bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupled-Mode Formulation of Acoustic Disturbances in Ducts of Variable Cross-Section With Baffled Ends
Authors: Pierce Allan D. , Cleveland Robin O.
Published: January 2022

Computational techniques are discussed for predicting acoustically induced flow within ducts whose cross-sectional dimensions vary continuously with axial distance along the duct. A formulation is introduced in which both the acoustic pressure and the axial component of the fluid velocity are expanded in terms of the local cross-sectional modal eigenfunctions, these depending implicitly on axial distance. A variational principle is derived and used to derive a set of coupled ordinary differential equations for the modal coefficients. A theory is also developed for the excitation of the field within the duct when a plane wave is incident at the baffled open end of the duct, the other end being closed. A potential application is in the design of an acoustic sensor that makes use of microclectromechanical sensor (MEMS) technology.
Experimental Analysis and Reduction of Alternator Noise
Authors: DiSalvo Michael J. , Wu Sean F.
Published: January 2022

This paper presents the analysis of alternator noise radiation from a passenger vehicle. Experimental data show that the noise spectra contain both narrow- and broad-band sounds, and the overall sound pressure level (SPL) from an unloaded alternator can be as high as 90 dB(A) with the engine running from 3,800 to 5,000 rpm (alternator speed from 11,400 to 15,000 rpm). The overall SPL values seem to be relatively independent of the current output. Results show that only at very low speeds the alternator noise levels increase with the current, and level off as the current increases. At high speeds, the noises are independent of the current. This is because at high speeds the alternator fan noise is so predominant that it masks all other noise sources. When the fans are removed, the overall SPL decreases by 15 to 20 dB (A). A closer look at the fans reveals that they not aerodynamically suited to run at such high speeds. The blades have large inclination angles, poor profiles, contain rough edges and sharp corners. Once the modified fans are installed, the overall SPL values are reduced by 5 dB (A) over the entire speed range. Flow measurements indicate that the cubic feet per minute (CFM) values for the redesigned fans are increased by 47% over the original fans. Furthermore, a working prototype on a two-speed accessory drive system is designed and fabricated. This accessory drive system allows the alternator to run at the optimum speed when the engine is idling, and switches to lower speeds as the engine speeds increase. With this accessory drive system, the alternator can deliver the desired current output with minimum noise radiation.
A Wave Approach for the Free Vibration Analysis of Axially Loaded, Rotating Timoshenko Shaft Systems
Authors: Tan Chin A. , Kang Bongsu
Published: January 2022

A systematic approach for the free vibration analysis of a rotating Timoshenko shaft system subjected to axial forces is presented in this paper. The system has multiple point discontinuities such as elastic supports, rotor masses, and cross-sectional changes. Wave reflection and transmission matrices are employed to characterize the wave motions between the sub-spans of the shaft system. These matrices are combined with the field transfer matrices expressed in wave forms to obtain the characteristic equation in a straight-forward manner. The solutions are exact since effects of attenuating wave components are included in the formulation. The wave propagation-based matrix algebra leads to recursive algorithms which are suitable for computer coding. Three examples are presented to illustrate the numerical procedure.
On a Mode Superposition Method for Fluid-Structure Interaction Problems
Authors: Wang Xiaodong
Published: January 2022

In this paper, we present a mode superposition method for fluid-structure interaction problems based on velocity potential and pressure formulation for acoustic fluids and displacement formulation for solids. The effectiveness of the proposed numerical procedure is demonstrated in a test example with seismic ground motion effects.
Estimating the Probability Distribution of von Mises Stress for Structures Undergoing Random Excitation: Part 2 — Example Calculations
Authors: Segalman Dan , Reese Garth , Field Richard , Fulcher Clay
Published: January 2022

The primary purpose of finite element stress analysis is to estimate the reliability of engineering designs. In structural applications, the von Mises stress due to a given load is often used as the metric for evaluating design margins. For deterministic loads, both static and dynamic, the calculation of von Mises stress is straightforward [2]. For random load environments typically defined in terms of power spectral densities, however, the deterministic theory normally applied to compute RMS acceleration, displacement, or stress tensor responses cannot be applied directly to calculate the probability distribution of von Mises stress, a nonlinear function of the linear stress components. Recently methods have been developed to solve this problem [4]. Those methods and are applied here to an example structure.
Control of Rolling in Ships by Means of Active Fins Governed by a Neural-Network Controller
Authors: Liut Daniel A. , Mook Dean T. , VanLandingham Hugh F. , Nayfeh Ali H.
Published: January 2022

A method to reduce the rolling motion of a ship in a seaway by means of actively controlled fins is described. The method is based on a multidisciplinary simulation: 1) the motion of the ship in a seaway is simulated by a numerical model called LAMP (Large-Amplitude-Motion Program), which is based on a source-panel method to model the flowfield around the ship, 2) the forces on the fins are simulated by a general unsteady vortex-lattice method, and 3) the commands to the fins are generated by a neural network. The ship is considered to be a rigid body and the complete equations of motion are integrated numerically in the time domain so that the motion of the ship and the complete flowfield are calculated simultaneously and interactively. The neural network controlling the fins can be progressively trained by a new moment-matching strategy. The results show substantial reductions in roll.
Active Vibration Control of Smart Composite Beams With Embedded Optical Fiber Sensor and ER Fluid
Authors: Leng Jinsong , Asundi A. , Liu Yanju
Published: January 2022

