Paper 8: Heat Transfer from a Wire in the Critical Region

1967 ◽  
Vol 182 (9) ◽  
pp. 52-57 ◽  
Author(s):  
U. Grigull ◽  
E. Abadzic
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Natural Convection ◽  
Critical Point ◽  
Critical Region ◽  
High Speed ◽  
Nucleate Boiling ◽  
Flow Patterns ◽  
Film Boiling ◽  
High Speed Camera

This work deals with experimental results on boiling from a horizontal platinum wire, 0·1 mm in diameter, submerged in saturated liquids as carbon dioxide (CO2) and Freon 13 (CF3Cl) in the critical region. Three discrete regimes without steady transition could be observed: natural convection, nucleate boiling, and film boiling. Near the critical point particular flow patterns appeared in the rising vapour in film boiling: regular bubbles, vapour columns, and vapour hazes with garland-like boundaries. These flow patterns could be simulated in model experiments with liquids and were also photographed with a high-speed camera.

The Effect of Density Variation on Heat Transfer in the Critical Region

1961 ◽  
Vol 83 (2) ◽  
pp. 176-181 ◽  
Author(s):  
Yih-Yun Hsu ◽  
J. M. Smith
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Critical Point ◽  
Critical Region ◽  
Large Density ◽  
The Heat Transfer Coefficient

The heat-transfer coefficient between fluid and tube wall in turbulent flow depends upon the physical and thermal properties of the fluid. When density changes across the diameter of the tube are large (for example, when the fluid is near the critical point), the variable density can affect the transfer of momentum and heat. Equations are developed for predicting the magnitude of this effect on the heat-transfer coefficient. Deissler’s [5] expressions for the eddy diffusivity are employed in solving the equations for heat and momentum transfer. For flow in vertical tubes large density variations can also affect the heat transfer by inducing natural convection. By considering the influence of body forces on the shear stress, equations are derived to predict the effect of natural convection on the heat-transfer coefficient for turbulent flow. The results indicate that the effect is significant only for relatively high Grashof numbers and low Reynolds numbers. Such conditions may be encountered in flow of a fluid near its thermodynamic critical point. The derived equations are applied for carbon dioxide flow in the critical region under the conditions for which experimental data were measured by Bringer and Smith [2]. Because of the high Reynolds and low Grashof numbers, natural convection is not significant. However, the effect of the large density variations is found to be significant, and the predicted results agree well with the experimental data.

Wave Theory of Heat Transfer in Film Boiling

1959 ◽  
Vol 81 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Yan Po Chang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Diffusivity ◽  
Prandtl Number ◽  
General Formula ◽  
Wave Theory ◽  
Nucleate Boiling ◽  
Film Boiling

This paper is an extension of a previous one [1] in which heat transfer has been analyzed by the wave theory for natural convection and for nucleate boiling in detail and for film boiling in principle. In the present paper, heat transfer in saturated and subcooled film boiling from horizontal and vertical surfaces is analyzed from the viewpoint of the previously presented idea. By means of the concept of equivalent thermal diffusivity a generalized Prandtl number is recommended. Thus a general formula is obtained for both convection and boiling. The predicted results agree well with the experiments of previous investigators.

scholarly journals CHF Phenomena by Photographic Study of Boiling Behavior due to Transient Heat Inputs

2012 ◽  
Vol 2012 ◽  
pp. 1-12 ◽  
Author(s):  
Jongdoc Park ◽  
Katsuya Fukuda ◽  
Qiusheng Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Video Camera ◽  
Nucleate Boiling ◽  
Horizontal Cylinder ◽  
Heat Transfer Process ◽  
Film Boiling ◽  
Bubble Behavior ◽  
Camera System

The transient boiling heat transfer characteristics in a pool of water and highly wetting liquids such as ethanol and FC-72 due to an exponentially increasing heat input of various rates were investigated using the 1.0 mm diameter experimental heater shaped in a horizontal cylinder for wide ranges of pressure and subcooling. The trend of critical heat flux (CHF) values in relation to the periods was divided into three groups. The CHF belonging to the 1st group with a longer period occurs with a fully developed nucleate boiling (FDNB) heat transfer process. For the 2nd group with shorter periods, the direct transition to film boiling from non boiling occurs as an explosive boiling. The direct boiling transition at the CHF from non-boiling regime to film boiling occurred without a heat flux increase. It was confirmed that the initial boiling behavior is significantly affected by the property and the wettability of the liquid. The photographic observations on the vapor bubble behavior during transitions to film boiling were performed using a high-speed video camera system.

