Accepted Manuscripts

Prakhar Jindal, Shubham Agarwal, R. P. Sharma and A.K. Roy
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039700
The current study deals with the film cooling enhancement in a combustion chamber by the use of rectangular winglet vortex generators. Rectangular winglet pair (RWP) in both the common-flow up and the common-flow down configuration is installed upstream of a coolant injection hole on the lower chamber wall. A three-dimensional numerical approach with complete solution of Navier-Stokes equations closed by the k-? turbulence model is used for analyzing the effect of vortex generator (VG) installation on film cooling effectiveness enhancement. The effect of rectangular winglet pair orientation is investigated to deduce the best configuration which is then optimized in terms of its geometrical parameters including its upstream distance from the hole and the angle it makes with the incoming flow. Results obtained show that a rectangular winglet pair located upstream of the coolant hole in common-flow down configuration gives the best effectiveness enhancement with certain other geometrical parameters specified. A novel "mushroom" adiabatic distribution scheme for film cooling effectiveness and temperature has been discussed in the paper. This characteristic scheme is developed as a result of RWPs' vortices interaction with the coolant inlet jet and the hot mainstream flow. A detailed discussion of the mechanisms and the flow field properties underlying the effectiveness enhancement and other phenomenon observed has also been presented in the paper.
TOPICS: Film cooling, Flow (Dynamics), Coolants, Vortices, Generators, Combustion chambers, Navier-Stokes equations, Temperature, Turbulence
Soheil Jafari, Julian Dunne, Mostafa Langari, Zhiyin Yang, Jean-Pierre Pirault, Chris Long and Jisjoe Thalackottore Jose
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039701
A novel approach is proposed for precise control of two-phase spray evaporative cooling for thermal management of road vehicle internal combustion engines. A reduced-order plant model is first constructed by combining published spray evaporative cooling correlations with approximate governing heat transfer equations appropriate for IC engine thermal management. Control requirements are specified to allow several objectives to be met simultaneously under different load conditions. A control system is proposed and modelled in abstract form to achieve spray evaporative cooling of a gasoline engine, with simplifying assumptions made about the characteristics of the coolant pump, spray nozzle, and condenser. The system effectiveness is tested by simulation to establish its ability to meet key requirements, particularly concerned with precision control during transients resulting from rapid engine load variation. The results confirm the robustness of the proposed control strategy in accurately tracking a specified temperature profile at various constant load conditions, and also in the presence of realistic transient load variation
TOPICS: Evaporative cooling, Internal combustion engines, Sprays, Stress, Thermal management, Transients (Dynamics), Gasoline engines, Condensers (steam plant), Motor vehicles, Robustness, Temperature profiles, Coolants, Nozzles, Pumps, Simulation, Heat transfer, Control systems, Engines
Mingjie Zhang, Nian Wang, Andrew F Chen and Je-Chin Han
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039703
This paper presents the turbine blade leading edge model film cooling effectiveness with shaped holes, using the pressure sensitive paint (PSP) mass transfer analogy method. The effects of leading edge profile, coolant to mainstream density ratio and blowing ratio are studied. Computational simulations are performed using the realizable k-? turbulence model. Effectiveness obtained by CFD simulations are compared with experiments. Three leading edge profiles, including one semi-cylinder and two semi-elliptical cylinders with an after body, are investigated. The ratios of major to minor axis of two semi-elliptical cylinders are 1.5 and 2.0, respectively. The leading edge has three rows of shaped holes. For the semi-cylinder model, shaped holes are located at 0 degrees (stagnation line) and ± 30 degrees. Row spacing between cooling holes and the distance between impingement plate and stagnation line are the same for three leading edge models. The coolant to mainstream density ratio varies from 1.0 to 1.5 and 2.0, and the blowing ratio varies from 0.5 to 1.0 and 1.5. Mainstream Reynolds number is about 100,900 based on the diameter of the leading edge cylinder, and the mainstream turbulence intensity is about 7%. The results provide an understanding of the effects of leading edge profile and on turbine blade leading edge region film cooling with shaped-hole designs.
