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research-article  
David Eckmann, Abhay Ranganathan, Shawn Owiredu and David Jang
J. Heat Transfer   doi: 10.1115/1.4042186
The intracellular production and transport of energetic substrate adenosine triphosphate (ATP) produced by mitochondria is dependent on multiple factors. These include local metabolic demand, mitochondrial motility and intracellular location, mitochondrial intermembrane potential, bioenergy substrate diffusion within the cell cytosol and energy transport to the cell nucleus, which itself does not contain any mitochondria. Herein we demonstrate via cell-based experiment and scaling argument that intracellular bioenergy transport is readily compartmentalized into perinuclear and peripheral regions of the cell. We draw on direct fluorescence-based measurement of quantum dot tracking, high-resolution respirometry, mitochondrial dynamics and intermembrane potential to assess intracellular quantum dot diffusion to define the intracellular milieu for small molecule transport, and chemical perturbations which challenge cells by altering bioenergetics states. We identify a heterogeneous environment for intracellular bioenergy transport, with a dominant feature being present: the intracellular bioenergy distribution in response to pharmacologically-induced cell challenge is determined to be preservation of perinuclear mitochondrial ATP-linked respiration in order to preserve, maintain or otherwise support bioenergy delivery to meet the metabolic requirements of the cell nucleus whereas there is a decrement in bioenergetic capacity in the cell periphery. This dynamic effect of motile intracellular bioenergy production yields efficient transport of ATP in the maintenance of cellular health.
TOPICS: Dynamics (Mechanics), Fluorescence, Diffusion (Physics), Maintenance, Preservation, Resolution (Optics), Quantum dots, Bioenergy conversion
research-article  
Vishal Anand and Ivan Christov
J. Heat Transfer   doi: 10.1115/1.4042157
We study hydrodynamics, heat transfer and entropy generation in pressure-driven microchannel flow of a power-law fluid. Specifically, we address the effect of asymmetry in the slip boundary condition at the channel walls. Constant, uniform but unequal heat fluxes are imposed at the walls in this thermally developed flow. The effect of asymmetric slip on the velocity profile, on the wall shear stress, on the temperature distribution, on the Bejan number profiles, and on the average entropy generation and the Nusselt number are established through the numerical evaluation of exact analytical expressions derived. Specifically, due to asymmetric slip, the fluid momentum flux and thermal energy flux are enhanced along the wall with larger slip, which in turn shifts the location of the velocity's maximum to an off-center location closer to the said wall. Asymmetric slip is also shown to redistribute the peaks and plateaus of the Bejan number profile across the microchannel, showing a sharp transition between entropy generation due to heat transfer and due to fluid flow at an off-center-line location. In the presence of asymmetric slip, the difference in the imposed heat fluxes leads to starkly different Bejan number profiles depending on which wall is hotter, and whether the fluid is shear-thinning or shear-thickening. Overall, slip is shown to promote uniformity in both the velocity field and the temperature field, thereby reducing irreversibility in this flow.
TOPICS: Pressure, Heat transfer, Entropy, Fluids, Heat, Flow (Dynamics), Shear (Mechanics), Flux (Metallurgy), Boundary-value problems, Microchannel flow, Temperature distribution, Microchannels, Shear stress, Hydrodynamics, Momentum, Fluid dynamics, Temperature, Thermal energy
research-article  
John H. Lienhard V
J. Heat Transfer   doi: 10.1115/1.4042158
The radiation fractional function is the fraction of black body radiation below a given value of λ-T. Edwards and others have distinguished between the traditional, or "external", radiation fractional function and an "internal" radiation fractional function. The latter is used for simplified calculation of net radiation from a non-gray surface when the temperature of an effectively black source is not far from the surface's temperature, without calculating a separate total absorptivity. This paper examines the analytical approximation involved in the internal fractional function, with results given in terms of the incomplete zeta function. A rigorous upper bound on the difference between the external and internal emissivity is obtained. Calculations using the internal emissivity are compared to exact calculations for several models and materials. A new approach to calculating the internal emissivity is developed, yielding vastly improved accuracy over a wide range of temperature differences. The internal fractional function can be useful for certain simplified calculations.
