Bubble Formation and Coalescence Under the Influence of Electric Fields

2013 ◽  
Author(s):  
Cila Herman
Keyword(s):  
Electric Fields ◽  
Heated Surface ◽  
Bubble Formation ◽  
Heat Removal ◽  
High Heat ◽  
Gravity Level ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Industrial Operations ◽  
Bubble Removal

The high heat transfer rates associated with phase-change processes, such as boiling, make them an attractive solution in a range of industrial operations. In terrestrial conditions, the buoyancy force is responsible for bubble removal from the surface, which is essential for heat removal from the surface. Since in space the gravity level is orders of magnitude smaller than on earth, bubbles formed during boiling remain attached at the surface and they also show a tendency to coalesce. As a result, the amount of heat removed from the heated surface is different from terrestrial conditions and it can decrease considerably.

Bubble Formation and Detachment Under the Influence of Electric Fields and the Role of Gravity

2005 ◽  
Author(s):  
C. Herman ◽  
Z. Liu ◽  
E. Iacona
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Heated Surface ◽  
Gravity Level ◽  
Reduced Gravity ◽  
Bubble Behavior ◽  
Transfer Coefficients ◽  
High Heat Transfer ◽  
The Impact ◽  
Bubble Removal

Boiling is an attractive solution to cooling problems in aerospace engineering because of the high heat transfer coefficients associated with phase change processes. Bubble detachment from an orifice shows some resemblance to bubble departure in boiling. The buoyancy force is responsible for bubble removal from the surface in terrestrial conditions. In space, with the gravity level being orders of magnitude smaller than on earth, bubbles formed during boiling can remain attached to the surface. As a result, the amount of heat removed from the heated surface can decrease, and it is difficult to predict reliably and accurately. The impact of electric fields is investigated with the aim to control bubble behavior and help bubble removal from the surface on which they form in reduced gravity. The behavior of single gas bubbles injected through an orifice into an electrically insulating liquid is studied in reduced gravity under the influence of static electric fields and the results of the experiments are compared with data obtained using a simplified model. The bubble life cycle was visualized in terrestrial conditions and reduced gravity. Bubble departure, volume and dimensions at detachment were measured and analyzed for different parameters such as gravity level, electric field magnitude and electric field uniformity. Results suggest that these parameters significantly affect bubble behavior, shape, volume and dimensions at detachment.

Comparison of Heat Transfer Rates Around Moving and Stationary Bubbles During Nucleate Boiling

2005 ◽  
Author(s):  
David M. Christopher ◽  
Hao Wang ◽  
Xiaofeng Peng
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Nucleate Boiling ◽  
High Heat ◽  
Marangoni Flow ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Nucleate Boiling Heat Transfer ◽  
Bubble Movement ◽  
Transfer Mechanisms

Nucleate boiling is known to be a very efficient method for generating high heat transfer rates from solid surfaces into liquids; however, the fundamental physical mechanisms governing nucleate boiling heat transfer are not well understood. This paper describes a numerical analysis of the heat transfer mechanisms around stationary and moving bubbles on a very thin microwire. The numerical analysis accurately models the experimentally observed bubble movement and fluid velocities. The analytical model was then used to study the heat transfer mechanisms around the bubbles. The analysis shows that the primary heat transfer mechanism is not the direct heat transfer to the bubble, but rather the large amount of convection around the outside of the bubble induced by the Marangoni flow that transfers at least twice as much energy from the wire than the heat transfer directly under the bubble. The enhanced heat transfer due to the Marangoni flow was evident for both stationary and moving bubbles.

Natural Convection Heat Transfer From a Cylinder With High Conductivity Permeable Fins

2003 ◽  
Vol 125 (2) ◽  
pp. 282-288 ◽  
Author(s):  
Bassam A/K Abu-Hijleh
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Convection Heat Transfer ◽  
High Heat ◽  
Horizontal Cylinder ◽  
High Conductivity ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Wide Range

The problem of laminar natural convection from a horizontal cylinder with multiple equally spaced high conductivity permeable fins on its outer surface was investigated numerically. The effect of several combinations of number of fins and fin height on the average Nusselt number was studied over a wide range of Rayleigh number. Permeable fins provided much higher heat transfer rates compared to the more traditional solid fins for a similar cylinder configuration. The ratio between the permeable to solid Nusselt numbers increased with Rayleigh number, number of fins, and fin height. This ratio was as high as 8.4 at Rayleigh number of 106, non-dimensional fin height of 2.0, and with 11 equally spaced fins. The use of permeable fins is very advantageous when high heat transfer rates are needed such as in today’s high power density electronic components.

