Accepted Manuscripts

Robert McMasters, Filippo de Monte and James Beck
J. Heat Transfer   doi: 10.1115/1.4038855
A desirable feature of any parameter estimation method is to obtain as much information as possible with one experiment. However, achieving multiple objectives with one experiment is often not possible. In the field of thermal parameter estimation, a determination of thermal conductivity, volumetric heat capacity, heat addition rate, surface emissivity and convection coefficient may be desired from a set of temperature measurements in an experiment where a radiant heat source is used. It would not be possible to determine all of these parameters from such an experiment; more information would be needed. The work presented in the present research shows how thermal parameters can be determined from temperature measurements using complementary experiments where the same material is tested more than once using a different geometry or heating configuration in each experiment. The method of ordinary least squares is used in order to fit a mathematical model to a temperature history in each case. Several examples are provided using one-dimensional conduction experiments, with some having a planar geometry and some having a cylindrical geometry. The parameters of interest in these examples are thermal conductivity and volumetric heat capacity. Sometimes both of these parameters cannot be determined simultaneously from one experiment but utilizing two complementary experiments may allow each of the parameters to be determined. A method is presented as part of the current research by which confidence regions can be found for results from a single analysis of multiple experiments.
TOPICS: Heat conduction, Transients (Dynamics), Geometry, Parameter estimation, Temperature measurement, Thermal conductivity, Heat capacity, Convection, Emissivity, Heat, Temperature, Radiant heat, Heating
Oussama Ibrahim, Farouk Fardoun, Rafic Younes and Mohamad Ibrahim
J. Heat Transfer   doi: 10.1115/1.4038827
The performance of a flat-plate solar collector is usually investigated by its efficiency. This efficiency is normally defined on a steady-state basis, which makes it difficult to correctly track the instantaneous performance of the collector in various case-studies. Accordingly, this paper proposes an improved definition of instantaneous efficiency of a flat-plate solar collector used as a part of a solar water heating system. Using a pre-developed model by the authors for such a system, the proposed efficiency-definition is examined and compared with the conventional one for a specific case study. Results show that the improved definition of efficiency records reasonable values, i.e. no over-range values are observed contrast to the case of conventional efficiency-definition. Furthermore, this suggested efficiency approximately coincides with the conventional one at a wide range of time, as long as the system is operating in the so-called trans-steady state phase or when the system is off-operational provided that the instantaneous rate of heat stored in heat transfer fluid is less than or equal to zero. As a result, the improved efficiency-definition yields more realistic results in reflecting the performance of a flat-plate collector in an active solar water heating system and is recommended to be used.
TOPICS: Modeling, Solar collectors, Flat plates, Solar water heating, Steady state, Case studies, Heat, Heat transfer, Fluids
Fatma Habbachi, Fakhreddine Segni Oueslati, Rachid Bennacer and Afif Elcafsi
J. Heat Transfer   doi: 10.1115/1.4038828
This paper is a numerical study was conducted to investigate the conjugate of the flow and heat transfer from the three-dimensional natural convection, in a cubic enclosure partially filled with a central cubic porous block which is in out thermal equilibrium with the fluid media. The physical model considered here assumes the existence of a temperature difference across the enclosure between the left and the right wall, the other walls are adiabatic. Under these conditions, flow from inside the enclosure is generated by the temperature difference across the enclosure and the interaction between the solid matrix and the fluid. Variations of Nusselt number on the hot and cold walls are also presented to show the overall characteristics of heat transfer to the interior of the enclosure. The study found that the fluid flow and heat transfer are governed by the dimensionless thickness of the porous layer , and the thermal conductivity ratio of the solid matrix of the porous media to that of the fluid . The complex obtained flow structure and corresponding heat transfer (velocity, temperature profiles) are discussed at a steady state. The numerical results are reported in terms of isotherms, velocity field, streamlines, and averaged Nusselt number. Thus, the results of this work can help develop new tools and means to optimize the overall heat transfer rate, which is important in many electronic energy components and other systems.
