Transient Mixed-Convection With Applications to Cooling of Biomaterials

2005 ◽  
Author(s):  
Saurabh Shrivastava ◽  
Bahgat Sammakia
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Convection Flow ◽  
Coupled Wall ◽  
Steady Stage ◽  
Basic Characteristics ◽  
Convection Dominated ◽  
Solid Block

2-Dimensional transient mixed-convection in a horizontal rectangular enclosed cavity heated from a lower solid block is numerically studied. The enclosure simulates the thermal reservoir for the storage and shipment of biomaterials. The lower solid block containing the thermal biomass that has adiabatic sides and bottom wall, is coupled along the top wall with a hollow cavity of aspect ratio (H/L = 0.5), whose side and top walls are assumed to be surrounded by a phase change material and has been assigned constant temperature of 273K. Initially, the temperature of the biomaterials is raised to 283K; the upper cavity is filled with quiescent air and uniform temperature at time zero. Laminar airflow is assumed with a fan in middle of the cavity. The basic characteristics and flow structures during the transition of natural-convection-dominated flow to forced-convection-dominated flow are determined. The problem is solved for the range of mixed-convection regime and the fluid flow structure and heat transfer is found to be dependent on mixed-convection as determined by the buoyancy parameter Gr/Re2. As anticipated, the forced-convection-dominated flow is found to be more effective in cooling of the thermal biomass than the natural-convection-dominated flow. This study shows that using the assisted forced convection results in an increase in the cooling performance of the biomaterial container in the natural-convection-dominated type mixed-convection flow. Examining the area averaged Surface Nusselt number along the coupled wall with time and the rate of heat transfer from the thermal biomass during the Quasi-steady stage validates the above hypothesis.

Mixed Convection Along a Wavy Surface

1989 ◽  
Vol 111 (4) ◽  
pp. 974-979 ◽  
Author(s):  
S. Ghosh Moulic ◽  
L. S. Yao
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Second Harmonic ◽  
Cumulative Effect ◽  
Leading Edge ◽  
Wavy Surface ◽  
Convection Flow ◽  
Dominant Component

The results of a study of mixed-convection flow along a wavy surface are presented. The forced-convection component of the heat transfer contains two harmonics. The amplitude of the first harmonic is proportional to the amplitude of the wavy surface; the second harmonic is proportional to the square of this amplitude. Thus, for a slightly wavy surface, only the influence of the first harmonic can be detected. The natural-convection component is a second harmonic, with a frequency twice that of the wavy surface. Since natural convection has a cumulative effect, the second harmonic eventually becomes the dominant component far downstream from the leading edge where forced convection is the dominant heat transfer mode. The results also demonstrate that the total mixed-convection heat flux along a wavy surface is smaller than that of a flat surface.

Mixed Convection Transport From an Isolated Heat Source Module on a Horizontal Plate

1990 ◽  
Vol 112 (3) ◽  
pp. 653-661 ◽  
Author(s):  
B. H. Kang ◽  
Y. Jaluria ◽  
S. S. Tewari
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Finite Thickness ◽  
Forced Flow ◽  
Maximum Temperature ◽  
Convection Dominated

An experimental study of the mixed convective heat transfer from an isolated source of finite thickness, located on a horizontal surface in an externally induced forced flow, has been carried out. This problem is of particular interest in the cooling of electronic components and also in the thermal transport associated with various manufacturing systems, such as ovens and furnaces. The temperature distribution in the flow as well as the surface temperature variation are studied in detail. The dependence of the heat transfer rate on the mixed convection parameter and on the thickness of the heated element or source, particularly in the vicinity of the source, is investigated. The results obtained indicate that the heat transfer rate and fluid flow characteristics vary strongly with the mixed convection variables. The transition from a natural convection dominated flow to a forced convection dominated flow is studied experimentally and the basic characteristics of the two regimes determined. This transition has a strong influence on the temperature of the surface and on the heat transfer rate. As expected, the forced convection dominated flow is seen to be significantly more effective in the cooling of a heat dissipating component than a natural convection dominated flow. The location of the maximum temperature on the module surface, which corresponds to the minimum local heat transfer coefficient, is determined and discussed in terms of the underlying physical mechanisms. The results obtained are also compared with these for an element of negligible thickness and the effect of a significant module thickness on the transport is determined. Several other important aspects of fundamental and applied interest are studied in this investigation.

