Developing upward flow in a uniformly heated circular duct under transitional mixed convection

2006 ◽  
Vol 45 (9) ◽  
pp. 932-937 ◽  
Author(s):  
Walter Grassi ◽  
Daniele Testi
Keyword(s):  
Mixed Convection ◽  
Upward Flow ◽  
Circular Duct

Developing 3-D turbulent mixed convection in a circular duct inserted with longitudinal strips

2001 ◽  
Vol 39 (12) ◽  
pp. 1327-1350 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Liang-Cheng Chang ◽  
Tsung-Ying Yang
Keyword(s):  
Mixed Convection ◽  
Circular Duct

Characterisation of Flow and Heat Transfer Regimes in Various Horizontal Ducts Submitted to Mixed Convection

2006 ◽  
Author(s):  
C. Abid ◽  
M. Medale ◽  
F. Koffi ◽  
F. Papini ◽  
A. Benderradji
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Mixed Convection ◽  
Thermal Gradient ◽  
Thermal Instability ◽  
Vertical Gradient ◽  
Working Fluid ◽  
Circular Duct ◽  
Flow And Heat Transfer ◽  
Wide Range

The emphasis of this communication is to make a synthesis of several results we have obtained in various mixed convection configurations. This study has been conducted for circular or rectangular ducts submitted to different ways of heating (vertical or horizontal thermal gradient in the rectangular case and combined vertical and horizontal in the circular case). The bibliography is rather poor for mixed convection in liquids, so the chosen working fluid used here is water. Moreover, a wide range of forced fluid flow and heat flux rates has been considered spreading from laminar to turbulent flow. The characterization of fluid flow and heat transfer regimes is based on temporal recording of temperature measurements obtained in several locations by means of thermocouples or infrared thermography. The analysis of these temperature signals highlights several regimes depending on control parameters. The flow structure in the cases of uniformly heated circular duct and the rectangular one heated from below is constituted of two longitudinal rolls and we notice only one roll in the case of the rectangular duct submitted to the horizontal thermal gradient. For low Reynolds and Rayleigh Numbers, the behavior of all these configurations is stable, however the increasing of these parameters induces thermal instability in the case of circular and rectangular ducts heated from below. That means that the thermal vertical gradient is responsible of the occurring of the thermal instability. This result shows that the horizontal thermal gradient is a stabilizing gradient while the vertical one is a destabilizing one. As this instability enhances heat transfer, it will be very helpful to characterize and to identify the domain where it is occurring in order to prevent or to provoke it depending on the expected performance of the heat exchanger. In this paper, we propose to establish a diagram showing the domain of occurrence of this instability for the various cases cited above and to describe the fluid flow and heat transfer associated to these configurations.

Heat Transfer to Supercritical Water in Gaseous State or Affected by Mixed Convection in Vertical Tubes

2006 ◽  
Author(s):  
E. N. Pis’menny ◽  
V. G. Razumovskiy ◽  
E. M. Maevskiy ◽  
A. E. Koloskov ◽  
I. L. Pioro
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Supercritical Water ◽  
Operating Conditions ◽  
Maximum Effect ◽  
Upward Flow ◽  
Downward Flow ◽  
Gaseous State ◽  
Transfer Data ◽  
Vertical Tubes

The results on heat transfer to supercritical water heated above the pseudocritical temperature or affected by mixed convection flowing upward and downward in vertical tubes of 6.28-mm and 9.50-mm inside diameter are presented. Supercritical water heat-transfer data were obtained at a pressure of 23.5 MPa, mass flux within the range from 250 to 2200 kg/(m2s), inlet temperature from 100 to 415°C and heat flux up to 3.2 MW/m2. Temperature regimes of the tubes cooled with supercritical water in a gaseous state (i.e., supercritical water at temperatures beyond the pseudocritical temperature) were stable and easily reproducible within a wide range of mass and heat fluxes. An analysis of the heat-transfer data for upward and downward flows enabled to determine a range of Gr/Re2 values corresponding to the maximum effect of free convection on the heat transfer. It was shown that: 1) the heat transfer coefficient at the downward flow of water can be higher by about 50% compared to that of the upward flow; and 2) the deteriorated heat-transfer regime is affected with the flow direction, i.e., at the same operating conditions, the deteriorated heat transfer may be delayed at the downward flow compared to that at the upward flow. These heat-transfer data are applicable as the reference dataset for future comparison with bundle data.

scholarly journals Combined Thermal Radiation and Mixed Convection in an Inclined Circular Duct

2009 ◽  
Vol 2 (4) ◽  
pp. 590-602 ◽  
Author(s):  
W. Lakhal ◽  
S. Trabelsi ◽  
E. Sediki ◽  
M. Moussa
Keyword(s):  
Mixed Convection ◽  
Thermal Radiation ◽  
Circular Duct

Gas-Liquid Bubbly Turbulent Upward Flow in Square Duct

2012 ◽  
Author(s):  
HaoMin Sun ◽  
Tomoaki Kunugi ◽  
DaZhuan Wu ◽  
HongNa Zhang ◽  
Hideo Nakamura ◽  
...  
Keyword(s):  
Cross Section ◽  
Bubble Size ◽  
High Speed ◽  
Liquid Velocity ◽  
Video Camera ◽  
Wall Region ◽  
Upward Flow ◽  
Two Phase ◽  
Square Duct ◽  
Circular Duct

As for the turbulent two-phase flow in the non-circular duct, the flow could show an anisotropic turbulence feature in liquid phase. In this study, the air-water bubbly turbulent upward flow experiment in the large square duct with the inside cross-section of 136mm×136mm has been conducted. Since the bubble size is very important for air-water bubbly flows, the bubble generating method was improved to get more uniform bubble size. After confirming the flow symmetry in the measuring cross-section, the distributions of local void fraction, bubble frequency and primary liquid velocity were measured by a hot-film anemometry, and the bubble behaviors were also investigated by using the high-speed video camera. The results show that the bubbles tend to accumulate to the wall region, where the liquid primary velocity shows the maximum especially at the corner.

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