This paper proposes the use of an fiber optic sensor (FOS) and electrorheological (ER) fluid actuator in the vibration active monitoring of smart composite structures. The intensity modulated fiber optic vibration sensor is developed following the face coupling theory. The characteristics of this optical fiber vibration sensor have been tested. The experimental results show that the new type intensity modulated optical fiber vibration sensor has higher sensitivity to measure the vibration frequency. At same time, our experimental investigations are focused on evaluating the elastodynamic response characteristics of a beam fabricated in an electrorheological fluid. It is noted that the most significant change in the material properties of ER fluid is the change of material stiffness and damping, which varies with the electric field intensity imposed upon ER fluid. Finally, the vibration of smart composite beam with embedded intensity modulated optical fiber vibration sensor and electrorheological fluids can be detected and controlled actively.
Transverse Vibration of Thin Rotating Disks: Nonlinear Modal Analysis
Authors: Hamidzadeh H. R. , Nepal N. , Dehghani M.
Published: January 2022

An analytical method is adopted to determine natural frequencies for a nonlinear spinning disk. The disk is assumed to be isotropic and rotating under steady state conditions. The effects of amplitude and rotating speed on natural frequencies are determined. The developed procedure is also capable of analyzing natural frequencies of linear free vibration, which is independent of amplitude. Attention is confined to determine natural frequencies for different number of nodal diameters. The developed procedure does not consider modes of vibration corresponding to nodal circles. Validity of this procedure is verified by comparing some of the computed results with those established for certain cases.
A Practical Approach for Impact Noise Prediction of Chain Drive Systems
Authors: Zheng H. , Xu Z. , Liu G. R. , Lam K. Y. , Wang Z. Z. , Ito T. , Takamori N.
Published: January 2022

This paper presents an analytical procedure for the noise level prediction of chain drive systems. The roller chain drive system for a motorcycle product is first modeled using finite element techniques and its operation under a typical operating condition is numerically simulated using a commercial software to obtain the acceleration response of each chain roller. An acoustical model relating the acceleration and its induced sound pressure is developed on the basis of the acoustic dipole field created by an oscillating rigid sphere. The acceleration time-histories of all rollers are thus used to predict the sound pressure level radiated by the roller chain drive under different driving conditions. The predicted time-history of sound pressure is further compared with available experimental results. It is shown that the prediction is in reasonable agreement with experimental measurements and the procedure works in an efficient manner for noise prediction of chain drive systems in a virtual acoustical design environment.
Numerical Modeling of Microwave Heating in Containerized Liquids
Authors: Zhang Qiong , Jackson T. H. , Ungan A.
Published: January 2022

This study reports on a three dimensional numerical model to simulate the convection of liquids in a rectangular single-mode microwave cavity. Three-dimensional Finite Difference Time Domain (FDTD) explicit method was employed to predict the electromagnetic field strengths and the absorbed power distributions both in the cavity and the liquid by solving transient Maxwell’s equations. Finite Control Volume method with the SIMPLER algorithm was used to obtain the temperature profiles and flow patterns by solving the unsteady Navier-Stokes equations and energy equations. The nonlinear coupling of the volumetric microwave heating source to the energy equation was handled through an iteration process. The results indicate the coupled phenomena of the microwave resonance, absorption of microwave energy, and convection driven flows. In order to illustrate the phenomena an example of microwave heating of containerized corn oil is provided.
Effect on Natural Convection of the Distance Between an Inclined Discretely Heated Plate and a Parallel Shroud Below
Authors: Manca Oronzio , Nardini Sergio , Naso Vincenzo
Published: January 2022

An experimental investigation into air natural convection on an inclined discretely heated plate with a parallel shroud below has been carried out. Three discrete strips were located in different positions on the heated wall. The distance between the walls, b, has been changed in the range 12.3–40.0 mm and two values of the heat flux dissipated by the heaters have been taken into account. Several inclination angles between the vertical and the horizontal have been tested. The wall temperature distribution as a function of the channel spacing and the inclination angle, the source heat flux, the number and the arrangement of the heat sources is presented. Dimensionless maximum wall temperatures are correlated to the process parameters. Flow visualized patterns of the air are also reported. Local Nusselt numbers are evaluated and correlated to the local Rayleigh numbers and the tilting angles. The analysis shows that for angles not greater than 85°, the greater b does not involve the smaller wall temperatures, whereas at greater tilting angles (> 85°) there is an opposite tendence. These behaviors are confirmed by flow visualization at angles equal to 85° and 90° and b = 20.0 and 32.3 mm. The exponent of monomial correlations among local Nusselt and Rayleigh numbers are in the 0.23–0.26 range.
A Numerical Investigation of the Convective Heat Transfer in Unsteady Laminar Flow Past a Single and Tandem Pair of Square Cylinders in a Channel
Authors: Rosales Jorge L. , Ortega Alfonso , Humphrey Joseph A. C.
Published: January 2022