TOPICS: Turbine blades, Film cooling, Cylinders, Engineering simulation, Density, Turbulence, Simulation, Coolants, Reynolds number, Pressure, Mass transfer, Cooling, Computational fluid dynamics
Song Mengjie, Liao Liyuan, Niu Fuxin, Mao Ning, Liu Shengchun and Hu Yanxin
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039702
Phase change materials (PCMs) are widely applied in recent decades due to their good thermal performance in energy systems. Their applications are mainly limited by the phase change temperature and latent heat. Many publications are reported around the characteristic improvement of binary organic PCMs. The thermal stability study on organic binary PCMs used in thermal energy storage applications becomes fundamental and meaningful. In this study, thermal stability of three types of organic binary PCMs was experimentally investigated, which are frequently used in building and industry applications. To qualitatively investigate the stability of composite PCMs, DSC and FT-IR spectra testing of samples were also conducted. Experimental results showed that, the selected composite PCMs, CA&MA, had the best thermal performances, with its phase change temperature unchanged and heat of fusion decreased only 8.88 J/g, or 4.55%, after 2,000 thermal cycles. Furthermore, quality ratio of required PCMs as the variation of operation duration was analyzed to quantitatively prepare the materials. The PCMs can successfully operate about 3,125 times when prepared as 1.20 times of its calculated value by starting fusion heat. Conclusions of this research work can also be used for guiding the selection and preparation of other energy storage materials.
TOPICS: Phase change materials, Thermal energy storage, Thermal stability, Composite materials, Temperature, Spectra (Spectroscopy), Stability, Heat, Energy / power systems, Energy storage, Testing, Cycles, Latent heat, Heat of fusion
Abbas Kosarineia and Sajad Sharhani
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039633
In this study, the influence of the applied magnetic field is investigated for magneto-micropolar fluid flow through an inclined channel of parallel porous plates with constant pressure gradient. The lower plate is maintained at constant temperature and upper plate at a constant heat flux. The governing motion and energy equations are coupled while effect of the applied magnetic field is taken into account, adding complexity to the already highly correlated set of differential equations. The governing equations are solved numerically by Explicit Runge-Kutta. The velocity, microrotation and temperature results are used to evaluate second law analysis. The effects of characteristic and dominate parameters such as Brinkman number, Hartmann Number, Reynolds number and micropolar viscosity parameter are discussed on velocity, temperature, microrotation, entropy generation and Bejan number in different diagrams. The results depicted that the entropy generation number rises with the increase in Brinkman number and decays with increase in Hartmann Number, Reynolds number and micropolar viscosity parameter. The application of the magnetic field induces resistive force acting in the opposite direction of the flow, thus causing its deceleration. Moreover, the presence of magnetic field tends to increases the contribution of fluid friction entropy generation to the overall entropy generation, in other words the irreversibilities caused by heat transfer reduced. Therefore, to minimize entropy, Brinkman number and Hartmann Number need to be controlled.
TOPICS: Fluid dynamics, Plates (structures), Entropy, Magnetic fields, Temperature, Viscosity, Reynolds number, Differential equations, Heat transfer, Flow (Dynamics), Pressure gradient, Heat flux
Su-Jong Yoon, James O'Brien, Piyush Sabharwall, Kevin R Wegman and Xiaodong Sun
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039543
Effective and robust high-temperature heat transport systems are essential for the successful deployment of advanced high temperature reactors. The printed circuit heat exchanger (PCHE) is a strong potential candidate for the intermediate or secondary loop of high temperature gas-cooled reactors due to their high power density and compactness. For high-temperature PCHE applications, the heat loss, which is difficult to be insulated completely, could lead to the degradation of heat exchanger performance. This paper describes an analytical methodology to evaluate the thermal-hydraulic performance of PCHEs from experimental data, accounting for extraneous heat losses. Experimental heat exchanger effectiveness results, evaluated without accounting for heat loss, exhibited significant data scatter while the data were in good agreement with the e-NTU method once the heat loss was accounted for. The deformation of PCHEs would occur during the diffusion-bonding fabrication process or high temperature operations due to the thermal deformation. Computational assessment of the PCHE performance test data conducted at the Ohio State University showed that the deformation of flow channels caused increase of pressure loss of the heat exchanger. The CFD simulation results based on the nominal design parameters underestimated the pressure loss of the heat exchanger compared to the experimental data. Image analysis for the flow channel inlet and outlet was conducted to examine the effect of channel deformation on the heat exchanger performance. The CFD analysis based on the equivalent channel diameter obtained from the image analysis resulted in a better prediction of PCHE pressure loss.
