Mass Flow Rate Characteristics Research Articles

Mass flow characteristics of CO2 operating in a transcritical cycle flowing through a needle expansion valve in a direct-expansion solar assisted heat pump

An expansion device is one of the key components of heat pump systems. Although in the literature there are several studies that analyze the effect of opening the expansion valve on heat pumps, none of them reported this effect for heat pumps that operate with solar energy. In this study, the mass flow rate characteristics through an expansion device in a direct-expansion solar assisted heat pump (DX-SAHP) operating with CO2 is investigated. With experimental data, a new correlation is proposed. A statistical method is used to determine the dimensionless Π-groups that most influences the mass flow rate. The parameters selected to compose the new correlation are: outlet and inlet pressures of the expansion device, geometric (cross-section area) and fluid viscosity. The proposed correlation shows good agreement with the measured data with average and standard deviations of 0.77% and 10.4%, respectively. The maximum relative deviation of all predictions of mass flow rate is less than ±30% and approximately 90% of mass flow rate experimental data are within ±20% of the predictions. In addition, for a same needle expansion valve opening, the mass flow rate increases with the augment in the solar radiation flux.

Control of Mass Flow-Rate of Viscoelastic Fluids Through Time-Periodic Electro-Osmotic Flows in a Microchannel

Abstract In the present research, we address the implications of the pulsating electric field on controlling mass flow-rate characteristics for the time-periodic electro-osmotic flow of a viscoelastic fluid through a microchannel. Going beyond the Debye-Hückel linearization for the potential distribution inside the Electric Double Layer, the Phan-Thien-Tanner constitutive model is employed to describe the viscoelastic behaviour of the fluid. The analytical/semi-analytical expressions for the velocity distribution corresponding to a steady basic part, and a transient perturbed part are obtained by considering periodic pulsations in the applied electrical field. Our results based on sinusoidal pulsations reveal that enhanced shear thinning characteristics of the viscoelastic fluids show higher amplitude of pulsations with the oscillations in the velocity gradients primarily contrived within the Electric Double Layer region. The amplitude of mass flow rates increases with increasing the viscoelastic parameter , whereas, the phase lag displays a reverse trend. The analysis for an inverse problem is extended where the required magnitude of electric field pulsations for a target mass flow rate in the form of sinusoidal pulsations. It is found that with increasing shear-thinning characteristics of the viscoelastic fluid, there is a progressive reduction in the required electric field strength to maintain an aimed mass flow rate. Besides, required electric fields for controlled mass flow with triangular and trapezoidal pulsations are also determined.

Mass flow rate prediction of R1233zd through electronic expansion valves based on ANN and power-law correlation models

Recently, the R1233zd refrigerant, which has low GWP and ODP, was introduced as an alternative for R245fa. This study investigates the mass flow rate characteristics of R1233zd flowing through electronic expansion valves (EEVs) under varying operational conditions. The basic experimental results are presented. Based on the experimental results, ANN(Artificial Neural Networks) model and Power-law correlation model are used to predict the mass flow rate of R1233zd flowing through EEVs. Compared with the experimental results, 95.6% of the predicted data of the ANN model have relative errors within 10%, 91% of Power-law correlation model within 10%. The ANN model give average deviation of −0.2% and standard deviation of 4.7%, the Power-law correlation model shows lower accuracy that with average deviation of −0.8% and standard deviation of 6.3%.

Empirical correlation development of R245fa flow in electronic expansion valves

The applications of electronic expansion valves in high temperature heat pump have increased rapidly. However, correlations for predicting R245fa mass flow rate through electronic expansion valves in high temperature heat pump are very limited in open literatures. In this study, mass flow rate characteristics of R245fa refrigerant flowing through electronic expansion valves with different operational conditions are studied experimentally, and empirical correlations are proposed based on the experimental data. The results reveal that the mass flow rate increases with increasing opening degree, condensation temperature, subcooling, and orifice diameter. Based on a modified single phase orifice equation, two empirical correlations are proposed by using the power-law correlation and the polynomial fit correlation, and over 92% of the predicted data deviate from the experimental data within ±15%.

