Modeling of Supercritical CO2 Flow Through Short Tube Orifices

2005 ◽  
Vol 127 (6) ◽  
pp. 1194-1198 ◽  
Author(s):  
Chun-Lu Zhang ◽  
Liang Yang
Keyword(s):  
Mass Flow ◽  
Supercritical Co2 ◽  
Fluid Model ◽  
Velocity Slip ◽  
Heat Pumps ◽  
Tube Length ◽  
Good Prediction ◽  
Two Phase ◽  
Promising Alternative ◽  
Short Tube

The transcritical cycle of carbon dioxide (CO2) is a promising alternative approach to heat pumps and automobile air conditioners. As an expansion device, the short tube orifice in a transcritical CO2 system usually receives supercritical fluid at the entrance and discharges a two-phase mixture at the exit. In this work, a two-fluid model (TFM) is developed for modeling the flow characteristics of supercritical CO2 through the short tube orifice. The deviations between the TFM predictions and the measured mass flow rates are within ±20%. Meanwhile, the TFM predicts reasonable pressure, temperature, and velocity distributions along the tube length. The small values of interphase temperature difference and velocity slip indicate that the nonequilibrium characteristics of the two-phase flow of CO2 in the short tube orifice are not significant. Consequently, the homogeneous equilibrium model reduced from the TFM gives a good prediction of the mass flow rate as well.

A Generalized Neural Network Model of Refrigerant Mass Flow Through Adiabatic Capillary Tubes and Short Tube Orifices

2007 ◽  
Vol 129 (12) ◽  
pp. 1559-1564 ◽  
Author(s):  
Ling-Xiao Zhao ◽  
Chun-Lu Zhang ◽  
Liang-Liang Shao ◽  
Liang Yang
Keyword(s):  
Neural Network ◽  
Experimental Data ◽  
Mass Flow ◽  
Transfer Functions ◽  
Heat Pumps ◽  
Capillary Tubes ◽  
Two Phase ◽  
Bp Network ◽  
Inlet Conditions ◽  
Short Tube

Adiabatic capillary tubes and short tube orifices are widely used as expansive devices in refrigeration, residential air conditioners, and heat pumps. In this paper, a generalized neural network has been developed to predict the mass flow rate through adiabatic capillary tubes and short tube orifices. The input/output parameters of the neural network are dimensionless and derived from the homogeneous equilibrium flow model. Three-layer backpropagation (BP) neural network is selected as a universal function approximator. Log sigmoid and pure linear transfer functions are used in the hidden layer and the output layer, respectively. The experimental data of R12, R22, R134a, R404A, R407C, R410A, and R600a from the open literature covering capillary and short tube geometries, subcooled and two-phase inlet conditions, are collected for the BP network training and testing. Compared with experimental data, the overall average and standard deviations of the proposed neural network are 0.75% and 8.27% of the measured mass flow rates, respectively.

Predicted performance of a two-phase underwater ramjet with a Laval nozzle

2018 ◽  
Vol 233 (3) ◽  
pp. 937-948
Author(s):  
Jiarui Zhang ◽  
Zhixun Xia ◽  
Liya Huang ◽  
Likun Ma
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Laval Nozzle ◽  
Fluid Model ◽  
Bubbly Flow ◽  
Engine Performance ◽  
Orifice Diameter ◽  
Two Phase ◽  
Convergent Nozzle

To predict engine performance and further instruct the integral engine design, a more reasonable and accurate numerical model of the two-phase underwater ramjet was introduced in this article by considering the bubble formation process. Two-fluid model was used to examine the bubbly flow in the nozzle and its mathematical model was solved by a fourth-order Runge–Kutta method. Subsequently, the influences of vessel velocity, gas mass flow rate, navigational depth, and orifice diameter of the bubble injector on the performance of the engine were discussed. Results show that, compared with convergent nozzle, Laval nozzle is proved to improve the thrust of the engine, especially at relatively high velocity and gas mass flow rate. With the other conditions fixed, there is an optimum vessel velocity for the ramjet, in which maximum thrust is generated. And a smaller orifice diameter always promotes the engine performance, while this promotion is negligible when the orifice diameter is smaller than 1 mm. Besides, increasing backpressure will cause serious performance drop, which means that the the two-phase underwater ramjet is only efficient for shallow depths.

scholarly journals A CFD Study on Two-Phase Frozen Flow of Air/Water Through a Safety Relief Valve

2015 ◽  
Vol 13 (4) ◽  
pp. 533-540 ◽  
Author(s):  
Moftah Alshaikh ◽  
William Dempster
Keyword(s):  
Fluid Model ◽  
Critical Mass ◽  
Velocity Slip ◽  
Flow Conditions ◽  
Complex Flow ◽  
Relief Valve ◽  
Two Phase ◽  
Mass Flows ◽  
Two Fluid Model ◽  
Two Fluid

Abstract The air-water two phase critical flows through a safety relief valve commonly used in the refrigeration industry is examined with particular emphasis on the prediction of the critical mass flowrates using CFD based approaches. The expansion of the gas through the valve and the associated acceleration is coupled to the liquid phase and results in changes to the velocity slip with the possibility of influencing the choking conditions and the magnitude of the critical mass flows. These conditions are poorly reported in the literature for safety valves. This paper presents a study where the ability of established two phase multi-dimensional modelling approaches to predict such conditions are investigated. Comparison with the simplified mixture model will show that this model tends to underestimate mass flowrates for medium to high liquid mass fraction. However, the two fluid model can adequately account for the thermal and mechanical non equilibrium for these complex flow conditions with the use of simplified droplet sizing rules.

