Liquid Heat Transfer Research Articles

Experimental studies on bubble aspect ratio and corresponding correlations under bubble swarm condition

The bubble shape affects the gas–liquid interface momentum, heat and mass transfer, as well as the flow field around the bubble. Correctly predicting the bubble shape is challenging but indispensable under bubble swarm conditions. In this work, the bubble aspect ratio, which is adopted for the characterization of the bubble shape, is obtained through high-speed photography combined with an image processing algorithm from several experiments with an oscillating bubble plume. The results show that the bubble aspect ratio tends to be a constant value with increasing the bubble diameter, rather than decreasing as predicted by various empirical correlations developed in single bubble experiments. None of the available empirical correlations can accurately correlate the bubble aspect ratio with Weber number or Tadaki number. Among the available correlations in literature, Eo based correlation proposed by Besagni and Inzoli (2016) and Eo-Re based correlation proposed by Besagni and Deen (2020) show a better performance. The predicted values of Eo-Re based correlation developed in this work are the closest to the experimental data compared with others.

A theoretical analysis and parametric study of filmwise condensation on three-dimensional pin fins

In this paper, a theoretical model of filmwise condensation of steam on three-dimensional pin fins fabricated by selective laser melting (SLM), an additive manufacturing (AM) technique, is developed. The model considers the effects of surface tension and gravity on the liquid film flow over the pin fin surface. The three-dimensional nature of the liquid film flow over the fin flank and the unique features of the fin structures as a result of the laser melting process are modeled. Visualization studies are performed to verify the assumptions made in the model. From the modeling results, the local heat transfer coefficient and length-averaged heat transfer coefficient are obtained. The liquid film thickness at various locations of the pin fin is analyzed. The effects of fin tip dimensions, fin stem radius and fin pitch on the liquid film characteristics and heat transfer coefficient are systematically investigated. Our results showed that a thin film region exists in the flat and circular segments of the fin tip which cover approximately 25 – 30% of the fin surface. For a fixed fin diameter, it is found that the length-averaged heat transfer coefficient can be optimized by varying the dimensions of the flat and circular segments. A locally thin film region resulting from the suction effect is observed near the fin base for small fin spacings. However, the suction effect reduces with increasing fin spacing. Due to the three-dimensional nature of the pin fins which induces surface tension in the circumferential direction, the liquid film distribution is uniform. The differences in the length-averaged heat transfer coefficient at different circumferential locations are smaller than 5%. Finally, a comparison with existing experimental results demonstrates that a relatively accurate prediction of the average heat transfer coefficient can be achieved by our model with a maximum deviation of 8.3%.

Mathematical description of recuperative heat transfer in a bioreactor during the filling of an apparatus

Despite the observed trend of a ubiquitous transition to continuously operating apparatuses, the specificity of the production technology of many microbiological products retains the advisability of using batch apparatuses. As an example, we mention the cooled bioreactors and yeast concentrate collectors used in the production of baker’s yeast. The work considers the problem of the mathematical description of unsteady recuperative heat transfer in a batch capacitive apparatus (bioreactor) with a product distributor on a heat transfer surface during countercurrent movement of coolants with a filling level of the apparatus changing during the process. The problem is formulated by partial differential equations (in coordinate and time) with a moving boundary between sections with different heat transfer conditions. When formulating the problem, simplifying assumptions and boundary conditions were adopted. The mathematical problem posed is solved using the Laplace transforms. The mathematical description of recuperative heat transfer in bioreactors during the filling of the apparatus showed that with countercurrent movement of heat transfer liquids and coolants, the apparatus has an advantage in terms of the main indicator - heat transfer capacity and has a higher energy efficiency. The performed calculations make it possible to choose the apparatus design correctly and determine the rational thermal regime of its operation regarding related technological operations.

