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### Research Papers

J. Thermal Sci. Eng. Appl. 2016;9(1):011001-011001-8. doi:10.1115/1.4034338.

This paper presents the thermo-economic limits of ambient heat rejection in vertical fin arrays with buoyancy-driven flow enhancement through the chimney effect. A one-dimensional semi-analytical thermo-fluidic model is developed to assess the cooling power enhancement of the proposed heat sink design. A bi-objective optimization is performed utilizing genetic algorithm to present the tradeoffs between the cost and the thermal performance of a heat sink. For the considered baseplate geometry, the maximal cooling power without a chimney amounts 1540 W at a heat flux of 1.03 W/cm2. By adding a chimney up to 2.5 m high, the cooling power is increased by 46% to 2250 W at a heat flux of 1.50 W/cm2.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011002-011002-12. doi:10.1115/1.4034178.

The transient source measurement technique is a nonintrusive, nondestructive method of measuring the thermal properties of a given sample. The transient source technique has been implemented using a wide variety of sensor shapes or configurations. The modern transient plane source (TPS) sensor is a spiral-shaped sensor element which evolved from transient line and transient hot strip (THS) source techniques. Commercially available sensors employ a flat interface that works well when test samples have a smooth, flat surface. The present work provides the basis for a new, cylindrical strip (CS) sensor configuration to be applied to cylindrical surfaces. Specifically, this work uses parameter estimation theory to compare the performance of CS sensor configurations with a variety of existing flat sensor geometries, including TPS and THS. A single-parameter model for identifying thermal conductivity and a two-parameter model for identifying both thermal conductivity as well as volumetric heat capacity are considered. Results indicate that thermal property measurements may be carried out with greater measurement sensitivity using the CS sensor configuration than similar configurations for flat geometries. In addition, this paper shows how the CS sensor may be modified to adjust the characteristic time scale of the experiment, if needed.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011003-011003-7. doi:10.1115/1.4034340.

The purpose of this study was to optimize the performance of a double-exposure solar cooker based on exergy efficiency. Two similar solar cookers with variable parabolic mirror position were used for this experimental research. The system's exergy depends on many variables, which were kept fixed with the exception of the mirror position and operation time. The mathematical model of exergy efficiency was obtained based on the experimental variables, which could be used to optimize the mirror positions at any time. As a result, a new system with a variable mirror on a parabolic curve was developed, which can yield up to 30% increased mean exergy efficiency. Validation of the results was carried out by both the variance analysis test and comparing with the experimental data. The experiments were carried out in Mashhad, Iran, at 37 latitude, 54 longitude, and a height of 985 m above sea level.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011004-011004-7. doi:10.1115/1.4034595.
OPEN ACCESS

Sensitivity analysis and design calculations are often best performed using low-order models. This work details work done on adding complementary pieces to a low-order, quasi-steady-state ablation model to facilitate uncertainty propagation. The quasi-steady-state ablation model is a one-dimensional, quasi-steady-state, algebraic ablation model that uses finite-rate surface chemistry and equilibrium pyrolysis-gas-production submodels to predict surface recession rate. The material response model is coupled to a film-transfer boundary layer model to enable the computation of heat and mass transfer from an ablating surface. For comparison to arcjet data, a simple shock heated gas model is coupled. A coupled model consisting of submodels for the shock heated gases, film heat and mass transfer, and material response is exercised against recession rate data for surface and in-depth ablators. Comparisons are made between the quasi-steady-state ablation model and the unsteady ablation code, Chaleur, as well as to other computations for a graphite ablator in arcjet facilities. The simple models are found to compare reasonably well to both the experimental results and the other calculations. Uncertainty propagation using a moment based method is presented. The results of this study are discussed, and conclusions about the utility of the method as well as the properties of the ablation code are drawn.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011005-011005-9. doi:10.1115/1.4034510.