TOPICS: Radiation (Physics), Emissivity, Temperature, Approximation, Blackbody radiation
research-article  
Yuanwei Lyu, Jing-zhou Zhang, Xicheng Liu and Yong Shan
J. Heat Transfer   doi: 10.1115/1.4042159
Impinging heat transferred by a pulsed jet induced by a 6-chevron nozzle on a semi-cylindrical concave surface is investigated. The semi-cylindrical concave surface has a cylinder diameter-to-nozzle diameter ratio (D/d) of 10. Results show that the nozzle-to-surface distance has a significant impact on the impingement heat transfer of the pulsed chevron jet. An optimal nozzle-to-surface distance for achieving the maximum stagnation Nusselt number appears at H/d=6. In the wall jet zone, the averaged Nusselt number is the largest at H/d=2 and the smallest at H/d=8. In comparison with the chevron steady jet impingement, the effect of nozzle-to-surface distance on the convective heat transfer becomes less notable for the pulsed chevron jet impingement. The stagnation Nusselt number under the pulsed chevron jet impingement is mostly less than that under the chevron steady jet impingement. However, at H/d=8, the pulsed chevron jet is more effective than the steady jet. This study confirmed that the pulsed chevron jet produced higher azimuthally-averaged Nusselt numbers than the steady chevron jet in the wall jet flow zone at large nozzle-to-surface distances. The stagnation Nusselt numbers by the pulsed chevron jet impingement has a maximum reduction of 21.0% (f=20Hz, H/d=4, Re=2000) compared with the steady chevron jet impingement. The pulsed chevron jet impingement heat transfer on a concave surface is less effective than compared to a flat surface.
TOPICS: Heat transfer, Nozzles, Cylinders, Jets, Convection, Heat
research-article  
Sunil K. Dwivedi and Sandip K. Saha
J. Heat Transfer   doi: 10.1115/1.4042148
The present experimental study on rhombic shaped microchannel is to understand the effect of low acute side angle on the Nusselt number and compare with the published numerical results for H1 (axially constant heat flux and circumferentially constant temperature) and H2 (constant axial and circumferential wall heat flux) boundary conditions. The hydraulic and heat transfer characteristics of rhombic geometry with a side angle of 30° for different mass flow rates and heat flux inputs are obtained using a three-dimensional conjugate heat transfer model, which is validated with the experimental results. It is found that the average Nusselt number obtained from the experimental and numerical results can be approximated closely with that computed using H1 boundary condition. The local Nusselt number of hydrodynamically and thermally developed region obtained from numerical analysis is compared with the correlation, published for H1 boundary condition. These results will be useful in design and optimization of rhombic shaped microchannel for electronic cooling applications.
TOPICS: Heat transfer, Microchannels, Heat flux, Boundary-value problems, Geometry, Computer cooling, Flow (Dynamics), Temperature, Design, Numerical analysis, Optimization
Technical Brief  
Mustafa Erguvan and David Macphee
J. Heat Transfer   doi: 10.1115/1.4042156
Numerical and thermodynamic analyses have been undertaken in this study to examine energy and exergy efficiencies of in-line tube banks for unsteady cross-flow. Pitch ratio and the number of in-line tubes are varied for Reynolds numbers of 500 and 10,000, and artificial heat leakages are modeled as a source term. Numerical results are compared with published values, and good agreements are obtained regarding Nusselt number and pressure drop. Whereas the energy efficiency varied between 72% and 99%, the exergy efficiency ranged from 40% to 70%. It was found that while viscous dissipation has a low effect on energy and exergy efficiencies for low Reynolds numbers, it has a significant effect for high Reynolds number cases. On the other hand, heat leakage had a greater effect on exergy efficiency compared to energy efficiency, especially for low Reynolds number cases. Overall, this study verified how heat leakage could play a vital role on efficiency for low-inlet temperature heat recovery systems.
