Accepted Manuscripts

Technical Brief  
Mostafa Langari, Zhiyin Yang, Julian Dunne, Soheil Jafari, Jean-Pierre Pirault, C. A. Long and Jisjoe Thalackottore Jose
J. Heat Transfer   doi: 10.1115/1.4040358
The accuracy of CFD-based heat transfer predictions have been examined of relevance to liquid cooling of IC engines at high engine loads where some nucleate boiling occurs. Predictions based on: i) the Reynolds Averaged Navier-Stokes (RANS) solution, and ii) Large Eddy Simulation (LES), have been generated. The purpose of these simulations is to establish the role of turbulence modelling on the accuracy and efficiency of heat transfer predictions for engine-like thermal conditions where published experimental data is available. A multi-phase mixture modelling approach, with a Volume-of-Fluid interface-capturing method, has been employed. To predict heat transfer in the boiling regime, the empirical boiling correlation of Rohsenow is used for both RANS and LES. The rate of vapour-mass generation at the wall surface is determined from the heat flux associated with the evaporation phase change. Predictions via CFD are compared with published experimental data showing that LES gives only slightly more accurate temperature predictions compared to RANS but at substantially higher computational cost.
TOPICS: Flow (Dynamics), Heat transfer, Fluids, Boiling, Subcooling, Reynolds-averaged Navier–Stokes equations, Modeling, Computational fluid dynamics, Engines, Simulation, Stress, Turbulence, Cooling, Temperature, Engineering simulation, Evaporation, Internal combustion engines, Nucleate boiling, Large eddy simulation, Heat flux
TC Ho, S.C. Fu, Christopher Y.H. Chao and Sharad Gupta
J. Heat Transfer   doi: 10.1115/1.4040348
A high velocity jet fire can cause catastrophic failure due to flame impingement or radiation. The scenario becomes more complicated when multiple jet fires exist following ignition of release from pressure relief valves as the thermal effect not only distorts the individual jet flame but also changes the flame height and temperature profile and such kind of high velocity jet flames have not been studied in the past. Therefore, prediction of the flame shape including the merging and interaction of multiple jet fires is essential in risk analysis. In this paper, fire interaction of two high velocity (>10 m/s) jet fires is investigated using computational fluid dynamics techniques. Different radiation models are analyzed and validated by experimental data from the literature. Based on the simulation result, the merging of high velocity jet fires is divided into three stages. An empirical equation considering the fire interaction for the average flame height with different release velocities and separation distance is developed. The flame height increases dramatically when the separation distance decreases resulting in a shortage of oxygen. So, part of the methane is reacted in a higher height which explains the change in the merging flame height and temperature.
TOPICS: Flames, Fire, Separation (Technology), Radiation (Physics), Temperature effects, Computational fluid dynamics, Risk analysis, Failure, Temperature, Ignition, Methane, Oxygen, Shapes, Simulation results, Temperature profiles, Relief valves
Ri Zhang, Feng Zhang and Sheng Dong
J. Heat Transfer   doi: 10.1115/1.4040346
The phase distribution and mechanical properties of annular flow have obvious, random characteristics because of the influence of turbulence. Thus, probability analysis is a suitable method for the study of annular flow. In the present work, the interchange rate and pressure gradient of fully developed annular flow are investigated in detail based on a probability model. The probability model tracks the atomization and deposition processes of a single particle to analyse the momentum and mass exchange between the gas and liquid phases. The interchange rate can be calculated by summing the generation or disappearance probability of droplets with different sizes. The pressure gradient can be obtained by solving the basic equations of the annular flow, which contains an improved relationship of interfacial shear stress. The predictions of the interchange rate and pressure gradient are well verified by comparison with experimental data available in the literature. Furthermore, the effects of many parameters on the interchange rate and pressure gradient are discussed in detail.
