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The purpose of this study is to investigate the effect of partial liquefaction (due to ageing) of the vitreous humor on the transport of ocular drugs. In our model, the gel part of the vitreous is treated as a Darcy-type porous medium. A spherical region within the porous part of vitreous is in a liquid state which, for computational purposes, is also treated as a porous medium but with a much higher permeability. Using the finite element method, a time-dependent, three-dimensional model has been developed to computationally simulate (using the Petrov–Galerkin method) the transport of intravitreally injected macromolecules where both convection and diffusion are present. From a fluid physics and transport phenomena perspective, the results show many interesting features. For pressure-driven flow across the vitreous, the flow streamlines converge into the liquefied region as the flow seeks the fastest path of travel. Furthermore, as expected, with increased level of liquefaction, the overall flow rate increases for a given pressure drop. We have quantified this effect for various geometrical considerations. The flow convergence into the liquefied region has important implication for convective transport. One effect is the clear diversion of the drug as it reaches the liquefied region. In some instances, the entry point of the drug in the retinal region gets slightly shifted due to liquefaction. While the model has many approximations and assumptions, the focus is illustrating the effect of liquefaction as one of the building blocks toward a fully comprehensive model.

This study explores thermal design aspects of nanowarming-assisted recovery of the heart from indefinite cryogenic storage, where nanowarming is the volumetric heating effect of ferromagnetic nanoparticles excited by a radio frequency electromagnet field. This study uses computational means while focusing on the human heart and the rat heart models. The underlying nanoparticle loading characteristics are adapted from a recent, proof-of-concept experimental study. While uniformly distributed nanoparticles can lead to uniform rewarming, and thereby minimize adverse effects associated with ice crystallization and thermomechanical stress, the combined effects of heart anatomy and nanoparticle loading limitations present practical challenges which this study comes to address. Results of this study demonstrate that under such combined effects, nonuniform nanoparticles warming may lead to a subcritical rewarming rate in some parts of the domain, excessive heating in others, and increased exposure potential to cryoprotective agents (CPAs) toxicity. Nonetheless, the results of this study also demonstrate that computerized planning of the cryopreservation protocol and container design can help mitigate the associated adverse effects, with examples relating to adjusting the CPA and/or nanoparticle concentration, and selecting heart container geometry, and size. In conclusion, nanowarming may provide superior conditions for organ recovery from cryogenic storage under carefully selected conditions, which comes with an elevated complexity of protocol planning and optimization.

Nanoparticles (NPs) are promising agents to absorb external energy and generate heat. Clusters of NPs or NP array heating have found an essential role in several biomedical applications, diagnostic techniques, and chemical catalysis. Various studies have shed light on the heat transfer of nanostructures and greatly advanced our understanding of NP array heating. However, there is a lack of analytical tools and dimensionless parameters to describe the transient heating of NP arrays. Here we demonstrate a comprehensive analysis of the transient NP array heating. Firstly, we develop a set of analytical solutions for the NP array heating and provide a useful mathematical description of the spatial-temporal evolution of temperature for 2D, 3D, and spherical NP array heating. Based on this, we introduce the concept of thermal resolution that quantifies the relationship between minimal heating time, NP array size, energy intensity, and target temperature. Lastly, we define a set of dimensionless parameters that characterize the transition from confined heating to delocalized heating. This study advances the understanding of nanomaterials heating and guides the rational design of innovative approaches for NP array heating.

Thermoregulation is a process that is essential to the maintenance of life for all warm-blooded mammalian and avian species. It sustains a constant core body temperature in the face of a wide array of environmental thermal conditions and intensity of physical activities that generate internal heat. A primary component of thermoregulatory function is the movement of heat between the body core and the surface via the circulation of blood. The peripheral vasculature acts as a forced convection heat exchanger between blood and local peripheral tissues throughout the body enabling heat to be convected to the skin surface where is may be transferred to and from the environment via conduction, convection, radiation, and/or evaporation of water as local conditions dictate. Humans have evolved a particular vascular structure in glabrous (hairless) skin that is especially well suited for heat exchange. These vessels are called arteriovenous anastomoses (AVAs) and can vasodilate to large diameters and accommodate high flow rates. We report herein a new technology based on a physiological principle that enables simple and safe access to the thermoregulatory control system to allow manipulation of thermoregulatory function. The technology operates by applying a small amount of heating local to control tissue on the body surface overlying the cerebral spine that upregulates AVA perfusion. Under this action, heat exchangers can be applied to glabrous skin, preferably on the palms and soles, to alter the temperature of elevated blood flow prior to its return to the core. Therapeutic and prophylactic applications are discussed.

In order to measure the effective diffusion coefficient D of Bevacizumab (Avastin, Genentech) in the vitreous humor, a new technique is developed based on the “contour method” and in vivo optical coherence tomography measurements. After injection of Bevacizumab-fluorescein conjugated compound solution into the rabbit eye, the contours of drug concentration distribution at the subsurface of injection were tracked over time. The 2D contours were extrapolated to 3D contours using reasonable assumptions and a numerically integrated analytical model was developed for the theoretical contours for the irregularly shaped drug distribution in the experimental result. By floating the diffusion coefficient, different theoretical contours were constructed and the least-squares best fit to the experimental contours was performed at each time point to get the best fit solution. The approach generated consistent diffusion coefficient values based on the experiments on four rabbit eyes over a period of 3 h each, which gave D=1.2±0.6×10−6 cm2/s, and the corresponding theoretical contours matched well with the experimental contours. The quantitative measurement of concentration using optical coherence tomography and fluorescein labeling gives a new approach for the “noncontact” in vivo drug distribution measurement within vitreous.

