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Editorial

J. Thermal Sci. Eng. Appl. 2018;10(3):030201-030201-3. doi:10.1115/1.4039021.
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Commentary by Dr. Valentin Fuster

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
J. Thermal Sci. Eng. Appl. 2018;10(3):031006-031006-14. doi:10.1115/1.4039054.

The present study investigates the effects of Coriolis force and centrifugal buoyancy force on heat transfer due to jet impingement on dimpled target surface (DT). Detailed heat transfer measurements were carried out using transient liquid crystal (LC) thermography, where the target surface was modeled as one-dimensional (1D) semi-infinite solid. Three different configurations of DT surfaces have been studied. The flow and rotation conditions have been kept the same for all the configurations, where the average Reynolds number (based on jet hole hydraulic diameter: Rej) was 2500 and the rotational speed was 400 rpm (corresponding to Roj of 0.00274). Under nonrotating conditions, DT surface showed positive heat transfer enhancements compared to smooth target surfaces. Under rotating conditions, it was observed that rotation was helpful in enhancing heat transfer on leading and trailing sides for smooth target surface. However, for the DT surfaces, rotation proved to be detrimental to heat transfer enhancement.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031007-031007-9. doi:10.1115/1.4038840.

The mixing of the two axial flows through the ware and through the gap between ware and walls using side nozzles in the preheating zone of tunnel kiln is investigated. The three-dimensional temperature field in the cross section between the two cars is calculated using the computational fluid dynamics (CFD) tool fluent. The mixing quality is evaluated using contours, the frequency of temperature distribution, and the maximum temperature difference. The influence on the mixing behavior of injection flow rate, injection velocity, nozzles position, and nozzle number has been analyzed. The results show that using two nozzles is more effective than one nozzle if the nozzles are installed at the opposite side walls with high vertical distance. The mixing quality increases strongly until an impulse flow rate (IFR) of about 4 N. For higher values, the influence becomes relatively low. The results for the mixing temperature obtained through CFD simulation compared with analytical results show a good agreement with maximum error of 0.5%.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031008-031008-12. doi:10.1115/1.4039299.

In the present work, a steady-state, finite difference-based computer model of heat transfer during production of lime in a rotary kiln has been developed. The model simulates calcination reaction in the solid bed region of the rotary kiln along with turbulent convection of gas, radiation heat exchange among hot gas, refractory wall and the solid surface, and conduction in the refractory wall. The solids flow countercurrent to the gas. The kiln is divided into axial segments of equal length. The mass and energy balances of the solid and gas in an axial segment are used to obtain solids and gas temperature at the exit of that segment. Thus, a marching type of solution proceeding from the solids inlet to solids outlet arises. To model the calcination of limestone, shrinking core model with surface reaction rate control has been used. The output data consist of the refractory wall temperature distributions, axial solids and gas temperature distributions, axial percent calcination profile, and kiln length. The kiln length predicted by the present model is 5.74 m as compared to 5.5 m of the pilot kiln used in the experimental study of Watkinson and Brimacombe (1982, Watkinson, A.P. and Brimacombe, J. K., “Limestone Calcination in a Rotary Kiln,” Metallurgical Transactions B, Vol. 13B, pp. 369–378). The other outputs have been also satisfactorily validated with the aforementioned experimental results. A detailed parametric study lent a good physical insight into the lime making process and the kiln wall temperature distributions.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031009-031009-10. doi:10.1115/1.4038763.

An experimental investigation of the effects of layers of nanoparticles formed during femtosecond laser surface processing (FLSP) on pool boiling heat transfer performance has been conducted. Five different stainless steel 304 samples with slightly different surface features were fabricated through FLSP, and pool boiling heat transfer experiments were carried out to study the heat transfer characteristics of each surface. The experiments showed that the layer(s) of nanoparticles developed during the FLSP processes, which overlay FLSP self-organized microstructures, can either improve or degrade boiling heat transfer coefficients (HTC) depending on the overall thickness of the layer(s). This nanoparticle layer thickness is an indirect result of the type of microstructure created. The HTCs were found to decrease with increasing nanoparticle layer thickness. This trend has been attributed to added thermal resistance. Using a focused ion beam milling process and transmission electron microscopy (TEM), the physical and chemical properties of the nanoparticle layers were characterized and used to explain the observed heat transfer results. Results suggest that there is an optimal nanoparticle layer thickness and material composition such that both the HTCs and critical heat flux (CHF) are enhanced.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031010-031010-10. doi:10.1115/1.4038702.