The unsteady laminar flow and heat transfer characteristics due to a square cylinder located in a channel with a fully-developed inlet velocity profile were studied numerically. The effects of an upstream eddy-promoting cylinder and the effects of the proximity of the cylinder to the channel wall were examined at a fixed cylinder Reynolds number of 500 and Prandtl number of 0.7. The local time-averaged Nusselt number for each face and the time-averaged cylinder Nusselt number were determined, as well as aerodynamic characteristics such as cylinder lift, drag, and eddy-shedding Strouhal number. The results show that the cylinder Nusselt number decreases for both the single and the tandem pair of cylinders as they approach the channel wall. This is primarily due to the reduced mean velocity near the wall. The front face of the cylinder consistently displays the highest Nusselt number. The time-mean drag coefficient decreases for both the single and the tandem cylinders as the wall is approached. The presence of the upstream eddy-promoting cylinder significantly reduces the drag of the downstream cylinder compared to that of the single cylinder but has little effect on the cylinder lift. However, the cylinder overall Nusselt number also decreases, in contrast to previous studies in uniform flow. The eddy shedding Strouhal number increases slightly as the wall is approached and is much larger for the tandem pair than for the single cylinder case for all positions. The amplitude of eddy shedding induced oscillations is significantly dampened as the cylinder approaches the channel wall.
On the Relationship Between Heat Transfer and Drag Reductions for Polymer and Surfactant Solutions
Authors: Aguilar G. , Gasljevic K. , Matthys E. F.
Published: January 2022

Drag-reducing solutions exhibit simultaneous friction and heat transfer reductions, yet it has been widely believed that there is a decoupling between the two effects, an unexplained and puzzling concept. In this work, we have conducted a dedicated study to reexamine this issue, using a wide range of flow conditions from onset to asymptotic, pipe diameters, and various fluids ranging from polymer to surfactant solutions. All our data and those of some other investigators were found to be remarkably well correlated by a constant ratio between the heat transfer and drag reductions over the entire range of conditions examined. In addition, this ratio was found to hold even at and near the onset of drag reduction phenomenon, and also upon departure from the asymptotic regime. We have also shown that the onsets for drag and heat transfer reductions are the same, and that degradation or dilution result in simultaneous departure from asymptotic conditions. All these results support the concept that heat transfer and drag are indeed strongly coupled under all conditions investigated. This information should provide new insight into the fundamental mechanisms underlying the relationship between the drag and heat transfer reduction phenomena. In addition, the practical engineering impact of this finding is very significant in that it allows us now to predict directly the heat transfer from friction measurements or vice-versa, for these fluids.
Effect of Jet Location on Impingement Cooling of a Rotating Disk
Authors: Saniei Nader , Yan Xiaojun
Published: January 2022

Heat transfer results are presented for a rotating disk cooled with an impinging air jet directed on its free surface. In this study, local heat transfer distribution was investigated for a disk under the combination of rotation and jet impingement. The main focus considered here was cooling by pure rotation and the effect of location of the jet center relative to the disk center. Several important factors, such as rotational Reynolds numbers, jet Reynolds numbers, and jet-to-disk spacing were considered when the jet was positioned in different distances from the center of the disk. Disk rotational speed was varied from 250 to 4,000 rpm while three jet Reynolds numbers of 6,800, 24,000, and 48,000 were used. The jet was placed perpendicular to the disk surface at four different distances from the center of the disk. These distances were, zero cm (center-to-center), 3.5 cm, 6.9 cm and 8.9 cm. The jet-to-disk diameter ratio was about 0.09. This ratio was kept constant for this study.

The heat transfer measuring technique for this study was a transient technique which employed liquid crystals. A near uniform wall temperature thermal boundary condition was achieved for the disk by constructing an enclosed insulated oven with well-controlled heating elements and a sliding door on the top for easy access. The results of this investigation reveal that, in most cases for rotating disk with jet impingement cooling, local heat transfer distribution follows a parabolic function which has a minimum at a radial distance (from the disk center) of about one half of the disk radius.
Heat Transfer in Vertically Vibrated Granular Materials
Authors: Wassgren Carl R. , Beasley Donald E. , DeWachter Ryan N.
Published: January 2022