Impinging jets are extensively investigated in numerous benchmarks. Such configurations are common in many industrial and engineering applications (e.g., manufacturing, material processing, electronic cooling, paper drying, textiles and tempering of glass). Various comprehensive reviews of jets impingement onto a motionless wall are available in the literature [1–9]. However, a small number of studies were devoted to the effects of the wall motion of impinging jets, on the flow structure and the heat transfer. The first study of a jet impingement on a moving wall was carried out experimentally by Subba Raju and Schlunder [10]. They investigated the heat transfer of a single jet impinging a moving belt. Huang et al. [11] performed numerically the case of a turbulent jet on a rectangular duct with surface motion effects. They have found that, when the plate velocity is great, Nusselt numbers becomes smaller around the area where the surface motion is opposed to that of the flow and augments when the moving wall and the flow evolve in the same direction. Zumbrunnen [12] have developed an analytical study for a single planar laminar impinging slot jet onto a moving plate subjected to a constant heat flux.They show that the heat transfer is more effective when the boundary layer development is slowed down by the plate motion. Chattopadhyay et al. [13] have numerically investigated the turbulent heat transfer of an array of slot jets impinging a moving plate using large Eddy simulation (LES), for jet exit Reynolds numbers ranging between 500 and 3000 and for several surface-jet velocities ratios R sj such as: 0 ≤ R sj ≤ 2. They found that the Nusselt number distribution over the plate becomes more uniform when the total heat transfer and the plate velocity decreases. Later, Chattopadhyay and Saha [14] used large Eddy simulation to investigate both the turbulent flow and the heat transfer resulting from a single slot jet impingement onto a moving hot isothermal plate. They have provided some results for a given jet exit Reynolds number of 5800 on a moving plate corresponding to a velocity ratio between 0 and 2. They were focused on the details of the flow structure, the velocity profiles and the turbulent shear stresses distribution. Similarly, the flow field of a confined turbulent slot air jet impinging perpendicularly a flat surface, was experimentally studied by Senter [15]. The experiments were carried out for a nozzle-to-plate spacing of eight slot nozzle thickness, at three Reynolds number (5300, 8000, and 10,600) and four surface-to-jet velocity ratios (0, 0.25, 0.5 and 1.0). Measurements are performed within the main regions of the jet. It appears that the flow structure patterns corresponding to a given surface-to-jet velocity ratio are independent with the jet exit Reynolds number between 5300 and 10,600. Also, a slight modification of the flow field is observed for a surface-to-jet velocity ratio of 0.25, whereas this effect is more significant for higher ratios of 0.5 and 1. On the other hand, Senter [15], determined the local Nusselt number by means the computation fluid dynamics (CFD) software Fluent using k–e WCP model for jet exit Reynolds number of Re = 10,600 and normalized plate velocities of 0, 0.25, 0.5, and 1.0. This study proves that the local Nusselt number tends to significantly decrease followed by an increasing around the stagnation zone. Sharif and Banerjee [16] have achieved a numerical study by the CFD code Fluent, using the standard k–e turbulence model coupled to the enhanced wall treatment. They showed that the local Nusselt numbers along the moving plate exceed the values in the vicinity of the impinging region for the cases corresponding to lower plate velocities ratios, which can be explained by the thinning of dynamical and thermal boundary layers. These values decrease for greatest plate velocities induced by the parallel dominating shear driven flow. For a given plate velocity, the average Nusselt number close to the plate augments whilst the average skin friction coefficient decreases when jet exit Reynolds number increases. On the other hand, for a given jet exit Reynolds number, these two parameters slightly decrease for small velocity ratio, followed by an increase for greater values In the present paper, the case of a confined slot jet impinging perpendicularly a moving heated wall is numerically investigated (Fig. ​(Fig.1).1). This study complements both the previous work of Senter [15] and Sharif and Banerjee [16] by considering values of jet-plate velocity ratios greater than 1 (0 ≤ R sj ≤ 4). We extend the velocity ratio surface-jet because Zumbrunnen et al. [17] reported that the impingement surface velocity can exceed as much as ten (10) times the jet velocity in some industrial application such as hot rolling process. Open in a separate window Fig. 1 Configuration and parameters

The main motivation of conducting this work is to present a rigorous analysis and investigation of the potential effect of the heat pipe adiabatic region on the flow and heat transfer performance of a heat pipe under varying evaporator and condenser conditions. A two-dimensional steady-state model for a cylindrical heat pipe coupling, for both regions, is presented, where the flow of the fluid in the porous structure is described by Darcy–Brinkman–Forchheimer model which accounts for the boundary and inertial effects. The model is solved numerically by using the finite volumes method, and a fortran code was developed to solve the system of equations obtained. The results show that a phase change can occur in the adiabatic region due to temperature gradient created in the porous structure as the heat input increases and the heat pipe boundary conditions change. A recirculation zone may be created at the condenser end section. The effect of the heat transfer rate on the vapor radial velocities and the performance of the heat pipe are discussed.

Microchannels are being used increasingly in microelectro- mechanical systems (MEMS) where heat transfer constitutes an important process step in many devices. The high heat transfer coefficient and low thermal resistance of these channels also make them attractive in compact heat exchanger applications. In order to design these devices for reliable operation, it is essential to understand the flow and heat transfer characteristics in microchannels. The heat transfer data for gas flow in microchannels reported by earlier researchers were found to deviate considerably from the established heat transfer correlations. Although deviations in the friction factor data for the microchannels are now understood as being attributable to experimental uncertainties, incorrect estimation of boundary conditions, and entrance region effects, the heat transfer data has not yet been clearly reconciled. In general, an effect of Reynolds number (Re) on Nussselt number (Nu) in the laminar flow region has been reported in previous literature. This could stem from a lack of understanding of how heat transfer is affected by parameters that are usually negligible at macroscale, such as roughness, entrance region effect (especially in turbulent flows in tubes with large length to diameter ratio), heat losses, axial heat conduction, viscous heating, and rarefaction effects. The flow characteristics and heat transfer performance in microchannels has been investigated by a few researchers who reported that their experimental data departed from conventional macroscale correlations [1–7]. In the work reported by Yu et al. [1], the friction factor data of water and gas flow in 52–102 μm channels were found to be lower than the predictions from conventional correlations. However, later publications, e.g., Judy et al. [8], have indicated that the data for water flow in microchannels was in good agreement with conventional correlations. Error in channel diameter measurement was noted as one of the main reasons for such deviations in the earlier water data. As to be expected, it has been experimentally verified that there are no microscale effects on friction factors for liquid flow in microchannels [9–12]. Gas flow with nitrogen in microtubes ranging in diameter from 30 to 500 μm and having surface roughness values

For many industrial applications, heat flow through composites relates directly to energy usage and thus is of highest interest. For multilayer composites, the heat flow is a result of multiple variables, such as the temperature gradient over the surface boundaries and each material's thermal conductivity, specific heat, and thickness. In addition, the transient heat flux also depends on how the materials are aligned together. The heat flow through composites can be estimated using advanced computer simulations for applied heat transfer. Although these tools are powerful, they are also time consuming. Therefore, approximations that allow the estimation of heat flow through composites can be very useful. This paper presents approximations to solve transient heat transfer in multilayer composites, with and without an interior surface resistance. Since the energy use for various applications relates to the heat transferred at the surface boundary, the main focus of this paper is to define approximate solutions for interior heat flow. In other words, these approximations are found by applying a unit step change in temperature on one side of a composite and then in real-time emulating the surface heat flux on the opposite side from which the step change occurs. The approximations are presented based on lumped analyses and Laplace network solutions and are validated against analytical and numerical solutions.

Solidification dynamics are crucial for determining microstructure development in additively manufactured parts. Multiphysics models based on finite element or finite volume methods may help gain insight for complicated phenomena such as fluid flow, keyholing, and porosity but are too computationally expensive to use for simulating actual builds. Recent analytic and semi-analytic solutions for moving heat sources in a semi-infinite three-dimensional space provide a way to accurately estimate the solidification conditions for entire builds. The downside to these methods is that, unlike finite element or finite volume methods, they cannot use the temperature distribution of the previous timesteps to march the solution forward in time. This paper provides the mathematical formulation and implementation of a forward time stepping (FTS) approach to an existing semi-analytic solution. The speed and accuracy of the two methods are then compared for various scan patterns. The result is that, for spot melts, the forward time-stepping model provides improvements in both speed and accuracy. This is especially true for longer simulations, where the simulation can be orders of magnitude faster. The longest simulation analyzed in this paper was roughly 30× faster when using the forward time-stepping model versus the straightforward implementation of the semi-analytic solution.