This paper focuses on the gas flow study of an ejector used in applications where moist gases are being entrained. Two parts of work are presented. In the first part, characteristics of gas flow inside an ejector, as well as the ejector's performance under various operating and geometric configurations, were studied with a three-dimensional computational model. Measurements were also performed for validation of the model. In the second part, focus was given to the potential condensation or desublimation phenomena that may occur inside an ejector when water vapor is included in the entrained stream. Experiments using light-attenuation method were performed to verify the presence of a second phase; then, the onset of phase change and the phase distribution were obtained numerically. A two-dimensional axis-symmetric model was developed based on the model used in the first part. User-defined functions were used to implement the phase-change criteria and particle prediction. A series of simulations were performed with various amounts of water vapor added into the entrained flow. It was found that both frost particles and water condensate could form inside the mixing tube depending on the operating conditions and water vapor concentrations. When the concentration exceeds 3% by mass, water vapor could condense throughout the mixing tube. Some preliminary results of the second phase particles formed, e.g., critical sizes and distributions, were also obtained to assist with the design and optimization of gas ejectors used in similar applications.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011006-011006-9. doi:10.1115/1.4034511.

The challenge in design and manufacturing tasks includes precise measurement of static friction, stiffness, deformation, raceway relative approach, and heat distribution of slewing ring bearings. These parameters affect the life and performance of the rolling elements bearing at elevated thermal environments. Toward that, sections of a complete bearing called linear model mock-up bearing (LMMB) have been designed and fabricated for the study of heat distribution. The physical significance of the heat distribution on bearing elements was studied using square-guarded hot-plate (SGHP) apparatus. The thermal contact conductance (TCC) experiments were carried out by varying surface roughnesses and interface temperatures under different loading conditions by using the combinations of steel plates and LMMB under dry and lubricated conditions. From this study, it is observed that the TCC values obtained from LMMB were significantly high across the contact surfaces of AISI 42100–AISI 52100–AISI 4140 steel plate's combination. Further, the finite element method (FEM) simulation has been carried out successfully to evaluate the temperature distribution in combination of bearing steel plates and LMMB by solidworks software, and the results are discussed.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011007-011007-10. doi:10.1115/1.4034596.

Humidification–dehumidification (HDH) desalination is a simple technique to produce desalinated water from saline water. Dehumidifier is a key component in the HDH system, which influences the desalination yield. In the current work, a three-dimensional multiphase numerical simulation study is carried out on third dehumidifier alone to evaluate its performance using computational fluid dynamics (CFD) code. The simulation result is validated with experimental readings, and it is found that there exists a very close agreement between the predicted and the experimental readings. The key parameters influencing the dehumidifier performance are chilled water temperature, humid air temperature, and volume fraction. Experiments are carried out on the combined two stage HDH plant at different hot water temperature and flow rates. A detailed study of dehumidification process is carried out using ansys cfx 15.0 tool by solving the governing equations, namely, mass, momentum, and energy, with turbulence modeled through shear stress transport (SST) k–ω model of closure. Multiphase is solved using a free-surface multiphase model. The measured average cooled air temperature and relative humidity (RH) at the exit of third dehumidifier are 21 °C and 67%. The desalinated water produced at a hot water flow of 100 LPH is found as 2205 ml/h from the experiments. The CFD results are deviated by 0.41%, 6.45%, and −0.70% with that of experimental results at the dehumidifier for air temperature, velocity, and chilled water temperature, respectively.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011008-011008-14. doi:10.1115/1.4034597.

The effect of rib orientation on flow and heat transfer in a four-pass square channel with skewed ribs in nonorthogonal-mode rotation was numerically studied by using omega-based Reynolds stress model ($SMC−ω$). Two cases are examined: in first case, the ribs are oriented with respect to the main flow direction at an angle of $−45 deg$ in the first and third passage and at an angle of in the second passage. The second case is identical to the first case with the ribs oriented at angle of $+45 deg$ in the three passages. The calculations are carried out for a Reynolds number of 25,000, a rotation number of 0.24, and a density ratio of 0.13. The results show that the secondary flows induced by $−45 deg$ ribs and by rotation combine partially destructively in the first and third passage of first case. In contrast, for second case, the secondary flows induced by $+45 deg$ ribs and by rotation combine constructively in the first passage, while the flow is dominated by the vortices induced by $+45 deg$ ribs in the third passage. In first case, a significant degradation of the heat transfer rate is observed on the coleading side of the first passage and on both cotrailing and coleading sides of the third as compared to second case. Consequently, the rib orientations at $+45 deg$ are preferred in the radial outward flowing passage with an acceptable pressure drop. The numerical results are in agreement with the available experimental data.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011009-011009-12. doi:10.1115/1.4034598.

