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Research Papers: Bio-Heat and Mass Transfer

Xu Hang. Lie Group Analysis of a Nanofluid Bioconvection Flow Past a Vertical Flat Surface With an Outer Power-Law Stream J. Heat Transfer 137(4), 041101 (2015) (9 pages);   Paper No: HT-14-1465;   doi:10.1115/1.4029362

In this paper, an analysis on a bioconvection flow of a nanofluid past a vertical flat plate in the presence of an out power-law stream is made. The passively controlled nanofluid model is used to approximate this flow problem, which is believed to be physically more realistic than previously commonly used actively controlled nanofluid models. The Lie group transformation method is introduced to seek similarity solutions of such nanobioconvection flows for the first time. The reduced governing equations are then solved numerically with a finite difference technique. Besides, the influences of various parameters such as the Grashof number, the Prandtl number, the bioconvection Rayleigh number, the Lewis number, the bioconvection Péclet number, and the Schimdt number on the distributions of the density of motile micro-organisms profiles, as well as the local skin friction coefficient, the local Nusselt number, the local wall mass flux, and the local density of the motile micro-organisms are analyzed and discussed.

Commentary by Dr. Valentin Fuster

Research Papers: Evaporation, Boiling, and Condensation

El-Genk Mohamed S., Ali Amir F. Saturation Boiling Critical Heat Flux of PF-5060 Dielectric Liquid on Microporous Copper Surfaces J. Heat Transfer 137(4), 041501 (2015) (11 pages);   Paper No: HT-13-1375;   doi:10.1115/1.4029455

Pool boiling experiments are performed to investigate potential enhancement of critical heat flux (CHF) of PF-5060 dielectric liquid on microporous copper (MPC) surfaces and the effect of surface inclination angle. The morphology and microstructure of the MPC surfaces change with thickness. The experiments tested seven 10 × 10 mm MPC surfaces with thicknesses from 80 to 230 μm at inclination angles of 0 deg (upward facing), 60 deg, 90 deg (vertical), 120 deg, 150 deg, 160 deg, 170 deg, and 180 deg (downward facing). CHF increases as the thickness of the surface increases and/or the inclination angle decreases. The values in the upward facing orientation are 36–59% higher than on smooth Cu. For all surfaces, CHF values in the downward facing orientation are approximately 28% of those in the upward facing orientation. A developed CHF correlation, similar to those of Zuber and Kutateladze, accounts for the effects of inclination angle and thickness of the MPC surfaces. It is in good agreement with experimental data to within ±8%. Still photographs of nucleate boiling on the MPC surfaces at different inclinations help the interpretation of the experimental results.

Commentary by Dr. Valentin Fuster
Qiu G. D., Cai W. H., Wu Z. Y., et al. Numerical Simulation of Forced Convective Condensation of Propane in a Spiral Tube J. Heat Transfer 137(4), 041502 (2015) (9 pages);   Paper No: HT-14-1162;   doi:10.1115/1.4029475

A numerical simulation of forced convective condensation of propane in an upright spiral tube is presented. In the numerical simulations, the important models are used: implicit volume of fluid (VOF) multiphase model, Reynolds stress (RS) turbulence model, Lee's phase change model and Ishii's concentration model, and also the gravity and surface tension are taken into account. The mass flux and vapor quality are simulated from 150 to 350 kg·m−2·s−1 and from 0.1 to 0.9, respectively. The numerical results show that in all simulation cases, only the stratified flow, annular flow, and mist flow are observed. The heat transfer coefficient and frictional pressure drop increase with the increase of mass flux and vapor quality for all simulation cases. Under different flow patterns and mass flux, the numerical results of void fraction, heat transfer coefficient, and frictional pressure drop show good agreement with the experimental results and correlations from the existing references.

Commentary by Dr. Valentin Fuster

Research Papers: Forced Convection

Croce Giulio, Rovenskaya Olga, D'Agaro Paola. Computational Analysis of Conjugate Heat Transfer in Gaseous Microchannels J. Heat Transfer 137(4), 041701 (2015) (7 pages);   Paper No: HT-13-1506;   doi:10.1115/1.4029259

A fully conjugate heat transfer analysis of gaseous flow in short microchannels is presented. Navier–Stokes equations, coupled with Maxwell and Smoluchowski slip and temperature jump boundary conditions, are used for numerical analysis. Results are presented in terms of Nusselt number, heat sink thermal resistance, and resulting wall temperature as well as Mach number profiles for different flow conditions. The comparative importance of wall conduction, rarefaction, and compressibility are discussed. It was found that compressibility plays a major role. Although a significant penalization in the Nusselt number, due to conjugate heat transfer effect, is observed even for a small value of solid conductivity, the performances in terms of heat sink efficiency are essentially a function only of the Mach number.