Experimental investigation on mass flow characteristics of R245fa through electronic expansion valve

In this paper, the mass flow rate characteristics of R245fa refrigerant flowing through electronic expansion valves (EEV) under varying operating conditions are studied experimentally. It is found that the mass flow rate increases with increasing EEV opening, condensing temperature, subcooling temperature, and orifice diameter. Based on the measured experimental data, two empirical correlations for mass flow rate prediction of R245fa through EEVs are proposed using the power-law correlation and the polynomial fit correlation. Predicted data of the polynomial fit method showed more consistency with the experimental results compared to that of power-law correlation, and 96.6% of the predicted mass flow rates deviate from the experimental data within ±10%.

Parameter identification of a jet pipe electro-pneumatic servo actuator

AbstractThis paper presents experimental parameter identification of a jet pipe electro-pneumatic servo actuator model, which represents a class of high performance fast actuation systems. Parameter identification is given including detailed representation of linear dynamics, hysteresis, and the mass flow rate characteristics of the jet pipe servo valve, besides the static friction model of the linear pneumatic cylinder. Model parameters are identified and the model formulation is validated through simulation and experimentation. The main contribution of this work is threefold. Firstly, the mass flow rate characteristics are identified using the pressure dynamic equation in one cylinder chamber without the use of a flow sensor. Secondly, a lag behaviour related to the non-modelled dynamics is found out by performing an experimental identification of the frequency response of the servo valve. Thirdly, a new experimental setup is presented to give the static friction model as a function of not only the rela...

Measurement of mass flow rate and evaluation of heat transfer coefficient for high-pressure pneumatic components during charge and discharge processes

Both the mass flow rate and heat transfer characteristics are significant factors to the flow behavior of the high-pressure air; however, they are not easy to be obtained by analytical model during discharge and charge processes. In this paper, the mass flow rate characteristics of high-pressure pneumatic components (HPPC) are measured by a compounding approach; two components under test with the same geometry and dimension are needed to be connected in series. Both the effective cross-section area and critical pressure ratio of HPPC are determined accurately, and only the pressure variation and the steady-state temperature of air in the chamber are utilized. The compared results between experimental and simulation data show that the accuracy of the measured effective cross-section area and critical pressure ratio of the HPPC is high when the sonic and adiabatic releasing time is less than 2s. And then, a new combined method of calculating the heat transfer coefficient during discharging and charging processes for the high-pressure air is proposed. The computational fluid dynamics (CFD) method is used to illustrate the intensity of heat exchange between the high-pressure air inside the chamber and outer atmosphere. The dynamic flow behavior is analyzed based on the tested flow rate characteristics of HPPC, mixed heat transfer theory and numerical results. The results show that the heat-transfer coefficient during charge process is much greater than discharge process, and the forced convection heat exchange happened owing to the strong “air agitation” during the charge process. The experimental results also validate that the proposed method of calculating the transient heat transfer coefficient is more reasonable to describe the heat transfer behavior. The findings may also have general implication in the development of the design and analysis of the high-pressure pneumatic system.

Mass flowrate characteristics of supercritical CO2 flowing through an electronic expansion valve

Electronic expansion valves (EEV) are employed increasingly in transcritical CO2 systems. In order to investigate the mass flowrate characteristics of supercritical CO2 flowing through an EEV, the effects of EEV outlet pressure on the mass flowrate of CO2 is studied under constant EEV inlet pressure and inlet temperature. The two-phase flow patterns of supercritical CO2 flowing through an EEV are revealed, and the conventional choked flow judgment formulas is proved effective for supercritical CO2. Based on Bernoulli Equation with expansion factor, the mass flowrate correlation of supercritical CO2 flowing through an EEV is presented. The influence of the expansion coefficient on the mass flowrate is considered in the correlation in which the correction coefficient is only affected by the EEV opening, the changing rate of the density and the pressure difference in the entrance region. The mass flowrate predicted by the correlation in this paper shows a good agreement with experimental data. The maximum relative errors are within 10%. The average and standard deviations are 0.76% and 5.9%, respectively.

