A Natural Convection Fin with a Solution-Determined Nonmonotonically Varying Heat Transfer Coefficient

1981 ◽  
Vol 103 (2) ◽  
pp. 218-225 ◽  
Author(s):  
E. M. Sparrow ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
First Principles ◽  
Numerical Solutions ◽  
Flow Direction ◽  
Operating Conditions ◽  
Fluid Temperature ◽  
Wide Range

A conjugate conduction-convection analysis has been made for a vertical plate fin which exchanges heat with its fluid environment by natural convection. The analysis is based on a first-principles approach whereby the heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, and energy in the fluid boundary layer adjacent to the fin. The natural convection heat transfer coefficient is not specified in advance but is one of the results of the numerical solutions. For a wide range of operating conditions, the local heat transfer coefficients were found not to decrease monotonically in the flow direction, as is usual. Rather, the coefficient decreased at first, attained a minimum, and then increased with increasing downstream distance. This behavior was attributed to an enhanced buoyancy resulting from an increase in the wall-to-fluid temperature difference along the streamwise direction. To supplement the first-principles analysis, results were also obtained from a simple adaptation of the conventional fin model.

Heat Transfer in Vertically Aligned Phase Change Energy Storage Systems

1999 ◽  
Vol 121 (2) ◽  
pp. 98-109 ◽  
Author(s):  
H. T. El-Dessouky ◽  
W. S. Bouhamra ◽  
H. M. Ettouney ◽  
M. Akbar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Energy Storage ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Storage Systems ◽  
Flow Direction ◽  
Vertically Aligned ◽  
Bottom To Top

Convection effects on heat transfer are analyzed in low temperature and vertically aligned phase change energy storage systems. This is performed by detailed temperature measurements in the phase change material (PCM) in eighteen locations forming a grid of six radial and three axial positions. The system constitutes a double pipe configuration, where commercial grade paraffin wax is stored in the annular space between the two pipes and water flows inside the inner pipe. Vertical alignment of the system allowed for reverse of the flow direction of the heat transfer fluid (HTF), which is water. Therefore, the PCM is heated from the bottom for HTF flow from bottom to top and from the top as the HTF flow direction is reversed. For the former case, natural convection affects the melting process. Collected data are used to study variations in the transient temperature distribution at axial and radial positions as well as for the two-dimensional temperature field. The data is used to calculate the PCM heat transfer coefficient and to develop correlations for the melting Fourier number. Results indicate that the PCM heat transfer coefficient is higher for the case of PCM heating from bottom to top. Nusselt number correlations are developed as a function of Rayleigh, Stefan, and Fourier numbers for the HTF flow from bottom to top and as a function of Stefan and Fourier numbers for HTF flow from top to bottom. The enhancement ratio for heat transfer caused by natural convection increases and then levels off as the inlet temperature of the HTF is increased.

Predicting Heat Transfer From Unsteady Synthetic Jets

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Mehmet Arik ◽  
Tunc Icoz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Small Scale ◽  
Wide Range ◽  
The Heat Transfer Coefficient

Synthetic jets are piezo-driven, small-scale, pulsating devices capable of producing highly turbulent jets formed by periodic entrainment and expulsion of the fluid in which they are embedded. The compactness of these devices accompanied by high air velocities provides an exciting opportunity to significantly reduce the size of thermal management systems in electronic packages. A number of researchers have shown the implementations of synthetic jets on heat transfer applications; however, there exists no correlation to analytically predict the heat transfer coefficient for such applications. A closed form correlation was developed to predict the heat transfer coefficient as a function of jet geometry, position, and operating conditions for impinging flow based on experimental data. The proposed correlation was shown to predict the synthetic jet impingement heat transfer within 25% accuracy for a wide range of operating conditions and geometrical variables.

Experimental Study of Thermal Performance and Pressure Drop in Compact Heat Exchanger Installed in Automotive

2006 ◽  
Author(s):  
M. H. Saidi ◽  
A. A. Mozafari ◽  
A. R. Esmaeili Sany ◽  
J. Neyestani
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Operating Conditions ◽  
Design Stage ◽  
Practical Usefulness ◽  
Experimental Prediction ◽  
Wide Range

In this Study, radiator performance for passenger car has been studied experimentally in wide range of operating conditions. Experimental prediction of Nusselt number and heat transfer coefficient for coolant in radiator tubes are also performed with ε–NTU method. The total effectiveness coefficient of radiator and heat transfer coefficient in air side is calculated via try and error method considering experimental data. The Colburn factor and pressure drop are also estimated for this heat exchanger. Examples of application demonstrate the practical usefulness of this method to provide empirical data which can be used during the design stage.

