scholarly journals Simulation of Supercritical CO2 Flow Through Circular and Annular Orifice

2015 ◽  
Vol 1 (2) ◽  
Author(s):  
Haomin Yuan ◽  
John Edlebeck ◽  
Mathew Wolf ◽  
Mark Anderson ◽  
Michael Corradini ◽  
...  
Keyword(s):  
Supercritical Co2 ◽  
High Efficiency ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Working Fluid ◽  
Operating Pressure ◽  
Two Phase ◽  
Choked Flow ◽  
Wide Range ◽  
Co2 Flow

Supercritical CO2 (sCO2) is a promising working fluid for future high-efficiency power conversion cycles. In order to develop these cycles, it is necessary to understand supercritical and two-phase CO2 flow. This paper presents a methodology for the computational fluid dynamic (CFD) simulation of sCO2 flowing through a restriction under a wide range of flow conditions. Under an accidental situation, such as a pipe break, the inventory of sCO2 leaks out through a small restriction. In this research, we use circular and annular orifices to mimic the behavior of restrictions. As the atmospheric pressure is much smaller than the operating pressure in the pipe, a two-phase choked flow will happen. Such behavior is considered in the simulation. The homogeneous equilibrium model (HEM) is employed to model the two-phase state. To correctly simulate the behavior of the power cycle under this accidental scenario, the inventory leakage rate should be calculated precisely. Therefore, at the current state, this study only focuses on the prediction of mass flow rate through orifices.

Computational Fluid Dynamics of a Radial Compressor Operating With Supercritical CO2

2012 ◽  
Author(s):  
Rene Pecnik ◽  
Enrico Rinaldi ◽  
Piero Colonna
Keyword(s):  
Critical Point ◽  
Gas Turbine ◽  
Supercritical Co2 ◽  
High Speed ◽  
Power Plants ◽  
Compressible Flows ◽  
High Efficiency ◽  
Fluid Dynamic ◽  
Working Fluid ◽  
Maximum Pressure

The merit of using supercritical CO2 (scCO2) as the working fluid of a closed Brayton cycle gas turbine is now widely recognized, and the development of this technology is now actively pursued. scCO2 gas turbine power plants are an attractive option for solar, geothermal and nuclear energy conversion. Among the challenges which must be overcome in order to successfully bring the technology to the market, the efficiency of the compressor and turbine operating with the supercritical fluid should be increased as much as possible. High efficiency can be reached by means of sophisticated aerodynamic design, which, compared to other overall efficiency improvements, like cycle maximum pressure and temperature increase, or increase of recuperator effectiveness, does not require an increase in equipment cost, but only an additional effort in research and development. This paper reports a three-dimensional CFD study of a high-speed centrifugal compressor operating with CO2 in the thermodynamic region slightly above the vapor-liquid critical point. The investigated geometry is the compressor impeller tested in the Sandia scCO2 compression loop facility [1]. The fluid dynamic simulations are performed with a fully implicit parallel Reynolds-averaged Navier-Stokes code based on a finite volume formulation on arbitrary polyhedral mesh elements. The CFD code has been validated on test cases which are relevant for this study, see Ref. [2,3]. In order to account for the strongly nonlinear variation of the thermophysical properties of supercritical CO2, the CFD code is coupled with an extensive library for the computation of properties of fluids and mixtures [4]. Among the available models, the one based on reference equations of state for CO2 [5,6] has been selected, as implemented in one of the sub-libraries [7]. A specialized look-up table approach and a meshing technique suited for turbomachinery geometries are also among the novelties introduced in the developed methodology. A detailed evaluation of the CFD results highlights the challenges of numerical studies aimed at the simulation of technically relevant compressible flows occurring close to the liquid-vapor critical point. The data of the obtained flow field are used for a comparison with experiments performed at the Sandia scCO2 compression-loop facility.

