Simultaneous Determination of Reference Free-Stream Temperature and Convective Heat Transfer Coefficients

2002 ◽  
Vol 26 (12) ◽  
pp. 1707-1714
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Simultaneous Determination ◽  
Convective Heat ◽  
Free Stream ◽  
Stream Temperature ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

scholarly journals EXPERIMENTAL DETERMINATION OF CONVECTIVE HEAT TRANSFER COEFFICIENTS IN THERMAL BUOYACY VENTILATION SYSTEM

2019 ◽  
Vol 45 (4) ◽  
pp. 133-141
Author(s):  
D. V. Abramkina ◽  
A. A. Abramyan ◽  
E. R. Shevchenko-Enns
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Experimental Determination ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Internal Problem ◽  
Convective Heat Transfer Coefficients

Objectives. The main goal of the article is to present the developed method for the experimental determination of convective heat transfer coefficients, suitable for studying the internal convection of models of complex configuration. Method. The study of free convection under the conditions of an internal problem was carried out by determining the conditional thickness of the boundary layer by a graphic method. The first was the selection of the calculated sections and planes for the experimental installation. The selection is carried out in such a way that the calculated planes are perpendicular to the heated walls of the channel in question. Installation of an experimental model is possible only in a room with low internal air mobility, as well as a stable temperature. In this room there should not be heating and heating devices that can create strong convective currents near the channel of the experimental installation. Result. The article presents the results of an experimental study to determine the temperature distribution of the air flow and average convective heat transfer coefficients over the height of the ventilation channel. A decrease in convective heat transfer coefficients at an altitude of 0.5 to 1 meter occurs less noticeably than at an altitude of 1 to 2 meters, which is associated with the restoration of flow after a vent removal. At the stabilization section, there is first a gradual decrease, and then an increase in axial velocity, which is caused by the merging of multidirectional air flows in this area. Conclusion. It was revealed that in the case of modeling free convection under the conditions of an internal problem in the presence of heat-removing boundaries  within the limits of the calculated temperature difference, taking into account the flow turbulization has practically no effect on the final results.

Guidelines for the Determination of Single-Phase Forced Convection Coefficients in Microchannels

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Gian Luca Morini ◽  
Yahui Yang
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
A Priori ◽  
Experimental Results ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Main Effects ◽  
Convective Heat Transfer Coefficients

This paper deals with the analysis of the main features of forced microconvection of liquid and gas flows through microchannels. A critical overview of the main effects that tends to play an important role in the determination of Nusselt number in microchannels is presented. Some experimental data obtained at the Microfluidics Lab of the University of Bologna together with the main results which appeared recently in the open literature both for liquids and gases are used in order to highlight the peculiar characteristics of the convective heat transfer through microchannels and to suggest the guidelines for a physically based interpretation to the experimental results. By means of specific examples, it is shown that the thermal behavior at microscale of gas and liquid flows through microchannels in terms of convective heat transfer coefficients can be strongly affected by scaling and micro-effects but also by practical issues linked to the geometry of the test rig, the real thermal boundary conditions, the presence of fittings, position and type of the sensors, and so on. All these aspects have to be taken into account during the data post processing in order to obtain a correct evaluation of the Nusselt numbers. It is also highlighted how it is always useful to couple to the experimental approach a complete computational thermal fluid-dynamics analysis of the whole tested microsystem in order to be able to recognize “a priori” the main effects which can play an important role on the convective heat transfer analysis. It is demonstrated in this paper that this “a priori” analysis is crucial in order to: (i) individuate the main parameters which influence the convective heat transfer coefficients (this is important for the development of new correlations); (ii) compare in a right way the conventional correlations with the experimental results.

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