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Accepted Manuscripts

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research-article  
Lu Junfeng and Lu Wen-qiang
J. Heat Transfer   doi: 10.1115/1.4037337
To allow a better adsorption performance inside a novel magnetic adsorption device designed in the process of hemodialysis, the mechanical properties of magnetic absorbents trapped inside a two-phase system are studied in this paper. A gradient magnetic coil field was assumed to produce the magnetic driving force that balances other hydraulic forces for the adsorbents. Applying this field, a complement practical form of winding equation for the solenoid coil is obtained. The case studies are also made in this paper to explore the design of the field.
TOPICS: Electric current, Magnetic fields, Absorbents, Mechanical properties, Design, Magnetic particles, Solenoids, Winding (process), Hemodialysis
research-article  
Yong Ren, Kai Seng Koh, Jit Kai Chin, Jing Wang, Conghua Wen and Yuying Yan
J. Heat Transfer   doi: 10.1115/1.4037338
With a novel platform of bilayer polydimethylsiloxane (PDMS) microchannel formed by bifurcated junction, we aim to investigate droplet formation and fission in a multiphase system with complex 3D structure; and understand the variations in mechanism associated with droplet formation and fission in the microstructure between shear-thinning/Newtonian system versus Newtonian/Newtonian system. The investigation concentrates on shear-thinning fluid because it is one of the most ubiquitous rheological properties of non-Newtonian fluids. Sodium carboxymethyl cellulose (CMC) solution and silicon oil have been used as model fluids and numerical model has been established to characterize the shear-thinning effect to formation of CMC-in-oil emulsions, as well as breakup dynamics when droplets flow through 3D bifurcated junction. The droplet volume and generation rate have been compared between two systems at the same Weber number and Capillary number. Variation in droplet fission has been found between two systems, demonstrating that the shear-thinning property and confining geometric boundaries significantly affect the deformation and breakup of each mother droplet into two daughter droplets at bifurcated junction. The understanding of the droplet fission in the novel microstructure will enable more versatile control over the emulsion formation and fission when non-Newtonian fluids are involved. The model systems in the study can be further developed to investigate the mechanical property of emulsion templated particles such as drug encapsulated microcapsules when they flow through complex media structures, such as blood capillaries or the porous tissue structure, which feature with bifurcated junction.
TOPICS: Nuclear fission, Drops, Shear (Mechanics), Microchannels, Junctions, Emulsions, Non-Newtonian fluids, Fluids, Flow (Dynamics), Ceramic matrix composites, Rheology, Deformation, Particulate matter, Computer simulation, Biological tissues, Blood, Drugs, Mechanical properties, Plasma desorption mass spectrometry, Dynamics (Mechanics), Silicon, Sodium
research-article  
Samuel D. Marshall, Rerngchai Arayanarakool, Lakshmi Balasubramaniam, Bing Li, Poh Seng Lee and Peter C. Y. Chen
J. Heat Transfer   doi: 10.1115/1.4037339
The efficiency of conventional heat exchangers is restricted by many factors, such as effectiveness of convective heat transfer and cost of operation. The current research deals with these issues by developing a novel method for building a lower-cost yet more efficient heat sink. This method involves using a specially designed curved microchannel to utilise the enhanced fluid mixing characteristics of Dean vortices, and thus transferring heat efficiently. Numerical models have been employed to investigate the heat transfer enhancement of curved channels over straight equivalents, with the aim of optimising the heat exchanger design based on the parameters of maximising heat transfer whilst minimising pressure drop and unit cost. A range of cross-sectional geometries for the curved channels were compared, showing significantly higher Nusselt Numbers than equivalent straight channels throughout, and finding superior performance factors for square, circular and symmetrical trapezoidal profiles. Due to the difficulty and expense in manufacturing circular microchannels, the relatively simple to fabricate square and symmetrical trapezoidal channels are put forward as the most advantageous designs. The variation of Nusselt Number over the length of the channel for a range of different curvatures (and hence Dean numbers) is also examined, showing significantly higher heat transfer occurring in areas where the generated Dean vortices are strongest. The variation in Nusselt Number was found to form the shape of an 'arc'. In this way, a relationship between the Dean Number and the Nusselt Number is characterised and discussed, leading to suggestions regarding optimal microfluidic heat transfer design.
