Accepted Manuscripts

Dr. Bai-tao An and Jian-jun Liu
J. Heat Transfer   doi: 10.1115/1.4036523
The diffusion hole constructed on a slot type cross section has the potential to obtain high film cooling performance. However, the end shape of the cross section can greatly affect film cooling characteristics. This study examined eight cases of diffusion slot holes with various cross-sectional end shapes. The comparison of the eight diffusion slot holes and a typical fan-shaped hole were performed with a flat plate model using a 3D steady CFD method. The rectangular cross section had an aspect ratio of about 3.4. The end shape variation can be described based on sidewall contraction location, size, and form. The simulations were performed under an engine-representative condition of mainstream inlet Mach number 0.3 and turbulence intensity of 5.2%. The simulated results showed that a strip separation bubble caused by inlet “jetting effect” occurs near the downstream wall of the diffusion slot hole and interacts with the diffusion flow. The different end shape of the rectangular cross section leads to different sidewall static pressure and exit velocity profiles, thereby produces three cooling effectiveness patterns, single-peak, bi-peak, and tri-peak patterns. The tri-peak pattern produces higher cooling effectiveness and relatively uniform film coverage. The structure with moderate contraction and smooth transition on two sides of the downstream wall favors creation of a tri-peak pattern. Compared with the fan-shaped hole, the discharge coefficient of diffusion slot hole is slightly small in low pressure ratio range, the pressure loss ratio has little difference.
TOPICS: Diffusion (Physics), Shapes, Pressure, Film cooling, Cooling, Separation (Technology), Turbulence, Engines, Simulation, Bubbles, Computational fluid dynamics, Engineering simulation, Discharge coefficient, Flat plates, Flow (Dynamics), Mach number, Strips
Francisco I. Valentin, Ryan Anderson and Masahiro Kawaji
J. Heat Transfer   doi: 10.1115/1.4036524
This work focuses on an experimental investigation of convection heat transfer to a gas and flow laminarization under strongly heated conditions at high temperature/pressure conditions. A unique test facility for convection heat transfer experiments has been constructed, and used to obtain experimental data useful for better understanding and validation of numerical simulation models. This test facility consists of a single flow channel in a 2.7 m long, 0.11 m diameter graphite column with four 2.3 kW heaters placed symmetrically around the 16.8 mm diameter flow channel. Convection experiments with air and nitrogen were conducted for inlet Reynolds numbers from 1,300 to 70,000, thus covering laminar, transition and fully turbulent flow regimes. Experiments were performed at different temperatures and pressures up to 943 K and 65 bar, respectively, various flow rates (20-600 SLPM), and heater power up to 6 kW. Importantly, the data analysis considered the thermophysical properties of the gas and graphite changing with temperature. Nusselt number results are further compared to existing correlations. The effects of pressure and heater power on flow laminarization are examined. The analyses of the experimental data showed significant reductions in Reynolds number of up to 50% and Nusselt numbers of up to 90% between the gas inlet and outlet.
TOPICS: Gas flow, High pressure (Physics), Convection, High temperature, Flow (Dynamics), Temperature, Graphite, Test facilities, Pressure, Reynolds number, Nitrogen, Turbulence, Computer simulation
Amir Homayoon Meghdadi Isfahani
J. Heat Transfer   doi: 10.1115/1.4036525
Hydrodynamics and heat transfer in micro/nano channels filled with porous media for different porosities and Knudsen numbers, Kn, ranging from 0.1 to 10 are considered. The performance of standard Lattice Boltzmann Method, LBM, is confined to the micro scale flows with a Knudsen number less than 0.1.Therefore, by considering the rarefaction effect on the viscosity and thermal conductivity, a modified thermal LBM is used which is able to extend the ability of LBM to simulate wide range of Knudsen flow regimes. The present study reports the effects of the Knudsen number and porosity on the flow rate, permeability and mean Nusselt number. The Knudsen’s minimum effect for micro/nano channels filled with porous media was observed. In addition to the porosity and Knudsen number, the obstacle sizes have important role in the heat transfer, so that, enhanced heat transfer is observed when the obstacle sizes decrease. For the same porosity and Knudsen number, the in line porous structure has the highest heat transfer performance.
