Numerical Analysis of Mass Flow Leakage Through Orifices for Supercritical CO2: Two-Phase Flow Effects

2020 ◽  
Author(s):  
Ladislav Vesely ◽  
Akshay Khadse ◽  
Andres Curbelo ◽  
Jayanta S. Kapat ◽  
Luca Petrungaro
Keyword(s):  
Mass Flow ◽  
Thermodynamic Equilibrium ◽  
Supercritical Co2 ◽  
Two Phase Flow ◽  
Operating Conditions ◽  
Working Fluid ◽  
Great Promise ◽  
Phase Flow ◽  
Computational Domain ◽  
Two Phase

Abstract Supercritical CO2 (sCO2) holds a great promise as a future working fluid for power generating Brayton cycles. One of the challenging research areas in sCO2 power cycles is flow leakage and the design of seals on the compressor side of the cycle. Given the compact nature of sCO2 turbomachinery, even a minimal amount of leakage can lead to a significant power efficiency loss. Hence accurate prediction of mass flow leakage rate becomes important. However, on the compressor side of the cycle, operating conditions across the seal lead to two-phase flow. This makes flow modeling very challenging because conventional one-phase flow CFD models cannot be used. This paper is an attempt to understand the behavior of two-phase sCO2 flow going through circular and annular orifices. The focus is to utilize commercially available CFD scheme for modeling phase change and two-phase flow through constrictions. Since the pressure loss across constrictions is also accompanied with reduction in temperature, the flow becomes two-phase by entering the saturation dome. CFD simulation is performed using commercially available software STAR CCM+. 2D axisymmetric geometry is considered as the computational domain. Eulerian Multi-phase Mixture model is used in conjunction with the Two-Phase Thermodynamic Equilibrium implementation. This model is intended for applications that involve two phases of the same substance that are in thermodynamic equilibrium. Fluid properties are defined over a large range of temperatures and pressures, including both the liquid and vapor phases.

Micro-Scale Two-Phase Flow Heat Transport Device Driven by Electrohydrodynamic Conduction Pumping

2013 ◽  
Author(s):  
Viral K. Patel ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transport ◽  
Two Phase Flow ◽  
Operating Conditions ◽  
Electrode Spacing ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Micro Scale ◽  
Flow Heat ◽  
Transport Device

Micro-scale two-phase flow heat transport involves specialized devices that are used to remove large amounts of heat from small surface areas. They operate by circulating a working fluid through a heated space which causes phase change from liquid to vapor. During this process, a significant amount of heat is transported away from the heat source. Micro-scale heat transport devices are compact in size and the heat transfer coefficient can be orders of magnitude higher than in macro-scale for similar operating conditions. Thus, it is of interest to develop such devices for cooling of next-generation electronics and other applications with extremely large heat fluxes. The heat transport device presented in this paper is driven by electrohydrodynamic (EHD) conduction pumping. In EHD conduction pumping, when an electric field is applied to a dielectric liquid, flow is induced. The pump is installed in a two-phase flow loop and has a circular 1 mm diameter cross section with electrode spacing on the order of 120 μm. It acts to circulate the fluid in the loop and has a simple yet robust, non-mechanical design. Results from two-phase flow experiments show that it is easily controlled and such electrically driven pumps can effectively be used in heat transport systems.

Numerical Analysis of Mass Flow Leakage Through Orifices for Supercritical CO2: Two-Phase Flow Effects

2021 ◽  
Author(s):  
Ladislav Vesely ◽  
Akshay Khadse ◽  
Andres Curbelo ◽  
Luca Petrungaro ◽  
Jayanta Kapat
Keyword(s):  
Numerical Analysis ◽  
Mass Flow ◽  
Supercritical Co2 ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Effects

Experimental and Numerical Study of Critical Flow Model Development for Supercritical CO2 Power Cycle Application

2018 ◽  
Author(s):  
Min Seok Kim ◽  
Bong Seong Oh ◽  
Hwa-Young Jung ◽  
Seong Jun Bae ◽  
Jeong Ik Lee
Keyword(s):  
Supercritical Co2 ◽  
Numerical Study ◽  
Operating Conditions ◽  
Working Fluid ◽  
Critical Flow ◽  
Phase System ◽  
Phase Flow ◽  
Two Phase ◽  
Gaseous State ◽  
Power Cycle

Supercritical CO2 (S-CO2) has the potential to be used as the working fluid in a power cycle since S-CO2 shows a density value high as its liquid phase while the viscosity value remains closer to its gaseous phase. Thus, it requires much less work to compress due to its low compressibility as well as relatively small flow resistance. However, the S-CO2 leakage flow from turbo-machinery via seal becomes one of the important issues since not only it influences the cycle efficiency due to parasitic loss but also it is important for evaluating the system safety under various operating conditions. In the previous turbo expo paper, the effect of the tooth length on the critical flow and comparing the results to the existing two phase system analysis code calculation were presented. In this paper, the gap effect, which is simulated by changing the diameter of a orifice and the number of tooth effect in a labyrinth seal geometry nozzle are presented by using the same experimental facility described in the previous paper. In addition, this paper includes the experimental results under various conditions including not only single phase flow such as supercritical, and gaseous state only but also two phase flow condition.

