An Experimental Study of Circulation Patterns in Natural Convection Using PIV

2003 ◽  
Author(s):  
K. M. Akyuzlu ◽  
S. Nemani ◽  
K. Chakravarthy
Keyword(s):  
Boundary Condition ◽  
Natural Convection ◽  
Velocity Field ◽  
Flow Patterns ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Constant Wall Temperature ◽  
Flux Boundary Condition ◽  
Circulation Patterns ◽  
Contour Plots

The objective of this study is to investigate, experimentally, using Particle Image Velocimeter (PIV), the effect of different heat transfer boundary conditions on natural convection (specifically on flow patterns) inside a storage tank (a rectangular enclosure in this case with an aspect ratio of 0.5.) Purified water is used as the working fluid and it is seeded with 10 micron hollow glass sphere particles. The results of the first set of experiments are used to verify the flow patterns expected for the constant wall temperature boundary condition, the benchmark case. Similar experiments are conducted for the constant heat flux boundary condition. The Rayleigh number for all the cases studied lie between 106 and 107. The time averaged velocity field is determined using standard cross correlation techniques. Streamlines, and velocity contour plots are generated using this velocity field. Finally, the results of both cases are compared to identify the differences in circulation patterns and thermal stratification in the fluid.

Design and Testing of a Natural Convection Experimental Setup on the External Surface of Heated Inclined Cylinders With a Constant Heat Flux Boundary Condition: Tests for Naked Cylinders

Volume 1 ◽  
2004 ◽  
Author(s):  
Jaime Antonio Sa´nchez Baquerizo ◽  
Jorge W. Duque Rivera
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Experimental Setup ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Heat Flux Boundary Condition

An experimental setup for natural convection heat transfer from inclined heated cylinders with a constant heat flux boundary condition has been designed and tested for various heat fluxes and inclination angles. For the horizontal cylinder experiment the results are in good agreement with [2] within the range of Ra* (1E5 to 1E6). For the variable inclination experiments, comparisons were made with a correlation available for inclined isothermal cylinders [1]. It was observed, that although the boundary conditions that have been compared are different, the decreasing tendency of the Nusselt number holds as the inclination of the cylinder increases. The results have been correlated in an experimental equation shown at the end of this paper.

An Experimental Study of Natural Convection in a Rectangular Enclosure Using PIV Measurement Techniques

2011 ◽  
Author(s):  
K. M. Akyuzlu ◽  
J. Farkas
Keyword(s):  
Experimental Study ◽  
Natural Convection ◽  
Measurement Techniques ◽  
Flow Patterns ◽  
Working Fluid ◽  
Two Dimensional ◽  
Rectangular Enclosure ◽  
Aspect Ratios ◽  
Circulation Patterns ◽  
Piv Measurement

An experimental study is conducted to determine the circulation patterns inside a rectangular enclosure due to natural convection using a Particle Image Velocimeter (PIV). Experiments were conducted using two different fluids (air and water) and for rectangular enclosures with aspect ratios 0.5 and 1.0. Natural convection in enclosures has been experimentally studied in the past. Many of these studies cited in the literature use some kind of an optical method like interferograms, shadowgraphs, streak photographs, or multi-exposure photographs to visualize the flow patterns in the enclosure. The present study employs a commercial two-dimensional PIV to capture, instantaneously, the circulation patterns inside the test section. The test cavity in the present setup is of rectangular shape, which is 5 inches (127 mm) wide, where the height of the enclosure can be changed to obtain aspect ratios of 0.5 and 1.0. The depth of the rectangular enclosure measures 12 inches (305 mm) to minimize the effect of walls normal to the two dimensional flow patterns that are expected in this type of arrangement. The walls of the cavity are made of Aluminum plates. These plates are kept at constant but different temperatures during the experiments. In the present study, hollow glass sphere particles with 10 microns in diameter were used as seeding for water experiments and fine particles/flakes of ash generated from burned incense were used as seeding in the air experiments. For each working fluid, the experiments were repeated for different aspect ratios and for different wall temperature differences which corresponded to Rayleigh numbers in the range of 106 and 107. Velocity fields were captured at steady state for each experiment using the two-dimensional PIV system. Numerical studies were also carried out using a commercial CFD software. Comparisons of the numerical and experimental results indicate a good match in terms of circulation patterns and velocity magnitudes in the core of the buoyancy driven flow. Discrepancies in measured and predicted values of velocities are more pronounced near to the boundaries of the enclosure. Separate measurements with finer interrogation areas and different PIV setting were required to improve the accuracy of the measurements near the corners (top and bottom) of the enclosure. The results of these measurements are also presented.

