scholarly journals PHYSICAL PROPERTIES AND HEAT TRANSFER CHARACTERISTICS OF AN ALKALI NITRATE- NITRATE SALT MIXTURE

1955 ◽  
Author(s):  
H. W. Hoffman
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Nitrate Salt ◽  
Heat Transfer Characteristics ◽  
Salt Mixture ◽  
Transfer Characteristics

A Numerical Study of Forced Convective Heat Transfer Characteristics of Supercritical Fluid in a Horizontal Circular-Pipe

2020 ◽  
Author(s):  
Alaba Bamido ◽  
V. K. Dhir ◽  
V. Prasad ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Convective Heat Transfer ◽  
Supercritical Fluid ◽  
Convective Heat ◽  
Circular Pipe ◽  
Heat Transfer Characteristics ◽  
Forced Convective Heat Transfer ◽  
Transfer Characteristics ◽  
Thermo Physical Properties

Abstract Analytical and computational studies were performed to compare the convective heat transfer characteristics of a supercritical fluid in a circular pipe for horizontal flow configuration. The motivation of this study was to explore the efficacy of heat exchangers involving forced convective heat transfer of supercritical fluids (tube side) integrated with air cooling (i.e., in free convection). The goal of this study was to determine the forced convective heat transfer characteristics of supercritical carbon dioxide (sCO2) in air-cooled tube heat-exchangers. The scope of this study was limited to the values of Reynolds number (Re) varying from 10∼104 (i.e., involving both laminar and turbulent flow correlations for analytical formulations and computational models). The predictions for the forced convection heat transfer characteristics (e.g., heat transfer coefficient, pressure drop, volume flow rate, mass flow rate, pump penalty/ pumping power/ required compressor ratings, Nusselt number (Nu) etc.) were obtained using analytical formulations and compared with that of computational models. The flow configurations involved a horizontal circular pipe of 1 m length and with different diameters (ranging from 1 mm – 10 mm). The supercritical properties of the working fluid were investigated at a fixed value of reduced pressure (Pr = 1.1) and a fixed range of temperatures, i.e., T, varying from 550 to 750 [K]. The fluid properties were gleaned from the NIST property database (available online at the NIST website). For the second part of this study, the forced convective heat transfer characteristics of sCO2 flowing in a horizontal tube with circular cross-section were studied using analytical correlations (e.g., Dittus-Boelter and Gnielinski correlation) and validated using commercial tools for Computational Fluid Dynamics (CFD)/ Computational Heat Transfer (CHT), i.e., using Fluent® (Ansys®). Validation of the analytical predictions using CFD/ CHT tools was performed to ascertain the level of uncertainty in the predicted results due to acute variation of the thermo-physical properties as a function of temperature and pressure (since the thermo-physical properties are expected to oscillate widely in the vicinity of the critical point). In the simulations, the inlet temperature for the supercritical fluid (sCO2) was fixed (at Tin = 700 [K]), and the ambient temperature was also fixed (at Tamb = 300 [K]), for the purpose of determining the values of the natural convection coefficients (external to the tube). Constant values of the thermo-physical properties of sCO2 at the mean film temperature (and corresponding to the inlet pressure values) were assumed for obtaining the analytical predictions. The results from the CFD / CHT simulations helped to quantify the level of uncertainties in the assumption of constant properties (in the analytical model) at different values of Reynolds number (i.e., for both laminar and turbulent flow regimes).

scholarly journals Numerical Study on Influences of Drag Reducing Additive in Supercritical Flow of Kerosene in a Millichannel

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6758
Author(s):  
Biao Li ◽  
Wenxi Li ◽  
Xin Zheng ◽  
Yue Wang ◽  
Mingming Tang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Physical Properties ◽  
Numerical Study ◽  
Simulation Method ◽  
Inlet Temperature ◽  
Heat Transfer Characteristics ◽  
Supercritical Flow ◽  
Transfer Characteristics ◽  
Drag Reducing Additive

To improve the performance of a high-pressure refueling liquid oxy-kerosene engine, the influence of drag-reducing additive on the heat transfer characteristics in the supercritical flow of kerosene in a microchannel for regenerative cooling is explored. The finite-volume CFD numerical simulation method is applied using the RNG k-ε turbulence model and enhanced wall function. The current work faithfully represents the effect of the drag-reducing additive in kerosene through numerical calculations by combining a 10-component model for the physical properties of the kerosene and the Carreau non-Newtonian fluid constitutive model from rheological measurements. Results suggest that the 10-component kerosene surrogate can describe the supercritical physical properties of kerosene. The inlet temperature, inlet velocity, and the heat flux on the channel wall are driving factors for the supercritical kerosene flow and heat transfer characteristics. The pressure influence on the heat transfer is negligible. With polymer additives, the loss in pressure drop and heat transfer performance of supercritical kerosene flow decrease 46.8% and 37.5% respectively. The enhancement of engine thrust caused by reduction in pressure drop is an attractive improvement of concern.

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