TOPICS: Flow (Dynamics), Pressure gradient, Probability, Shear stress, Momentum, Particulate matter, Turbulence, Drops, Mechanical properties
Yutao Huo and Zhonghao Rao
J. Heat Transfer   doi: 10.1115/1.4040345
A new lattice Boltzmann (LB) model used to solve the solid-liquid phase change problem, which is based on the enthalpy-transforming model has been developed in this paper. The problems of two-region phase change and phase change by convection are solved to verify the present LB model. No significant differences of the temperature distributions between present LB model and analytical solution are obtained in the problem of two-region phase change. The benchmark solutions are applied to evaluate the present LB model in natural convections of air and phase change material (PCM) as well. The results show that the present LB model is able to obtain the temperature distribution and capture the location of solid-liquid interface in the cavity accurately. Moreover, the present LB model is effective in computing since no iterations are necessary during the simulations.
TOPICS: Enthalpy, Lattice Boltzmann methods, Temperature distribution, Simulation, Phase change materials, Convection, Engineering simulation, Cavities
Caixi Liu, Shuai Tang, Yuhong Dong and Lian Shen
J. Heat Transfer   doi: 10.1115/1.4040347
We study the effects of particle-turbulence interactions on heat transfer in a particle-laden turbulent channel flow using direct numerical simulation for turbulence and Lagrangian tracking for particles. Our study focuses on the modulations of the temperature field and heat transfer process by inertial particles with different particle momentum Stokes numbers (St), which in combination of the particle-to-fluid specific heat ratio and the Prandtle number results in different particle heat Stokes numbers. It is found that as St increases, while the turbulent heat flux decreases, the particle feedback heat flux increases significantly and results in an increase in the total heat flux. Moreover, by taking advantage of the ability of numerical simulation to address different momentum and heat processes separately, we investigate the different roles played by the particle-to-fluid momentum feedback and heat feedback. It is found that the momentum feedback increases the fluid temperature fluctuation while the heat feedback decreases it, and both reduce the turbulent heat flux. The analyses of simulation data illustrate the two processes of particles affecting heat transfer, namely the direct effect of particle thermal feedback to the fluid and the indirect effect of the modulation of turbulent heat flux due to the suppression of wall-normal turbulence velocity fluctuation by the particles. Our results indicate that both the momentum feedback and the heat feedback are important when the particle inertia is large, suggesting that both feedback processes need be taken into account in computation and modeling.
TOPICS: Particulate matter, Turbulence, Heat transfer, Channel flow, Feedback, Heat flux, Momentum, Heat, Fluids, Temperature, Computer simulation, Simulation, Specific heat, Modeling, Computation, Inertia (Mechanics)
Loong Ee Loh, JIe Song, Fenglin Guo and Guijun Bi
J. Heat Transfer   doi: 10.1115/1.4040256
Selective laser melting (SLM) has received increasing attention in recent years as an innovative manufacturing technique. The present SLM process only uses a single laser beam to melt and consolidate the powder which may result in excessive evaporation. In this paper, a double beam scanning strategy is investigated in which the first laser beam pre-heats the powder just below the sintering point while the second laser beam completely melts the powder. An analytical solution on the temperature distribution heated by a moving laser beam in the powder-bulk domain is derived and is used to determine the critical radius of the first laser beam. The single and double beam scanning strategies are compared numerically and it is found that double beam scanning can effectively reduce material evaporation and increase the amount of powder melted in the SLM process.
TOPICS: Lasers, Laser beams, Melting, Temperature distribution, Evaporation, Manufacturing, Sintering
Ping Li and Junfeng Zhang
J. Heat Transfer   doi: 10.1115/1.4040257
To simulate heat transfer processes through periodic devices with non-uniform wall temperature distributions, we propose to decompose the regular temperature into two parts: namely the transient part and the equilibrium part. These two parts can be solved independently under their individual wall and inlet/outlet conditions. By calculating the flow field and the two component functions in one periodic module, one can easily generate the distributions of regular temperature in one or multiple modules. The algorithm and implementation are described in details, and the method is discussed thoroughly from mathematical, physical, and numerical aspects. Sample simulations are also presented to demonstrate the capacity and usefulness of this method for future simulations of thermal periodic flows using various numerical schemes.