Electrocaloric cooling over high device temperature span

Summary Electrocaloric cooling demonstrates direct electricity utilization and high energy efficiency, and is often proposed as an environmentally benign, solid-state alternative to the conventional vapor compression cooling technology. As a result, the fabrication of effective electrocaloric materials and engineering of electrocaloric cooling devices have attracted increasing attention in the cooling community. However, the limited material adiabatic temperature change under safe operation field poses a major challenge to practical electrocaloric cooling device development, since real-world applications usually require device temperature span over 20 K. This perspective presents recent efforts devoted to design electrocaloric cooling devices based on active heat regeneration and cascading approaches; both strategies have achieved significant device temperature lift ~10 K with adiabatic temperature change of 2~3 K. The strategies discussed in this work are broadly applicable to the design of efficient and compact cooling systems.

Vibrational model of thermal conduction for fluids with soft interactions.

A vibrational model of heat transfer in simple liquids with soft pairwise interatomic interactions is discussed. A general expression is derived, which involves an averaging over the liquid collective mode excitation spectrum. The model is applied to quantify heat transfer in a dense Lennard-Jones liquid and a strongly coupled one-component plasma. Remarkable agreement with the available numerical results is documented. A similar picture does not apply to the momentum transfer and shear viscosity of liquids.

Effect of Heat Transfer Surface Shape in Condensation Process of CO<sub>2</sub> Refrigerant Passing Through Fine Grooves on Liquid Film Formation and Heat Transfer Characteristics

Effect of Heat Transfer Surface Shape in Condensation Process of CO<sub>2</sub> Refrigerant Passing Through Fine Grooves on Liquid Film Formation and Heat Transfer Characteristics

Effect of the MoSi2 coating on operational reliability of bipropellant rocket engine

This present study investigated the MoSi2 coating and its effect on reliability of bipropellant rocket engine. This coating is developed to protect the chamber substrate material form oxidization under hightemperature oxidative circumstance as bipropellant engine works. The multilayer structure of the MoSi2 coating shows excellent high-temperature and thermal-cycle resistance. Its characteristic of self-healing leads to the good performance under the long-time steady working condition for rocket engines. A 25000-seconds firing test was conducted to testify the performance of MoSi2 coating under high temperature above 1400℃. In addition, the influence of coating surface morphology on liquid film cooling was fully discussed in experiment and simulation. High-speed microscopy camera was used to study the effects of Weber number on the spreading and lasting of cooling liquid-film. the simulative comparison was conducted by OpenFOAM to present different transfer-heat modes, when a droplet impinges on the high-temperature surface of MoSi2 coating. All results show that higher smoothness of the coating is suitable for liquid-film cooling, strengthening liquid film spread and heat transfer. Moreover, scanning electron microscope (SEM) was used to study the effect of Mo layer residue on the coating thermal-cycle profermance. The test results indicates that Mo layer residue significantly cause penetrating cracks of the coating and then weaken the self-healing of the coating at downstream of throat. Therefore, it is important to strictly control the thickness of Mo layer by means of matching Mo target in ion plating. Thus after properly prolonging the infiltration time, Mo layer can be silicified completely without residue.

A review on multiple liquid jet impingement onto flat plate

Multiple jet impingement has been an important industrial application for a long time. Processes like quenching of hot steel surfaces in steel industry utilize the high heat-carrying capacity of liquid multiple impinging jets in order to achieve the uniform temperature of the metallic surface. The objective of this paper is to summarise the state of the art of the process of multiple jet impingement onto flat plate and highlight the future scope of research space in this field. This study focuses on the arrays of impinging liquid jets and to summarize relevant experimental and numerical results on multiple liquid jet impingement heat transfer and hydrodynamic behavior together with the latest developments published in the literature. The present work is limited to the normal impingement of multiple liquid jets on flat surfaces and the physics behind the single and multiple liquid jet configurations are discussed in the paper followed by the experimental studies. The effect of various paprameters like the jet diameter, jet velocity, velocity-profile, jet to target distances, jet to jet distances, and surface boundary conditions. The numerical studies discuss the studies conducted on multiple jet impingement and compare the accuracy of the different numerical methods utilized in the studies. The extrapolation of the results obtained from single liquid jet impingement have been discussed to suggest efficient methodologies for multiple jet impingement studies. It has been found that the study of hydrodynamic characteristics of multiple jet impingement is an important aspect that affects the heat transfer rate due to the jet impingement and needs to be explored further to find a better correlation between heat transfer rate and different hydrodynamic parameters of the flow.

