Accepted Manuscripts

Technical Brief  
Kuldeep Singh, B. Premachandran and M.R. Ravi
J. Heat Transfer   doi: 10.1115/1.4039761
In the present work, a numerical study is conducted to investigate film cooling of a corrugated surface. A conjugate heat transfer analysis is carried out, accounting for the presence of thermal barrier coating (TBC) and gas radiation. The Mach number of mainstream flow is maintained at Ma = 0.6 while cold stream Mach number is varied from 0.3 to 0.58 and density ratio is kept 4. From this study, it is observed that the overall film cooling effectiveness increases by a value ranging from 0.10 to 0.15 with the use of TBC. The hot side metallic wall temperature increases in the range of 100°C to 150°C when the effect of gas radiation is considered. It is also found that film cooling effectiveness decreases with decrease in the cold side Mach number.
TOPICS: Radiation (Physics), Thermal barrier coatings, Film cooling, Mach number, Heat transfer, Density, Flow (Dynamics), Accounting, Wall temperature
Arjun C. K., Jayakumar J S, Y. Giridhara Babu and Felix J.
J. Heat Transfer   doi: 10.1115/1.4039684
The present study aims to evaluate the adiabatic and conjugate effusion cooling effectiveness of combustion chamber liner plate of gas turbines. Validation of adiabatic model was done by comparing the CFD result with experimental results obtained using the subsonic cascade tunnel facility available at Heat Transfer Lab of CSIR-NAL. Computational simulation for the conjugate model is validated against published results. Numerical simulation is carried out for a 1:3 scaled up flat plate test geometry for the adiabatic cooling effectiveness analysis and actual flat plate geometry is considered for the conjugate cooling effectiveness analysis. The test plate was having 11 rows of cooling holes and the holes were arranged in staggered manner with each row containing eight holes. For both adiabatic and conjugate cases, the same mainstream conditions are maintained with the inlet temperature of 329K, velocity of 20 m/s, density ratio 1.3. The coolant to mainstream blowing ratios were maintained at 0.4, 1.15 and 1.6. The coolant temperature was 253K with the flow rates were according to the blowing ratios. Cooling effectiveness was obtained by using CFD simulation with ANSYS Fluent package. From the comparison of adiabatic and conjugate results, it is found that conjugate model is giving superior cooling protection than the adiabatic model and effusion cooling effectiveness increases with increase in blowing ratio. Investigations on comparison of angle of injection holes show that, 30o model give maximum effusion cooling effectiveness as compared to 45 and 60o models.
TOPICS: Cooling, Plates (structures), Combustion chambers, Computational fluid dynamics, Flat plates, Geometry, Simulation, Coolants, Temperature, Heat transfer, Density, Flow (Dynamics), Cascades (Fluid dynamics), Computer simulation, Adiabatic cooling, Tunnels, Gas turbines
Xiaoming Zhou, Xunfeng Li, Keyong Cheng and Xiulan Huai
J. Heat Transfer   doi: 10.1115/1.4039685
Investigation of nano liquid-metal fluid (consists of liquid metal Ga and nanoparticles copper) as heat transfer medium in circular tube is performed for the first time. The numerical simulations of heat transfer enhancement of nano liquid-metal fluid in a circular tube subject to a constant wall heat flux are carried out. The two-phase mixture model is used to simulate the flow of nanoparticles-liquid mixture for Reynolds number (Re) from 250 to 1000 and nanoparticles volume fraction (ap) from 0.02 to 0.1. The results show that, the average heat transfer coefficient of nano liquid-metal fluid Ga-Cu is 23.8 times of that of nanofluid water-Cu at Re=500 and ap=0.04, and the average wall shear stress of Ga-Cu is 0.0154Pa, whereas for water-Cu is 0.0259Pa. As Re increases from 250 to 1000, the average heat transfer coefficient of water-Cu is improved by 40%, whereas for Ga-Cu is 45.4%. So the nano liquid-metal fluid can be considered as an excellent heat transfer medium. Moreover, the nanoparticles volume fraction and Reynolds number on heat transfer performance of nano liquid-metal fluid are discussed.
