Microscale Heat Transfer Measurements of the Lateral Merger During Subcooled Pool Boiling of Pentane

2009 ◽  
Author(s):  
Payam Delgoshaei ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Contact Line ◽  
High Speed ◽  
Pool Boiling ◽  
Side View ◽  
Time Resolved ◽  
Array Data ◽  
Earth Gravity ◽  
Microscale Heat Transfer ◽  
Line Movement

Measurements of space and time resolved heat transfer during lateral bubble merger during subcooled pool boiling of pentane in earth gravity environments were obtained using a microscale heater array. Data from individual heater elements in the array were synchronized with bottom and side view images from two high-speed cameras. The heat transfer due to the lateral merger was found to be closely related to the contact line movement on the heater.

Microscale Heat Transfer Measurements During Subcooled Pool Boiling of Pentane

2009 ◽  
Author(s):  
Payam Delgoshaei ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Pool Boiling ◽  
Superheated Liquid ◽  
Side View ◽  
Heat Transfer Mechanism ◽  
Time Resolved ◽  
Earth Gravity ◽  
Microscale Heat Transfer ◽  
Transient Conduction ◽  
Microlayer Evaporation

Measurements of space and time resolved subcooled pool boiling of pentane in earth gravity environments were made using a microscale heater array. Data from individual heater elements in the array were synchronized with bottom and side view images from two highspeed cameras. The bubble growth was primarily due to energy transfer from the superheated liquid layer. Transient conduction and/or microconvection was found to be the dominant heat transfer mechanism. A composite model consisting of microlayer evaporation and transient conduction was developed and compared with the experimental data.

Microscale Heat Transfer Measurements During Subcooled Pool Boiling of Pentane: Effect of Bubble Dynamics

2010 ◽  
Author(s):  
Payam Delgoshaei ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
High Speed ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Growth Time ◽  
Two Phase ◽  
Time Resolved ◽  
Earth Gravity ◽  
Transfer Mechanisms

Measurements of space and time resolved heat transfer during subcooled pool boiling of pentane in earth gravity were obtained using a microscale heater array. Data from individual heater elements in the array were synchronized with bottom and side view images from two high-speed cameras. The heat transfer mechanisms during bubble growth were found to be dependent on bubble dynamics and bubble growth time. Single phase heat transfer mechanisms (transient conduction and/or microconvection) were found to be dominant for single bubbles with short growth times. Two phase heat transfer mechanisms (microlayer evaporation and/or contact line evaporation) were found to be dominant for bubbles with longer growth times.

Phase-Change Heat Transfer Measurements Using Temperature-Sensitive Paints

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Husain Al Hashimi ◽  
Caleb F. Hammer ◽  
Michel T. Lebon ◽  
Dan Zhang ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Uv Light ◽  
Flow Boiling ◽  
Low Cost ◽  
Data Interpretation ◽  
Temperature Sensitive ◽  
Time Resolved ◽  
Light Emitting ◽  
Phase Change Heat Transfer

Techniques based on temperature-sensitive paints (TSP) to measure time-resolved temperature and heat transfer distributions at the interface between a wall and fluid during pool and flow boiling are described. The paints are excited using ultraviolet (UV) light emitting diodes (LEDs), and changes in fluorescence intensity are used to infer local temperature differences across a thin insulator from which heat flux distribution is obtained. Advantages over infrared (IR) thermometry include the ability to use substrates that are opaque to IR (e.g., glass, plexiglass and plastic films), use of low-cost optical cameras, no self-emission from substrates to complicate data interpretation, high speed, and high spatial resolution. TSP-based methods to measure wall heat transfer distributions are validated and then demonstrated for pool and flow boiling.

scholarly journals Effect of Uniformly and Nonuniformly Coated Al2O3 Nanoparticles over Glass Tube Heater on Pool Boiling

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Nitin Doifode ◽  
Sameer Gajghate ◽  
Abdul Najim ◽  
Anil Acharya ◽  
Ashok Pise
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Pool Boiling ◽  
Glass Tube ◽  
Al2o3 Nanoparticles ◽  
High Speed Camera ◽  
Coated Nanoparticles ◽  
Nucleation Sites ◽  
Coated Surface

Effect of uniformly and nonuniformly coated Al2O3 nanoparticles over plain glass tube heater on pool boiling heat transfer was studied experimentally. A borosilicate glass tube coated with Al2O3 nanoparticle was used as test heater. The boiling behaviour was studied by using high speed camera. Result obtained for pool boiling shows enhancement in heat transfer for nanoparticle coated surface heater and compared with plain glass tube heater. Also heat transfer coefficient for nonuniformly coated nanoparticles was studied and compared with uniformly coated and plain glass tube. Coating effect of nanoparticles over glass tube increases its surface roughness and thereby creates more nucleation sites.

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.