Computational and Experimental Investigation of the Vertical Flash Tank Separator Part 1: Effect of Parameters on Separation Efficiency

2019 ◽  
Vol 27 (01) ◽  
pp. 1950005 ◽  
Author(s):  
Raid Ahmed Mahmood ◽  
David Buttsworth ◽  
Ray Malpress
Keyword(s):  
Separation Efficiency ◽  
Fluid Dynamic ◽  
Effective Area ◽  
Working Fluid ◽  
Cfd Simulations ◽  
Liquid Separation ◽  
Two Phase ◽  
Flash Tank ◽  
Tank Design ◽  
The Heat Transfer Coefficient

The flash tank separator is one of the most important components that can be used to improve the performance of a refrigeration cycle by separating the liquid from the gas–liquid two-phase flow and providing the evaporator with only liquid refrigerant. This technique increases the effective area and enhances the heat transfer coefficient in the evaporator. To optimize the size of the vertical flash tank separator for obtaining high separation efficiency, the effect of the size of the vertical flash tank separator needs to be considered. This paper investigates the effect of the size on the liquid separation efficiency of the vertical flash tank separator. This paper also assesses the usefulness of Computational Fluid Dynamic (CFD) in flash tank design, and this is achieved through experiments and simulations on a range of relevant configurations using water as the working fluid. The results revealed that the size has a significant effect on the liquid separation efficiency, as the highest value was achieved by the largest size (VFT-V5). The CFD simulations give a good agreement with the experiments; all the simulations underestimated the liquid separation efficiency by approximately 0.02 over the range of conditions tested.

A Comparison Study for Off-Design Performance Prediction of a Supercritical CO2 Compressor With Similitude Analysis

2019 ◽  
Author(s):  
Yongju Jeong ◽  
Seongmin Son ◽  
Seong kuk Cho ◽  
Seungjoon Baik ◽  
Jeong Ik Lee
Keyword(s):  
Critical Point ◽  
Supercritical Co2 ◽  
Power Plants ◽  
Cycle Performance ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Power Cycle ◽  
Design Performance ◽  
Wide Range ◽  
Phase Fluid

Abstract Most of the power plants operating nowadays mainly have adopted a steam Rankine cycle or a gas Brayton cycle. To devise a better power conversion cycle, various approaches were taken by researchers and one of the examples is an S-CO2 (supercritical CO2) power cycle. Over the past decades, the S-CO2 power cycle was invented and studied. Eventually the cycle was successful for attracting attentions from a wide range of applications. Basically, an S-CO2 power cycle is a variation of a gas Brayton cycle. In contrast to the fact that an ordinary Brayton cycle operates with a gas phase fluid, the S-CO2 power cycle operates with a supercritical phase fluid, where temperatures and pressures of working fluid are above the critical point. Many advantages of S-CO2 power cycle are rooted from its novel characteristics. Particularly, a compressor in an S-CO2 power cycle operates near the critical point, where the compressibility is greatly reduced. Since the S-CO2 power cycle greatly benefits from the reduced compression work, an S-CO2 compressor prediction under off-design condition has a huge impact on overall cycle performance. When off-design operations of a power cycle are considered, the compressor performance needs to be specified. One of the approaches for a compressor off-design performance evaluation is to use the correction methods based on similitude analysis. However, there are several approaches for deriving the equivalent conditions but none of the approaches has been thoroughly examined for S-CO2 conditions based on data. The purpose of this paper is comparing these correction models to identify the best fitted approach, in order to predict a compressor off-design operation performance more accurately from limited amount of information. Each correction method was applied to two sets of data, SCEIL experiment data and 1D turbomachinery code off-design prediction code generated data, and evaluated in this paper.

scholarly journals Experimental Investigation of the Thermal Performance of a Wickless Heat Pipe Operating with Different Fluids: Water, Ethanol, and SES36. Analysis of Influences of Instability Processes at Working Operation Parameters

Energies ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 80 ◽  
Author(s):  
Rafal Andrzejczyk
Keyword(s):  
Heat Pipe ◽  
Input Power ◽  
Liquid Pool ◽  
Filling Ratio ◽  
Working Fluid ◽  
Operating Pressure ◽  
Two Phase ◽  
Condenser Section ◽  
Transfer Resistance ◽  
Working Fluids

In this study, the influences of different parameters on performance of a wickless heat pipe have been presented. Experiments have been carried out for an input power range from 50 W to 300 W, constant cooling water mass flow rate of 0.01 kg/s, and constant temperature at the inlet to condenser of 10 °C. Three working fluids have been tested: water, ethanol, and SES36 (1,1,1,3,3-Pentafluorobutane) with different filling ratios (0.32, 0.51, 1.0). The wall temperature in different locations (evaporation section, adiabatic section, and condenser section), as well as operating pressure inside two phase closed thermosyphon have been monitored. The wickless heat pipe was made of 0.01 m diameter copper tube, which consists of an evaporator, adiabatic, and condensation sections with the same length (0.4 m). For all working fluids, a dynamic start-up effect caused by heat conduction towards the liquid pool was observed. Only the thermosyphon filled with SES36 was observed to have operation limitation caused by achieving the boiling limit in TPCTs (two-phase closed thermosyphons). The geyser boiling effect has been observed only for thermosyphon filled with ethanol and for a high filling ratio. The performance of the thermosyphon determined the form of the heat transfer resistance of the TPCT and it was found to be dependent of input power and filling ratio, as well as the type of working fluid and AR (aspect ratio). Comparison with other authors would seem to indicate that lower AR results in higher resistance; however, the ratio of condenser section length to inside diameter of pipe is also a very important parameter. Generally, performance of the presented thermosyphon is comparable to other constructions.

