scholarly journals Bubble Dynamics of a Single Condensing Vapor Bubble from Vertically Heated Wall in Subcooled Pool Boiling System: Experimental Measurements and CFD Simulations

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Arijit A. Ganguli ◽  
Aniruddha B. Pandit ◽  
Jyeshtharaj B. Joshi
Keyword(s):  
Vapor Bubble ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Heated Wall ◽  
Experimental Measurements ◽  
Cfd Simulations

Self-Propelled Sliding Bubble Motion Induced by Surface Microstructure in Pool Boiling of a Dielectric Fluid Under Microgravity

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Naveenan Thiagarajan ◽  
Sushil H. Bhavnani ◽  
Vinod Narayanan
Keyword(s):  
Vapor Bubble ◽  
Bubble Dynamics ◽  
Heated Surface ◽  
Pool Boiling ◽  
Bubble Nucleation ◽  
Radius Of Curvature ◽  
Dielectric Fluid ◽  
Bubble Motion ◽  
Reduced Gravity ◽  
Modification Technique

This paper reports bubble dynamics observed during pool boiling over microstructures with an asymmetric saw-tooth cross section, under reduced gravity. The periodic saw-toothed ratchets etched on a silicon surface include fabricated vapor bubble nucleation sites only on the shallow slope. Reduced gravity pool boiling experiments were conducted aboard a Boeing 727 aircraft carrying out parabolic maneuvers. The fluid used was FC-72, a highly wetting dielectric fluid used as a coolant for electronics. Under microgravity, it was observed that the bubble diameters were six times larger than in terrestrial gravity. Also, self-propelled sliding bubble motion along the surface of the saw teeth was observed in reduced gravity. The velocity of the sliding bubbles across the saw teeth, following lateral departure from the cavities, was measured to be as high as 27.4 mm/s. A model for the sliding bubble motion is proposed by attributing it to the force due to pressure differences that arise in the liquid film between the vapor bubble and the saw-toothed heated surface. The pressure difference is due to difference in the radius of curvature of the interface between the crest and trough of the saw teeth. The surface modification technique, which resulted in the sliding bubble motion, has the potential to alleviate dry-out caused due to stagnant vapor bubbles over heat sources under microgravity when the buoyancy forces are negligible compared to the surface tension forces.

Sliding Bubble-Pumped Motion Induced by Surface Micro-Structure in Pool Boiling of a Dielectric Fluid Under Reduced Gravity

2014 ◽  
Author(s):  
Naveenan Thiagarajan ◽  
Sushil H. Bhavnani ◽  
Vinod Narayanan
Keyword(s):  
Vapor Bubble ◽  
Bubble Dynamics ◽  
Heated Surface ◽  
Pool Boiling ◽  
Bubble Nucleation ◽  
Radius Of Curvature ◽  
Dielectric Fluid ◽  
Bubble Motion ◽  
Reduced Gravity ◽  
Modification Technique

This paper reports bubble dynamics observed during pool boiling over micro-structures with an asymmetric saw-tooth cross-section, under reduced gravity. The periodic saw-toothed ratchets etched on a silicon surface include fabricated vapor bubble nucleation sites only on the shallow slope. Reduced gravity pool boiling experiments were conducted aboard a Boeing 727 aircraft (Zero-g Inc.) carrying out parabolic maneuvers to achieve reduced gravity. The fluid used was FC-72, a highly wetting dielectric fluid used as a coolant for electronics. Under microgravity, it was observed that the bubble diameters were six times larger than in terrestrial gravity. Also, self-propelled sliding bubble motion along the surface of the saw teeth was observed in reduced gravity. The velocity of the sliding bubbles across the saw teeth, following lateral departure from the cavities, was measured to be as high as 27.4 mm/s. A model for the sliding bubble motion is proposed by attributing it to the force due to pressure differences that arise in the liquid film between the vapor bubble and the saw-toothed heated surface. The pressure difference is due to difference in the radius of curvature of the interface between the crest and trough of the saw teeth. The surface modification technique has the potential to alleviate dry out caused due to vapor blanketing of heat sources in microgravity due to negligible buoyancy forces compared to the surface tension forces.

