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Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
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
research-article  
Elumalai Kannan, Seralathan Sivamani, Dibyakanti Ghosh Roychowdhury, T. Micha Premkumar and Venkatesan Hariram
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041937
Three dimensional Reynolds Averaged Navier Stokes equations with shear stress transport turbulence model is used to analyze the film cooling effectiveness on a flat plate having single row of film hole involving cylindrical and laidback holes. The cylindrical and laidback holes are inclined at 35° to the surface with a compound angle (ß) orientation ranging from favorable to adverse inclination (i.e., ß = 0° to 180°) and examined at high and low blowing ratios (M = 1.25 and 0.60). Cylindrical hole (CH) with a adverse compound angle of 135° gives the highest area averaged film cooling effectiveness in comparison with laidback hole (LBH) configuration. Also, CH ß =135° film hole shows a higher lateral coolant spread. Later, double jet film cooling concept is studied for this cylindrical hole. In all the cases, the first hole compound angle is fixed as 135° and the second hole angle is varied from 135° to 315°. At high blowing ratio, the dual jet cylindrical hole (DJCH) with ß =135°, 315° gives a higher area averaged film cooling effectiveness by around 66.50% compared to baseline CH ß = 0°. On comparing all CH, LBH and DJCH cases, the highest area averaged film cooling effectiveness is obtained by CH configuration with ß = 135°. Hence, the cylindrical hole with its adverse compound angle (ß = 135°) orientation could be an appropriate film cooling configuration for gas turbine blade cooling.
TOPICS: Film cooling, Shear stress, Cooling, Turbulence, Coolants, Gas turbines, Blades, Flat plates, Reynolds-averaged Navier–Stokes equations
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
research-article  
Ramanathan Velmurugan, Jaikumar Mayakrishnan, Induja S, Selvakumar Raja, Sasikumar Nandagopal and Dr. Ravishankar Sathyamurthy
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041878
The present investigation aims at analyzing various parameters of single cylinder 4-stroke CI engine fueled with Waste Cooking Oil Biodiesel (WCOB), Waste Cooking Oil Biodiesel Water Emulsion (WCOBE) while the engine is operated with a constant speed of 1500 rpm. Furthermore, an attempt is made to study the impact of nanofluids in the behavior of the engine fueled with WCOB blended with nanofluids (WCOBN50). This work also explored a novel method of producing nanofluids using one-step chemical synthesis method. Copper Oxide (CuO) nanofluids were prepared by the above mentioned method and blended with Waste Cooking Oil Biodiesel (WCOBN50) using ethylene glycol as a suitable emulsifier. Results revealed that Brake Thermal Efficiency (BTE) and Brake Specific Fuel Consumption (BSFC) of WCOBN50 are significantly improved when compared to WCOB and WCOBE. Furthermore, a higher reduction in Oxides of Nitrogen (NOx), Carbon Monoxide (CO), Hydrocarbon (HC), and smoke emissions were observed with WCOBN50 on comparison with all other tested fuels at different power outputs. It is also identified that one step chemical synthesis method is a promising technique for preparing nanofluids with a high range of stability.
TOPICS: Engines, Nanofluids, Biodiesel, Brakes, Thermal efficiency, Stability, Copper, Fuels, Nitrogen, Smoke, Water, Nitrogen oxides, Fuel consumption, Emissions, Carbon, Cylinders, Diesel engines, Emulsions
research-article  
Umer Farooq, Dianchen Lu, Saleem Ahmed, Muhammad Ramzan, Dr. J.D. Chung and Farman Ali Chandio
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041873
Magnetohydrodynamic (MHD) mixed convection in an exponentially stretching surface saturated with viscous fluid has been studied. BVPh2.0 is employed which is Mathematica based algorithm developed on the basis of optimal homotopy analysis method (OHAM). Adequate transformations are utilized for the reduction of governing equations (eqs) to non-linear ordinary differential system. Convergence of BVPh2.0 results is demonstrated through tabular values of squared residual errors. Graphical analysis are executed for broad range of governing parameters. It has been revealed an increase in buoyancy leads to the growth of boundary layer width. Further results predict the heat infiltration into the fluid increases as Brownian motion and Biot number enlarges. Mathematically this work demonstrate the potential and reliability of BVPh2.0 for non-linear differential systems.
TOPICS: Flow (Dynamics), Nanoparticles, Fluids, Magnetohydrodynamics, Buoyancy, Heat, Algorithms, Boundary layers, Mixed convection, Errors, Brownian motion, Reliability
Discussion  
Asterios Pantokratoras
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041885
The present discussion concerns some doubtful results included in the above paper
TOPICS: Magnetohydrodynamics, Heat, Heat transfer, Absorption, Melting, Stagnation flow
Discussion  
Asterios Pantokratoras
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041884
The present discussion concerns some doubtful results included in the above paper.
