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research-article  
Sebastian Cano, Gustavo David Cordova Cardenas, Christian Narváez, Luis Segura and Luis Carrion
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042351
The current study allows the recognition of the most optimal combination of a variety of parameters (excitation frequency, kind of orifice, and synthetic jet-to-surface spacing) in order to obtain the lowest cooling time using a Taguchi experimental design. Furthermore, the heat transfer and synthetic jet velocity behavior using different kinds of orifices are demostrated experimentally. A piezoelectric diaphragm has been selected as vibrating actuator. Four kinds of orifices have been studied: circular, rectangular, triangular and square. First, the study consists of recognizing the excitation frequency in which each orifice produces the highest flow velocity. A hotwire anemometer has been used in order to measure the synthetic jet velocity. Furthermore, a steel plate has been heated and then cooled using the synthetic jet set at the excitation frequency in which the jet velocity was the largest for each orifice . For the statistical analysis, the input study variables have been kind of orifice and jet-to-surface spacing. The output variable has been the cooling time.The results demostrate that using a combination of a rectangle orifice, 20 mm of jet-to-surface spacing and an excitation frequency of 2000 Hz, the cooling time is the least. In addition, using these parameters, a mean heat transfer coefficient of 11.05 (W/m^2°K) with a coefficient of performance (COP) of 49.21 have been obtained. Finally, for each kind of orifice there is the presence of two resonant frequencies, the Helmholtz (acoustic resonance) frequency and piezoelectric diaphragm natural frequency.
TOPICS: Heat transfer, Taguchi methods, Excitation, Cooling, Diaphragms (Mechanical devices), Diaphragms (Structural), Resonance, Orifices, Statistical analysis, Flow (Dynamics), Heat transfer coefficients, Actuators, Experimental design, Steel, Acoustics
research-article  
Abdelraheem Mahmoud Aly and Zehba Raizah
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042352
The contribution of the current study is to investigate the mixed convection in an inclined nanofluid filled-cavity saturated with a partially layered non-Darcy porous medium. Moreover, due to the advantage of the particle-based methods, we presented the improved version of an incompressible smoothed particle hydrodynamics (ISPH) method. The current ISPH method was improved in boundary conditions treatment using renormalization kernel function. In the current investigation, we assumed that the inclined cavity is filled with a Cu-water nanofluid. The upper half of the cavity is saturated with a non-Darcy porous medium. Here, one domain approach is used for coupling the nanofluid and the porous medium layer. The cooled top wall of the cavity is carrying a tangential unit velocity and the bottom wall is heated. The other two wall sides are adiabatic at zero velocity. Here, we investigated the effects of the Richardson parameter Ri(0.0001-100), Darcy parameter Da (?10?^(-5)-?10?^(-2) ), an inclination angle a (0°-90°) and a various solid volume fraction ?(0-0.05) on the heat transfer of a Cu-water nanofluid. The obtained results showed that the average Nusselt number decreases as the Richardson number increases. An addition of 1% to 5% Cu nanoparticles slightly increased the overall heat transfer rate.
TOPICS: Porous materials, Simulation, Mixed convection, Cavities, Nanofluids, Water, Particulate matter, Heat transfer, Hydrodynamics, Boundary-value problems, Renormalization (Physics), Nanoparticles
research-article  
Mirza Mohammed Shah
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042354
Heat exchangers with boiling in coils are widely used in the industry. Various researchers have recommended different correlations for heat transfer but there has been no comprehensive comparison of data and correlations to identify the most reliable ones. This was done in the present study. Eight correlations for straight tubes and six for coils were compared with data from 12 studies. The data included four fluids, tube diameters 2.8 to 14.5 mm, coil to tube diameter ratios 12 to 107, reduced pressure 0.0046 - 0.7857, flow rates 80 to 1200 kgm-2s-1, and boiling number 0.16 to 13.6 x 104. None of the correlations for coils were found satisfactory. Four general correlations for straight tubes gave good agreement with the 484 data points, mean absolute deviation being 19.8 to 22.6 %.
