Flow Rate Fraction Research Articles

Development of Delayed Equilibrium Model for CO2 convergent-divergent nozzle transonic flashing flow

The one-dimensional implementation of the Delayed Equilibrium Model (DEM) is known as a relatively simple yet accurate approach for prediction of critical mass flow rate, pressure and void fraction distributions for two-phase water transonic flows in ducts of variable geometry. However, the direct application of DEM equipped with original saturation index evolution law and Lockhart-Martinelli approach (the original setup) is incapable of accurate prediction of CO2 transonic flow. Moreover, the Darcy friction factor approach has a significant impact on the simulation results. Consequently, this paper presents a new law of the saturation index evolution and a new frictional pressure gradient approach for CO2 transonic two-phase flows together with experimental validation and discussion of obtained data. A comparative analysis of the developed DEM setup and the referential Homogeneous Equilibrium Model revealed that application of the proposed approaches decreases the mean maximal discrepancy between experimental and calculated static pressure values by a factor of app. 2, with simultaneous decrease of the standard deviation by a factor of app. 4. That proves that both the frictional pressure gradient approach and the proper introduction of the thermal non-equilibrium effects are substantial for accurate modelling of the flashing process in CO2 flows.

Energy and Exergy Analyses of Regenerative Gas Turbine Air-Bottoming Combined Cycle: Optimum Performance

The current paper presents a thermodynamic analysis of an air-bottoming cycle (ABC) operated by the exhaust gasses of a regenerative gas turbine cycle. The partial exhaust heat of a topping gas turbine cycle is utilized to heat the compressed air of the ABC by passing it through a heat exchanger (H.E.2), whereas remaining heat is used to heat the compressed air of the topping cycle before entering a combustion chamber by passing it through a heat exchanger (H.E.1). The effects of the turbine inlet temperature of the topping cycle (1000 K ⩽ $${\text{TIT}}$$ ⩽ 1500 K) and fraction of mass flow rate of the exhaust gas (0 ⩽ $$x$$ ⩽ 1) on the net output, combined thermal efficiency, exergy destruction, exergy loss by exhaust gasses, and specific fuel consumption (SFC) are investigated parametrically for a particular value of the pressure ratio of the topping and bottoming cycles. At $$x = 0$$ , the net output and thermal efficiency of the combined cycle increase by 15.1% and 31.3%, respectively, whereas the SFC decreases by 13.1% and 15.5% at $${\text{TIT}} = 1000\;{\text{K}}$$ and $${\text{TIT}} = 1500\;{\text{K}}$$ , respectively. The exergy destruction of the heat exchanger of the topping cycle increases, whereas that of the bottoming cycle decreases with an increase in x. Overall, in terms of the net output and thermal efficiency, a simple gas turbine cycle with an air-bottoming combined cycle performs better than a simple regenerative gas turbine cycle; however, in view of the exergy loss by exhaust gasses, a simple regenerative gas turbine cycle is better than the combined cycle.

Dual-stream of monodisperse droplet generator

The generation of droplets with controllable sizes is important in various engineering applications. However, existing studies commonly focused on generating a single monodisperse droplet stream. The generation of dual-stream droplets with different controllable sizes and spacings has not been clearly investigated. Here we design a piezoelectric droplet generator characterized by two different-sized orifices in a metal plate. On the basis of Rayleigh breakup theory, the practical diameter ratio of the larger and smaller orifices is qualitied, with a value less than 2.4. Experiments are carried out on four different designed orifice plates. The ranges of excitation frequency that facilitate monodisperse dropletformation are identified. The formation process and transformation characteristics of the droplet streams are visually analysed with high speed shadowgraphy. Meanwhile, a non-dimensional number Rs is proposed to describe the volume flow rate fraction in the operation of orifice plates. Experimental results show that the design works with high stability.

Energy and cost estimates for separating and capturing CO2 from CO2/H2O using condensation coupled with pressure/vacuum swing adsorption

Condensation coupled with pressure swing adsorption (CPSA) and condensation coupled with vacuum swing adsorption (CVSA) were used to separate CO2 from CO2/H2O mixtures. Six methods are compared using numerical simulations in terms of the energy consumption, separation efficiency and total annual costs for separating CO2/H2O mixtures. The effects of inlet CO2 mole fraction, mass flow rate, and pressure on the total annual cost are also studied. A parametric study shows that the total annual costs of all these methods increase as the CO2 mole fraction and mass flow rate increase and decrease with increasing inlet gas pressure. In addition, for CO2/H2O mixtures with inlet pressure of 10 kPa, mass flow rate of 40 kg/s, and CO2 mole fraction of 0.1, the average heat rejection of the CPSA processes is higher than that of the CVSA process. Although the CPSA recovery (90.02%) is much lower than that of CVSA (96.26%), the H2O remove efficiencies of Adsorption for CPSA and CVSA are very close, because that the remained amount of H2O before Adsorption is very little. A type of CVSA named CcCVSA has the lowest total annual cost with this being the recommended system.

Thermal and Hydraulic Performance of CuO/Water Nanofluids: A Review.

This paper discusses the behaviour of different thermophysical properties of CuO water-based nanofluids, including the thermal and hydraulic performance and pumping power. Different experimental and theoretical studies that investigated each property of CuO/water in terms of thermal and fluid mechanics are reviewed. Classical theories cannot describe the thermal conductivity and viscosity. The concentration, material, and size of nanoparticles have important roles in the heat transfer coefficient of CuO/water nanofluids. Thermal conductivity increases with large particle size, whereas viscosity increases with small particle size. The Nusselt number depends on the flow rate and volume fraction of nanoparticles. The causes for these behaviour are discussed. The magnitude of heat transfer rate is influenced by the use of CuO/water nanofluids. The use of CuO/water nanofluids has many issues and challenges that need to be classified through additional studies.

