•Heat transfer coefficients for mixtures were measured on a vertical falling film.•Ethanol/water and ethanol/MM were investigated at 1 bar between 40 and 100 kW/m².•Increase in heat transfer ...coefficients may have been caused by the Marangoni effect.•An enhanced heat transfer correlation has been developed.
To replace state-of-the-art working fluids in thermodynamic cycles in respect to environmental and efficiency perspective is a current engineering task. In this context, fluid mixtures represent an important research approach. However, the existing correlations for heat transfer coefficient for mixture boiling are complex and uncertain due to diverse thermophysical properties.
In this study, nucleate boiling heat transfer coefficients were experimentally determined for the binary mixtures ethanol/water and ethanol/MM on a vertical falling film at a copper tube for 1 bar and a heat flux range of 40 to 100 kW/m². The heat transfer measurements for ethanol/water show a well-known behavior, and coefficients decrease below the pure fluid heat transfer coefficients due to mass transfer resistances. In contrast, measurement data for the ethanol/MM mixture has shown an increase in heat transfer coefficients compared to the pure fluids. The Marangoni effect may have caused this increase. An enhanced heat transfer correlation was proposed based on the correlation of Schlünder under consideration of surface tension and density differences of the pure components. This newly developed correlation is able to predict the heat transfer characteristics of ethanol/water and ethanol/MM very well, and the deviation in the calculation is reduced significantly. The average mean deviation for ethanol/water was 13.3 % and for ethanol/MM only 11.1 %. The general validity of the developed correlation was determined based on ten additional binary mixtures from literature in a pressure range of 1–6 bar and in a heat flux range of 30–1000 kW/m². The overall mean deviation concerning the entire data set for the binary mixtures was 18.5 % for Fujita and Tsutsui, 20 % for Inoue and Monde, 18.6 % for the Thome and Shakir correlation, 16.1 % for Schlünder, and 11.6 % for the enhanced correlation.
•A novel refrigerant-based battery thermal management system is proposed.•Temperature distributions and boiling characteristics are predicted.•The maximum temperature is inversely correlated with ...refrigerant inlet velocity.•Temperature uniformity is predominantly affected by nucleate boiling heat transfer.
In this paper, a novel battery thermal management system (BTMS) using the dielectric, non-flammable HFE-7000 refrigerant is proposed for electric vehicles (EVs). Its thermal performance is studied both numerically and experimentally. The refrigerant flows and boils on the battery wall surfaces, which lowers the thermal contact resistance as well as enhances the heat transfer process. Therefore, the thermal performance of the battery module is improved. The results indicate that forced convection heat transfer of the liquid refrigerant is dominating in the control of the temperature rise in the battery module. The maximum battery temperature drops to 35.10°C at 0.3ms-1 inlet velocity and a 5C discharge rate. In contrast, the temperature uniformity between individual battery cells primarily depends on the nucleate boiling heat absorption and local perturbation of the two-phase turbulent flow. A temperature difference of no more than 3.71°C can be observed at 5C discharge rate and 0.1ms- 1. In addition, good agreement was found between the numerical results and experimental data.
•CFD based analysis and modeling of the Onset of Nucleate Boiling for convective liquid boiling in narrow rectangular upward channels.•Onset of Nucleate Boiling model development based on CFD data to ...allow wide validity range.•The proposed Onset of Nucleate Boiling model takes into account features of convective boiling.•The new Onset of Nucleate Boiling model provides accurate predictions.
Despite that mechanistic and accurate correlations predicting the Onset of Nucleate Boiling (ONB) for pool boiling are widely presented in the literature, models for forced convective boiling remain few. These models do not provide the desired quality, principally because they do not consider important features of convective boiling. In this work, numerical investigations of the ONB for water boiling flow at atmospheric pressure upward a narrow rectangular channel (3 mm × 100 mm × 400 mm) are carried out based on Computational Fluid Dynamics (CFD) simulations. The predictions of the CFD calculations are validated with the available experimental data. A new ONB model incorporating the convective boiling features is developed and proposed. This model is derived based on several CFD simulation data, covering wide operating conditions. The flow Reynolds number ranges from 959 to 13500, inlet subcooling from 2.5 to 30 K and applied heat flux from 5 to 90 kW/m2. The new model predictions have a standard deviation of 2.7% where its performance is better than ±0.3 K when compared with additional simulation data that are provided for validation.
•A physics-informed machine learning-aided (hybrid) framework is proposed.•Prediction of critical heat flux is performed using the hybrid framework.•The hybrid framework has demonstrated superior ...performance over standalone approaches.•The framework applicability domain and model complexity can be extended on the fly.•Window-type extrapolation mapping is proposed to help inform future experiments.
The critical heat flux (CHF) corresponding to the departure from nucleate boiling (DNB) crisis is essential to the design and safety of a two-phase flow boiling system. Despite the abundance of predictive tools available to the thermal engineering community, the path for an accurate, robust CHF model remains elusive due to lack of consensus on the DNB triggering mechanism. This work aims to apply a physics-informed machine learning (ML)-aided hybrid framework to achieve superior predictive capabilities. Such a hybrid approach takes advantage of existing understanding in the field of interest (i.e., domain knowledge) and uses ML to capture undiscovered information from the mismatch between the actual and domain knowledge-predicted target. A detailed case study is carried out with an extensive DNB-specific CHF database to demonstrate (1) the improved performance of the hybrid approach as compared to traditional domain knowledge-based models, and (2) the hybrid model’s superior generalization capabilities over standalone ML methods across a wide range of flow conditions. The hybrid framework could also readily extend its applicability domain and complexity on the fly, showing an elevated level of flexibility and robustness. Based on the case study conclusions, the window-type extrapolation mapping methodology is further proposed to better inform high-cost experimental work.