TOPICS: Flow (Dynamics), Heat, Temperature, Reynolds number, Heat recovery, Energy dissipation, Energy efficiency, Exergy, Low temperature, Pressure drop, Leakage, Cross-flow
Errata  
Hai-Dong Wang
J. Heat Transfer   doi: 10.1115/1.4042106
Erratum for the published paper "Non-Fourier heat conduction in carbon nanotubes"
TOPICS: Heat conduction, Carbon nanotubes
Design Innovation Paper  
Federico Belfi, Filomena Iorizzo, Claudio Galbiati and Fabio Lepore
J. Heat Transfer   doi: 10.1115/1.4042082
In this paper is described the development and the experimental study of a Flat Plate Pulsating Heat Pipe (FPPHP) built by means of metal additive manufacturing. In the recent years, small/medium aerospace companies have gained interest in the development of small satellites. The small dimensions, coupled with the need of high power devices for science and communications, increase the interest in thermally functional structures. The space business is characterized by a very small production lot, and custom designs from project to project. The Additive Manufacturing (AM) exactly fits these needs and, in the past years, the use of this technology in aerospace projects has grown significantly. This paper, after a brief review of the Pulsating Heat Pipe (PHP), focuses on the development and testing of a panel with an embedded closed loop Flat Plate Pulsating Heat Pipe built by means of metal AM technique. The article presents a trade-off analysis between the metal AM technologies available on the market; by means of the trade-off analysis a design strategy is proposed by the authors. A comparison between available FPPHP results in literature and the 3D printed structure will show the differences between the common subtractive technology and the innovative AM technique.
TOPICS: Space frame structures, Flat plates, Technology development, Additive manufacturing, Heat pipes, Metals, Aerospace industry, Tradeoffs, Testing, Design, Dimensions, Satellites
research-article  
Shobhana Singh, Kim S⊘rensen and Thomas Condra
J. Heat Transfer   doi: 10.1115/1.4042050
In the present work, a numerical analysis of conjugate heat transfer and fluid flow in vortex generator enhanced double-fin and tube heat exchanger is carried out. The enhanced design aims to improve the heat transfer performance of a conventional double-fin and tube heat exchanger for waste heat recovery applications. A three-dimensional numerical model is developed using ANSYS CFX to simulate fluid flow and conjugate heat transfer process. Numerical simulations with rectangular winglet vortex generators (RWVGs) at five different angles of attack (-20<= a <= 20), in the Reynolds number range of 5000 <= Re <= 11000, are performed. Salient performance characteristics are analyzed in addition to the temperature and fluid flow fields. Based on the numerical results, it is concluded that the overall performance of the double-fin and tube heat exchanger can be improved by 27-91% by employing RWVGs at a = -20, over the range of Reynolds number investigated. The study provides useful design information and necessary performance data that can be adopted for a design and development of the enhanced heat exchanger design at a lower manufacturing cost.
TOPICS: Heat exchangers, Vortices, Generators, Design, Fluid dynamics, Heat transfer, Computer simulation, Reynolds number, Heat recovery, Numerical analysis, Manufacturing, Temperature, Performance characterization
research-article  
Wang Qiang, Qian Zuoqin, Cheng Junlin, Ren Jie and Huang Weilong
J. Heat Transfer   doi: 10.1115/1.4042008
The numerical simulation was carried out to investigate mechanism of the heat transfer enhancement in the fin-and-tube heat exchangers. As known, the vortex generators were widely used to improve the thermal performance with bad flow resistance characteristics and led to bad comprehensive performance. This paper was aimed to expound the mechanism of thermal hydraulic characteristics and explore the effect of vortex generators position on the comprehensive performance. Three types of fins (Type 1, Type 2, and Type 3) were discussed in this paper. The j factor, f factor and PEC of three types of vortex generators in different positions were discussed and compared. Based on the numerical results, a detailed description of the effect of three types of vortex generators on the heat transfer performance and flow resistance characteristics was presented at different Reynolds number in the range between 1300 and 2000. In addition, local velocity distribution, local temperature distribution and local pressure drop distribution were analyzed and discussed. And the effect of VG angle on the thermal performance and flow resistance were presented. It can be concluded that the main heat transfer occurred in the region before the tube, and the wake region behind the tube was harmful to improve the thermal performance and reduce the flow resistance. Besides, vortex generator in the wake region was obviously beneficial to the enhancement of the thermal performance with less energy loss.