Solar Hot Air for Industrial Applications Using Linear Fresnel Concentrating Collectors and Open Brayton Cycle Layout

Many industrial processes use hot air as a medium. This is especially relevant for drying. Nowadays, most of them consume fossil energy. This study analyses an innovative facility for direct solar heating of air up to 400 °C. For this aim, a medium-scale solar field of linear Fresnel collectors is proposed to heat ambient air inside it. No other dedicated heat transfer fluid is necessary. A simpler layout avoids costs, hurdles, and risks of heat transfer liquids and the related machinery. A Brayton cycle configuration avoids auxiliary energy consumption for pumping air through the collectors by coupling the solar field with a turbocharger. A mathematical model simulates a system of industrial size along a typical meteorological year. It confirms the feasibility of the proposal and the high potential of helping the energy transition to sustainability.

Using CFD to improve the performance of a heat exchanger from a gasifier

In this paper, a Computational Fluid Dynamics (CFD) analysis is performed on a gas-liquid heat exchanger fitted on a gasification equipment. The flow and temperature patterns are preliminary investigated using SolidWorks Flow Simulation software, in order to gain insight into the involved physical processes, and to find the exchanger weak points before being manufactured and tested. The analysed equipment tranfers heat from the flue gasses generated by a gasification system, towards a liquid heat transfer medium. This is subsequently sent to a second liquidliquid heat exchanger used to heat water from a boiler. As a result of the analysis, solutions aiming at performance improvement of the equipment are discussed and proposed.

Hydrodynamic behavior of liquid falling film over horizontal tubes: Effect of hydrophilic circular surface on liquid film thickness and heat transfer

Falling film configurations have widely been used in various types of refrigeration systems, and wettability has played an important role in characterizing the heat and mass transfer due to varying hydrodynamic behavior. The present paper focuses on a three-dimensional computational fluid dynamics (CFD) simulation to investigate the effect of hydrophilic circular surface on hydrodynamic behavior of liquid falling film over the heated horizontal circular tubes. First, the thickness of the liquid falling film and the liquid distribution around the circumferential and axial directions were analyzed at a feed water temperature of 20 °C for three film Reynolds numbers of 12, 24, and 36 (50 ≤ Q̇feed ≤ 150 ml·min-1) and three heat fluxes of 5, 10, and 15 kW m-2. The influences of the contact angle on the liquid film hydrodynamics and heat transfer were then analyzed. The results showed that at a low feed film Reynolds number, even for super-hydrophilic nature (e.g., contact angles of 0° or 10°), the liquid film failed to cover the first-row tube surface. Increasing the feed film Reynolds number enhanced the liquid film distribution over the tubes and the dry spot decreased, which enhanced the heat transfer performance. At relatively higher contact angles of 30° and 60° (but still hydrophilic nature), the wetted area decreased and dry spots covered most of the second- and third-row tubes, which significantly influenced the thermal performance. Validation of the CFD model based on the volume-of-fluid approach was achieved by comparison with the experimental data, and the experimentally measured values of local heat transfer coefficient were employed for the comparison to support the validity of the present study.

