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IN THIS ISSUE

### Editorial

J. Thermal Sci. Eng. Appl. 2009;1(1):010201-010201-1. doi:10.1115/1.3183810.
FREE TO VIEW

The first question that springs to many people's minds when they hear of a new journal in the thermal sciences is: Why is another journal being started? Consider this field. The thermal sciences are used in a very wide range of devices and processes, from electronics cooling to heat treatment of metals, from power production to biomedical devices, from chemical processes to alternative energy conversion systems. Different industries and user communities have different needs. Most current journals deal with long-term, basic issues, often largely of academic interest. Frequently, the information in these papers is not presented in a manner that is easy to implement in real applications. Consequently, industrial practitioners and individuals in government labs do not seem to consult many of these journals; rather, they generate the information in-house. There is much duplication of effort, and emerging techniques and technologies discussed in journals often are not translated into practice.

Commentary by Dr. Valentin Fuster

### Research Papers

J. Thermal Sci. Eng. Appl. 2009;1(1):011001-011001-8. doi:10.1115/1.3159482.

The performance of hydronic heating coils with nanoparticle enhanced heat transfer fluids (nanofluids) is evaluated and compared with their performance with a conventional heat transfer fluid comprised of 60% ethylene glycol (EG) and 40% water, by mass (60% EG). The nanofluids analyzed are comprised of either CuO or $Al2O3$ nanoparticles dispersed in the 60% EG solution. The heating coil has a finned tube configuration commonly used in commercial air handling and ventilating systems. Coil performance is modeled using methods that have been previously developed and validated. The methods are modified by incorporating Nusselt number correlations for nanofluids that have been previously documented in the literature. Similarly, correlations for nanoparticle thermophysical properties that have been documented in the literature are employed. The analyses show that heating coil performance may be enhanced considerably by employing these nanofluid solutions as a heat transfer medium. The model predicts a 16.6% increase in coil heating capacity under certain conditions with the 4% $Al2O3$/60% EG nanofluid, and a 7.4% increase with the 2% CuO/60% EG nanofluid compared with heating capacity with the base fluid. The model predicts that, for a coil with the $Al2O3$/60% EG nanofluid, liquid pumping power at a given heating output is reduced when compared with a coil with the base fluid.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2009;1(1):011002-011002-8. doi:10.1115/1.3159479.

To meet the performance goals of advanced fossil power generation systems, future coal-gas fired turbines will likely be operated at temperatures higher than those in the current commercial natural gas-fired systems. The working fluid in these future turbines could contain substantial moisture (steam), mixed with carbon dioxide, instead of air or nitrogen in conventional gas turbines. As a result, the aerothermal characteristics among the advanced turbine systems are expected to be significantly different, not only from the natural gas turbines but also will be dependent strongly on the compositions of turbine working fluids. Described in this paper is a quantitative comparison of thermal load on the external surface of turbine airfoils that are projected to be utilized in different power cycles the U.S. Department of Energy plans for the next 2 decades. The study is pursued with a computational simulation, based on the three-dimensional computational fluid dynamics analysis. While the heat transfer coefficient has shown to vary strongly along the surface of the airfoil, the projected trends were relatively comparable for airfoils in syngas and hydrogen-fired cycles. However, the heat transfer coefficient for the oxyfuel cycle is found to be substantially higher by about 50–60% than its counterparts in syngas and hydrogen turbines. This is largely caused by the high steam concentration in the turbine flow. Results gained from this study overall suggest that advances in cooling technology and thermal barrier coatings are critical for developments of future coal-based turbine technologies with near zero emissions.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2009;1(1):011003-011003-10. doi:10.1115/1.3159480.