TOPICS: Flow (Dynamics), Heat transfer, Heat exchangers, Vortices, Generators, Wakes, Pressure drop, Temperature distribution, Fins, Computer simulation, Reynolds number, Energy dissipation
research-article  
Idrees Afridi, Muhammad Qasim and O.D Makinde
J. Heat Transfer   doi: 10.1115/1.4041951
This study examines the effects of viscous and porous dissipation on entropy generation in the viscoelastic fluid flow induced by a linearly stretching surface. Analysis of mass transfer is also performed. Consideration of rheological characteristics of viscoelastic fluid in the energy conservation law and entropy generation number in terms of viscous dissipation makes a striking difference in the energy equation and entropy generation number for Newtonian and viscoelastic fluid. This important concern which is yet not properly attended is also be examined in the present study. The dimensional governing equations are reduced to a set of self-similar differential equations. The energy and concentration equations are solved exactly by employing the Laplace transform technique. The obtained exact solutions of reduced set of governing equations are utilized to compute the entropy generation number. To analyze the impacts of flow parameter on velocity profile, temperature distribution, concentration profile and entropy generation number inside the boundary layer, graphs are plotted and discussed physically. The permeability and viscoelastic parameter have strong influence on the entropy generation in the vicinity of stretching surface.
TOPICS: Flow (Dynamics), Heat, Mass transfer, Fluids, Porous materials, Entropy, Viscoelastic fluids, Energy dissipation, Boundary layers, Differential equations, Energy conservation, Laplace transforms, Temperature distribution, Permeability, Rheology
research-article  
Fayeza Al Sulti
J. Heat Transfer   doi: 10.1115/1.4041959
Stagnation-point flow towards a stretching sheet with slip effects has been investigated. Unlike most classical works, Cattaneo-Christov heat flux model is utilized for the formulation of the energy equation instead of Fourier's law of heat conduction. A similarity transformation technique is adopted to reduce partial differential equations into a system of nonlinear ordinary differential equations. Numerical solutions are obtained by using shooting method to explore the features of various parameters for the velocity and temperature distributions. The obtained results are graphically presented and analyzed. It is found that fluid temperature has a converse relationship with the thermal relaxation time. A comparison of Cattaneo-Christov heat flux model and Fourier's law is also presented.
TOPICS: Stagnation flow, Heat flux, Temperature distribution, Temperature, Fluids, Heat conduction, Relaxation (Physics), Differential equations, Partial differential equations
research-article  
Banjara Kotresha and Gnanasekaran N
J. Heat Transfer   doi: 10.1115/1.4041955
This paper discusses about the numerical prediction of forced convection heat transfer through high porous metal foams with discrete heat sources in a vertical channel. The physical geometry considered for this study consists of a discrete heat source assembly placed at the center of the channel along with high thermal conductivity porous metal foams on either side to enhance the heat transfer. The novelty of the present work is the use of the local thermal equilibrium (LTE) model for the metal foam region and the local thermal non-equilibrium (LTNE) model for the metal region to investigate the temperature distribution of the heat sources and to get the optimal heat distribution so as to achieve an isothermal condition. Aluminum and copper metal foams of 10 PPI having a thickness of 20 mm are considered for the numerical simulations. The metal foam region is considered as homogeneous porous media and numerically modeled using Darcy Extended Forchheimer model. The proposed methodology is validated using the experimental results available in literature. Finally, the results of excess temperature for both empty and metal foam filled vertical channel are presented in this work.
TOPICS: Metal foams, Temperature distribution, Heat, Temperature, Heat transfer, Foams (Chemistry), Metals, Copper, Aluminum, Porous materials, Computer simulation, Manufacturing, Equilibrium (Physics), Thermal conductivity, Thermal equilibrium, Forced convection, Geometry
research-article  
Sharad Pachpute and B. Premachandran
J. Heat Transfer   doi: 10.1115/1.4041958
In this paper, heat transfer and effectiveness of a turbulent slot jet impinging over a heated circular cylinder has been investigated numerically by varying the inlet jet temperature (Tj) from 223K to 350K. In all cases, the ambient temperature (Tamb) is assumed to be constant (300K). The Reynolds number defined based on the average nozzle exit velocity, the diameter of the cylindrical target (D) and properties at the nozzle exit temperature, ?Re?_D=?VD/µ is varied from 6000 to 20000. The ratio of cylinder diameter to the slot width, D/S =5.5, 8.5 and 17 are considered and the non-dimensional distance from the nozzle exit to the cylinder, H/S is varied in the range of 2 = H/S =12. The turbulence model was used for numerical simulations. Numerical results reveal that the local Nusselt number is found to be higher at the stagnation point in the case of cold jet impingement at Tj = 223K. The local heat transfer at the rear side of the cylinder is 8 to 18% less as compared to that of Tj =Tamb for ReD = 6000. The local effectiveness calculated over a circular cylinder strongly depends on H/S and D/S. Based on the parametric study, a correlation has been provided for the local effectiveness at the stagnation point.
