•This review explores passive enhancement of pool boiling using surface modification.•Examined are macrosacle, microscale, nanoscale and multiscale (hybrid-scale) techniques.•Addressed are ...performance goals of inhibiting incidence hysteresis and increasing both nucleate boiling heat transfer coefficient and CHF.•Shown is that micro and nano surface features are susceptible to blockage and changes in performance over time.
This paper provides a comprehensive review of published articles addressing passive enhancement of pool boiling using surface modification techniques. They include macroscale, microscale, and nanoscale surfaces, as well as multiscale (hybrid-scale), and hybrid-wettability techniques. Different enhancement methods are assessed in terms of underlying fluid routing mechanisms and ability to achieve three distinct heat transfer goals: eliminating incipient boiling hysteresis, increasing nucleate boiling heat transfer coefficient, and ameliorating critical heat flux (CHF), especially for inert dielectric coolants that are both highly wetting and possess relatively poor thermophysical properties. While different enhancement scales are shown to provide different degrees of success in achieving the three goals, it is shown that both microscale and nanoscale surface features are susceptible to blockage, resulting in deterioration of the enhancement over time. This review also points to scarcity of sufficiently sized databases for a given enhancement scheme in terms of fluid type, surface material, size, and orientation, enhancement shape, pattern, and scale, and operating pressure. This renders available findings less-than-adequate tools for design of practical cooling systems.
•Single-phase liquid and nucleate boiling regimes, and critical heat flux for spray cooling are reviewed.•Discussed are dominant mechanisms, data trends, and predictive correlations and models.•Also ...discussed are enhancement schemes, including surface modifications, additives to the liquid, and use of nanofluids.•It shows future work that must be conducted using many fluids and broad ranges of operating conditions.
This study is the first part of a two-part review of spray cooling, which addresses the relatively high-flux, low-temperature mechanisms and predictive tools associated with the single-phase liquid cooling and nucleate boiling regimes, as well as critical heat flux (CHF). The second part will be focused on the relatively high-temperature transition boiling and film boiling regimes, and the Leidenfrost point, which are encountered in quenching of metal alloy parts. In this part, key spray hydrodynamic parameters influencing heat transfer performance are identified, including volumetric flux, mean droplet diameter, and mean droplet velocity. This is followed by detailed identification of dominant mechanisms, data trends, correlations, and predictive models recommended by different research teams. Also discussed are spray cooling enhancement schemes, including micro and macro modifications to the surface itself, additives to the liquid, and use of nanofluids. Overall, contradictory findings point to a need for future experimental work that must be conducted systematically using many fluids with vastly different thermophysical properties, and broad ranges of operating conditions. There is also a need for further research to investigate parameters that influence CHF, including dissolved gas, spray inclination angle, and interaction between neighboring sprays when using multi-nozzle arrays to cool large surfaces.
•Popular two-phase computational schemes are discussed and contrasted.•Implementation of interfacial mass, momentum, and energy transfer are also discussed.•Presented are examples of computational ...models in boiling and condensation.•Review included bubble nucleation, film boiling, flow boiling, and flow condensation.•Identifies phase change phenomena that demand extensive computational modeling.
Developments in many modern applications are encountering rapid escalation in heat dissipation, coupled with a need to decrease the size of thermal management hardware. These developments have spurred unprecedented interest in replacing single-phase hardware with boiling and condensation counterparts. While computational methods have shown tremendous success in modeling single-phase systems, their effectiveness with phase change systems is limited mostly to simple configurations. But, given the complexity of phase change phenomena important to many modern applications, there is an urgent need to greatly enhance the capability of computational tools to tackle such phenomena. This article will review the large pool of published papers on computational simulation of boiling and condensation. In the first part of the article, popular two-phase computational schemes will be discussed and contrasted, which will be followed by discussion of the different methods adopted for implementation of interfacial mass, momentum and energy transfer across the liquid-vapor interface. This article will then review papers addressing computational modeling of bubble nucleation, growth and departure, film boiling, flow boiling, and flow condensation, as well as discuss validation of predictions against experimental data. This review will be concluded with identification of future research needs to improve predictive computational capabilities, as well as crucial phase change phenomena found in modern thermal devices and systems that demand extensive computational modeling.
•Transition boiling and film boiling regimes, and the Leidenfrost point for spray cooling are reviewed.•Discussed are dominant mechanisms, data trends, and predictive correlations and models.•Shown ...is how to predict the quench curve using spray correlations as boundary conditions.•Also shown is how the spray system can be configured to optimize mechanical properties of a quenched alloy part.
This paper is the second part of a comprehensive two-part review of spray cooling. The first part addressed the mechanisms and predictive tools associated with the relatively low-temperature single-phase liquid cooling and nucleate boiling regimes, as well as critical heat flux (CHF). The present part is focused on the relatively high-temperature transition boiling and film boiling regimes, and the Leidenfrost point. Discussed are dominant mechanisms, data trends, and predictive correlations and models. This information is especially important to the quenching of metal alloy parts from high initial temperature during heat treating. It is shown how correlations for the different spray cooling regimes and transition points can be implemented into boundary conditions for heat diffusion models to predict the temperature-time (quench) curve everywhere within the quenched part. It is also shown how the quench curve can be combined with the alloy’s transformation kinetics to predict mechanical properties. By properly configuring the sprays used to quench complex-shaped parts, it is also possible to greatly enhance the mechanical properties while minimizing residual stresses.
•Different pool boiling CHF mechanisms and parametric trends are reviewed.•Also reviewed are modifications to mechanisms proposed to improve predictive accuracy.•Available models are shown to focus ...on specific parametric influences but not others.•The study points to the need for better understanding of near-wall interfacial behavior.