TOPICS: Heat transfer, Fluids, Liquid metals, Forced convection, Nanoparticles, Water, Heat transfer coefficients, Reynolds number, Flow (Dynamics), Copper, Computer simulation, Shear stress, Heat flux, Nanofluids
Aleksandar G. Ostrogorsky and Borivoje B. Mikic
J. Heat Transfer   doi: 10.1115/1.4039688
Time dependent participating volume to surface ratio, V(t)/A, was used to derive "extended time" model, Fo+, for heat conduction transients in cylindrical and spherical solids. Fo+ model is valid for temperature, flux and convection boundary conditions. It extends the time span of the semi-infinite solid solution by ~10 times, up to Fo~0.05 or d ~R (d is transient penetration depth). For comparison, in cylindrical and spherical solids, the planar semi-infinite solid solution is valid for d<
TOPICS: Solids, Solid solutions, Boundary-value problems, Transients (Dynamics), Convection, Approximation, Heat conduction, Laplace transforms, Heat flux, Temperature
Salam Hadi and Mustafa Rahomey
J. Heat Transfer   doi: 10.1115/1.4039642
Numerical simulations are carried out for fluid flow and natural convection heat transfer induced by a temperature difference between a hot inner cylinder with different geometries (i.e. circular; triangular; elliptic; rectangular; and rhombic) and a cold outer square enclosure filled with nanofluid superposed porous-nanofluid layers. The Darcy-Brinkman model is applied for the saturated porous layer with nanofluid. Moreover, the transport equations (mass, momentum, and energy) are solved numerically using the Galerkin weighted residual method by dividing the domain into two sets of equations for every layer with incorporating a non-uniform mesh size. The considered domains in this investigation are closely examined over a wide range of Rayleigh number (103 = Ra= 106), Darcy number (10-5 = Da = 10-1), the thickness of porous layer (0% = Xp = 100%), thermal conductivity ratio (1 = Rk = 20) and nanoparticle volume fraction (0 = ? = 0.1), respectively. The nanofluid is considered to be composed of Cu-nanoparticle and water as a base fluid. The results showed that the obtained total surfaces-averaged Nusselt numbers of the enclosure, in all cases, at the same operating conditions, the rate of heat transfer from the enclosure which the triangular cylinder is located inside is better. Also, as the thickness of the porous layer is increased from 20% to 80%, the free convection performance will decrease significantly (to about 50%) due to the hydrodynamic properties of the porous material.
TOPICS: Natural convection, Circular cylinders, Cylinders, Nanofluids, Heat transfer, Nanoparticles, Thermal conductivity, Momentum, Fluid dynamics, Temperature, Fluids, Porous materials, Computer simulation, Rayleigh number, Water
Alan Lugarini, Dr. Admilson T. Franco, Silvio L. M. Junqueira and Jose L. Lage
J. Heat Transfer   doi: 10.1115/1.4039643
The present study considers the coupled natural convection and surface radiation process through an open fracture of a solid wall facing a reservoir containing isothermal quiescent fluid (air). The fracture is modeled as a regular, C-shape path through the wall, with the vertical surface being heated and the horizontal ones adiabatic. The solid center section of the fracture is thermally participant inasmuch it can be heated or cooled by the natural convection process and by the radiation effect from the other surfaces of the fracture. The convection-radiation phenomenon is mathematically modeled and numerically simulated in a systematic parametric study of the thermal process as affected by changes in the fracture channel size, via changes in the size of the solid center section (block) 0 < D < 1.0, surface emissivity 0 = e = 1.0, Rayleigh number 10^5 = Ra = 10^8 and Pr = 0.71. Attention is given to the radiation shadowing effect caused by the center section of the fracture and of the interference effect, as the fracture channel changes in size, affecting the natural convection process through the fracture. An analytical prediction of the interference effect and an empirical correlation for predicting the total Nusselt number, both validated against the numerical results, are presented.
