Vapor condensation plays a key role in a wide range of industrial applications including power generation, thermal management, water harvesting and desalination. Fast droplet nucleation and efficient droplet departure as well as low interfacial thermal resistance are important factors that determine the thermal performances of condensation; however, these properties have conflicting requirements on the structural roughness and surface chemistry of the condensing surface or condensation modes (e.g., filmwise vs dropwise). Despite intensive efforts over the past few decades, almost all studies have focused on the dropwise condensation enabled by superhydrophobic surfaces. In this work, we report the development of a bioinspired hybrid surface with high wetting contrast that allows for seamless integration of filmwise and dropwise condensation modes. We show that the synergistic cooperation in the observed recurrent condensation modes leads to improvements in all aspects of heat transfer properties including droplet nucleation density, growth rate, and self-removal, as well as overall heat transfer coefficient. Moreover, we propose an analytical model to optimize the surface morphological features for dramatic heat transfer enhancement.

Recurrent filmwise and dropwise condensation on a beetle mimetic surface.

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

Condensation is a phase change phenomenon often encountered in nature, as well as used in industry for applications including power generation, thermal management, desalination, and environmental control. For the past eight decades, researchers have focused on creating surfaces allowing condensed droplets to be easily removed by gravity for enhanced heat transfer performance. Recent advancements in nanofabrication have enabled increased control of surface structuring for the development of superhydrophobic surfaces with even higher droplet mobility and, in some cases, coalescence-induced droplet jumping. Here, we provide a review of new insights gained to tailor superhydrophobic surfaces for enhanced condensation heat transfer considering the role of surface structure, nucleation density, droplet morphology, and droplet dynamics. Furthermore, we identify challenges and new opportunities to advance these surfaces for broad implementation in thermofluidic systems.

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Condensation Heat Transfer on Superhydrophobic Surfaces

Although conventional electromechanical circuit breakers have a proven record as effective and reliable devices for circuit protection, emerging power distribution technologies and architectures, such as dc microgrids, require improved interruption performance characteristics (eg, faster switching speed) The need for faster switching operation, in combination with the latest developments of advanced power semiconductor technologies, has spurred an increase in the research and development in the area of solid-state circuit breakers This article provides a comprehensive review of various solid-state circuit breaker technologies that have been reported in the literature during recent years First, we categorize solid-state circuit breakers based on key features and subsystems, including power semiconductor devices, main circuit topologies, voltage clamping methods, gate drivers, fault detection methods, and commutation methods for power semiconductor devices Second, we discuss the various challenges associated with the design of solid-state circuit breakers from the perspective of generic applications and provide a comparison of several solid-state breaker technologies based on key metrics Finally, we provide a useful framework and point of reference for future development of solid-state circuit breakers for many emerging power distribution applications

A Review of Solid-State Circuit Breakers

Superhydrophobic surfaces have shown excellent ability to promote dropwise condensation with high droplet mobility, leading to enhanced surface thermal transport. To date, however, it is unclear how superhydrophobic surfaces would perform under the stringent flow condensation conditions of saturated vapor at high temperature, which can affect superhydrophobicity. Here, we investigate this issue employing "all-copper" superhydrophobic surfaces with controlled nanostructuring for minimal thermal resistance. Flow condensation tests performed with saturated vapor at a high temperature (110 °C) showed the condensing drops penetrate the surface texture (i.e., attain the Wenzel state with lower droplet mobility). At the same time, the vapor shear helped ameliorate the mobility and enhanced the thermal transport. At the high end of the examined vapor velocity range, a heat flux of ~600 kW m(-2) was measured at 10 K subcooling and 18 m s(-1) vapor velocity. This clearly highlights the excellent potential of a nanostructured superhydrophobic surface in flow condensation applications. The surfaces sustained dropwise condensation and vapor shear for five days, following which mechanical degradation caused a transition to filmwise condensation. Overall, our results underscore the need to investigate superhydrophobic surfaces under stringent and realistic flow condensation conditions before drawing conclusions regarding their performance in practically relevant condensation applications.

Flow condensation on copper-based nanotextured superhydrophobic surfaces.

The present paper reports local heat transfer coefficients measured during condensation of R1234yf within a single circular 0.96 mm diameter minichannel and compares them to the ones of R134a. This experimental work is carried out in a unique test apparatus which allows to determine the local heat flux extracted from the condensing fluid from the temperature profile of the coolant. For this purpose, the temperatures of the coolant and of the wall are measured along the test section. The saturation temperature is determined from the saturation pressure which is measured at inlet and outlet of the test channel. Condensation tests are carried out at mass fluxes ranging between 200 and 1000 kg m−2 s−1 and the heat transfer coefficients result to be lower as compared to the ones of R134a. Since the saturation temperature drop directly affects the heat transfer rate, the pressure drop during adiabatic two-phase flow of R1234yf is also measured and compared to R134a.

Heat transfer and pressure drop during condensation of the low GWP refrigerant R1234yf

In this paper, we present the development of an air-cooled 1MW bi-directional DC Solid State Circuit Breaker (SSCB) based on recently developed 91mm, 25kV Reverse Blocking-IGCT (RB-IGCT) The power electronic switch (RB-IGCT) has been designed and optimized to have very low conduction losses, less than 1kW at 1kA (on-state voltage drop 65kA at 16kV, 400K) which are the most important concerns of semiconductor based circuit breaker We also present the simulation and experimental results at the system level ie analyzed the influence of the Surge Arrester (SA) on the over-voltage transients during current interruption We also analyzed the thermal management for the newly developed SSCB using ANSYS Icepak and validated experimentally

1MW bi-directional DC solid state circuit breaker based on air cooled reverse blocking-IGCT

Since many HFC refrigerants have relatively large values of GWP, recent development efforts have been initiated to investigate halogenated olefins as possible refrigerants, with fluorinated propene isomers, in particular, having emerged as possible solutions. Specifically, R1234yf has emerged as an R134a replacement for automotive applications. In this paper, the local heat transfer coefficient measured during flow boiling of R1234yf in a 1 mm diameter circular microchannel is reported and compared to R134a. During tests, the heat is provided to the boiling fluid by using a secondary fluid. Therefore the heat flux is not imposed but instead it is the result of the inlet temperatures of the two fluids and the thermal resistances on the two sides, as it occurs in actual heat exchangers for automotive and air-conditioning applications. Flow boiling tests are carried out at 31 °C saturation temperature and mass fluxes ranging between 200 kg m−2 s−1 and 600 kg m−2 s−1.

Flow boiling of R1234yf in a 1 mm diameter channel.

Experiments and updated model for two phase frictional pressure drop inside minichannels

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