Computer simulation of the operating pressure of tungsten halogen lamps

Temperature and velocity fields in high-temperature lead coolant flows in a circular clearance for controlled oxygen impurity content in a flow were experimentally studied at the Nizhny Novgorod State Technical University by R.E. Alekseev (NNSTU). Temperature and velocity fields were simultaneously studied in “cold” and “hot” parts of the circuit in the following operating conditions: the lead temperature is t = 400–550 °C, the thermodynamic activity of oxygen is a = 10−5–100; the Peclet number is Pe = 500–7000, the coolant flow velocity is w = 0.1–1.5 m/s, and the average heat flux is q = 50–160 kW/m2. It has been found that the oxygen impurity content and characteristics of protective oxide coatings affect temperature and velocity fields in round and circular channels. This is due to the fact that oxygen in a coolant and oxide coatings on the surfaces limiting a liquid metal flow influence characteristics of the wall boundary region. The heat transfer process that occurs when HLMC transversely flows around heat exchange pipes is investigated now at the NNSTU. The experimental facility is a combination of two high-temperature liquid-metal stands, i.e., FT-2 with the lead coolant and FT-1 with the lead-bismuth coolant combined with an experimental section. The temperature of a heat-exchange surface is measured by thermocouples of diameter 1 mm mounted in walls of heat-exchange pipes. Velocity and temperature fields in a high-temperature HLMC flow are measured by special sensors placed in the flow cross section between rows of heat-exchange pipes. Heat transfer characteristics and temperature and velocity fields in a high-temperature lead coolant flow are studied in the following operating conditions: the lead temperature is t = 450–500 °C, the thermodynamic activity of oxygen is a = 10−5–100, and the coolant flow rate through the experimental setup is Q = 3–6 m3/h, which corresponds to coolant flow velocities of V = 0.4–0.8 m/s. Integrated experimental studies of characteristics of the heat transfer that occurs when the lead coolant transversely or obliquely flows around pipes have been carried out for the first time and the dependences Nu = f(Pe) for controlled content of thermodynamically active oxygen impurity and sediments of impurities have been obtained. It is assumed that the obtained experimental data on distribution of velocity and temperature fields in a HLMC flow will permit to study heat transfer processes and to use them for developing program codes for engineering calculations of heat exchange surfaces (steam generators) with a HLMC flow around them.

Natural convection in a cubical cavity with a coaxial heated cylinder

An analytical investigation is conducted to study the unsteady free convection heat and mass transfer flow through a non-homogeneous porous medium with variable permeability bounded by an infinite porous vertical plate in slip flow regime while taking into account the thermal radiation, chemical reaction, the Soret number, and temperature gradient dependent heat source. The flow is considered under the influence of magnetic field applied normal to the flow. Approximate solutions for velocity, temperature, and concentration fields are obtained using perturbation technique. The expressions for skin-friction, rate of heat transfer, and rate of mass transfer are also derived. The effects of various physical parameters, encountered in the problem, on the velocity field, temperature field, and concentration field are numerically shown through graphs, while the effects on skin-friction, rate of heat, and mass transfer are numerically discussed by tables.

Natural-convection enhancement methods may provide more efficient and effective, low-cost, reliable alternative cooling options for certain operating conditions. In this work, the introduction of locally applied oscillations is explored as a means of improving natural-convection cooling. A simple geometric system consisting of a vertically oriented flow path with one uniformly heated wall and one transversely oscillating, insulated wall is utilized. A finite-volume SIMPLER-based technique is developed to study the system in a transformed “fixed” domain. Analysis over a range of oscillation frequencies and displacements, flow channel length-to-width ratios, and heat rates allows for the examination of the characteristics of the resulting velocity and temperature fields under various operating conditions. The combination of the oscillations, the natural convection, the fluid inertia, and other flow drivers produced up to a 340% increase in the local heat transfer coefficient.

We analyze the velocity and temperature fields due to thermocapillary convection around a gas bubble that is stationary in a liquid. A linear temperature field is imposed in the undisturbed liquid. Our interest is in the effect of convective transport of momentum and energy on the velocity and temperature fields. We assume that buoyant convection is negligible. The relevant Reynolds and Marangoni numbers are assumed to be small compared with unity. When the Reynolds and Marangoni numbers are set equal to zero, the steady velocity field far from the bubble decays inversely with distance from it. We show that this behavior of the velocity field, coupled with the linear variation of the imposed temperature far away from the bubble, leads to an ill-posedness in the problem for the perturbation temperature field at steady state for small Marangoni numbers, when the Reynolds number is zero. We also consider the effect of convective transport of momentum for small Reynolds number, when the Marangoni number is zero. In this case, the velocity field far away from the bubble decays inversely as the distance from the bubble even in the presence of inertia. It follows that, for a fixed Prandtl number, when both the Marangoni and Reynolds number are nonzero, the behavior of the velocity field far from the bubble continues to yield an ill-posed problem for the steady perturbation temperature field. Therefore, inertia cannot relieve the ill-posedness of the perturbation problem for the steady temperature field. In order to understand the origin of this ill-posedness, we analyze a related problem involving the unsteady development of the temperature field in the liquid from the moment that a point force is applied to it, and held constant subsequently. We show that including the effect of convective transport of energy by a perturbation expansion leads to a temperature field in the liquid that is always time dependent. The temperature field never achieves a steady state.

