scholarly journals Theoretical and Numerical Study of Heat Transfer Deterioration in High Performance Light Water Reactor

2008 ◽  
Vol 2008 ◽  
pp. 1-5 ◽  
Author(s):  
David Palko ◽  
Henryk Anglart
Keyword(s):  
Heat Transfer ◽  
Water Flow ◽  
Mass Flow ◽  
High Performance ◽  
Stokes Equations ◽  
Numerical Study ◽  
International Association ◽  
Flow Rates ◽  
Heat Transfer Deterioration ◽  
Mass Flow Rates

A numerical investigation of the heat transfer deterioration (HTD) phenomena is performed using the low-Re k-ωturbulence model. Steady-state Reynolds-averaged Navier-Stokes equations are solved together with equations for the transport of enthalpy and turbulence. Equations are solved for the supercritical water flow at different pressures, using water properties from the standard IAPWS (International Association for the Properties of Water and Steam) tables. All cases are extensively validated against experimental data. The influence of buoyancy on the HTD is demonstrated for different mass flow rates in the heated pipes. Numerical results prove that the RANS low-Re turbulence modeling approach is fully capable of simulating the heat transfer in pipes with the water flow at supercritical pressures. A study of buoyancy influence shows that for the low-mass flow rates of coolant, the influence of buoyancy forces on the heat transfer in heated pipes is significant. For the high flow rates, buoyancy influence could be neglected and there are clearly other mechanisms causing the decrease in heat transfer at high coolant flow rates.

Application of the Transient Heat Transfer Measurement Technique Using Thermochromic Liquid Crystals in a Network Configuration With Intersecting Circular Passages

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Anika Steurer ◽  
Rico Poser ◽  
Jens von Wolfersdorf ◽  
Stefan Retzko
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Mass Flow ◽  
Stokes Equations ◽  
Fluid Temperature ◽  
Thermochromic Liquid Crystal ◽  
Flow Rates ◽  
Flow Network ◽  
Mass Flow Rates ◽  
Time Information

The present study deals with the application of the transient thermochromic liquid crystal (TLC) technique in a flow network of intersecting circular passages as a potential internal turbine component cooling geometry. The investigated network consists of six circular passages with a diameter d = 20 mm that intersect coplanar at an angle θ = 40 deg, the innermost in three, the outermost in one intersection level. Two additional nonintersecting passages serve as references. Such a flow network entails specific characteristics associated with the transient TLC method that have to be accounted for in the evaluation process: the strongly curved surfaces, the mixing and mass flow redistribution at each intersection point, and the resulting gradients between the wall and passage centerline temperatures. All this impedes the choice of a representative fluid reference temperature, which results in deviations using established evaluation methods. An alternative evaluation approach is introduced, which is supported by computational results obtained from steady-state three-dimensional (3D) Reynolds-averaged Navier–Stokes equations (RANS) simulations using the shear-stress transport (SST) turbulence model. The presented analysis uncouples local heat transfer (HT) coefficients from actually measured local temperatures but uses the time information of the thermocouples (TC) instead that represents the fluid temperature step change and evolution along the passages. This experimental time information is transferred to the steady-state numerical bulk temperatures, which are finally used as local references to evaluate the transient TLC experiments. As effective local mass flow rates in the passage sections are considered, the approach eventually allows for a conclusion whether HT is locally enhanced due to higher mass flow rates or the intersection effects.

Numerical Investigation on the Cooling Effectiveness Among Air and Steam and Mist/Steam for a Gas Turbine Vane

2017 ◽  
Author(s):  
Junfei Zhou ◽  
Xinjun Wang ◽  
Jun Li ◽  
Feng Zhang ◽  
Daren Zheng
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Stokes Equations ◽  
Numerical Comparison ◽  
Cooling Effectiveness ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
The Mean