TOPICS: Temperature, Heat transfer, Circular cylinders, Cylinders, Nozzles, Turbulence, Computer simulation, Reynolds number
Technical Brief  
Mohammad Parhizi and Ankur Jain
J. Heat Transfer   doi: 10.1115/1.4041956
Theoretical understanding of phase change heat transfer problems is of much interest for multiple engineering applications. Exact solutions for most phase change heat transfer problems are not available, and approximate analytical methods are needed to be used. This paper presents a solution for one-dimensional phase change problem with time-dependent heat flux boundary condition using the perturbation method. Two different expressions for propagation of the phase change front are derived. For the special case of constant heat flux, the present solution is shown to offer key advantages over past papers. Specifically, the present solution results in greater accuracy and does not diverge at large times unlike past results. The theoretical result is used for understanding the nature of phase change propagation for linear and periodic heat flux boundary conditions. In addition to improving the theoretical understanding of phase change heat transfer problems, these results may contribute towards design of phase change based thermal management for a variety of engineering applications, such as cooling of Li-ion batteries.
TOPICS: Heat flux, Heat transfer, Engineering systems and industry applications, Boundary-value problems, Thermal management, Lithium-ion batteries, Cooling, Analytical methods, Design
Technical Brief  
Xiaohui Bai and Akira Nakayama
J. Heat Transfer   doi: 10.1115/1.4041957
An analytical and numerical study was conducted for estimation of the effective thermal conductivities of curved metal frame core structures, which can replace metal foams, in views of their advantages over the metal foams for both load bearing and heat dissipation. The trajectory of the frame ligament and its cross-sectional area were allowed to vary arbitrarily in the three-dimensional space. The analytical formula obtained by extending the formula previously proposed by Bai et al. was examined by comparing it with the numerical results directly obtained from full 3D numerical computations. An air layer partially filled with a collection of coiled circular rods was treated both analytically and numerically. Furthermore, the effect of lattice nodes on the effective thermal conductivity was investigated by introducing an analytical model with the lattice ligaments merging together at one nodal point. The analytical expressions thus derived for the lattice structures with nodes, were applied to tetrahedral structure, pyramidal structure and octet-truss structure to find their effective thermal conductivities, which are found to agree closely with the 3D numerical results. Thus, the present analytical expressions can be used to customize the structure to meet its desired thermal performance.
TOPICS: Metals, Thermal conductivity, Metal foams, Rods, Heat, Trajectories (Physics), Bearings, Computation, Stress, Trusses (Building), Energy dissipation
research-article  
Recep Ekiciler, Muhammet Samet Ali Çetinkaya and Kamil Arslan
J. Heat Transfer   doi: 10.1115/1.4041954
In this present study, air jet impingement cooling on flat, triangular-corrugated and sinusoidal-corrugated surfaces were conducted numerically. Constant surface temperature was subjected to the bottom surface Air, was the working fluid. The air was exited from a rectangular shape slot and impinged to the bottom surface. The Reynolds number was changed between 125 and 500. The governing equations were solved using the finite volume method (FVM). The effect of shape of bottom surface was investigated on heat and flow characteristics. Average and local Nusselt number were calculated for each case. It is obtained that Nusselt number increases by increasing Reynolds numbers. The optimum conditions were determined to get much more enhancement in terms of Nusselt number. It was revealed that the shape of the cooling surface (bottom wall) is substantially influence the heat transfer.
