Whole Field Measurements to Understand the Role of Varying Depths of Nucleation Site on Vapor Bubble Dynamics and Heat Transfer Rates

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Surya Narayan L ◽  
Pasi Vijaykumar ◽  
Atul Srivastava
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
High Speed ◽  
Bubble Formation ◽  
Nucleation Site ◽  
Heat Transfer Process ◽  
Cavity Depth ◽  
Bulk Fluid ◽  
Transfer Rates ◽  
Transfer Processes

Abstract This work studies the possible effects of varying depths of cavity on bubbling features and the associated heat transfer rates in nucleate pool boiling regime. A single vapor bubble has been generated on a substrate with a cylindrical cavity at its center that acts as the nucleation site. Experiments have been conducted for three cavity depths (250, 500, and 1000 μm), while keeping its throat diameter constant at 200 μm. With the bulk fluid maintained under saturated conditions, for each cavity depth, surface superheat level has been varied in the range of ΔTsuperheat = 8, 10 and 12 °C. A gradient-based visualization technique, coupled with a high speed camera, has been employed to simultaneously map the changes in thermal gradients during the formation of the vapor bubble as well as bubble dynamic parameters. The image sequence obtained has been qualitatively and quantitatively analyzed to elucidate the dependence of bubbling features and various heat transfer processes on cavity depth. With an increase in the depth of cavity, the net effect of reduction in the available thermal energy due to the increased convection effects and significant depletion of superheated layer are identified as the dominant heat transfer processes that influence the bubbling features. Furthermore, based on the statistics of bubble departure characteristics, the cavity with higher depth (1000 μm) showed a much stable bubble formation with minimal variation in the bubble departure frequency as compared to the bubbling features from a cavity with smaller depth (250 μm). Evaporative heat transfer process has been identified as the primary cause for increased inconsistency of bubbling features at high superheat conditions for experiments performed for low cavity depths.

Computational and Experimental Investigation of Heat Transfer Within a Column Photobioreactor

2011 ◽  
Author(s):  
S. M. Mortuza ◽  
Stephen P. Gent ◽  
Anil Kommareddy ◽  
Gary A. Anderson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Speed ◽  
Bubble Formation ◽  
Heat Transfer Process ◽  
Mass Force ◽  
Transfer Coefficients ◽  
Transfer Effects ◽  
Two Phase ◽  
Heat Transfer Effects

The goal of this research is to investigate heat transfer effects of two phase gas-liquid flows in a column photobioreactor (PBR) experimentally as well as computationally using Computational Fluid Dynamics (CFD). The authors have completed a preliminary study on bubble formation, rise and resulting circulation patterns using lab-scale experiments and CFD simulations. This study extends on this previous work by investigating the relationships of bubble drag coefficient and bubble Reynolds number with superficial gas velocity and a study of heat transfer within the PBR. It is hypothesized that a greater understanding the bubble movement patterns will aid in predicting heat transfer rates within the PBR. Dispersed gas–liquid flow in the rectangular column PBR are modeled using the Eulerian–Lagrangian approach. The heat transfer process has been considered for the case of a steady state three dimensional PBR. A low Reynolds number k–epsilon CFD model is used for the description of flow pattern near the wall. The velocity profiles and eddy diffusivity obtained by the model are utilized to predict heat transfer coefficients for different superficial gas velocities. The information on heat transfer effects between cooling or heating surfaces and a gas-liquid dispersed bed is essential for designing a PBR. Carbon dioxide, which is necessary for photosynthetic microalgae growth, is added to the system. Bubble size distribution measurements are carried out using a high-speed digital camera. The main interaction forces, i.e. the drag force, the added mass force, and lift force are considered. Heat transfer and internal hydrodynamics of a column reactor are studied and the numerical simulations results are presented for heat transfer and hydrodynamics in column PBRs. The results are validated with experimental data and with data from current literature.