TOPICS: Flow (Dynamics), Heat transfer, Knudsen number, Porosity, Porous materials, Viscosity, Thermal conductivity, Knudsen flow, Permeability, Hydrodynamics, Lattice Boltzmann methods
Yuanpeng Yao, Huiying Wu and Zhenyu Liu
J. Heat Transfer   doi: 10.1115/1.4036526
In this paper, a numerical model employing 3D foam structure represented by Weaire-Phelan foam cell is developed to study the steady-state heat conduction of high porosity open-cell metal foam/paraffin composite at the pore-scale level. The conduction problem is considered in a cubic representative computation unit of the composite material with constant temperature difference between one opposite sides of the cubic unit (the other outer surfaces of the cubic unit are thermally insulated). The effective thermal conductivities (ETCs) of metal foam/paraffin composites are calculated with the developed pore-scale model and compared to the reported experimental data. Then the reason that foam pore size has no evident effect on ETC as reported in the previous macroscopic experimental studies is explored at pore scale. Finally, the effect of air cavity within paraffin on heat conduction is investigated. It is found that our ETC data agree well with the reported experimental results. The essential reason that pore size has no evident effect on ETC is due to the negligible interstitial heat transfer between metal foam and paraffin under the present thermal boundary conditions usually used to determine the ETC. It also shows that overlarge volume fraction of air cavity significantly weakens the conduction capacity of paraffin, which however can be well overcome by the adoption of high conductive metal foam due to enhancement of conduction.
TOPICS: Composite materials, Paraffin wax, Heat conduction, Metal foams, Porosity, Cavities, Computation, Boundary-value problems, Computer simulation, Temperature, Heat transfer, Steady state
Paul Aghasi and Ephraim Gutmark
J. Heat Transfer   doi: 10.1115/1.4036509
Film Cooling Effectiveness is closely dependent on the geometry of the hole emitting the cooling film. These holes are sometimes quite expensive to machine by traditional methods so 3D printed test pieces have the potential to greatly reduce the cost of film cooling experiments. What is unknown is the degree to which parameters like layer resolution and the choice among 3D printing technologies influence the results of a film cooling test. A new flat-plate film cooling facility employing oxygen sensitive paint (OSP) verified by gas sampling and the mass transfer analogy and measurements both by gas sampling and OSP is verified by comparing measurements by both gas sampling and OSP. The same facility is then used to characterize the film cooling effectiveness of a diffuser shaped film cooling hole geometry. These diffuser holes are then produced by a variety of additive manufacturing technologies with different build layer thicknesses. The objective is to determine if cheaper manufacturing techniques afford usable and reliable results. The coolant gas used is CO2 yielding a density ratio of 1.5. Surface quality is characterized by an Optical Microscope that measures surface roughness. Test coupons with rougher surface topology generally showed delayed blow off and higher film cooling effectiveness at high blowing ratios compared to the geometries with lower measured surface roughness. At the present scale, none of the additively manufactured parts consistently matched the traditionally machined part, indicating that caution should be exercised in employing additively manufactured test pieces in film cooling work.