TOPICS: Heat transfer, Energy / power systems, Optimization, Cavities, Flow (Dynamics), Fluids, Temperature, Natural convection, Porous materials, Thermal conductivity, Thermal equilibrium, Steady state, Temperature profiles, Fluid dynamics
Vivekananthan Balakrishnan, Toan Dinh, Hoang-Phuong Phan, Dzung Viet Dao and Nam Trung Nguyen
J. Heat Transfer   doi: 10.1115/1.4038829
This paper presents an analytical solution for the Joule heating problem of a segmented wire made of two materials with different properties and suspended as a bridge across two fixed ends. The paper first establishes the one-dimensional governing equations of the steady-state temperature distribution along the wire with the consideration of heat conduction and free-heat convection phenomena.The temperature coefficient of resistance of the constructing materials, and the dimension of the each segmented wires were also taken into account to obtain analytical solution of the temperature. COMSOL Numerical solutions were also obtained for initial validation. Experimental studies were carried out using copper and nichrome wires, where the temperature distribution was monitored using an IR thermal camera. The data showed a good agreement between experimental data and the analytical data, validating our model for the design and development of thermal sensors based on multi-segmented structures.
TOPICS: Wire, Joules, Heating, Temperature distribution, Temperature, Copper, Bridges (Structures), Sensors, Dimensions, Convection, Design, Steady state, Heat, Heat conduction
Ritunesh Kumar, Gurjeet Singh and Dariusz Mikielewicz
J. Heat Transfer   doi: 10.1115/1.4038830
The problem of flow maldistribution is very critical in microchannel heat sinks (MCHS). It induces temperature non-uniformity, which may ultimately lead to the breakdown of associated system. In the present communication, a novel approach for the mitigation of flow maldistribution problem in parallel MCHS has been proposed using variable width microchannels. Numerical simulation of copper made parallel microchannel heat sink consisting of twenty five channels has been carried out for the conventional design (CD) and the proposed design (PD). It is observed that the proposed design contributed to reduction of flow maldistribution by 93.7%, which facilitated in effective uniform cooling across the entire projected area of MCHS. Temperature fluctuation at fluid - solid interface is reduced by 4.3ºC whereas, maximum and average temperatures of microchannels projected area are reduced by 2.3ºC and 1.1ºC respectively. Proposed design is suitable in alleviating flow maldistribution problem for the extended range of off design conditions.
TOPICS: Flow (Dynamics), Heat sinks, Microchannels, Design, Temperature, Cooling, Fluids, Copper, Computer simulation, Temperature nonunifomity
Simon Game, Marc Hodes, Toby Kirk and Demetrios Papageorgiou
J. Heat Transfer   doi: 10.1115/1.4038831
We numerically compute Nusselt numbers for laminar, hydrodynamically and thermally fully-developed Poiseuille flow of liquid in the Cassie state through a parallel plate-geometry microchannel symmetrically textured by a periodic array of isoflux ridges oriented parallel to the flow. Our computations are performed using an efficient, multiple domain, Chebyshev collocation (spectral) method. The Nusselt numbers are a function of the solid fraction of the ridges, channel height to ridge pitch ratio and protrusion angle of menisci. Significantly, our results span the entire range of these geometrical parameters. We quantify the accuracy of two asymptotic results for Nusselt numbers corresponding to small meniscus curvature, by direct comparison against the present results. The first comparison is with the exact solution of the dual series equations resulting from a small boundary perturbation. The second comparison is with the asymptotic limit of this solution for large channel height to ridge pitch ratio.
TOPICS: Poiseuille flow, Microchannels, Flow (Dynamics), Computation, Geometry
Asterios Pantokratoras
J. Heat Transfer   doi: 10.1115/1.4038832
This discussion concerns some doubtful results included in the above papers.
TOPICS: Flow (Dynamics), Heat transfer, Fluids, Mixed convection
Technical Brief  
Bernard Bahaya, Drew Johnson and C. C. Yavuzturk
J. Heat Transfer   doi: 10.1115/1.4038835
Experiments were conducted with graphene nanoplatelets (GNP) to investigate the relative benefit of the thermal conductivity increase in relationship to the potential detriment of increased viscosity. The maximum enhancement ratio for GNP nanofluid thermal conductivity over water was determined to be 1.43 at a volume fraction of 0.014. Based on GNP aspect ratios, the differential effective media (DEM) model of Chu, Li [1] is shown to describe the experimental results of this study when using a fitted interfacial resistance value of 6E -8 m2 K W-1. The viscosity model of Einstein [2] provided close agreement between measured and predicted values when the effects of temperature where included and the intrinsic viscosity model term was adjusted to a value representative for GNP. Heat transfer in external flows in laminar regime is predicted to decrease for GNP nanofluids when compared to water alone.