Research on Two-Phase Flow Instability in Evaporator of Refrigeration System

2010 ◽  
Author(s):  
Nan Liang ◽  
Changqing Tian ◽  
Shuangquan Shao
Keyword(s):  
Pressure Drop ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Density Wave ◽  
Phase Flow ◽  
Constant Mass ◽  
Refrigeration System ◽  
Two Phase

As one kind of fluid machinery related to the two-phase flow, the refrigeration system encounters more problems of instability. It is essential to ensure the stability of the refrigeration systems for the operation and efficiency. This paper presents the experimental investigation on the static and dynamic instability in an evaporator of refrigeration system. The static instability experiments showed that the oscillatory period and swing of the mixture-vapor transition point by observation with a camera through the transparent quartz glass tube at the outlet of the evaporator. The pressure drop versus mass flow rate curves of refrigerant two phase flow in the evaporator were obtained with a negative slope region in addition to two positive slope regions, thus making the flow rate a multi-valued function of the pressure drop. For dynamic instabilities in the evaporation process, three types of oscillations (density wave type, pressure drop type and thermal type) were observed at different mass flow rates and heat fluxes, which can be represented in the pressure drop versus mass flow rate curves. For the dynamic instabilities, density wave oscillations happen when the heat flux is high with the constant mass flow rate. Thermal oscillations happen when the heat flux is correspondingly low with constant mass flow rate. Though the refrigeration system do not have special tank, the accumulator and receiver provide enough compressible volume to induce the pressure drop oscillations. The representation and characteristic of each oscillation type were also analyzed in the paper.

Experimental Characterization of Oil-Refrigerant Two-Phase Flow

2000 ◽  
Author(s):  
V. T. Lacerda ◽  
A. T. Prata ◽  
F. Fagotti
Keyword(s):  
Flow Visualization ◽  
Two Phase Flow ◽  
Working Fluid ◽  
Phase Flow ◽  
Oil Viscosity ◽  
Two Phase ◽  
Mixture Flow ◽  
Horizontal Tubes ◽  
Constant Diameter ◽  
Oil Flow

Abstract Several phenomena occurring inside refrigerating systems depend on the interaction between the refrigeration oil and the refrigerant working fluid. Regarding the refrigeration cycle, good miscibility of oil and refrigerant assure easy return of circulating oil to the compressor through the reduction of the oil viscosity. Inside the compressor the lubricant is mainly used for leakage sealing, cooling of hot elements and lubrication of sliding parts. In the compressor bearing systems the presence of refrigerant dissolved in the oil greatly influences the performance and reliability of the compressor due to the outgassing experienced by sudden changes in temperature and pressure resulting in a two-phase mixture with density and viscosity strongly affecting the lubricant characteristics. A general understanding of the oil-refrigerant mixture flow is crucial in developing lubrication models to be used in analysis and simulation of fluid mechanics problems inside the compressor. In the present investigation the refrigeration oil flow with refrigerant outgassing is explored experimentally. A mixture of oil saturated with refrigerant is forced to flow in two straight horizontal tubes of constant diameter. One tube is used for flow visualization and the other is instrumented for pressure and temperature measurements. At the tubes inlet liquid state prevails and as flow proceeds the pressure drop reduces the gas solubility in the oil and outgassing occurs. Initially small bubbles are observed and eventually the bubble population reaches a stage where foaming flow is observed. The flow visualization allowed identification of the two-phase flow regimes experienced by the mixture. Pressure and temperature distributions are measured along the flow and from that mixture quality and void fraction were estimated.

scholarly journals Pressure Signal Analysis for the Characterization of High-Viscosity Two-Phase Flows in Horizontal Pipes

2020 ◽  
Vol 8 (12) ◽  
pp. 1000
Author(s):  
Lizeth Torres ◽  
José Noguera ◽  
José Enrique Guzmán-Vázquez ◽  
Jonathan Hernández ◽  
Marco Sanjuan ◽  
...  
Keyword(s):  
Mass Flow ◽  
Two Phase Flow ◽  
High Viscosity ◽  
Flow Rate Ratio ◽  
Phase Flow ◽  
Two Phase ◽  
Local Flow ◽  
Horizontal Pipes ◽  
Pressure Time ◽  
Mass Flow Rates

We study a high-viscosity two-phase flow through an analysis of the corresponding pressure signals. In particular, we investigate the flow of a glycerin–air mixture moving through a horizontal pipeline with a U-section installed midway along the pipe. Different combinations of liquid and air mass flow rates are experimentally tested. Then, we examine the moments of the statistical distributions obtained from the resulting pressure time series, in order to highlight the significant dynamical traits of the flow. Finally, we propose a novel correlation with two dimensionless parameters: the Euler number and a mass-flow-rate ratio to predict the pressure gradient in high-viscosity two-phase flow. Distinctive variations of the pressure gradients are observed in each section of the pipeline, which suggest that the local flow dynamics must not be disregarded in favor of global considerations.