TOPICS: Cooling, Film cooling, Additive manufacturing, Diffusers, Geometry, Surface roughness, Coolants, Resolution (Optics), Density, Mass transfer, Machinery, Manufacturing, Optical microscopes, Oxygen, Topology, Carbon dioxide, Flat plates, Surface quality
M. Halimi, A. Abbas Nejad and M. Norouzi
J. Heat Transfer   doi: 10.1115/1.4036460
CLPHPs are a new type of two-phase heat transfer devices that can transfer considerable heat in a small space via two-phase vapor and liquid pulsating flow and work with various types of two-phase instabilities so the oprating mechanism of CLPHP is not well understood. In this work, two CLPHPs, made of Pyrex, were manufactured to observe and investigate the flow regime that occurs during the operation of CLPHPand thermal performance of the device under different laboratory conditions. In general, various working fluids were used in filling ratios of 40%, 50%, and 60% in horizontal and vertical modes to investigate the effect of thermophysical parameters, filling ratio, nanoparticles, gravity, CLPHP structure, and input heat flux on the thermal performance of CLPHP. The results indicate that three types of flow regime may be observed given laboratory conditions. Each flow regime exerts a different effect on the thermal performance of the device. There is an optimal filling ratio for each working fluid. The increased number of turns in CLPHP generally improves the thermal performance of the system reducing the effect of the type of the working fluid on the aforementioned performance. The adoption of copper nanoparticles, which positively affect fluid motion, decreases the thermal resistance of the system as much as 6.06%-42.76% depending on laboratory conditions. Moreover, gravity brings about positive changes in the flow regime decreasing thermal resistance as much as 32.13%-52.58%.
TOPICS: Gravity (Force), Flow (Dynamics), Heat, Heat transfer, Fluids, Vapors, Copper, Nanoparticles, Heat pipes, Borosilicate glasses, Pulsatile flow, Thermal resistance, Heat flux
Soumen Shaw
J. Heat Transfer   doi: 10.1115/1.4036461
In this note, two aspects in the theory of heat conduction model with memory dependent derivatives are studied. Firstly, the discontinuity solutions of the memory dependent generalized thermo-elasticity model is analysed. The fundamental equations of the problem are expressed in the form of a vector matrix differential equation. Applying modal decomposition technique the vector matrix differential equation is solved by eigenvalue approach in Laplace transform domain. In order to obtain the solution in the physical domain an approximate method by using asymptotic expansion is applied for short time domain and analyse the nature of the waves and discontinuity of the solutions. Secondly, a suitable Lyapunov function, which will be an important tool to study several qualitative properties, is proposed.
TOPICS: Thermoelasticity, Differential equations, Eigenvalues, Laplace transforms, Heat conduction, Waves
Abdullah Al-Sharafi, Bekir Sami Yilbas and Haider Ali
J. Heat Transfer   doi: 10.1115/1.4036388
The present study examines the flow filed and heat transfer inside a sessile droplet on oil impregnated surface when subjected to a small temperature disturbance at the droplet-oil interface. Temperature and flow fields inside the droplet are predicted and the flow velocities predicted are validated through the data obtained from a Particle image velocimetry. Several images of droplets in varying sizes are analyzed and the droplet geometric features and experimental conditions are incorporated in the simulations. A polycarbonate wafer is used to texture the surface via incorporating a solvent induced crystallization method. Silicon oil is used for impregnation of the textured surfaces. It is found that two counter rotating circulation cells are formed in the droplet because of the combine effect of the Maragoni and buoyant currents on the flow field. A new dimensionless number (Merve number) is introduced to assess the behavior of the Nusselt and the Bond numbers with the droplet size. The Merve number represents the ratio of the gravitational force over the surface tension force associated with the sessile droplet and it differs than the Weber number. The Nusselt number demonstrates three distinct behaviors with the Merve number; in which case, the Nusselt number increases sharply for the range 0.8 ? MN ? 1. The Bond number increases with increasing the Merve number, provided that its values remain less than unity, which indicates the Marangoni current is dominant in the flow field.