Scale buildup on water-side heat transfer surfaces poses a potential operating challenge for steam-assisted gravity drainage (SAGD) boilers used in the production of bitumen since produced water, which has a high dissolved solid content, is recycled. Scale from deposition of dissolved solids on boiler tubes acts as a thermal insulating layer, decreasing heat transfer and lowering boiler efficiency. Understanding scale deposit composition on heat transfer surfaces is beneficial in the determination of adequate boiler maintenance practices and operating parameters. This research determined the effect of feedwater pH (7.5, 9.0, and 10.0) on scale composition resulting from deposition of dissolved solids under commercially relevant boiler operating conditions at 8.96 MPa (1300 psig) and 37.86 kW/m2 (12,000 Btu/h ft2). Scale deposits were analytically investigated using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDS), powder X-ray diffraction (XRD), and Raman spectroscopy. At feedwater pH values of 7.5 and 9.0, anhydrite (CaSO4), xonotlite (Ca6Si6O17(OH)2), and pectolite (NaCa2Si3O8(OH)) were detected. At the pH of 10.0, xonotlite and pectolite were identified in the absence of anhydrite. Furthermore, the magnesium silicate phase, serpentine (Mg3Si2O5(OH)4), was also postulated to be present.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011010-011010-9. doi:10.1115/1.4034599.

The natural convection fluid flow and heat transfer in an annulus of two differentially heated confocal elliptic cylinders filled with the Cu–water nanofluid are investigated numerically. The outer cylinder is maintained at a constant temperature Tc while the inner cylinder is kept at a differentially higher constant temperature Th. Equations of continuity, momentum, and energy are formulated using the dimensionless form in elliptic coordinates for two-dimensional steady, laminar, and incompressible flow, which is expressed in terms of stream function, vorticity, and temperature. The basic equations are discretized using the finite-volume method. Using a developed code, calculations were performed for Rayleigh number (103 ≤ Ra ≤ 3 × 105), volume fraction of nanoparticles (0 ≤ ϕ  ≤ 0.12), and eccentricity of the inner ellipse, ε1 = 0.7, 0.8, and 0.9. The eccentricity of outer ellipse and the angle of orientation are fixed at 0.6 deg and 0 deg, respectively. Results are presented in the form of stream lines, isotherm plots, and local and average Nusselt numbers. The results discussed in this present work show the existence of a very good agreement between the present results and those from the previous researches.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011011-011011-8. doi:10.1115/1.4034817.

In this research, a very popular alternative computational technique, the lattice Boltzmann method (LBM), has been used to simulate the indoor airflow and heat transfer in a model hospital ward. Different Reynolds numbers have been used to study the airflow pattern. Boundary conditions for velocity and temperature have also been discussed in detail. Several tests have been conducted for code validation. LBM is demonstrated through simulation in forced convection inside hospital ward with six beds for two different situations: ward without partition and ward with partition. Changes in average rate of heat transfer in terms of average Nusselt numbers have also been recorded for those situations. Average Nusselt numbers were found to differ for different cases. In terms of airflow, it has been found that, for various Reynolds numbers, airflow changes its pattern and leads to few recirculations for relatively higher Reynolds number but remains steady for low Reynolds number. It was observed that partition narrowed the channel for airflow and once the air overcame this barrier, it gets free space and recirculation appears more. For higher Reynolds number, the average rate of heat transfer increases and patients near the recirculation zone release maximum heat and will feel more comfortable.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011012-011012-9. doi:10.1115/1.4034904.
OPEN ACCESS

The transient thermal response of a 15-cell, 48 V, lithium-ion battery pack for an unmanned ground vehicle (UGV) was simulated using ANSYS fluent. Heat generation rates and specific heat capacity of a single cell were experimentally measured and used as input to the thermal model. A heat generation load was applied to each battery, and natural convection film boundary conditions were applied to the exterior of the enclosure. The buoyancy-driven natural convection inside the enclosure was modeled along with the radiation heat transfer between internal components. The maximum temperature of the batteries reached 65.6 °C after 630 s of usage at a simulated peak power draw of 3600 W or roughly 85 A. This exceeds the manufacturer's maximum recommended operating temperature of 60 °C. We present a redesign of the pack that incorporates a passive thermal management system consisting of a composite expanded graphite (EG) matrix infiltrated with a phase-changing paraffin wax. The redesigned battery pack was similarly modeled, showing a decrease in the maximum temperature to 50.3 °C after 630 s at the same power draw. The proposed passive thermal management system kept the batteries within their recommended operating temperature range.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011013-011013-12. doi:10.1115/1.4034851.

