
Oronzio Manca ◽  
Marilena Musto ◽  
Vincenzo Naso
Keyword(s):  
Heat Flux ◽  
Experimental Investigation ◽  
Natural Convection ◽  
Aspect Ratio ◽  
Vertical Channel ◽  
Expansion Ratio ◽  
Uniform Heat Flux ◽  
Geometrical Parameters ◽  
Nusselt Numbers ◽  
Lower Maximum

An experimental investigation on air natural convection, in a vertical channel asymmetrically heated at uniform heat flux, with downstream unheated parallel extensions, is carried out. One extension is coplanar to the unheated channel wall and the distance between the extensions is equal to or greater than the channel gap (geometrically asymmetric chimney). Experiments are performed with different values of the wall heat flux, aspect ratio (Lh∕b), extension ratio (L∕Lh) and expansion ratio (B∕b). For the largest value of the aspect ratio (Lh∕b=10), the adiabatic extensions improve the thermal performance in terms of lower maximum wall temperature of the channel. Optimal configurations of the system with asymmetrical chimney are detected. Flow visualization shows a cold inflow in the channel-chimney system that penetrates down below the channel exit section. Maximum wall temperatures and channel Nusselt numbers are correlated to the channel Rayleigh number, Ra*, and to the geometrical parameters, in the ranges 3.0×102⩽Ra*B∕b⩽1.0105, 1.0⩽B∕b⩽3.0 and 1.0⩽L∕Lh⩽4.0 with Lh∕b=5.0 and 10.0.

Experimental and Numerical Investigation on Natural Convection in Horizontal Channels Partially Filled With Aluminium Foam and Heated From Below

2016 ◽  
Author(s):  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Sergio Nardini ◽  
Alessandra Diana
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Wall Temperature ◽  
Aluminum Foam ◽  
Rectangular Channel ◽  
Lower Surface ◽  
Heated Wall ◽  
Working Fluid ◽  
Bottom Plate ◽  
Uniform Heat Flux

Natural convection in horizontal rectangular channel without or with aluminum foam is experimentally and numerically investigated. In the case with aluminum foam the channel is partially filled. In both cases, the bottom wall of the channel is heated at a uniform heat flux and the upper wall is unheated and it is not thermally insulated to the external ambient. The experiments are performed with working fluid air. Different values of wall heat flux at lower surface are considered in order to obtain some Grashof numbers and different heated wall temperature distributions. Two different aluminum foams are considered in the experimental investigation, one from “M-pore”, with 10 and 30 pore per inch (PPI), and the other one from “ERG”, with 10, 20 and 40 PPI. The numerical simulation is carried out by a simplified two-dimensional model. It is found that the heat transfer is better when the channel is partially filled and the emissivity is low, whereas the heated wall temperature values are higher when the channel is partially filled and the heated bottom plate has high emissivity. The investigation is achieved also by flow visualization which is carried out to identify the main flow shape and development and the transition region along the channel. The visualization of results, both experimental and numerical, grants the description of secondary motions in the channel.

Design of a Mobile Probe to Predict Convection Heat Transfer on Building Integrated Photovoltaic (BIPV) at University of Technology Sydney (UTS)

2015 ◽  
Author(s):  
Jafar Madadnia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Simple Technique ◽  
Convection Heat Transfer ◽  
Thermal Design ◽  
Uniform Heat Flux ◽  
Convection Heat ◽  
Empirical Correlations ◽  
Building Integrated Photovoltaic

In the absence of a simple technique to predict convection heat transfer on building integrated photovoltaic (BIPV) surfaces, a mobile probe with two thermocouples was designed. Thermal boundary layers on vertical flat surfaces of a photovoltaic (PV) and a metallic plate were traversed. The plate consisted of twelve heaters where heat flux and surface temperature were controlled and measured. Uniform heat flux condition was developed on the heaters to closely simulate non-uniform temperature distribution on vertical PV modules. The two thermocouples on the probe measured local air temperature and contact temperature with the wall surface. Experimental results were presented in the forms of local Nusselt numbers versus Rayleigh numbers “Nu=a * (Ra)b”, and surface temperature versus dimensionless height [Ts -T∞= c*(z/h)d]. The constant values for “a”, “b”, “c” and “d” were determined from the best curve-fitting to the power-law relation. The convection heat transfer predictions from the empirical correlations were found to be in consistent with those predictions made by a number of correlations published in the open literature. A simple technique is then proposed to employ two experimental data from the probe to refine empirical correlations as the operational conditions change. A flexible technique to update correlations is of prime significance requirement in thermal design and operation of BIPV modules. The work is in progress to further extend the correlation to predict the combined radiation and convection on inclined PVs and channels.

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