TOPICS: Fluid dynamics, Heat transfer, Drops, Flow (Dynamics), Temperature, Gravity (Force), Surface tension, Crystallization, Particulate matter, Semiconductor wafers, Simulation, Texture (Materials), Engineering simulation, Currents, Silicon, Dimensionless numbers
B Vasu, Chetteti RamReddy, P V S N Murthy and Rama Gorla
J. Heat Transfer   doi: 10.1115/1.4036332
This article emphasizes the significance of entropy generation analysis and non-linear temperature density relation on thermally stratified viscous fluid flow over a vertical plate embedded in a porous medium with thermal dispersion effect. In addition, the convective surface boundary condition is taken into an account. By using the suitable transformations the governing flow equations in dimensional form are converted into set of non-dimensional partial differential equations. Then the local similarity and non-similarity procedure is applied to transform the set of non-dimensional partial differential equations into set of ordinary differential equations and then the resulting system of equations are solved by Chebyshev spectral collocation method along with the successive linearization. The effect of pertinent parameters namely, Biot number, mixed convection parameter and thermal dispersion on velocity, temperature, entropy generation rate and heat transfer rate are displayed graphically and the salient features are explored in detail.
TOPICS: Flow (Dynamics), Fluids, Porous materials, Entropy, Convection, Boundary-value problems, Partial differential equations, Temperature, Heat transfer, Density, Fluid dynamics, Differential equations, Mixed convection, Vertical plates
Francisco Herrera, Tengfei Luo and David Go
J. Heat Transfer   doi: 10.1115/1.4036339
A thermal rectifier transmit heat asymmetrically, transmitting heat conductor in one direction and insulating heat in the opposite direction. For conduction at steady state, thermal rectification can occur naturally in systems where the thermal conductivity of the material(s) vary in space and with temperature. However, in virtually all practical applications, rectification will need to be controlled under transient conditions. Using a bulk composite as a model system, we analyze transient rectifying behavior. First, we found that transient rectification can be several times larger than steady state rectification. More specifically, both the thermal diffusivity of the system and temperature-dependent thermal conductivity play an important role in affecting the transient rectifying behavior of the system, with the non-linearity of the system leading to unusual behavior where rectification is maximized.
TOPICS: Capacitance, Transients (Dynamics), Thermal conductivity, Thermal rectification, Heat, Temperature, Steady state, Composite materials, Heat conduction, Thermal diffusivity
Chariton Christou and S.Kokou Dadzie
J. Heat Transfer   doi: 10.1115/1.4036340
Volume diffusion (or bi-velocity) continuum model offers an alternative modification to the standard Navier-Stokes-Fourier for simulating rarefied gas flows. According to this continuum model, at higher Knudsen numbers the contribution of molecular spatial stochasticity increases. In this paper, we study a micro-cavity heat transfer problem as it provides an excellent test for new continuum flow equations. Simulations are carried out for Knudsen numbers within the slip and higher transition flow regimes where non-local-equilibrium and rarefaction effects dominate. We contrast predictions by a Navier-Stokes-Fourier model corrected by volume diffusion flux in its constitutive equations to that of the direct simulation Monte Carlo (DSMC) method and the standard Navier-Stokes-Fourier model. The results show improvement in the Navier-Stokes-Fourier prediction for the high Knudsen numbers. The new model exhibits proper Knudsen boundary layer in the temperature and velocity fields.
TOPICS: Heat transfer, Cavity flows, Simulation, Flow (Dynamics), Diffusion (Physics), Temperature, Equilibrium (Physics), Boundary layers, Constitutive equations, Cavities, Rarefied fluid dynamics
Technical Brief  
Mustafa Turkyilmazoglu
J. Heat Transfer   doi: 10.1115/1.4036328
The present work is concerned with the heat transfer enhancement and efficiency in the moving longitudinal fins having trapezoidal cross sections. Finding analytical solutions is targeted so that efficiency of trapezoidal fins over the known fin sections can be comparatively searched. It is shown that certain type of trapezoidal fins may have advantageous fin design features. The formulas given in this paper may also be used as benchmark analysis.
