•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.
Efficient electronics cooling has always been a perpetual challenge, with the limits of single-phase cooling almost being reached. Two-phase cooling in the form of pool boiling is an attractive next ...step, with much research being devoted to it. While refrigerants operating at lower saturation temperatures are key to achieving effective cooling, surface modifications have been shown to also affect bubble dynamics and enhance nucleate pool boiling heat transfer. A simple, easy to implement fabrication method was sought, with the goal of expanding the knowledge of bubble dynamics. To this end, single bubble growth on structured surfaces that are achievable on a lathe, with an average roughness of 75 μm and differing indentation angles between 90° and 46°, was studied numerically using an OpenFOAM multiphase library. Conjugate heat transfer was applied, with heat fluxes ranging between 7.6 and 28 kW/m2 for pure refrigerants R32 and R1234yf. By comparing the bubble equivalent diameter with that of a smooth surface at a fixed heat flux, it was found that the bubble growth rates of structured surfaces were largely independent of indentation angles less than 90°, but lower than for smooth surfaces. For structured surfaces, a critical indentation angle of approximately 60° was identified which affected the bubble dynamics. For angles greater than the critical angle the bubble growth time was up to 150 % longer, which also resulted in larger departure diameters. However, the opposite trend was observed as the indentation angle was decreased below the critical angle. From a force analysis, it was found that the physical limitation imposed on the bubble growth was responsible for the critical indentation angle behaviour, with the most acute angle of 46° showing the shortest departure time. Furthermore, the bubble growth from a single cavity corresponded better with the trends of a smooth surface than a structured surface with comparable indentation angles. On a structured surface, once the bubble reached the edge of the cavity, its base diameter was limited by the physical characteristics of the surface. For the single cavity surface, however, bubble growth was uninhibited beyond the cavity, mimicking a completely smooth surface. The marked difference between results of a fully structured surface and the single cavity implies that future research will have to take the structural limitations on bubble growth imposed by a roughened surface into account.
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•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.
The pool boiling of slush nitrogen (SlN2) with various solid volume fractions at subatmospheric pressures is studied to establish a semi-empirical model considering the effects of phase-change solid ...nitrogen (SN2) particles on convective heat flux and boiling heat flux. The convective heat flux is studied with the modified correlation based on Sindt's fitting, while an improved correlation based on Rohsenow correlation with the dimensionless form of wall superheat in the range of 0<Ja∗ρ∗0.14<0.04 is obtained for the boiling heat flux. With the increasing wall superheat, the enhancement weakens till vanishes at the transition point. This point marks the separation between low- and high-heat-flux regions, where the probability of SN2 invading to thermal boundary layer diminishes to 0 %. The low-heat-flux boiling correlation considers the heat transfer enhancement due to SN2 concentration while the high-heat-flux one ignores the impact of SN2. As the components of SlN2 nucleate boiling model, the convective and boiling heat flux both show the accuracy of ±20 % with experiments. Upon analyzing the boiling curves of SlN2 with various solid volume fractions, SlN2 outperforms LN2 in coolant efficiency at moderate heat load.
•A composite model for the slush nitrogen nucleate boiling is developed with the modified Sindt's and Rohsenow correlations.•The semi-empirical model considers the effects of phase-change solid particles on the convective and boiling heat flux•The latent heat of melting and volume fraction of solid nitrogen are considered in the composite model.•The proposed concept of “bubble barrier” quantifies the reduction in the probability of solid nitrogen particle invasion.
•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.
•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.
•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.