An advanced, high-effectiveness film cooling design, the antivortex hole (AVH) has been investigated by several research groups and shown to mitigate or counter the vorticity generated by conventional holes and increase film effectiveness at high blowing ratios and low freestream turbulence levels. The effects of increased turbulence on an AVH geometry were previously investigated in a preliminary steady computational fluid dynamics (CFD) study by Hunley et al. on the film effectiveness and net heat flux reduction (NHFR) at high blowing ratio. The current paper presents the results of an extended numerical parametric study, which attempts to separate the effects of turbulence intensity and length scale on film cooling performance of the AVH concept at high blowing ratio (2.0) and density ratio (2.0). In this extended study, steady Reynolds-averaged Navier–Stokes (RANS) analysis was performed with turbulence intensities of 5, 10, and 20% and length scales based on cooling hole diameter of Λx/dm = 1, 3, and 6. Increasing turbulence intensity was shown to increase the centerline, span-averaged, and area-averaged adiabatic film cooling effectiveness and NHFR. Larger turbulent length scales in the steady RANS analysis were shown to have little to no effect on the centerline, span-averaged, and area-averaged adiabatic film cooling effectiveness and NHFR at lower turbulence levels, but moderate effect at the highest turbulence levels investigated. Heat transfer results were in good agreement with the findings from adiabatic cases from previous work. Unsteady RANS results also provided supplementary flow visualization for the AVH film cooling flow under varying turbulence levels.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011014-011014-9. doi:10.1115/1.4034852.

In this study, the performance evaluation and optimization of a recently developed battery-powered vehicle air conditioning (BPVAC) system is investigated. A mathematical model is developed to simulate the thermodynamic and heat transfer characteristics of the BPVAC system and calculate the coefficient of performance (COP). Utilizing environmental chambers and a number of measuring equipment, an experimental setup is built to validate the model accuracy and to conduct performance optimization by changing the charge of refrigerant in the system. The model is validated and employed for performance simulation and optimization in a wide range of speed for the evaporator and condenser fans. The modeling results verify that for any operating condition an optimum performance can be achieved by adjusting the speed of condenser and evaporator fans. The optimum refrigerant charge is obtained, and a potential improvement of 10.5% is calculated for the performance of system under ANSI/AHRI 210/240-2008 specifications.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011015-011015-10. doi:10.1115/1.4034686.

The current detailed experimental study focuses on the optimization of heat transfer performance through jet impingement by varying the coolant flow rate to each individual jet. The test section consists of an array of jets, each jet individually fed and metered separately, that expel coolant into the channel and exit through one end. The diameter D, height-to-diameter H/D, and jet spacing-to-diameter S/D are all held constant at 9.53 mm, 2, and 4, respectively. Upon defining the optimum flow rate for each jet, varying diameter jet plates are designed and tested using a similar test setup with the addition of a plenum. Two test cases are conducted by varying the jet diameter within 10% compared to the benchmark jet diameter, 9.53 mm. The Reynolds number, which is based on hydraulic diameter of the channel and total mass flow rate entering the channel, ranges from approximately 52,000 up to 78,000. The transient liquid crystal technique is employed in this study to determine the local and average heat transfer coefficient distributions on the target plate. Commercially available computational fluid dynamics software, ansys cfx, is used to qualitatively correlate the experimental results and to fully understand the flow field distributions within the channel. The results revealed that varying the jet flow rates, total flow varied by approximately ±5% from that of the baseline case, the heat transfer enhancement on the target surface is enhanced up to approximately 35%. However, when transitioning to the varying diameter jet plate, this significant enhancement is suppressed due to the nature of flow distribution from the plenum, combined with the complicated crossflow effects.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011016-011016-10. doi:10.1115/1.4034916.