Future advanced turbine systems for electric power generation, based on coal-gasified fuels with $CO2$ capture and sequestration, are aimed for achieving higher cycle efficiency and near-zero emission. The most promising operating cycles being developed are hydrogen-fired cycle and oxyfuel cycle. Both cycles will likely have turbine working fluids significantly different from that of conventional air-based gas turbines. In addition, the oxyfuel cycle will have a turbine inlet temperature target at approximately 2030 K $(1760°C)$, significantly higher than the current level. This suggests that aerothermal control and cooling will play a critical role in realizing our nation’s future fossil power generation systems. This paper provides a computational analysis in comparing the internal cooling performance of a double-wall or skin-cooled airfoil to that of an equivalent serpentine-cooled airfoil. The present results reveal that the double-wall or skin-cooled approach produces superior performance than the conventional serpentine designs. This is particularly effective for the oxyfuel turbine with elevated turbine inlet temperatures. The effects of coolant-side internal heat transfer coefficient on the airfoil metal temperature in both hydrogen-fired and oxyfuel turbines are evaluated. The contribution of thermal barrier coatings toward overall thermal protection for turbine airfoil cooled under these two different cooling configurations is also assessed.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2009;1(1):011004-011004-5. doi:10.1115/1.3159524.

A quasisteady multimode heat-transfer model for boiler concentric-tube overfire air ports has been developed that predicts the effect of geometry, furnace heat source and heat sink temperatures, axial injector wall conduction, and coolant flow rate on the tube wall temperature distributions. The model imposes a radiation boundary condition at the outlet tip of the ports, which acts as a heat source. The model was validated using field data and showed that both the airflow distribution in the ports and tube diameter can be used to control the maximum tube wall temperature. This helps avoid tube overheating and thermal degradation. For nominal operating conditions, highly nonlinear axial temperature distributions were observed in both tubes near the hot outlet end of the port.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2009;1(1):011005-011005-7. doi:10.1115/1.3159525.

A dynamic treatment of interfacial area concentration has been studied over the last decade by employing the interfacial area transport equation. When coupled with the two-fluid model, the interfacial area transport equation replaces the flow regime dependent correlations for interfacial area concentration and eliminates potential artificial bifurcation or numerical oscillations stemming from these static correlations. An extensive database has been established to evaluate the model under various two-phase flow conditions. These include adiabatic and heated conditions, vertical and horizontal flow orientations, round, rectangular, annulus, and $8×8$ rod-bundle channel geometries, and normal-gravity and reduced-gravity conditions. Currently, a two-group interfacial area transport equation is available and applicable to comprehensive two-phase flow conditions spanning from bubbly to churn-turbulent flow regimes. A framework to couple the two-group interfacial area transport equation with the modified two-fluid model is established in view of multiphase computational fluid dynamics code applications as well as reactor system analysis code applications. The present study reviews the current state-of-the-art in the development of the interfacial area transport equation, available experimental databases, and the analytical methods to incorporate the interfacial area transport equation into the two-fluid model.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2009;1(1):011006-011006-7. doi:10.1115/1.3159498.

High solidity pin and pedestal arrays are beneficial in reducing temperature gradients and distributing stress across double wall cooling channels such as trailing edge regions. In this study two high solidity (45%) cooling channel geometries were selected and tested in both constant channel height and converging channel configurations. One geometry consisted of a high solidity round pin fin array and the other geometry consisted of a rounded diamond pedestal array designed to minimize pressure drop. Heat transfer rates for both geometries were determined on a row by row basis for both the constant channel and converging channel configurations. Heat transfer and pressure drop measurements were acquired in a bench scale test rig. Reynolds numbers ranged from approximately 3000 to 60,000 for the constant channel arrays and 3500 to 100,000 for the converging arrays based on the characteristic dimension of the pin or pedestal and the local maximum average velocity across a row. The high solidity pin fin array had an axial spacing $(X/D)$ of 1.043 and a cross channel spacing $(Z/D)$ of 1.674. The high solidity diamond pedestal array had an axial spacing of 1.00 and a cross channel spacing of 1.93. The constant section pin fin array had a channel height to diameter of 0.95 while the constant section diamond pedestal array had a height to characteristic dimension of 0.96. The converging pin fin array had an inlet to exit convergence ratio of 2.87 over five heated rows while the converging pedestal array had an inlet to exit convergence ratio of 3.53 over seven heated rows. The constant channel height internal cooling schemes have shown that the high solidity pin fin and the rounded diamond pedestal arrays produce comparable heat transfer and array pressure drop. Both the converging channel arrays show a noticeable (5–7%) reduction in heat transfer compared with the constant height channels. Array pressure drop for the two converging geometries was found to be quite consistent.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2009;1(1):011007-011007-9. doi:10.1115/1.3159526.