Characterization of a new total heat recovery system using CaCl2 as working fluid: Thermal modeling and physical analysis

• A new type of heat pump system is proposed. • The variation trend of three working medium in absorber is analyzed. • The rise of flue gas temperature can reduce the harmful substances by more than 50%. • The advantages of the system compared with LiBr absorption heat pump are analyzed. This paper introduces a kind of open cycle absorption heat wet flue gas heat recovery system, which use CaCl 2 as the working medium. The system will use the wet heat recovery method and combined with an efficient heat pump system for flue gas as a heat source generator. Through direct contact with the solution in the absorber, the flue gas is going to carry out gas, liquid heat transfer between heat exchanger, realization of sensible heat and latent heat step by step. As the key part of the system, absorber is established by one-dimensional steady-state heat transfer and mass transfer model. This paper uses the finite difference method to model the discrete numerical methods, and analyzes the characteristics of heat and mass transfer in the absorber. We obtain the concentration curves of the three kinds of working medium's temperature and flow along the height direction. We also analyze the influence of CaCl 2 solution parameters changes on the absorption process, parsing the reason of the temperature change by analyzing the three working medium's energy flow trend. We found that the temperature change of flue gas is non-monotonic, which decreases gradually in the range of absorption tower height 0–0.9 m, and then increases gradually. The reason for this change is that sensible heat exchange and latent heat exchange exist between flue gas and solution. Although such a change has an impact on the efficiency of the system, it prevents the "white smoke" from condensing in the air, which effectively protects the environment. Compared with conventional LiBr absorption heat pump, the system constructed in this paper has certain advantages in latent heat recovery, flue gas heat energy utilization, energy conservation and emission reduction and economy.

Recommendation for prediction of pool boiling heat transfer of various liquids on microstructured surfaces

Recommendations for prediction heat transfer coefficients and critical heat flux according to available in the literature experimental data of heat transfer and critical heat flux for boiling different liquids on microstructured surfaces made by deformed cutting method are obtained. In the work, on available in the literature sources of experimental data on heat transfer and critical heat flux at boiling of various liquids on the microstructured surfaces made by the deforming cutting method, recommendations for prediction of heat transfer coefficients and critical heat fluxes are received. Microstructured surfaces allow to intensify the heat transfer is 1.1 to 6 times. Due to the variable wettability of microstructured surfaces elements, critical heat flux increase before 4 times. The proposed criteria equations allow predicting heat transfer coefficients with an error of 30%, and critical heat fluxes with an error of 30-35%. In order to improve the accuracy of forecasting, the possibility of using an artificial neural network model for generalizing heat transfer coefficients is shown. Forecasting using an artificial neural network model allows us to determine the heat transfer coefficients with an error of ±20%.The equations are of interest for designing cooling systems for microelectronic devices, heat and mass transfer devices, boiling zones of heat pipes and thermosyphons, etc.

Preface

D M Markovich, S V Golovin and I V Marchuk The origins of the Conference start from 1970 in the Soviet Union, Novosibirsk. It was organized by Kutateladze Institute of Thermophysics SB RAS. The name of the conference was «Actual problems of thermophysics and physical hydrodynamics». The conference has been organized under this name up to 2015. The conference chairs were academicians of RAS V. E. Nakoryakov, S. V. Alekseenko and D. M. Marckovich. Peer reviewed proceedings of the conference have been published in the format of printed books. In 2016 the conference is reorganized in a new format with a shorter name: «Thermophysics and physical hydrodynamics». The proceedings of the renewal Conference were published in the Journal of physics: conference series.The conference takes place in Yalta, a beautiful city in Crimea on the bank of the Black Sea. Ministry of Science and Higher Education of the Russian Federation, Siberian Branch of the Russian Academy of Sciences, National Committee on Heat and Mass Transfer RAS, Lavrentyev Institute of Hydrodynamics SB RAS, Novosibirsk State University, Novosibirsk State Technical University, Marine Hydrophysical Institute RAS are among other conference organizers besides Kutateladze Institute of thermophysics. The present Conference covers the following topics: heat transfer and hydrodynamics in single phase flows, hydrodynamics and heat and mass transfer in multiphase flows, phase transitions, reacting flow dynamics, detonation processes, numerical methods in thermophysics and physical hydrodynamics, techniques of thermophysics and hydrodynamics experiment, thermophysical properties of substances, heat and mass transfer on micro- and nanoscales, electrophysical phenomena in gaseous and liquid media, heat transfer and hydrodynamics in industrial processes and environment protection.There are more than 170 participants. The proceedings contain 123 papers grouped by topic. The scientific committee appreciates the enormous work of the editorial board and reviewers in the preparation of this volume. We would like to express our sincere thanks to all authors for their research contributions, and to organizers of the conference for their valuable spadework, especially to specialists of MKS LLC.List of Chair, Co-chair, Scientific secretary, Scientific committee, Technical committee are available in this pdf.