TOPICS: Temperature, Heat transfer, Periodic structures, Wall temperature, Flow (Dynamics), Engineering simulation, Simulation, Equilibrium (Physics), Transients (Dynamics), Algorithms
Hosein Majdi and Javad Abolfazli Esfahani
J. Heat Transfer   doi: 10.1115/1.4040259
In this paper, an optimization procedure is presented by response surface method to optimize the temperature and velocity of drying air and thickness of the moist object inside the dryer. The optimization procedure is performed to determine the minimum drying time and energy consumption as responses. A two-dimensional numerical solution is accomplished to analyze coupled heat and mass transfer occurring during drying of an apple slice. The air flow and the moist object are solved conjugate while the heat and mass transfer equations are solved coupled together using lattice Boltzmann method. Beside this, a sensitivity analysis is executed to calculate the sensitivity of the responses (drying time and energy consumption) to the control factors. Results reveal that the real optimized parameters for the minimum drying time and energy consumption are temperature (T=80 °C), velocity (V=0.10404 m/s) and thickness ratio (TR=0.1). The results of numerical solution are compared to the experimental results, presenting a reasonable agreement. This analysis could be useful in food drying.
TOPICS: Drying, Optimization, Energy consumption, Heat, Temperature, Mass transfer, Air flow, Food products, Response surface methodology, Sensitivity analysis, Lattice Boltzmann methods
Elsayed Abo-Dahab
J. Heat Transfer   doi: 10.1115/1.4040258
In this paper, an estimation to theory of generalized magneto-thermoelasticity to solve the problems of two dimensional half-space under thermal shock, initial stress and two temperatures. The governing equations are solved by using Lame's potentials method in the context of (CD) Classical Dynamical and (LS) Lord-Shulman theories. The boundary conditions that: (i)The total normal stresses in the boundary equivalent the initial stress; (ii) The shear stresses are vanish at the boundary; and (iii)The incidence boundary is thermal insulated. The reflection coefficients have been obtained for two incident p- and SV-waves. The results obtained for the incident waves calculated numerically by using appropriate metal and presented graphically. Comparisons have been made with the results with the results obtained in the presence and absence of magnetic field and initial stress.
TOPICS: Temperature, Reflection, Stress, Waves, Thermal shock, Thermoelasticity, Shear stress, Boundary-value problems, Reflectance, Metals, Magnetic fields
Andrew F Chen, Hao-Wei Wu, Nian Wang and Je-Chin Han
J. Heat Transfer   doi: 10.1115/1.4040260
Experimental investigation on rotation and turning vane effects on heat transfer was performed in a two-pass rectangular internal cooling channel. The channel has an aspect ratio of AR = 2:1 and a 180 deg tip-turn, which is a scaled up model of a typical internal cooling passage of gas turbine airfoils. The leading and trailing surfaces are roughened with 45 deg angled parallel ribs (staggered, P/e = 8, e/Dh = 0.1). Tests were performed in a pressurized vessel (570 kPa) where higher rotation numbers (Ro) can be achieved with a maximum Ro = 0.42. Five Reynolds numbers (Re) were examined (Re = 10,000 to 40,000). At each Reynolds number, five rotational speeds (? = 0 to 400 rpm) were considered. Results showed that rotation effects are stronger in the tip regions as compared to other surfaces. Heat transfer enhancement up to 4 times was observed on the tip wall at the highest rotation number. However, heat transfer enhancement is reduced to about 1.5 times with the presence of a tip turning vane at the highest rotation number. Generally, the tip turning vane reduces the effects of rotation, especially in the turn portion.
TOPICS: Heat transfer, Cooling, Turning vanes, Rotation, Reynolds number, Gas turbines, Vessels, Airfoils
Technical Brief  
Viacheslav Karmalita
J. Heat Transfer   doi: 10.1115/1.4040255
This paper deals with exercising the autoregressive method determining the logarithmic decrement and natural frequency of gas oscillations in a combustion chamber. Evaluation of a combustion noise impact by oscillation decrement estimates was resulted in finding out a parry solution based by modeling vibrating combustion phenomena. Results of the proposed solution implementation for afterburner tests are presented as well.
