https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1137&context=me_pubs

Boiling heat transfer on superhydrophilic, superhydrophobic, and superbiphilic surfaces

Owing to advances in micro- and nanofabrication methods over the last two decades, the degree of sophistication with which solid surfaces can be engineered today has caused a resurgence of interest in the topic of engineering surfaces for phase change heat transfer. This review aims at bridging the gap between the material sciences and heat transfer communities. It makes the argument that optimum surfaces need to address the specificities of phase change heat transfer in the way that a key matches its lock. This calls for the design and fabrication of adaptive surfaces with multiscale textures and non-uniform wettability. Among numerous challenges to meet the rising global energy demand in a sustainable manner, improving phase change heat transfer has been at the forefront of engineering research for decades. The high heat transfer rates associated with phase change heat transfer are essential to energy and industry applications; but phase change is also inherently associated with poor thermodynamic efficiency at low heat flux, and violent instabilities at high heat flux. Engineers have tried since the 1930s to fabricate solid surfaces that improve phase change heat transfer. The development of micro and nanotechnologies has made feasible the high-resolution control of surface texture and chemistry over length scales ranging from molecular levels to centimeters. This paper reviews the fabrication techniques available for metallic and silicon-based surfaces, considering sintered and polymeric coatings. The influence of such surfaces in multiphase processes of high practical interest, e.g., boiling, condensation, freezing, and the associated physical phenomena are reviewed. The case is made that while engineers are in principle able to manufacture surfaces with optimum nucleation or thermofluid transport characteristics, more theoretical and experimental efforts are needed to guide the design and cost-effective fabrication of surfaces that not only satisfy the existing technological needs, but also catalyze new discoveries.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/8A3CC28A80AFA422AB5C8266816ECF6B/S2329222914000099a.pdf/div-class-title-surface-engineering-for-phase-change-heat-transfer-a-review-div.pdf

Surface engineering for phase change heat transfer: A review

Experiments are performed to understand the effects of surface orientation on the pool boiling characteristics of a highly wetting fluid from a flush-mounted, micro-porous-enhanced square heater Micro-porous enhancement was achieved by applying copper and aluminum particle coatings to the heater surfaces Effects of heater orientation on CHF and nucleate boiling heat transfer for uncoated and coated surfaces are compared A correlation is developed to predict the heater orientation effect on CHF for those surfaces

Heater orientation effects on pool boiling of micro-porous-enhanced surfaces in saturated FC-72

Performance of different structured surfaces in nucleate pool boiling

In-vessel retention (IVR) of core melt is a key severe-accident-management strategy adopted by some operating nuclear power plants and proposed for some advanced light water reactors (LWRs). If the...

In-Vessel Retention of Molten Corium: Lessons Learned and Outstanding Issues

One-dimensional critical heat flux concerning surface orientation and gap size effects

This paper addresses the pool boiling critical heat flux (CHF) phenomena in one-dimensional inclined rectangular channels by changing the orientation of a copper test heater assembly. In a pool of saturated water at atmospheric pressure, an account is taken of the gap sizes of 1, 2, 5, and 10 mm and the surface orientation angles from the downward-facing position (180 deg) to the vertical position (90 deg). Tests are conducted on the basis of the visualization of boiling phenomena utilizing a high-speed digital camera. In addition, an engineering correlation relating to the CHF near the vertical position is developed anchored in the experimental results. It is observed that the CHF generally decreases as the surface inclination angle increases and as the gap size decreases. In the downward-facing position (180 deg), on the other hand, the vapor escape and liquid refill are accelerated by the squeezing gap so that the CHF tends to increase as the gap size decreases. It is also found that there exists a transition angle, around which the CHF changes with a rapid slope on account of the CHF triggering mechanism differing with the inclination angle.

Internal vessel cooling feasibility attributed by critical heat flux in inclined rectangular gap