This paper presents corrections for existing hydrodynamic instability-based critical heat flux (CHF) models in pool boiling by taking into account the effect of the viscosity, geometry and size of the liquid–vapor interface. Based on the existing literature, the Kelvin–Helmholtz (KH) theory, used by the most commonly adopted CHF models, can lead to noticeable errors when predicting the instability conditions. The errors are mainly due to the inaccuracy of the inviscid flow assumptions and the oversimplification of the interface geometry. In addition, the literature suggests the most unstable condition predicted by the viscous correction for viscous potential flow (VCVPF) theory for the cylindrical interfaces best match the observed air column breakup conditions in water. In this paper, the most unstable instability conditions predicted by the VCVPF theory are used to correct the existing CHF models. The comparison between the existing and corrected CHF models suggests that the corrected models always predict a higher CHF value. In addition, the corrected Zuber model predicts similar CHF value to the Lienhard and Dhir model. The comparison with experimental data suggests that the correction to the Zuber model can increase its prediction accuracy in most cases, but not necessary for the Lienhard and Dhir model. When compared to experimental CHF data for boiling cryogens at different pressures, the corrected CHF models are consistently more accurate than the original CHF models.

This paper presents an analytical solution for the Joule heating problem of a segmented wire made of two materials with different properties and suspended as a bridge across two fixed ends. The paper first establishes the one-dimensional (1D) governing equations of the steady-state temperature distribution along the wire with the consideration of heat conduction and free-heat convection phenomena. The temperature coefficient of resistance of the constructing materials and the dimension of the each segmented wires were also taken into account to obtain analytical solution of the temperature. COMSOL numerical solutions were also obtained for initial validation. Experimental studies were carried out using copper and nichrome wires, where the temperature distribution was monitored using an IR thermal camera. The data showed a good agreement between experimental data and the analytical data, validating our model for the design and development of thermal sensors based on multisegmented structures.

This paper presents a computational fluid dynamics (CFD) methodology to accurately predict the heat transfer characteristics of an unconfined steady impinging air jet in the transitional flow regime, impinging on a planar constant-temperature surface. The CFD methodology is validated using detailed experimental measurements of the local surface heat transfer coefficient. The numerical model employs a transitional turbulence model which captures the laminar–turbulent transition in the wall jet which precisely predicts the intensity and extent of the secondary peak in the radial Nusselt number distribution. The paper proposes a computationally low-cost turbulence model which yields the most accurate results for a wide range of operating and geometrical conditions. A detailed analysis of the effect of mesh grid size and properties, inflow conditions, turbulence model, and turbulent Prandtl number Prt is presented. The numerical uncertainty is quantified by the grid convergence index (GCI) method. In the range of Reynolds number 6000 ≤ Re ≤ 14,000 and nozzle-to-surface distance 1 ≤ H/D ≤ 6, the model is in excellent agreement with the experimental data. For the case of H/D = 1 and Re = 14,000, the maximum deviations are 5%, 3%, and 2% in terms of local, area-averaged and stagnation point Nusselt numbers, respectively. Experimental and numerical correlations are presented for the stagnation point Nusselt number.

Matrix heat exchangers are used in a number of applications such as helium liquefiers, sorption refrigerators, and in Kleemenko cryocoolers. In this paper the methods for the optimum sizing of balanced flow and unbalanced flow matrix heat exchangers of rectangular and circular shapes are presented. Using the methods developed, the relative size of matrix heat exchangers of rectangular and circular shapes are compared.Matrix heat exchangers are used in a number of applications such as helium liquefiers, sorption refrigerators, and in Kleemenko cryocoolers. In this paper the methods for the optimum sizing of balanced flow and unbalanced flow matrix heat exchangers of rectangular and circular shapes are presented. Using the methods developed, the relative size of matrix heat exchangers of rectangular and circular shapes are compared.

This paper discusses the “inlet temperature difference” (ITD) based heat-exchanger (and its variants) design methodology frequently used by designers of electronic heat sinks. This is at variance with the accepted methodology recommended in standard heat-exchanger textbooks—the “log-mean temperature difference,” or the equivalent ε-NTU design method. The purpose of this paper is to evaluate and discuss the ITD based design methodology. The paper shows that the ITD based method is an approximation at best. Variants of the method can lead to either under- or overprediction of the heat transfer rate. Its shortcomings are evaluated and designers are directed to the well established and accepted design methodology.

This paper presents a history of the ASME Heat Transfer Division (HTD) over the past 75 years. The foundations, birth, growth, and maturation of the division are addressed. An overview of honors and awards is presented and selected developments and trends are discussed. Noteworthy events and workshops, including the 50th anniversary celebration, are considered in some detail. The growing trend toward internationalization is addressed through several conferences and initiatives. Publications, with a focus on the Journal of Heat Transfer, are addressed. The Heat Transfer Division story is told through the contributions and dedicated service of the men and women of the division. The paper concludes with some thoughts about the future.