TOPICS: Oscillations, Combustion, Turbulence, Noise (Sound), Modeling, Combustion chambers
Frederico Rodrigues, José Páscoa and Michele Trancossi
J. Heat Transfer   doi: 10.1115/1.4040152
DBD plasma actuators have several applications within the field of active flow control. Separation control, wake control, aircraft noise reduction, modification of velocity fluctuations or boundary layer control are just some examples of their applications. They present several attractive features such as, their simple construction, very low mass, fast response, low power consumption and robustness. Besides their aerodynamic applications, these devices have also possible applications within the field of heat transfer, for example film cooling applications or ice formation prevention. However, due to the extremely high electric fields in the plasma region and consequent impossibility of applying classic intrusive techniques, there is a relative lack of information about DBDs thermal characteristics. In an attempt to overcome this scenario, this work describes the thermal behaviour of DBD plasma actuators under different flow conditions. Infra-red thermography measurements were performed in order to obtain the temperature distribution of the dielectric layer and also of the exposed electrode. During this work we analysed DBD plasma actuators with different dielectric thicknesses and also with different dielectric materials, whose thermal behaviour is reported for the first time. The results allowed to conclude that the temperature distribution is not influenced by the dielectric thickness, but it changes when the actuator operates under an external flow. We also verified that, although in quiescent conditions the exposed electrode temperature is higher than the plasma region temperature, the main heat energy dissipation occurs in the dielectric, more specifically in the plasma formation region.
TOPICS: Plasmas (Ionized gases), Flow (Dynamics), Actuators, Experimental analysis, Temperature distribution, Electrodes, Temperature, Heat transfer, Electric fields, Separation (Technology), Noise control, Dielectric materials, Thermography, Construction, Boundary layers, Heat, Energy dissipation, Fluctuations (Physics), Wakes, Ice, Aircraft, Energy consumption, Film cooling, Flow control, Robustness
Dr. Asis Giri and Swastika Patel
J. Heat Transfer   doi: 10.1115/1.4040140
A computational study of natural convection from bi-heaters of finite thickness and finite conductivity placed on a finite thickness and finite conductive bottom plate of a cavity is performed under constant heat input condition. Cavity is cooled by the sidewalls, while the top and backside of the bottom plate are insulated. Streamline, isotherms and local heat flux distribution of the sidewalls are discussed. Base Grashof number is chosen as 2.5×106. Bi-heater maintains a non-dimensional distance of 0.4 between them. Left heater is placed at a non-dimensional distance of 0.2 from the left wall. Heater length ratio is varied from 0.4 to 1.7, while heater strength ratio is varied from 0.4 to 3.0. Optimum operating temperature condition is found from the analysis.
TOPICS: Buoyancy, Convection, Cavities, Heat flux, Operating temperature, Electrical conductivity, Natural convection, Heat, Thermal conductivity
Foluso Ladeinde, Ken Alabi and Wenhai Li
J. Heat Transfer   doi: 10.1115/1.4040141
Manifold-microchannel (MM) combinations used on heat transfer surfaces have shown the potential for superior heat transfer performance to pressure drop ratio when compared to chevron-type corrugations for plate (frame) heat exchangers (PHEs). This paper presents an advanced genetic algorithm (GA)-based procedure for analyzing and optimizing the MM-based PHE. One distinctive feature of our implementation is the blended variable formulation for the chromosomes to allow the use of continuous variables rather than bitwise variables as in older GA methods. The resulting GA procedure is particularly well suited for PHEs for several reasons, including the fact that it does not require continuous variables or functional dependence on the design variables. In addition, the computational effort required for the GA technique in our implementation scales linearly with the number of design variables, making it appropriate for MM-based PHEs, which have several variables. The computed results compare well with experimental data, which also show better performance with conventional PHE of the same volume utilizing chevron corrugations. Although a full-scale CFD analysis may give more accurate results than the semi-empirical approach used in this paper, the former cannot efficiently support rapid concept de-selection during the preliminary stage of design. Optimization based on CFD also cannot support discontinuous functions. To improve the fidelity of the current analysis, a discrete, finite-volume-type, one-dimensional reduced-order modeling is carried out, in addition to a purely bulk approach. Our discrete approach obviates the need for the ?-NTU-type models.