Technical Brief  
Pawan Karki, Ajay K Yadav and D. Arumuga Perumal
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041875
This study involves the effect of adiabatic obstacles on two-dimensional natural convection in a square enclosure using Lattice Boltzmann Method (LBM). The enclosure embodies square shaped adiabatic obstacles with one, two and four in number. The single obstacle in cavity is centrally placed whereas for other two configurations, a different arrangement has been made such that the core fluid zone is not hampered. The four boundaries of the cavity considered here, consists of two adiabatic horizontal walls and two differentially heated vertical walls. The current study covers the range of Rayleigh number (10^3 = Ra = 10^6) and a fixed Prandtl number of 0.71 for all cases. The effect of size of obstacle (Ø) is studied in detail for single obstacle. It is found that the average heat transfer along the hot wall increases with the increase in size (Ø) of obstacle until it reaches an optimum value and then with further increase in size, the heat transfer rate deteriorates. Study is carried out to delineate the comparison between the presences of obstacle in and out of the conduction dominant zone in the cavity. The number of obstacles (two and four) outside of this core zone shows that heat transfer decreases despite the obstacle being adiabatic in nature.
TOPICS: Natural convection, Cavities, Lattice Boltzmann methods, Heat transfer, Fluids, Heat conduction, Rayleigh number, Prandtl number
research-article  
Isaac Rose, Aaron P. Wemhoff and Dr. Amy Fleischer
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041804
A numerical model of a water storage system is developed, validated and used to analyze the impact of a water storage tank system in a chiller-less data center design. The results show that during times of high wet bulb operating conditions, a water storage tank can be an effective method to significantly reduce chip operating temperatures for warm-water cooled systems by reducing operating temperatures 5-7°C during the hottest part of the day.. The overall system performance was evaluated using both an exergy analysis and a modified PUE metric defined for the water storage system. This unique situation also necessitates the development of a new exergy definition in order to properly capture the physics of the situation. The impact of tank size, tank aspect ratio, fill percentage, and charging/discharging time on both the chip temperature and modified PUE are evaluated. It is determined that tank charging time must be carefully matched to environmental conditions in order to optimize impact. Interestingly, the water being stored is initially above ambient, but the overall system performance improves with lower water temperatures. Therefore, heat losses to ambient are found to beneficial to the overall system performance. The results of this analysis demonstrate that in application, data centers operators will see a clear performance benefit if water storage systems are used in conjunction with warm water cooling. This application can be extended to data center failure scenarios and could also lead to downsizing of equipment and a clear economic benefit.
TOPICS: Design, Data centers, Water storage, Water, Operating temperature, Computer simulation, Exergy, Exergy analysis, Failure, Heat losses, Physics, Temperature, Cooling, Water temperature
research-article  
Wei Wang, Jun Wang, Xiaopei Yang and Yanyan Ding
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041793
An entropy analysis and design optimization methodology is combined with airfoil shape optimization to demonstrate the impact of entropy generation on aerodynamics designs. In the work herein, the entropy generation rate is presented as an extra design objective along with lift-drag ratio, while the lift coefficient is the constraint. Model equation, which calculates the local entropy generation rate in turbulent flows, is derived by extending the Reynolds-averaging of entropy balance equation. The class-shape function transform (CST) parametric method is used to model the airfoil configuration and combine the radial basis functions (RBFs) based mesh deformation technique with flow solver to compute the quantities such as lift-drag ratio and entropy generation at the design condition. From the multi-objective solutions which represent the best trade-offs between the design objectives, one can select a set of airfoil shapes with a low relative energy cost and with improved aerodynamic performance. It can be concluded that the methodology of entropy generation analysis is an effective tool in the aerodynamic optimization design of airfoil shape with the capability of determining the amount of energy cost.