The chief motivation for the present study is the simulation of the thermal motion of a nanoparticle in a fluid flow that occurs in targeted drug delivery [1–6] where the drug carrying nanocarriers are intravascularly introduced into the vasculature. Nanoparticles allow more precise and successful infiltration of drugs to target cells. In general, nanoparticle drug-delivery systems have been shown to enhance the solubility of compounds, and to reduce the impact of drugs on nontarget tissue, thereby eliminating unwanted and dangerous side effects. In order to more broadly integrate this technology into medicine, a precise understanding of how to guide the nanoparticle to the target site is necessary. To achieve this goal, as a first step, it is necessary to determine the motion of a nanocarrier (due to thermal and hydrodynamic effects) in a fluid medium. The nanocarrier with a loaded cargo may be studied subsequently. A nanoparticle suspended in a fluid undergoes random motion due to the thermal fluctuations in the fluid. As a consequence, translational and rotational degrees of freedom become important. In determining the translational and rotational motions of the nanoparticle in an incompressible Newtonian medium, there exist two methods that couple the thermal fluctuations with the hydrodynamic interactions. These are the generalized Langevin method [7] and the fluctuating hydrodynamics method [8]. Either procedure would require numerical simulations for covering extensive parameter space. In the fluctuating hydrodynamics approach, the nanoparticle motion incorporates both the Brownian motion and the effect of hydrodynamic force acting on its surface imparted from the surrounding fluid. This method essentially consists of adding stochastic stresses (random stress) to the stress tensor in the momentum equation of the fluid and stochastic fluxes to the heat flux where the energy equation is present [9]. The stochastic stress tensor depends on the temperature and the transport coefficients of the fluid medium [10,11]. Numerical simulations of the fluctuating hydrodynamics approach have been carried out employing the finite volume method [12–14], Lattice-Boltzmann method [15–21], finite element method [8,22,23] and stochastic immersed boundary method [24]. In the Langevin dynamics method, the effect of thermal fluctuations are incorporated as random forces and torques in the particle equation of motion [7,25–30]. The properties of these forces depend on the grand resistance tensor. The tensor in turn depends on the fluid properties, particle shape, and its instantaneous location such as its proximity to a wall or a boundary. This is a robust thermostat, which preserves equilibrium distributions at constant temperatures (i.e., adheres to the equipartition theorem). Clearly, coupling to a thermostat will alter the hydrodyamics of the nanoparticle system. The characterizations of the performance of the thermostat as well as how it alters the associated hydrodynamic correlations are important. Numerical schemes for studying the nanoparticle motion in a fluid must simultaneously consider the momentum (Langevin) equation for the particle and the Navier–Stokes equation for the fluid. The random force/torque in the particle equation can then be related to the frictional force/torque via the generalized fluctuation–dissipation theorem [31,32]. The implementation can occur in two ways: (i) directly adjust the variance of the random force term in the classical Langevin equation to play the role of a thermostat and (ii) a second, more direct approach that preserves the structure of the generalized Langevin equation, is to consider the power spectrum for the variance of the random force term using a correlated or colored noise with a well defined characteristic memory time. Such a formalism simultaneously preserves the equipartition theorem and the nature of the long time hydrodynamic correlations, and proves to be a versatile thermostat [7]. The fluctuating hydrodynamics approach in an incompressible fluid [8] captures the correct hydrodynamic correlations and conserves thermal equipartition only after adding the mass correction [10]. On the other hand, the generalized Langevin dynamics yields the correct thermal equipartition (without any mass correction), but modifies the nature of the hydrodynamics correlations (due to the coupling of the fluid equations with the thermostat degrees of freedom) [7]. Recently, we have formulated a novel hybrid approach combining Markovian fluctuating hydrodynamics of the fluid and the non-Markovian Langevin dynamics with the Ornstein–Uhlenbeck noise perturbing the translational and rotational equations of motion of the nanocarrier [33]. For this hybrid approach, we have verified the conservation of thermal equipartition and the nature of hydrodynamic correlations by comparisons with well-known analytical results [10]. This approach effectively produces a thermostat that also simultaneously preserves the true hydrodynamic correlations [33]. With this procedure, we have also evaluated adhesive interactions between a receptor on the nanocarrier surface and a ligand (tethered by a spring force) on the surface of an endothelial cell lining the cylindrical vessel wall at a specified finite temperature [34]. In this paper, we demonstrate the thermal equilibrium and hydrodynamic correlations of a nearly neutrally buoyant nanoparticle using our recently developed hybrid approach. A direct numerical simulation procedure adopting an arbitrary Lagrangian–Eulerian based finite element method is employed to simulate the Brownian motion of a nearly neutrally buoyant particle in an incompressible Newtonian fluid contained in a horizontal micron sized cylindrical vessel. The results for the attainment of thermal equilibrium between the particle and the surrounding medium, diffusivity for the particle in the medium, effect of the presence of the confining vessel wall on particle displacement and diffusivity are evaluated and discussed in detail. A major advantage of our novel hybrid approach employed in this paper as compared to either the fluctuating hydrodynamics approach or the generalized Langevin approach by itself is that only the hybrid method has been shown to simultaneously preserve both hydrodynamic correlations and equilibrium statistics in the incompressible limit.

The original paper reported a heat transfer gain of up to 80% of the optimized elliptical tubes arrangement with respect to the optimized circular one. In fact, the actual heat transfer gain found experimentally is up to 23% only. Therefore corrections are needed in the paper, as follows.

An alternative weighted-sum-of-gray-gases (WSGG) model is proposed with a single set of constant pressure-based absorption coefficients that accounts for different mole fraction ratios (MRs) of H2O–CO2. The method requires no further interpolation, which in turn brings not only less uncertainty into the model but also simplifies its use. The hitemp2010 spectral database along with the line-by-line (LBL) integration is employed to generate a set of accurate total emissivities from which the WSGG coefficients are fitted. The fitting procedure employs a novel formulation to account for the MR dependence, leading to a more compact set of WSGG correlations when compared to the alternatives available in the literature. The new formulation takes advantage of the weak interdependence of temperature and molar fraction ratio in the weight factors and therefore separates their effects by two independent correlations. As oxy-fired combustion usually occurs in two distinct scenarios, dry- and wet-flue gas recirculation (FGR), the paper also proposes two other sets of coefficients intended to support the MR ranges corresponding to these specific conditions. Comparisons made against the benchmark LBL integration and other WSGG models, for one- and three-dimensional calculations, show the satisfactory level of accuracy of the proposed sets of correlations. In particular, the three-dimensional test case illustrates that the new model is also applicable to conditions observed in air–fuel combustion.

During the COVID19 pandemic, various investigations have been conducted to determine if personal protective equipment (PPE), and specifically N95 masks, can be decontaminated for reuse when unused equipment is not available. One method under investigation that may be particularly adaptable in lower resource communities is the use of heat and humidity for the de-activation of SARS-CoV-2. Food-warming cabinets (also known as holding cabinets) may reach applicable temperatures and thus the purpose of this study was to characterize the temperatures achieved in a typical food-warming cabinets that has been adapted for the de-activation of N95 masks. This paper provides a general description of how a food-warming cabinet operates and describes aspects that are important for heat de-activation including characterizing cyclical heating and temperature variations within the cabinet. The described experimental procedure could be used as a guide to characterize similar food-warming cabinets.

This paper proposes an efficient numerical method for transient heat conduction in a quasi-periodic structure with nonlinear defects. According to the physical features of transient heat conduction, a quasi-superposition principle for transient heat conduction in a quasi-periodic structure with nonlinear defects is presented, and then a new method is developed to separate the above nonlinear problem to be solved into a linear problem of a perfect periodic structure and nonlinear problems of some small-scale structures with defects. As the scale of nonlinear problem to be solved is significantly reduced and low computational resource is required, outstanding efficiency is achieved. Finally, a numerical example shows that the proposed method is effective and accurate.

Energy cost contributes a large portion of the overall cost of desalinated water. Improving the energy efficiency of desalination plants is therefore a primary design goal. However, accurately evaluating and comparing the energy consumption of desalination plants that use different forms and grades of energy is difficult, especially for power–water coproduction systems in which primary energy (PE) consumption leads to both salable electricity and potable water. The power plant converts PE into grades of thermal energy and electricity usable by the desalination plant. To fully capture the thermodynamic and economic cost of energy, and to fairly compare desalination systems that use different grades of input energy, we must compare energy consumption not at the point where energy enters the desalination plant itself, but as PE consumption entering the power plant. This paper investigates a variety of metrics for comparing the energy and exergy consumption attributable to desalination in coproduction plants. Previous results have shown that reverse osmosis (RO) is approximately twice as efficient as multiple effect distillation (MED) on a PE basis. We then compare the PE consumption of MED and RO from a thermoeconomic perspective. The entropy generation at the RO membrane and in the MED effects are derived in similar terms, which enables a comparison of the overall heat transfer coefficient in an MED system to the permeability of an RO membrane. RO outperforms MED in energy efficiency because of a balance of material costs, transport coefficients, and cost of energy.