Experimental Investigation of Micro-Scale Heat Transfer at an Evaporating Moving 3-Phase Contact Line

2010 ◽  
Author(s):  
K. Ibrahem ◽  
M. F. Abd Rabbo ◽  
T. Gambaryan-Roisman ◽  
P. Stephan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Line ◽  
High Speed ◽  
Local Maximum ◽  
Back Side ◽  
Phase Contact ◽  
Flat Plates ◽  
Maximum Heat ◽  
Micro Scale

An experimental study is conducted to investigate the micro-scale heat transfer at an evaporating moving 3-phase contact line. The moving evaporating meniscus is formed by pushing or sucking a liquid column of HFE7100 in a vertical channel of 600 μm width using a syringe pump. The gas atmosphere is pure HFE7100 vapor. This channel is built using two parallel flat plates. A 10 μm thick stainless steel heating foil forms a part of one of the flat plates. Two-dimensional micro-scale temperature field at the back side of the heating foil is observed with a high speed infrared camera with a spatial resolution of 14.8 μm × 14.8 μm and an in-situ calibration procedure is used at each pixel element. A high speed CMOS camera is used to capture the shape of the moving meniscus, the images are post-processed to track the free surface of the meniscus. Local heat fluxes from the heater to the evaporating meniscus are calculated from the measured transient wall temperature distributions using an energy balance for each pixel element. In the vicinity of the 3-phase contact line the heat flux distribution shows a local maximum due to high evaporation rates at this small region. The local maximum heat flux at the 3-phase contact line area is found to be dependent on the input heat flux, the velocity and the direction of the meniscus movement. The results give detailed insight into the specific dynamic micro-scale heat and fluid transport process.

Two Phase Boiling and Flow Instabilities in a Microchannel

2007 ◽  
Author(s):  
Jacqueline Barber ◽  
K. Sefiane ◽  
D. Brutin ◽  
L. Tadrist
Keyword(s):  
Heat Transfer ◽  
Contact Line ◽  
High Speed ◽  
Flow Instability ◽  
High Heat ◽  
Heat Fluxes ◽  
Flow Reversal ◽  
Flow Instabilities ◽  
Moving Contact Line ◽  
Moving Contact

Boiling in microchannels is a very efficient mode of heat transfer. High heat and mass transfer coefficients are achieved. Evaporation of the liquid meniscus is the main contributor to the high heat fluxes achieved due to phase change at thin liquid films in a microchannel. The microscale hydrodynamic motion and the mechanisms at the immediate vicinity of the moving contact line are still not fully comprehended. There are several flow instabilities during boiling in microchannels. These instabilities need to be well understood and predicted due to their adverse effects on the heat transfer. It is hoped to understand particular flow instabilities, such as flow reversal, through experimental research at the contact line. A simultaneous visualisation and measurement experiment was carried out to investigate these flow instabilities in microchannels. Boiling has been induced in a microchannel (dh 570 μm), stabilising just one liquid-vapour interface, and observing its progression through various microchannel geometries. Images and video sequences have been achieved with both a high speed camera and an infra red camera. Analysis of these images allow the application of several existing models to be fitted to our flow instability observations, namely flow reversal and its possible mechanism of vapour recoil, at the moving contact line.

Effect of Fouling on Nucleate Pool Boiling in Microgravity and Earth Gravity

1999 ◽  
Author(s):  
Daiju Motoya ◽  
Ikuya Haze ◽  
Masahiro Osakabe
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Pool Boiling ◽  
Film Boiling ◽  
Gravity Level ◽  
Nucleate Pool Boiling ◽  
Bubble Volume ◽  
High Speed Video ◽  
Earth Gravity ◽  
Bare Surface

Abstract Nucleate pool boiling of water on clean and fouling surfaces was conducted in microgravity and earth gravity. The microgravity experiments were conducted in 8 s JAMIC drop shaft in Hokkaido of Japan. Platinum wires of 0.2 mm in diameter with or without fouling scale were used to provide uniform heat flux and measurement of the mean temperature of wires. The generated bubble volume was measured with high-speed video or CCD images. The more vigorous bubbling was observed on the fouling wire compared to that on the clean wire at a same heat flux both in earth gravity and microgravity. The enhancement of the bubbling was associated with the fact that the hydrophilic porous structure in the fouling scale provided the sufficient number of active sites for bubbling nucleation. The wettability of the surface with the fouling scale was much higher than that of the clean bare surface. The bubble departure diameter on the fouling wire was smaller due to the high wettability than that on the clean wire. The latent heat transportation ratio to the total heat flux was calculated with the generated bubble volume measured with high-speed video or CCD images. The ratio was approximately the same at the clean and fouling wires in spite of the apparent difference in bubbling behavior, but it was significantly affected with the gravity level. The ratio increased with an increase of the heat flux in the earth gravity but it remained at the smaller value in the microgravity. The nucleate heat transfer coefficient on the bare surface did not depend on the gravity levels although the bubbling behavior strongly affected with the gravity level. As the wire radius is small compared to the capillary length scale in microgravity, a growing and coalescing bubble sometimes completely covered the clean wire, evaporating all liquid in contact with the surface and inducing a transition to film boiling. However, on the fouling wire, many small bubbles were generated and sprang from the surface in various directions in microgravity. The spring out action of bubbles suppressed the transition to the film boiling on the fouling wire in the present experimental range.

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