In order to enhance heat transfer from a heated surface to a granular material, the surface is sometimes subject to vibration with the expectation that the oscillations will promote material renewal at the surface and result in increased heat transfer to the bed. Indeed, previous studies have shown that depending on the vibration parameters and bed depth, the bed of material will exhibit a variety of dynamic phenomena including side wall convection cells, surface waves, and kink waves; all of which influence the motion of particles within the bed. This paper investigates the time-averaged heat transfer coefficient from a vertically-vibrated, heated plate to a deep bed of granular material over a range of oscillation parameters. An experimental apparatus was designed consisting of a narrow plexiglass container with a heated copper base embedded in a Delrin jacket. The container was partially filled with soda lime glass spheres and mounted on an electromagnetic shaker which provided the vertical, sinusoidal oscillations with controllable amplitude and frequency. The resulting heat transfer coefficient measurements are presented as a function of the oscillation parameters for oscillation frequencies between 15–60 Hz and oscillation acceleration amplitudes between 0 and approximately 7.0g where g is the acceleration due to gravity. The steady state heat transfer coefficient is found to increase over 300% for an acceleration amplitude between one and two g.
Computational Aspects of the Sectional Modeling Method for Predicting Spray Combustion
Authors: Greenberg J. Barry , Kalma Avinoam
Published: January 2022

In this paper we discuss computational aspects of using the sectional modeling method for calculating combusting sprays. We consider a model problem concerning the propagation of a spherical laminar flame into a mixture of air, fuel vapor and a polydisperse spray of fuel droplets. A detailed description is given of (i) a new numerical treatment of the spray equations for sectional mass and momentum conservation using an implicit scheme and a certain ordering that takes advantage of their special structure, and (ii) a scheme in which the chemical reaction source terms are computed implicitly, thus enabling larger time steps to be used without loss of stability. As an example of the application of the proposed method sample results are presented for the case in which the chemistry is modeled using a global scheme, and for which the droplets are permitted to be in dynamic disequilibrium with their surroundings. These new results (i) demonstrate the efficacy of the numerical procedure, (ii) provide evidence that for a qualitative understanding of spray combustion in the current context it is sufficient to neglect the velocity differences between the gas and liquid phases, and (iii) show that for a quantitative understanding these velocity differences must be accounted for.
Modeling of Thermal Performance of a Porous Radiant Burner
Authors: Fu X. , Viskanta R. , Gore J. P.
Published: January 2022

A one-dimensional model accounting for the interaction of convection, conduction, radiation and chemical reaction in a porous radiant burner/healer has been developed to predict the thermal performance of the natural gas burner. The porous radiant burner consists of two layers of cellular (reticulated) ceramics of different porosity and mechanical structure. The chemical heat release was simulated using a uniform heat source model to avoid the uncertainties associated with chemical kinetics parameters in a reduced chemical mechanism under strongly non-adiabatic conditions. Radiative transfer in the porous medium is modeled using the two-flux approximation. The model predictions reveal quantitatively conjugate heat transfer between convection, conduction, radiation and chemical heat release. A study of the effects of various parameters on the thermal performance of the porous radiant burner and comparison of predictions with experimental data are reported. The results obtained show that the flame thickness in this type of burners is much broader than that of conventional adiabatic combustion due to the strong conduction and radiation feedback from the high temperature (flame) region to the preheat region. The peak gas temperature is lower than that for conventional adiabatic premixed combustion conditions since part of the chemical heat release is convected to the solid.
A Computational Model for Enclosure Fires Incorporating Pyrolysis of Cellulosic Fuel
Authors: Yuen R. , de Vahl Davis G. , Leonardi E. , Yeoh G. H. , Chandrasekaran V.
Published: January 2022

Flame spread and fire over cellulosic materials occur when the burning region supplies sufficient heat to the virgin solid to cause gasification. Under proper conditions, the reaction between the generated volatiles and the oxidant (air) may be sustained. The characteristics of the flame spread are therefore the result of heat and mass transfer processes as well as finite-rate gas phase chemical kinetics.

We describe here a new three-dimensional mathematical model to study flame spread over cellulosic fuels. Both the pyrolysis and burning of a vertical timber wall of a room and the turbulent flow, combustion and radiation in the room, are included. The predictions of this model have been compared with the results of an experiment. Excellent agreement has been achieved.
A Numerical Investigation of the Scaled-up Effects on Flow, Heat Transfer, and Kinetics Processes of FCC Units
Authors: Chang S. L. , Zhou C. Q. , Lottes S. A. , Golchert B. , Petrick M.
Published: January 2022

Fluid Catalytic Cracking (FCC) technology is the most important process used by the refinery industry to convert crude oil to valuable lighter products such as gasoline. Process development is generally very time consuming especially when a small pilot unit is being scaled-up to a large commercial unit because of the lack of information to aide in the design of scaled-up units. Such information can now be obtained by analysis based on the pilot scale measurements and computer simulation that includes controlling physics of the FCC system. A Computational fluid dynamic (CFD) code, ICRKFLO, has been developed at Argonne National Laboratory (ANL) and has been successfully applied to the simulation of catalytic petroleum cracking risers. It employs hybrid hydrodynamic-chemical kinetic coupling techniques, enabling the analysis of an FCC unit with complex chemical reaction sets containing tens or hundreds of subspecies. The code has been continuously validated based on pilot-scale experimental data. It is now being used to investigate the effects of scaled-up FCC units. Among FCC operating conditions, the feed injection conditions are found to have a strong impact on the product yields of scaled-up FCC units. The feed injection conditions appear to affect flow and heat transfer patterns and the interaction of hydrodynamics and cracking kinetics causes the product yields to change accordingly.
Far-Infrared Transmittance and Reflectance of YBa2Cu3O7-δ Films on Si Substrates
Authors: Kumar A. Ravi , Zhang Zhuomin M. , Boychev Vladimir A. , Tanner David B. , Vale Leila R. , Rudman David A.
Published: January 2022