TOPICS: Deformation, Heat exchangers, Circuits, Heat losses, High temperature, Pressure, Flow (Dynamics), Computational fluid dynamics, Accounting, Very high temperature reactors, Power density, Simulation results, Testing performance, Thermal deformation, Design, Heat, Manufacturing, Diffusion bonding (Metals), Electromagnetic scattering
Sadia Hina and Maria Yasin
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039544
In present framework, a model is constituted to explore the peristalsis of MHD viscoelastic (second grade) fluid with wall properties. The study is beneficial in understanding blood flow dynamics through microchannels. The mechanisms of heat and mass transfer are also modeled in the existence of viscous dissipation and Soret effects. The conducting second grade fluid is permeated by a vertical magnetic field. Perturbation technique is opted to present series solutions by assuming that wavelength of the sinusoidal wave is small in comparison to the half-width of the channel. The solution profiles are computed and elucidated for certain range of embedded parameters. Moreover, plots of heat transfer coefficient against the axial coordinate are also portrayed and deliberated. The main outcome of current research is that both viscoelasticity and slip effect considerably alter the flow fields. Moreover, an increasing trend in solute concentration is anticipated for increasing Soret effect strength.
TOPICS: Magnetohydrodynamics, Heat, Mass transfer, Fluids, Peristaltic flow, Microchannels, Heat transfer coefficients, Blood flow, Dynamics (Mechanics), Flow (Dynamics), Magnetic fields, Viscoelasticity, Waves, Energy dissipation, Performance, Wavelength
J. Emily Cousineau, Kevin Bennion, Victor Chieduko, Rajiv Lall and Alan Gilbert
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039459
Cooling of electric machines is key to increasing power density and improving reliability. This paper focuses on the design of a machine using a cooling jacket wrapped around the stator. The thermal contact resistance between the electric machine stator and cooling jacket is a significant factor in overall performance and is also not well characterized. This interface is typically an interference fit subject to compressive pressure exceeding 5 MPa. An experimental investigation of this interface was carried out using a thermal transmittance setup using pressures between 5 and 10 MPa. The results were compared to currently available models for contact resistance, and one model was adapted for prediction of thermal contact resistance in future motor designs.
TOPICS: Cooling, Machinery, Stators, Contact resistance, Experimental characterization, Modeling, Press fits, Pressure, Engine design, Power density, Reliability, Design
Andrea Helmns and Van P. Carey
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039460
This paper establishes a multi-scale design evaluation framework that integrates performance models for a thermal energy storage unit and a subsystem heat exchanger. The modeling facilitates analysis of transient input and extraction processes for the thermal energy storage (TES) device which uses solid-liquid phase change to store thermal energy. We investigate sensible and latent heat transfer through the unit’s matrix structure which contains phase change material (PCM) in the interstitial spacing. The heat transfer is driven by a temperature difference between fluid flow passages and the phase change material matrix which experiences sensible heat transfer until it reaches the phase change material fusion point; then it undergoes melting or solidification in order to receive, or reject, energy. To capture these physics, we establish a dimensionless framework to model heat transfer in the storage device much like effectiveness- NTU analysis methods for compact heat exchangers. Solution of the non-dimensional governing equations is subsequently used to predict the effectiveness of the transient energy input and extraction processes. The TES is examined within the context of a larger subsystem to illustrate how a high efficiency design target can be established for specified operating conditions that correspond to a variety of applications. The general applicability of the model framework is discussed and example performance calculations are presented for enhancement of a Rankine power plant via asynchronous cooling.