TOPICS: Heat transfer, Boiling, Heat exchangers, Fluids, Pressure, Flow (Dynamics)
Review Article  
Yogesh Jaluria
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042353
A common occurrence in many practical systems is that the desired result is known or given, but the conditions needed for achieving this result are not known. This situation leads to inverse problems, which are of particular interest in thermal processes. For instance, the temperature cycle to which a component must be subjected in order to obtain desired characteristics in a manufacturing system, such as heat treatment or plastic thermoforming, is prescribed. However, the necessary boundary and initial conditions are not known and must be determined by solving the inverse problem. Similarly, an inverse solution may be needed to complete a given physical problem by determining the unknown boundary conditions. Solutions thus obtained are not unique and optimization is generally needed to obtain results within a small region of uncertainty. This paper discusses inverse problems that arise in a variety of practical processes and presents some of the approaches that may be used to solve them and obtain acceptable and realistic results. Optimization methods that may be used to for reduce the error are presented.
TOPICS: Thermal systems, Inverse problems, Optimization, Manufacturing systems, Uncertainty, Temperature, Heat treating (Metalworking), Boundary-value problems, Cycles, Errors
Discussion  
Asterios Pantokratoras
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042355
The present discussion concerns some doubtful results included in the above paper.
research-article  
Alfredo Iranzo, Antonio Salva, Jose Julio Guerra Macho, Gonzalo Barea and Javier Pino
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042218
This paper presents a CFD analysis of the air and temperature distribution in a representative railway vehicle, with the objective of evaluating passengers thermal comfort. The CFD model developed is featuring the wagon geometry in detail including air diffusers geometry, passengers, and luminaires. A set of different scenarios are studied, covering occupancy levels, state of the doors and windows (open/closed), inlet temperature, and air diffuser design. The results show a clear influence of the air supply system and design geometry on comfort, as local velocities well above 1 m/s were obtained for the original design. A new diffuser design proposed clearly improved the velocity field distribution enhancing passengers thermal comfort. Exhaust vents are also presenting high velocities, which are significantly reduced down to 2 m/s when windows are open. It is observed that thermal comfort is not appropriate when air inlet temperature is conditioned to 19 ºC, especially for the original diffuser design.
TOPICS: Ventilation, Railway vehicles, Design, Diffusers, Geometry, Computational fluid dynamics, Temperature, Doors, Temperature distribution, Vents, Exhaust systems
research-article  
Nian Wang and Dr. Je-Chin Han
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042151
Jet impingement cooling has been extensively investigated due to its significant applications on the airfoil leading edge region, however, most of which are about normal jet impingement. The systematic research on swirl jet impinging cooling on leading edge is relatively rare. The present study comprehensively investigated the heat transfer distribution of swirl jet impingement with one row of tangential jets. The location of the cross-over jets is offset from the centerline toward either suction or pressure side. Five jet Reynolds numbers varying from 10,000 to 80,000 are tested to reach real engine cooling condition. Jet plates with jet-to-jet spacing (s/d = 2, 4 and 6) and the ratio of surface diameter-to-jet diameter (D/d = 4, 6.6 and 13.3) are tested. We conducted the experiments with a test matrix of 45 cases. The optimum geometric parameters of the jet plate are revealed. Results indicate that for a given Reynolds number the jet plate configuration with D/d = 4 and s/d = 2 provides the highest Nusselt number profile than the other jet plate configurations, while the jet plate configuration with D/d = 13.3 and s/d = 8 provides the lowest Nusselt number profiles. The best heat transfer region shifts by varying the jet plate configuration depending on the strength of swirl flow. Additionally, correlation of tangential jet impingement has been developed to predict the area-averaged Nusselt number, which is useful for airfoil leading edge cooling design and heat transfer analysis.
TOPICS: Cooling, Reynolds number, Airfoils, Heat transfer, Jets, Design, Impingement cooling, Plates (structures), Suction, Engines, Pressure, Flow (Dynamics)
research-article  
Kazuhiro Yamamoto, Ryo Komiyama and Tatsuya Sakai
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042152
To improve air pollution, we must reduce soot particulates in vehicle exhaust gas, which are inevitably harmful to the environment as well as to human health. Many countries are setting new regulations of nanoscale particle emission. Then, a ceramic porous filter such as DPFs (diesel particulate filters) has been developed. However, as more particles are trapped inside the filter, the filter backpressure corresponding to the pressure drop across the filter increases, which could worsen the fuel consumption rate, together with the abatement of the available torque. Usually, the filter regeneration process for particle oxidation inside the filter should be periodically needed. Thus, a filter with lower pressure drop would be preferable. In the current stage, the responses of the pressure drop during both particle filtration and oxidation are not fully understood. This is because these are the small-scale processes, and it is difficult to observe the phenomena experimentally. In this study, to consider the soot filtration, the exhaust gas flow with soot particles was simulated by a lattice Boltzmann method (LBM). Then, the time-variation of the pressure was discussed, which is important for the transport phenomena in the porous filter. For comparison, the pressure drop during the filter regeneration was also simulated to show the different pressure response affected by the soot oxidation zone.