TOPICS: Heat, Optimization, Manifolds, Microchannels, Design, Heat transfer, Computational fluid dynamics, Heat exchangers, Modeling, Pressure drop, Genetic algorithms
Jingjie Zhang, Carlos Polanco and Dr. Avik Ghosh
J. Heat Transfer   doi: 10.1115/1.4040144
We theoretically explore the influence of end-group chemistry (bond stiffness and mass) on the interfacial thermal conductance at a gold-alkane interface. We accomplish this using the Non-Equilibrium Green's Function (NEGF) coupled with first principle parameters in Density Functional Theory (DFT) within the harmonic approximation. Our results indicate that the interfacial thermal conductance is not a monotonic function of either chemical parameters, but instead maximizes at an optimal set of mass and bonding strength. This maximum is a result of the interplay between the overlap in local density of states of the device and that in the contacts, as well as the phonon group velocity. We also demonstrate the intrinsic relationship between the Diffusive Mismatch Model (DMM) and the properties from NEGF, and provide an approach to get DMM from first principles NEGF. By comparing the NEGF based DMM conductance and range of conductance while altering the mass and bonding strength, we show that DMM provides an upper bound for elastic transport in this dimensionally mismatched system. We thus have a prescription to enhance the thermal conductance of systems at low temperatures or at low dimensions where inelastic scattering is considerably suppressed.
TOPICS: Thermal conductivity, Junctions, Electrical conductance, Bonding, Density functional theory, Equilibrium (Physics), Phonons, Radiation scattering, Electromagnetic scattering, Low temperature, Approximation, Chemistry, Stiffness, Density, Scattering (Physics), Dimensions
Claire K. Wemp and Van P. Carey
J. Heat Transfer   doi: 10.1115/1.4040142
Spraying water droplets on air fin surfaces is often used to augment performance of air-cooled Rankine power plant condensers and wet cooling tower heat exchangers for building air-conditioning systems. To get the best performance in such processes, the water droplets delivered to the surface should spread rapidly into an extensive, thin film and evaporate with no liquid leaving the surface due to recoil or splashing. This paper presents predictions of theoretical/computational modeling and results of experimental studies of droplet spreading on thin-layer, nanostructured, superhydrophilic surfaces that exhibit very high wicking rates (wickability) in the porous layer. Analysis of the experimental data in the model framework illuminates the key aspects of the physics of the droplet spreading process and evaporation heat transfer. This analysis also predicts the dependence of droplet spreading characteristics on the nanoporous surface morphology and other system parameters. The combined results of this investigation indicate specific key strategies for design and fabrication of surface coatings that will maximize the heat transfer performance for droplet evaporation on heat exchanger surfaces. The implications regarding wickability effects on pool boiling processes are also discussed.
TOPICS: Heat transfer, Drops, Evaporation, Water, Heat exchangers, Power stations, Condensers (steam plant), Cooling towers, Pool boiling, Spraying (Coating processes), Design, Physics, Thin films, Air conditioning, Coatings, Computer simulation, Manufacturing, Plasma spraying
Ablimit Aili, Qiaoyu Ge and TieJun Zhang
J. Heat Transfer   doi: 10.1115/1.4040143
Micro/nanostructured surfaces have been widely explored to enhance condensation heat transfer over the past decades. When there is no flooding, micro/nanostructures can enable dropwise condensation by reducing solid-droplet adhesion. However, micro/nanostructures have mixed effects on filmwise condensation because the structures can simultaneously thin the condensate film and increase the liquid-solid friction. Although oil-infusion of structured surfaces has recently been shown to render filmwise condensation dropwise in many cases, challenges remain in the case of extremely low-surface-tension fluids. This work aims to provide a unified experimental platform to reveal the impact of mini/micro/nanostructures on condensation heat transfer of low-surface-tension fluids in a custom-made condensation chamber. We first investigate the effect of microstructures, hydrophobic coating, as well as oil-infusion on the filmwise condensation of a low-surface-tension fluid, e.g. refrigerant, on microporous aluminum surfaces. And we show that for low-surface-tension condensates, microstructures, hydrophobic coating, or oil-infusion do not play a considerable role in enhancing or deteriorating heat transfer. Next, we study how the addition of nanostructures affects the condensation performance of the refrigerant on copper mini-fin structures. It is found that nanostructures slightly deteriorate the condensation performance due to the dominance of solid-liquid friction, although the performance of these nanostructured fins is still better than that of the mini-pin-fins. The results carry the implication that mini/micro/nanoscale surface structures should be carefully designed for enhanced filmwise condensation applications.