TOPICS: Flow (Dynamics), Heat transfer, Viscosity, Graphene, Nanofluids, Water, Thermal conductivity, Discrete element methods, Interfacial thermal resistance, Temperature effects
Technical Brief  
Kaustubh S. Kulkarni, Umesh Madanan, Terrence W. Simon and Richard J. Goldstein
J. Heat Transfer   doi: 10.1115/1.4038790
If a steady thermal boundary layer is sufficiently thick, wall heat fluxes and associated convective heat transfer coefficients can be directly calculated from measured temperature distributions taken within it using a traversing thermocouple probe. The boundary layer can be laminar, turbulent or transitional and on a surface of arbitrary surface temperature distribution and geometry. Herein, this technique is presented and validated in a steady, turbulent, two-dimensional boundary layer on a flat, uniform-heat-flux wall. Care is taken to properly account for radiation from the wall and conduction within the thermocouple wire. In the same setting, heat flux measurements are made for verification purposes using an energy balance on a segment of the test wall carefully designed to minimize and include radiation and conduction effects. Heat flux values measured by the boundary layer measurement technique and by the energy balance measurement agree to within 4.4% and the difference between the two lie completely within their respective measurement uncertainties of 5.74% and 0.6%.
TOPICS: Boundary layers, Heat flux, Temperature distribution, Thermocouples, Heat, Radiation (Physics), Turbulence, Energy budget (Physics), Heat conduction, Wire, Flux (Metallurgy), Convection, Geometry, Probes, Thermal boundary layers, Measurement uncertainty
M. Enrique Huerta L., Tania M. Flores F., Claudia Barraza de la P. and Alfonso Humberto Castillejos Escobar
J. Heat Transfer   doi: 10.1115/1.4038792
Heat extraction and drop impact regimes occurring when a local portion of a horizontal flat-fan air-mist impinges the active surface of a Pt-disk hold at Tw from ~60 to 1200 °C are investigated. Boiling curves comprise single-phase, nucleate, transition and film boiling. Mists are generated under wide ranges of water and air flow rates, and the disk is placed at center and off-center positions along the mist footprint major axis. Conditions generate a wide spectrum of water impact flux, w, droplet diameter, dd, droplet velocity, uzs, and impingement angle. Heat flux extracted, -q, along each boiling regime correlates very well with expressions involving Reynolds, Weber, and Jakob numbers evaluated in terms of local average characteristics of free non-impinging mists - w, volume mean diameter, d30, normal volume weighted mean velocity, uz,v - and Tw; close estimation indicates that hydrodynamic and thermal forces are well accounted. During arrival of sparse parcels visualization of mist-wall interactions, using a high speed camera aided by laser illumination, allows determination of the predominance area diagram of droplet impact regimes in terms of normal impinging Weber number, Wez, and Tw. The regimes include stick, rebound, spread and splash; the last subclassified as fine-, crown- and jet-atomization. Arrival of parcels in close succession is ubiquitous causing rapid surface flooding and leading to formation of discontinuous well agitated thick liquid films which interacts longer with the surface than drops in sparse parcels, acting as heat sinks for longer periods of time.
TOPICS: Heat, Drops, Visualization, Steady state, Water, Disks, Boiling, Lasers, Air flow, Film boiling, Floods, Heat sinks, Liquid films, Heat flux
Guest Editorial  
Chang Kyoung Choi and Nenad Miljkovic
J. Heat Transfer   doi: 10.1115/1.4038762
The K-22 Heat Transfer Visualization Committee sponsored the 24th Heat Transfer Photogallery during the 2017 Summer Heat Transfer Conference at the Hyatt Regency Bellevue, Bellevue, Washington, on July 9~12, 2017. Nine entries were submitted to the Photogallery sessions. A peer-reviewed evaluation was conducted by both the participants and selected HTD K-22 Technical Committee members, which identified four final entries for publication in the 2018 ASME Journal of Heat Transfer February issue. Among the selected entries, two visualize droplet phenomena, and the remainder visualizes phase change at extreme temperatures. The purpose of publishing photogallery entries in JHT is to draw attention to innovative features of visualization techniques and to present aesthetic qualities of heat and mass transport phenomena. To focus on visualization images and schematics for each entry, a text is kept to a minimum and further details should be sought directly from the corresponding authors. Our wish is that the journal readers enjoy viewing these collections, acquire knowledge in state-of-the-art visualization techniques, and promote participation in future Photogallery sessions at the SHTC and ASME-IMECE conferences.
