scholarly journals Fundamental Evaluation of Thermal Switch Based on Ionic Wind

Energies ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2963 ◽  
Author(s):  
Keiichiro Yoshida
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Waste Heat ◽  
Copper Plate ◽  
Ionic Wind ◽  
Transfer Coefficients ◽  
Heat Management ◽  
Heat Transfer Coefficients ◽  
Thermal Switch ◽  
Basic Characteristics

A significant amount of thermal energy (mainly under 200 °C) is wasted in the world. To utilize the waste heat, efficient heat management and thermal switching is required. The basic characteristics of a thermal switch that controls the flow of heat by switching on/off the ionic wind is discussed in this study. The study was conducted through experiments and numerical simulations. A heater made of aluminum block maintained at 100 °C was used as a heat source, and the rate of heat flow to a copper plate placed over it was measured. Ionic wind was induced by corona discharge with a needle placed on the heater. The ratio of heat transfer coefficients was obtained in the range of 3–4, with an energy efficiency of around 10. The heat flux at this condition was approximately 400 W/m2. The numerical simulations indicate that the heat transfer is enhanced by ionic winds, and the results were found to corroborate well with the experimental ones.

scholarly journals Specifics in the operating modes of thermosyphon air heater of steam generators №1 and №2 in TPP "Republika" at fuel switch from coal to natural gas

2019 ◽  
Vol 85 ◽  
pp. 01003 ◽  
Author(s):  
Iliya Iliev ◽  
Angel Terziev ◽  
Hristo Beloev ◽  
Christiyan Iliev
Keyword(s):  
Heat Transfer ◽  
Natural Gas ◽  
Complex Geometry ◽  
Waste Heat ◽  
Numerical Study ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Operating Modes ◽  
Heat Transfer Coefficients ◽  
Harmful Emissions

A fuel switch is motivated both by the necessity of increasing energy efficiency and the compliance with the ever-stricter regulations regarding the release of harmful emissions in the environment. In this paper a thorough financial and energy analysis on the fuel switch from coal to natural gas is carried out, in particular with respect to waste heat recovery systems (two phase thermosyphons). As a result of the calculation of the heat transfer coefficients for both fuels, it is established that the system running on natural gas has a lower value, due to the lower air velocity, caused in turn by the lower requirement for excess air. The heat transfer coefficients of the evaporation and condensation zones respectively are established hfgas=104.9 И hair=84.9 (W/m2.K) for coal and hfgas И hair =84.7 (W/m2.K) respectively for gas. A numerical study is also carried out and a methodology for the analysis of the efficiency of two phase thermosyphons with complex geometry is presented.

scholarly journals Gas-Solid Heat Transfer Computation from Particle-Resolved Direct Numerical Simulations

Fluids ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 15
Author(s):  
Mohamed-Amine Chadil ◽  
Stéphane Vincent ◽  
Jean-Luc Estivalèzes
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Penalty Method ◽  
Accurate Estimate ◽  
Second Order ◽  
High Order ◽  
Direct Numerical Simulations ◽  
Transfer Coefficients ◽  
Carrier Fluid ◽  
Heat Transfer Coefficients

Particle-Resolved simulations (PR-DNS) have been conducted using a second order implicit Viscous Penalty Method (VPM) to study the heat transfer between a set of particles and an incompressible carrier fluid. A Lagrange extrapolation coupled to a Taylor interpolation of a high order is utilized to the accurate estimate of heat transfer coefficients on an isolated sphere, a fixed Faced-Centered Cubic array of spheres, and a random pack of spheres. The simulated heat transfer coefficients are compared with success to various existing Nusselt laws of the literature.

Heat Transfer Measurements and Numerical Simulations in the Cooling of a Circular Cylinder by a Slot Jet of Air

2003 ◽  
Author(s):  
F. Gori ◽  
I. Petracci
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Numerical Simulations ◽  
Convective Heat Transfer ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Commercial Code ◽  
Convective Heat Transfer Coefficients

The present paper reports heat transfer measurements on a circular cylinder, electrically heated, and cooled by a slot jet of air. The diameter of the cylinder is equal to the slot height. Temperature measurements in five positions along the circumference of the circular cylinder, allow the evaluation of the convective heat transfer coefficients or Nusselt numbers at several Reynolds numbers. The Nusselt numbers are compared with the corresponding results in uniform flow around a circular cylinder. The experiments have been performed at several distances from the slot jet exit and different Reynolds numbers. Numerical simulations have been carried out with a commercial code.

scholarly journals Simulations of Hot-Gas Flow in Internally Cooled Cascade of Turbine Vanes

