Microflow Heat Transfer Effectiveness: Questioning the “Area/Volume-Argument”

2011 ◽  
Author(s):  
Heinz Herwig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Steady State ◽  
Thermal Boundary Layer ◽  
Heat Transfer Performance ◽  
Characteristic Length ◽  
Transfer Performance ◽  
Layer Behavior ◽  
Steady State Heat ◽  
Steady State Heat Transfer

The often used argument that heat transfer in micro-sized devices is superior due to the fact that the transfer area scales like L2 but the volume like L3 with L as a characteristic length is critically analyzed for various heat transfer situations. It turns out that for steady state heat transfer cases the thermal boundary layer behavior is more important. In general, dimensional analysis should be applied to understand how the heat transfer performance changes when scales are reduced from macro- to micro-size.

scholarly journals Evaluation model of the steady-state heat transfer performance of two-phase closed thermosyphons

2021 ◽  
pp. 166-166
Author(s):  
Yafeng Wu ◽  
Zhe Zhang ◽  
Wenbin Li ◽  
Daochun Xu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Steady State ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Two Phase ◽  
Equivalent Thermal Conductivity ◽  
State Heat ◽  
Steady State Heat ◽  
Steady State Heat Transfer

Two-phase closed thermosyphons have good thermal conductivity and are widely used in heat transfer applications. It is essential to establish an effective method for evaluating the steady-state heat transfer performance of two-phase closed thermosyphons, as such a method can help to select appropriate designs and to improve the efficiency of these devices. In this paper, the equivalent thermal conductivity is derived by the principle of equal total thermal resistance, in which the influence of the adiabatic length is eliminated. An evaluation model of the steady-state heat transfer performance of two-phase closed thermosyphons is established. Test results of three two-phase closed thermosyphons with total lengths of 220 mm, 320 mm and 500 mm show that as the heat transfer rate increases, the equivalent thermal conductivity of these devices decreases by 28.91%, increases by 6.10% and increases by 10.02%, respectively, among which the minimum value is 831.63 W?m-1?K-1and the maximum value is 1694.19 W?m-1?K-1. The decrease (increase) in the equivalent thermal conductivity in the evaluation model indicates a decrease (increase) in the heat transfer performance. The results show that the equivalent thermal conductivity of the model can effectively evaluate the heat transfer performance of two-phase closed thermosyphons.

scholarly journals Effect of the Inclination Angle on the Steady-State Heat Transfer Performance of a Thermosyphon

2019 ◽  
Vol 9 (16) ◽  
pp. 3324
Author(s):  
Wu ◽  
Zhang ◽  
Li ◽  
Xu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Resistance ◽  
Inclination Angle ◽  
Heat Transfer Performance ◽  
Heat Transfer Process ◽  
Transfer Performance ◽  
Steady State Heat ◽  
Predicted Values ◽  
Steady State Heat Transfer

A two-phase closed thermosyphon is an efficient heat transfer element. The heat transfer process of this type of thermosyphon includes conduction and convective heat transfer accompanied by phase changes. Variations in the inclination angle of a thermosyphon affect the steady-state heat transfer performance of the device. Therefore, the inclination angle is an important factor affecting the performance of a thermosyphon. In this paper, an equation for the actual heating area variations with respect to the inclination angle is deduced, and a model for the areal thermal resistance of a thermosyphon is proposed by analyzing the main influence mechanisms of the inclination angle on the heat transfer process. The experimental results show that the areal thermal resistance, which accounts for the effect of the actual heating area, does not change with respect to the inclination angle and exhibits a linear relationship with the heat transfer rate. The thermal resistance equation is fit according to the experimental data when the inclination angle of the thermosyphon is vertically oriented (90°), and the predicted values of the thermosyphon’s thermal resistance are obtained when the thermosyphon is inclined. The deviations between the experimental data and predicted values are less than ±0.05. Therefore, the theoretical equation can accurately predict the thermosyphon’s thermal resistance at different inclination angles.

Nonuniqueness in Steady-State Heat Transfer in Prestressed Duplex Tubes—Analysis and Case History

1985 ◽  
Vol 52 (2) ◽  
pp. 257-262 ◽  
Author(s):  
M. G. Srinivasan ◽  
D. M. France
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Heat Transfer Performance ◽  
Steady State Solution ◽  
State Solution ◽  
Multiple Steady State ◽  
State Heat ◽  
Steady State Heat ◽  
Steady State Heat Transfer ◽  
Generating System

More than one steady-state solution is shown to exist for the problem of steady-state heat transfer across the walls of a duplex tube when the initial prestress between the inner and outer tubes is sufficiently low. This determination was used in explaining the apparently erratic heat-transfer performance of prestressed duplex tubes in the steam generating system of the Experimental Breeder Reactor II. The importance of the results lies not only in showing that nonuniqueness of steady-state solution applies to more complex geometries than heretofore analyzed, but also in demonstrating that such multiple steady-state conditions appear in practical situations.

An Investigation of the Effect of interrupted fin arrangements on the Thermal Performance of a Heat Sink under a Free Convection Condition

2019 ◽  
Vol 7 (1) ◽  
pp. 43-53
Author(s):  
Abbas Jassem Jubear ◽  
Ali Hameed Abd
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Convection ◽  
Thermal Performance ◽  
Heat Sink ◽  
Numerical Study ◽  
Ansys Fluent ◽  
Fluent Software ◽  
Steady State Heat ◽  
Steady State Heat Transfer

The heat sink with vertically rectangular interrupted fins was investigated numerically in a natural convection field, with steady-state heat transfer. A numerical study has been conducted using ANSYS Fluent software (R16.1) in order to develop a 3-D numerical model.  The dimensions of the fins are (305 mm length, 100 mm width, 17 mm height, and 9.5 mm space between fins. The number of fins used on the surface is eight. In this study, the heat input was used as follows: 20, 40, 60, 80, 100, and 120 watts. This study focused on interrupted rectangular fins with a different arrangement and angle of the fins. Results show that the addition of interruption in fins in various arrangements will improve the thermal performance of the heat sink, and through the results, a better interruption rate as an equation can be obtained.

Steady State Heat Transfer in the Left Ventricle

1983 ◽  
pp. 623-648 ◽  
Author(s):  
B. H. Smaill ◽  
J. Douglas ◽  
P. J. Hunter ◽  
I. Anderson
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Left Ventricle ◽  
State Heat ◽  
Steady State Heat ◽  
Steady State Heat Transfer
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