In this study, closed loop chilldown experiments are performed on a 0.009525 m outer diameter SS-316 tube of length 0.6 m and thickness 0.001651 m in a horizontal flow configuration with PF-5060 as ...the working fluid. The challenges associated with the development of a closed loop chilldown test section in comparison with conventional open loop cryogenic chilldown experiments are discussed and the methods to overcome this are presented. The test section tube is heated to around 246–249 °C to perform the chilldown tests and the film, transition and nucleate boiling regimes along with the single phase liquid convective regimes are captured in the present experiments. To understand the effect of inlet mass flux on the chilldown characteristics of the tube, tests are performed at different inlet mass fluxes ranging from 132.83 kg/m2s – 1303.96 kg/m2s (Inlet Reynolds number ranging from 1,291–12,679) covering the entire regime of laminar to transition to turbulent inlet flows for inlet subcoolings of 33.3 – 41.9 °C. The effect of the inlet conditions on the behavior of chilldown curves, temperature of transition points (rewetting and onset of nucleate boiling), critical heat fluxes, heat flux curves, parasitic heat losses, regime-specific time-averaged heat fluxes and heat transfer coefficients are analyzed at different wall locations. The chilldown performance parameters such as chilldown time, liquid consumption and quench front propagation/rewetting velocities are compared at different inlet conditions and axial wall locations.
•Demonstrated the working of a closed loop chilldown test section.•Chilldown process able to mimic the cryogenic chilldown process.•Rewetting temperatures increase with increase in inlet mass flux.•Critical heat fluxes increase with increase in inlet mass flux.•Time-averaged heat flux and HTC’s increase with increase in inlet mass flux.
•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.
Effects of heater's thermal properties and vapor phase's thermal conductivity on saturated pool boiling above a large horizontal heater are simulated numerically based on an improved pseudo-potential ...liquid-vapor phase change lattice Boltzmann model. A transient conjugate heat transfer problem is under consideration, where the conjugate thermal boundary condition is imposed and heater's thermal responses during boiling processes are investigated. Saturated pool boiling curves from onset of nucleate boiling to critical heat flux (CHF), to transition boiling regime to stable film boiling regime are obtained numerically. It is found that the simulated critical heat flux (CHF) agrees reasonably well with existing analytical models. Also, the simulated boiling heat fluxes in stable film boiling regime are shown to be in good agreement with the existing analytical solution. Thus, this improved pseudo-potential liquid-vapor phase change lattice Boltzmann model is quantitatively validated. Simulation results demonstrate that there is significant maldistribution in temperature distribution near the top of heater surface in nucleate boiling regime, CHF point and transition boiling regime. As a result, two-dimensional heat conduction can not be ignored when evaluating heat flux closely beneath the heater's top surface. It is also shown that both heater's thermal conductivity and thermal mass (the product of density and specific heat at constant pressure) have no effect on CHF value as well as the boiling curve in nucleate boiling regime and film boiling regime for a thick heater. However, the transition boiling regime of the boiling curve moves to the left with the increasing heater thermal conductivity and heater thermal mass for a thick heater. Increasing the vapor theraml conductivity has no effect on CHF but would increase boiling heat flux in film boiling regime, and hence shortening the transition boiling regime.
Effects of wettability on saturated pool boiling heat transfer from a smooth superheated substrate, with a finite thickness at constant wall temperatures at the bottom, are investigated based on a ...recently developed liquid–vapor phase-change lattice Boltzmann method. For a hydrophilic surface, it is shown that bubble departure diameter and bubble departure frequency increase with the increase of contact angle and superheat, and the whole bubble departs from the surface with a waiting period in the ebullition cycle. A microlayer of liquid exists between the bubble and the heated hydrophilic surface and this region exhibits a high local heat flux during bubble growth period. On the other hand, a residual bubble will be left on the surface when bubble departs from a hydrophobic surface and hence no waiting period exists. No microlayer exists on the heated hydrophobic surface, and the three-phase contact line region has the highest local heat flux and lowest local temperature. Time histories of the wall temperature on the top of a hydrophilic substrate and a hydrophobic substrate as well as the associated heat flux are studied in details during the nucleate boiling process. Effects of wettability, superheat and heater size on number of nucleation sites in saturated pool boiling are investigated. Saturated boiling curves (from onset of nucleate boiling to critical heat flux, to transition boiling to stable film boiling) for hydrophilic and hydrophobic heating surfaces are obtained by numerical simulation for the first time.