In this paper, from the heat transfer mechanisms between perforated horizontal well and formation, the mathematical models for the heat transfer and pressure drops of the horizontal well with different steam injection pipe configurations are developed. All the conventional single-pipe, concentric dual-pipe, and parallel dual-pipe configurations are considered. A correlation is proposed to represent a relationship between the thermophysical properties of the formation and the formation pressure and temperature. Then, using the method of wellbore microcontrol elements and node analysis, the steam injection process in the three different well configurations is numerically investigated. Based on the test data of a parallel dual-pipe horizontal well from an actual oilfield, a steam backflow procedure for the parallel dual-pipe configuration is proposed to confirm the sealed status of a thermal packer. The theoretical investigation plays an important role in the performance evaluation and productivity prediction of horizontal well-based thermal recovery projects. Furthermore, it also sheds some important insights on a steam injection project design with dual-pipe horizontal wells.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):011017-011017-10. doi:10.1115/1.4034913.

Jet impingement cooling has been studied extensively as this finds applications in the areas of reactor safety, electronic cooling, etc. Here, the convective heat transfer process between the air jet impingement on a uniformly heated inclined flat plate is studied numerically. In this numerical study, 3D simulations are carried out using commercial CFD code to investigate the effect of angle of inclination of plate, Reynolds number, and distance between the nozzle exit and the plate on the heat transfer characteristics. V2F model has been used to model turbulence for various nozzle–plate distance and Reynolds number. It can be concluded that V2F model predicts the Nusselt number variation on the plate satisfactorily. It is observed that point of maximum heat transfer is at the stagnation point in case of vertical jet impinging on a horizontal plate, while it shifts away from the point of impingement for the case of a vertical jet impinging on an inclined flat surface. The shift is toward the “compression side” or the “uphill side” of the air jet. The results are validated with experimental data from the literature. Detailed analysis of local heat transfer coefficients, velocity contours, temperature contours, and Nusselt number variations on the flat plate is presented.

Commentary by Dr. Valentin Fuster

### Technical Brief

J. Thermal Sci. Eng. Appl. 2016;9(1):014501-014501-4. doi:10.1115/1.4032606.

A methodology has been developed for coupling the one-dimensional (1D) solution of flow inside the nonpermeable channels with the 3D outer flow in shell and tube type of configurations. In the proposed reacting channel, the 1D channels have detailed reactions while the outer 3D flow can be reactive or nonreactive. The channels are discretized into 1D grid points and a parabolic solver is used to solve the species transport and energy equations inside the channels. Since the walls of the channels are nonpermeable, the two zones are coupled only through the heat transfer. The current approach is tested and validated for a series of problems with increasing complexities. The predictions of the channel model (CM) are compared with 3D modeling of the channels and experimental data. The CM predictions are in excellent agreement with the fully resolved (FR) model with much less computational cost. The discussed methodology is useful for applications such as fuel reformers, hydrocarbon cracking furnaces, heat exchangers, etc.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):014502-014502-3. doi:10.1115/1.4034853.

Mechanical and thermal property values of carbon fiber-reinforced polymer (CFRP) composites are readily available. However, the small diameter and thermal anisotropy of the carbon filaments pose significant challenges for measuring thermal diffusivity of the constituent fibers. As a result, the literature describes many techniques to address this issue. Here, a new method for the direct, bulk measurement of on-axis thermal diffusivity of a matrix-free carbon fiber bundle is reported. Aligned carbon fiber tows were uniformly compacted into a collimated, cylindrical bundles using heat-shrink tubing, and fixed such that the fibers remained unwetted, in the center of an epoxy disk, which was subsequently analyzed for thermal diffusivity using laser flash analysis.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2016;9(1):014503-014503-9. doi:10.1115/1.4034914.

According to the particular aerodynamic heating loads which hypersonic aerospace aircrafts suffered from in-service environment, a lightweight integrated thermal protection system (ITPS) named pyramidal core sandwich panel is designed. This is considered not only as an insulation structure but also a load-bearing structure. Compared to traditional thermal protection systems (TPSs), the sandwich panel has simultaneous lightweight, load-bearing, and excellent thermal protection property. The finite-element heat transfer analysis for the pyramidal core sandwich structure is performed, and the distributions of temperature in the structure are presented. Then sequential coupling method is adopted to analyze the thermomechanical performance of the structure and presentations of field of stress and displacement under aerodynamic and thermal load are provided. A comparison between corrugated-core sandwich panels and pyramidal core sandwich panels from the perspectives of heat insulation, strength, and mass is carried out. The results indicate that the particular performance of pyramidal-core structure is superior to that of corrugated-core structure.

Commentary by Dr. Valentin Fuster