The transmittance and reflectance of superconductive YBa2Cu3O7-δ (YBCO) thin films deposited on Si substrates have been measured in the far-infrared frequency region from 10 to 100 cm−1 (wavelength from 1000 to 100 μm) at temperatures between 10 and 300 K. The effects of interference, optical resonance, and antireflection on the radiative properties of high-temperature superconducting (HTSC) films are observed and quantitatively analyzed. Furthermore, we have measured the reflectance of the HTSC film-substrate composites for radiation incident on the substrate side (backside reflectance) for the first time. The backside reflectance increases significantly from the normal state to the superconducting state at certain frequencies; this experimentally demonstrates that HTSC films can be used to build far-infrared intensity modulators. The complex refractive index of the YBCO films is determined from the measured transmittance using the Drude model in the normal state and a two-fluid model in the superconducting state. The complex refractive index obtained from this study is useful for various applications of YBCO films, including radiation modulators, detectors, and Fabry-Perot resonators.
Radiative Heat Transfer in Periodic Geometries Using a Finite Volume Scheme
Authors: Mathur S. R. , Murthy J. Y.
Published: January 2022

A procedure for computing radiative heat transfer in translationally and rotationally periodic geometries is presented. The finite volume scheme is applied to meshes composed of arbitrary polyhedral control volumes. The angular domain is discretized into a finite number of control angles over which radiant energy is conserved. At periodic boundaries, control angle overhang occurs because of the misalignment of the arbitrary periodic face with the global angular discretization and due to the arbitrary rotation of adjacent modules with respect to each other. A discretization scheme using control angle pixelation is developed to conservatively transfer radiant energy between adjacent modules. The method is tested against analytical solutions and shown to perform satisfactorily.
Class-Room Experiences and Impact Evaluation of the Educational Software Heat Transfer 1.0 in a Heat Conduction Course
Authors: Maliska Clovis R. , Filgueiras dos Reis Marcus V. , Dihlmann Axel
Published: January 2022

This paper reports the first classroom experience using the package Heat Transfer 1.0 (Maliska et al, 1997) in an introductory heat conduction course. The key objective in conceiving Heat Transfer 1.0 was to stimulate the physical reasoning in heat transfer, bringing to the students the possibility of having intimacy with the flow of heat in physical situations where this flow is more complex than the usual 1D patterns presented in normal textbooks. Therefore, the basic idea behind its conceptual form was to have more than merely a tool to help the student to solve the heat conduction equation. The key objective was to create a tool that allows students to formulate new problems and to speculate about its physical behavior. More, the software should appear attractive and easy-to-use, becoming part of the students toolbox, and not seen as “one more package” whose use is compulsory in the course. Student’s opinions taken through a questionnaire submitted to them just after the end of the course revealed that they found the software easy-to-use and that it broadened their knowledge of conduction heat transfer.
An Analytical Study of Turbine Disks Incorporating Radially Rotating Heat Pipes
Authors: Cao Yiding , Chang Won S. , MacArthur Charles D.
Published: January 2022

In modern aero-engines, a turbine disk is normally cooled by compressed air bled from the engine compressor. A literature survey regarding the turbine disk cooling reveals that although the average air-cooling heat transfer coefficient is generally high, the local heat-transfer coefficient at the disk rim is low. Impinging jet cooling could be used to enhance the heat transfer at the rim, but its implementation is costly. One of the major causes of the high temperature at the rim is the low thermal conductivity associated with the turbine disk material. Based on this understanding, a turbine disk that incorporates radially rotating heat pipes has been introduced. The incorporation of the heat pipe would significantly increase the effective thermal conductance of the disk and spread the heat from the disk rim to a much large surface area, A unique disk design that employs interconnected heat pipe branches is also described for the purpose of cost reduction. To evaluate the effectiveness of the new turbine disk, a simplified analysis based on the one-dimensional and steady-state assumptions is made. The analytical results indicate that a disk that incorporates the heat pipe could reduce the disk rim temperature by more than 300°C, with only a moderate increase in the disk bore temperature. A turbine disk that employs rotating heat pipes is very effective for the disk rim temperature reduction. It also represents a new approach for cooling turbine rotor blades, and could find important applications in advanced gas turbines working at very high inlet temperatures.
A Frozen Startup Limit for Room Temperature Heat Pipes
Authors: Allred R. S. , Ochterbeck J. M.
Published: January 2022