•Overview of new universal cryogenic flow boiling and pressure drop correlations is presented.•Logic for patching the individual boiling correlations is presented.•Numerical model is presented for ...solving steady state cryogenic flow boiling wall temperature.•Example cases are given for heat flux or temperature-drive boundary conditions.
To enable the design of future in-space cryogenic propellant vehicles such as Lunar and Martian ascent and descent stages, fuel depots, and nuclear thermal propulsion systems, high-accuracy models of various phases of the propellant transfer process are required. This paper focuses on modeling steady-state flow boiling through the transfer line that connects a propellant tank to an engine or customer receiver tank, which is required to set limits on the allowable heat flux into the line. Using the largest-ever collection of available cryogenic heated tube data, universal cryogenic flow boiling correlations were recently developed for various regimes of the boiling curve and their transition points. However, to model flow boiling in heated tubes, these individual correlations must be patched together to provide a continuous predictive curve of wall superheat as a function of preponderant parameters. This paper provides an overview of the individual flow boiling correlations along with the logic and rationale for patching the correlations together to produce a single continuous boiling curve. Resulting flow boiling curves are presented for different possible permutations of independent inlet and flow conditions for illustration.
Highlights•Indicate the correlation among the temporal and spatial behaviors of the vapor bubbles, the averaged heat transfer characteristics, and the accompanying boiling sound in so-called ...“microbubble emission boiling (MEB).”•Indicate the synchronous oscillation of the vapor bubbles on the heat transfer surface.•Quantify the homogeneity of the vapor bubble oscillation via cross-correlation between the local oscillations at different radial positions.
We investigate so-called “microbubble emission boiling (MEB)” on a horizontal circular heat transfer surface in a pool via experimental approach. We indicate the correlation among the temporal and spatial behaviors of the vapor bubbles, the averaged heat transfer characteristics, and the accompanying boiling sound. We show that the vapor bubbles oscillate in a non-uniform manner in the radial direction immediately after the MEB transition. As the MEB develops by increasing the power input to the heaters, the vapor bubbles exhibit synchronous oscillation on the heat transfer surface as if they oscillate homogeneously. The homogeneity of the vapor bubble oscillation in the radial direction is quantified by the cross-correlation between the local oscillations. We illustrate significant variations of the heat transfer characteristics and the boiling sound driven by the homogeneous vapor bubble oscillation after the transition to the fully developed MEB.
•Boiling states with microbubble emission boiling are identified by deep learning.•Subcooled pool boiling was investigated in three cases of subcooled temperatures.•Boiling sounds were analyzed by a ...cepstrum algorithm.•Algorithms were tested for accuracy in predicting wall superheat and heat flux.•Boiling sound analyzed by cepstrum plays an important role in heat flux prediction.
Microbubble emission boiling (MEB) is a cooling technology in which the heat flux can potentially exceed the critical heat flux (CHF). Reliable predictions of the occurrence of MEB are necessary to achieve stable MEB and to induce it under actual environment conditions. In this study, we developed a method based on deep learning with boiling sound to predict the boiling state of the interval before the low-heat-flux level reaches MEB. The boiling sound was acquired by a hydrophone, and the sound was adopted to machine learning algorithms, which were subsequently applied to classification and regression models. The feature extraction algorithms for the boiling sounds were spectrum or cepstrum methods. Both methods were comparatively investigated in terms of the machine learning accuracy. As a result, in the case of the cepstrum method as the feature extraction, the accuracy was improved. In particular, we found that the regression model demonstrated substantially better accuracy than the classification model. In addition, accurate predictions were possible even when the degree of subcooling was changed.