TOPICS: Fluids, Nanostructures , Film condensation, Tension, Condensation, Heat transfer, Friction, Refrigerants, Fins, Coating processes, Coatings, Condensed matter, Drops, Nanoscale phenomena, Adhesion, Copper, Aluminum, Floods
Naveen Kumar Gupta, Arun Kumar Tiwari and Subrata Kumar Ghosh
J. Heat Transfer   doi: 10.1115/1.4040146
The enhancements in thermal performance of mesh wick heat pipe using TiO2/H2O nanofluid (0.5, 1.0 & 1.5 vol. %) as working fluid for different (50,100, & 150 watts) power input were investigated. Results showed maximum 17.2 % reduction in thermal resistance and maximum 13.4% enhancement in thermal efficiency of heat pipe using 1.0 vol. % nanofluid as compared to water. The wick surface of the heat pipe was then coated with TiO2 nanoparticles by physical vapor deposition method. The experimental investigation had been also carried out on coated wick heat pipe using water as working fluid. Results showed 12.1% reduction in thermal resistance and 11.9% enhancement in thermal efficiency of the heat pipe as compared to uncoated wick heat pipe using water. Temporal deteriorations in thermal performance during prolonged working (2, 4 and 6 months) of heat pipe were also studied. Temporal deterioration in thermal performance of heat pipe filled with nanofluid depends upon the deterioration in thermophysical properties of nanofluids. The deterioration is due to the agglomeration and sedimentation of nanoparticles with respect to the time. Comparative study shows that after a certain time of operation, thermal performance of heat pipe with nanoparticle coated wick superseded that of the heat pipe filled with nanofluid. Therefore, nanoparticle coating might be a good substitute for nanofluid to avoid the stability issues. The present paper provides incentives for further research to develop nanofluids that avoid the encountered sedimentation or agglomeration.
TOPICS: Nanoparticles, Heat pipes, Nanofluids, Water, Thermal efficiency, Agglomeration (Materials), Sedimentation, Thermal resistance, Fluids, Coating processes, Coatings, Electrical measurement, Vapor deposition, Stability
Wei Li, Yang Luo, Jing-zhi Zhang and W. J. Minkowycz
J. Heat Transfer   doi: 10.1115/1.4040147
This paper presents a fundamental research on hydrodynamics and heat transfer about an elongated bubble flow boiling in a circular microchannel. In present study, continuum Surface Force (CSF) model based on Volume of Fluid (VOF) methodis combined withthermocapillaryforce to explore the effects of thermocapillarity for flow boiling in microchannels. To validate the self-defined codes, a two-phase thermocapillary-driven flow and a Taylor bubble growing in a capillary tube are performed. Results of both test cases show good convergence and are in good agreement with data from other literatures. Bubble motion and local heat transfer coefficient (HTC) on the heated wall with respect to time are discussed in present study. It is found that for large Marangoni number (case 3), variation of surface tension has an influenceon bubble shape and temperature profile. Thermocapillary effect induces convection in liquid film region, which augments the HTCs at specified positions. The numerical investigation also shows that average HTC has increased by 6.7% in case 3 when compared with case 1. Thus, it is very significative to further study the influence of themocapillarity and Marangoni effect on bubble growth in microchannels.
TOPICS: Simulation, Bubbles, Evaporation, Gravity (Force), Microchannels, Boiling, Flow (Dynamics), Hydrodynamics, Heat transfer, Fluids, Bubbly flow, Convection, Heat transfer coefficients, Surface tension, Liquid films, Shapes, Temperature profiles
Xiao He, Tianzhi Yang and Linzhi Wu
J. Heat Transfer   doi: 10.1115/1.4040148
We recently shown theoretically that the infinite singularity of the thermal cloak designed by transformation thermodynamics could be eliminated by a new method-the path design of the heat flux without any approximation. In this paper, we present the experimental evidence of such a new strategy of thermal cloak, that is, a truly singularity-free thermal cloak. We fabricate such a transient thermal cloak device without using extreme material parameters. The experimental results show fully controlled, transient cloaking behavior, which are perfectly consistent with the theoretical derivations and simulated results. The new method provides a new blue print for the transient thermal protection of a specific target.
TOPICS: Design, Heat flux, Transients (Dynamics), Thermodynamics, Approximation

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