TOPICS: Pressure, Flow (Dynamics), Filtration, Filters, Soot, Particulate matter, Pressure drop, oxidation, Exhaust systems, Torque, Lattice Boltzmann methods, Fuel consumption, Emissions, Gas flow, Nanoparticles, Vehicles, Transport phenomena, Air pollution, Diesel, Ceramics, Regulations
research-article  
Ahmed T. Eltaweel and Dr. Ibrahim Hassan
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042153
In the present study, a multi-variable comparative study of the effect of microchannel heat sink configurations on their thermal performance is conducted by numerically simulating three-dimensional fluid flow and heat transfer in multiple microchannel heat sink configurations. Thermal analysis is performed to investigate a novel wavy-tapered channel configuration of microchannel heat sinks with directionally alternating coolant flow for high-end electronics cooling. Simulations were conducted at different tapering and aspect ratios, focusing on how effectively previously proven geometric enhancements combine with one another in novel ways. Results confirmed the superiority of wavy channels over straight channels due to the development of the secondary flow (Dean Vortices), which enhance the advection mixing and consequently the overall heat sink thermal performance. Moreover, widthtapering of the wavy channel showed improved channel performance in terms of thermal resistance compared to untapered wavy channels. Almost 10% improvement in thermal resistance is obtained with width tapering. Also, the thermal performance showed a strong dependency on channel aspect ratio. Overall performance suggests that optimum tapering and aspect ratio conditions exist. The numerical investigations are then extended to novel heat sink design includes wavy tapered microchannels with directionally alternating flow to improve heat sink thermal performance. A 15% reduction in thermal resistance and highly improved substrate surface temperature distribution uniformity are obtained using alternating flow compared to corresponding parallel flow channels.
TOPICS: Fluid dynamics, Flow (Dynamics), Heat transfer, Simulation, Coolants, Design, Engineering simulation, Vortices, Heat sinks, Microchannel flow, Temperature distribution, Thermal analysis, Thermal resistance, Computer cooling, Microchannels, Heat flux
research-article  
Tarfaoui Mostapha, Mourad Nachtane and Hicham Boudounit
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042123
World energy demand has increased immediately and is expected to continue to grow in the foreseeable future. Therefore, an overall change of energy consumption continuously from fossil fuels to renewable energy sources, and low service and maintenance price and taking the benefits of using renewable energies such as using wind turbines as an electricity generator. In this context, offshore wind power refers to the development of wind parks in bodies of water to produce electricity from wind. Better wind speeds are available offshore compared to on land, so offshore wind power's contribution in terms of electricity supplied is higher. However, these structures are very susceptible to degradation of their mechanical properties considering various hostile loads. The scope of the present work is the study of the damage noticed in full-scale 48m fiberglass composite blades for offshore wind turbine. In this paper, the most advanced features currently available in finite element (FE) Abaqus/Implicit have been employed to simulate the response of blades for a sound knowledge of the mechanical behavior of the structures and then localize the susceptible sections.
TOPICS: Composite materials, Finite element analysis, Blades, Offshore wind turbines, Ocean engineering, Wind, Wind power, Wind farms, Wind turbines, Bodies of water, Damage, Energy consumption, Fossil fuels, Generators, Mechanical properties, Mechanical behavior, Maintenance, Wind velocity, Glass reinforced plastics, Stress, Renewable energy sources
research-article  
Imane Aslib, Hamid Hamza, Nisrine Hanchi, Jawad Lahjomri and Abdelaziz Oubarra
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042056
This paper deals with the transient thermal analysis of two-dimensional cylindrical anisotropic pin fin that contains tip convection and subjected to a step change in base temperature. The heat conduction equation should involve a dual second-order derivation, which precludes solving the equation by direct application of common exact methods. Therefore, an appropriate canonical mapping is selected as a solution to cancel the dual derivation of temperature in the mapped equations. The alternating-direction implicit finite-difference method (ADI) performs the integration of the mapped equations in the novel space, which involve a complicate geometry. Applying the inverse spatial transformation provides transient temperature profile in the real geometry for full field configuration. The established numerical code has been validated successfully with the analytical solutions of the usual fins (orthotropic and isotropic). The anisotropy effect is investigated by means of various contour plots of the temperature profile as well as, heat transfer rate from the fin base and the effectiveness for different parameters of study (kr/kz, krz/kz and Bir) in transient and steady sate heat conduction. A comparative study with the case of the orthotropic fins heat sink reveals that anisotropy has insignificant effect on the optimal operating conditions and by consequently on the performance of the fin while it has a very important and non-neglecting effect in the shape and the behavior of the temperature profile and the heat transfer rate from the fin base.