Numerical investigation on the reservoir heat production capacity of a downhole heat exchanger geothermal system

Full-scale experimental and computational fluid dynamics (CFD) methods were used to investigate the velocity and temperature fields in a mechanically ventilated room. Detailed airflow fields were measured in three cases of ventilation air temperature: an isothermal case, a hot case and a cold case. The ventilation system created a round jet which developed near the ceiling. The experimental data were used to test two turbulence models: a first order k-ε turbulence model and a second order RSM turbulence model. The RSM model predicted the temperature and velocity fields better than the k-ε turbulence model. In particular, experimental global values of velocity and temperature were in good agreement with the RSM turbulence model. This model is recommended for simulation of ventilated enclosures with thermal effects.

Simultaneous measurement of microscale fluid viscosity, temperature, and velocity fields by tracking Janus particle on microparticle image velocimetry

In the investigation of natural convection, many empirical equations have been proposed. However, almost all of them are for rarefied gas regions or over atmospheric pressure. The purpose of this study is to propose an empirical equation of natural convection heat transfer which considers the pressure dependency caused by pressure change. The pressure is given between the vacuum region and more than atmospheric pressure. In this study, the temperature field formed under the cooled disk is analyzed by an experimental measurement using laser holographic interferometry. The test section is set in a vacuum chamber, and the pressure ratio between the test field and atmospheric pressure is set as 0.1 to 2.0. The medium gas chosen here is dry air, argon, CO2, helium, and neon in order to expand the range of experimental conditions. The temperature difference between the cooled disk and the medium gas is adjusted from 30 K to 50 K every 10 K. As a result, the average Nusselt number near the cooled surface is expressed as a function of Rayleigh number in the range of 56 1× 10 < < 6 × 10 Ra .

Field synergy analysis on thermal-hydraulic behavior of phase change slurry in porous microchannel heat sink with graded porosity configuration

The lattice Boltzmann modeling on the nanofluid natural convective transport in a cavity filled with a porous foam

The aim of the work is to investigate the basic phenomena of heat generation and transfer in inductively-coupled RF plasma torches working at atmospheric pressure. Many fundamental works on the subject &#91;1,2&#93; propose a detailed treatment of the electromagnetic, temperature and velocity fields inside the torch. In the present work, in order to highlight the effects due to the distribution of the electromagnetic and temperature fields when separated from the effect of the complex behaviour of the fluid circulation, simplified slab and cylindric geometries for the cross section of the torch have been considered. The mathematical model takes into account heat conduction and convection, using a simplified expression for the velocity field; a two-dimensional treatment of the electromagnetic field is employed. The results presented refer to torch working near the minimum plasma sustaining power and well above threshold, showing temperature and power density distributions; comparisons between results obtained using the exact two-dimensional treatment for the electromagnetic field and a simplified one-dimensional approach are presented. A simple model is also presented explaining why the transverse temperature profile tends to change its shape in order to induce an increase of the mean power along the axial coordinate when the mean plasma temperature decreases.

The use of thermal imaging camera to estimate velocity profiles based on temperature distribution in a free convection boundary layer

Due to increase in the power generation from renewable sources, steam and gas turbines will be required to adapt for more flexible operations with frequent start-ups and shut-downs to provide load levelling capacity. During shut-down regimes, mixed convection takes place with natural convection dominance depending on the operating conditions in turbine cavities. Buoyant flows inside the turbine that are responsible for non-uniform cooling leading to thermal stresses and compromise clearances directly limits the operational flexibility. Computational fluid dynamics (CFD) tools are required to predict the flow field during these regimes since direct measurements are extremely difficult to conduct due to the harsh operating conditions. Natural convection with the presence of cross-flow -mixed convection has not been extensively studied to provide detailed measurements. Since the literature lacks of research on such flows with real engine representative operating conditions for CFD validation, the confidence in numerical predictions is rather inadequate. This paper presents a novel experimental facility that has been designed and commissioned to perform very accurate unsteady temperature and flow field measurements in a simplified turbine casing geometry. The facility is capable of reproducing a wide range of Richardson, Grashof and Reynolds numbers which are representative of engine realistic operating conditions. In addition, high fidelity, wall resolved LES with dynamic Smagorinsky subgrid scale model has been performed. The flow field as well as heat transfer characteristics have been accurately captured with LES. Lastly, inadequacy of RANS for mixed type of flows has been highlighted.

The purpose of this chapter is to conduct numerical calculation on nanofluid’s natural convection. The Al2O3-water nanofluids are taken as an example, and systems of numerical solutions of velocity and temperature fields of boundary layer are obtained with consideration of nanofluid’s variable physical properties. They will become the basis of further investigation on hydrodynamics and heat transfer of nanofluid’s natural convection.