The Effects of Nucleate Boiling Versus Film Boiling on Heat Transfer in Power Boiler Tubes

1962 ◽  
Vol 84 (4) ◽  
pp. 365-371 ◽  
Author(s):  
H. S. Swenson ◽  
J. R. Carver ◽  
G. Szoeke
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Inside Surface ◽  
Film Boiling ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Heat Transfer Coefficients

In large, subcritical pressure, once-through power boilers heat is transferred to steam and water mixtures ranging in steam quality from zero per cent at the bottom of the furnace to 100 per cent at the top. In order to provide design information for this type of boiler, heat-transfer coefficients for forced convection film boiling were determined for water at 3000 psia flowing upward in a vertical stainless-steel tube, AISI Type 304, having an inside diameter of 0.408 inches and a heated length of 6 feet. Heat fluxes ranged between 90,000 and 180,000 Btu/hr-sq ft and were obtained by electrical resistance heating of the tube. The operation of the experimental equipment was controlled so that nucleate boiling, transition boiling, and stable film boiling occurred simultaneously in different zones of the tube. The film boiling data were correlated with a modified form of the equation Nu = a a(Re)m(Pr)n using steam properties evaluated at inside surface temperature. Results of a second series of heat-transfer tests with tubes having a helical rib on the inside surface showed that nucleate boiling could be maintained to much higher steam qualities with that type of tube than with a smooth-bore tube.

Predicting heat extraction due to boiling in the cooling channels during the pressure die casting process

2000 ◽  
Vol 214 (3) ◽  
pp. 465-482 ◽  
Author(s):  
L D Clark ◽  
I Rosindale ◽  
K Davey ◽  
S Hinduja ◽  
P J Dooling
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Die Casting ◽  
Casting Process ◽  
Nucleate Boiling ◽  
Heat Extraction ◽  
Film Boiling ◽  
Cooling Channels ◽  
Die Casting Process ◽  
Pressure Die Casting

The effect of boiling on the rate of heat extraction by cooling channels employed in pressure die casting dies is investigated. The cooling effect of the channels is simulated using a model that accounts for subcooled nucleate boiling and transitional film boiling as well as forced convection. The boiling model provides a continuous relationship between the rate of heat transfer and temperature, and can be applied to surfaces where forced convection, subcooled nucleate boiling and transitional film boiling are taking place in close proximity. The effects of physical parameters such as flow velocity, degree of subcooling, system pressure and bulk temperature are taken into account. Experimental results are obtained using a rig that simulates the pressure die casting process. The results are compared with the model predictions and are found to show good agreement. Instrumented field tests, on an industrial die casting machine, are also reported. These tests show the beneficial effects of boiling heat transfer in the pressure die casting process, including a 75 per cent increase in the production rate for the test component.

Investigation of Hydrodynamics and Heat Transfer Effects due to Light Guides in a Column Photobioreactor

2013 ◽  
Author(s):  
Caitlin Gerdes ◽  
Taylor N. Suess ◽  
Gary A. Anderson ◽  
Stephen P. Gent
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Mass Transfer ◽  
Temperature Distribution ◽  
Light Guide ◽  
Flow Patterns ◽  
Light Penetration ◽  
Algae Growth ◽  
Computational Fluid Dynamics Cfd ◽  
Light Guides

Proper light penetration is an essential design consideration for effective algae growth in column photobioreactors. This research focuses on the placement of light guides within a photobioreactor (PBR), and the effect they have on heat transfer, mass transfer, bubble and fluid flow patterns, and mixing. Studies have been done on a rectangular column photobioreactor (34.29 cm long × 15.25 cm wide × 34.29 cm tall) with two light panels along the front and back of the PBR. A bubble sparger is placed along the center of the bottom length of the PBR with both height and width of 1.27 cm and a length of 33.02 cm. Different configurations and numbers of light guides (1.27 cm diameter) running horizontally from the front to the back of the PBR are modeled using the Computational Fluid Dynamics (CFD) software Star-CCM+. It is hypothesized that the addition of light guides will change the flow pattern but not adversely affect the heat or mass transfer of the carbon dioxide bubbles within the PBR. Potential concerns of light guide placement include inhibiting the flow of the carbon dioxide bubbles or creating regions of high temperature, which could potentially kill the algae. Benefits of light guides include increased light penetration and photosynthesis within the PBR. Five different light guide setups are tested with the carbon dioxide bubbles and water modeled as a turbulent multiphase gas-liquid mixture. The near wall standard k-epsilon two layer turbulence model was used, as it takes into account the viscosity influences between the liquid and gaseous phases. Eight different bubble volumetric flow rates are simulated. The bubble flow patterns, temperature distribution, Nusselt number, Reynolds number, and velocity are all analyzed. The results indicate square arrays of light guides give the most desirable velocity distribution, with less area of zero velocity compared to the staggered light guide setup. Temperature distribution is generally even for all configurations of light guides.

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