How Equation of State Selection Impacts Accuracy Near the Critical Point: Forced Convection Supercritical CO2 Flow Over a Cylinder

A parametric equation of state was derived for water and water vapor in the critical region from experimental P-V-T data. It is valid in that part of the critical region encompassed by pressures from 3000 to 4000 psia, specific volumes from 0.0400 to 0.1100 ft3/lb, and temperatures from 698 to 752 deg F. The equation of state satisfies all of the known conditions at the critical point. It also satisfies the conditions along certain of the boundaries which probably separate “supercritical liquid” from “supercritical vapor.” The equation of state, though quite simple in form, is probably superior to any equation heretofore derived for water and water vapor in the critical region. Specifically, the deviations between the measured and computed values of pressure in the large majority of the cases were within three parts in one thousand. This coincides approximately with the overall uncertainty in P-V-T measurements. In view of these factors, the author recommends that the equation be used to derive values for such thermodynamic properties as specific heat at constant pressure, enthalpy, and entropy in the critical region.

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Erratum: Scaled-equation-of-state analysis of the specific heat in fluids and magnets near critical point

Physical Review B ◽

10.1103/physrevb.13.474 ◽

1976 ◽

Vol 13 (1) ◽

pp. 474-474

Author(s):

M. Barmatz ◽

P. C. Hohenberg ◽

A. Kornblit

Keyword(s):

Equation Of State ◽

Specific Heat ◽

Critical Point ◽

State Analysis

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Experiments and Analyses of Supercritical CO2 flow instability with study of wall heat-storage and dimensionless parameters

Applied Thermal Engineering ◽

10.1016/j.applthermaleng.2020.116378 ◽

2020 ◽

pp. 116378

Author(s):

Inderjit Singh ◽

Vijay Chatoorgoon

Keyword(s):

Supercritical Co2 ◽

Heat Storage ◽

Flow Instability ◽

Dimensionless Parameters ◽

Co2 Flow

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Numerical Approach for Real Gas Simulations: Part II — Flow Simulation for Supercritical CO2 Centrifugal Compressor

Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy ◽

10.1115/gt2017-63149 ◽

2017 ◽

Cited By ~ 1

Author(s):

Swati Saxena ◽

Ramakrishna Mallina ◽

Francisco Moraga ◽

Douglas Hofer

Keyword(s):

Critical Point ◽

Centrifugal Compressor ◽

Supercritical Co2 ◽

Operating Conditions ◽

Inlet Guide Vane ◽

Thermodynamic Quantities ◽

3D Flow ◽

Real Gas ◽

The Real ◽

Operating Range

This paper is presented in two parts. Part I (Tabular fluid properties for real gas analysis) describes an approach to creating a tabular representation of the equation of state that is applicable to any fluid. This approach is applied to generating an accurate and robust tabular representation of the RefProp CO2 properties. Part II (this paper) presents numerical simulations of a low flow coefficient supercritical CO2 centrifugal compressor developed for a closed loop power cycle. The real gas tables presented in part I are used in these simulations. Three operating conditions are simulated near the CO2 critical point: normal day (85 bar, 35C), hot day (105 bar, 50 C) and cold day (70 bar, 20C) conditions. The compressor is a single stage overhung design with shrouded impeller, 155 mm impeller tip diameter and a vaneless diffuser. An axial variable inlet guide vane (IGV) is used to control the incoming swirl into the impeller. An in-house three-dimensional computational fluid dynamics (CFD) solver named TACOMA is used with real gas tables for the steady flow simulations. The equilibrium thermodynamic modeling is used in this study. The real gas effects are important in the desired impeller operating range. It is observed that both the operating range (minimum and maximum volumetric flow rate) and the pressure ratio across the impeller are dependent on the inlet conditions. The compressor has nearly 25% higher operating range on a hot day as compared to the normal day conditions. A condensation region is observed near the impeller leading edge which grows as the compressor operating point moves towards choke. The impeller chokes near the mid-chord due to lower speed of sound in the liquid-vapor region resulting in a sharp drop near the choke side of the speedline. This behavior is explained by analyzing the 3D flow field within the impeller and thermodynamic quantities along the streamline. The 3D flow analysis for the flow near the critical point provides useful insight for the designers to modify the current compressor design for higher efficiency.

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