TOPICS: Waves, Convection, Impingement cooling, Shapes, Reynolds number, Finite volume methods, Air jets, Flow (Dynamics), Heat, Temperature, Heat transfer, Cooling, Fluids
research-article  
Dr. Isaac Lare Animasaun, B Mahanthesh, A. O. Jagun, T. D. Bankole, Sivaraj R, N. A. Shah and Salman Saleem
J. Heat Transfer   doi: 10.1115/1.4041971
Combination of electric and magnetic forces on charged molecules of flowing fluid in the presence of a significant electromagnetic fields on surfaces with a non-uniform thickness (as in the case of upper pointed surface of an aircraft and bonnet of a car which are examples of upper horizontal surfaces of a paraboloid of revolution - uhspr) is inevitable.} In this study, the influence of imposed magnetic field and Hall effects on the flow of 29 nm CuO-Water nanofluid over such object is presented. Suitable similarity variables were employed to non-dimensionalize and parameterize the dimensional governing equation. The numerical solutions of the corresponding boundary value problem were obtained using Runge-Kutta fourth order integration scheme along with shooting technique. The domain of cross-flow velocity can be highly suppressed when the magnitude of imposed magnetic strength and that of Hall parameter are large. A significant increase in the cross-flow velocity gradient near an upper horizontal surface of the paraboloid of revolution is guaranteed with an increase in the Hall parameter. Enhancement of temperature distribution across the flow is apparent due to an increase in the volume fraction.
TOPICS: Flow (Dynamics), Heat transfer, Nanofluids, Water, Cross-flow, Magnetic fields, Electromagnetic fields, Aircraft, Boundary-value problems, Temperature distribution, Hall effect, Fluid dynamics
research-article  
Pradeep GV and K Rama Narasimha
J. Heat Transfer   doi: 10.1115/1.4041953
This paper describes the experimental investigations conducted on a closed loop pulsating heat pipe (CLPHP) for assessing the thermal performance. The pulsating heat pipe has a single closed loop made of copper. The working fluids used are water and titanium-di-oxide nano fluids with varying concentrations of TiO2 nano particles (1.5% and 1%) on weight basis. The TiO2 particles are mixed in water to form a stable suspension using a sonicator. The heat input is varied between 40W-100W in steps of 20W. All experiments are conducted in the bottom heating mode (evaporator at the top) in vertical and horizontal orientations. The parameters considered for evaluating the thermal performance are the temperature difference between evaporator and condenser, thermal resistance, heat transfer coefficient and thermal conductivity. The results of the investigation reveals that, the vertical orientation and increase in nano particle concentration favors better heat transfer performance of the PHP
TOPICS: Heat pipes, Nanofluids, Water, Nanoparticles, Thermal conductivity, Condensers (steam plant), Weight (Mass), Heat, Temperature, Heat transfer, Fluids, Copper, Particulate matter, Heating, Heat transfer coefficients, Thermal resistance, Titanium
research-article  
Oguzhan Der, Dr. Marco Marengo and Volfango Bertola
J. Heat Transfer   doi: 10.1115/1.4041952
A low-cost, flexible pulsating heat pipe (PHP) was built in a composite polypropylene sheet consisting of three layers joint together by selective laser welding, to address the demand of heat transfer devices characterized by low weight, small unit thickness, low cost, and high mechanical flexibility. A thin, flexible and lightweight heat pipe is advantageous for various aerospace, aircraft and portable electronic applications where the device weight and its mechanical flexibility are essential. The concept is to sandwich a serpentine channel, cut out in a polypropylene sheet and containing a self- propelled mixture of a working fluid with its vapour, between two transparent sheets of the same material; this results into a thin, flat enclosure with parallel channels hence the name "pulsating heat stripes" (PHS). The transient and steady- state thermal response of the device was characterised for different heat input levels and different configurations, either straight or bent at different angles. The equivalent thermal resistance was estimated by measuring the wall temperatures at both the evaporator and the condenser, showing a multi- fold increase of the equivalent thermal conductance with respect to solid polypropylene.
TOPICS: Heat, Plastics, Weight (Mass), Heat pipes, Aircraft, Condensers (steam plant), Thermal resistance, Transparency, Wall temperature, Heat transfer, Fluids, Composite materials, Transients (Dynamics), Laser welding, Thermal conductivity, Aerospace industry

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