Made available in DSpace on 2020-12-10T17:40:56Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) An experimental apparatus and a computational routine were developed and implemented in order to obtain the sessile drop images and the contact angle measurement for different fluids and surface conditions. Moreover, experimental results of heat transfer coefficients (HTCs) during pool boiling of de-ionized water (DI water), Al2O3-DI water- and Fe2O3-DI water-based nanofluids are presented in this paper. Based on these results, the effect of surface roughness and nanofluid concentration on the surface wettability, contact angle, and the heat transfer coefficient was analyzed. The experiments were performed on copper heating surfaces with different roughness values (corresponding to a smooth surface or a rough surface). The coated surfaces were produced by the nanofluid pool boiling process at two different volumetric concentrations. All surfaces were subjected to metallographic, wettability and roughness tests. For smooth surfaces, in comparison to DI water, heat transfer enhancement up to 60% is observed for both nanofluids at low concentrations. As the concentration of the nanofluid increases, the surface roughness increases and the contact angle decreases, characterizing a hydrophilic behavior. The analyses indicate that the boiling process of nanofluid leads to the deposition of a coating layer on the surface, which influences the heat transfer performance in two-phase systems. Sao Paulo State Univ UNESP, Sch Nat Sci & Engn, Av Brasil 56, BR-15385000 Ilha Solteira, SP, Brazil Fed Univ Technol Akure FUTA, Sch Engn & Engn Technol, Dept Mech Engn, PMB 704, Akure, Ondo State, Nigeria Sao Paulo State Univ UNESP, Sch Nat Sci & Engn, Av Brasil 56, BR-15385000 Ilha Solteira, SP, Brazil CNPq: 458702/2014-5 FAPESP: 2013/15431-7 FAPESP: 2017/13813-0 FAPESP: 2019/02566-8

The laminar and turbulent regimes of a boundary layer on a flat plate are often represented with separate correlations under the assumption of a distinct “transition Reynolds number.” Average heat coefficients are then calculated by integrating across the “transition point.” Experimental data do not show an abrupt transition, but rather an extended transition region in which turbulence develops. The transition region may be as long as the laminar region. Although this transitional behavior has been known for many decades, few correlations have incorporated it. One attempt was made by Stuart Churchill in 1976. Churchill, however, based his curve fit on some doubtful assumptions about the data sets. In this paper, we develop different approximations through a detailed consideration of multiple data sets for 0.7 ⩽ Pr ⩽ 257, 4000 ⩽ Rex ⩽ 4,300,000, and varying levels of freestream turbulence for smooth, sharp-edged plates at zero pressure gradient. The result we obtain is in good agreement with the available measurements and applies smoothly over the full range of Reynolds number for either a uniform wall temperature or a uniform heat flux boundary condition. Fully turbulent air data are correlated to ±11%. Like Churchill's result, this correlation should be matched to the estimated transition condition of any particular flow. We also review the laminar analytical solutions for a uniform wall heat flux, and point out limitations of the classical Colburn analogy.

Desalination systems can be conceptualized as power cycles in which the useful work output is the work of separation of fresh water from saline water. In this framing, thermodynamic analysis provides powerful tools for raising energy efficiency. This paper discusses the use of entropy generation minimization for a spectrum of desalination technologies, including those based on reverse osmosis (RO), humidification–dehumidification (HDH), membrane distillation (MD), electrodialysis (ED), and forward osmosis (FO). Heat and mass transfer are the primary causes of entropy production in these systems. The energy efficiency of desalination is shown to be maximized when entropy generation is minimized. Equipartitioning of entropy generation is considered and applied. The mechanisms of entropy generation are characterized, including the identification of major causes of irreversibility. Methods to limit discarded exergy are also identified. Prospects and technology development needs for further improvement are mentioned briefly.

Shape factors for steady heat conduction enable quick and highly simplified calculations of heat transfer rates within bodies having a combination of isothermal and adiabatic boundary conditions. Many shape factors have been tabulated, and most undergraduate heat transfer books cover their derivation and use. However, the analytical determination of shape factors for any but the simplest configurations can quickly come to involve complicated mathematics, and, for that reason, it is desirable to extend the available results as far as possible. In this paper, we show that known shape factors for the interior of two-dimensional objects are identical to the corresponding shape factors for the exterior of those objects. The canonical case of the interior and exterior of a disk is examined first. Then, conformal mapping is used to relate known configurations for squares and rectangles to the solutions for the disk. Both a geometrical and a mathematical argument are introduced to show that shape factors are invariant under conformal mapping. Finally, the general case is demonstrated using Green's functions. In addition, the “Yin-Yang” phenomenon for conduction shape factors is explained as a rotation of the unit disk prior to conformal mapping.

The radiation fractional function is the fraction of black body radiation below a given value of λT. Edwards and others have distinguished between the traditional, or “external,” radiation fractional function and an “internal” radiation fractional function. The latter is used for linearization of net radiation from a nongray surface when the temperature of an effectively black environment is not far from the surface's temperature, without calculating a separate total absorptivity. This paper examines the analytical approximation involved in the internal fractional function, with results given in terms of the incomplete zeta function. A rigorous upper bound on the difference between the external and internal emissivity is obtained. Calculations using the internal emissivity are compared to exact calculations for several models and materials. A new approach to calculating the internal emissivity is developed, yielding vastly improved accuracy over a wide range of temperature differences. The internal fractional function should be used for evaluating radiation thermal resistances, in particular.

Pulse thermography (PT) is a nondestructive testing method in which an energy pulse is applied to a surface while the surface temperature evolution is measured to detect sub surface defects and estimate their depth. This nondestructive test method was developed on the assumption of instantaneous surface heating, but recent work has shown that relatively long pulses can be used to accurately determine defect depth in polymers. This paper examines the impact of varying input pulse length on the accuracy of defect depth quantification as a function of the material properties. Simulations using both thermoplastics and metals show that measurement error is dependent on a nondimensionalized pulse length. The simulation results agree with experimental results for three-dimensional (3D) printed acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) components. Analysis and experiments show that defects can be accurately detected with minor modification to the standard methods as long as the pulse ends before the characteristic defect signal is detected.

This paper quantifies the pool boiling performance of R134a, R1234yf, R513A, and R450A on a flattened, horizontal reentrant cavity surface. The study showed that the boiling performance of R134a on the Turbo-ESP exceeded that of the replacement refrigerants for heat fluxes greater than 20 kW m−2. On average, the heat flux for R1234yf and R513A was 16% and 19% less than that for R134a, respectively, for R134a heat fluxes between 20 kW m−2 and 110 kW m−2. The heat flux for R450A was on average 57% less than that of R134a for heat fluxes between 30 kW m−2 and 110 kW m−2. A model was developed to predict both single-component and multicomponent pool boiling of the test refrigerants on the Turbo-ESP surface. The model accounts for viscosity effects on bubble population and uses the Fritz equation to account for increased vapor production with increasing superheat. Both loss of available superheat and mass transfer resistance effects were modeled for the refrigerant mixtures. For most heat fluxes, the model predicted the measured superheat to within ±0.31 K.