Mass Flow Rate Control in a Cylindrical Capillary by an AC Electric Field at High Zeta Potential

In the present study we obtain the mass flow rate characteristics in a cylindrical capillary due to a time-periodic electric field at high zeta potential, extending the conventional thin electrical double layer limit. The capillary cross section is divided into two regimes, the high potential regime (near surface region), and the low potential regime (capillary central line region). To obtain the potential distribution inside the capillary, the nonlinear part of the Poisson-Boltzmann equation is approximated by a linear function for the low potential regime and by an exponential function for high potential regime. Using the approximated potential distributions, the governing electro-hydrodynamic equation is then solved semi-analytically, where the imposed electric field and the velocity field is assumed to have the form which consist of a steady state term and a time-periodic term. A theoretical investigation on the mass flow rate, the phase difference is carried out on the basis of pulsation frequency, e...

Mass flow-rate control through time periodic electro-osmotic flows in circular microchannels

The present study is directed towards devising a scientific strategy for obtaining controlled time-periodic mass flow-rate characteristics through the employment of pulsating electric fields in circular microchannels by exploiting certain intrinsic characteristics of periodic electro-osmosis phenomenon. Within the assumption of thin electrical double layers, the governing equations for potential distribution and fluid flow are derived, corresponding to a steady base state and a time-varying perturbed state, by assuming periodic forms of the imposed electrical fields and the resultant velocity fields. For sinusoidal pulsations of the electric field superimposed over its mean, a signature map depicting the amplitudes of the mass flow rate and the electrical field as well as their phase differences is obtained from the theoretical analysis as a function of a nondimensional frequency parameter for different ratios of the characteristic electric double layer thickness relative to the microchannel radius. Distinctive characteristics in the signature profiles are obtained for lower and higher frequencies, primarily attributed to the finite time scale for momentum propagation away from the walls. The signature characteristics, obtained from the solution of the prescribed sinusoidal electric field, are subsequently used to solve the “inverse” problem, where the mass flow rate is prescribed in the form of sinusoidal pulsations and the desired electric fields that would produce the required mass flow-rate variations are obtained. The analysis is subsequently extended for controlled triangular and trapezoidal pulsations in the mass flow rate and the required electric fields are successfully obtained. It is observed that the higher the double layer thickness is in comparison to the channel radius, the more prominent is the deviation of the shape of the required electric field pulsation from the desired transience in the mass flow-rate characteristics. Possible extensions of the analysis to more complicated pulsation profiles are also outlined.

Mass flow rate of R-410A through short tubes working near the critical point

Experimental data were taken to examine R-410A mass flow rate characteristics through short tube restrictors at upstream pressures approaching the critical point. Four short tube restrictors were tested by varying upstream pressure from 2619 to 4551 kPa (corresponding to saturation temperature from 43.9 to 71.7 °C), upstream subcooling from 2.8 to 11.1 °C and downstream pressure from 772 to 1274 kPa. The experimental data were represented as a function of major operating parameters and short tube diameter. As compared to mass flow trends at typical upstream pressures, flow dependency on upstream subcooling was more significant at high upstream pressures due to a higher density change. Based on the database obtained from this study and literature, an empirical correlation was developed from a power law form of dimensionless parameters generated by the Buckingham Pi theorem. The post-predictions of the new correlation yielded average and mean deviations of 0.11 and 2.4%, respectively.

A NEW MASS FLOW-RATE MODEL OF GAS THROUGH ORIFICE-TYPE RESTRICTORS IN AEROSTATIC BEARINGS

This paper proposes a new mathematical model to describe the mass flow-rate characteristics of gas through orifice-type restrictors in aerostatic bearings. In the conventional design of gas-lubricated aerostatic bearings, the mass flow-rate of gas through an orifice-type restrictor is generally derived from a well-known mathematical model, which is originally developed to describe the mass flow-rate property of gas through an ideal nozzle. In this paper, however, a series of CFD-simulations and experiments according to ISO 6358 are carried out and the results show that the mass flow-rate characteristics through an orifice-type restrictor are different from those through an ideal nozzle. Consequently, the conventional model to determine the mass flow-rate of gas through orifice-type restrictors in aerostatic bearings may have to be modified and updated to the proposed new model for more precise design and modeling of the gas-lubricated aerostatic bearings.

