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This paper deals with the analysis of the main features of forced microconvection of liq-uid and gas flows through microchannels. A critical overview of the main effects that tends to play an important role in the determination of Nusselt number in microchannels is presented. Some experimental data obtained at the Microfluidics Lab of the University of Bologna together with the main results which appeared recently in the open literature both for liquids and gases are used in order to highlight the peculiar characteristics of the convective heat transfer through microchannels and to suggest the guidelines for a physically based interpretation to the experimental results. By means of specific exam-ples, it is shown that the thermal behavior at microscale of gas and liquid flows through microchannels in terms of convective heat transfer coefficients can be strongly affected by scaling and micro-effects but also by practical issues linked to the geometry of the test rig, the real thermal boundary conditions, the presence of fittings, position and type of the sensors, and so on. All these aspects have to be taken into account during the data post processing in order to obtain a correct evaluation of the Nusselt numbers. It is also highlighted how it is always useful to couple to the experimental approach a complete computational thermal fluid-dynamics analysis of the whole tested microsystem in order to be able to recognize "a priori" the main effects which can play an important role on the convective heat transfer analysis. It is demonstrated in this paper that this "a priori" analysis is crucial in order to: (i) individuate the main parameters which influence the convective heat transfer coefficients (this is important for the development of new corre-lations); (ii) compare in a right way the conventional correlations with the experimental results. [ABSTRACT FROM AUTHOR]

Nonthermal irreversible electroporation (NTIRE) is an new minimally invasive tissue ablation modality that uses high electric field pulses to produce irreversible permeation of the cell membrane (irreversible electroporation) while avoiding thermal damage and is applied to treat malignant tumors. This paper describes efforts to develop NTIRE as a new minimally invasive treatment modality for uveal melanoma, the most common pri-mary intraocular malignancy in adults, and other ocular malignancies. The paper deals with a 3D mathematical simulation model of the eye that employs the simultaneous solution to the electric field equation and to the Pennes bioheat equation to predict the electric field in the eye as well as the rise in eye temperature in response to the application of a high power electric pulse. Treatment efficacy was defined as the fraction of tumor vol-ume in which the electric field exceeded a predefined target field and treatment safety was calculated by the ratio of the electric field in the tumor to the electric field in the vitreous humor or in the macula. Results show that treatment efficacy and safety are criteria that can be used to optimize the NTIRE treatment protocol. [ABSTRACT FROM AUTHOR]

In a recent paper by Abbassi and Rahimi (2009, "Nonaxisymmetric Three-Dimensional Stagnation-Point Flow and Heat Transfer on a Flat Plate,'' ASME J. Fluids Eng, 131(7), p. 074501) the existence of a new nonaxisymmetric 3D stagnation-point flow has been reported. The present paper shows, however, that the model of Abbassis and Rahimi is fully equivalent to the classical 3D stagnation-point flow of Howarth (1951, "The Boundary Layer in Three-Dimensional Flow--Part II: The Flow Near a Stagnation Point,'' Philos. Mag., 42, pp. 1433--1440) published more than sixty years ago. Thus their "new'' solution can be recovered from Howarth's known solution by simple transformations, without any additional research effort. Once this flow problem is solved, the solution of the heat transfer problem of Abbassi and Rahimi (2009, "Nonaxisymmetric Three-Dimensional Stagnation-Point Flow and Heat Transfer on a Flat Plate,'' ASME J. Fluids Eng, 131(7), p. 074501) can be calculated by a semi-analytical or by a usual numerical procedure. [ABSTRACT FROM AUTHOR]

Noncondensable gases deteriorate heat transfer in the condensation process. It is there-fore necessary to study vapor-gas condensation heat transfer process and analyze main factors influencing the process. Based on the double-film theory and the Prandtl bound-ary layer theory, this investigation developed a mathematical model of gas-liquid film thicknesses and local heat transfer coefficient for studying laminar film condensation in the presence of noncondensable gas over a horizontal tube. Induced velocity in the gas film, gas-liquid interfacial shear stress, and pressure gradient were considered in the study. Importantly, gas-liquid film separations were analyzed in depth in this paper. It obtained the distributions of gas-liquid film thicknesses, local heat transfer coefficient, condensate mass flux, and gas-liquid interfacial temperature along the tube surface, and analyzed the influences of bulk velocity, total pressure, bulk mass concentration of non-condensable gas and wall temperature on them, providing a theoretical guidance for understanding and enhancing vapor-gas condensation heat transfer. Gas film thickness and gas-liquid film separations have certain effects on vapor-gas condensation heat transfer. The average dimensionless heat transfer coefficients are in agreement with the data from related literatures. [ABSTRACT FROM AUTHOR]