TOPICS: Heat transfer, Visualization, Transport phenomena, Drops, Heat, Temperature
Belal Al-Khamaiseh, Y. S. Muzychka and Serpil Kocabiyik
J. Heat Transfer   doi: 10.1115/1.4038712
In the microelectronics industry, the multilayer structures are found extensively where the microelectronic device/system is manufactured as a compound system of different materials. Recently, a variety of new materials have emerged in the microelectronics industry with properties superior to Silicon, enabling new devices with extreme performance. Such materials include ??-Gallium-oxide (??-Ga2O3 ), and Black Phosphorus (BP), which are acknowledged to have anisotropic thermal conductivity tensors. In many of these devices, thermal issues due to self-heating are a problem that affect the performance, efficiency, and reliability of the devices. Analytical solutions to the heat conduction equation in such devices with anisotropic thermal conductivity tensor offer significant computational savings over numerical methods. In this paper, general analytical solutions of temperature distribution and thermal resistance of a multilayered orthotropic system are obtained. The system is considered as a compound three dimensional flux channel consisting of N-layers with different thermal conductivities in the three spatial directions in each layer. A single eccentric heat source is considered in the source plane while a uniform heat transfer coefficient is considered along the sink plane. The solutions account for the effect of interfacial conductance between the layers and for considering multiple eccentric heat sources in the source plane. For validation purposes, the analytical results are compared with numerical solution results obtained by solving the problem with the Finite Element Method (FEM) using ANSYS commercial software package.
TOPICS: Heat, Heat conduction, Reliability, Anisotropy, Finite element methods, Thermal conductivity, Electrical conductance, Tensors, Numerical analysis, Computer software, Gallium, Indium compounds, Silicon, Temperature distribution, Thermal resistance, Heating, Microelectronic devices, Heat transfer coefficients
Nian Wang, Andrew F Chen, Mingjie Zhang and Je-Chin Han
J. Heat Transfer   doi: 10.1115/1.4038691
Jet impingement cooling has been extensively used in the leading edge region of a gas turbine blade. This study focuses on the effect of jet impinging position on leading edge heat transfer. A row of cylindrical injection holes is located along the axis (normal jet) or the edge (tangential jet) of the semi-cylinder, on the jet plate. The jet-to-target-plate distance to jet diameter ratio (z/d) is 5 and the ratio of jet-to-jet spacing to jet diameter (s/d) is 4. The jet Reynolds number is varied from 10,000 to 30,000. Detailed impingement heat transfer coefficient distributions were experimentally measured by using the transient liquid crystal technique. To understand the thermal flow physics, numerical simulations were performed using RANS with two turbulence models: realizable k-e (RKE) and shears stress transport k-? model (SST). Comparisons between the experimental and the numerical results are presented. The results indicate that the local Nusselt numbers on the test surface increase with the increasing jet Reynolds number. The tangential jets provide more uniform heat transfer distributions as compared with the normal jets. For the normal jet impingement and the tangential jet impingement, the RKE model provides better prediction than the SST model. The results can be useful for selecting a jet impinging position in order to provide the proper cooling distribution inside a turbine blade leading edge region.