Investigation of Liquid Water Formation in PEMFC By Direct Simulation and Operando X-Ray Computed Tomography

Direct modeling-based Lattice Boltzmann Method (LBM) [1-3] combined with in-operando X-ray computed tomography (CT) is used to investigate the liquid water formation in the porous layers of polymer electrolyte membrane fuel cell (PEMFC). Studies of the local saturation of liquid water, heat transfer, species transport, and electrochemical kinetics with platinum metal group (PGM) and PGM-free catalyst layers are explored under different cell operating conditions. The detailed structure of dry (i.e., GDL, MPL, and CL) and wet samples (i.e., liquid saturation) used in this study were obtained by in-operando X-ray CT, which allows for accurate visualization of water transport in operating PEMFCs. The overall predictions were compared and validated with experimental data [4, 5]. Figure 1 shows the comparison examination of liquid formation on the detailed structure of porous layer with PGM and PGM-free catalyst layers. The results reveal that the liquid water evolution/saturation inside the GDL samples are different when the cell operating conditions and transport properties are changed. More results will be presented and discussed.

Separated Phase Analysis of Heat Transfer in Liquid–Liquid Taylor Flow in a Miniscale Straight Tube

Abstract Heat transfer analysis of liquid–liquid Taylor flow in previous studies almost never shows the effect of slug length on heat transfer. The homogenous or single-phase analysis is often the only method available to deal with flow of multicomponents. In this study, a new approach is developed to model the segmented liquid–liquid Taylor flow as two separated systems to present heat transfer enhancement for each component. The effect of internal circulation and boundary layer renewal within the two fluid components is clearly observed. An experimental setup was assembled using an open loop system at miniscale size in which liquid–liquid Taylor flow is heated under a constant wall temperature. Three silicone oils of 1, 3, and 5 cSt were segmented using distilled water at three volume fractions 0.25, 0.5, and 0.75. Finally, heat transfer data of the dimensionless mean wall heat flux shows good agreement with a predictive model proposed in an earlier work by the second author. The results show an impact of the fluid cell dimensions on the rate of heat transfer.

Characteristic analysis of fluctuating liquid film flow behavior and heat transfer in nitrogen condensation

Liquid film fluctuation is supposed to be an important mean of film condensation enhancement for the cryogenic fluids with extremely low surface tension. However, the flow characteristics of the cryogenic liquid film in condensation process are seldom observed and revealed due to the difficulty of cryogenic experiment. In this study, the flow behavior and heat transfer of the fluctuating liquid film in nitrogen condensation are discussed by CFD simulation. A numerical model of nitrogen condensation on a vertical plate is established in accordance to a practical experimental setup, and is further validated with a good accuracy using the experimental data. The liquid film thickness, wave velocity and wall shear force are then analyzed. Statistical tools are employed to reveal the probability distribution of the film thickness and the frequency domain characteristics of the heat transfer coefficient. The FFT analysis of the heat transfer coefficient shows the interface waves around 30 Hz can induce a stronger fluctuation effect and bring about a better heat transfer performance. The velocity in the large solitary wave is regulated by the wall shear force, and a more appropriate correlation is proposed to reveal the physical properties of the solitary wave, which manifests as rolling on the film substrate. In addition, the simulation reveals that an important reason leading to the higher heat transfer coefficient in the experiments than that predicted by the Nusselt’s theory is the decrease of film substrate thickness and the increasing probability of thinner liquid film during practical liquid fluctuating. It can be inferred that the condensation process of fluctuating liquid film is an effective way to enhance the heat transfer for cryogenic fluids.

