A review of the recent advances in superhydrophobic surfaces and the emerging energy-related applications

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

Review on improvement for air source heat pump units during frosting and defrosting

Activating the Microscale Edge Effect in a Hierarchical Surface for Frosting Suppression and Defrosting Promotion

/pdf/activating-the-microscale-edge-effect-in-a-hierarchical-3v9a312w5a.pdf

This study reviewed the defrosting techniques applicable for the heating, ventilation, air-conditioning, and refrigeration industry, including passive, active, and system techniques. The passive methods normally use treated surfaces by changing the surface morphology through micro-grooved, anti-frost coating, hydrophilic, hydrophilic, or superhydropholic coating. For passive defrosting techniques, the microgrooved surfaces can improve the drainage of the frost melt effectively. It is generally agreed that the superhydropholic coating can delay the initialization of frosting and provides less water adhesion during defrosting. Yet defrosting performance for hydrophobic surfaces outperforms hydrophilic and uncoated surfaces. Active and system techniques, including electrohydrodynamic (EHD), low-frequency oscillation, and ultrasonic vibration methods, hot gas reverse cycle, electric heater, desiccant dehumidifiers and controlling strategies are reviewed. The EHD defrosting method is proved to be comparatively effective in natural or laminar flow operation. Test results also indicate that utilization of alternative current source is superior to the direct current source. The electrode with negative polarity is better than positive polarity as far as frost accumulation is concerned. The low-frequency oscillation is ineffective in defrosting while ultrasonic vibration provides effective frost removal and can delay the frost growth appreciably. Test results indicate that the ultrasonic oscillation poses considerable positive influence on defrosting either operated continuously or intermittently, in direct contact or not. For system defrosting, the hot gas reverse cycle is comparatively expensive to install but the efficiency, COP, and energy consumption are superior to the other system methods. Desiccants, either solid or liquid, can be employed in association with the system defrosting methods to lower energy consumption. There were various controlling strategies to detect the frost formation and to decide the best time to initiate defrosting. However, many of them were applicable to some specific systems and environments and require further investigations to test the relevant reliability, stability, and repeatability.

Review of defrosting methods

Prediction of the frost formation on a cold flat surface

The effects of the heat exchanger surface treatment on the frosting/defrosting behavior in a fin-tube heat exchanger are investigated experimentally. It is found that the hydrophilic surface mainly influences the frosting behavior, while the hydrophobic surface has some influence on the defrosting behavior. In view of the frosting, a surface-treated heat exchanger with either hydrophilic or hydrophobic characteristic shows little improvement in the thermal performance rather than the bare aluminum heat exchanger. The results reveal that the heat exchanger with a hydrophobic surface treatment is more effective in view of the defrosting efficiency and time. The amount of residual water on the surface-treated heat exchangers is shown to be smaller than that of the bare heat exchanger. Therefore further improvements on the performance of re-operations are expected.

Effect of surface treatments on the frosting/defrosting behavior of a fin-tube heat exchanger

This invention relates to refrigerators, and more particularly to a refrigerator in which a vacuum space is formed between an outer case and an inner case of a body thereof for enhancing a heat insulating function. The refrigerator includes a body having a storage space for storing a predetermined storage object, wherein the body includes an inner case having the storage space, an outer case having an inside surface spaced a predetermined gap from an outside surface of the inner case to house the inner case, and a vacuum space provided between the inner case and the outer case sealed to maintain a vacuum state for heat insulating between the inner case and the outer case.

Refrigerator comprising vacuum space

A refrigerator and a driving method thereof are disclosed. A primary compressor(11) and a secondary compressor(12) can form independent cycles together with corresponding evaporators(14,15) so as to reduce unnecessary power consumption. Also, a backflow prevention valve(20) is installed between the primary and secondary compressors to prevent an increase in pressure of the secondary compressor, or an auxiliary heat exchanger(30) is installed at the outlet side of a second evaporator(15) with high temperature to allow heat exchange of an inlet side pipe(L1) of a first evaporator with low temperature so as to shift a load of a freezing chamber into a relatively large refrigerating chamber, thereby improving efficiency of the refrigerator. In addition, an oil separator(120,130) or an oil collection pipe(121,131) is installed at the outlet sides of the compressors or an oil balancing pipe(221) and an oil balancing valve(222) are installed between the compressors, so as to uniformly maintain an oil amount between the compressors.

Refrigerator and driving method thereof

A refrigerator includes: a refrigerator body having a cooling chamber for storing food items and a mechanic chamber provided at one side thereof; a heat exchanger disposed in the mechanic chamber and performing heat exchanging while a refrigerant passes therethrough; a cross flow fan disposed facing the heat exchanger and blowing air for heat exchange; and a compressor mounted inside the mechanic chamber and compressing a refrigerant. A space for the mechanic chamber can be reduced, and thus, a cooling chamber for keeping food items can be enlarged.

Sung Jhee

Papers

Prediction of the frost formation on a cold flat surface

Effect of surface treatments on the frosting/defrosting behavior of a fin-tube heat exchanger

Refrigerator comprising vacuum space

Refrigerator and driving method thereof

Refrigerator having cross flow fan