The frozen startup performance of two room temperature heat pipes (one copper/water and one stainless-steel/biphenyl) was investigated. Biphenyl was selected as the second fluid due to its above ambient melting temperature of 69°C. The effects of steady-state input power, restart power, and non-condensable gas (NCG) charging on startup were examined. Also, the effects of the evaporator/ condenser length ratio were examined using the stainless-steel/biphenyl heat pipe. The presence of a non-condensable gas charge was found to have a more pronounced effect on startup characteristics than restart power or geometry. For cases typically of greater evaporator length to condenser length, the presence of NCG was not required to restart a room temperature heat pipe from the frozen state. All other cases were found to require NCG charging to successfully restart. Additionally, a previous analytical frozen startup limit developed for liquid metal heat pipes was modified for room temperature heat pipes to predict startup success/failure. It was shown that the newly developed frozen startup limit can successfully predict the startup performance of room temperature heat pipes.
Microtube Convection Heat Transfer for a Power-Law Fluid in Laminar Slip Flow With an Isoflux Boundary Condition
Authors: Wang Meili , Ameel Tim A. , Frazier A. Bruno , Warrington Robert O.
Published: January 2022

An analytical solution to the problem of flow in a tube with a diameter of the same order as the mean free path of the fluid is presented. Under these conditions, the Knudsen number becomes an important parameter and the fluid may exhibit slip flow and thermal nonequilibrium at the tube walls. A power-law fluid is considered to be hydrodynamically fully developed at the tube entrance and an isoflux thermal condition is assumed. A direct solution technique is applied to the Energy Equation to determine the temperature field in the thermal entrance region of the tube as well as in the thermally fully-developed region. The direct solution technique is in contrast to an indirect method reported earlier for a Newtonian fluid only. For all values of the Knudsen number, the fully-developed Nusselt number is seen to increase with a decreasing flow index n. The increase in the fully-developed Nusselt number for a shear-thinning non-Newtonian fluid (n = 0.5) relative to that for the Newtonian fluid (n = 1) decreases from approximately 9 to 3.5 percent as the Knudsen number increases from 0 (non-slip flow) to 0.12. Thus, the slip flow and temperature jump effects tend to diminish the non-Newtonian effects as they apply to the temperature field.
A Parameter Estimation Technique for Determining Soil Thermal Properties in the Design of Heat Exchangers for Geothermal Heat Pumps
Authors: Beck James V. , Shonder John A.
Published: January 2022

A one-dimensional thermal model is derived to describe the temperature field around a vertical borehole heat exchanger (BHEx) for a geothermal heat pump. The inlet and outlet pipe flows are modeled as one, and an effective heat capacity is added to model the heat storage in the fluid and pipes. Parameter estimation techniques are then used to estimate various parameters associated with the model, including the thermal conductivity of the soil and of the grout which fills the borehole and surrounds the u-tube. The model is validated using test data from an experimental rig containing sand with known thermal conductivity. The estimates of the sand thermal conductivity derived from the model are found to be in good agreement with independent measurements.
Numerical Analysis of Fluid Flow and Heat Transfer in Plate-and-Frame Heat Exchangers
Authors: Sundén Bengt , Di Piazza Ivan
Published: January 2022

A numerical investigation of laminar and turbulent convective flow and heat transfer for single-phase flow in plate-and-frame heat exchangers is carried out. A unit cell is considered and a finite volume technique is applied for solving the governing equations. Periodic flow and heat transfer fields are assumed. For turbulence modelling the RNG k-ε model is adopted. The grid is created by using a multiblock approach and the unit cell is covered by a three-dimensional array of hexahedral control volumes in a structured body-fitted grid fashion. The Reynolds number range is from 900 to 20 000 while the Prandtl number is set to 4.33 corresponding to water at an average temperature of 40°C. The agreement between the numerical results and available experimental data is decent and encouraging. The details of the flow and temperature fields achieved by the numerical solutions, improved the understanding of the transport processes of heat and momentum.
Effect of Inlet Header Pre-Heating on the Temperature Distribution in a Steam Furnace Tube Bank
Authors: Botros Kamal K. , Weiss Marvin H. , Price Glenn R.
Published: January 2022

Steam furnaces encountered in chemical and power generation plants often experience a maldistribution of steam temperature at furnace tube outlets despite attempts to ensure good flow distribution in these tubes from the inlet feed header. An investigation of an existing tube bank configuration was carried out utilizing field measurements, a CFD analysis of the thermal/flow field, flow experiments with a 1:7 scale laboratory model using air as the working fluid, and a 1-D analysis of the temperature/flow distribution. The results indicate that although the inlet header does not actually run through the furnace, heat transfer by conduction from the tube walls to the inlet header wall causes preheating of the incoming steam, resulting in a substantial increase in steam temperature towards the end of the header. This steam temperature maldistribution at the inlet to the tubes persists along the tubes and manifests itself as a similar maldistribution in the tube skin wall temperatures. The latter has an impact on the system integrity if the skin wall temperature exceeds the metallurgical limit of the tube material used.
The Convective Transport Phenomena Over a Turbine Blade Near the Endwall Region With and Without Film Cooling
Authors: Miao Jr-Ming , Chen Ping-Hei
Published: January 2022

The present study aims to investigate the film cooling effect on the local mass transfer distributions on both suction and pressure surfaces near the endwall region of a showerhead film-cooled turbine blade by employing the naphthalene sublimation technique. The mass transfer measurements are also conducted with a smooth turbine blade for comparison. For film-cooled blade, there are three rows of injection holes staggered at the leading edge of test blade. Each row consists of seven equally spaced injection holes at a ratio of pitch to diameter equals 3. The inclined angles of injection hole are 90 degrees to the streamwise direction and 30 degrees to spanwise direction. The closest distance from the center of injection hole located on the front stagnation line to the endwall is just one pitch of hole. Experiments are conducted over a six-blade planar cascade in an open-type wind tunnel with mainstream turbulence level of 0.4%, inlet boundary layer momentum thickness of 0.955 and shape factor of 1.355. For all measurements, the exit Reynolds number is kept at a constant value of 397,000 and the blowing ratio is 0.8.