Spraying water droplets on air fin surfaces is often used to augment the performance of air-cooled Rankine power plant condensers and wet cooling tower heat exchangers for building air-conditioning systems. To get the best performance in such processes, the water droplets delivered to the surface should spread rapidly into an extensive, thin film and evaporate with no liquid leaving the surface due to recoil or splashing. This paper presents predictions of theoretical/computational modeling and results of experimental studies of droplet spreading on thin-layer, nanostructured, superhydrophilic surfaces that exhibit very high wicking rates (wickability) in the porous layer. Analysis of the experimental data in the model framework illuminates the key aspects of the physics of the droplet-spreading process and evaporation heat transfer. This analysis also predicts the dependence of droplet-spreading characteristics on the nanoporous surface morphology and other system parameters. The combined results of this investigation indicate specific key strategies for design and fabrication of surface coatings that will maximize the heat transfer performance for droplet evaporation on heat exchanger surfaces. The implications regarding wickability effects on pool boiling processes are also discussed.

The paper gives a comprehensive study on the space fractional boundary layer flow and heat transfer over a stretching sheet with variable thickness, and the variable magnetic field is applied. Novel governing equations with left and right Riemann–Liouville fractional derivatives subject to irregular region are formulated. By introducing new variables, the boundary conditions change as the traditional ones. Solutions of the governing equations are obtained numerically where the shifted Grünwald formulae are applied. Good agreement is obtained between the numerical solutions and exact solutions which are constructed by introducing new source items. Dynamic characteristics with the effects of involved parameters on the velocity and temperature distributions are shown and discussed by graphical illustrations. Results show that the velocity boundary layer is thicker for a larger fractional parameter or a smaller magnetic parameter, while the temperature boundary layer is thicker for a larger fractional parameter, a smaller exponent parameter, or a larger magnetic parameter. Moreover, it is thicker at a smaller y and thinner at a larger y for the velocity boundary layer with a larger exponent parameter while for the velocity and temperature boundary layers with a smaller weight coefficient.

Enhanced pool boiling heat transfer, with simultaneous increase in critical heat flux (CHF) and heat transfer coefficient (HTC), is desired to improve overall system efficiency and reduce equipment size and cost. This paper focuses on combining graphene oxide (GO) and porous copper particles to generate microstructures based on their ability to enhance HTC, CHF, or both. Three pool boiling performance characteristics based on CHF improvements and wall superheat reductions are identified: Type I—reduction in wall superheat only, type II—increase in CHF only, and type III—increase in CHF with reduction in wall superheat at higher heat fluxes. Specific microscale morphologies were generated using (a) screen-printing and (b) electrodeposition techniques. In type-I, rapid bubble activity due to increased availability of nucleation cavities was seen to influence the reduction in the wall superheats, while no increase in CHF was noted. Roughness-augmented wettability was found to be the driving mechanism in type-II enhancement, while wicking and increased nucleation site density were responsible for the enhancement in type-III. An HTC enhancement of ∼216% in type-I and a CHF improvement of ∼70% in type-II were achieved when compared to a plain copper surface with water. In type-III enhancement, a CHF of 2.2 MW/m2 (1.8× over a plain surface) with a HTC of 155 kW/m2 °C (∼2.4× over a plain surface) was obtained. Furthermore, close correlation between the boiling performance and the microscale surface morphology in these three categories has been identified.

In this paper, the new optimal perturbation iteration method (OPIM) is introduced and applied for solving nonlinear differential equations arising in heat transfer. The effectiveness of the proposed method will be tested by considering two specific applications: the temperature distribution equation in a thick rectangular fin radiation to free space and cooling of a lumped system with variable specific heat. Comparing different methods shows that the results obtained by optimal perturbation iteration method are very good agreement with the numerical solutions and perform better than the most existing analytic methods. Copyright © 2017 by ASME.

This paper extends previous liquid film flow boiling studies by including the effect of an additional electrohydrodynamic (EHD) force, namely, the dielectrophoretic (DEP) force. Rather than using only EHD conduction pumping of the liquid film to electro-wet the heater surface, a localized nonuniform electric field above the heater surface is established to generate a DEP force for improved vapor bubble extraction during the nucleate boiling regime. The effects of liquid film height and applied potential are studied as a function of heater superheat and heat flux. A brief analytical study is also used to estimate the expected DEP force magnitude to explain the results. All of the above studies are also used to quantify the enhancement in heat transfer that can be achieved when heat transport systems are driven or augmented by these two EHD mechanisms. The results show remarkable enhancement of up to 1217% in boiling heat transfer coefficient at a given superheat when both mechanisms are used simultaneously. The experimental data are important for applications in thermal management in terrestrial and space conditions.

The photon transport and energy conversion of a near-field thermophotovoltaic (TPV) system with a selective emitter composed of alternate tungsten and alumina layers and a photovoltaic cell sandwiched by electrical contacts are theoretically investigated in this paper. Fluctuational electrodynamics along with the dyadic Green's function for a multilayered structure is applied to calculate the spectral heat flux, and the photocurrent generation and electrical power output are solved from the photon-coupled charge transport equations. The tungsten and alumina layer thicknesses are optimized to obtain maximum electrical power output for bare TPV cell. The spectral heat flux is much enhanced when plain tungsten emitter is replaced with the multilayer emitter due to the effective medium intrinsic lossy property and additional surface plasmon polariton coupling in the tungsten thin film, for which the invalidity of effective medium theory to predict photon transport in the near field with multilayer emitters is discussed. Effects of a gold back reflector and indium tin oxide front coating with nanometer thickness, which could practically act as the electrodes to collect the photon-generated charges on the TPV cell, are explored. The conversion efficiency of 23.7% and electrical power output of 0.31 MW/m2 can be achieved at a vacuum gap distance of 100 nm when the emitter and receiver temperature are, respectively, set as 2000 K and 300 K.

In this paper we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are iso-thermal and they are aligned with the Earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between -1 and 1. Two values of center to center spacing (s=3.6d - 4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri=-1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard deviation of the force coefficients and heat flux. In fact the transition occurs due to rearrangement of the near field flow in a more ordered wake pattern. Therefore, attention is focused on the influence of geometrical and buoyancy parameters on the heat and momentum exchange and their fluctuations. The available heat exchange models for cylinders array provide a not accurate prediction of the Nusselt number in the cases here studied., ASME Journal of Heat Transfer

This paper introduces a numerical strategy to estimate the thermophysical properties of a saturated porous medium (volumetric heat capacity (ρC)s, thermal conductivity λs, and porosity ϕ), where a phase change problem (liquid/vapor) appears due to strong heating. The estimation of these properties is done by inverse problem knowing the heating curves at selected points of the medium. To solve the inverse problem, we use both the damped Gauss Newton (DGN) and the Levenberg Marquardt methods to deal with high nonlinearity of the system and to tackle the problem with large residuals. We use the method of lines where time and space discretizations are considered separately. Special attention has been paid to the choice of the regularization parameter of the apparent heat capacity (AHC) method which may prevent the convergence of the inverse problem.