A cooling mechanism due to boiling in a gap between the debris crust and the reactor pressure vessel (RPV) wall was proposed for the TMI-2 reactor accident analysis. If there is enough heat transfer through the gap to cool the outer surface of the debris and the inner surface of the wall, the RPV wall may preserve its integrity during a severe core melt accident. If the heat removal through gap cooling relative to the counter-current flow limitation (CCFL) is pronounced, the safety margin of the reactor can be far greater than what had been previously known in the severe accident management arena. Should a severe accident take place, the RPV integrity will be maintained because of the inherent nature of degraded core coolability inside the lower head due to boiling in a narrow gap between the debris crust and the RPV wall. As a defense-in-depth measure, the heat removal capability by gap cooling coupled with external cooling can be examined for the Korean Standard Nuclear Power Plant (KSNPP) and the Advanced Power Reactor 1400MWe (APR1400) in light of the TMI-2 vessel survival. A number of studies were carried out to investigate the complex heat transfer mechanisms for the debris cooling in the lower plenum. However, these heat transfer mechanisms have not been clearly understood yet. The CHFG (Critical Heat Flux in Gap) experiments at KAERI were carried out to develop the critical heat flux (CHF) correlation in a hemispherical gap, which is the upper limit of the heat transfer. According to the CHFG experiments performed with a pool boiling condition, the CHF in a parallel gap was reduced by 1/30 compared with the value measured in the open pool boiling condition. The correlation developed from the CHFG experiment is based on the fact that the CHF in a hemispherical gap is governed by the CCFL and a Kutateladze type CCFL parameter correlates CCFL data well in hemispherical gap geometry. However, the results of the CHFG experiments appear to be limited in their value because the power of the heaters was restricted by the three-dimensional (3D) geometry. The two-dimensional (2D) geometry relative to the 3D geometry enables the heaters to produce higher power. Experiments were conducted to develop the CHF correlation for gap cooling with the 2D slices. The experimental facility consisted of a heater, a pressure vessel, a heat exchanger and the pressure and temperature measurement system. Tests were carried out in the pressure range of 0.1 to 1 MPa for the gap sizes of 1mm and 2mm using demineralized water.Copyright © 2002 by ASME

An Experimental Study of Critical Heat Flux in Narrow Gap With Two-Dimensional Slices

In light of the TMI-2 accident, in which the reactor vessel lower head survived the attack by molten core material, the in-vessel retention strategy was suggested to benefit from cooling the debris through a gap between the lower head and the core material. The GAMMA 1D (Gap Apparatus Mitigating Melt Attack One Dimensional) tests were conducted to investigate the critical heat flux (CHF) in narrow gaps with varying surface orientations. The CHF in an inclined gap, especially in case of the downward-facing narrow gap, is dictated by bubble behavior because the departing bubbles are squeezed. The orientation angle affects the bubble layer and escape of the bubbles from the narrow gap. The test parameters include gap sizes of 1, 2, 5 and 10 mm and the open periphery, and the orientation angles range from the fully downward-facing (180o) to the vertical (90o) position. The 15 ×35 mm copper test section was electrically heated by the thin film resistor on the back. The heater assembly was installed to the tip of the rotating arm in the heated water pool at the atmospheric pressure. The bubble behavior was photographed utilizing a high-speed camera through the Pyrex glass spacer. It was observed that more » the CHF decreased as the surface inclination angle increased and as the gap size decreased in most of the cases. However, the opposing results were obtained at certain surface orientations and gap sizes. Transition angles, at which the CHF changed in a rapid slope, were also detected, which is consistent with the existing literature. A semi-empirical CHF correlation was developed for the inclined narrow rectangular channels through dimensional analysis. The correlation provides with best-estimate CHF values for realistically assessing the thermal margin to failure of the lower head during a severe accident involving relocation of the core material. « less

/pdf/critical-heat-flux-in-inclined-rectangular-narrow-gaps-1jgoy7frjh.pdf

Critical Heat Flux in Inclined Rectangular Narrow Gaps

The GAMMA (Gap Apparatus against Molten Material Attack) experiments were performed using twodimensional (2D) circular slices employing the uniform heating method. The experimental facility consisted of a heater, a pressure vessel, a heat exchanger and the pressure and temperature measurement system. Tests were carried out in the pressure range of 0.1 to 1 MPa for the gap sizes of 1, 2 and 5 mm using demineralized water. In order to determine the local wall heat flux and the wall temperature, thirty-eight Type-K thermocouples were inserted at eighteen locations along the heated surface. The GAMMA 2D experiments were conducted to investigate the inherent cooling mechanism in the narrow gap. The critical heat flux (CHF) took place at the bottom earlier than at the top. Symmetric two-phase flows were not sustained in the 2D slice channel. There was thus a random flow pattern observed in the narrow gap cooling. The bubble size for the case of downward-facing heating was greater than that for the upward-facing heating. The counter-current flow limitation occurred due to transition from bubbly flow to slug and plug flow. The temperature in the bottom region increases due to dryout in high void fraction. The reason is that coalescence and departure of the isolated bubbles and slugs by the downward-facing heating are rather difficult to take place than in the upward-facing heating condition.

Yong Hoon Kim

Papers

One-dimensional critical heat flux concerning surface orientation and gap size effects

Internal vessel cooling feasibility attributed by critical heat flux in inclined rectangular gap

An Experimental Study of Critical Heat Flux in Narrow Gap With Two-Dimensional Slices

Critical Heat Flux in Inclined Rectangular Narrow Gaps

Critical Heat Fluxi in Narrow Gap in Two-dimensional Slices under Uniform Heating Condition (F451)