Simulation of Aerosol Sampling Inlet for Different Outlet Angle

2013 ◽  
Vol 483 ◽  
pp. 234-237
Author(s):  
Bao Qing Wang ◽  
Ze Bei Wang ◽  
Yang Yang Li ◽  
Rong Hui Chen ◽  
Shu Yao
Keyword(s):  
Pressure Distribution ◽  
Computational Fluid Dynamic ◽  
High Efficiency ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Aerosol Sampling ◽  
Outlet Angle ◽  
Final Design

Performance of aerosol sampling inlet for different diffuser outlet angle is compared with its velocity and pressure distribution. To get information on velocity and pressure distribution for different outlet angle, Computational Fluid Dynamic (CFD) simulation can be used. At the same time, it can achieve high efficiency of aerosol sampling and minimize disturbance to the aircraft which carries the system. The final design for the sampling inlet is determined to be a design with diffuser outlet angle of 15 degree. This design was selected to keep stable for velocity and pressure, and have a less length.

Development of a Capacitance Based Void Fraction Sensor for Two-Phase Flow Measurements

2013 ◽  
Author(s):  
Rodward L. Hewlin ◽  
John P. Kizito
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Full Range ◽  
Working Fluid ◽  
Phase Flow ◽  
Calibration Data ◽  
Two Phase ◽  
Flow Measurements ◽  
Static Calibration ◽  
Wide Range

The aim of this paper was to develop a capacitance based sensor capable of measuring void fraction in a continuous two-phase flow field. The design methodology and operation of the capacitance based void fraction sensor is discussed. Two designs of capacitance void fraction sensors were developed and tested. Some of the problems associated with the first were identified and a new sensor electrode configuration was developed which presented a more sensitive and repeatable response. Data was collected covering a wide range of void fraction measurements ranging from 0 to 1 for water as the working fluid. Calibration of the sensor required that the air gap or void capacitance (dry signal) be measured followed by an increase in liquid levels (wet signal) to obtain a range of void fraction measurements for static calibration. The static calibration data obtained was nonlinear for the full range of void fraction measurements for water. This paper covers the design requirements, calibration procedure and static calibration data obtained for the developed sensor, and dynamic void fraction data measurements. The sensor was tested in both a horizontal and vertical orientation and proved to be orientation insensitive. The experimental results are promising for water and verify successful operation for measuring void fraction in continuous two-phase flows.

A Modified, High-Efficiency, Recuperated Gas Turbine Cycle

1988 ◽  
Vol 110 (2) ◽  
pp. 233-242 ◽  
Author(s):  
M. A. El-Masri
Keyword(s):  
Gas Turbine ◽  
High Efficiency ◽  
Water Flow Rate ◽  
Component Technology ◽  
Pure Substance ◽  
Working Fluid ◽  
Recovery Processes ◽  
Dead State ◽  
Percentage Points ◽  
Wide Range

The thermal efficiency of an intercooled/recuperated cycle may be increased by: (a) evaporatively aftercooling the compressor discharge; and (b) injecting and evaporating an additional amount of water in the recuperator. Comparative computations of such a modified cycle and intercooled/recuperated cycles carried out over a wide range of pressure ratios and turbine inlet temperatures and at two different levels of component technologies show an advantage of over five percentage points in efficiency for the modified cycle. About 60 percent of this improvement results from modification (a) and 40 percent from modification (b). The modified intercooled/recuperated cycle is compared with nonintercooled steam-injected gas turbine systems at each component technology level. The present cycle is found to be superior by about 2.75 percentage points in efficiency and to require a substantially smaller water flow rate. To assist in interpreting those differences, the method of available-work analysis is introduced and applied. This is identical to exergy analysis for systems with a pure-substance working fluid, but differs from the latter for systems using a mixture of pure substances insofar as the thermodynamic dead state is defined for the chemical and phase composition realized at the exhaust conditions of practical engineering devices and systems. This analysis is applied to the heat-recovery processes in each of the three systems considered. It shows that the substantial, fundamental available-work loss incurred by mixing steam and gases in the steam-injected system is the main reason for the superior efficiency of the precent cycle.