An entropic wall with circulating water inside could be a solution for acclimatizing a new building with high-energy efficiency and high levels of internal comfort. If circulating water is thermally stabilized by exchanging in the ground such has it happens in geothermal plants, a thermal shield could be realized keeping walls in comfort conditions and minimizing energy needs for further temperature regulations. This paper presents optimization guidelines of such a wall with the objective of maximizing the performances of the wall for reaching optimal internal wellness conditions. Optimization has been realized by a constructal law based method, which has been personalized by a step-by-step process and has been named constructal design for efficiency (CDE). The optimization of the system has been produced at different levels. It starts from a preliminary analysis at system levels, which allow defining the best objectives that could be reached. After this preliminary process, the system has been divided into modules, and the critical ones which have higher influence on the performances of the system have been evaluated. This analysis has been coupled also with an industrial analysis with the goal of defining an effective layout, which could be also manufactured with acceptable costs. The result has produced a final solution with a very good compromise between energetic performances and minimization of costs at industrial level. The results open interesting perspectives for the constructal law to become the core of an effective methodology of an industrial design which can couple perfectly with the modular approach which is currently the major part of industrial companies.

Computational fluid dynamics (CFD) is a powerful tool for analyzing the performance of heat exchangers. However, such an approach may be often limited by unaffordable computational time. In this paper, a multiscale CFD capable of accurately and efficiently prediction of the heat transfer of compact heat exchangers is presented. This methodology is based on a small-scale CFD analysis of a single tube and a small element of the compact heat exchanger, and it is able to predict the thermal performance of an entire heat exchanger in a wide range of inlet conditions, with a reduced computational time. The proposed up-scaling procedure makes use of specific approximations and correlations derived from the CFD model and literature, in order to consider the typical phenomena occurring in compact heat exchangers under laminar flow conditions. Results demonstrate an excellent accuracy when compared to experimental data (discrepancies

Reported experimental and computational results confirm that both the flow features and heat-transfer rates inside a condenser depend on the specification of inlet, wall, and exit conditions. The results show that the commonly occurring condensing flows’ special sensitivity to changes in exit conditions (i.e., changes in exit pressure) arises from the ease with which these changes alter the vapor flow field in the interior. When, at a fixed steady mass flow rate, the exit pressure is changed from one steady value to another, the changes required of the interior vapor flow toward achieving a new steady duct flow are such that they do not demand a removal of the new exit pressure imposition back to the original steady value—as is the case for incompressible single phase duct flows with an original and “required” exit pressure. Instead, new steady flows may be achieved through appropriate changes in the vapor/liquid interfacial configurations and associated changes in interfacial mass, heat-transfer rates (both local and overall), and other flow variables. This special feature of these flows has been investigated here for the commonly occurring large heat sink situations, for which the condensing surface temperature (not heat flux) remains approximately the same for any given set of inlet conditions while the exit-condition changes. In this paper’s context of flows of a pure vapor that experience film condensation on the inside walls of a vertical tube, the reported results provide an important quantitative and qualitative understanding and support an exit-condition-based categorization of the flows. Experimental results and selected relevant computational results that are presented here reinforce the fact that there exist multiple steady solutions (with different heat-transfer rates) for multiple steady prescriptions of the exit condition—even though the other boundary conditions do not change. However, for some situations that do not fix any specific value for the exit condition (say, exit pressure) but allow the flow the freedom to choose any exit pressure value within a certain range, experiments confirm the computational results that, given enough time, there typically exists, under normal gravity conditions, a self-selected “natural” steady flow with a natural exit condition. This happens if the vapor flow is seeking (or is attracted to) a specific exit condition and the conditions downstream of the condenser allow the vapor flow a range of exit conditions that includes the specific natural exit condition of choice. However, for some unspecified exit-condition cases involving partial condensation, even if computations predict that a natural exit-condition choice exists, the experimental arrangement employed here does not allow the flow to approach its steady natural exit-condition value. Instead, it only allows oscillatory exit conditions leading to an oscillatory flow. For the reported experiments, these oscillatory pressures are induced and imposed by the instabilities in the system components downstream of the condenser.

Our bodies depend on an exquisitely sensitive and refined temperature control system to maintain a state of health and homeostasis. The exceptionally broad range of physical activities that humans engage in and the diverse array of environmental conditions we face require remarkable strategies and mechanisms for regulating internal and external heat transfer processes. On the occasions for which the body suffers trauma, therapeutic temperature modulation is often the approach of choice for reversing injury and inflammation and launching a cascade of healing. The focus of human thermoregulation is maintenance of the body core temperature within a tight range of values, even as internal rates of energy generation may vary over an order of magnitude, environmental convection, and radiation heat loads may undergo large changes in the absence of any significant personal control, surface insulation may be added or removed, all occurring while the body's internal thermostat follows a diurnal circadian cycle that may be altered by illness and anesthetic agents. An advanced level of understanding of the complex physiological function and control of the human body may be combined with skill in heat transfer analysis and design to develop life-saving and injury-healing medical devices. This paper will describe some of the challenges and conquests the author has experienced related to the practice of heat transfer for maintenance of health and enhancement of healing processes.

Due to excessive droplet feeding, a period of flooding occurs as part of a typical droplet based thermal management cycle. The conventional superhydrophilic surface, which is designed for thin film evaporation because of its highly wettable character, has a limited improvement on the thermal performance during the flooded condition. This paper investigates microstructures which combine micropillars and four engineered wettability patterns to improve the heat dissipation rate during flooding. Using the transient, 3D volume-of-fluid (VOF) model, the bubble behaviors of growth, coalescence, and departure are analyzed within different microstructures and the effects of pillar height and wettability patterns on the thermal performance are discussed. The wettability gradient patched on the pillar's side is demonstrated to promote the bubble's upward movement due to the contact angle difference between the upper and lower interfaces. However, insufficient pulling force results in large bubbles being pinned at the pillar tops, which forms a vapor blanket, and consequently decreases the heat transfer coefficient. When only a patch of hydrophobic material is present on the pillar top, effective pulling forces can be developed to help bubbles in the lower level depart from the pillar forest, since bubble merging between them generates most of the power required to pull the bubbles to the surface. The simulation results, including heat source temperatures and heat transfer coefficients, indicate that a patch of hydrophobic material on the pillar top works best out of all of the cases studied.

Hydrogen release in confined spaces is an important safety issue, which is even more important in the context of severe accident in nuclear reactors. In severe accidents, hydrogen release is associated with release of steam and the condensation of steam on walls leads to increase in concentration of hydrogen in residual gas as well as condensation induced mixing. In the present paper, a model for falling film steam condensation in the presence of noncondensable gases is presented. The steam condensation model is incorporated into an in-house developed cfd code called hydrogen distribution simulator (HDS) and is used for hydrogen distribution studies. The validation of the CFD model with steam condensation against the experimental results from the CONAN facility is discussed. Subsequently, the model is applied to a typical release situation involving release of hydrogen and steam for some time and its distribution for a long time beyond it. The heat and mass transfer aspects of the problem are highlighted. It is seen that steam condensation has an important bearing on the distribution of hydrogen and the mixing behavior of gases in the enclosure. Copyright � 2015 by ASME.

