Influence of Intense Symmetric Heating and Variable Physical Properties on the Thermo-Buoyant Airflow Inside Vertical Parallel-Plate Channels

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
Biagio Morrone ◽  
Antonio Campo
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Parallel Plate ◽  
Detailed Comparison ◽  
Computational Domain ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Joint Influence ◽  
Mass Flow Rates ◽  
Symmetric Heating

This paper deals with the steady, laminar, and two-dimensional natural convection inside vertical parallel-plate channels with isoflux heating. The main objective of this paper is to assess the joint influence of intense heating and variable physical properties on the flow and heat transfer characteristics of the upward air. To capture the physics of the problem, the discretized conservation equations are solved by the finite-volume technique in an aggrandized computational domain that is much larger than the physical domain. Representative numerical results based on the FLUENT computer program are presented in terms of local quantities such as air velocity and temperature profiles, as well as global quantities such as the average heat transfer coefficients and mass flow rates, all in response to the controlling geometrical and thermal parameters. A detailed comparison of these results is made against those produced by the simple model limited to constant physical properties.

Experiments on Turbulent Heat Transfer in an Asymmetrically Heated Rectangular Duct

1966 ◽  
Vol 88 (2) ◽  
pp. 170-174 ◽  
Author(s):  
E. M. Sparrow ◽  
J. R. Lloyd ◽  
C. W. Hixon
Keyword(s):  
Heat Transfer ◽  
Rectangular Cross Section ◽  
Heated Wall ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
First Case ◽  
Symmetric Heating

An experimental investigation of the effect of asymmetrical heating on fully developed turbulent heat transfer has been carried out. The test apparatus was a rectangular duct of aspect ratio 5:1. The duct was constructed so that the two long sides of the rectangular cross section could be heated at different preselected rates, while the two short sides were unheated. Two cases of asymmetrical heating were studied: (a) One of the two long sides was heated, while the second was unheated; (b) both of the long sides were heated, with the heating rate at one side being twice that of the other. For the first case, the heat transfer coefficients are lower than those for the symmetrically heated duct. For the second case, the coefficients for the more strongly heated wall are also below the values for symmetrical heating, while the coefficients for the lesser-heated wall are greater than the symmetric heating results. These findings are in qualitative agreement with analytical predictions for the parallel-plate channel. Furthermore, by applying an analytically motivated correlation procedure (reference [10]), it was shown that overall Nusselt number results for asymmetric heating could be brought into virtual coincidence with those for symmetric heating.

scholarly journals Numerical and experimental investigation of heat transfer of ZnO/Water nanofluid in the concentric tube and plate heat exchangers

2011 ◽  
Vol 15 (1) ◽  
pp. 183-194 ◽  
Author(s):  
Fard Haghshenas ◽  
Mohammad Talaie ◽  
Somaye Nasr
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Plate Heat ◽  
Heat Transfer Coefficients ◽  
Mass Flow Rates

The plate and concentric tube heat exchangers are tested by using the water-water and nanofluid-water streams. The ZnO/Water (0.5%v/v) nanofluid has been used as the hot stream. The heat transfer rate omitted of hot stream and overall heat transfer coefficients in both heat exchangers are measured as a function of hot and cold streams mass flow rates. The experimental results show that the heat transfer rate and heat transfer coefficients of the nanofluid in both of the heat exchangers is higher than that of the base liquid (i.e., water) and the efficiency of plate heat exchange is higher than concentric tube heat exchanger. In the plate heat exchanger the heat transfer coefficient of nanofluid at mcold = mhot = 10 gr/sec is about 20% higher than base fluid and under the same conditions in the concentric heat exchanger is 14% higher than base fluid. The heat transfer rate and heat transfer coefficients increases with increase in mass flow rates of hot and cold streams. Also the CFD1 code is used to simulate the performance of the mentioned heat exchangers. The CFD results are compared to the experimental data and showed good agreement. It is shown that the CFD is a reliable tool for investigation of heat transfer of nanofluids in the various heat exchangers.

Boiling Heat Transfer Coefficients in a Falling Film Helical Coil Heat Exchanger for the NH3–LiNO3 Mixture

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
J. A. Hernández-Magallanes ◽  
W. Rivera
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Boiling Heat Transfer ◽  
Helical Coil ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Heat Transfer Coefficients ◽  
Mass Flow Rates

This paper reports the experimental data of boiling heat transfer coefficients for the ammonia–lithium nitrate mixture in a laminar falling film. The analyzed heat exchanger consists of a shell with an internal helical coil. More than one hundred test runs were carried out in steady-state conditions to determine the boiling heat transfer coefficients at generation temperatures, concentrations, and mass flow rates typical of absorption cooling systems of capacities between 5 and 10 kW. Ammonia vapor was produced at generation temperatures between 80 °C and 105 °C obtaining boiling heat transfer coefficients between 85 and 340 W/m2K. Semi-empirical correlations were used by diverse authors to correlate the experimental data. A new correlation was proposed with which the best adjustments were obtained. Also, the influence of the heat flux, the refrigerant solution mass flow rates, and the exit vapor qualities were analyzed in the boiling heat transfer coefficients.

Experimental Investigation of Condensation Heat Transfer in Annular Helicoidal Pipes at Different Orientations

Volume 3 ◽  
2004 ◽  
Author(s):  
H. L. Mo ◽  
R. Prattipati ◽  
C. X. Lin ◽  
M. A. Ebadian
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cooling Water ◽  
Saturation Temperature ◽  
Experimental Investigations ◽  
Percentage Increase ◽  
Transfer Coefficients ◽  
Cooling Water Temperature ◽  
Heat Transfer Coefficients ◽  
Mass Flow Rates

Experimental investigations were conducted on condensation of R134a in annular helicoidal pipes with three orientations, 0°, 45° and 90°. The experimental results indicated that the refrigerant heat transfer coefficients increased with the increase of cooling water temperature, mass flow rates of refrigerant and cooling water, and decreased with the increase of saturation temperature of R134a. When the orientation increased from 0° to 90°, the refrigerant Nusselt number increased around 11% at refrigerant Reynolds number of 80, and around 16% at 200, the percentage increase of refrigerant Nusselt number from 0° to 45° accounted for more than two times of that from 45° to 90°. The performance of annular helicoidal pipe was evaluated by comparing with equivalent smooth straight pipe and identical helicoidal pipe.

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