TOPICS: Cooling, Transients (Dynamics), Energy storage, Modeling, Heat transfer, Phase change materials, Design, Heat exchangers, Thermal energy storage, Power stations, Solidification, Latent heat, Storage, Thermal energy, Melting, Physics, Fluid dynamics, Temperature
Mohammad Mehdi Keshtkar and Mohammad Dadkhoda Zadeh
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039422
In this paper, affecting parameters of porous medium to improve the rate of convective heat transfer in a 2D Porous Gas Heat Exchanger (PGHE) for two arrangements (symmetric and asymmetric) of barriers are numerically investigated. Two barriers have been located on the top and bottom walls and one obstacle was placed in the central zone of the PGHE. In the present study, solving the momentum and energy equations has been done by Lattice-Boltzmann method with multiple-relaxation-time (LBM-MRT). The boundary conditions in both arrangements include the left and right walls which are kept at the cold constant temperature and both top and bottom walls are insulated. There is a volumetric heat source within the PGHE. The temperature of barriers and fixed obstacle are kept at warm temperature . In this study, impact of effective parameters in porous medium and heat transfer including dimensionless number of Darcy, porosity and Rayleigh number on the flow and temperature fields have been investigated. According to the numerical results, it has been shown that the porous medium and barriers cause increase and improvement in the heat transfer within PGHE in both symmetrical and asymmetrical arrangements. The results also demonstrate that as dimensionless Darcy number increases, more convection occurs within the chamber. Examining arrangement of barriers shows that in asymmetrical arrangement more space appears in chamber and convective heat transfer is done better.
TOPICS: Heat transfer, Simulation, Heat exchangers, Temperature, Convection, Porous materials, Symmetry (Physics), Momentum, Flow (Dynamics), Heat, Relaxation (Physics), Rayleigh number, Boundary-value problems, Porosity, Lattice Boltzmann methods, Dimensionless numbers
Hanno C. Reuter, Michael Owen and John Goodenough
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039354
Paint-based protective films (PPFs) are used to protect condenser tubes from corrosion and erosion but have been shown to be susceptible to biofouling. Here the biocidal properties of copper-oxide fillers incorporated into PPFs are explored in this paper. Specifically two PPFs filled with 20% and 50% filler (by weight) are tested in parallel with a non-biocidal ordinary epoxy PPF, and bare stainless steel tube. Using double-pipe co-current flow heat exchangers installed at a thermal power plant, actual cooling water exiting the condenser is evenly distributed between the test tubes. Heat transfer in the condenser is simulated by heated water flowing through each annulus of the double-pipe heat exchangers, thereby maintaining repeatable outer convection conditions. An exposure test of 125 days shows that the 50% biocide filled PPF has the lowest fouling factor of all the tubes. The non-biocidal epoxy has the highest fouling factor and the 20% filled PPF behaves similarly. Both of these are greater than the bare stainless steel control tube. The 50 % filled PPF is compared to the fouling of an existing admiralty brass tube and the shape of the fouling curves are similar. This evidence suggests that provided the filler concentration is sufficiently high, there is the potential for the copper-oxide filler to reduce the asymptotic composite fouling factor by virtue of its antibacterial properties.
