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 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.

Saturated Pool Boiling Mechanisms During Single Bubble Heat Transfer: Comparison at Two Wall Superheats

2000 ◽  
Author(s):  
Jungho Kim ◽  
Fatih Demiray ◽  
Nagaraja Yaddanapudi
Keyword(s):  
Heat Transfer ◽  
Constant Temperature ◽  
Pool Boiling ◽  
Minor Role ◽  
Dominant Mechanism ◽  
Different Temperatures ◽  
Transient Conduction ◽  
Microlayer Evaporation ◽  
A Minor ◽  
Transfer Mechanisms

Abstract A study of single bubbles growing on a microscale heater array kept at nominally constant temperature was performed. The behavior of bubbles nucleating at a single site at two different temperatures (22.5 K and 27.5 K superheat) is compared for saturated pool boiling of FC-72 at 1 atm. It is concluded that energy is transferred from the surface through similar heat transfer mechanisms at both superheats. Microlayer evaporation was observed to play a minor role in the overall heat transfer, with microconvection/transient conduction being the dominant mechanism. Evaluation of various heat transfer models are made.

Nucleate Pool Boiling: The Dominant Bubble Heat Transfer Mechanisms

2009 ◽  
Author(s):  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Contact Line ◽  
Pool Boiling ◽  
Nucleate Pool Boiling ◽  
Transfer Energy ◽  
Numerical Work ◽  
Transient Conduction ◽  
Microlayer Evaporation ◽  
Transfer Mechanisms ◽  
Fitting Parameters

Enhanced convection, transient conduction, microlayer evaporation, and contact line heat transfer have all been proposed as mechanisms by which bubbles transfer energy during boiling. Models based on these mechanisms contain fitting parameters that are used to fit them to the data, resulting a proliferation of “validated” models. A review of the recent experimental, analytical, and numerical work into single bubble heat transfer is presented to determine the contribution of each of the above mechanisms to the overall heat transfer. Transient conduction and microconvection are found to be the dominant heat transfer mechanisms.

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.

Contribution of Microlayer Evaporation During Flow Boiling Inside Microchannels

2008 ◽  
Author(s):  
A. Mukherjee
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism ◽  
Cross Sectional ◽  
Thin Film Evaporation ◽  
Nucleate Boiling Heat Transfer ◽  
Microlayer Evaporation

Flow boiling through microchannels is characterized by nucleation and growth of vapor bubbles that fills the entire channel cross-sectional area. As the bubble nucleates and grows inside the microchannel, a thin film of liquid or a microlayer gets trapped between the bubble and the channel walls. The heat transfer mechanism present at the channel walls during flow boiling is studied numerically. These mechanisms are compared to the heat transfer mechanisms present during nucleate boiling and in a moving evaporating meniscus. It is shown that the thermal and the flow fields present inside the microchannels around the bubbles are fundamentally different compared to nucleate boiling or in a moving evaporating meniscus. It is explained that how thin film evaporation is responsible for creating an apparent nucleate boiling heat transfer mechanism inside the microchannels.

Enhanced Macroconvection Mechanism With Separate Liquid–Vapor Pathways to Improve Pool Boiling Performance

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Bubble Diameter ◽  
Pool Boiling ◽  
Nucleation Site ◽  
Enhancement Mechanism ◽  
Performance Improvements ◽  
Wall Superheat ◽  
Significant Performance ◽  
Multiscale Structures ◽  
Microlayer Evaporation

Understanding heat transfer mechanisms is crucial in developing new enhancement techniques in pool boiling. In this paper, the available literature on fundamental mechanisms and their role in some of the outstanding enhancement techniques is critically evaluated. Such an understanding is essential in our quest to extend the critical heat flux (CHF) while maintaining low wall superheats. A new heat transfer mechanism related to macroconvection is introduced and its ability to simultaneously enhance both CHF and heat transfer coefficient (HTC) is presented. In the earlier works, increasing nucleation site density by coating a porous layer, providing hierarchical multiscale structures with different surface energies, and nanoscale surface modifications were some of the widely used techniques which relied on enhancing transient conduction, microconvection, microlayer evaporation, or contact line evaporation mechanisms. The microconvection around a bubble is related to convection currents in its immediate vicinity, referred to as the influence region (within one to two times the departing bubble diameter). Bubble-induced convection, which is active beyond the influence region on a heater surface, is introduced in this paper as a new macroconvection mechanism. It results from the macroconvection currents created by the motion of bubbles as they grow and depart from the nucleating sites along a specific trajectory. Directing these bubble-induced macroconvection currents so as to create separate vapor–liquid pathways provides a highly effective enhancement mechanism, improving both CHF and HTC. The incoming liquid as well as the departing bubbles in some cases play a major role in enhancing the heat transfer. Significant performance improvements have been reported in the literature based on enhanced macroconvection contribution. One such microstructure has yielded a CHF of 420 W/cm2 with a wall superheat of only 1.7 °C in pool boiling with water at atmospheric pressure. Further enhancements that can be expected through geometrical refinements and integration of different techniques with macroconvection enhancement mechanism are discussed here.

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