Simulation of Single Bubble Dynamics in Nucleate Pool Boiling Using a Conservative Level Set Method

2009 ◽  
Author(s):  
Muhammad Sajid ◽  
Rachid Bennacer
Keyword(s):  
Surface Tension ◽  
Level Set ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Heated Wall ◽  
Nucleate Pool Boiling ◽  
Vapor Interface ◽  
Level Set Function ◽  
Conservative Level Set ◽  
Liquid Vapor

Most energy conversion systems and cooling devices employ nucleate pool boiling because of its high efficiency of heat exchange. It is a liquid-vapor phase change process associated with ebullition, characterized by cyclic growth and departure of vapor bubbles from heated wall and greatly influenced by the bubble growth mechanism. Bubble dynamics is difficult to simulate due to the difficulty of tracking the liquid vapor interface without smearing it, the discontinuity in material properties due to high density ratio and the need to take surface tension into account that introduces a jump in the pressure field. This paper focuses on the accurate representation of surface tension effects on bubble dynamics in nucleate pool boiling. The complete Navier-Stokes equations are solved and liquid-vapor interface is captured using a conservative level-set technique, curvature of interface is computed using the level set function and surface tension forces are evaluated as a body force according to the continuum surface force method. This enables us to simulate flows with large density and viscosity differences, to capture the shape of the deforming interface of the bubble while maintaining good mass conservation. The ability of the model is demonstrated with the numerical example of a growing bubble.

Effect of Temperature Nonuniformity on Heat Transfer in an Unshrouded Transonic HP Turbine: An Experimental and Computational Investigation

2010 ◽  
Author(s):  
Imran Qureshi ◽  
Andy D. Smith ◽  
Kam S. Chana ◽  
Thomas Povey
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Test Facility ◽  
Effect Of Temperature ◽  
Inlet Temperature ◽  
Experimental Measurements ◽  
Turbine Stage ◽  
Cfd Simulations ◽  
Turbine Inlet

Detailed experimental measurements have been performed to understand the effects of turbine inlet temperature distortion (hot-streaks) on the heat transfer and aerodynamic characteristics of a full-scale unshrouded high pressure turbine stage at flow conditions that are representative of those found in a modern gas turbine engine. To investigate hot-streak migration, the experimental measurements are complemented by three-dimensional steady and unsteady CFD simulations of the turbine stage. This paper presents the time-averaged measurements and computational predictions of rotor blade surface and rotor casing heat transfer. Experimental measurements obtained with and without inlet temperature distortion are compared. Time-mean experimental measurements of rotor casing static pressure are also presented. CFD simulations have been conducted using the Rolls-Royce code Hydra, and are compared to the experimental results. The test turbine was the unshrouded MT1 turbine, installed in the Turbine Test Facility (previously called Isentropic Light Piston Facility) at QinetiQ, Farnborough UK. This is a short duration transonic facility, which simulates engine representative M, Re, Tu, N/T and Tg /Tw at the turbine inlet. The facility has recently been upgraded to incorporate an advanced second-generation temperature distortion generator, capable of simulating well-defined, aggressive temperature distortion both in the radial and circumferential directions, at the turbine inlet.

Thermal Bubble Dynamics Under the Effect of Acoustic Vibration

2009 ◽  
Author(s):  
Xiaopeng Qu ◽  
Huihe Qiu
Keyword(s):  
Heat Transfer ◽  
Acoustic Field ◽  
Vapor Bubble ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Bubble Dynamics ◽  
Acoustic Vibration ◽  
Micro Electro Mechanical System ◽  
Mems Technology ◽  
Enhanced Boiling

The effect of acoustic field on the dynamics of micro thermal bubble is investigated in this paper. The micro thermal bubbles were generated by a micro heater which was fabricated by standard Micro-Electro-Mechanical-System (MEMS) technology and integrated into a mini chamber. The acoustic field formed in the mini chamber was generated by a piezoelectric plate which was adhered on the top side of the chamber’s wall. The dynamics and related heat transfer induced by the micro heater generated vapor bubble with and without the existing of acoustic field were characterized by a high speed photograph system and a micro temperature sensor. Through the experiments, it was found that in two different conditions, the temperature changing induced by the micro heater generated vapor bubble was significantly different. From the analysis of the high speed photograph results, the acoustic force induced micro thermal bubble movements, such as forcibly removing, collapsing and sweeping, were the main effects of acoustic enhanced boiling heat transfer. The experimental results and theoretical analysis were helpful for understanding of the mechanisms of acoustic enhanced boiling heat transfer and development of novel micro cooling devices.

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