TOPICS: Cooling, Jets, Turbine blades, Heat transfer, Reynolds number, Stress, Physics, Flow (Dynamics), Liquid crystals, Turbulence, Computer simulation, Transients (Dynamics), Gas turbines, Impingement cooling, Blades, Cylinders, Reynolds-averaged Navier–Stokes equations, Heat transfer coefficients
Jeffrey Braun, Chester Szwejkowski, Ashutosh Giri and Patrick Hopkins
J. Heat Transfer   doi: 10.1115/1.4038713
In this study, we calculate the steady-state temperature rise that results from laser heating for multilayer thin films using the heat diffusion equation. For time- and frequency-domain thermoreflectance (TDTR and FDTR) relying on frequency modulated laser sources, we decouple the modulated and steady-state temperature profiles to understand the conditions needed to achieve a single temperature approximation throughout the experimental volume, allowing for the estimation of spatially invariant thermal parameters within this volume. We consider low thermal conductivity materials, including amorphous silicon dioxide (a-SiO2), polymers, and disordered C60, to demonstrate that often-used analytical expressions fail to capture this temperature rise under realistic experimental conditions, such as when a thin-film metal transducer is used or when pump and probe spot sizes are significantly different. To validate these findings and demonstrate a practical approach to simultaneously calculate the steady-state temperature and extract thermal parameters in TDTR, we present an iterative algorithm for obtaining the steady-state temperature rise and measure the thermal conductivity and thermal boundary conductance of a-SiO2 with a 65 nm gold thin film transducer. Furthermore, we discuss methods of heat dissipation to include the use of conductive substrates as well as the use of bidirectional heat flow geometries. Finally, we discuss the influence of the optical penetration depth (OPD) on the steady-state temperature rise to reveal that only when the OPD approaches the characteristic length of the temperature decay does it alter the temperature profile relative to the surface heating condition.
TOPICS: Thin films, Temperature, Lasers, Pumps, Steady state, Probes, Heating, Heat, Quartz, Temperature profiles, Transducers, Thermal conductivity, Electrical conductance, Algorithms, Polymers, Metals, Flow (Dynamics), Approximation, Energy dissipation, Thermal diffusion, Thermoreflectance, Silicon
Youssef Abdo, Vandad Rohani, Francois Cauneau and Laurent Fulcheri
J. Heat Transfer   doi: 10.1115/1.4038602
The motion of the gliding electric arc under the effect of magnetic field is investigated. When the arc is exposed to a magnetic field, a gas flow is generated perpendicularly across its section. Consequently, the arc moves at a relative velocity that corresponds to the velocity of the temperature distribution through the arc. The resulting relative velocity gives rise to heat convection which has great impact on the arc motion. A practical analytical solution is derived using MGD (magneto gas dynamic) equations in order to investigate the heat transfer occurring in the arc and its vicinity and to estimate the magnitude of its velocity.
TOPICS: Electric arcs, Dynamics (Mechanics), Heat transfer, Magnetic fields, Gas flow, Convection, Temperature distribution
Jackson R Harter, Laura de Sousa Oliveira, Agnieszka Truszkowska, Todd Palmer and P. Alex Greaney
J. Heat Transfer   doi: 10.1115/1.4038554
We present a method for solving the Boltzmann transport equation (BTE) for phonons by modifying the neutron transport code Rattlesnake which provides a numerically efficient method for solving the BTE in its Self-Adjoint Angular Flux form. Using this approach, we have computed the reduction in thermal conductivity of uranium dioxide (UO$_2$) due to the presence of a nanoscale xenon bubble across a range of temperatures. For these simulations, the values of group velocity and phonon mean free path in the UO$_2$ were determined from a combination of experimental heat conduction data and first principles calculations. The same properties for the Xe under the high pressure conditions in the nanoscale bubble were computed using classical molecular dynamics. We compare our approach to the other modern phonon transport calculations, and discuss the benefits of this multiscale approach for thermal conductivity in nuclear fuels under irradiation.
TOPICS: Phonons, Thermal conductivity, Uranium, Nanoscale phenomena, Bubbles, Mean free path, Engineering simulation, Temperature, Neutrons, Heat conduction, Irradiation (Radiation exposure), Simulation, High pressure (Physics), Molecular dynamics, Nuclear fuels
Ao Xu, Prof. Tim S. Zhao, Le Shi and Jianbo Xu
J. Heat Transfer   doi: 10.1115/1.4038555
We present lattice Boltzmann simulations of the mass transfer coefficient from the bulk flow to pore surfaces for chemically reactive flows in both ordered and disordered porous structures. The ordered porous structure under consideration consists of cylinders in a staggered arrangement and in a line arrangement, while the disordered one is composed of randomly placed cylinders. Results show the ordered porous structure of staggered cylinders exhibits a larger mass transfer coefficient than ordered porous structure of inline cylinders does. It is also found that in the disordered porous structures, the Sherwood number increases linearly with Reynolds number at the creeping flow regime; the Sh and Re exhibit a one-half power law dependence at the inertial flow regime. Meanwhile, for Schmidt number (Sc) between 1 and 10, the Sh is proportional to Sc^0.8; for Sc between 10 and 100, the Sh is proportional to Sc^0.3.