2019 ◽  
Vol 26 (2) ◽  
pp. 151-158
Author(s):  
Janusz Sznajder
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Simulations ◽  
Gas Flow ◽  
Turbulence Models ◽  
Turbulence Energy ◽  
Transfer Coefficients ◽  
Cooling Channels ◽  
Heat Transfer Coefficients ◽  
Outlet Flow

Abstract An experiment in cooling of gas turbine nozzle guide vanes was modelled numerically with a conjugate viscous-flow and solid-material heat conduction solver. The nozzle vanes were arranged in a cascade and operated in high-pressure, hot-temperature conditions, typical for first turbine stage in a flow of controlled-intensity, artificially-generated turbulence. The vane cooling was internal, accomplished by 10 channels in each vane with cooling-air flow. Numerical simulations of the experiment were conducted applying two turbulence models of the k-omega family: k-omega-SST and Transition SST implemented in the ANSYS Fluent solver. Boundary conditions for the simulations were set based on conditions of experiment: total pressures and total temperature on inlet to cascade, static pressure on the outlet of the cascade and heat flux on the surface of cooling channels. The values of heat flux on the surface of cooling channels were evaluated based on Nusselt numbers obtained from experiment and varied in time until steady-state conditions were obtained. Two test cases, one with subcritical outlet flow, and another one, with supercritical outlet flow were simulated. The result of experiment – distributions of pressure, surface temperature, and heat transfer coefficients on the vane external surface were compared to results of numerical simulations. Sensitivity of the vane surface temperatures and heat transfer coefficients to turbulence models and to boundary-condition values of parameters of turbulence models: turbulence energy and specific dissipation of turbulence energy was also studied.

Experimental Investigation of Heat Transfer Enhancement of CuO–Water and ZnO–Water Nanofluids Flowing Over a Heated Plate

2019 ◽  
Vol 11 (4) ◽  
Author(s):  
Dale A. McCants ◽  
Andrew M. Hayes ◽  
Titan C. Paul ◽  
Jamil A. Khan ◽  
Aly H. Shaaban
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Constant Heat Flux ◽  
Copper Plate ◽  
Heated Plate ◽  
Transfer Coefficients ◽  
Constant Heat ◽  
Heat Transfer Coefficients ◽  
Transmission Electron ◽  
Zno Nanofluids

In this paper, experimental investigation has been performed to characterize the heat transfer behavior of CuO–water and ZnO–water nanofluids. Nanofluids containing different volume percent (vol %) of nanoparticle concentrations flowed over a flat copper plate under a constant heat load. The constant heat flux was maintained using evenly placed cartridge heaters. The heat transfer coefficients of nanofluids were measured and compared with the results obtained from identical experiments performed with de-ionized (DI) water. In order to thoroughly characterize the nanofluids, nanoparticle size was investigated to inspect for possible agglomeration. The particle size was measured by using both a transmission electron microscope (TEM) and a dynamic light scattering system (DLS). Enhancement of convective heat transfer of nanofluids was 2.5–16% depending on the nanoparticle concentrations and Reynolds number. The plausible mechanisms of the enhanced thermal performance of CuO and ZnO nanofluids will be discussed in the following paper.

Impingement Cooling Experiments With Flat Plate and Pin Plate Target Surfaces

1999 ◽  
Author(s):  
Rainer Hoecker ◽  
Bruce V. Johnson ◽  
Josef Hausladen ◽  
Matthias Rothbrust ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Copper Plate ◽  
Orifice Plate ◽  
Plate Model ◽  
Transfer Coefficients ◽  
Flat Plates ◽  
Target Plate ◽  
Average Heat ◽  
Heat Transfer Coefficients

Heat transfer experiments were conducted with three (3) different target plate configurations: a baseline copper flat smooth plate, a copper plate model with copper pins and a copper plate model with Teflon pins, to determine average heat transfer coefficients on the flat and pin surfaces for application with different plate materials. For each target plate surface configuration, the heat transfer experiments were conducted with selected impingement orifice plate configurations and with selected spacing between the orifice plate and the heat transfer target plate. The heat transfer results for the baseline copper smooth flat plate were in good agreement with a well-recognized correlation for the flow regions used in the correlation. An analytical procedure, similar to that used by Metzger et al. for pin-fins in coolant channels, was developed to separate the average heat transfer coefficients on the flat and pin surfaces. The results with the copper pins showed modest increases of approximately 35 percent in heat transfer at lower Reynolds numbers, decreasing with increased Reynolds number. Application of the experimental results to an analysis for high-pressure engine conditions with modest thermal conductivity materials showed that the overall heat transfer coefficient can decrease with pin surfaces for some conditions, compared to flat plates.

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