TOPICS: Microfluidics, Heat exchangers, Vortices, Geometry, Heat transfer, Symmetry (Physics), Design, Microchannels, Heat sinks, Pressure drop, Shapes, Heat, Convection, Fluids, Computer simulation, Manufacturing
research-article  
Tingting Hao, Xuehu Ma and Zhong Lan
J. Heat Transfer   doi: 10.1115/1.4037341
Flow patterns and heat transfer performance in the start-up stage of oscillating heat pipes (OHPs) with different surface wetting characteristics were investigated. The inner surfaces of the OHPs were superhydrophilic surface, hydrophilic surface, copper, hydrophobic surface, and superhydrophobic surface, respectively. Results showed that the start-up performance was improved in hydrophilic OHP and deteriorated in hydrophobic OHP as opposed to the copper OHP. For the OHPs with hydrophilic surface, the phenomena of vapor expansion and contraction accompanying liquid slug oscillatory movements, and the OHPs started up. There was a thin liquid film between the vapor bubble and the surface. However, the hydrophobic OHP failed to start up. For the superhydrophobic OHP, nucleate boiling took place in the evaporation section. Heat transfer results showed that wall temperature fluctuations were observed at the start-up stage. The start-up time for the hydrophilic OHP was lowest in the five OHPs and the amplitude of temperature oscillations in hydrophilic OHP was higher than that in the copper OHP.
TOPICS: Heat pipes, Copper, Heat transfer, Vapors, Oscillations, Flow (Dynamics), Temperature, Fluctuations (Physics), Bubbles, Wetting, Evaporation, Slug flows, Wall temperature, Nucleate boiling, Lubrication theory
research-article  
Dhruv C Hoysall, Khoudor Keniar and Srinivas Garimella
J. Heat Transfer   doi: 10.1115/1.4037342
Microchannel heat exchangers offer the potential for high heat transfer coefficients; however, implementation challenges must be addressed to realize this potential. Maldistribution of phases among the microchannels and the changing phase velocities associated with phase change present design challenges. Flow maldistribution and oscillatory instabilities can affect transfer rates and pressure drops. In condensers, evaporators, absorbers and desorbers, changing phase velocities can change prevailing flow regimes from favorable to unfavorable. Geometries with serpentine passages containing pin fins can be configured to maintain favorable flow regimes throughout the component for phase-change heat and mass transfer applications. Due to the possibility of continuous redistribution of the flow across the pin fins along the flow direction, maldistribution can also be reduced. These features enable high heat transfer coefficients, thereby achieving considerable compactness. The characteristics of two-phase flow through a serpentine passage with micro-pin fin arrays with diameter 350 µm and height 406 µm are investigated. An air-water mixture is used to represent two-phase flow through the serpentine test section, and flow features are investigated using high-speed photography. Improved flow distribution is observed in the serpentine geometry. Distinct flow regimes, different from those observed in microchannels, are also established. Void fraction and interfacial area along the length of the serpentine passages are compared with the corresponding values for microchannels. A model developed for the two-phase frictional pressure drops across this serpentine micro-pin fin geometry predicts experimental values with a mean absolute error of 7.16%.