TOPICS: Anisotropy, Transients (Dynamics), Temperature profiles, Temperature, Heat transfer, Heat conduction, Fins, Geometry, Heat sinks, Shapes, Convection, Biomedical measurement, Finite difference methods, Thermal analysis
research-article  
Chao-Cheng Shiau, Izzet Sahin, Nian Wang, Dr. Je-Chin Han, Hongzhou Xu and Michael Fox
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042057
The effects of upstream injection angle on film cooling effectiveness of a turbine vane endwall with various endwall film-hole designs were examined by applying PSP measurement technique. As the leakage flow from the slot between the combustor and the turbine vane is not considered an active source to protect the vane endwall in certain engine designs, discrete cylindrical holes are implemented near the slot to create an additional controllable upstream film to cool the vane endwall. Three potential injection angles were studied: 30o, 40o, and 50o. To explore the optimum endwall cooling design, five different film-hole patterns were tested: axial row, cross row, cluster, mid-chord row, and downstream row. Experiments were conducted in a four-passage linear cascade facility in a blowdown wind tunnel at the exit isentropic Mach number of 0.5 corresponding to inlet Reynolds number of 380,000 based on turbine vane axial chord length. A freestream turbulence intensity of 19% with an integral length scale of 1.7 cm was generated at the cascade inlet plane. Detailed film cooling effectiveness for each design was analyzed and compared at the design operation conditions (coolant mass flow ratio 1% and density ratio 1.5). The results are presented in terms of high-fidelity film effectiveness contours and laterally (spanwise) averaged effectiveness. This paper will provide the gas turbine designers valuable information on how to select the best endwall cooling pattern with minimum cooling air consumption over a range of upstream injection angle.
TOPICS: Turbines, Design, Film cooling, Cooling, Cascades (Fluid dynamics), Chords (Trusses), Gas turbines, Engine design, Wind tunnels, Leakage flows, Combustion chambers, Density, Flow (Dynamics), Mach number, Turbulence, Reynolds number, Coolants
Technical Brief  
Ozgur Atik and Dr. Hakan Erturk
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4042022
Cooling performance enhancement of computer liquid cooling systems using hBN-water nanofluids are investigated experimentally. The particle volume fractions of 0.1-2% are considered at constant flow rates varying from 0.3-2 L/min for systems with two different cold plates. A commercial closed loop liquid cooling system is also tested to examine performance of hBN-water nanofluids at constant pumping power. It was observed that the maximum cooling enhancement is obtained with 2% particle volume fraction of hBN-water nanofluid in all experimental systems. Moreover, the enhancement rate depends on the flow rate and the cold plate design. The cooling performance increase for the commercial system is observed to be limited with the reduced flow rate at increasing particle volume fractions. Therefore, cold plates must be optimized to maximize the cooling capacity, considering the increasing viscosity and thermal conductivity of nanofluids.
TOPICS: Cooling, Nanofluids, Water, Flow (Dynamics), Particulate matter, Cooling systems, Plates (structures), Computers, Viscosity, Thermal conductivity, Design
research-article  
Ziad Saghir, Christopher Welsford, Pirassanth Thanapathy, Ayman, A.M. Bayomy and Cayley Delisle
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041936
The rapid rate of improvement in electronic devices has led to an increased demand for effective cooling techniques. The purpose of this study is to investigate the heat transfer characteristics of an aluminum metallic foam for use with an Intel core i7 processor. The metal foams used have a porosity of 0.91 and different permeabilities ranging from 10 PPI to 40 PPI. The flow rate at the entrance of the porous cavity varied from 0.22 USGPM to 0.1 USGPM. The fluid consists of water with aluminum nanoparticles having a concentration from 0.1% to 0.5%. The heat fluxes applied at the bottom of the porous test cell vary from 13.25 W/cm2 to 8.34 W/cm2. It has been observed that nanofluid improves heat extraction, it is a known fact that when a metallic porous material is circulated with the working fluid. It adds to the heat extraction rate and the combined effect of the flow rate. These observations lead to the conclusion that heat enhancement is possible with nanofluid and it is enhanced further in the presence of a high flow rate. However, it was detected experimentally, verified numerically and agreed upon by different researchers that higher heat extraction is found for a nanofluid concentration of 0.2%. This observation is independent of the porous permeability or applied heat flux. It has also been shown that heat enhancement in the presence of nanofluid is evident, when experimental results were compared to water.