In the production process of large-diameter seamless steel pipes, the blank heating quality before roll piercing has an important effect on whether subsequently conforming piping is produced. Obtaining accurate pipe blank heating temperature fields is the basis for establishing and optimizing a seamless pipe heating schedule. In this paper, the thermal process in a regenerative heating furnace was studied using fluent software, and the distribution laws of the flow field in the furnace and of the temperature field around the pipe blanks were obtained and verified experimentally. The heating furnace for pipe blanks was analyzed from multiple perspectives, including overall flow field, flow fields at different cross sections, and overall temperature field. It was found that the changeover process of the regenerative heating furnace caused the temperature in the upper part of the furnace to fluctuate. Under the pipe blanks, the gas flow was relatively thin, and the flow velocity was relatively low, facilitating the formation of a viscous turbulent layer and thereby inhibiting heat exchange around the pipe blanks. The mutual interference between the gas flow from burners and the return gas from the furnace tail flue led to different flow velocity directions at different positions, and such interference was relatively evident in the middle part of the furnace. A temperature “layering” phenomenon occurred between the upper and lower parts of the pipe blanks. The study in this paper has some significant usefulness for in-depth exploration of the characteristics of regenerative heating furnaces for steel pipes.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031011-031011-11. doi:10.1115/1.4038706.

A clamp-on measurement system for flexible and accurate fluid temperature measurements for turbulent flows with Reynolds numbers higher than 30,000 is presented in this paper. This noninvasive system can be deployed without interference with the fluid flow while delivering the high accuracies necessary for performance and acceptance testing for power plants in terms of measurement accuracy and position. The system is experimentally validated in the fluid flow of a solar thermal parabolic trough collector test bench, equipped with built-in sensors as reference. Its applicability under industrial conditions is demonstrated at the 50 MWel AndaSol-3 parabolic trough solar power plant in Spain. A function based on large experimental data correcting the temperature gradient between the measured clamp-on sensor and actual fluid temperature is developed, achieving an uncertainty below ±0.7 K (2σ) for fluid temperatures up to 400 °C. In addition, the experimental results are used to validate a numerical model. Based on the results of this model, a general dimensionless correction function for a wider range of application scenarios is derived. The clamp-on system, together with the dimensionless correction function, supports numerous combinations of fluids, pipe materials, insulations, geometries, and operation conditions and should be useful in a variety of industrial applications of the power and chemical industry where temporal noninvasive fluid temperature measurement is needed with good accuracy. The comparison of the general dimensionless correction function with measurement data indicates a measurement uncertainty below 1 K (2σ).

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(3):031012-031012-12. doi:10.1115/1.4038707.

The aim of this study is to simulate and analyze the heat transfer and fluid flow characteristics for a tube of a heat exchanger fitted with inserts. The purpose of these inserts is to increase the heat transfer rate and improve the thermal performance of the heat exchanger. In this study, several types of tube inserts are simulated via a commercial computational fluid dynamics (CFD) solver. These insert types are presented as a single tube fitted with twisted tapes (TTs), twisted tapes with rod (TTR), and helical twisted tapes (HTT) with rod. To assess the performance of each insert type, the CFD results are presented in dimensionless form such as the Nusselt number (Nu), friction factor (f), and performance evaluation criteria (PEC). Additionally, useful dimensionless correlations are developed and presented in this paper to predict the performance of the heat exchanger over a wide range of Reynolds number and tape twist ratio. To ensure accurate CFD results, grid independence test and model validation study against previously reported experimental data were performed.

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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