This paper presents a numerical comparison of the flow and conjugate heat transfer characteristics about the internal cooling of a nozzle guide vane with three kinds of coolants, including air, steam and mist/steam. Five radial cooling channels are established inside the vanes. The Reynolds-averaged Navier–Stokes equations, coupled with a fully-developed Shear Stress Transport (with γ-θ transition) turbulent model, are adopted and solved. Different coolant mass flow rates are examined. Different initial mist diameters and mist concentrations are numerically calculated. The mist tracks in five internal channels and the cooling effectiveness at the mid-span are obtained and compared among different initial mist diameters and mist concentrations. The turbulence kinetic energy and heat transfer coefficient inside the internal channel are used to further investigate the effects of the droplet size. The mean cooling effectiveness of the vane outer surface is obtained at different coolant mass flow rates. Results show that the mist/steam cooling has a best cooling performance compared with that of the air and steam. The influence of the mist concentration is much smaller than the initial mist diameter on the mists evaporation. The mists can evaporate entirely at a relative small initial diameter and the evaporation distance increases about two times with the mist mass flow rate increases from 1% ∼ 5% coolant mass flow rate. With a same mist concentration, the faster the mists evaporate, the higher the cooling effectiveness is obtained. Under a certain coolant mass flow rate, the amplification of the mean cooling effectiveness decreases with the increase of the mist concentration. With the increase of the coolant mass flow rate, the differences of the mean cooling effectiveness among different mist concentrations become larger.

Application of the Transient Heat Transfer Measurement Technique Using TLC in a Network Configuration With Intersecting Circular Passages

2018 ◽  
Author(s):  
Anika Steurer ◽  
Rico Poser ◽  
Jens von Wolfersdorf ◽  
Stefan Retzko
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Mass Flow ◽  
Fluid Temperature ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Flow Network ◽  
Mass Flow Rates ◽  
Time Information

The present study deals with the application of the transient thermochromic liquid crystal (TLC) technique in a flow network of intersecting circular passages as a potential internal turbine component cooling geometry. The investigated network consists of six circular passages with a diameter d = 20mm that intersect coplanar at an angle θ = 40°, the innermost in three, the outermost in one intersection level. Two additional non-intersecting passages serve as references. Such a flow network entails specific characteristics associated with the transient TLC method that have to be accounted for in the evaluation process: the strongly curved surfaces, the mixing and mass flow redistribution at each intersection point, and the resulting gradients between the wall and passage centerline temperatures. All this impedes the choice of a representative fluid reference temperature, which results in deviations using established evaluation methods. An alternative evaluation approach is introduced, which is supported by computational results obtained from steady-state three-dimensional RANS simulations using the SST turbulence model. The presented analysis uncouples local heat transfer coefficients from actually measured local temperatures but uses the time information of the thermocouples instead that represents the fluid temperature step change and evolution along the passages. This experimental time information is transferred to the steady-state numerical bulk temperatures, which are finally used as local references to evaluate the transient TLC experiments. As effective local mass flow rates in the passage sections are considered, the approach eventually allows for a conclusion whether heat transfer is locally enhanced due to higher mass flow rates or the intersection effects.

scholarly journals Numerical Investigation of Mixing Characteristic for CH4/Air in Rotating Detonation Combustor

2020 ◽  
Vol 10 (4) ◽  
pp. 1298
Author(s):  
Shan Jin ◽  
Qingyang Meng ◽  
Zhiming Li ◽  
Ningbo Zhao ◽  
Hongtao Zheng ◽  
...  
Keyword(s):  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Equivalence Ratio ◽  
Numerical Study ◽  
Ignition Energy ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Critical Ignition ◽  
Rotating Detonation

The mixing process of fuel and oxidizer is a very critical factor affecting the real operating performance of non-premixed rotating detonation combustor. In this paper, a two-dimensional numerical study is carried out to investigate the flow and mixing characteristics of CH4/air in combustor with different injection structures. On this basis, the effect of CH4/air mixing on the critical ignition energy for forming detonation is theoretically analyzed in detail. The numerical results indicate that injection strategies of CH4 and air can obviously affect the flow filed characteristic, pressure loss, mixing uniformity and local equivalence ratio in combustor, which further affect the critical ignition energy for forming detonation. In the study for three different mass flow rates (the mass flow rates of air are 12.01 kg/s,8.58 kg/s and 1.72 kg/s, respectively), when air is radially injected into combustor (fuel/air are injected perpendicular to each other), although the mixing quality of CH4 and air is improved, the total pressure loss is also increased. In addition, the comparative analysis also shows that the increase of mass flow rate of CH4/air can decrease the difference of the critical ignition energy for forming detonation at a constant total equivalence ratio. The ignition energy decreases with the decrease of the total flow rate and then increases gradually.

