Heat Transfer in Air Enclosures of Aspect Ratio Less than One

1981 ◽  
Vol 103 (4) ◽  
pp. 617-622 ◽  
Author(s):  
V. Sernas ◽  
E. I. Lee
Keyword(s):  
Heat Transfer ◽  
Vertical Wall ◽  
The Other ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Rates ◽  
Aspect Ratios ◽  
Vertical Walls ◽  
Adiabatic Boundary Condition ◽  
Better Than

The heat transfer rates inside rectangular air enclosures of aspect ratios between 0.1 and 1.0 were investigated interferometrically for a Grashof number range between 2.64 × 106 and 5.45 × 106. The enclosures were composed of dissimilar temperature vertical walls and two types of ceilings and floors. One type was made from constant temperature plates kept at the vertical wall temperatures, and the other type was made of low thermal conductivity polyurethane foam rubber. The heat transfer characteristics and flow patterns within these two types of enclosures were found to be significantly different. For aspect ratios between 0.4 and 1.0 the isothermal ceiling and floor approximate an adiabatic boundary condition much better than foam because much less heat was interchanged between the floor (or ceiling) and the air in the enclosure.

Numerical Analysis of Flow Structure and Heat Transfer Characteristics in Dimpled Channels With Secondary Protrusions

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Yonghui Xie ◽  
Zhongyang Shen ◽  
Di Zhang ◽  
Phillip Ligrani
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Analysis ◽  
Thermal Performance ◽  
The Other ◽  
Combination Effect ◽  
Enhancement Ratio ◽  
Heat Transfer Characteristics ◽  
Transfer Rates ◽  
Heat Transfer Augmentation

Dimple structure is an effective heat transfer augmentation approach on coolant channel due to its advantage on pressure penalty. The implication of secondary protrusion, which indicates protrusion with smaller dimension than dimple, will intensify the Nusselt number Nu inside dimple cavity without obvious extra pressure penalty. The objective of this study is to numerically analyze the combination effect of dimples and secondary protrusion. Different protrusion–dimple configurations including protrusion print-diameter Dp, protrusion–dimple gap P, and staggered angle α are investigated. From the results, it is concluded that the implication of secondary protrusion will considerably increase the heat transfer rates inside dimple cavity. Cases 4 and 6 possess the highest Nusselt number enhancement ratio Nu/Nu0 reaching up to 2.1–2.2. The additional pressure penalty brought by the protrusion is within 15% resulting in total friction ratio f/f0 among the range of 1.9–2.1. Dimpled channels with secondary protrusions possess higher thermal performance factor TP, defined as (Nu/Nu0)/(f/f0)1/3, among which cases 4 and 6 are the optimal structures. Besides this, the TP of protrusion–dimple channels are comparable to the other typical heat transfer devices, and higher TP can be speculated after a more optimal dimple shape or combination with ribs and fins.

Maximizing Heat Transfer Through Joint Fin Systems

2005 ◽  
Vol 128 (2) ◽  
pp. 203-206 ◽  
Author(s):  
A.-R. A. Khaled
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Performance ◽  
Critical Length ◽  
The Other ◽  
Rigid Fixation ◽  
Convection Coefficient ◽  
Heat Transfer Characteristics ◽  
Cold Side ◽  
Transfer Characteristics

Heat transfer through joint fins is modeled and analyzed analytically in this work. The terminology “joint fin systems” is used to refer to extending surfaces that are exposed to two different convective media from its both ends. It is found that heat transfer through joint fins is maximized at certain critical lengths of each portion (the receiver fin portion which faces the hot side and the sender fin portion that faces the cold side of the convective media). The critical length of each portion of joint fins is increased as the convection coefficient of the other fin portion increases. At a certain value of the thermal conductivity of the sender fin portion, the critical length for the receiver fin portion may be reduced while heat transfer is maximized. This value depends on the convection coefficient for both fin portions. Thermal performance of joint fins is increased as both thermal conductivity of the sender fin portion or its convection coefficient increases. This work shows that the design of machine components such as bolts, screws, and others can be improved to achieve favorable heat transfer characteristics in addition to its main functions such as rigid fixation properties.

Heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity

2021 ◽  
pp. 095440622110272
Author(s):  
Salaika Parvin ◽  
Nepal Chandra Roy ◽  
Litan Kumar Saha ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Wide Range

A numerical study is performed to investigate nanofluids' flow field and heat transfer characteristics between the domain bounded by a square and a wavy cylinder. The left and right walls of the cavity are at constant low temperature while its other adjacent walls are insulated. The convective phenomena take place due to the higher temperature of the inner corrugated surface. Super elliptic functions are used to transform the governing equations of the classical rectangular enclosure into a system of equations valid for concentric cylinders. The resulting equations are solved iteratively with the implicit finite difference method. Parametric results are presented in terms of streamlines, isotherms, local and average Nusselt numbers for a wide range of scaled parameters such as nanoparticles concentration, Rayleigh number, and aspect ratio. Several correlations have been deduced at the inner and outer surface of the cylinders for the average Nusselt number, which gives a good agreement when compared against the numerical results. The strength of the streamlines increases significantly due to an increase in the aspect ratio of the inner cylinder and the Rayleigh number. As the concentration of nanoparticles increases, the average Nusselt number at the internal and external cylinders becomes stronger. In addition, the average Nusselt number for the entire Rayleigh number range gets enhanced when plotted against the volume fraction of the nanofluid.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

scholarly journals Effect of the size of graded baffles on the performance of channel heat exchangers

2020 ◽  
Vol 24 (2 Part A) ◽  
pp. 767-775 ◽  
Author(s):  
Djamel Sahel ◽  
Houari Ameur ◽  
Touhami Baki
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchangers ◽  
Computer Code ◽  
Channel Length ◽  
Heat Transfer Characteristics ◽  
Enhancement Of Heat Transfer ◽  
Transfer Rates ◽  
Flow And Heat Transfer ◽  
Friction Factors

The baffling technique is well-known for its efficiency in terms of enhancement of heat transfer rates throught channels. However, the baffles insert is accompanied by an increase in the friction factor. This issue remains a great challenge for the designers of heat exchangers. To overcome this issue, we suggest in the present paper a new design of baffles which is here called graded baffle-design. The baffles have an up- or down-graded height along the channel length. This geometry is characterized by two ratios: up-graded baffle ratio and down-graded baffle ratio which are varied from 0-0.08. For a range of Reynolds number varying from 104 to 2 ? 104, the turbulent flow and heat transfer characteristics of a heat exchanger channel are numerically studied by the computer code FLUENT. The obtained results revealed an enhancement in the thermohydraulic performance offered by the new suggested design. For the channel with a down-graded baffle ratio equal to 0.08, the friction factors decreased by 4-8%

The Effect of the Top Wall Temperature on the Laminar Natural Convection in Rectangular Cavities With Different Aspect Ratios

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
Wenjiang Wu ◽  
Chan Y. Ching
Keyword(s):  
Natural Convection ◽  
Aspect Ratio ◽  
Wall Temperature ◽  
Vertical Wall ◽  
Flow Region ◽  
Temperature Profiles ◽  
Aspect Ratios ◽  
Vertical Walls ◽  
C And N ◽  
Laminar Natural Convection

The effect of the top wall temperature on the laminar natural convection in air-filled rectangular cavities driven by a temperature difference across the vertical walls was investigated for three different aspect ratios of 0.5, 1.0, and 2.0. The temperature distributions along the heated vertical wall were measured, and the flow patterns in the cavities were visualized. The experiments were performed for a global Grashof number of approximately 1.8×108 and nondimensional top wall temperatures from 0.52 (insulated) to 1.42. As the top wall was heated, the flow separated from the top wall with an undulating flow region in the corner of the cavity, which resulted in a nonuniformity in the temperature profiles in this region. The location and extent of the undulation in the flow are primarily determined by the top wall temperature and nearly independent of the aspect ratio of the cavity. The local Nusselt number was correlated with the local Rayleigh number for all three cavities in the form of Nu=C⋅Ran, but the values of the constants C and n changed with the aspect ratio.

Simulation of time-dependent radiative heat motion over a stretching/shrinking sheet of hybrid Nanofluid: Stability analysis for dual solutions

2022 ◽  
pp. 239779142110690
Author(s):  
Seema Tinker ◽  
SR Mishra ◽  
PK Pattnaik ◽  
Ram Prakash Sharma
Keyword(s):  
Heat Transfer ◽  
Stability Analysis ◽  
Dual Solutions ◽  
The Other ◽  
Time Dependent ◽  
Shrinking Sheet ◽  
Hybrid Nanofluid ◽  
Heat Transfer Characteristics ◽  
Suction Parameter ◽  
Transfer Characteristics