TOPICS: Copper, Fillers (Materials), Condensers (steam plant), Steam, Stainless steel, Water, Heat exchangers, Pipes, Epoxy adhesives, Epoxy resins, Paints, Composite materials, Brass (Metal), Weight (Mass), Flow (Dynamics), Heat transfer, Cooling, Biofouling, Convection, Corrosion, Erosion, Annulus, Shapes, Thermal power stations
Dipanka Bhuyan, Asis Giri and Pradip Lingfa
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039355
Present paper conducts an extensive numerical study on entropy analysis of mixed convective condensation inside a vertical parallel plate channel. A new approach is proposed to separate pump velocity component/Reynolds number from inlet mixed convection velocity. Influence of inlet governing parameters on condensation heat and mass transfer at different inlet pressure, velocity, channel length, and width are widely studied. The central focus of this paper is to study entropy generation under mixed convective condensation. Variation of local as well as overall entropy generation and second law efficiency for different geometric and environmental conditions are presented. For effective condenser design, present study provides two important correlations of overall volumetric entropy generation due to thermal transport and overall volumetric entropy generation due to mass transport.
TOPICS: Condensation, Entropy, Design, Mixed convection, Pumps, Condensers (steam plant), Mass transfer, Reynolds number, Pressure, Heat
Abhipsit Singh and Nanda Kishore
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039300
Numerical results on laminar mixed convective heat transfer phenomenon between a confined circular cylinder and shear-thinning type nanofluids are presented. The cylinder is placed horizontally in a confined channel through which nanofluids flow vertically upward. The effect of buoyancy is same as the direction of the flow. Because of existence of mixed convection, governing continuity, momentum and energy equations are simultaneously solved within the limitations of Boussinesq approximation. The ranges of parameters considered are: volume fraction of nanoparticles, ? = 0.005 - 0.045; Reynolds number, Re = 1 - 40; Richardson number, Ri = 0 - 40; and confinement ratio of circular cylinder, ? = 0.0625 - 0.5. Finally, the effects of these parameters on the streamlines, isotherm contours, individual and total drag coefficients and local and average Nusselt numbers are thoroughly delineated. The individual and total drag coefficients decrease with the increasing both ? and Re; and/or with the decreasing both Ri and ?. The rate of heat transfer increases with the increasing Re, ?, Ri and ?; however, at Re = 30-40, when ? > 0.005 and Ri < 2, the average Nusselt number decreases with the increasing Richardson number. Finally, correlations for the total drag coefficient and average Nusselt number are proposed as functions of pertinent dimensionless parameters on the basis of present numerical results.
TOPICS: Mixed convection, Circular cylinders, Nanofluids, Drag (Fluid dynamics), Flow (Dynamics), Buoyancy, Heat transfer, Approximation, Reynolds number, Shear (Mechanics), Nanoparticles, Convection, Momentum, Cylinders
Beshoy Morkos, Surya Venkata Sumanth Dochibhatla and Joshua Summers
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039302
This paper presents an experimental study of air flow through open cell metal foams for use in thermal energy dissipation. The goal of this research is to identify the optimum configuration of metal foam design parameters for maximum flow. Four foam blocks were used in this partial factorial study, representing a range of design parameters: material (Copper and Aluminum), pore size (5-10 pores per inch), and relative density (e = 0.875 - 0.952). A series of wind tunnel tests were performed to measure the velocity of air flowing through the foam as a function of the free stream air velocity, ranging from 0 to 17.4 mph (7.5 m/s). Results indicated small pore sizes and larger densities decreased the amount of airflow through the foam. However, one foam sample produced results that did not fit this trend. Further investigation found this was likely due to the differences in the cross-sectional geometry of the foam ligaments. The ligament geometry of metal foams is affected by density and manufacturing method. The cross-section shape of the ligaments was found to vary from a convex triangular shape to a triangle shape with concave surfaces, increasing the amount of drag in the airflow through the sample. Multinomial logit regression was performed on the data to analyze the effects of the design parameters on velocity loss. Results indicate that effect of Porosity on velocity loss is significant, and that of ppi is insignificant.