Two-Phase Flow Characteristics in a Co-Flow Induced Microchannel With Microbubbles Generation

2007 ◽  
Author(s):  
Sujin Yeom ◽  
Seung S. Lee ◽  
Sang Yong Lee
Keyword(s):  
Two Phase Flow ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
Gas Pressure ◽  
Superficial Velocity ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Gas Channel ◽  
Micro Bubble

This paper presents a micro-fluidic device which generates micro-bubbles, ranging from 70μm to 160μm in diameter, and two-phase flow characteristics in the device were tested. The device is composed of three sub-channels: a centered gas channel (10μm×50μm) and two liquid channels (both with 85μm×50μm) on each side of the gas channel. Micro-bubbles are generated by co-flow of gas and liquid at the exit of the gas channel when the drag force becomes larger than the surface tension force as bubbles grow. Methanol and a gas mixture of CO2 and N2 were used as the working fluid. Since the flow rate of gas was very small, the gas momentum effect was considered negligible. Thus, in the present case, the controlling parameters were the liquid superficial velocity and the inlet pressure of the gas. A high speed camera was used to record two-phase flow patterns and micro-bubbles of the device. To confine the ranges of the micro-bubbles generation, two-phase flow patterns in the device is observed at first. Four different flow patterns were observed: annular, annular-slug, slug, and bubbly flow. In bubbly flows, uniform-sized micro-bubbles were generated, and the operating ranges of the liquid superficial velocity and the gas pressure were below 0.132 m/s and 0.7 bar, respectively. Diameters of the micro-bubbles appeared smaller with the higher superficial liquid velocity and/or with a lower gas pressure. Experimental results showed that, with the gas pressure lower than a certain level, the sizes of micro-bubbles were almost insensitive to the gas pressure. In such a ranges, the micro-bubble diameters could be estimated from a drag coefficient correlation, CDw = 31330/Re3, which is different from the correlations for macro-channels due to a larger wall effect with the micro-channels. In the latter part of the paper, as a potential of application of the micro-bubble generator to gas analysis, dissolution behavior of the gas components into the liquid flow was examined. The result shows that the micro-bubble generator can be adopted as a component of miniaturized gas analyzers if a proper improvement could be made in controlling the bubble sizes effectively.

A Visual and Photographic Study of the Inception of Vaporization in Adiabatic Flow

1964 ◽  
Vol 86 (2) ◽  
pp. 257-261 ◽  
Author(s):  
E. P. Mikol ◽  
J. C. Dudley
Keyword(s):  
Experimental Method ◽  
Two Phase Flow ◽  
Operating Conditions ◽  
Phase Flow ◽  
Two Phase ◽  
Adiabatic Flow ◽  
Index Data ◽  
Flow Phenomena ◽  
Glass Tubes

Data and observations obtained during the study of two-phase flow phenomena for refrigerants flowing in small bore copper and glass tubes have been examined for their significance to the cavitation. Visual and photographic observations have been made of the inception of vaporization and of the movement of the point of inception as operating conditions are varied. Liquid tension has been deduced as occurring in these tests. Liquid tension and cavitation index data are presented. The experimental method is recommended as a means for studying many aspects of the phenomenon of cavitation.

Experiment of Adiabatic Two-Phase Flow in an Annulus Under Low-Frequency Vibration

2012 ◽  
Author(s):  
Shao-Wen Chen ◽  
Caleb S. Brooks ◽  
Chris Macke ◽  
Takashi Hibiki ◽  
Mamoru Ishii ◽  
...  
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Low Frequency ◽  
Flow Regimes ◽  
Operating Conditions ◽  
Phase Flow ◽  
Two Phase ◽  
Specific Flow ◽  
Low Frequency Vibration ◽  
Fft Analysis

In order to investigate the possible effect of seismic vibration on two-phase flow dynamics and thermal-hydraulics of a nuclear reactor, experimental tests of adiabatic air-water two-phase flow under low-frequency vibration were carried out in this study. An eccentric cam vibration module operated at low motor speed (up to 390rpm) was attached to an annulus test section which was scaled down from a prototypic BWR fuel assembly sub-channel. The inner and outer diameters of the annulus are 19.1mm and 38.1mm, respectively. The two-phase flow operating conditions cover the ranges of 0.03≤<jg> ≤1.46m/s and 0.25≤<jf>≤1.00m/s and the vibration displacement ranges from ±0.8mm to ±22.2mm. Steady-state area-averaged instantaneous and time-averaged void fraction was recorded and analyzed in stationary and vibration experiments. A neural network flow regime identification technique and fast Fourier transformation (FFT) analysis were introduced to analyze the flow regimes and void signals under stationary and vibration conditions. Experimental results reveal possible changes in flow regimes under specific flow and vibration conditions. In addition, the instantaneous void fraction signals were affected and shown by FFT analysis. Possible reasons for the changes include the applied high acceleration and/or induced resonance at certain ports under the specific flow and vibration conditions.

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