TOPICS: Entropy, Design, Optimization, Shapes, Airfoils, Drag (Fluid dynamics), Shape optimization, Tradeoffs, Flow (Dynamics), Aerodynamics, Deformation, Turbulence
research-article  
Faisal Al-Malki
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041794
The aim of this paper is to examine the response of twin premixed flames formed in a counterflow configuration to the presence of an unsteady straining flow. We began by describing the problem mathematically using the thermo- diffusive model with constant density and then adopted a finite elements approach to solve the problem numerically. The study has shown that the role of flow on flame propagation is determined by three main parameters, namely: flow amplitude A, strain rate ? and fuel Lewis number Le F . For Le F = 1, the flow is seen to promote flame extinction, while Le F < 1 the flow clearly enhances the flame reactivity. Qualitatively, it has been shown that for Le F = 1, there exists a critical value of A (that varies with ?) below which the reactivity decreases monotonically with A. For small Le F < 1, on the other hand, the re- activity were seen to increase with A. For Le F > 1, however, a non-monotonic dependence, especially for small ?, is predicted
TOPICS: Flow (Dynamics), Computer simulation, Flames, Density, Finite element analysis, Fuels
research-article  
Rajneesh Kumar, Sourabh Khurana, Anoop Kumar and Varun Goel
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041683
The sharp corner significantly affects the flow through triangular duct. In the corners, flow gets stagnant and results in poor heat transfer. Therefore, in the present study, one corner of the duct is kept rounded with variable curvature radius values (Rc). The curvature radius is selected in such a way that, it varied from the minimum value (i.e. Rc=0.333?duct height; h) to a maximum value (i.e. Rc=0.67h). In addition to this, the combined effect of both rounded corner and dimple-shaped intrusion has also been studied on flow of air and heat transfer. ANSYS (Fluent) 12.1 software is used to perform numerical simulations and good match is observed between the simulated and experimental results. Due to rounded corner and dimple intrusions, velocity near the corner region has higher value in comparison to the conventional duct. The uniform temperature distribution is seen in the case of dimple intruded duct as compared to conventional and rounded corner duct. In comparison to conventional duct with Rc of 0.67h, the heat transfer increased 21-25%, 13-20%, and 5-8%, for the Rc value of 0.33h, 0.49h, and 0.57h, respectively, but, the combination of rounded corner and dimple-shaped intrusions gives more heat transfer by 46-94%, 75-127%, 60-110%, for the z/e value of 6, 10, and 14, respectively, with the Reynolds number increase from 5600 to 17700.
TOPICS: Fluid dynamics, Heat transfer, Corners (Structural elements), Ducts, Flow (Dynamics), Computer simulation, Reynolds number, Temperature distribution, Computer software
research-article  
Ales Vojacek, Vaclav Dostal, Tomas Melichar, Martin Rohde and Friedrich Gottelt
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041686
This technical paper presents results of an air cooled supercritical CO2 (sCO2) finned-tube sink heat exchanger (HX) performance test comprising wide range of variable parameters (26-166 °C, 7-10 MPa, 0.1-0.32 kg/s). The measurement covered both supercritical and subcritical pressures including transition of pseudocritical region in the last stages of the sink HX. The test was performed in a newly built sCO2 experimental loop which was constructed within SUSEN (Sustainable Energy) project at Research Centre Rez (CVR). The experimental set-up along with the boundary conditions are described in detail, hence the gained data set can be used for benchmarking of system thermal hydraulic codes. Such benchmarking was performed on the open source Modelica-based code ClaRa. Both steady-state and transient thermal hydraulic analyses were performed using the simulation environment DYMOLA 2018 on a state of the art PC. The results of calculated averaged overall heat transfer coefficients (using Gnielinsky correlation for sCO2 and IPPE or VDI for the air) and experimentally determined values shows reasonably low error of + 25 % and - 10 %. Hence, using the correlations for the estimation of the heat transfer in the sink HX with a similar design and similar conditions gives a fair error and thus is recommended.
TOPICS: Heat exchangers, Testing performance, Supercritical carbon dioxide, Errors, Steady state, Energy sustainability, Boundary-value problems, Heat transfer, Simulation, Transients (Dynamics), Design, Heat transfer coefficients
research-article  
Omid Ali Zargar, Rong Fung Huang and Ching Min Hsu
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4041685
The effects of acoustic excitation at resonance on the flame appearances, flame lengths, flame temperatures, and combustion product concentrations of combusting swirling dual-disk double-concentric jets were studied. The Reynolds number of the annular swirling air jet was varied, while it was fixed at 2500 for the central propane jet. The central fuel jet was acoustically forced by a loudspeaker, which was installed using downstream longitudinal irradiation. The central jet pulsation intensities were measured by a calibrated, one-component hot-wire anemometer. The instantaneous full-length and close-up flame images were captured to identify the characteristic flame modes. Long-exposure flame images were taken to measure the flame lengths. The axial and radial temperature distributions of flames were measured using a homemade, fine-wire R-type thermocouple. The concentrations of combustion products were measured by a gas analyzer. Four characteristic flame modes, blue-base wrinkled flame, yellow-base anchored flame, blue-base anchored flame, and lifted flame, were observed in the domain of central jet pulsation intensity and annular swirling jet Reynolds number. The lifted flame, which was formed at large central jet pulsation intensities, presented characteristics of a premixed flame due to significant mixing induced by violent, turbulent flow motions. It was short and stable, with high combustion efficiency and low toxic emissions, when compared with the unexcited flame and other excited characteristic flame modes, which presented characteristics of diffusion flame.
TOPICS: Resonance, Acoustics, Jets, Flames, Swirling flow, Excitation, Combustion, Reynolds number, Wire, Irradiation (Radiation exposure), Air jets, Fuels, Turbulence, Temperature, Temperature distribution, Thermocouples, Diffusion flames, Emissions, Loudspeakers, Disks

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