Close to the endwall the local mass transfer rate over both surfaces of the tested smooth turbine blade is much higher than that in the two-dimensional flow region. Measured results indicate that the vortex system on the suction side of tested smooth blade consists of a leading edge corner vortex, a suction leg of horseshoe vortex, a suction side corner vortex, a passage vortex and the wall vortex induced by the strong passage vortex. Downstream of S/C ≈ 0.431, the passage vortex and the wall vortex become dominant. On the pressure side of smooth turbine blade, the leading edge corner vortex, the pressure leg of horseshoe vortex and the pressure corner vortex are still visible but they all are swept out from the blade surface by the secondary flows at Sp/C ≈ 0.256.

The presence of film cooling has little influence on the leading edge corner vortex and suction side corner vortex but results in a later induction of comer vortex on pressure side compared to that without film cooling. Instead of a three-peak vortex system, the impact location of the passage vortex occurs far downstream. Therefore, the wall vortices induced by passage vortex that might be observed from smooth blade vanished in the mid-curvature portions of suction side of film-cooled blade. In addition, the ejected flows hold the leading edge comer vortex and the pressure side corner vortex on the pressure side of film-cooled blade.
Measurements of Aerodynamic Penalties Associated With Film Cooling
Authors: Burd Steven W. , Oke Rohit A. , Simon Terrence W.
Published: January 2022

Film cooling in gas turbine engine designs has shown great benefit over the years. Film cooling flows perturb the boundary layer flow, however, as they emerge from discrete holes. The impact on aerodynamics is experimentally evaluated for both streamwise and lateral film cooling injection. Injection is with a hole length-to-diameter ratio of 2.3 and a 35° angle of inclination. Data for two coolant-to-freestream momentum flux ratios, 0.25 and 1.0, with a high freestream turbulence intensity of 11.3% are given. Comparisons are made to similar cases without coolant injection. Evaluation is in terms of momentum thickness, shape factor, and skin friction coefficient distributions. Turbulence data are also provided. The injection geometry and coolant-to-freestream momentum flux ratio are shown to greatly influence aerodynamic penalties. Lateral injection imposes more losses, but lower skin friction values, than does streamwise injection. In some instances, the emerging coolant is capable of energizing the boundary layer, reducing losses relative to those present without coolant injection.
Enhanced Heat Transfer Charateristics of a Chevron Plate Heat Exchanger for Viscous Fluid Thermal Processing Applications
Authors: Muley Arun , Manglik Raj M.
Published: January 2022

Steady-state heat transfer and pressure drop data are presented for single-phase viscous fluid flows (2 ≤ Re ≤ 400) in a plate heat exchanger (PHE) with chevron plates. With vegetable oil as test fluid (130 < Pr < 290), the data are for three different plate arrangements, two symmetric (β = 30°/30° and 60°/60°) and one mixed (β = 30°/60°), in a single-pass, U-type, counter-flow PHE. The effects of chevron angle β, and flow conditions (Re, Pr, μ/μw) on Nu and f characteristics of the PHE are investigated. Depending upon β and Re, up to 3 times higher Nu are obtained in chevron plates compared to an equivalent flat-plate channel, though the corresponding f are also up to 6.6 times higher. Comparisons of these data with previously reported Nu and f results highlight the complex influence of chevron plate surface corrugations. Also, relative to equivalent flat-plate packs, chevron plates sustain up to 2.9 times higher heat transfer rates on a fixed geometry and constant pumping power basis, and require up to 48% less surface area for the fixed heat load and pressure drop constraint.
Experimental and 2-D Numerical Studies on Micro-Scale Bending of Stainless Steel With Pulsed Laser
Authors: Chen Guofei , Xu Xianfan , Poon Chie C. , Tam Andrew C.
Published: January 2022

Laser forming or laser bending is a newly developed, flexible technique which modifies the curvature of sheet metal by thermal residual stresses instead of external forces. The process is influenced by many parameters such as laser parameters, material properties and specimen dimensions. In this work, a pulsed Nd:YLF laser was used as the energy source. The laser beam was focused into a line shape irradiating on the stainless steel specimen to induce bending. The bending angle was measured at various processing conditions. A finite element analysis was performed with the use of a 2-D plane strain model to simulate the temperature field and the thermo-elasto-plastic deformation process. Experimental measurement and computational results were in good agreement. Numerical sensitivity studies were performed to evaluate the effects of the unavailable material property data at high temperature. It was found that both optical reflectivity and thermal expansion coefficient influenced the bending angle significantly, while other extrapolated material properties at high temperatures yielded acceptable results.
Interfacial Phase Growth in Metal Matrix Composites
Authors: Chen J. K. , Beraun J. E. , Tzou D. Y.
Published: January 2022