Influence of operational parameters on performance of twin thermoacoustic prime mover – CFD studies

2016 ◽  
Vol 33 (3) ◽  
Author(s):  
Jabbar P ◽  
Hariharan N.M ◽  
Palani Sivashanmugam ◽  
S. Kasthurirengan
Keyword(s):  
Temperature Gradient ◽  
Design Methodology ◽  
Cfd Simulation ◽  
Working Fluid ◽  
Geometrical Parameters ◽  
Pressure Amplitude ◽  
Prime Mover ◽  
Operational Parameters ◽  
Fluid Medium ◽  
Wide Range

Purpose The present investigation deals with the analysis of the performance of twin thermoacoustic prime mover (TAPM) which are measured in terms of frequency and pressure amplitude by varying the parameters such as temperature gradient along the length of stack and the operating pressures of fluid medium argon using CFD simulation. With the help of CFD researchers and Engineers can evaluate the performance of a wide range of thermoacoustic systems on the computer without the time, expense, and disruption required to make actual changes onsite (stack) which is tedious to fabricate. Design/methodology/approach For the present simulation, the operating pressures of argon such as 1bar, 3bar and 5bar, and the temperature gradient is varied from 600K to 1400K with the regular intervals of each 200K. The geometry of twin TAPM is created using GAMBIT processor, and the simulation is carried out using FLUENT. The geometrical parameters of twin TAPM are kept constant throughout the simulation. The results for frequency and pressure amplitude obtained from the CFD simulation of twin TAPM for various temperature gradient and operating pressures are analysed and reported. Findings The computational results of twin thermoacoustic prime mover shows an increase in pressure amplitude with an increase in the temperature gradient and also it increases with an increase in operating pressures of the fluid medium. The parameter operating pressures of the working fluid medium and the stack hot end temperature has no significant effect on the output, frequency. Originality/value Though several experimental works had been published based on the twin thermoacoustic prime mover, an attempt has been made in the present investigation for the first time to estimate the performance of twin thermoacoustic prime mover using CFD package (ANSYS-FLUENT) by varying temperature gradient. The temperature gradient and operating pressures were varied and the performance of twin thermoacoustic prime mover was measured in terms of frequency and pressure amplitude.

scholarly journals An urban large-eddy-based dispersion model for marginal grid resolutions: CAIRDIO v1.0

2020 ◽  
Author(s):  
Michael Weger ◽  
Oswald Knoth ◽  
Bernd Heinold
Keyword(s):  
Dynamic Models ◽  
Numerical Models ◽  
Dispersion Model ◽  
Fluid Dynamic ◽  
Horizontal Resolution ◽  
Two Phase ◽  
Data Set ◽  
Wide Range ◽  
Large Eddy ◽  
Diffusive Interface

Abstract. The capability for high spatial resolutions is an important feature of accurate numerical models dedicated to simulate the large spatial variability of urban air pollution. On the one hand, the well established mesoscale chemistry transport models have their obvious short-comings attributed to their extensive use of paramterizations. On the other hand, obstacle resolving computational fluid dynamic models, while accurate, still often demand too high computational costs, to be applied on a regular and holistic basis. The major reason for the inflated numerical costs is the required horizontal resolution to meaningfully apply the obstacle discretization, which is most often based on boundary-fitted grids, like e.g. the marker-and-cell method. Here we present a large-eddy-simulation approach that uses diffusive obstacle boundaries, which are derived from a simplified diffusive interface approach for moving obstacles. The diffusive interface approach is well established in two-phase modeling, but to the author’s knowledge has not been applied in urban boundary layer simulations so far. Our dispersion model is capable of representing buildings over a wide range of spatial resolutions, including marginally coarse resolutions inaccessible for standard methods. This opens up a very promising opportunity for application of accurate air quality simulations and forecasts on entire mid-sized city domains. Furthermore, our approach is capable of incorporating the influence of the land orography by the additional optional use of terrain-following coordinates. We validated the dynamic core against a set of numerical benchmarks and a standard high-quality wind-tunnel data set for dispersion-model evaluation.

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