Commentary by Dr. Valentin Fuster

Research Papers: Natural and Mixed Convection

Shankar B. M., Kumar Jai, Shivakumara I. S. Effect of Horizontal Alternating Current Electric Field on the Stability of Natural Convection in a Dielectric Fluid Saturated Vertical Porous Layer J. Heat Transfer 137(4), 042501 (2015) (9 pages);   Paper No: HT-14-1424;   doi:10.1115/1.4029348

The stability of natural convection in a dielectric fluid-saturated vertical porous layer in the presence of a uniform horizontal AC electric field is investigated. The flow in the porous medium is governed by Brinkman–Wooding-extended-Darcy equation with fluid viscosity different from effective viscosity. The resulting generalized eigenvalue problem is solved numerically using the Chebyshev collocation method. The critical Grashof number $Gc$, the critical wave number $ac$, and the critical wave speed $cc$ are computed for a wide range of Prandtl number Pr, Darcy number Da, the ratio of effective viscosity to the fluid viscosity $Λ$, and AC electric Rayleigh number $Rea$. Interestingly, the value of Prandtl number at which the transition from stationary to traveling-wave mode takes place is found to be independent of $Rea$. The interconnectedness of the Darcy number and the Prandtl number on the nature of modes of instability is clearly delineated and found that increasing in Da and $Rea$ is to destabilize the system. The ratio of viscosities $Λ$ shows stabilizing effect on the system at the stationary mode, but to the contrary, it exhibits a dual behavior once the instability is via traveling-wave mode. Besides, the value of Pr at which transition occurs from stationary to traveling-wave mode instability increases with decreasing $Λ$. The behavior of secondary flows is discussed in detail for values of physical parameters at which transition from stationary to traveling-wave mode takes place.

Commentary by Dr. Valentin Fuster

Research Papers: Porous Media

Mahmood Gazi I., Simonson Carey J., Besant Robert W. Experimental Pressure Drop and Heat Transfer in a Rectangular Channel With a Sinusoidal Porous Screen J. Heat Transfer 137(4), 042601 (2015) (11 pages);   Paper No: HT-14-1499;   doi:10.1115/1.4029349

Experiments are conducted to investigate turbulence enhancing effects of a porous mesh-screen with a sinusoidal shape normal to the flow direction inside a rectangular cross section air channel at low Reynolds numbers (i.e., Re = 1360–3800). The baseline measurements are obtained at the same channel and Reynolds numbers without the screen present. The surface of the screen pores are oriented parallel to the mean flow. Data are presented for the total and wall-static pressure drop along the channel, Nusselt number distributions on the heated wall at several constant heat rates, and air temperature distributions at the channel exit with and without (baseline cases) the screen. The heat transfer measurements are obtained with one wall heated as well as two parallel walls heated to simulate different applications for air channels in the flat plate heat exchangers. The results indicate that the ratio of screen channel to baseline Nusselt number (Nu/Nu0) and the ratio of screen channel to baseline friction factor (f/f0) increase with the Reynolds number (Re). The fully developed Nu/Nu0 is 2.0–2.5 as the fully developed f/f0 is 4.4 at 3100 < Re ≤ 3800. However, the screen channel heat convection performance index, (Nu/Nu0)/(f/f0)1/3 is only greater than 1.0 when Re > 2500 which is the design objective of reducing the pumping power and heat transfer area in the channel. Nonetheless, the screen insert is only beneficial to augment the convective heat transfer in the channel over the range of transition Reynolds number tested. The average total pressure drop across the channel and average exit air temperature suggest that the screen insert promotes good mixing of fluid across the channel for the Reynolds numbers tested.

Commentary by Dr. Valentin Fuster

Research Papers: Two-Phase Flow and Heat Transfer

Sharipov Vasilii. High Order Bubble Dynamics in Incompressible Liquid J. Heat Transfer 137(4), 042901 (2015) (6 pages);   Paper No: HT-13-1442;   doi:10.1115/1.4029457

A semi-analytical approximation to the solution of the radial Fourier equation describing liquid temperature dynamics in the vicinity of a spherical bubble is presented. This approximation opens a possibility to construct a computationally efficient bubble model that is flexible enough to simulate different bubble dynamics behavior like bubble growth, collapse, and oscillations. In turn, it allows development of two-pressure computer codes aiming at simulation of processes in liquid with bubbles that are important for industrial applications. The model is based on the system of ordinary differential equations (ODEs) and is presented together with results of simulations and comparison with some available experimental data. Additionally, scenarios like strong bubble parameter oscillations in largely subcooled water and abrupt liquid pressure change are considered. As respective simulations show, the latter may lead to subsequent hydrogen explosion if hydrogen–oxygen mixture is presented in the bubble. This may be important for boiling water reactor piping safety analysis.

Commentary by Dr. Valentin Fuster

Technical Brief

Wang Xiaowu, Li Yaochao, Wan Zhenpin. Thermal Conduction Performance of Fiber-Enhanced Polyalcohol Binary Systems J. Heat Transfer 137(4), 044501 (2015) (4 pages);   Paper No: HT-14-1128;   doi:10.1115/1.4029269

Polyalcohol has poor heat conduction performance. A fiber-enhanced polyalcohol binary system combines polyalcohol with a copper fiber net to improve its heat conduction performance. In a binary system without fibers, more heat input increases the wall temperature near the container than when the fiber is present. Compared to a polyalcohol binary system, pentaerythritol/Tris hydroxymethyl aminomethane (PE/TRIS) without fibers, fiber-enhanced polyalcohol system PE/TRIS shows quicker response to energy input from the exterior region. The phase change temperature in a fiber-enhanced polyalcohol binary system is much lower than that in a polyalcohol system without fibers. This is because of the metastate plastic state that presents a nonfaceted phase interface with a larger radius of curvature in a polyalcohol system without fibers. The porous structure of the fiber is smaller than the size of the phase interface in a polyalcohol system without fibers and can increase the equilibrium pressure and make the phase change easier.

Commentary by Dr. Valentin Fuster