The time dependence of a reinforcement-matrix interfacial layer growth (RMILG) in most metal matrix composites (MMCs) is not t1/2 as described by Fick’s diffusion law. Moreover, the RMILG versus t1/2 could be linear for relatively short and long times, and an anomalous transition behavior exhibits in between. In this paper a dual-phase-lag diffusion (DPLD) model, extending from Fick’s diffusion law, is proposed to characterize the RMILG kinetics. It accounts for two lagging times required for the interdiffusion process between dissimilar materials and the chemical reaction that forms an interfacial compound. This inclusion of the lagging times uniquely represents the four types of growth kinetics and can capture multiple-stage response over the entire RMILG history. Numerical results show that the DPLD modeling agrees very well with experimental data.
Modeling of Fluid Flow and Heat Transfer in a Hydrothermal Crystal Growth System: Use of Fluid-Superposed Porous Layer Theory
Authors: Chen Q.-S. , Prasad V. , Chatterjee A.
Published: January 2022

Hydrothermal synthesis, which uses aqueous solvents under high pressure and relatively low temperature, is an important technique for the growth of crystalline materials such as quartz, bismuth silicate and various kinds of oxides, all of which are difficult to grow. A hydrothermal growth system usually consists of finely divided particles of the nutrient, predetermined volume of a solvent and a suitably oriented crystal seed (Fig. 1) under very high pressures, generally several thousand psi. The nutrient dissolves at a higher temperature in the lower region, moves to the upper region due to buoyancy-induced convective flows and deposits on the seed due to lower solubility if the seed region is maintained at a lower temperature. The system can be modeled as a composite fluid and porous layer using the Darcy-Brinkman-Forchheimer flow model in the porous bed. Since the growth process is very slow, the process can be considered quasi-steady and the effect of dissolution and growth can be neglected. This first study on transport phenomena in a hydrothermal system therefore focuses on the flow and temperature fields without the presence of the seed and mass transfer. A three-dimensional algorithm based on the curvilinear finite volume technique and a non-staggered grid layout has been developed to simulate the flow and heat transfer in a typical autoclave system. An axisymmetric flow pattern at low Grashof numbers and three dimensional flow pattern at high Grashof numbers are predicted. The study is also extended to study the onset of oscillatory flow with a variation in the porous bed height. These results, for the first time, depict the possible flow patterns in a hydrothermal system, that can have far reaching consequences on the growth process and crystal quality.
Substrate Melting and Resolidification After Contact With a Molten Layer of High Melting Point Material
Authors: Wang S.-P. , Wang G.-X. , Matthys E. F.
Published: January 2022

High-melting-point metals and their alloys have wide use as coating materials because of their improved properties. A good understanding of the bonding mechanism between the coating layer and the substrate is therefore a very important concern in thermal spray processing of these high-melting-point materials. In this work we have conducted a numerical study of the cooling and solidification of such materials, and in particular of the substrate melting and resolidification phenomena for a substrate impacted by a high melting point droplet. A model has been developed and a non-dimensional analysis led to the identification of the independent non-dimensional parameters controlling the process. The critical conditions needed for substrate melting in the case of given pairs of deposit and substrate materials were quantified, and are presented in terms of non-dimensional operational maps of wide applicability. Information on the critical conditions under which the substrate surface melts, and on the maximum melting depth achieved into the substrate was also generated for various process parameters including deposit undercooling, initial substrate temperature, variations in interfacial heat transfer coefficient, and others.
Depth of Thermal Penetration in the Fast Transient Process of Heat Transport
Authors: Tzou D. Y. , Chiu Kevin K. S. , Beraun Jorge E. , Chen J. K.
Published: January 2022

This work studies the depth of thermal penetration in the fast-transient process of heat transport, with emphasis on the rapid evolution of heat affected zone that reflects the combined behavior of thermalization and relaxation during the short-time transient. Employing the dual-phase-lag model, the heat balance integral is derived that contains both the phase lag of the heat flux vector (reflecting the relaxation behavior) and the phase lag of the temperature gradient (reflecting the thermalization behavior). The early-time responses where both phase lags are strong functions of temperature are modeled in detail, which emphasize the ways in which the classical diffusion behavior is retrieved as the thermalization and relaxation behaviors gradually diminish in the time-history. It shows that the classical diffusion model assuming Fourier’s law does not provide a conservative estimate for the response of temperature in the thermal process zone, which may result in unexpected early-time failure of conductors if not properly controlled. From a microscopic point of view, these unexpected factors are interpreted in terms of the microscopic parameters, including the coupling factor in phonon-electron interactions (for metallic structure) and the umklapp and normal relaxation times in phonon scattering (for semiconductors and insulators.