TOPICS: Heat transfer, Porous materials, Computation, Heat, Nanofluids, Flow (Dynamics), Water, Metal foams, Fluids, Permeability, Aluminum, Heat flux, Porosity, Cooling, Flux (Metallurgy), Nanoparticles, Cavities
Technical Brief  
Antonio Campo and Yunesky Masip Macia
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041938
Simple formulas for the prediction of three important thermal quantities: the center temperature, the mean temperature and the total heat transfer in regular configurations (large plane wall, long cylinder and sphere) cooled/heated with uniform surface temperature during "small time" and "large time" are addressed. Two immediate engineering applications deal with quenching of metals and sterilization of canned food. The simple formulas emanate from the truncated one term series of the supplementary infinite series at "small time". In the heat conduction literature, the "small time" sub-region has been described by dimensionless time or Fourier number ? < 0.24 in the large plane wall, ? < 0.21 in the long cylinder and ? < 0.19 in the sphere. Excellent agreement between the simple formulas and the traditional solutions (namely the exact, analytical infinite series for "all time") are attained for the center and mean temperatures and total heat transfer in the large plane wall, long cylinder and sphere.
TOPICS: Temperature, Heat transfer, Cylinders, Food products, Sterilization, Metals, Heat conduction, Quenching (Metalworking), Engineering systems and industry applications
research-article  
Omer F. Guler, Oguz Guven and Murat K. Aktas
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041877
The oscillatory flows are often utilized in order to augment heat transfer rates in various industrial processes. It is also well known fact that nanofluids provide significant enhancement in heat transfer at certain conditions. In this research, heat transfer in an oscillatory pipe flow of both water and water-alumina nanofluid was studied experimentally under low frequency regime laminar flow conditions. The experimental apparatus consists of a capillary tube bundle connecting two reservoirs which are placed at the top and bottom ends of the capillary tube bundle. The upper reservoir is filled with the hot fluid while the lower reservoir and the capillary tube bundle filled with the cold fluid. The oscillatory flow in the tube bundle is driven by the periodic vibrations of a surface mounted on the bottom end of the cold reservoir. The effects of the frequency and the maximum displacement amplitude of the vibrations on thermal convection were quantified based on the measured temperature and acceleration data. It is found that the instantaneous heat transfer rate between DI (deionized) water (or the nanofluid) filled reservoirs is proportional to the exciter displacement. Significantly reduced maximum heat transfer rates and effective thermal diffusivities are obtained for larger capillary tubes. The nanofluid utilized oscillation control heat transport tubes achieve high heat transfer rates. However heat transfer effectiveness of such systems is relatively lower compared to DI water filled tubes.
TOPICS: Heat transfer, Nanofluids, Water, Reservoirs, Fluids, Flow (Dynamics), Vibration, Displacement, Excitation systems, Oscillations, Heat, Temperature, Laminar flow, Convection, Pipe flow
research-article  
Zhu Yannan, Zhang Qiang, Jianfeng Tao, Tan Dun and Wang Xuyong
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041880
A new method of building electro-hydraulic servo valve's thermal model is proposed. In this method, coupled pressure and temperature equations inside control volume were deduced based on fluid mass continuity equation and energy conservation equation; relationship among servo valve's heat conduction, heat convection and heat radiation was also obtained according to thermodynamics. Servo valve's thermal model and thermal characteristics model were built and simulated in AMESim. Experiment was carried out in four working pressures ranging from 3MPa to 12MPa. Simulation and experimental results indicate that valve reaches thermal equilibrium in less than 2.5 hours, and with pressure's increase, valve reaches thermal equilibrium more quickly. Maximum and steady temperature error between simulation and experimental results are approximately 5.2°C and 1.8°C, and when lowering pressure, they both reduce. The temperature error can mainly result from motor's heat production in experiment, which will vanish when the whole hydraulic motor servo system is modeled. Therefore, experimental results verified the validity of valve's thermal characteristics model. The significance of this study is to provide a theoretical basis for subsequent researches of thermal characteristics of other hydraulic components, which include hydraulic motor, valve block, hydraulic oil source and so on.