A Transducer for Measuring High Heat Transfer Rates

1970 ◽  
Vol 41 (12) ◽  
pp. 1732-1740 ◽  
Author(s):  
E. H. Schulte ◽  
R. F. Kohl
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Transfer Rates ◽  
High Heat Transfer

Forced Air Cooling With Synthetic Jet Ejectors

2005 ◽  
Author(s):  
Raghav Mahalingam ◽  
Ari Glezer
Keyword(s):  
Mass Flux ◽  
Heated Surface ◽  
High Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Low Flow ◽  
Air Cooling ◽  
Zero Mass ◽  
High Heat Transfer ◽  
Forced Air

This paper discusses the concept of synthetic jet ejectors for forced air cooling and some practical implementations of the same. Synthetic or “zero-mass-flux” jets, unlike conventional jets, require no mass addition to the system, and thus provide means of efficiently directing airflow across a heated surface. Because these jets are zero net mass flux in nature and are comprised entirely of the ambient fluid, they can be conveniently integrated with the surfaces that require cooling without the need for complex plumbing. A synthetic jet ejector mechanism for obtaining high heat transfer rates at low flow rates is discussed. Synthetic jet ejectors consist of a primary “zero-mass-flux” unsteady jet driving a secondary airflow through a channel. Several practical implementations of synthetic jets are introduced from low form factor, low power spot cooling applications to high heat dissipation applications and flow bypass control where synthetic jets are used to enhance fan performance.

scholarly journals Properties of Kerosene-Aluminium Nanofluid used to Estimate the Overall Heat Transfer Rates during Regenerative/Film Cooling of Thrust Chambers

2019 ◽  
Vol 9 (1S3) ◽  
pp. 165-169
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Space Station ◽  
High Heat ◽  
Nano Particles ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Rocket Propulsion ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Large heat transfer rates are always desired for rocket propulsion applications as high heat loads are associated at the nozzle exit. Different strategies have been employed in order to have high heat transfer coefficients including use of liquid nitrogen, spray cooling etc. ISRO has planned to use aluminium based nano-particles with kerosene in order to cool launching vehicles including GSLV Mk III as it is the heaviest rocket that can carry large payloads. Recently, ISRO has announced to install its own International Space Station (ISS) in future and in such applications larger payloads are to be carried by the rocket. In this work, an analytical study on the thermodynamic properties of the aluminium nano-particles based kerosene nanofluid has been done and an attempt has also been made to develop a temperature and pressure dependent correlation that can be used in computational analysis of thrust chambers while film/regenerative cooling.

Gas Turbine Electrical Power and Steam Generation at Allison Division of General Motors

1967 ◽  
Author(s):  
G. W. Bixler ◽  
H. J. Clifford
Keyword(s):  
Gas Turbine ◽  
Electrical Power ◽  
Aircraft Engine ◽  
High Heat ◽  
General Motors ◽  
Steam Boiler ◽  
Steam Generation ◽  
Air Inlet ◽  
High Heat Transfer ◽  
Industrial Operations

At the 1962 and 1964 ASME meetings, Allison submitted papers describing the possibilities of industrializing the T56 aircraft engine and the applications of the 501 gas turbine to industrial operations. Since 1964, Allison has been evaluating a prototype electrical power and steam generation set which has operated for approximately 20,000 hr. This paper describes the test program and the results obtained. Operating data from various engine configurations using natural gas and diesel fuel, four lubricating oils, two types of air-inlet filters, and a Harrison special high heat transfer rate exhaust gas steam boiler are also presented.