Orientation effects on liquid-vapor phase change heat transfer on nanoporous membranes

Liquid-vapor phase change heat transfer on nanoporous membranes in facing horizontal upwards, downwards and vertically was investigated. Anodic aluminum oxide (AAO) membranes were as the nanoporous substrates. Water was supplied through nanoporous membranes by pressure difference. Heat transfer characteristics and temperature instability were analyzed and compared among three orientations. Results showed that negative slope and “special points” appeared on boiling curves. The interaction between liquid film thickness and heat transfer coefficient (HTC) was proposed and verified to be the main mechanism that leading to this phenomenon. Because the rapid replenishment of liquid and removal of heated liquid under gravity, horizontal downward surface always had the best heat transfer performance which exhibited maximal enhancement of HTC was 170% and 70% at heat flux of 39 W/cm2 over horizontal upward and vertical surfaces. Temperature instability in horizontal downward and vertical surfaces had the similar trend and became more pronounced at higher heat fluxes. In horizontal upward surface, temperature was stable at the heat flux range of 40– 55 W/cm2 and “thin film evaporation” was realized. In addition, the maximum heat flux was calculated by liquid transport limit and kinetic theory limit for evaporation and a comprehensive understanding was established.

Optimization of porous media flow field for proton exchange membrane fuel cell using a data-driven surrogate model

Flow field design plays a key role in proton exchange membrane (PEM) fuel cells due to its decisive influence on reactant gas transfer, liquid water discharge, electron conductance, and heat transfer. Porous media flow field (e.g. metal foam) shows promise to improve cell performance in the concentration polarization regime and to benefit uniform distributions of oxygen, liquid, current density, and temperature, etc. In this study, a data-driven surrogate model based on support vector machine (SVM) is applied to optimize porous media flow field geometry. The training data is obtained from a validated three-dimensional (3D), multi-phase non-isothermal model. For better characterization, the complex structure is simplified as a 3D structured mesh consisting of a set of fibers with each fiber perpendicular to each other at the joint. The results show that the data-driven surrogate model based on SVM predicts similar results as the 3D physical model. The genetic algorithm (GA) is further used for optimization, in which the data-driven surrogate model is selected as a fitness evaluation function. The optimal values obtained by the surrogate model are verified by the 3D physical model, indicating that the proposed data-driven surrogate model is effective in the design and optimization of porous media flow field.

Analytical Modeling for Vapor Condensation in the Presence of Noncondensable Gas and Experimental Validation

Abstract The sensible and latent heat transfer are two essential considerations in investigating vapor condensation in the presence of noncondensable gases. In this paper, a new model for filmwise condensation heat transfer was developed using similarity-based solution. The expression of gas–liquid interfacial temperature, film thickness, and heat transfer coefficient were derived and calculated, respectively. The analytical results showed that the temperature difference between gas–liquid interfacial and cooling surface is decreased as there is an increase in cooling surface temperature. In addition, the forced-convective condensation heat transfer and film thickness on the vertical surface were experimentally carried out. The proportion of latent heat is 62–67% and relatively larger than sensible heat in the range of wall temperature (17–32.5 °C). The experimental film thickness is less than analytical film thickness by 2–10%. It is because that the liquid film may evaporate back to water vapor in the neighboring wall area due to high temperature of flue gas. Further, a new nondimensional correlation of condensation heat transfer of flue gas is fitted with Nu = 0.62Re0.5Ja0.67 and applicable range is Re = 1000–2500, Ja = 1.7–4.4. The fitting shows a good agreement between experimental and correlated values except some points in the low Nu number. The model proposed is applicable to predict the temperature and velocity distribution for condensation heat and mass transfer of multicomponent gases.