TOPICS: Heat, Servomechanisms, Valves, Temperature, Pressure, Hydraulic motors, Simulation, Errors, Thermal equilibrium, Convection, Energy conservation, Thermal radiation, Heat conduction, Thermodynamics, Fluids
research-article  
Shikuan Wang, Zhikai Guo, Dr. Xiaohong Han, Xiangguo Xu, Qin Wang, Shiming Deng and Dr. Guangming Chen
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041881
HFO-1336mzz-Z with low Global Warming Potential (GWP) was considered as a promising alternative of HCFC-123, HFC-245fa in air conditioning and heat pump, respectively. In order to understand the operation performances of HFO-1336mzz-Z and HCFC-123, HFC-245fa in different working conditions, an experimental setup for testing the refrigeration cycle performance was built. The cycle performances of HFO-1336mzz-Z and HCFC-123 in air conditioning conditions, HFO-1336mzz-Z and HFC-245fa in heat pump conditions were investigated by experiment. It was found in air conditioning conditions, the discharge temperatures for the systems with HFO-1336mzz-Z and HCFC-123 were lower than 115°C, the cooling capacity of the system with HFO-1336mzz-Z was 27% less than that with HCFC-123 at least, and the coefficient of performance (COP) of the system with HFO-1336mzz-Z was 0.1 lower than that with HCFC-123; in heat pump conditions, the discharge temperature with HFO-1336mzz-Z was lower than that with HFC-245fa, the former was never over 115°C while the latter was up to 126°C, the power input to the compressor with HFO-1336mzz-Z was 20% less than that with HFC-245fa in the same heat pump conditions, the heating capacity of the system with HFO-1336mzz-Z was 30%~40% less than that with HFC-245fa.
TOPICS: Temperature, Cooling, Air conditioning, Compressors, Testing, Cycles, Heat pumps, Heating, Climate change, Refrigeration cycles
research-article  
Xiao-ming Tan, Jing-zhou Zhang and Qingzhi Cai
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041882
Experimental and numerical research is performed to illustrate the effects of pin-fin shapes on mesh-fed slot film cooling performance on a flat-plate model. Three types of pin-fin shapes (such as circular, elliptical, and drop-shaped) with the same cross-sectional area are taken into consideration. The results show that a pair of counter rotating vortices is still generated for the mesh-fed slot film cooling scheme due to the strong "jetting" effect of coolant flow at the slot outlet. As the coolant jet ejecting from mesh-fed slot is capable of establishing more uniform film layer over the protected surface, the kidney vortices are illustrated to have weakly detrimental role on the film cooling performance. By the shaping of pin fins, the uniformity of coolant flow exiting mesh-fed slot is improved in comparison to the baseline case of circular shape, especially for the elliptical-shape pin-fin array. Therefore, the "jetting" effect of coolant flow is alleviated for the elliptical and drop-shaped pin-fin meshes when compared to the circular pin-fin mesh. In general, the pin-fin shape has nearly no influence on cooling effectiveness immediately downstream the film cooling-hole outlet. However, beyond x/s=5, the elliptical and drop-shaped pin fins are demonstrated to be advantageous over the circular pin fins.
TOPICS: Flat plates, Shapes, Film cooling, Coolants, Flow (Dynamics), Fins, Cooling, Vortices, Kidney
research-article  
Medhat Sorour, Mohamed Fayed and Noha Alaa El-Din
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041883
The steady forced convection between two stationary parallel circular disks in a radial sink flow cooling system is investigated numerically. This investigation is devoted to study the effect of swirling flow and /or grooved surface on the heat transfer and on the thermo-hydraulic parameter. A wide range of inlet Reynolds number (Re), 100 = Re = 105, inlet swirl ratio (S), 0 = S = 20 and the gap spacing ratio (G), 0.01 = G = 0.1 is considered in the study. The rectangular grooves are characterized by ribs with three dimensionless lengths; height (t/d), 0.1 = t/d = 0.35, the interval spacing between ribs (i /Ro), 0.025 = i /Ro = 0.1, and the width of rib (w/Ro), 0.025 = w/Ro = 0.1. The results of the heat transfer analysis indicate that swirling flow enhance the cooling system for plain and ribbed surfaces. However, the thermal hydraulic study indicated that swirling flow is beneficial for plain surfaces only. And the ribs are beneficial with pure radial inflow.
TOPICS: Flow (Dynamics), Heat transfer, Cooling systems, Swirling flow, Inflow, Reynolds number, Forced convection, Disks

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