액체로켓 추진제 공급계에서 캐비테이션 벤튜리의 유량 제어 특성

액체로켓 추진제 공급장치에 정착된 캐비테이션 벤튜리의 유량 제어 특성을 해석하였다. 해석에는 실험과 수치해석이 병행되었으며 캐비테이션이 존재하는 유동에서 두 결과의 유량 차이는 약 10%로 나타났다. 벤튜리 상류의 압력을 <TEX>$22.8{\times}10^5$</TEX>pa로 일정하게 유지하고 하류의 압력을 변동시켰을 때 <TEX>$3{\times}10^5$</TEX>pa 이상의 압력 차이에 대하여 유량이 증가하지 않음을 확인하였다. 비응축 기체의 농도 변화에 의하여 벤튜리 내부에 발생하는 증기의 분포는 크게 달라지지만 유량은 같은 수준이 유지되어 비응축 기체의 농도가 1.5PPM에서 150PPM로 커질 경우, 유량이 약 2% 감소하였다. 이는 작동유체가 포함하고 있는 비응축 기체의 팽창과 생성된 증기가 압력 회복을 저해하는 영향이 유사하기 때문으로 풀이된다. Characteristics of flow rate control has been studied for a cavitating venturi adopted in a liquid rocket propellant feed system. Both experiment and numerical simulation have been performed to give about 10% discrepancy of mass flow rate for cavitating flow regime. Mass flow rate is confirmed to be saturated for pressure difference higher than <TEX>$3{\times}10^5$</TEX>pa when the upstream pressure is fixed to <TEX>$22.8{\times}10^5$</TEX>pa and the downstream pressure is varied. The evaporation amount depends substantially to non-condensable gas concentration. However the mass flow rate characteristics is relatively insensitive to the mass fraction of non-condensable gas. So it reduces by only 2% when the non-condensable gas concentration is increased from 1.5PPM to 150PPM. From the previous comparison the expansion of the non-condensable gas and the evaporation of liquid are verified to gave same effect to the pressure recovery pattern.

Predictions and observations of the flow field induced by laminar flow control microperforations

Hybrid laminar flow control (HLFC) aims to reduce aircraft skin friction drag by controlling the boundary-layer characteristics through a combination of surface suction and surface profile shaping. Suction is applied through an array of microperforations in the surface; and, to enable HLFC design criteria to be established with confidence, a full understanding of how these suction perforations affect the boundary layer is required. The objective of this paper is to predict the flow field induced by surface suction through single and multiple rows of microperforations, at transonic cruise conditions. A broad range of cases are studied for a variety of geometric and flow configurations by solving the compressible, laminar, Navier-Stokes equations. The geometric parameters considered are perforation diameter, inclination to the surface, and perforation duct profile. The flow parameters consist of the boundary-layer displacement thickness and suction mass flow rate through the hole. From the predictions and analyses of the results, a wide variety of flow field patterns and features are observed; including longitudinal vortices, streamline curvature, large cross-flow velocities, inherently unstable velocity profiles, and a recirculation region at the perforation entrance. The perforation inlet shape is found to have a minimal effect on the induced flow field, but the level of streamwise vorticity is increased for inclined perforations. The size and shape of the sucked stream tube, which is currently used to predict the critical suction velocity, also is determined. For multiple rows of perforations, the flow field characteristics are shown to be influenced by significant interhole effects. The mass flow rate characteristics of microperforations are found to be insensitive to the ratio of hole diameter to boundary-layer displacement thickness. Also, conical bore holes are shown to provide substantial static pressure recovery due to diffusion effects.