Microscale Vapor Bubble Interactions During Subcooled Nucleate Boiling on a Heated Wire

2007 ◽  
Author(s):  
Lu Zhang ◽  
David M. Christopher
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Bubble Behavior ◽  
Transfer Rates ◽  
Bubble Interactions ◽  
Heated Wire ◽  
Nucleate Boiling Heat Transfer ◽  
Transfer Mechanisms

Bubbles have been observed moving along heated wires during subcooled nucleate boiling as they are driven by Marangoni convection around the bubbles. This paper presents more detailed observations of the vapor bubble interactions and moving bubble behavior during subcooled nucleate boiling on a heated microwire. The experimental results show that moving bubbles coalesce or rebound from other bubbles and that bubbles hop on the wire. These observations show how bubble interactions significantly affect nucleate boiling heat transfer rates and how Marangoni flow plays an important role in microscale nucleate boiling heat transfer mechanisms.

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.

Microscale Study of the Boiling Process in Low-Surface-Tension Fluids

2006 ◽  
Author(s):  
Saeed Moghaddam ◽  
Kenneth T. Kiger
Keyword(s):  
Heat Transfer ◽  
Sensor Array ◽  
Nucleation Site ◽  
Temperature Data ◽  
Surface Heat ◽  
Distributed Sensor ◽  
Transfer Processes ◽  
Measure Surface Temperature ◽  
Boiling Process ◽  
Composite Wall

A novel MEMS device has been developed to study some of the fundamental issues surrounding the physics of the nucleation process intrinsic to boiling heat transfer. The device generates bubbles from an artificially generated nucleation site centered within a radially distributed sensor array. The array is fabricated within a Silicon/Benzocyclobutene (BCB) composite wall, with the capability to measure surface temperature with an unprecedented radial resolution of 22-40 μm underneath and around the bubble. The temperature data enabled numerical calculation of the surface heat flux with the same spatial resolution as of the temperature data. The temperature of the sensors and the synchronized images of the bubbles were recorded with a sampling frequency of 8 kHz. The unique data determined in this study were used to address some of the unresolved issues regarding the boiling process including 1) dynamics of bubble growth and associated heat transfer processes and 2) the bubble's role in surface heat transfer during the boiling process.

Numerical Computation of the Effects of Brownian Motion on the Effective Thermal Conductivity of Suspensions

2007 ◽  
Author(s):  
P. E. Phelan ◽  
J. R. Pacheco
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Dimensional Space ◽  
Numerical Technique ◽  
Heat Transfer Process ◽  
Immersed Boundary ◽  
Brownian Dynamic ◽  
Dynamic Simulations ◽  
Bulk Fluid

In this paper, a numerical scheme based on the immersed boundary method is used to study the motion of nano-sized particles subjected to Brownian motion and heat transfer. Our objective is to use this numerical technique as a tool to better understand the effect that Brownian forces have on the overall heat transfer process. The conventional approach to perform Brownian dynamic simulations is based on the use of a random force in the particle motion such that the fluctuation-dissipation theorem is satisfied. Our preliminary computational results suggest an increase in the thermal conductivity of the bulk fluid. Results are presented for several particles in a two-dimensional space.

Experimental Study of Enhanced Pool Boiling Heat Transfer Using Graphite Foam Inserts

2011 ◽  
Vol 312-315 ◽  
pp. 352-357 ◽  
Author(s):  
K.C. Leong ◽  
L.W. Jin ◽  
I. Pranoto ◽  
H.Y Li ◽  
J.C. Chai
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Bubble Formation ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Copper Block ◽  
Different Types ◽  
Graphite Foam

This paper presents the results of an experimental study of heat transfer in a pool boiling evaporator with porous insert. Different types of graphite foams were tested with the phase change coolant FC-72 in a designed thermosyphon. Comparisons between the graphite foams and a solid copper block show that the porous structure enhances pool boiling significantly. The boiling thermal resistance of the tested graphite foams was found to be about 2 times lower than that of the copper block. The bubble formation recorded by a high speed camera indicates that boiling from a graphite foam is more vigorous than from a copper block. The designed thermosyphon with graphite foam insert can remove heat fluxes of up to 112 W/cm2 with the maximum heater temperature maintained below 100°C.