•Effects of liquid subcooling, surface coating, material property, and surface oxidation are examined.•Liquid subcooling affects remarkably the quenching phenomena.•Cr-coated surfaces for ATF might ...extend the quenching duration.•Solids with low heat capacity shorten the quenching duration.•Surface oxidation can affect strongly the film boiling heat transfer and MFB point.
In this work, the effects of liquid subcooling, surface coating, material property, and surface oxidation on transient pool boiling heat transfer were investigated experimentally using the vertical metal rod and quenching method. The change in rod temperature was measured with time during quenching, and the visualization of boiling around the test specimen was performed using the high-speed video camera. As the test materials, the zircaloy (Zry), stainless steel (SS), niobium (Nb), and copper (Cu) were tested. In addition, the chromium-coated niobium (Cr-Nb) and chromium-coated stainless steel (Cr-SS) were prepared for accident tolerant fuel (ATF) application. Low liquid subcooling and Cr-coating shifted the quenching curve to the right, which indicates a prolongation of quenching duration. On the other hand, the material with small heat capacity and surface oxidation caused the quenching curve to move to the left. To examine the influence of the material property and surface oxidation on the film boiling heat transfer performance and minimum film boiling (MFB) point in more detail, the wall temperature and heat flux were calculated from the present transient temperature profile using the inverse heat transfer analysis, and then the curves of wall temperature and heat flux in the film boiling regime were obtained. In the present experimental conditions, the effect of material property on the film boiling heat transfer performance and MFB point seemed to be minor. On the other hand, based on the experimental results of the Cu test specimen, the surface oxidation had great impact on them. As compared with the as-received Cu test specimen, the pre-oxidized one showed the higher film boiling heat transfer performance and MFB heat flux, but it had the lower MFB temperature.
•This review includes effects of magnetic fields and electric fields on boiling heat transfer and CHF.•Mechanisms of CHF and boiling heat transfer enhancement by magnetic fields and electric fields ...are explored.•The achievements, results and inconsistencies existing in the literature are discussed in detail.•Some recommendations and future research directions for future studies are suggested.
Taking advantage of electric fields and magnetic fields during boiling processes can be a very beneficial way for enhancement of boiling heat transfer and increase of the critical heat flux values. Applying magnetic fields and electric fields are promising active techniques which contribute to higher heat flux accompanied by small wall superheat temperature. This paper consist a complete review of published literature about effects of applying magnetic fields and electric fields on heat transfer and critical heat flux during pool boiling and flow boiling processes. The paper also includes the major affecting parameters and mechanisms reported in the literature about the boiling heat transfer and critical heat flux in the presence of magnetic fields and electric fields. The related achievements, results, inconsistencies and contradictions existing in the literature are identified and discussed in detail. Some recommendations and research directions for future studies are suggested.
•Study of surface roughness effect on pool boiling of water on hydrophobic surfaces.•Boiling heat transfer coefficients varied with surface roughness and contact angle.•Trends related to number of ...nucleation sites and vapor blanketing.•Proposed empirical heat flux correlation with contact angle.
The effect of surface roughness on the pool boiling of water on hydrophobic surfaces was investigated over the entire boiling regime, from the onset of nucleate boiling to film boiling. The hydrophobic surfaces were fabricated by coating a polytetrafluoroethylene layer on 10 × 10 mm2 copper surfaces roughened by various sandpapers. The average roughness of the hydrophobic surfaces ranged from 0.042 to 1.54 μm and the corresponding contact angles varied from 116° to 153°. Boiling heat transfer coefficients (BHTC) for the rough surfaces were initially high, but decreased rapidly as the heat flux increased, whereas the BHTCs for the smooth surfaces slowly increased to reach their maximum values and then decreased. The variation in BHTC was explained in terms of the number of nucleation sites and vapor blanketing on the boiling surface, which were related to both the roughness and contact angle. An empirical critical heat flux (CHF) correlation, which showed a 12.2% mean absolute error with the present data, was proposed. Inclusion of the current CHF data for the hydrophobic region provided a complete understanding of the effect of surface roughness and wettability on the CHF in pool boiling of water.