First and second thermodynamic law analyses applied to a solar dish collector

2014 ◽  
Vol 39 (4) ◽  
Author(s):  
Vahid Madadi ◽  
Touraj Tavakoli ◽  
Amir Rahimi
Keyword(s):  
Heat Transfer ◽  
Solar Radiation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Exergy Efficiency ◽  
Exergy Destruction ◽  
Flow Rates ◽  
Energy And Exergy ◽  
Mass Flow Rates

AbstractThe energy and exergy performance of a parabolic dish collector is investigated experimentally and theoretically. The effect of receiver type, inlet temperature and mass flow rate of heat transfer fluid (HTF), receiver temperature, receiver aspect ratio and solar radiation are investigated. To evaluate the effect of the receiver aperture area on the system performance, three aperture diameters are considered. It is deduced that the fully opened receivers have the greatest exergy and thermal efficiency. The cylindrical receiver has greater energy and exergy efficiency than the conical one due to less exergy destruction. It is found that the highest exergy destruction is due to heat transfer between the sun and the receivers and counts for 35 % to 60 % of the total wasted exergy. For three selected receiver aperture diameters, the exergy efficiency is minimum for a specified HTF mass flow rate. High solar radiation allows the system to work at higher HTF inlet temperatures. To use this system in applications that need high temperatures, in cylindrical and conical receivers, the HTF mass flow rates lower than 0.05 and 0.09 kg/s are suggested, respectively. For applications that need higher amounts of energy content, higher HTF mass flow rates than the above mentioned values are recommended.

scholarly journals Verification and Improving the Heat Transfer Model in Radiators in the Wide Change Operating Parameters

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6543
Author(s):  
Mieczysław Dzierzgowski
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Water Mass ◽  
Heat Transfer Model ◽  
Operating Conditions ◽  
Transfer Model ◽  
Flow Rates ◽  
Wide Range ◽  
Different Types ◽  
Mass Flow Rates

Laboratory measurements and analyses conducted in a wide range of changes of water temperature and mass flow rate for different types of radiators allowed to provides limitations and assessment of the current radiators heat transfer model according to EN 442. The inaccuracy to determinate the radiator heat output according to EN 442, in case of low water mass flow rates may achieve up to 22.3% A revised New Extended Heat Transfer Model in Radiators NEHTMiRmd is general and suitable for different types of radiators both new radiators and radiators existing after a certain period of operation is presented. The NEHTMiRmd with very high accuracy describes the heat transfer processes not only in the nominal conditions—in which the radiators are designed, but what is particularly important also in operating conditions when the radiators water mass flow differ significantly from the nominal value and at the same time the supply temperature changes in the whole range radiators operating during the heating season. In order to prove that the presented new model NEHTMiRmd is general, the article presents numerous calculation examples for various types of radiators currently used. Achieved the high compatibility of the results of the simulation calculations with the measurement results for different types of radiators: iron elements (not ribbed), plate radiators (medium degree ribbed), convectors (high degree ribbed) in a very wide range of changes in the water mass flow rates and the supply temperature indicates that a verified NEHTMiRmd can also be used in designing and simulating calculations of the central heating installations, for the rational conversion of existing installations and district heating systems into low temperature energy efficient systems as well as to directly determine the actual energy efficiency, also to improve the indications of the heat cost allocators. In addition, it may form the basis for the future modification of the European Standards for radiator testing.

scholarly journals Performance Analysis of Air and Oxy-Fuel Laminar Combustion in a Porous Plate Reactor

