Materials, technological status, and fundamentals of PEM fuel cells – A review

While superhydrophilic coatings with enhanced wetting properties have been shown to increase the pool boiling critical heat flux (CHF), the role of nanostructures on its enhancement is not clear. Here, biological templates have been used to demonstrate that wickability is the single factor dictating CHF on structured superhydrophilic surfaces. The flexibility of biotemplating using the Tobacco mosaic virus has been leveraged to create surfaces with varying scales, morphologies, and roughness factors. Their wickabilities have been quantified via the wicked volume flux, a phenomenological parameter analogous to the contact angle, and the role of wickability on CHF has been demonstrated using data from over three dozen individual surfaces. These results are repeatable and independent of the substrate material, surface fouling, structure material, morphology, and contact angle as well as the structure scale. An experimentally validated correlation for CHF has been reported on the basis of the dimensionless wickability. Additionally, the surfaces have achieved a CHF of 257 W/cm(2) for water, representing the highest reported value to date for superhydrophilic surfaces. While the role of wickability on CHF has often been cited anecdotally, this work provides a quantitative measure of the phenomena and provides a framework for designing and optimizing coatings for further enhancement.

Role of wickability on the critical heat flux of structured superhydrophilic surfaces

Liquid–vapour phase change is a useful and efficient process to transfer energy in nature, as well as in numerous domestic and industrial applications. Relatively recent advances in altering surface chemistry, and in the formation of micro- and nanoscale features on surfaces, have led to exciting improvements in liquid–vapour phase-change performance and better understanding of the underlying science. In this Review, we present an overview of the surface, thermal and material science to illustrate how new materials and designs can improve boiling and condensation. There are many parallels between boiling and condensation, such as nucleation of a phase and its departure from a surface; however, the particular set of challenges associated with each phenomenon results in different material designs used in different manners. We also discuss alternative techniques, such as introducing heterogeneous surface chemistry or direct real-time manipulation of the phase-change process, which can offer further control of heat-transfer processes. Finally, long-term robustness is essential to ensure reliability and feasibility but remains a key challenge. Recent works in boiling and condensation have achieved unprecedented performance and revealed new mechanistic insights that will aid in material design. In this Review, we focus on nanoengineered materials, with emphasis on further improving the heat-transfer performance and long-term robustness.

Nanoengineered materials for liquid–vapour phase-change heat transfer

A critical review of cooling techniques in proton exchange membrane fuel cell stacks

Review of pool boiling enhancement by surface modification

Effect of open microchannel geometry on pool boiling enhancement

Pool boiling is of interest in high heat flux applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is not adequate to match the cooling ability provided by enhanced microchannels operating under single-phase conditions. The objective of this work is to evaluate the pool boiling performance of structured surface features etched on a silicon chip. The performance is normalized with respect to a plain chip. This investigation also focuses on the bubble dynamics on plain and structured microchannel surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism. It was determined that surface modifications to silicon chips can improve the heat transfer coefficient by a factor up to 3.4 times the performance of a plain chip. Surfaces with microchannels have shown to be efficient for boiling heat transfer by allowing liquid to flow through the open channels and wet the heat transfer surface while vapor is generated. This work is expected to lead to improved enhancement features for extending the pool boiling option to meet the high heat flux removal demands in electronic cooling applications.

Pool Boiling Heat Transfer and Bubble Dynamics Over Plain and Enhanced Microchannels

Uneven gas diffusion layer intrusion in gas channel arrays of proton exchange membrane fuel cell and its effects on flow distribution

Pool boiling is of interest in high heat flux applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is not adequate to match the cooling ability provided by enhanced microchannels operating under single-phase conditions. The objective of this work is to evaluate the pool boiling performance of structured surface features etched on a silicon chip. The performance is normalized with respect to a plain chip. This investigation also focuses on the bubble dynamics on plain and structured microchannel surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism. This work is expected to lead to improved enhancement features for extending the pool boiling option to meet the high heat flux removal demands in electronic cooling applications.Copyright © 2010 by ASME

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Dwight Cooke

Papers

Effect of open microchannel geometry on pool boiling enhancement

Pool Boiling Heat Transfer and Bubble Dynamics Over Plain and Enhanced Microchannels

Uneven gas diffusion layer intrusion in gas channel arrays of proton exchange membrane fuel cell and its effects on flow distribution

Pool Boiling Heat Transfer and Bubble Dynamics Over Plain and Enhanced Microchannels

Experimental study of pool boiling heat transfer enhancement over microchanneled surfaces