TOPICS: Fluid dynamics, Geometry, Metal foams, Porosity, Shapes, Air flow, Design, Density, Drag (Fluid dynamics), Energy dissipation, Flow (Dynamics), Copper, Aluminum, Manufacturing, Thermal energy, Wind tunnels
Hanna Sara, David Chalet and Mickaël Cormerais
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039304
One third of the injected fuel energy in an internal combustion engine is evacuated with the exhaust gases. To answer the severe emissions regulations, automotive industries tend to improve the engine efficiency by increasing its thermal efficiency. Exhaust gas heat recovery is one of the interested thermal management strategies that aim to improve the cold start of the engine and thus reduce its fuel consumption. In this work, an overview of the heat exchanger used as well as the experimental setup and the different tests will be presented first. These tests were used to model the heat transfer between the two fluids in the exchanger as well as the pressure drops on the two sides. The exchanger model was then added to a high frequency 4-cylinder turbocharged Diesel engine model coupled with its hydraulic circuits. Numerical simulations were run to assess and valorise the exhaust gas heat recovery strategy. The application were divided into three parts: an indirect heating of the oil with the coolant as a medium fluid, a direct heating of the oil and direct heating of the oil and the coolant. The different ideas were tested over five different driving cycles: NEDC, WLTC, CADC (Urban and highway), and one in-House Developed Cycle. The simulations were performed over two ambient temperatures. Different configurations were proposed to control the engine's lubricant maximum temperature. Results concerning the temperature profiles as well as the assessment of fuel consumption were stated for each case.
TOPICS: Computer simulation, Heat recovery, Internal combustion engines, Cycles, Exhaust systems, Heating, Fuel consumption, Coolants, Engines, Temperature, Fluids, Gases, Air pollution control, Fuels, Heat transfer, Engineering simulation, Heat exchangers, Lubricants, Simulation, Cylinders, Diesel engines, Cities, Hydraulic circuits, Thermal efficiency, Highways, Pressure drop, Temperature profiles, Thermal management
Ashish Agrawal and P.S. Ghoshdastidar
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039299
In the present work, a steady state, finite-difference based computer model of heat transfer during production of lime in a rotary kiln has been developed. The model simulates calcination reaction in the solid bed region of the rotary kiln along with turbulent convection of gas, radiation heat exchange among hot gas, refractory wall and the solid surface, and conduction in the refractory wall. The solids flow countercurrent to the gas. The kiln is divided into axial segments of equal length. The mass and energy balances of the solid and gas in an axial segment are used to obtain solids and gas temperature at the exit of that segment. Thus, a marching type of solution proceeding from the solids inlet to solids outlet arises. To model the calcination of limestone, shrinking core model with surface reaction rate control has been used. The output data consist of the refractory wall temperature distributions, axial solids and gas temperature distributions, axial percent calcination profile, and kiln length. The kiln length predicted by the present model is 5.74 m as compared to 5.5 m of the pilot kiln used in the experimental study of Watkinson and Brimacombe (1982, Watkinson, A.P. and Brimacombe, J. K., "Limestone Calcination in a Rotary Kiln", Metallurgical Transactions B, Vol. 13B, pp. 369-378). The other outputs have been also satisfactorily validated with the aforementioned experimental results. A detailed parametric study lent a good physical insight into the lime making process and the kiln wall temperature distributions.