Bouyancy Effect on Forced Convection in Vertical Tubes at High Reynolds Numbers

2010 ◽  
Vol 2 (4) ◽  
Author(s):  
LiDong Huang ◽  
Kevin J. Farrell
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Flow Regime ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Buoyancy Effect ◽  
Vertical Tubes

The complex interaction of forced and natural convections depends on flow regime and flow direction. Aiding flow occurs when both driving forces act in the same direction (heating upflow fluid and cooling downflow fluid), opposing flow occurs when they act in different directions (cooling upflow fluid and heating downflow fluid). To evaluate mixed convection methods, Heat Transfer Research, Inc. (HTRI) recently collected water and propylene glycol data in two vertical tubes of different tube diameters. The data cover wide ranges of Reynolds, Grashof, and Prandtl numbers and differing ratios of heated tube length to diameter in laminar, transition, and turbulent forced flow regimes. In this paper, we focus the buoyancy effect on forced convection of single-phase flows in vertical tubes with Reynolds numbers higher than 2000. Using HTRI data and experimental data in literature, we demonstrate that natural convection can greatly increase or decrease the convective heat transfer coefficient. In addition, we establish that natural convection should not be neglected if the Richardson number is higher than 0.01 or the mixed turbulent parameter Ra1/3/(Re0.8 Pr0.4) is higher than 0.05 even in forced turbulent flow with Reynolds numbers greater than 10,000. High resolution Reynolds-averaged Navier–Stokes simulations of several experimental conditions confirm the importance of the buoyancy effect on the production of turbulence kinetic energy. We also determine that flow regime maps are required to predict the mixed convection heat transfer coefficient accurately.

scholarly journals Investigation of the effect of different materials on convective heat transfer

2020 ◽  
Vol 14 (2) ◽  
pp. 6642-6651
Author(s):  
Abdulwehab Ibrahim ◽  
Perk Lin Chong ◽  
Vicnesvaran Rajasekharan ◽  
Mohamed Muzuhin Ali ◽  
Omar Suliman Zaroong ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Cast Iron ◽  
Natural Convection ◽  
Flat Plate ◽  
Forced Convection ◽  
Air Flow ◽  
Convection Heat Transfer ◽  
Simulation Software ◽  
Convection Flow ◽  
Flow Temperature

Conventionally, the study of convection heat transfer merely focuses on the behavior of air flow without considering the conductive effect of the horizontal flat plate. However, it is expected that the conductive effect of the horizontal plate somewhat affects the air flow temperature across the flat plate. Therefore, it is motivated to study the variation of air flow temperature across different materials of flat plate in various time frame. The materials used in this study are aluminium, stainless steel and cast iron. Infrared camera and FloEFD simulation software are used to measure the upper surface temperature of the flat plate. For forced convection, the study is carried out within the range of 103 £ Re £ 104 and within the range of 1 × 107 £ Ra < 2.2 × 107 for natural convection. Flow velocity of 2.3 m/s, 4.1 m/s and 5.2 m/s are used for the forced convection. The results showed that aluminium plate cools down faster than the other two metal plates used in all scenarios. Stainless steel’s temperature goes down faster compared to cast iron. These results were supported by the fact that aluminium has higher heat transfer rate of other metals. For forced convection, the discrepancies of temperatures between experimental and simulation studies are below 10%, which demonstrates that the results are reasonably acceptable. For natural convection, even though the discrepancies between simulation and experimental results on temperature variations are relatively large, the temperatures varied in similar pattern. This indicates that the results are reliable.