TOPICS: Fins, Heat transfer, Cross section (Physics), Design
Georgios Karamanis, Marc Hodes, Toby Kirk and Demetrios T. Papageorgiou
J. Heat Transfer   doi: 10.1115/1.4036281
We consider convective heat transfer for laminar flow of liquid between parallel plates that are textured with isothermal ridges oriented parallel to the flow. Three different configurations are analyzed: one plate textured and the other one smooth; both plates textured and the ridges aligned symmetrically; and both plates textured but the ridges staggered by half a pitch. Heat is exchanged with the liquid either through the ridges of one plate with the other plate adiabatic, or through the ridges of both plates. The liquid is assumed to be in the Cassie state on the textured surfaces, to which a mixed boundary condition of no-slip on the ridges and no-shear along flat menisci applies. The thermal energy equation is subjected to a mixed isothermal-ridge and adiabatic-meniscus boundary condition on the textured surfaces of the non-adiabatic plates. Axial conduction is neglected and the inlet temperature profile is arbitrary. We solve for the three-dimensional developing temperature profile assuming a hydrodynamically-developed flow, i.e., we consider the Graetz-Nusselt problem. Using the method of separation of variables, the thermal problem is essentially reduced to a two-dimensional eigenvalue problem in the spanwise coordinates, which must be solved numerically. Expressions are found for the local, average and fully developed Nusselt number in terms of the eigenfunctions, eigenvalues and inlet temperature profile. The present analysis allows the aforementioned quantities to be computed in a small fraction of the time required by a general computational fluid dynamics solver.
TOPICS: Flow (Dynamics), Plates (structures), Temperature profiles, Boundary-value problems, Eigenvalues, Heat, Separation (Technology), Thermal energy, Laminar flow, Heat conduction, Shear (Mechanics), Eigenfunctions, Computational fluid dynamics, Convection
Raoudha Chaabane, Faouzi Askri, Jemni Abdelmajid and Sassi Ben Nasrallah
J. Heat Transfer   doi: 10.1115/1.4036154
In this paper a new hybrid numerical algorithm is developed to solve coupled convection-radiation heat transfer in a two dimensional cavity containing an absorbing, emitting and scattering medium. The radiative information is obtained by solving the radiative transfer equation (RTE) using the control volume finite element method (CVFEM) and the density, velocity and temperature fields are calculated using the two double population lattice Boltzmann equation (LBE). To the knowledge of the authors, this hybrid numerical method is applied at the first time to simulate combined transient convective radiative heat transfer in 2D participating media. In order to test the efficiency of the developed method two configurations are examined: (i) free convection with radiation in a square cavity bounded by two horizontal insulating sides and two vertical isothermal walls and (ii) Rayleigh Benard convection with and without radiative heat transfer. The obtained results are validated against available works in literature and the proposed method is found to be efficient, accurate and numerically stable.
TOPICS: Transients (Dynamics), Finite element methods, Radiation (Physics), Convection, Lattice Boltzmann methods, Radiative heat transfer, Cavities, Rayleigh-Benard convection, Natural convection, Numerical analysis, Radiation scattering, Scattering (Physics), Density, Temperature, Heat transfer, Electromagnetic scattering, Algorithms
J. Heat Transfer   doi: 10.1115/1.4036039
This work present a simple thinking based on material's electrical and thermal properties which permit to searchers in domain of manufacturing and characterization of thin and thick films in solid state to take appropriate experimental conditions before the execution. Treatment of heat equations based on the photothermal deflection (PTD) technique, using some approximations founded on the determination of the thermal conductivity and thermal diffusivity and the calculation of the thermal diffusion length and comparing it with thicknesses of the substrate and the film deposited on it which constitute the sample and using the Cahill's law; we arrive to highlight, necessary conditions that allow searchers to manufacture samples with high thermoelectric power. These conditions are based on the experimental objectives that aspire many modern researches such as materials with low thermal conductivity and high electrical conductivity and the relationship between them to obtain materials with high figure of merit.

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