This study is concerned with building a computational fluid dynamics (CFD) model to simulate the combustion process occurring in the combustion chamber of some domestic boilers. The burner used in this boiler is a conventional cylindrical premix burner with small inlet holes on its surface. A two-dimensional CFD model is built to simulate the combustion chamber domain, and the partially premixed combustion model with a postprocessor for $NOx$ calculations is used to simulate the combustion process inside the combustion chamber. A complete description of the formation characteristics of $NOx$ produced from the boiler is discussed in detail. A comparison between the CFD numerical results and the experimental measurements at different boiler loads is performed in order to validate the numerical model and investigate the accuracy of the CFD model. The validated CFD model is used to investigate the effect of different boundaries temperatures and the mixture inlet velocity on the flue gas average temperature, residence time, and hence the CO and $NOx$ concentrations produced from the combustion chamber. The concept of changing the mixture inlet velocity is found to be an effective method to improve the design of the burner in order to reduce the pollutant emissions produced from the boiler with no effect on the boiler efficiency.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2009;1(1):011008-011008-7. doi:10.1115/1.3192771.

With the simulation of engineering processes via numerical methods on the rise comes the need for a quantitative measure of the agreement between computational results and experimental measurements. The use of quantitative methods in the comparison of the results of numerical and experimental analyses supersedes the traditional qualitative approach. In the present paper, the importance of the role of modeling assumptions in a verification and validation effort is illustrated through a mesoscale combustor example. The various types of uncertainties encountered in the experimentation and numerical simulation are investigated. Through the investigation the initial modeling assumptions proved to be insufficient, producing a comparison error outside of the acceptable range. Thus, the modeling assumptions were sequentially revised, minimizing the comparison error and producing a successful verification and validation effort.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2009;1(1):011009-011009-12. doi:10.1115/1.3192772.

Petroleum coke is processed into calcined coke in a rotary kiln, where the temperature profiles of flue gas and coke bed are highly nonuniform due to different flow and combustion mechanisms. Motivated by saving energy costs, the effect of refractory brick’s thermal properties on potential energy savings is investigated. This study focuses on investigating potential energy savings by replacing inner one-third of existing bricks with higher thermal capacity $(Cp)$ and/or higher thermal-conductivity $(k)$ bricks. This paper investigates the postulation: the bricks with higher thermal capacity could store more thermal energy during the period in contact with the hot gas and would release more heat to the cock bed when the bricks rotate to the position in contact with the coke bed. A rotational transient marching conduction numerical simulation is conducted using the commercial software FLUENT . The impact of brick heat capacity and thermal conductivity on transporting thermal energy to the coke bed is analyzed. The results show the following: (a) Increasing the heat capacity of brick layer reduces brick temperature, which helps increase the heat transfer between the hot gas and brick. In other words, it does help brick to store more heat from the hot gas, but heat transfer between brick and coke is reduced, which is opposite to the original postulation. (b) Higher brick thermal conductivity decreases brick temperature, thus increases heat transfer between hot gas and the brick layer. The heat transfer from brick to coke bed is also increased but not significantly. (c) Since usually a brick with a higher $Cp$ value also has a higher $k$-value, simulation of a brick layer with both four times higher $Cp$ and $k$-values actually shows a reduction in the brick temperature, and hence a degradation of the heat transfer between the brick and coke bed. Therefore, replacing the existing brick layer with a high $Cp$- and/or high $k$-value brick is not recommended.

Commentary by Dr. Valentin Fuster

### Technical Briefs

J. Thermal Sci. Eng. Appl. 2009;1(1):014501-014501-5. doi:10.1115/1.3159477.

The study presented here concerns the impact of car inclination on the temperatures in the vehicle underhood compartment. We report here underhood thermal measurements carried out on a vehicle in wind tunnel S4 of Saint-Cyr, France. The underhood is instrumented by 80 surface and air thermocouples. Measurements are carried out for three different thermal charges (thermal functioning points). During tests, the engine is in operation, and the front wheels positioned on the test facility equipped with rollers, permitting the wheel power and rotational speed control. Three car inclinations are tested.

Commentary by Dr. Valentin Fuster