TOPICS: Heat exchangers, Microscale devices, Two-phase flow, Visualization, Fins, Flow (Dynamics), Microchannels, Heat transfer coefficients, Geometry, Pressure drop, Water, Porosity, Photography, Heat, Mass transfer, Design, Condensers (steam plant), Errors
research-article  
Daniel Lorenzini and Yogendra Joshi
J. Heat Transfer   doi: 10.1115/1.4037343
The computational fluid dynamics (CFD) modeling of boiling phenomena has remained a challenge due to numerical limitations for accurately simulating the two-phase flow and phase-change processes. In the present investigation, a CFD approach for such analysis is described using a three-dimensional (3D) Volume of Fluid (VOF) model coupled with a phase-change model accounting for the interfacial mass and energy transfer. This type of modeling allows the transient analysis of flow boiling mechanisms, while providing the ability to visualize in detail temperature, phase, and pressure distributions for microscale applications with affordable computational resources. Results for a plain microchannel are validated against benchmark correlations for heat transfer coefficients and pressure drop as a function of the heat flux and mass flux. Furthermore, the model is used for the assessment of two-phase cooling in microelectronics under a realistic scenario with non-uniform heat fluxes at localized regions of a silicon microchannel, relevant to the cooling layer of 3D integrated circuit (IC) architectures. Results indicate the strong effect of two-phase flow regime evolution and vapor accumulation on heat transfer. The effects of reduced saturation pressure, subcooling and flow arrangement are explored in order to provide insight about the underlying physics and cooling performance.
TOPICS: Flow (Dynamics), Modeling, Boiling, Microchannels, Heat flux, Computational fluid dynamics, Cooling, Two-phase flow, Pressure, Physics, Microscale devices, Heat transfer coefficients, Accounting, Architecture, Integrated circuits, Pressure drop, Silicon, Subcooling, Transient analysis, Microelectronic devices, Fluids, Vapors, Flux (Metallurgy), Heat, Temperature, Energy transformation, Heat transfer
research-article  
Fengmin Su, Nannan Zhao, Yangbo Deng and Hongbin Ma
J. Heat Transfer   doi: 10.1115/1.4037327
Ultra-fast cooling is the key to successful cell vitrification cryopreservation of lower concentration cryoprotective solution. This research develops a cell cryopreservation methodology which utilizes thin film evaporation and achieves vitrification of relatively low concentration cryoprotectant with an ultra-fast cooling rate. Experimental results show that the average cooling rate of dimenthylsulphoxide cryoprotective solution reaches 150,000°C/min in a temperature range from 10°C to -180°C. The ultra-fast cooling rate can remarkably improve the vitrification tendencies of the cryoprotective solution. This methodology opens the possibility for more successful cell vitrification cryopreservation.
TOPICS: Cryonics, Vitrification, Cooling, Cell vitrification, Evaporation, Thin films, Temperature
Guest Editorial  
Zhuomin Zhang, Chun Yang and Robert D. Tzou
J. Heat Transfer   doi: 10.1115/1.4037326
None
TOPICS: Heat, Mass transfer, Nanoscale phenomena
research-article  
Lakehal Abdelhak, Nait Bouda Nora, Pellé Julien and Harmand Souad
J. Heat Transfer   doi: 10.1115/1.4037208
Both experimental and numerical studies of a turbulent flow in a bifurcating channel are performed to characterize the dynamical behavior of the flow and its impact on the convective heat transfer on the sides of the branch. This configuration corresponds to the radial vents placed in the stator vertically to the rotor-stator air gap in theelectrical machines. Indeed, our analysis focuses on the local convective heat transfer on the vents internal surface under a turbulent mass flow rate. The flow field measurements were carried with two components particle image velocimetry (PIV) system and the local heat transfer on the sides of the bifurcation branch was measured using an infrared thermography device. The convective heat transfer and the flow dynamics through the geometry are investigated numerically considering a three-dimensional flow. The closure system of the Navier- Stokes equations for steady and incompressible flow is based on the low-Reynolds numbers RSM-model (RSM-Stress-?). The comparison of the three-dimensional computed results with the measurements in the xy symmetry plane is satisfactory in the vertical and horizontal channels. The numerical prediction of the secondary flow in the vertical branch was analyzed and complement the experimental results. It particularly noticed that accelerated flow observed at the right side of the branch's inlet allows more pronounced heat transfer comparatively to the left side.