Critical heat flux (CHF) is arguably the most important design and safety parameter for any heat-flux controlled boiling application. The present two-part study is focused on CHF for pool boiling from flat surfaces. The first part will review different CHF models and associated mechanisms and parametric trends, while the second part will be dedicated to assessment of CHF models and correlations. Aside from Kutateladze’s 1948 pioneering CHF formulation, which is based on dimensional analysis, five different CHF mechanisms are prevalent in the literature: bubble interference, hydrodynamic instability, macrolayer dryout, hot/dry spot, and interfacial lift-off. Additionally, many modifications to these mechanisms have been proposed to improve predictive accuracy in tackling the parametric influences of pressure, surface size and roughness, surface orientation, and contact angle. Among the five mechanisms, Zuber’s hydrodynamic instability theory has received the most attention because of both its mechanistic formulation and theoretical appeal. More recently, the interfacial lift-off mechanism, which is also theoretically based, has received significant experimental validation, and offers the advantage of tackling different surface orientations. Overall, it is shown that, despite the large body of published pool boiling CHF literature, there are major data gaps in the coverage of relevant parameters. This points to a need for more strategically planned future experiments that would also include microphotographic analysis of near-wall interfacial features, in order to validate or dispute proposed CHF mechanisms.
•This review article explores the evolution of liquid drop impact on a liquid film.•Both experimental and numerical methods used in prior studies are highlighted.•Emphasis is placed on high velocity ...impact, and formation of ejecta sheet, crown sheet, and splashing of secondary droplets.•Other topics reviewed are impact on curved wetted surfaces, multi-drop impact, and low-velocity impact.•Recommendations are provided for future research to address poorly understood and/or contradictory issues.
Research on liquid drop impact, especially during the past two decades, has been motivated by a need for better predictive capability in many industries. This paper will review published works concerning mass and momentum interactions during drop impact on a liquid film. First, both experimental and numerical methods for capturing the evolution of the impact will be highlighted. This will be followed by a detailed description of the impact, including formations of the ejecta sheet, crown sheet, and splashing of secondary droplets during high-velocity impact. Other topics reviewed are impact on curved wetted surfaces, multi-drop impact, and the phenomena of spreading, coalescence and rebound in low-velocity impact. Each of these phenomena is discussed in terms of underlying physical mechanisms and predictive correlations and/or models. Despite significant past efforts to understand and characterize these phenomena, it is shown that much uncertainty remains, especially in regards to the interfacial features around the drop-film neck region during the earliest stages of the impact. Recent state-of-art advances in both experimental and numerical methods are shown to play a crucial enabling role in future research. The review is concluded with recommendations concerning future work that is needed to address poorly understood and/or contradictory issues.
Space agencies worldwide are actively exploring the implementation of two-phase thermal management systems to support astronaut life onboard future space vehicles and planetary bases. Key motivations ...for these efforts are to increase the efficiency of power utilization and reduce overall weight and volume. These advantages are realized by orders of magnitude enhancement in heat transfer coefficient achieved with flow boiling and condensation compared to single-phase systems. This study will review published literature concerning two-phase flow and heat transfer in reduced gravity. Discussed are the different methods and platforms dedicated to exploring the influence of reduced gravity, including ground flow boiling experiments performed at different orientations relative to Earth gravity, as well as reduced gravity adiabatic two-phase flow, pool boiling, flow boiling and CHF experiments. Despite the extensive data and flow visualization results available in the literature, it is shown that there is a severe shortage of useful correlations, mechanistic models and computational models, which compromises readiness to adopt flow boiling in future space systems. Key recommendations are provided concerning platform, heater design, and operating conditions for future studies to expedite the deployment of two-phase thermal management in future space missions.
The importance of flow boiling and condensing mini/micro-channel devices to a large number of modern applications has spurred an unusually large number of research efforts that culminated in many ...types of predictive tools. These efforts have inadvertently contributed enormous confusion when selecting a suitable predictive method. This study reviews methods for predicting heat transfer in condensing and boiling mini/micro-channel flows. Systematic assessment of predictive accuracy of individual methods requires the development of consolidated mini/micro-channel databases for condensation heat transfer, dryout incipience quality, and saturated boiling heat transfer. These databases cover numerous working fluids and broad ranges of geometrical and flow parameters. It is shown that, despite the success of previous predictive methods for specific fluids and narrow databases, these methods are incapable of providing accurate predictions against entire consolidated databases. The consolidated databases are used to develop 'universal' correlations with very broad application range. These include two separate correlations for condensation heat transfer, one for annular flow and the other for slug and bubbly flows. Also developed are correlations for dryout incipience quality and saturated boiling heat transfer; the later is shown to accurately tackle both nucleate boiling dominated and convective boiling dominated regimes up to the location of incipient dryout.
Experiments were performed to explore the micro-channel cooling benefits of water-based nanofluids containing small concentrations of Al
2O
3. The high thermal conductivity of nanoparticles is shown ...to enhance the single-phase heat transfer coefficient, especially for laminar flow. Higher heat transfer coefficients were achieved mostly in the entrance region of micro-channels. However, the enhancement was weaker in the fully developed region, proving that nanoparticles have an appreciable effect on thermal boundary layer development. Higher concentrations also produced greater sensitivity to heat flux. Despite this enhancement, the overall cooling effectiveness of nanoparticles was quite miniscule because of the large axial temperature rise associated with the decreased specific heat for the nanofluid compared to the base fluid. For two-phase cooling, nanoparticles caused catastrophic failure by depositing into large clusters near the channel exit due to localized evaporation once boiling commenced. These and other practical disadvantages bring into question the overall merit of using nanofluids in micro-channel heat sinks.
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