Effect of Static Bed Height on the Combustion of Rice Husk in a Fluidized Bed Combustor

2005 ◽  
Author(s):  
M. Rozainee ◽  
S. P. Ngo
Keyword(s):  
Fluidized Bed ◽  
Residence Time ◽  
Rice Husk ◽  
Bubble Formation ◽  
Combustion Process ◽  
High Heat ◽  
Transfer Rates ◽  
Bed Height ◽  
Bed Temperature ◽  
Bed Material

The combustion process is largely controlled by temperature, turbulence and residence time. When the temperature is sufficiently high so that the reaction is no longer kinetically-controlled, turbulence and residence time play a significant role. The reaction is thus diffusion-controlled. During the combustion of rice husk in a fluidized bed, the turbulence is largely governed by the mixing behavior in the inert sand bed, which in turn is governed by the bubble formation characteristics. Further, the residence time among the reactants (air and rice husk) and the heat source is also dependent on the turbulence in the bed. When all other parameters are held constant, the bubble phenomena vary according to the expanded bed height corresponding to a given static bed height. For high heat and mass transfer rates, small slowly rising bubbles are desired. Thus, the purpose of this study is to investigate the effect of static bed height on the quality of ash during the combustion of rice husk. The degree of rice husk burning in the bed could be deduced from the bed temperature as a higher bed temperature indicated that a higher portion of the rice husk feed is being burnt in the bed. Moreover, the particle size of the resulting ash is also able to give indication of the degree of rice husk burning in the bed as the turbulence arising from the bubbling action of the bed material is known to break down the char skeleton of the rice husk, thereby, resulting in ash with finer size. From this study, the static bed height of 0.5 DC was found to give the lowest residual carbon content in the ash (1.9 wt%) and the highest bed temperature (670°C) among the other range of static bed heights investigated.

The Influence of Evaporation in Shear-Driven Liquid Film on Heat Removal From Local Heater

2006 ◽  
Author(s):  
Elizaveta Gatapova ◽  
Oleg Kabov
Keyword(s):  
Liquid Film ◽  
Thin Liquid Film ◽  
Heat Removal ◽  
Film Surface ◽  
Numerical Data ◽  
High Heat ◽  
Liquid Films ◽  
High Heat Flux ◽  
Maximal Surface ◽  
High Heat Transfer

The present work focuses upon shear-driven liquid film evaporative cooling of high heat flux local heater. Thin evaporating liquid films may provide very high heat transfer rates and can be used for cooling of high power microelectronic systems. Thermocapillary convection in a liquid film falling down a locally heated substrate has recently been extensively studied. However, non-uniform heating effects remain only partially understood for shear-driven liquid films. The combined effects of evaporation, thermocapillarity and gas dynamics as well as formation of microscopic adsorbed film have not been studied. The effect of evaporation on heat and mass transfer for 2D joint flow of a liquid film and gas is theoretically and numerically investigated. The convective terms in the energy equations are taken into account. The calculations reveal that evaporation from film surface essential influences on heat removal from local heater. It is shown that the thermal boundary layer plays significant role for cooling local heater by evaporating thin liquid film. Measured by an infrared scanner temperature distribution at the film surface is compared with numerical data. Calculations satisfactorily describe the maximal surface temperature value.

Experimental and Numerical Analyses of a Micro-Heat Exchanger for Ethanol Excess Recovery From Biodiesel

2019 ◽  
pp. 167-194
Author(s):  
João Lameu da Silva Júnior ◽  
Harrson Silva Santana
Keyword(s):  
Heat Exchanger ◽  
Flow Rate ◽  
Continuous Process ◽  
Volume Ratio ◽  
High Heat ◽  
Molar Ratio ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Micro Heat Exchanger ◽  
Elevated Surface

The use of micro-heat exchangers increased with the advancement of microfluidics. These microdevices present some advantages like elevated surface area-to-volume ratio resulting in high heat transfer rates. Micro-heat exchanger with phase change is a new application of such devices. The simultaneous momentum, heat, and mass transfer at microscale still require investigations due to the inherent complexity. The main goal of the chapter is to demonstrate experimentally and numerically the capability of the micro-heat exchanger use in the continuous process of ethanol excess recovery from the biodiesel. The influence of flow rate, ethanol/biodiesel molar ratio, and temperature on the ethanol evaporation performance was evaluated. The flow rate and the ethanol/biodiesel molar ratio influenced negatively the evaporation. In contrast, the temperature was affected positively. The mathematical model was able to capture the main features of the continuous evaporation; however, further improvements must be performed in order to consider the thermodynamics characteristics.

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