Made available in DSpace on 2019-09-12T16:56:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2015 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) This paper aims to present numerical solutions for the problem of steady natural convection heat transfer by double diffusion from a heated cylinder buried in a saturated porous media exposed to constant uniform temperature and concentration in the cylinder and in the media surface. A square finite domain 3 x 3 and acceptance criterion converged solution with an absolute error under 1 x 10(-3) were considered to obtain results presented. The Patankar's power law for approaching of variables calculated T, C, and phi also was adopted. In order of method validation, an investigation of mesh points number as function of Ra, Le, and N was done. A finite volume scheme has been used to predict the flow, temperature, and concentration distributions at any space from a heat cylinder buried into a fluid-saturated porous medium for a bipolar coordinates system. Examples presented show that the differences in the flow distribution caused not only when Rayleigh number range is considered but also when Lewis number range is considered. Further, increase in the Rayleigh number has a significant influence in the flow distribution when the concentration distribution is considered. Steady natural convection heat transfer by double diffusion from a heated cylinder buried in a saturated porous medium is studied numerically using the finite volume method. To model fluid flow inside the porous medium, the Darcy equation is used. Numerical results are obtained in the form of streamlines, isotherms, and isoconcentrations. The Rayleigh number values range from 0 to 1000, the Lewis number values range from 0 to 100, and the buoyancy ratio number is equal to zero. Calculated values of average heat transfer rates agree reasonably well with values reported in the literature. [Chaves, Carlos Alberto; Nicolini do Patrocinio Nunes, Luiz Eduardo; Camargo, Jose Rui; Grandinetti, Francisco José] Universidade de Taubaté (Unitau), Dept Mech Engn, BR-12060440 Taubate, SP, Brazil [Lamas, Wendell de Queiroz] Univ Sao Paulo, Sch Engn Lorena, Dept Basic Sci & Environm, BR-12602810 Lorena, SP, Brazil

A new approach to account for finite thermal conductivity and turbulence effects within atomizing droplets of an evaporating spray is presented in this paper. The model is an extension of the T-blob and T-TAB atomization/spray model of Trinh and Chen [Atomization and Sprays, 16(6), pp. 907–932]. This finite conductivity model is based on the two-temperature film theory in which the turbulence characteristics of the droplet are used to estimate the effective thermal diffusivity for the liquid-side film thickness. Both one-way and two-way coupled calculations were performed to investigate the performance of this model against the published experimental data.

Cooling of gas turbine hot-section components, such as combustor liners, combustor transition pieces, and turbine vanes (nozzles) and blades (buckets), is a critical task for improving the life and reliability of them. Conventional cooling techniques using air-film cooling, impingement jet cooling, and turbulators have significantly contributed to cooling enhancements in the past. However, the increased net benefits that can be continuously harnessed by using these conventional cooling techniques seem to be incremental and are about to approach their limit. Therefore, new cooling techniques are essential for surpassing these current limits. This paper investigates the potential of film-cooling enhancement by injecting mist into the coolant. The computational results show that a small amount of injection (2% of the coolant flow rate) can enhance the adiabatic cooling effectiveness about 30–50%. The cooling enhancement takes place more strongly in the downstream region, where the single-phase film cooling becomes less powerful. Three different holes are used in this study including a two-dimensional (2D) slot, a round hole, and a fan-shaped diffusion hole. A comprehensive study is performed on the effect of flue gas temperature, blowing angle, blowing ratio, mist injection rate, and droplet size on the cooling effectiveness with 2D cases. Analysis on droplet history (trajectory and size) is undertaken to interpret the mechanism of droplet dynamics.

Methods of thermal property measurements based on steady-periodic heating are indirect techniques, in which the thermal properties are deduced from a systematic comparison between experimental data and heat-transfer theory. In this paper heat-transfer theory is presented for a variety of two-dimensional geometries applicable to steady-periodic thermal-property techniques. The method of Green’s functions is used to systematically treat rectangles, slabs (two dimensional), and semi-infinite bodies. Several boundary conditions are treated, including convection and boundaries containing a thin, highconductivity film. The family of solutions presented here provides an opportunity for verification of numerical results by the use of distinct, but similar, geometries. A second opportunity for verification arises from alternate forms of the Green’s function, from which alternate series expressions may be constructed for the same unique temperature solution. Numerical examples are given to demonstrate both verification techniques for the steady-periodic response to a heated strip. DOI: 10.1115/1.2194040

Impingement channels are often used in turbine blade cooling configurations. This paper examines the heat transfer performance of a typical integrally cast impingement channel. Detailed heat transfer coefficient distributions on all heat transfer surfaces were obtained in a series of low temperature experiments carried out in a large-scale model of a turbine cooling system using liquid crystal techniques. All experiments were performed on a model of a 19-hole, low aspect ratio impingement channel. The effect of flow introduced at the inlet to the channel on the impingement heat transfer within the channel was investigated. A novel test technique has been applied to determine the effect of the initial cross flow on jet penetration. The experiments were performed at an engine representative Reynolds number of 20,000 and examined the effect of additional initial cross flow up to 10 percent of the total mass flow. It was shown that initial cross flow strongly influenced the heat transfer performance with just 10 percent initial cross flow able to reduce the mean target plate jet effectiveness by 57 percent. Copyright © 2005 by ASME.

Numerical simulations of laminar, forced convection heat transfer for reciprocating, two-dimensional channel flows are performed as a function of the penetration length, Womersley (α) and Prandtl (Pr) numbers. The numerical algorithm is based on a spectral element formulation, which enables high-order spatial resolution with exponential decay of discretization errors, and second-order time-accuracy. Uniform heat flux and constant temperature boundary conditions are imposed on certain regions of the top surface, while the bottom surface is kept insulated. Periodicity of velocity and temperature fields is imposed on the side boundaries, while the flow is driven by an oscillating pressure gradient. These sets of boundary conditions enable time-periodic solution of the problem. Instantaneous and time-averaged surface and bulk temperature distributions, and Nusselt number variations are presented. For high α flows, the temperature field is significantly affected by the Richardson’s annular effect. Overall, forced convection increases by increasing the penetration length, α and Pr. Corresponding steady-flow simulations are performed by matching the volumetric flowrate. For the limited parameter space investigated in this paper, steady unidirectional forced convection is more effective than the reciprocating flow forced convection.

Presented in this paper is an experimental study focusing on the effects of diffusion hole-geometry on overall film cooling performance. The study consists of three different but closely related hole shapes: (1) Shape A: straight circular hole with a 30-degree inclined injection, (2) Shape B: same as Shape A but with a 10-degree forward diffusion, and (3) Shape C: same as Shape B with an additional 10-degree lateral diffusion. The blowing ratios tested are 0.5 and 1.0. The density ratio is nominally equal to one. Measurements of the experiment use a transient liquid crystal technique that reveals local distributions of both film effectiveness (η) and heat transfer coefficient (h). The data obtained indicate that Shape C with a combined forward and lateral diffusion produces a significant increase in η and decrease in h as compared to Shape A, the baseline case. These improvements combined yield an about 30% to 50% reduction in heat transfer or thermal load on the film protected surface. Shape B, with forward diffusion only, shows a much less significant change in both film effectiveness and overall heat transfer reduction than Shape C. However, it has the lowest heat transfer coefficient in the vicinity of the injection hole among all the three hole-shapes studied. A flow visualization study using pulsed laser sheet-light reveals that Shape A and Shape B inherit quite similar flow structures. The coolant injected out of Shape C flows much closer to the protected wall than that of Shape A and Shape B.Copyright © 1999 by ASME