A transient three-dimensional heat transfer model of the human body

The objective of this work is to develop an improved model of the human thermal system. The features included are important to solve real problems: 3D heat conduction, the use of elliptical cylinders to adequately approximate body geometry, the careful representation of tissues and important organs, and the flexibility of the computational implementation. Focus is on the passive system, which is composed by 15 cylindrical elements and it includes heat transfer between large arteries and veins. The results of thermal neutrality and transient simulations are in excellent agreement with experimental data, indicating that the model represents adequately the behavior of the human thermal system.     

Modeling of convective heat transfer of a nanofluid in the developing region of tube flow with computational fluid dynamics

In this article, convective heat transfer effect on the nanofluid flow in the developing region of a tube with constant heat flux was investigated using computational fluid dynamics (CFD). For this purpose, nanofluid containing Al₂O₃ and water as a liquid single phase with two average particle sizes of 45 and 150 nm and four particle concentrations of 1, 2, 4 and 6 wt.% were used. Effect of particle size on convective heat transfer coefficient was investigated in different Reynolds numbers (500 < Re < 2500) for various axial locations of tube. According to the modeling results, an equation was obtained for Nusselt number prediction using the dimensionless numbers. The results showed that the predicted data were in very good agreement with experimental data obtained from the literature. The maximum error was around 10%.     

Modeling of forced convective heat transfer of a non-Newtonian nanofluid in the horizontal tube under constant heat flux with computational fluid dynamics

In this paper, convective heat transfer effect on the non-Newtonian nanofluid flow in the horizontal tube with constant heat flux was investigated using computational fluid dynamics (CFD). For this purpose, non-Newtonian nanofluid containing Al₂O₃ and Xanthan aqueous solution as a liquid single phase with two average particle sizes of 45 and 150 nm and four particle concentrations of 1, 2, 4 and 6 wt.% and two concentrations of Xanthan aqueous solutions (0.6,1.0 wt.%) were used. Effect of particle size and concentration of Xanthan solution on convective heat transfer coefficient was investigated in different Reynolds numbers (500 < Re < 2500) for various axial locations of tube. The results showed that heat transfer coefficient and Nu number of non-Newtonian nanofluid increased with increasing concentration of Xanthan solution. By applying the modeling results, an equation was obtained for Nusselt number prediction using the dimensionless numbers. The results showed that the correlated data were in very good agreement with predicted data. The maximum error was around 5%.     

计算流体力学在喷淋塔内流场模拟方面的研究进展及展望

介绍了采用计算流体力学方法对湿法脱硫喷淋塔内流场模拟的理论研究情况,对研究结果进行了分析,并对以后的研究工作进行了展望.     

Modeling and simulation of a proton exchange membrane fuel cell using computational fluid dynamics

An isothermal, three dimensional, single phase model was presented to evaluate a proton exchange membrane fuel cell (PEMFC) with serpentine flow. The mass, momentum and electrochemical equations were solved simultaneously for the steady state condition using computational fluid dynamics (CFD) software based on the finite element method. The model considered reactions as mass source/sink terms, and electron transport in the catalyst layers and GDLs. To validate the model, the numerical results were compared to the experimental data collected from the fabricated membrane electrode assemblies. The exchange current density parameter of the catalysts was fitted by the model to calibrate the results. The model showed good agreement with experimental data and predicted a higher current density for the catalyst with a higher surface area and Pt content. The oxygen, hydrogen and water mass fraction distribution, velocity magnitude and pressure distribution were estimated by the model. Moreover, the effect of pressure and temperature, as two important operating conditions, on the current density was predicted by the validated model.     

Optimisation of a solid oxide fuel cell reformer using surrogate modelling,design of experiments and computational fluid dynamics

The present paper proposes a trio approach including surrogate modelling, design of experiments and computational fluid dynamics. An experimentally validated 3D continuum model has been used in the aid to optimise the performance, weight and the associated manufacturing costs of a plate type pre-reformer. The effect of plate number, plate porosity, wire mesh porosity and alternative materials on the pre-reformer performance has been studied in detail using a D-optimal experimental design plan and computational fluid dynamics. Multi-regression analyses depict that the number of reformer plates has the greatest potential for optimisation. A surrogate model has been derived and employed to perform rapid process and design optimisations. Results show that the methane reforming can be 40% increased by reducing the pre-reformer plate number to half of the actual value. A mass reduction of 50%, associated with a saving of 50% may be enabled. The surrogate model is proven to be a powerful tool to aid in reduced physical prototype costs and product development time.     

Modeling of turbulent forced convective heat transfer and friction factor in a tube for Fe3o4 magnetic nanofluid with computational fluid dynamics

A numerical study based on the computational fluid dynamics (CFD) method, with a single phase approach, has been presented to determine the effects of nanoparticle concentration and flow rate on the convective heat transfer and friction factor of nanofluid flowing through a plain copper tube in turbulent regime with different Reynolds numbers (3000 < Re < 22000). The nanofluid consists of Fe₃o₄ magnetic nanoparticles, with the average diameter of 36 nm, suspended in water as a base fluid with four particle concentrations of 0.02, 0.1, 0.6 vol.%. Applying the modeling results, two relations were developed to estimate the Nusselt number and friction factor, based on the dimensionless numbers. The results showed that the modeling data were in very good agreement with experimental data. The maximum error was around 10%.     

