Heat Exchange and Friction Analysis in Noble Gas Mixtures for Closed Gas Turbines

2021 ◽  
pp. 4-18
Author(s):  
K.S. Egorov ◽  
L.V. Stepanova
Keyword(s):  
Heat Exchange ◽  
Prandtl Number ◽  
Gas Turbines ◽  
Power Plants ◽  
Transient Flow ◽  
Noble Gas ◽  
Gas Mixtures ◽  
Space Applications ◽  
Prandtl Numbers ◽  
Analytical Relations

The types of heat exchange surfaces used in closed gas turbines for space applications and their conversion version (ground application) as autonomous long-resource power plants of low power (less than 10 kW) are considered. The data of the works currently known in Russia and abroad on the developed turbulent flow in the tube when using gas mixtures with abnormally low Prandtl numbers (0.2) have been analyzed. Recommendations on the application of the analytical relations of Kays, Petukhov and Popov for the calculation of the Nusselt number in pipes are given. The influence of non-isothermal flow and initial pipe section on friction as well as the working body Prandtl number on heat exchange and friction for highly compact plate and fin heat exchange surfaces with staggered arrangement of ribs are analyzed. It is revealed that the relations obtained for the air model are inapplicable for working bodies with Prandtl numbers different from the air Prandtl number. The necessity of further experimental and analytical investigations of heat exchange and friction in tubes under transient flow regime and in highly compact finned surfaces with staggered ribs is confirmed

scholarly journals Thermophysical properties of noble gas mixtures with low Prandtl number

2019 ◽  
Author(s):  
K.S. Egorov ◽  
L.V. Stepanova
Keyword(s):  
Prandtl Number ◽  
Gas Turbine ◽  
Thermophysical Properties ◽  
Gas Turbines ◽  
Noble Gas ◽  
Gas Mixtures ◽  
Inert Gases ◽  
Space Applications ◽  
Working Medium ◽  
Working Parameters

The article investigates thermal (thermal conductivity and viscosity) and thermodynamic (density, heat capacity, enthalpy, compression coefficient) properties of inert gases and their mixtures, which are used as the main working medium in promising closed gas turbine for the space needs. Closed gas turbines can be used in various space applications – unmanned spacecrafts, communication satellites and manned martian mission. Experimental research into thermodynamic and thermophysical properties of noble gases and their mixtures is considered. It was revealed that by this time enough amounts of experimental data concerning the properties of both single inert gases and their mixtures had been obtained. These data are used in different models based on kinetic theory of gases and virial real gas condition equation which makes possible to predict necessary thermophysical parameters. While calculating and designing closed gas-turbine installations it is necessary to take into account adiabatic change and Prandtl number of inert gas mixtures. While approaching working parameters to xenon saturation line one should consider the increase of calculated dependency errors

scholarly journals INTENSIFIED HEAT EXCHANGE AT THE TURBULENT CURRENT IN PIPES WITH TURBULIZERS WITH THE APPLICATION OF THE FOUR-LAYER MODEL OF THE TURBULENT BORDER LAYER DEPENDING ON THE NUMBER PRANDTLE

2018 ◽  
Vol 1 (12) ◽  
pp. 76-81
Author(s):  
Igor' Lobanov
Keyword(s):  
Mathematical Modeling ◽  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Exchange ◽  
Turbulent Boundary Layer ◽  
Prandtl Number ◽  
Layer Model ◽  
Fourth Degree ◽  
Proportionality Coefficient ◽  
Prandtl Numbers

The main aspects of mathematical modeling of intensified heat transfer in turbulent flow in pipes with turbulators with the use of a four-layer model of a turbulent boundary layer are analyzed in the article, depending on the Prandtl number. The advantage of the law of the "fourth" degree is shown for large Prandtl numbers for the calculation of heat transfer in tubes with turbulators; It is shown that for tubes with turbulators the proportionality coefficient in this law is much higher than in smooth tubes, which indicates an increased level of turbulence in them at the boundary of the viscous and buffer sublayers. The results of calculating heat transfer for large Prandtl numbers have shown that the relative heat exchange with increasing Prandtl number increases rather insignificantly, especially after Pr>102; after Pr>103 it almost stabilizes

scholarly journals Monatomic Working Gases vs Air for the Closed Brayton Cycle

1985 ◽  
Author(s):  
J. L. Mason ◽  
E. A. Mock ◽  
R. T. Caldwell ◽  
A. Pietsch
Keyword(s):  
Prandtl Number ◽  
Heat Exchangers ◽  
Economic Incentive ◽  
Gas Mixtures ◽  
Brayton Cycle ◽  
System Study ◽  
Prandtl Numbers ◽  
Monatomic Gas

Monatomic gas mixtures have low Prandtl numbers, as low as 0.25 or even lower, compared to about 0.7 for air. In a closed Brayton cycle using a low Prandtl number working gas, the three heat exchangers in the cycle will in general be smaller than in a comparable cycle using air. A system study has been made to compare several promising monatomic gases with air, and to explore the economic incentive to replace air in the closed Brayton cycle with a monatomic gas.