TOPICS: Flow (Dynamics), Convection, Heat transfer, Turbulence, Stators, Vents, Thermography, Stress, Machinery, Particulate matter, Rotors, Bifurcation, Geometry
research-article  
Wei Zheng, Xiangyi Zhang, Rong Ma and Yong Li
J. Heat Transfer   doi: 10.1115/1.4037194
Transient thermal behavior modeling and computation is a key issue in predicting flight performance of a stratospheric lighter-than-air (LTA) vehicle, such as an airship or balloon. To reduce computational load of the numerical thermal transient model without significant loss of accuracy, firstly this paper adopted an analytical model of view factor from the element surface to the earth, and constructed a full distributed parameter transient thermal model. Then the full model was validated by comparing simulation output data with flight experimental data. The results show that the difference between simulation and experimental data is less than 2.4%. Furthermore, considering that the effect of the net radiation heat transfer among the hull inner surface enclosure on average inner gas temperature is far less than the hull outer surface, the full model was simplified by omitting radiant heat exchange within the inner surface enclosure. The model discrepancy was investigated by comparing the simulation results of average inner gas temperature and skin temperature distribution between the two models under various conditions, such as operating time, altitude, different exterior skin thermal properties. The comparison results indicate that the simplified model agreed well with the full model. A maximum deviation is about 0.3% for the average inner gas temperature in most conditions, and the difference of temperature distribution of the surface between the two models is also allowable when the LTA vehicle, especially with low absorptivity/emissivity ratio coatings, operates at about 20km altitude.
TOPICS: Vehicles, Temperature, Transients (Dynamics), Simulation, Skin, Temperature distribution, Flight, Hull, Computation, Radiant heat, Simulation results, Stress, Emissivity, Thermal properties, Modeling, Heat transfer, Coatings, Radiation (Physics)
research-article  
Christophe Frankiewicz and Daniel Attinger
J. Heat Transfer   doi: 10.1115/1.4037162
Solid-fluid interfaces switching from a superhydrophilic to a superhydrophobic wetting state are desired for their ability to control and enhance phase change heat transfer. Typically, these functional surfaces are fabricated from polymers and modify their chemistry or texture upon the application of a stimulus. For integration in relevant phase change heat transfer applications, several challenges need to be overcome, of chemical stability, mechanical and thermal robustness, as well as large scale manufacturing. Here, we describe the design and fabrication of metallic surfaces that reversibly switch between hydrophilic and superhydrophobic states, in response to pressure and temperature stimuli. Characterization of the surfaces in pool boiling experiments verifies their thermal and mechanical robustness, and the fabrication method is scalable to large areas. During pool boiling experiments, it is experimentally demonstrated that the functional surfaces can be actively switched between a high-efficiency mode suitable for low heat fluxes, and a high-power mode suitable for high heat flux applications.
TOPICS: Heat transfer, Boiling, Manufacturing, Pool boiling, Robustness, Switches, Heat flux, Chemical stability, Design, Polymers, Chemistry, Flux (Metallurgy), Wetting, Metal surfaces, Texture (Materials), Fluids, Pressure, Heat, Temperature
research-article  
Abdul Khan, Nejdet Erkan and Koji Okamoto
J. Heat Transfer   doi: 10.1115/1.4037154
During a severe accident, ex-vessel cooling may pose a risk for larger-powered reactors. The current In-Vessel Retention (through ex-vessel cooling) capability may not be sufficient for the larger-powered reactors, and Critical Heat Flux (CHF) conditions may eventually lead to vessel failure. A manner in which the CHF can be increased is by applying a structured surface design on the outer surface of the Reactor Pressure vessel. A simple design proposed in this work is the pin-fin. An experimental investigation was performed to observe the effect of the pin-fin on CHF with a downward-facing heated surface in flow boiling conditions. A reduced pressure of increase in the CHF when compared to a bare surface. An average CHF enhancement of 61% approximately 0.05 MPa allowed for saturation at approximately 81 °C. A range of flow rates corresponding to mass flux of 202 - 1456 kg/m2-s were applied in the experiments. The results showed an was observed from the finned surface. An enhancement of approximately 19% was observed in the heat transfer coefficient. As seen in nanoparticle/nanofluid enhancement, an increase in the CHF also leads to an increase in the superheat. Even though an increase in the CHF had been observed, the CHF for the finned and bare surfaces occurred at approximately similar superheat.