This paper presents a detailed exergy analysis of homogeneous charge compression ignition (HCCI) engines, including a crank-angle resolved breakdown of mixture exergy and exergy destruction. Exergy analysis is applied to a multizone HCCI simulation including detailed chemical kinetics. The HCC1 simulation is validated against engine experiments for ethanol-fueled operation. The exergy analysis quantifies the relative importance of different loss mechanisms within HCCI engines over a range of engine operating conditions. Specifically, four loss mechanisms are studied for their relative impact on exergy losses, including (1) the irreversible combustion process (16.4%-21.5%), (2)physical exergy lost to exhaust gases (12.0%-18.7%), (3) heat losses (3.9%-17.1%), and (4) chemical exergy lost to incomplete combustion (4.7%-37.8%). The trends in each loss mechanism are studied in relation to changes in intake pressure, equivalence ratio, and engine speed as these parameters are directly used to vary engine power output. This exergy analysis methodology is proposed as a tool to inform research and design processes, particularly by identifying the relative importance of each loss mechanism in determining engine operating efficiency. [ABSTRACT FROM AUTHOR]

In this paper a mathematical model was developed to predict temperature profiles for two-phase oil-water stratified flows. Based on the energy balance of a control volume, analytical solutions were derived for the prediction of temperature profiles for two-phase oil/water stratified flow pattern in pipe flows. The model has been verified with a single-phase heat transfer model, which is available in most heat transfer textbooks. Two typical cases were simulated for extreme operating conditions with water cuts of 0% and 100%, respectively. This analytical model was also validated against experimental dam. The test was conducted on a multiphase faciLity with accurate flow control devices and effective thermal treating units. The water cut was set at 50% for this test. The simulation results and experimental data agree within the experimental uncertainty. The closure relationships can be conveniently applied to a two-phase oil/water paraffin deposition model, which is dependent on the heat transfer process. The model was also used to predict the temperature profiles for two-phase oil and water flows with different water cuts. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of the film-cooling peiformance of a novel film-cooling hole in comparison with a fan-shaped hole. The novel shaped hole is designed to increase the lateral spreading of coolant on the cooling surface. The film-cooling performance of the novel shaped hole is evaluated at a density ratio of 1.75 and the range of the blowing ratio of 0.5-2.5. The simulations were performed using three-dimensional Reynolds-averaged Navier-Stokes analysis with the SST k-ω model. The numerical results for the fan-shaped hole show very good agreement with the experimental data. For the blowing ratio of 0.5, the novel shaped film-cooling hole shows a similar cooling peiformance as the fan-shaped hole. However, as the blowing ratio increases, the novel shaped hole shows greatly improved lateral spreading of the coolant and the cooling peiformance in terms of the film-cooling effectiveness in comparison with the fan-shaped hole. [ABSTRACT FROM AUTHOR]

In this paper, the effects of uncertainties in physical properties on predicting entropy gen-eration for a steady laminar flow of Al2O3-ethylene glycol nanofluid (0 ≤ ɸ ≤ 6%) between two concentric rotating cylinders are investigated. For this purpose, six different models by combining of three relations for thermal conductivity (Bruggeman, Hamilton-Crosser, and Yu-Choi) and two relations for dynamic viscosity (Brinkman and Maiga et al.) are applied. The governing equations with reasonable assumptions in cylin-drical coordinates are simplified and solved to obtain analytical expressions for average entropy generation (Ns)ave end average Bejan number (Be)ave. The results show that, when the contribution of heat transfer to entropy generation for the base fluid is domi-nant, a critical radius ratio (Πc) can be determined at which all six models predict the reduction in entropy generation with increases of volume fraction of nanoparticles. It is also found that, when the contribution of viscous effects to entropy generation is adequately high for the base fluid (ɸ = 0), all models predict the increase of entropy generation with increases of particle loading. [ABSTRACT FROM AUTHOR]

The relatively poor understanding of gravity effects on pool boiling heat transfer can be attributed to the lack of long duration high-quality microgravity data, g-jitter associated with ground-based low gravity facilities, little data at intermediate gravity levels, and a poor understanding of the effect of important parameters even at earth gravity conditions. The results of over 200 pool boiling experiments with n-perfluorohexane as the test fluid per-formed aboard the International Space Station (ISS) are presented in this paper. A flat, trans-parent, constant temperature microheater array was used to peiform experiments over a wide range of temperatures (55 °C