TOPICS: Radiation (Physics), Fracture (Materials), Fracture (Process), Natural convection, Shapes, Convection, Reservoirs, Radiation effects, Emissivity, Rayleigh number, Fluids
Je-Chin Han
J. Heat Transfer   doi: 10.1115/1.4039644
Gas turbines have been extensively used for aircraft engine propulsion, land-based power generation, and industrial applications. Power output and thermal efficiency of gas turbines increase with increasing turbine rotor inlet temperatures (RIT). Currently, advanced gas turbines operate at turbine RIT around 1700°C far higher than the yielding point of the blade material temperature about 1200°C. Therefore, turbine rotor blades need to be cooled by 3-5% of high-pressure compressor air around 700°C. To design an efficient turbine blade cooling system, it is critical to have a thorough understanding of gas turbine heat transfer characteristics within complex 3-D unsteady high-turbulence flow conditions. Moreover, recent research trend focuses on aircraft gas turbines operate at even higher RIT up to 2000°C with a limited amount of cooling air, and land-based power generation gas turbines (including 300-400 MW combined cycles with 60% efficiency) burn alternative syngas fuels with higher heat load to turbine components. It is important to understand gas turbine heat transfer problems with efficient cooling strategies under new harsh working environments. Advanced cooling technology and durable thermal barrier coatings (TBCs) play most critical roles for developments of new-generation high-efficiency gas turbines with near-zero emissions for safe and long-life operation. This paper reviews basic gas turbine heat transfer issues with advanced cooling technologies and documents important relevant papers for future research references.
TOPICS: Cooling, Gas turbines, Turbines, Heat transfer, Temperature, Rotors, Blades, Energy generation, Thermal barrier coatings, Aircraft engines, Emissions, Combined cycles, Thermal efficiency, Turbine components, Syngas, Aircraft, Flow (Dynamics), Heat, Cooling systems, Fuels, Turbulence, Compressors, Stress, Propulsion, Turbine blades, High pressure (Physics), Design
Technical Brief  
Basant K. Jha and Babatunde Aina
J. Heat Transfer   doi: 10.1115/1.4039641
In this research paper, steady natural convection flow in a vertical parallel plates microchannel in the presence of viscous dissipation is theoretically examined by using a perturbation series method. The effects of velocity slip and temperature jump are taken to consideration. Due to the presence of viscous dissipation, the momentum and energy equations are couped system of ordinary differential equations. The influences of Knudsen number, fluid wall interaction parameter and Brinkman number on the flow formation are demonstrated through graphs. The results indicate that, increasing Knudsen number decreases the effect of viscous dissipation on the Nusselt number.
TOPICS: Flow (Dynamics), Energy dissipation, Natural convection, Microchannels, Knudsen number, Differential equations, Temperature, Fluids, Momentum, Plates (structures)
Francisco Valentin, Narbeh Artoun, Masahiro Kawaji and Donald McEligot
J. Heat Transfer   doi: 10.1115/1.4039585
High pressure/high temperature forced and mixed convection experiments have been performed with helium and nitrogen at temperatures and pressures up to 893K and 64 bar, respectively. The test section had a 16.8-mm ID flow channel in a 108-mm OD graphite column. Flow regimes included turbulent, transitional and laminar flows with the inlet Reynolds numbers ranging from 1,500 to 15,000. Due to strong heating, the local Reynolds number decreased by up to 50% over the 2.7-m test section. In addition, heat transfer degradation and flow laminarization caused by intense heating led to Nusselt numbers 20~50% lower than the values given by the modified Dittus-Boelter and modified Gnielinski correlations. Flow laminarization criteria were considered based on a dimensionless acceleration parameter (Kv) and buoyancy parameter (Bo*). Upward turbulent flows displayed higher wall temperatures than downward flows, due to the impact of flow laminarization which is not expected to affect buoyancy-opposed flows. Laminar Reynolds number flows presented an opposite behavior due to the enhancement of heat transfer for buoyancy-aided flows. At low Reynolds numbers, downward flows displayed higher and lower wall temperatures in the upstream and downstream regions, respectively, than the upward flow cases. In the entrance region of downward flows, convection heat transfer was reduced due to buoyancy leading to higher wall temperatures, while in the downstream region, buoyancy-induced mixing caused higher convection heat transfer and lower wall temperatures.
TOPICS: Flow (Dynamics), High pressure (Physics), Graphite, High temperature, Buoyancy, Reynolds number, Wall temperature, Heating, Heat transfer, Turbulence, Convection, Mixed convection, Entrance region, Laminar flow, Temperature, Helium, Nitrogen
Technical Brief  
Debkumar Ghosh and Abhijit Lahiri
J. Heat Transfer   doi: 10.1115/1.4039554
A vector-matrix differential equation is formulated using normal mode analysis from the governing equations of a three dimensional anisotropic half space in presence of heat source and gravity. The corresponding solution is obtained with the help of eigenvalue approach. Numerical computations for displacement, thermal strain and stress component, temperature distribution are evaluated and presented graphically.