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1706
Author(s):  
Furqan Tahir ◽  
Haider Ali ◽  
Ahmer A.B. Baloch ◽  
Yasir Jamil
Keyword(s):  
Mass Flow ◽  
Carbon Capture ◽  
Numerical Study ◽  
Porous Plate ◽  
Flame Temperature ◽  
Fuel Combustion ◽  
Mitigation Measures ◽  
Outlet Temperature ◽  
Flow Rates ◽  
Mass Flow Rates

Greenhouse gas emissions from the combustion of fossil fuels pose a serious threat to global warming. Mitigation measures to counter the exponential growth and harmful impact of these gases on the environment require techniques for the reduction and capturing of carbon. Oxy-fuel combustion is one such effective method, which is used for the carbon capture. In the present work, a numerical study was carried out to analyze characteristics of oxy-fuel combustion inside a porous plate reactor. The advantage of incorporating porous plates is to control local oxy-fuel ratio and to avoid hot spots inside the reactor. A modified two-steps reaction kinetics model was incorporated in the simulation for modeling of methane air-combustion and oxy-fuel combustion. Simulations were performed for different oxidizer ratios, mass flow rates, and reactor heights. Results showed that that oxy-combustion with an oxidizer ratio (OR) of 0.243 could have the same adiabatic flame temperature as that of air-combustion. It was found that not only does OR need to be changed, but also flow field or reactor dimensions should be changed to achieve similar combustion characteristics as that of air-combustion. Fifty percent higher mass flow rates or 40% reduction in reactor height may achieve comparable outlet temperature to air-combustion. It was concluded that not only does the oxidizer ratio of oxy-combustion need to be changed, but the velocity field is also required to be matched with air-combustion to attain similar outlet temperature.

Experimental Investigation of Turbine Leakage Flows on the Three-Dimensional Flow Field and Endwall Heat Transfer

2006 ◽  
Vol 129 (3) ◽  
pp. 608-618 ◽  
Author(s):  
Hans-Jürgen Rehder ◽  
Axel Dannhauer
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Secondary Flow ◽  
Mass Flow ◽  
Test Section ◽  
Flow Behavior ◽  
Leakage Flow ◽  
Flow Rates ◽  
Low Pressure Turbine ◽  
Mass Flow Rates

Within a European research project, the tip endwall region of low pressure turbine guide vanes with leakage ejection was investigated at DLR in Göttingen. For this purpose a new cascade wind tunnel with three large profiles in the test section and a contoured endwall was designed and built, representing 50% height of a real low pressure turbine stator and simulating the casing flow field of shrouded vanes. The effect of tip leakage flow was simulated by blowing air through a small leakage gap in the endwall just upstream of the vane leading edges. Engine relevant turbulence intensities were adjusted by an active turbulence generator mounted in the test section inlet plane. The experiments were performed with tangential and perpendicular leakage ejection and varying leakage mass flow rates up to 2%. Aerodynamic and thermodynamic measurement techniques were employed. Pressure distribution measurements provided information about the endwall and vane surface pressure field and its variation with leakage flow. Additionally streamline patterns (local shear stress directions) on the walls were detected by oil flow visualization. Downstream traverses with five-hole pyramid type probes allow a survey of the secondary flow behavior in the cascade exit plane. The flow field in the near endwall area downstream of the leakage gap and around the vane leading edges was investigated using a 2D particle image velocimetry system. In order to determine endwall heat transfer distributions, the wall temperatures were measured by an infrared camera system, while heat fluxes at the surfaces were generated with electric operating heating foils. It turned out from the experiments that distinct changes in the secondary flow behavior and endwall heat transfer occur mainly when the leakage mass flow rate is increased from 1% to 2%. Leakage ejection perpendicular to the main flow direction amplifies the secondary flow, in particular the horseshoe vortex, whereas tangential leakage ejection causes a significant reduction of this vortex system. For high leakage mass flow rates the boundary layer flow at the endwall is strongly affected and seems to be highly turbulent, resulting in entirely different heat transfer distributions.

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