The heat transfer characteristics for the flow of a time-dependent hybrid nanofluid with thermal radiation and source/sink over a stretching/shrinking sheet are examined in the current investigation. We have transformed the governing equations of the presented study into the similarity equations utilizing similarity variables. However, a numerical solution is obtained by using in-build MATLAB code bvp5c. The mass and energy profiles for diverse values of thermophysical parameters are studied together with their physical quantities. It is observed that dual solutions exist, that is, one is upper, and the other is lower branch solution for a definite choice of the unsteadiness parameter. Also, stability analysis is executed to determine the long-term stability of dual solutions, indicating that out of the two, only one is stable and the other is unstable. It is revealed that comparatively, the first solution shows stability, while the second solution shows instability. There is a considerable influence of second-order slip on the problem’s respective flow and heat transfer characteristics. Further, major outcomes also show the dimensionless frictional stress and the magnitude of conventional heat transfer enhancement with growing suction parameter values.

Numerical Study of Droplet Evaporation in a High-Temperature Stream

1983 ◽  
Vol 105 (2) ◽  
pp. 389-397 ◽  
Author(s):  
M. Renksizbulut ◽  
M. C. Yuen
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Number Range ◽  
Transfer Rates ◽  
Pressure Drag ◽  
Continuity Equations ◽  
Stream Density ◽  
Solid Spheres

Numerical solutions for high-temperature air flowing past water and methanol droplets and solid spheres, and superheated steam flowing past water droplets were obtained in the Reynolds number range of 10 to 100. The coupled momentum, energy, and specie continuity equations of variable thermophysical properties were solved using finite difference techniques. The numerical results of heat transfer and total drag agree well with existing experimental data. Mass transfer decreases friction drag significantly but at the same time increases pressure drag by almost an equal amount. The net effect is that the standard drag curve for solid spheres can be used for evaporating droplets provided the density is the free stream density and the viscosity of the vapor mixture is evaluated at an appropriate reference temperature and concentration. Both the mass efflux and variable properties decrease heat transfer rates to the droplets.

Numerical Investigation of Impingement Heat Transfer on Concave- and Convex-Dimpled Plate With Different Dimple Arrangements

2016 ◽  
Author(s):  
Feng Zhang ◽  
Xinjun Wang ◽  
Jun Li ◽  
Rui Tan ◽  
Dongliang Wei
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Pressure Loss ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Impingement Cooling ◽  
Transfer Characteristics

The present numerical study is conducted to investigate the flow and heat transfer characteristics for impingement cooling on concave or convex dimpled plate with four different dimple arrangements. The investigation of the impingement cooling on the flat plate is also conducted to serve as a contrast and these results are compared with experimental measurements to verify the computational method. Dimples studied here are placed, relative to impingement holes, in either spanwise shifted, in staggered, in in-line, or in streamwise shifted arrangements. The flow structure, pressure loss and heat transfer characteristics of the concave and convex dimpled plate of four different dimple arrangements have been obtained and compared with flat plate for the Reynolds number range of 15000 to 35000. The results show that compared with flat plate, the added concave or convex dimples only causes a negligible increase in the pressure loss, and the pressure loss is insensitive to concave or convex dimple arrangement patterns. In addition, compared with flat plate, both spanwise shifted and staggered concave dimple arrangements show better heat transfer performance, while in-line concave dimple arrangement show worse results. Besides that, the heat transfer performance for streamwise shifted concave dimple arrangement is the worst. Furthermore, compared with flat plate, all convex dimple arrangements studied here show better heat transfer performance.

Experimental Study of Droplet Evaporation in a High-Temperature Air Stream

1983 ◽  
Vol 105 (2) ◽  
pp. 384-388 ◽  
Author(s):  
M. Renksizbulut ◽  
M. C. Yuen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Liquid Droplets ◽  
Transfer Number ◽  
Number Range ◽  
Transfer Rates ◽  
Hot Air ◽  
Air Stream ◽  
Stream Density ◽  
Freely Suspended

Heat transfer rates to simulated and freely suspended liquid droplets were measured in an atmospheric hot air tunnel. The experiments were limited to water, methanol, and heptane droplets in a Reynolds number range of 25 to 2000, and a mass transfer number range of 0.07 to 2.79. The present experimental data together with data by others can best be correlated by Nuf(1+Bf).7 = 2 + 0.57 ReM1/2 Prf1/3, where properties are evaluated at film conditions except for the density in the Reynolds number which is the free-stream density. Thus the data shows that at higher temperatures, evaporation reduces heat transfer rates directly by a factor of (1 + Bf).7. Indirectly, evaporation affects heat transfer rates through the changes in both the composition and temperature of the surrounding gaseous medium.

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