scholarly journals EXPERIMENTAL STUDY OF HEAT TRANSFER OF A SINGLE-ROW BUNDLE OF FINNED TUBES IN MIXED CONVECTION OF AIR

2017 ◽  
Vol 60 (4) ◽  
pp. 352-366 ◽  
Author(s):  
A. B. Sukhotskii ◽  
G. S. Sidorik
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Free Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Convection Flow ◽  
Single Bundle ◽  
Single Row

The technique and results of experimental study of heat transfer of a single bundle consisting of bimetallic tubes with helically knurled edges, in natural and mixed convection of air are presented. Mixed convection, i.e. a heat transfer, when the contribution of free and forced convection is comparable, was created with the help of the exhaust shaft mounted above the heat exchanger bundle and forced air movement was created by the difference in density of the air in the shaft and the environment. The experimental dependence of the heat transfer of finned single row of bundles in the selected ranges of Grashof and Reynolds numbers has been determined. It is demonstrated that heat transfer in the mixed convection is 2.5−3 times higher than in free one and the growth rate of heat transfer with increasing Reynolds number is more than in the forced convection. Different forms of representation of results of experiments were analyzed and it was determined that the Nusselt number has a single power dependence on the Reynolds number at any height of the exhaust shafts. A linear dependence of the Reynolds number on the square root of the Grashof number was determined as well as the proportionality factors for different shaft heights. It is noted that the characteristics of the motion of air particles in the bundle in free convection is identical to the motion of particles in forced convection at small Reynolds numbers, i.e. a free convection flow smoothly flows into a forced convection one without the typical failures or surges if additional driving forces arise.

Laminar Mixed Convection of Cold Water in a Vertical Annulus With a Heated Rotating Inner Cylinder

1992 ◽  
Vol 114 (2) ◽  
pp. 418-424 ◽  
Author(s):  
C. J. Ho ◽  
F. J. Tu
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Cold Water ◽  
Convection Heat Transfer ◽  
Axial Rotation ◽  
Convection Heat ◽  
Density Inversion ◽  
Vertical Annulus

A numerical investigation is made to evaluate the perturbing effect of forced convection due to axial rotation of the inner cylinder on natural convection heat transfer of cold water with density inversion effects in a vertical cylindrical annulus. The mixed convection heat and fluid flow structures in the annulus are found to be strongly affected by the density inversion effects. The centrifugally forced convection can result in significant enhancement of the buoyant convection heat transfer of cold water with the density inversion parameter being equal to 0.4 or 0.5; thus the slow axial rotation of the inner cylinder can be a viable means for heat transfer augmentation of cold water natural convection in a vertical annulus.

Numerical Simulations of Natural Convection With Radiation in an Open Cavity Containing a Conducting and Centered Solid Body

2014 ◽  
Author(s):  
A. Lugarini de Souza ◽  
A. T. Franco ◽  
S. L. M. Junqueira ◽  
J. L. Lage
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Solid Body ◽  
Radiation Effects ◽  
Radiation Heat Transfer ◽  
Block Size ◽  
Heat Transfer Process ◽  
Open Cavity ◽  
Convection Flow ◽  
Solid Block

Although of relevance to a variety of engineering applications, the study of natural convection within an open cavity containing a conducting solid body is rarely found in the literature. Moreover, previous studies have pointed out that radiation heat transfer rates are at least of the same order of the laminar natural convection rates in cavities, making the inclusion of radiation effects and important step toward obtaining more realistic and practical results. The present study considers then a square cavity, with one wall heated and the other opened to an adjacent fluid reservoir, having a square conducting solid block centered in it and accounting for natural convection and radiation effects. Notice, for a large block size, the geometric configuration of the resulting flow channel is similar to that of a fracture along a reservoir wall. The resulting natural convection flow is simulated numerically for performing a nondimensional parametric study seeking to unveil the effects of block dimension, surface emissivity and Rayleigh number into the heat transfer process. The cavity filling fluid is assumed to have constant and uniform properties, as is the solid block, and the fluid-to-solid conductivity ratio is set as unity in the present study. The screening (radiation) effect caused by the presence of the solid block is discussed, as well as the convective and radiative drop phenomena. The convection and radiation Nusselt numbers are evaluated and compared for each simulated case.

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