•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.
•Cryogenic flow boiling CHF database was amassed from world literature•Database consists of 2312 data points for LH2, LHe, LN2 and LCH4•Using the database, new universal CHF correlations are ...constructed•Separate correlations are developed for Departure from Nucleate Boiling (DNB) and Dryout
Experiments to determine critical heat flux (CHF) for cryogen flow in uniformly heated, round tubes have been performed throughout the globe during the past sixty years. However, experimental CHF data for cryogens are rarely published, remaining in the archives of authors, or in obscure technical reports of an organization or other inaccessible sources. In the present study, the Purdue University-Boiling and Two-Phase Flow Laboratory (PU-BTPFL) Cryogen Flow Boiling CHF Database is consolidated from world literature dating back to 1959. With 2312 data points for LH2, LHe, LN2 and LCH4, it represents the largest cryogen CHF database assembled to date. The database encompasses diameters from 0.5 to 14.1 mm, critical length-to-diameter ratios from 2.5 to 230.8 (term ‘critical’ refers to axial location where CHF is detected), system pressures from 0.01 to 4.07 MPa, reduced pressures from 0.1 to 0.93, mass velocities from 2.2 to 8203.9 kg m−2 s−1, inlet subcoolings from 0 to 78.9 K, inlet qualities from -2.06 to 0.95, critical subcoolings from 0 to 48.5 K, critical qualities from -1.23 to 1.00, critical void fractions from 0 to 1, and CHF values from 0.05 to 8203.9 kW m−2. The consolidated database represents an invaluable tool for development of CHF correlations – a primary goal for the present study – as well as future analytic and computational models. Using this database, new universal CHF correlations are constructed for two distinct CHF mechanisms, Departure from Nucleate Boiling (DNB) and Dryout, after careful physics-based segregation of the data. With mean absolute errors below 30%, the new CHF correlations are shown to provide good predictive agreement with the database.
The effect of characteristic of heating surface on nucleate boiling heat transfer is well reported via many previous results. However, until recently, the study of surface influences on nucleate ...boiling was complicated by coupled surface factors; wettability and surface roughness. This study focuses on nucleate pool boiling under different wetting conditions, in the absence of microscale roughness, which is coupled with wetting phenomena. Heterogeneous boiling occurs on hydrophilic (54°) and hydrophobic (123°) surfaces, even without microstructures that can trap water vapor. In the very low heat flux regime, hydrophobic surfaces offer better nucleate boiling heat transfer than hydrophilic surfaces. Moreover, a heterogeneous wettability surface composed of hydrophobic dots on a hydrophilic surface provides better nucleate boiling heat transfer than a homogeneous wettability surface (hydrophilic or hydrophobic). Analysis of bubble generation and departure was carried out via a high-speed visualization technique in order to understand these experimental results. Based on the bubble analysis, it was inferred that changes in wettability could lead to totally different boiling performance when microstructures are absent. Also, the number of hydrophobic dots and the pitch distance between dots were key parameters for explaining boiling performance under heterogeneous wetting conditions.
•Subcooled boiling is predicted to initiate at a thermal power of 223 kW.•The transition to saturated nucleate boiling occurs between 326 kW and 640 kW of thermal power.•Direct comparisons were made ...between calculated results and actual fuel temperatures measured by Instrumented Fuel Elements (IFE).•From a Departure from Nucleate Boiling Ratio (DNBR) perspective, the reactor remains within safety limits when operated between 223 kW and 427 kW thermal power.
The TRIGA® (Training, Research, Isotopes production by General Atomics) 2000 research reactor in Bandung (TRIGA® 2000 Bandung) has undergone fuel reshuffling, and therefore there is a potential for subcooled nucleate boiling to occur in the reactor core, thus it is necessary to conduct a thorough investigation by calculation to explain whether the TRIGA® 2000 Bandung reactor can still operate below the operation safety limit. Herein, the optimization of the neutronic and thermal–hydraulic calculations using the MCNP® and COOLOD-N2 codes, respectively, has been carried out to reveal the main parameters to justify the operating safety limits, including superheat temperature and Departure from Nucleate Boiling Ratio (DNBR). The calculation results show that the predicted subcooled boiling condition occurs at a thermal power of 223 kW, while saturated nucleate boiling occurs at a reactor thermal power of 326 kW – 640 kW. The calculation results were also compared with the fuel temperature measured by Instrumented Fuel Element (IFE) at each power variation. Meanwhile, from the DNBR value perspective, the reactor still meets the operating safety limit if the reactor power is operated at 223 kW – 427 kW thermal power.
Pillar structure surfaces and surface vibrations are considered to be two individual techniques to enhance nucleate boiling. In this work, a volume of fluid (VOF) based numerical model is developed ...to study bubble growth promotion during nucleate pool boiling on a pillar structure surface under the aid of surface vibration. Three vibration modes of the pillar structure, including the horizontal vibration mode (HVM), vertical vibration mode (VVM) and angular vibration mode (AVM), are considered, and their effects on the bubble dynamics and heat transfer are discussed with various vibration amplitudes and frequencies. It is found that the pillar structure surface is favorable for bubble detachment as it constrains the bubble base radius and forces the bubble to grow more vertically compared to the plain surface. Although the HVM and AVM exert no or less vertical force component on the bubble for its detachment than the VVM does, but their horizontal force component significantly alters the bubble shape profile, breaks the force balance, and greatly increases the bubble departure frequency and heat transfer. The largest increment of liquid-vapor phase change rate is found to be 30.9% for the HVM. The bubble departure frequency and the vapor volume flux quantity increase with the pillar vibration amplitude and frequency. This work will deepen our understanding of fundamental bubble growth mechanisms as altered by vibration on the pillar structure surface for better heat transfer applications.
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