This is the second part of a two-part paper which proposes a new theory explaining the experimentally observed enhancement of the thermal conductivity, knf, of nanofluids (Part I) and discusses simulation results of nanofluid flow in an axisymmetric jet-impingement cooling system using different knf-models (Part II). Specifically, Part II provides numeri-cal simulations of convective nanofluid heat transfer in terms of velocity profiles, friction factor, temperature distributions, and Nusselt numbers, employing the new knf-model. Flow structures and the effects of nanoparticle addition on heat transfer and entropy gen-eration are discussed as well. Analytical expressions for velocity profiles and friction fac-tors, assuming quasi-fully-developed flow between parallel disks, have been derived and validated for nanofluids as well. Based on the numerical simulation results for both alumina-water nanofluids and pure water, it can be concluded that nanofluids show better heat transfer performance than convectional coolants with no great penalty in pumping power. Furthermore, the system's entropy generation rate is lower for nanofluids than for pure water [ABSTRACT FROM AUTHOR]

This paper presents an analysis of transient heat transfer in sandwich pipelines with active electrical heating. The mathematical models governing the heat conduction in the composite pipeline and the energy transport in the produced fluid were solved by using finite difference methods. Numerical results of computational simulation of cool-down for three sandwich pipeline configurations under typical production conditions were presented. The analysis showed that the sandwich pipe with active heating is a viable solution to meet severe flow assurance requirements of ultra-deepwater oil production even under unplanned and prolonged cool-down conditions. [ABSTRACT FROM AUTHOR]

The paper deals with the possible use of existing oil wells for geothermal energy production. A mathematical model, describing the process of exploitation of a borehole heat exchanger, has been worked out. It was used for determining energy efficiency, employing the main parameter, i.e., flow of produced heat energy. The results of simulation of borehole heat exchanger operation in deep conditions of Iwonicz Zdrój field's depleted deposits (Polish Carpathians) are presented. A considerable part of oil deposits in the Carpathian region—a cradle of the world's oil industry—are to be decommissioned. Owing to the high density of population, the wells are planned to be adapted for borehole heat exchangers for clean energy production for local purposes. The decommissioning costs will be avoided. [ABSTRACT FROM AUTHOR]

In this paper we are concerned with the solution of a Robin boundary conditioned problem associated with the local heat transfer equation. The results are obtained using both symmetrical system features and expansions of a Boubaker polynomial subsequence. The yielded profile is compared with some recently proposed models. [ABSTRACT FROM AUTHOR]

Modern complex engineering applications are often nondeterministic systems that include sources of uncertainty that cannot be parametrized numerically; this is unparametrizable uncertainty. One example is the uncertainty in the behavior of a mechanical system due to heterogeneous material properties on the microscale (e.g., grain boundary effects on microstructure). Another example is the uncertainty in the performance of a complex topology structure due to random topology imperfections. In this paper, we propose a method for metamodeling these nondeterministic systems for efficient uncertainty analysis in robust design. Generalized linear models for mean responses and heteroscadastic response variances are estimated iteratively in an integrated manner. Estimators that may be used for predicting mean and variance models are introduced. The usefulness of this metamodeling approach is demonstrated with the example of a linear cellular alloy heat exchanger. Applications for these heat exchangers include actively cooled supersonic aircraft skins and engine combustor liners. Linear cellular alloy heat exchangers have unparametrizable uncertainty due to randomly distributed cracks in cell walls, as well as parametrizable uncertainty due to variability in wall thickness and inlet air velocity. Nondeterministic metamodels for estimating total steady state heat transfer rates in linear cellular alloy heat exchangers are developed and the results of using these metamodels are compared with those obtained by the finite element analysis (FEA) models of the linear cellular alloys. [ABSTRACT FROM AUTHOR]

In this paper, we present a transient mathematical model for a V-shaped microgrooved heat pipe considering the temporal variations in the fluid flow, and heat and mass transfer, and utilizing a macroscopic approach. Unlike other heat pipe models, the shear stress at the liquid-vapor interface and the disjoining pressure have been used in the momentum balance equation of the model. The sensible heat used by the substrate is also taken into account using a pseudo-lump capacity model. The coupled nonlinear partial differential equations governing the transient fluid flow, heat and mass transfer have been solved numerically. The transient and steady-state profiles for the radius of curvature, liquid and vapor velocity, liquid pressure, and substrate temperature have been obtained. The mathematical model is capable of predicting the time required for the onset of dry out at the hot end, and for a micro heat pipe to reach steady state. The time required to reach steady state is independent of heat input, heat pipe inclination, groove angle, and Qss profile. However, the time required for the onset of dry out at the hot end decreases with increasing heat input, inclination, and groove angle. The model predicted results have been successfully compared to the results from the literature. The general nature of this model and the associated study can be useful for many practical applications in the microscale heat exchange. [ABSTRACT FROM AUTHOR]