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Research Papers

J. Thermal Sci. Eng. Appl. 2018;10(3):031001-031001-10. doi:10.1115/1.4038538.

Rotational effects lead to significant nonuniformity in heat transfer (HT) enhancement and this effect is directly proportional to the rotation number (Ro=ΩD/V). Hence, the development of cooling designs, which have less dependence on rotation, is imperative. This paper studied the effect of rotation on crossflow-induced swirl configuration with the goal of demonstrating a new design that has lesser response toward rotational effects. The new design passes coolant from one pass to the second pass through a set of angled holes to induce impingement and swirling flow to generate higher HT coefficients than typical ribbed channels with 180-deg bend between the two passages. Detailed HT coefficients are presented for stationary and rotating conditions using transient liquid crystal (TLC) thermography. The channel Reynolds number based on the channel hydraulic diameter and channel velocity at inlet/outlet ranged from 25,000 to 100,000. The rotation number ranged from 0 to 0.14. Results show that rotation reduced the HT on both sides of the impingement due to the Coriolis force. The maximum local reduction of HT in the present study was about 30%. Rotation significantly enhanced the HT near the closed end because of the centrifugal force and the “pumping” effect, which caused local HT enhancements up to 100%. Compared to U-bend two pass channels, impingement channels had advantages in the upstream channel and the end region, but HT performance was not beneficial on the leading side of the downstream channel.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031002-031002-9. doi:10.1115/1.4038560.

The aim of this work is to perform a thermal analysis of the operational conditions of a large-scale roller conveyor furnace in a ceramic factory. The entire furnace was divided into three subzones according to the combustion conditions, and the temperature and gas (CO2, H2O vapor, and O2) distributions of each subzone were evaluated. The computational fluid dynamics (CFD) approach was employed to simulate the flow, temperature profile, and heat transfer. The realizable k–ε model was applied for turbulence simulation of the fluid flow coming from the burners. The discrete ordinates method (DOM) and weighted sum of gray gases (WSGG) model were used for simulation of the radiative heat transfer of the furnace. The high accuracy of the simulation methods was validated with the temperature data of the furnace measured by an infrared thermal camera. From the comparisons between the furnace's operating conditions and the numerical simulations, it was concluded that the simulation methods yielded successful results, and relative deviations of up to 22% were observed in the side wall.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031003-031003-6. doi:10.1115/1.4038700.

The present paper examines magnetohydrodynamic (MHD) three-dimensional (3D) flow of viscous nanoliquid in the presence of heat and mass flux conditions. A bidirectional nonlinearly stretching surface has been employed to create the flow. Heat and mass transfer attribute analyzed via thermophoresis and Brownian diffusion aspects. Viscous liquid is electrically conducted subject to applied magnetic field. Problem formulation is made through the boundary layer approximation under small magnetic Reynolds number. Appropriate transformations yield the strong nonlinear ordinary differential system. The obtained nonlinear system has been solved for the convergent homotopic solutions. Effects of different pertinent parameters with respect to temperature and concentration are sketched and discussed. The coefficients of skin friction and heat and mass transfer rates are computed numerically.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031004-031004-8. doi:10.1115/1.4038564.

This study investigates peristaltic transport of Sutterby fluid in an inclined channel. Applied magnetic field is also inclined. Thermal radiation, Joule heating, and Soret and Dufour effects are present. The channel boundaries satisfy wall compliant and partial slip conditions. The problem description is simplified by employing long wavelength and low Reynolds number assumptions. Graphical solutions for axial velocity, temperature, concentration, and heat transfer coefficient are obtained via built-in numerical approach NDSolve. Similar response of velocity and concentration profiles has been recorded for larger inclination. The results reveal temperature drop with larger thermal radiation. Here, radiation and thermal slip increase heat transfer rate.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031005-031005-7. doi:10.1115/1.4038701.

Buoyancy-induced natural convective heat transfer along a vertical cylinder immersed in Water–Al2O3 nanofluids for various concentrations (0, 0.05, 0.1, 0.2, 0.4, 0.6 vol %) under constant heat flux condition was investigated experimentally and presented. Thermal stratification was observed outside the boundary layer in the ambient fluid after steady-state condition is achieved as the fluid temperature goes on increasing along the axial direction. Temperature variations of the cylinder along the axial direction and temperature variations of fluid in radial direction are shown graphically. It is observed that the temperatures of the cylinder and the fluid increases along the axial direction and the fluid temperature decreases in the radial direction. Experiments were conducted for various heat inputs (30 W, 40 W, 45 W, and 50 W) and volume concentrations and observed that the addition of alumina nanoparticles up to 0.1 vol % enhances the thermal performance and then the further addition of nanoparticles leads to deterioration. The maximum enhancement in the natural convection heat transfer performance is observed as 13.8%, i.e., heat transfer coefficient is increased from 382 W/m2 K to 435 W/m2 K at 0.1 vol % particle loading.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Thermal Sci. Eng. Appl. 2018;10(3):034501-034501-5. doi:10.1115/1.4038587.

In this study, turbulent natural convection heat transfer during the charge cycle of an isochoric vertically oriented thermal energy storage (TES) tube is studied computationally and analytically. The storage fluids considered in this study (supercritical CO2 and liquid toluene) cover a wide range of Rayleigh numbers. The volume of the storage tube is constant and the thermal storage happens in an isochoric process. A computational model was utilized to study turbulent natural convection during the charge cycle. The computational results were further utilized to develop a conceptual and dimensionless model that views the thermal storage process as a hot boundary layer that rises along the tube wall and falls in the center to replace the cold fluid in the core. The dimensionless model predicts that the dimensionless mean temperature of the storage fluid and average Nusselt number of natural convection are functions of L/D ratio, Rayleigh number, and Fourier number that are combined to form a buoyancy-Fourier number.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):034502-034502-5. doi:10.1115/1.4038539.

For the analysis of unsteady heat conduction in solid bodies comprising heat exchange by forced convection to nearby fluids, the two feasible models are (1) the differential or distributed model and (2) the lumped capacitance model. In the latter model, the suited lumped heat equation is linear, separable, and solvable in exact, analytic form. The linear lumped heat equation is constrained by the lumped Biot number criterion Bil=h¯(V/S)/ks < 0.1, where the mean convective coefficient h¯ is affected by the imposed fluid velocity. Conversely, when the heat exchange happens by natural convection, the pertinent lumped heat equation turns nonlinear because the mean convective coefficient h¯ depends on the instantaneous mean temperature in the solid body. Undoubtedly, the nonlinear lumped heat equation must be solved with a numerical procedure, such as the classical Runge–Kutta method. Also, due to the variable mean convective coefficient h¯(T), the lumped Biot number criterion Bil=h¯(V/S)/ks < 0.1 needs to be adjusted to Bil,max=h¯max(V/S)/ks < 0.1. Here, h¯max in natural convection cooling stands for the maximum mean convective coefficient at the initial temperature Tin and the initial time t = 0. Fortunately, by way of a temperature transformation, the nonlinear lumped heat equation can be homogenized and later channeled through a nonlinear Bernoulli equation, which admits an exact, analytic solution. This simple route paves the way to an exact, analytic mean temperature distribution T(t) applicable to a class of regular solid bodies: vertical plate, vertical cylinder, horizontal cylinder, and sphere; all solid bodies constricted by the modified lumped Biot number criterion Bil,max<0.1.

Commentary by Dr. Valentin Fuster

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