TOPICS: Heat transfer, Computer simulation, Lime kilns, Kilns, Solids, Rotary kilns, Wall temperature, Shrinkage (Materials), Convection, Computers, Steady state, Temperature distribution, Radiation (Physics), Turbulence, Heat conduction, Flow (Dynamics), Heat, Temperature
Pankaj Srivastava and Anupam Dewan
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039088
A microchannel heat sink with convergent-divergent shape and bifurcation is presented and flow and heat transfer characteristics are analyzed for Re ranging from 120 to 900. The three-dimensional governing equations for the conjugate heat transfer with temperature-dependent solid and fluid properties are solved using the finite volume method. Comparisons have been carried out for four cases, namely, rectangular shape with and without bifurcation and convergent-divergent (CD) shape with and without bifurcation. The pressure drop, flow structure and average Nusselt number are analyzed in detail, and thermal resistance and overall performance are compared. It is shown that the CD shape with bifurcation has more uniform and lower temperature at the bottom wall and better heat transfer performance compared to other geometries. The heat transfer augmentation in the CD shape microchannel with bifurcation can be attributed not only to the accelerated and redirected flow towards the constant cross-section segment but also to periodically interrupted and redeveloped thermal boundary-layers due to bifurcation. It is also shown that increasing Re leads to thinning of thermal boundary-layers resulting in an enhanced heat transfer in terms of an increased average Nusselt number from 38% to 74%. However, there is an increased pressure drop due to channel shape and obstacle in fluid flow. Further, due to a high pressure drop penalty at high Re, CD shape microchannel with bifurcation loses its heat transfer effectiveness.
TOPICS: Bifurcation, Microchannels, Shapes, Heat transfer, Flow (Dynamics), Temperature, Pressure drop, Thermal boundary layers, Thermal resistance, Fluid dynamics, Finite volume methods, Heat sinks, Fluids, High pressure (Physics)
Prashant Singh and Srinath V. Ekkad
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039054
The present study investigates the effects of Coriolis force and centrifugal buoyancy force on heat transfer due to jet impingement on dimpled target surface. Detailed heat transfer measurements were carried out using transient liquid crystal thermography, where the target surface was modeled as one-dimensional semi-infinite solid. Three different configurations of dimpled target surfaces have been studied. The flow and rotation conditions have been kept the same for all the configurations, where the average Reynolds number (based on jet hole hydraulic diameter: Re_j) was 2500 and the rotational speed was 400 RPM (corresponding to Ro_j of 0.00274). Under non-rotating conditions, dimpled target surface showed positive heat transfer enhancements compared to smooth target surfaces. Under rotating conditions, it was observed that rotation was helpful in enhancing heat transfer on leading and trailing sides for smooth target surface. However, for the dimpled target surfaces, rotation proved to be detrimental to heat transfer enhancement.
TOPICS: Heat transfer, Rotation, Flow (Dynamics), Buoyancy, Liquid crystals, Coriolis force, Reynolds number, Thermography, Transients (Dynamics)
Rong Fung Huang, Reuben Mwanza Kivindu and Ching Min Hsu
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039055
The flame behavior and thermal structure of gaseous fuel jets issued from rectangular nozzles of high and low aspect ratios with co-flowing air were experimentally studied. Two rectangular nozzles with aspect ratios AR = 36 and 3.27 and with side channels for co-flowing air were examined. Flame behaviors were studied by photography techniques. Flame temperatures were measured using a fine-wire thermocouple. The AR = 36 burner exhibited three characteristic flame modes: attached flame, transitional flame, and lifted flame. The AR = 3.27 burner presented three characteristic flame modes: diffusion flame, transitional flame, and triple-layered flame. High AR jets promoted entrainment and mixing in the region around the flame base, whereas low AR jets enhanced mixing in the regions along the flame edges. At low co-flows, at Rec < 1200, the low AR burner flames were shorter, but at Rec > 1200, the high AR burner flames became shorter and wider. At Rec > 950, the high AR burner recorded higher flame temperatures, compared to the low AR burner by over 100 ºC. At high fuel jet Reynolds numbers and moderate co-flow, high AR burner flames presented better combustion performances when compared to low AR jet flames. The good combustion performance of the high AR jet flames was due to enhanced entrainment and mixing, which were induced by flame lifting. However, at low Rec and high co-flow, the low AR jet flames exhibited desirable flame characteristics due to improved entrainment and turbulence at the jet interfaces.
TOPICS: Jets, Nozzles, Flames, Flow (Dynamics), Temperature, Combustion, Fuels, Turbulence, Reynolds number, Wire, Thermocouples, Diffusion flames, Photography
Judith E. Sierant
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4039021
List of reviewers for 2017.

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