TOPICS: Flow (Dynamics), Heat transfer, Boiling, Critical heat flux, Vessels, Design, Cooling, Nanoparticles, Accidents, Failure, Nanofluids, Heat transfer coefficients, Reactor vessels, Risk, Pressure
research-article  
Yu Feng, Jie Cao, Xin Li, Silong Zhang, Jiang Qin and Yu Rao
J. Heat Transfer   doi: 10.1115/1.4037086
An idea of using dimples as heat transfer enhancement device in a regenerative cooling passage is proposed to extend the cooling limits for liquid-propellant rocket and scramjet. Numerical studies have been conducted to investigate the flow and heat transfer characteristics of supercritical hydrocarbon fuel in a rectangular cooling channel with dimples applied to the bottom wall. The numerical model is validated through experimental data and accounts for real fuel properties at supercritical pressures. The study shows that the dimples can significantly enhance the convective heat transfer and reduce the heated wall temperature. The average heat transfer rate of the dimpled channel is 1.64 times higher than that of its smooth counterpart. While the pressure drop in the dimpled channel is only 1.33 times higher than that of the smooth channel. Furthermore, the thermal stratification in a regenerative cooling channel is alleviated by using dimples. Although heat transfer deterioration of supercritical fluid flow in the trans-critical region cannot be eliminated in the dimpled channel, it can be postponed and greatly weakened. The strong variations of fuel properties are responsible for the local acceleration of fuel and variation of heat transfer performance along the cooling channel.
TOPICS: Fuels, Flow (Dynamics), Heat transfer, Cooling, Computer simulation, Supercritical fluids, Convection, Pressure drop, Propellants, Rockets, Wall temperature, Thermal stratification, Scramjets
research-article  
Ammar Alsabery, Ali J. Chamkha, Ishak Hashim and Pradeep G. Siddheshwar
J. Heat Transfer   doi: 10.1115/1.4037087
The effects of non-uniform heating and a finite wall thickness on natural convection in a square porous cavity based on the local thermal non-equilibrium (LTNE) model are studied numerically using the finite difference method. The finite thickness horizontal wall of the cavity is heated either uniformly or non-uniformly and the vertical walls are maintained at constant cold temperatures. The top horizontal insulated wall allows no heat transfer to the surrounding. The Darcy law is used along with the Boussinesq approximation for the flow. The results of this study are obtained for various parametric values of the Rayleigh number, thermal conductivity ratio, ratio of the wall thickness to its height and the modified conductivity ratio. Comparisons with previously published work verify good agreement with the proposed method. The effects of the various parameters on the streamlines, isotherms, and the weighted average heat transfer are shown graphically. It is shown that a thicker bottom solid wall clearly inhibits the temperature gradient which then leads to the thermal equilibrium case. Further, the overall heat transfer is highly affected by the presence of the solid wall. The results have possible applications in the heat-storage fluid-saturated porous systems and the applications of the high power heat transfer.