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.

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

Effect of Nanoparticle Concentration on Thermo-Hydraulic Behavior of a Nanofluid in a Horizontal Tube with Constant Heat Flux and Mass Flow Rate

2011 ◽  
Vol 110-116 ◽  
pp. 3650-3656
Author(s):  
S. Mirmasoumi ◽  
A. Behzadmehr
Keyword(s):  
Heat Flux ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Horizontal Tube ◽  
Constant Heat Flux ◽  
Tube Length ◽  
Nanoparticle Concentration ◽  
Constant Heat ◽  
Two Phase

How nanoparticle concentration affects on thermal and hydrodynamic parameters of a nanofluid (water+Al2O3) is numerically investigated in a horizontal tube while these parameters are impressed by buoyancy force under constant heat flux and mass flow rate. Comparisons with previously published experimental and numerical works on mixed convection in horizontal tubes show good agreements between the results. Results which are obtained using the two – phase mixture model indicate that adding the nanoparticles causes changes in the properties of nanofluid and finally increases the temperature of the flow. Whereas, dimensionless pressure drop along the tube length could increase with the nanoparticle concentration.

Comprehensive Two Fluid Model Simulation of Critical Two-Phase Flow Through Short Tube Orifices

2015 ◽  
Author(s):  
Puya Javidmand ◽  
Klaus A. Hoffmann
Keyword(s):  
Flow Condition ◽  
Two Phase Flow ◽  
Fluid Model ◽  
Phase Flow ◽  
Two Phase ◽  
Choked Flow ◽  
Flow Through ◽  
Two Fluid Model ◽  
Two Fluid ◽  
Short Tube

Small-diameter tubes are utilized widely as expansion devices in refrigeration systems. They are employed in either kinds of short-tube orifices or long capillary tubes. Performance of these tubes is reliant upon critical flashing of the two-phase flow that controls the mass flow rate of the refrigeration system resulting in a steep reduction in pressure and temperature. The critical flow condition is approached whenever the mass flow rate increases to an amount whereby the choked-flow phenomenon occurs at the outlet of the tube. Due to their very small tube diameter, the evaporating two-phase flow, and the choked-flow condition, numerical analysis of flow through short-tube orifices is challenging. Accordingly, all available numerical analyses of such flows are performed as one-dimensional and in the majority of them, auxiliary correlations are applied to simplify the solution procedure. Typical approaches include homogeneous flow models and separated flow models, both of which consider the two-phase region in thermal equilibrium. The most comprehensive method for analyzing such flows is the two-fluid model in which there is no assumption of equilibrium between phases. Because of the complicated nature of this model, it has been used in a very limited number of previous investigations. Furthermore, two-phase flow calculations at the entrance and vena contracta region were eliminated. In the current investigation, additional steps utilized to improve the accuracy of computations include the following: (1) applying the most comprehensive two-fluid model including the effect of various two-phase flow patterns and the metastability of liquid phase, and (2) performing a two-phase analysis of the evaporating flow through the entrance and vena contracta regions which involves simulating the region as a converging diverging tube and performing a quasi-one-dimensional solution of governing equations through this region. Results showed more compatibility with experimental data in comparison with those of previous investigations for predicting the critical flow condition of common refrigerants HFC-134a and HFC-410a through short-tube orifices and long capillary tubes.

Study of Interfacial Friction Force for Bubble Flows in a 2×1 Rods Channel Simplifying BWR

2010 ◽  
Author(s):  
Akimaro Kawahara ◽  
Michio Sadatomi ◽  
Yutaro Nakamoto ◽  
Takatoshi Masuda
Keyword(s):  
Drag Coefficient ◽  
Friction Force ◽  
Fluid Model ◽  
Interfacial Area ◽  
Interfacial Friction ◽  
Good Prediction ◽  
Dimensionless Numbers ◽  
Concentration Data ◽  
Two Phase ◽  
Interfacial Area Concentration

Most of recent subchannel analysis codes are based on a multi-fluid model, and accurate evaluation of the constitutive equations in the model is essential. In order to get an accurate one of the interfacial friction force in two-phase bubble flows, experimental data on drag coefficient and interfacial area concentration have been obtained for air-water flows in 2×1 rods channel simplifying a BWR fuel rod bundle. In order to know the effects of liquid properties on the data, temperature of the test water was changed from 18 to 50 °C. The data are compared with the existing correlations reported in literatures. As a result, Hibiki and Ishii (2001) semi-theoretical correlation is found to give the best prediction against the present interfacial area concentration data. Delhaye and Bricard (1994) correlation also gives reasonably good prediction if their correlation were modified by incorporating liquid property effects. As for the drag coefficient, no correlation exist which can predict well the present data. Therefore, we developed a new correlation including three dimensionless numbers, i.e., bubble Capillary number, Morton number and Eo¨tvo¨s number. The correlation could predict well Liu et al.’s data (2008) as well as the present data.

Sign in / Sign up

Export Citation Format

Share Document