Modelling solar effects on the heat and mass transfer in a street canyon, a simplified approach

In urban areas, the climatic loads on buildings in summer conditions are largely affected by solar radiation. In this paper a modified simplified method for radiant interchange determination is used in a solar energy study. The good agreement with the radiosity method allows one to use this simplified method in the street canyon case. In a building pilot study, parametric analysis and building thermal behaviour can be assessed by simplified models which are useful for long-period simulation. Then this radiant interchange model is introduced in a zonal model of a canyon street and performed with a variable climatic conditions show case. The solar radiation is the only driving force in the street air movement. The interest of such approach for complex coupled phenomena studies is highlighted by obtained results and the assessment of variable climatic loads for different building zones can be considered with the model detailed herein. Future developments are planned in order to improve simulation accuracy by the addition of other local phenomena.     

Production of hydrogen and carbon by solar thermal methane splitting. IV. Preliminary simulation of a confined tornado flow configuration by computational fluid dynamics

The confined tornado flow configuration has been developed at the Solar Research Facilities Unit, Weizmann Institute of Science, as a means for protection of the window of a solar reactor from contact with incandescent solid particles in gas suspension in the reactor cavity.

The results of a computational fluid dynamics (CFD) simulation of a tornado flow confined in a simplified reaction chamber are compared in this paper with information about such a flow obtained by gas dynamics experimentation. All the information obtained by experiment was corroborated by CFD. Moreover, the CFD simulation brought to view some important unexpected features of the confined tornado flow, which are discussed in detail.     

Turbulence models application on CFD simulation of hydrodynamics,heat and mass transfer in a structured packing

In this study, turbulence model applications on two-phase flow simulation in a structured packing are investigated using CFD application. Dry pressure drop, irrigated pressure drop, mass transfer and heat transfer are studied by k–ε, RNG k–ε, k–ω and BSL turbulence models. The best results obtained by k–ω and BSL models, but k–ω is recommended because it is more robust than BSL. The mean absolute relative error (MARE) between CFD prediction of k–ω model and experimental data for dry pressure drop, irrigated pressure drop, mass transfer and heat transfer are 16.9%, 10.7%, 8.1%, 0.9%, respectively.     

Characteristics of heat transfer and fluid flow in a channel with single-row plates array oblique to flow direction for photovoltaic/thermal system

This study has been carried out to investigate the characteristics of convective heat transfer and fluid flow for a single row of oblique plates array to the flow direction inside a channel. The flow inside the channel is laminar and the plates array have spanwise distance between the plates and heated by radiation. This configuration has been designed to be used for Photovoltaic/Thermal system (PV/T) applications. The theoretical results are validated with measured values, and a good agreement prevailed. The results show that an increase in the plate oblique angle (γ) in the range from 0 to 15 degrees, leads to an increase in the Nusselt number (Nu) up to a maximum value and then decreases. The oblique angle at the maximum value of Nu depends on the flow Reynolds Number (Re), and (?_w/?_pl), where (?_w/?_pl) is defined as the ratio of the plates’ spacing at zero oblique angle to the plate length. Furthermore, increasing (?_w/?_pl) results in a significant increase in the heat transfer coefficient depending on the values of Re, and plate oblique angle (γ). In addition, increasing (γ) from 0 to 15 degrees results in a decrease in the friction factor up to a certain value, after which the friction value approaches a constant value depending on Re value and (?_w/?_pl). It was found that for any value of the plate oblique angle (γ), the friction factor decreases with the increase of the values of (?_w/?_pl) and Re, respectively.     

Modelling of fluid flow and heat transfer to assess the geothermal potential of a flooded coal mine in Lorraine,France

The flooding of the Lorraine coal mines (France), representing a huge reservoir of about 154 × 10⁶ m³, began in June 2006. After attaining thermal equilibrium with the surrounding rocks, the water temperature in the deepest parts is expected to reach 55 °C, giving the opportunity for the extraction of low-enthalpy geothermal waters that may be suitable for district heating purposes. We present some numerical modelling results of the thermally driven convective flow in an open vertical shaft and in the entire mine reservoir. A dual permeability/porosity approach was used in the reservoir model, which includes open galleries and vertical shafts, coal panels backfilled with sand, and intact rock masses. Two scenarios of heat extraction with different flow regimes were investigated. A sensitivity analysis shows that the temperature decline in the production zone is highly dependent on the permeability of the surrounding porous rocks. Larger permeabilities result in higher water temperatures at the production shaft due to greater inflows of warm water from those rock masses.     

Investigation of fluid flow and heat transfer in a vertical channel heated from one side by PV elements, part I - Numerical Study

The impetus of this paper is to analyse numerically the fluid flow and heat transfer characteristics of buoyancy-driven convection between two vertical parallel walls, heated from one side. Both convection and radiation heat exchanges are considered as the heat transfer mechanisms by which the thermal energy is transferred into the air. A steady-state two-dimensional model is used for the analysis. Numerical results are derived for a channel of 6.5 m in height and different widths of the channel. Various heat fluxes are considered in order to show the effect of the input heat on the heat transfer across the air layer. Detailed studies of the flow and thermal fields in the air are presented in order to explore the thermal behavior of air in the channel. Velocity and temperature profiles of the outlet air and the surface temperature of the heated and insulated wall are presented. In Part II of this paper the findings from an experimental study are reported.