TOPICS: Rotation, Gravity (Force), Heat, Space, Differential equations, Computation, Displacement, Eigenvalues, Temperature distribution, Stress, Anisotropy
James Grisham, Ashkan Akbariyeh, Weiya Jin, Dr. Brian H. Dennis and Bo P. Wang
J. Heat Transfer   doi: 10.1115/1.4039541
Sensitivity information is often of interest in engineering applications (e.g., gradient-based optimization). Heat transfer problems frequently involve complicated geometries for which exact solutions cannot be easily derived. As such, it is common to resort to numerical solution methods such as the finite element method. The semi-analytic complex variable method is an accurate and efficient approach to computing sensitivities within a finite element framework. The method is introduced and a derivation is provided along with a detailed description of the algorithm which requires very minor changes to the analysis code. Three benchmark problems in steady-state heat transfer are studied including a nonlinear problem, an inverse shape determination problem and a reliability analysis problem. It is shown that the semi-analytic complex variable method is superior to the other methods considered in terms of computation time and sensitivity to perturbation size.
TOPICS: Heat transfer, Event history analysis, Finite element methods, Algorithms, Engineering systems and industry applications, Finite element analysis, Optimization, Computation, Shapes, Steady state
Jinlin Song, Lu Lu, Dr. Qiang Cheng and Luo Zixue
J. Heat Transfer   doi: 10.1115/1.4039542
We investigate the near-field (NF) radiative heat transfer of the three-body system consisting of anisotropic magneto-dielectric hyperbolic metamaterials (AMDHMs), which can support coupled surface phonon polaritons and hyperbolic modes for both p and s polarizations. We numerically demonstrate that the NF heat transfer between two AMDHMs bodies can be further enhanced by inserting an AMDHMs slab. Due to the loss in AMDHMs, there exists an optimum thickness of the intermediate slab to maximize the NF heat flux flowing to the receiver for a fixed gap distance. Results obtained from this work will facilitate investigations of the NF heat transfer involving magnetic hyperbolic metamaterials.
TOPICS: Heat transfer, Anisotropy, Metamaterials, Slabs, Heat flux, Phonons, Polaritons, Radiative heat transfer
Hyun Jin Kim, Leon Liebenberg and Anthony M Jacobi
J. Heat Transfer   doi: 10.1115/1.4039397
Heat transfer and pressure drop characteristics of R-134a boiling in a chevron-patterned brazed plate heat exchanger (BPHE) are studied experimentally. With corrugated BPHE channels having hydraulic diameter of 3.4 mm and low refrigerant mass flux, boiling near the micro-macroscale transition is speculated. Heat exchanger performance is characterized with varying mass flux, saturation pressure, heat flux, and vapor quality. The two-phase refrigerant heat transfer coefficient increases with heat flux as often observed during nucleate boiling. It also weakly increases with saturation pressure and the associated lower latent heat during convective boiling; heat transfer is improved by the decreased liquid film thickness surrounding confined bubbles inside the narrow BPHE channels, which is the main characteristic of microscale boiling. As often observed in macroscale boiling, the inertial forces of the liquid and vapor phases cause an unsteady annular film, leading to premature partial dryout. The onset of dryout is accelerated at the lower saturation pressure, due to increased surface tension, another microscale-like characteristic. Higher surface tension retains liquid in sharp corners of the corrugated channel, leaving lateral surface areas of the wall dry. Two-phase pressure drop increases with mass flux and vapor quality, but with decreasing saturation pressure. Dryout decreases the friction factor due to the much lower viscosity of the gas phase in contact with the wall. Several semi-empirical transition criteria and correlations buttress the current analyses that the thermal-fluidic characteristics peculiar to BPHEs might be due to macro-microscale transition in boiling.
TOPICS: Boiling, Heat exchangers, Pressure, Microscale devices, Vapors, Surface tension, Pressure drop, Refrigerants, Heat flux, Heat transfer, Heat transfer coefficients, Nucleate boiling, Friction, Viscosity, Bubbles, Corners (Structural elements), Latent heat, Liquid films
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

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