Forced Convective Heat Transfer From Helicoidal Pipes

2001 ◽  
Author(s):  
Ahmad Fakheri ◽  
Abdelrahman H. A. Alnaeim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Characteristic Length ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Operating Conditions ◽  
Straight Pipe ◽  
Wide Range ◽  
The Heat Transfer Coefficient

Abstract Forced convection heat transfer from helicoidal pipes is experimentally investigated over a wide range of operating conditions. Based on the experimental results, a characteristic length incorporating the tube diameter, the coil diameter, and the coil spacing, is proposed as the relevant scale for defining Nusselt and Reynolds numbers. Based on this characteristic length, Nusselt number for helicoidal pipes can be predicated from the correlations available for cylinders in the range of available experimental data. It is shown that the performance of the coils depends on the Reynolds number. At high Reynolds numbers, the heat transfer coefficient is essentially equal to that of the straight pipe and the coil pitch has little influence on the heat transfer rate. On the other hand, at low Reynolds numbers, the heat transfer coefficient is lower than that of a straight pipe and its value is a strong function of the coil spacing.

Local Heat Transfer Coefficient During Condensation in a 0.8 mm Diameter Pipe

2006 ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Operating Conditions ◽  
Local Heat Transfer Coefficient ◽  
Wide Range ◽  
The Heat Transfer Coefficient

The first preliminary tests carried on a new experimental rig for measurement of the local heat transfer coefficient inside a circular 0.8 mm diameter minichannel are presented in this paper. The heat transfer coefficient is measured during condensation of R134a and is obtained from the measurement of the heat flux and the direct gauge of the saturation and wall temperatures. The heat flux is derived from the water temperature profile along the channel, in order to get local values for the heat transfer coefficient. The test section has been designed so as to reduce thermal disturbances and experimental uncertainty. A brief insight into the design and the construction of the test rig is reported in the paper. The apparatus has been designed for experimental tests both in condensation and vaporization, in a wide range of operating conditions and for a wide selection of refrigerants.

Prediction of Natural Convection Heat Transfer in Layered Porous Cavities by Homogeneous Anisotropic Model

2008 ◽  
Author(s):  
R. L. Marvel ◽  
F. C. Lai
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
System Model ◽  
Porous System ◽  
Anisotropic Model ◽  
Wide Range ◽  
Sublayer Thickness ◽  
The Heat Transfer Coefficient

Steady-state heat transfer by natural convection in a layered porous cavity is examined by using homogeneous anisotropic model. The geometry considered is a two-dimensional square enclosure comprising of three or four porous layers with non-uniform thickness and distinct permeability. The cavity is subjected to differential heating from the vertical walls. The results, which include the flow patterns and temperature profiles as well as the heat transfer coefficients, are presented for a wide range of permeability ratio, sublayer thickness ratio, and Rayleigh number. Particularly, the heat transfer results obtained are compared with those reported from a rigorous numerical model for layered porous media. In addition, the results are compared with the lumped system model that was proposed recently. It has been found that homogeneous anisotropic model predicts the heat transfer coefficient reasonably well within the conductive flow regime. However, beyond this regime, the model fails to represent the layered case for the effective permeabilities and sublayer thickness ratios considered. On the other hand, it is observed that the lumped system model offers better agreement to the heat transfer coefficient of the actual layered porous system over a wider range of parameters and which also significantly reduces computational efforts.

Natural Convection From Horizontal Cylinders at Near-Critical Pressures—Part I: Experimental Study

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Yohann Rousselet ◽  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Bulk Temperature ◽  
Natural Convection Heat Transfer ◽  
Fluid Temperature ◽  
Convection Heat

An experimental study of free convection heat transfer from horizontal wires to carbon dioxide at near-critical pressures has been performed. In the experiments, platinum wires ranging in size from 25.4 μm to 100 μm and a nichrome 60/20 wire of 101.6 μm diameter were used. The pressure (P) and bulk temperature (Tb) of the fluid were varied in the range: 6.34 MPa ≤ P ≤ 9.60 MPa and 10 °C ≤ Tb ≤ 33.3 °C, respectively. The wall temperature (Tw) was systematically increased from Tb + 0.1 °C to 250 °C. Visual observations of the fluid flow were made using a high speed camera. The similarity between natural convection heat transfer at Tw < Tsat (for P < Pc) and Tw < Tpc (for P > Pc), as well as the similarity between film boiling at Tw > Tsat (for P < Pc) and natural convection heat transfer at Tw > Tpc (for P > Pc), was demonstrated. The dependence of the heat transfer coefficient on the wire diameter was found to be h ∝ D−0.5, for both P < Pc and P > Pc. The bulk fluid temperature is introduced as a new reference temperature for the calculation of fluid properties. Correlations have been developed to predict the natural convection heat transfer coefficient at both subcritical and supercritical pressures. The developed correlations predict almost all the experimental data from the current study and those reported in the literature to within ±15%.

Sign in / Sign up

Export Citation Format

Share Document