TOPICS: Mass transfer, Porous materials, Simulation, Chemically reactive flow, Lattice Boltzmann methods, Cylinders, Flow (Dynamics), Creeping flow, Reynolds number
C Thomas Avedisian, Wei-Chih Kuo, Wing Tsang and Adam Lowery
J. Heat Transfer   doi: 10.1115/1.4038572
In this paper we apply a new method based on the film boiling regime of multiphase heat transfer to study pyrolysis of saturated diethyl carbonate (DEC) at temperatures up to 1500K. Detailed measurements are made of the composition of bubbles that percolate through the system which are used to infer the decomposition reactions. The results show that below about 1100K the decomposition products are ethylene (C2H4), carbon dioxide (CO¬2) and ethanol (EtOH, C2H5OH) with the concentration ratio [C2H4]/[CO2] =1 corresponding to a first order decomposition process. At higher temperatures, [C2H4]/[CO2] > 1 which is explained by an additional route to forming C2H4 from decomposition of radicals formed by EtOH. The presence of H2, CO, CH4 and C2H6 in the product stream was noted at all temperatures examined with concentrations that increased from trace values at low temperatures to values comparable to DEC decomposition products at the highest temperatures. The role of EtOH decomposition radicals attacking DEC is also speculated to provide another DEC conversion route at high temperatures. Formation of a carbon layer on the tube was observed but did not appear to influence the decomposition process.
TOPICS: Film boiling, High temperature, Ethanol, Temperature, Carbon dioxide, Methane, Pyrolysis, Heat transfer, Bubbles, Carbon, Low temperature
Xiao Yuan, Songping Mo, Ying Chen, Lisi Jia, Tao Yin, Zhi Yang and Zhengdong Cheng
J. Heat Transfer   doi: 10.1115/1.4038558
Phase-change materials (PCM) with low supercooling degree (SD) are important in cold thermal energy storage applications. The SD of nanosuspension PCM usually decreases with increasing nanoparticle concentration. However, the performance variation of nanosuspension PCM at high concentrations has been rarely studied, though it is important because nanoparticles tend to aggregate. In this paper, the supercooling degree and dispersion stability of nanosuspensions of TiO2, zirconium phosphate (ZrP) and TiO2 coupled with zirconium phosphate (TiO2-ZrP) were investigated at nanoparticle concentrations up to 5.0 wt.%. Results show that the supercooling degree of TiO2 suspension did not remarkably varied with mass concentrations above 2.0 wt. %. In contrast, the supercooling degree of TiO2-ZrP and ZrP were low and continuously decreased with increasing mass concentration of nanoparticles. The dispersion stability of TiO2-ZrP suspension improved compared with that of TiO2 suspension. Hence, TiO2-ZrP suspension provided more nucleation sites than TiO2 suspension to induce heterogeneous in water.
TOPICS: Supercooling, Zirconium, Nanoparticles, Stability, Nucleation (Physics), Phase change materials, Thermal energy storage, Water
Alan Lugarini, Admilson T. Franco and Marcelo Risso Errera
J. Heat Transfer   doi: 10.1115/1.4038559
This work presents the development and analysis of constructal microchannel network architectures for heat dissipation. The network configurations are characterized by multiple flow ramifications and changes in length and hydraulic diameter scales through each ramification level. Architectures investigated experimentally in the past years have constant scaling rules throughout their ramification levels. In this study constructal theory inspires the design of network architectures with variable scaling rules and up to three ramification levels. As result, it was verified that constructal networks allow significant pumping power reduction with respect to networks with same ramification levels. Architecture's selection criteria using performance curves is proposed and it was demonstrated that the bifurcated network with diameter ratio according to Hess-Murray law is not appropriated for heat dissipation purposes in miniaturized devices.
TOPICS: Design, Performance evaluation, Microchannels, Architecture, Heat, Energy dissipation, Flow (Dynamics)

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