Heat Transfer Controlled Collapse of a Cylindrical Vapor Bubble in a Vertical Isothermal Tube

1977 ◽  
Vol 99 (3) ◽  
pp. 392-397 ◽  
Author(s):  
D. R. Pitts ◽  
H. C. Hewitt ◽  
B. R. McCullough
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
High Speed ◽  
Experimental Results ◽  
Heat Transfer Analysis ◽  
Experimental Program ◽  
Bubble Collapse ◽  
Electric Heater ◽  
Vapor Bubbles ◽  
Experimental Apparatus

An experimental program was conducted to determine the collapse rate of slug-type vapor bubbles rising due to buoyancy through subcooled parent liquid in a vertical isothermal tube. The experimental apparatus included a vertical glass tube with an outer glass container providing a constant temperature water bath for the inner tube. The inner tube contained distilled, deaerated water, and water vapor bubbles were generated at the bottom of this tube with a pulsed electric heater. The parent liquid was uniformly subcooled with respect to the vapor bubble resulting in heat transfer controlled bubble collapse. Collapse rates and rise velocities were recorded by high-speed motion picture photography. Over a limited range of subcooling, the bubble collapse was well behaved, and a simple, quasi-steady boundary layer heat transfer analysis adapted from slug flow over a flat plate correlated the experimental results with a high degree of accuracy. Experimental results were obtained with tubes having inside diameters of 0.0127, 0.0218, and 0.0381 m and for a range of subcooling from 0.5 to 9.0 K.

scholarly journals Self-Similar Heat Transfer Processes in a Radiation-Transparent Solid Body Containing an Absorptive Inclusion with the System Featuring Phase Transitions

2019 ◽  
pp. 60-70
Author(s):  
A.V. Attetkov ◽  
I.K. Volkov ◽  
K.A. Gaydaenko
Keyword(s):  
Heat Transfer ◽  
Phase Transitions ◽  
Solid Body ◽  
Transfer Process ◽  
Sufficient Conditions ◽  
Heat Transfer Process ◽  
Similar Process ◽  
Transfer Processes ◽  
Self Similar ◽  
Phase Transition Boundary

The paper considers the problem of determining temperature field parameters in a radiation-trans-parent isotropic solid body containing an absorptive inclusion, when the system features phase transitions. We identify sufficient conditions, meeting which ensures the possibility of self-similar heat transfer process taking place in the system under con-sideration. We qualitatively investigated physical properties of the self-similar process under study and determined its specifics. We provide a theoretical validation of implementing a thermostating mode of the moving phase transition boundary in the heat transfer process investigated

Correlation Between Behaviors of the Vapor Bubbles and the Characteristics of the Heat Transfer Over the Heated Surface on MEB

2013 ◽  
Author(s):  
Takahito Saiki ◽  
Tomohiko Osawa ◽  
Ichiro Ueno ◽  
Chungpyo Hong
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
High Speed ◽  
Heated Surface ◽  
High Heat ◽  
Frame Rate ◽  
High Heat Flux ◽  
Heated Plate ◽  
Thin Wire ◽  
Vapor Bubbles

A series of experiments on subcooled pool boiling on a plate and on a thin wire are carried out. We focus on the condensation and collapse processes of vapor bubbles generated on the heated surface. We find the different patterns of the vapor bubble behaviors resulting in the emission of the microbubbles around the heated plate and the thin wire by employing high-speed observation with frame rate up to 150,000 frame per second (fps). From the experimental results, we provide a physical explanation on the correlation between the behavior of the vapor bubble at a high heat flux and the heat transfer characteristics. We propose this simple core-periphery model as a qualitative model for understanding the generation of the MEB.

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