TOPICS: Heat conduction, Convection, Cavities, Heating, Heat transfer, Thermal conductivity, Wall thickness, Temperature gradient, Finite difference methods, Natural convection, Approximation, Darcy's law, Thermal equilibrium, Equilibrium (Physics), Rayleigh number, Fluids, Heat storage, Flow (Dynamics), Temperature
research-article  
John Tencer, Kevin Carlberg, Marvin Larsen and Roy E. Hogan
J. Heat Transfer   doi: 10.1115/1.4037098
Radiation heat transfer is an important phenomenon in many physical systems of practical interest. When participating media is important, the radiative transfer equation (RTE) must be solved for the radiative intensity as a function of location, time, direction, and wavelength. In many heat-transfer applications, a quasi-steady assumption is valid, thereby removing time dependence. The dependence on wavelength is often treated through a weighted sum of gray gases (WSGG) approach. The discrete ordinates method (DOM) is one of the most common methods for approximating the angular (i.e., directional) dependence. The DOM exactly solves for the radiative intensity for a finite number of discrete ordinate directions and computes approximations to integrals over the angular space using a quadrature rule; the chosen ordinate directions correspond to the nodes of this quadrature rule. This work applies a projection-based model-reduction approach to make high-order quadrature computationally feasible for the DOM for purely absorbing applications. First, the proposed approach constructs a reduced basis from (high-fidelity) solutions of the radiative intensity computed at a relatively small number of ordinate directions. Then, the method computes inexpensive approximations of the radiative intensity at the (remaining) quadrature points of a high-order quadrature using a reduced-order model constructed from the reduced basis. This results in a much more accurate solution than might have been achieved using only the ordinate directions used to compute the reduced basis. One- and three-dimensional test problems highlight the efficiency of the proposed method.
TOPICS: Approximation, Heat transfer, Wavelength, Gases, Radiation (Physics), Radiative heat transfer
Technical Brief  
Akihiro Kishimoto, Hideki Moriai, Kenichiro Takenaka, Takayuki Nishiie, Masaki Adachi, Akira Ogawara and Ryoichi Kurose
J. Heat Transfer   doi: 10.1115/1.4037099
A new non-adiabatic procedure of the flamelet/progress-variable approach (NA-FPV approach) is proposed, and the validity is assessed by performing a large-eddy simulation (LES) employing the NA-FPV approach for an O2/H2 combustion field in a single element coaxial combustor under a pressurized condition. The results show that the LES employing the NA-FPV approach can successfully predict the heat flux and capture the effects of heat loss through the cooled walls on the combustion characteristics. This procedure is quite useful especially for the numerical simulations of combustion fields with high temperatures, where there remain reactive radicals (e.g. OH, CH) with high concentrations, such as pressurized combustion, supercritical combustion, and oxygen combustion.
TOPICS: Combustion, Computer simulation, Combustion chambers, Heat losses, Oxygen, Large eddy simulation, Heat flux, High temperature
research-article  
Weihong Li, Wei Shi, Xueying Li, Jing Ren and Hongde Jiang
J. Heat Transfer   doi: 10.1115/1.4037085
The effects of hole length to diameter ratio and compound angle on flat plate film cooling effectiveness are investigated from an experimental and numerical view. Film cooling effectiveness measurements are performed for seven blowing ratios (M) ranging from 0.3 to 2, five hole length to diameter ratios (L/D) from 0.5 to 5 and two compound angle (ß: 0°, 45°) using pressure sensitive paint (PSP) technique. Results indicate that discrete holes with L=0.5 and 1 show highest film cooling effectiveness regardless of compound angle. Round hole generally shows an increasing trend as L increases from 2 to 5, while compound angle hole shows a complex trend concerning with blowing ratios and length to diameter ratios. Compound angle enhances film cooling effectiveness with high blowing ratios and length to diameter ratios. In a parallel effort, LES approach is employed to solve the flow field and visualize vortex structures of in-tube and mainstream regions. It is demonstrated that the counter rotating vortex pair (CRVP) which is observed in the time-averaged flow field is originated in different vortex structures with varying blowing ratios and length to diameter ratios. Scalar field transportation features are also investigated to clarify how different vortex structures affect the temperature distribution and the film cooling effectiveness.
TOPICS: Pressure, Flow (Dynamics), Paints, Large eddy simulation, Film cooling, Vortices, Flat plates, Temperature distribution, Scalar field theory, Transportation systems

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