On Effects of Temperature Boundary Conditions on Heat Transfer in Turbulent Low-Prandtl-Number Flows

2020 ◽  
Author(s):  
Ivan Otic
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Large Eddy ◽  
Heat Flux Boundary Condition ◽  
Effects Of Temperature

Abstract One important issue in understanding and modeling of turbulent heat transfer is the behavior of fluctuating temperature close to the wall. Common engineering computational approach assumes constant heat flux boundary condition on heated walls. In the present paper constant heat flux boundary condition was assumed and effects of temperature fluctuations are investigated using large eddy simulations (LES) approach. A series of large eddy simulations for two geometries is performed: First, forced convection in channels and second, forced convection over a backward facing step. LES simulation data is statistically analyzed and compared with results of direct numerical simulations (DNS) from the literature which apply three cases of heat flux boundary conditions: 1. ideal heat flux boundary condition, 2. non-ideal heat flux boundary condition, 3. conjugate heat transfer boundary condition. For low Prandtl number flows LES results show that, despite very good agreement for velocities and mean temperature, predictions of temperature fluctuations may have strong deficiencies if simplified boundary conditions are applied.

Study of the MHD Flow of Casson Nanofluid in the Presence of Oxides Nanoparticles Based C2H6O2/H2O Under Constant Heat Flux Boundary Condition

2021 ◽  
Vol 15 (3) ◽  
pp. 149
Author(s):  
Feras M. Al Faqih ◽  
Mohammed Z. Swalmeh ◽  
Sulaiman Mohammed Ibrahim ◽  
Hebah G. Bani Saeed ◽  
Hamzeh T. Alkasasbeh ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Mhd Flow ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Casson Nanofluid ◽  
Heat Flux Boundary Condition

Boundary Condition Dependent Natural Convection in a Rectangular Pool With Internal Heat Sources

2006 ◽  
Vol 129 (5) ◽  
pp. 679-682 ◽  
Author(s):  
Seung Dong Lee ◽  
Jong Kuk Lee ◽  
Kune Y. Suh
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Internal Heat ◽  
Working Fluid ◽  
Natural Convection Heat Transfer ◽  
Heat Sources ◽  
Internal Heat Sources ◽  
Volumetric Heat Generation

This paper presents results of steady-state experiments concerned with natural convection heat transfer of air in a rectangular pool in terms of the Nusselt number (Nu) versus the modified Rayleigh number (Ra′) varying from 109 to 1012. Cartridge heaters were immersed in the working fluid to simulate uniform volumetric heat generation. Two types of boundary conditions were adopted in the test: (I) top cooled, and (II) top and bottom cooled. The other sides were kept insulated. In the case of boundary condition II, the upward heat transfer ratio, Nuup∕(Nuup+Nudn), turned out to be 0.7–0.8 in the range of Ra′ between 1.05×1010 and 3.68×1011.

Natural Convection From a Tube Bundle in a Thin Inclined Enclosure

2003 ◽  
Author(s):  
Wei Liu ◽  
Jane H. Davidson ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Tube Bundle ◽  
Storage System ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Measured Temperature ◽  
Transfer Coefficients ◽  
Rectangular Array

Natural convection heat transfer coefficients for a rectangular array of eight tubes contained in a thin enclosure of aspect ratio 9.3:1 and inclined at 30 degrees to the horizontal are measured for a range of transient operating modes typical of a load side heat exchanger in unpressurized integral collector-storage systems. Water is the working fluid, and thermal charging is accomplished via a constant heat flux on the upper boundary. All other boundaries are well insulated. Results for isothermal and stratified enclosures yield the following correlation for the overall Nusselt number: NuD=(0.728±0.002)RaD0.25,4.0×105≤RaD≤1.4×107. The flow field in the enclosure is inferred from measured temperature distributions. The temperature difference that drives natural convection is also determined. The results extend earlier work for the case of a single tube and provide limiting case heat transfer data for a tube bundle that occupies the upper portion of the collector storage system.

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