The Influence of Recent Heat Transfer Data on Gas Mixtures (He-Ar, H2-CO2) on Closed Cycle Gas Turbines

1981 ◽  
Vol 103 (1) ◽  
pp. 114-117 ◽  
Author(s):  
B. L. Pierce
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Gas Turbines ◽  
Scaling Laws ◽  
Transfer Characteristic ◽  
Gas Mixtures ◽  
Working Fluid ◽  
Closed Cycle ◽  
Flow Area ◽  
Transfer Data

Previous studies have been made on the composition of an optimal working fluid for closed cycle gas turbines. Those studies were based on the assumption that the objective could be achieved by mixing helium with a gas of higher molecular weight. The results of those calculations, based on heat transfer data of pure gases and air, indicated the possibility of significant cost advantages of gas mixtures relative to pure helium. Recent heat transfer measurements of low Prandtl number gas mixtures indicate that existing scaling laws for normal Prandtl number (∼0.7) gases do not adequately represent the heat transfer characteristic of these gas mixtures. In this paper the influence of these gas mixture heat transfer data on closed cycle gas turbine coolers, recuperators and heat source exchangers is presented. The characteristic dimensions (flow area, surface area, and length) of these heat exchangers utilizing pure gases and gas mixtures are compared.

Stability of thermocapillary flows in non-cylindrical liquid bridges

2002 ◽  
Vol 458 ◽  
pp. 35-73 ◽  
Author(s):  
CH. NIENHÜSER ◽  
H. C. KUHLMANN
Keyword(s):  
Reynolds Number ◽  
Prandtl Number ◽  
Critical Reynolds Number ◽  
Volume Fraction ◽  
Thermocapillary Flow ◽  
Surface Shape ◽  
Liquid Bridges ◽  
Gravity Level ◽  
Neutral Curves ◽  
Prandtl Numbers

The thermocapillary flow in liquid bridges is investigated numerically. In the limit of large mean surface tension the free-surface shape is independent of the flow and temperature fields and depends only on the volume of liquid and the hydrostatic pressure difference. When gravity acts parallel to the axis of the liquid bridge the shape is axisymmetric. A differential heating of the bounding circular disks then causes a steady two-dimensional thermocapillary flow which is calculated by a finite-difference method on body-fitted coordinates. The linear-stability problem for the basic flow is solved using azimuthal normal modes computed with the same discretization method. The dependence of the critical Reynolds number on the volume fraction, gravity level, Prandtl number, and aspect ratio is explained by analysing the energy budgets of the neutral modes. For small Prandtl numbers (Pr = 0.02) the critical Reynolds number exhibits a smooth minimum near volume fractions which approximately correspond to the volume of a cylindrical bridge. When the Prandtl number is large (Pr = 4) the intersection of two neutral curves results in a sharp peak of the critical Reynolds number. Since the instabilities for low and high Prandtl numbers are markedly different, the influence of gravity leads to a distinctly different behaviour. While the hydrostatic shape of the bridge is the most important effect of gravity on the critical point for low-Prandtl-number flows, buoyancy is the dominating factor for the stability of the flow in a gravity field when the Prandtl number is high.

Flow birefringence in binary para hydrogen-noble gas mixtures

1985 ◽  
Vol 130 (3) ◽  
pp. 490-504 ◽  
Author(s):  
H. van Houten ◽  
F. Baas ◽  
P.M.J. Marée ◽  
J.J.M. Beenakker
Keyword(s):  
Noble Gas ◽  
Gas Mixtures ◽  
Flow Birefringence ◽  
Para Hydrogen

Analytical Study of the Convection Heat Transfer From an Isothermal Wedge Surface to Fluids

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
M. Bachiri ◽  
A. Bouabdallah
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Ad Hoc ◽  
Convection Heat Transfer ◽  
Analytical Approximation ◽  
Numerical Results ◽  
Convection Heat ◽  
Governing Equations ◽  
Wedge Surface ◽  
Prandtl Numbers

In this work, we attempt to establish a general analytical approximation of the convection heat transfer from an isothermal wedge surface to fluids for all Prandtl numbers. The flow has been assumed to be laminar and steady state. The governing equations have been written in dimensionless form using a similarity method. A simple ad hoc technique is used to solve analytically the governing equations by proposing a general formula of the velocity profile. This formula verifies the boundary conditions and the equilibrium of the governing equations in the whole spatial region and permits us to obtain analytically the temperature profiles for all Prandtl numbers and for various configurations of the wedge surface. A comparison with the numerical results is given for all spatial regions and in wide Prandtl number values. A new Nusselt number expression is obtained for various configurations of the wedge surface and compared with the numerical results in wide Prandtl number values.

Thermal Conductivity and Prandtl Number of Carbon Dioxide and Carbon-Dioxide Air Mixtures at One Atmosphere

1961 ◽  
Vol 83 (2) ◽  
pp. 125-131 ◽  
Author(s):  
Jerome L. Novotny ◽  
Thomas F. Irvine
Keyword(s):  
Carbon Dioxide ◽  
Thermal Conductivity ◽  
Prandtl Number ◽  
Maximum Error ◽  
Intermolecular Force ◽  
Temperature Range ◽  
Average Temperature ◽  
Pure Carbon ◽  
Prandtl Numbers ◽  
Pure Carbon Dioxide

By measuring laminar recovery factors in a high velocity gas stream, experimental determinations were made of the Prandtl number of carbon dioxide over a temperature range from 285 to 450 K and of carbon-dioxide air mixtures at an average temperature of 285 K with a predicted maximum error of 1.5 per cent. Thermal conductivity values were deduced from these Prandtl numbers and compared with literature values measured by other methods. Using intermolecular force constants determined from literature experimental data, viscosities, thermal conductivities, and Prandtl numbers were calculated for carbon-dioxide air mixtures over the temperature range 200 to 1500 deg for mixture ratios from pure air to pure carbon dioxide.

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