Experimental investigation of convective heat transfer and pressure drop of SiC/water nanofluid in a shell and tube heat exchanger

In this study, the heat transfer enhancement due to using Silicon Carbide nanofluid flowing through the tube side in a shell and tube heat exchanger is studied. Nano-fluid concentrations are 0.25, 0.5, 0.75 and 1 Vol.%, respectively. The hot water is passed through the shell side at temperatures of 35, 45 and 55 °C. The flow rate of nanofluid is adjusted at 100, 150, 200, 250 and 300 (L/h), while, the hot water flow rate of the outer tube is 180(L/h). The results show that heat transfer and pressure drop increase with increasing volume fraction of nanoparticles and mass flow rate. 19.8% increase in heat transfer is observed due to adding nanoparticles.

Thermal-hydraulic characteristics and optimization of a liquid-to-suction triple-tube heat exchanger

The highly effective heat-transfer characteristic of a triple-tube heat exchanger was applied to the liquid-to-suction heat exchanger of an R410A refrigerator. A one-dimensional analytical model was established and validated against numerical and experimental models. The study aimed to find the optimum refrigerant flow-rate fraction and diameter of the three tubes in terms of the heat-transfer rate and pressure drop. The results indicated that the liquid-to-suction triple-tube heat exchanger had a much higher heat transfer and lower pressure loss than the double-tube heat exchanger. The TOPSIS decision-making technique determined that the triple-tube heat exchanger with diameters of 1, 1-1/4, and 1-1/2 inch and a mass flow-rate fraction of 0.66 obtained the lowest pressure loss and highest heat transfer.

Waste heat recovery from the stripped gas in carbon capture process by membrane technology: Hydrophobic and hydrophilic organic membrane cases

AbstractIn this study, hydrophobic polytetrafluoroethylene (PTFE) and hydrophilic polyetheretherketone (PEEK) membranes were used as heat exchangers in rich‐split CO2 capture process to recover the waste heat from the stripped gas (i.e., mixture of water vapor and CO2). Technical feasibilities of these two membrane exchangers were assessed by heat recovery and energy intensity in the monoethanolamine (MEA)‐based carbon capture process. The heat recovery of these two membrane exchangers with different pore sizes were then systematically compared under various operating parameters. The underlying mass and heat transfer mechanisms of two membranes were also investigated and compared to figure out the suitable candidate for heat recovery. Additionally, the potential risks of using these membrane exchangers were identified and investigated. Results showed that the PTFE membrane displays a better heat recovery performance than the PEEK membrane with the same pore size. The heat recovery of both PTFE and PEEK membranes first increases to a plateau and then drops slightly with the increased CO2‐rich solvent flow rate. The heat recovery of PTFE and PEEK membranes decreases with the increased flow rate and water vapor fraction of the inlet stripped gas, MEA temperature, and MEA concentration. Furthermore, the larger pore size results in higher heat recovery for both PTFE and PEEK membranes. PTFE membranes displayed lower MEA transfer flux than PTFE membranes at any rich MEA flow rate as the enhanced MEA transfer from the cold solution to the other side via PEEK membrane pores filled with liquid water. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Experimental and Numerical Evaluation of Thermal Performance of Parabolic Solar Collector Using Water/Al2O3 Nano-fluid: A Case Study

Energy demand keeps growing all over the world and is contributing to climate change. So, fossil fuels must be replaced by renewable energies. Solar energy is the most accessible energy in Iran as well as in many other countries. Parabolic solar collectors appear to be a very promising technology in solar energy absorption. Meanwhile, nano-fluids are known to improve the heat transfer capabilities in comparison with ordinary pure fluids. In this work, an experimental study was applied to solar collectors using water/Al2O3 nano-fluid located in a renewable energy site of Islamic Azad university of Khomenishahr branch followed by numerical simulations. Experimental tests were conducted for 2, 3, and 4 L·min−1 flow rates with pure water and 0.1 %, 0.2 %, and 0.3 % volume fraction of nanoparticles, respectively, with the results validating the numerical simulations. The results revealed that reductions in flow rate and elevations in volume fraction led to increased outlet temperature of solar collector, inlet and outlet temperature difference in collector, tank and radiator, and improved solar collector efficiency. Also, heat transfer coefficient rose with augmenting the flow rate and volume fraction.

Influence of Dimensionless Parameter on De-Ionized Water-alumina Nanofluid Based Parabolic Trough Solar Collector.

Aqueous-alumina nanofluid was prepared using magnetic stirrer and ultrasonication process. Then, the prepared nanofluid was subjected to flow through the unshielded receiver of the parabolic trough solar collector to investigate the performance of the nanofluid and the effects of the dimensionless parameter were determined. The experimental work has been divided into two sections. First, the nanofluid was prepared and tested for its morphology, dimensions, and sedimentation using X-Ray Diffraction and Raman shift method. Then, the nanofluids of various concentrations from 0 to 4.0% are used as heat transfer fluid in unshielded type collector. Finally, the effect of the dimensionless parameter on the performance was determined. For the whole test period, depending upon the bulk mean temperature, the dimensionless parameters such as Re and Nu varied from 1098 to 4552 & 19.30 to 46.40 for air and 2150 to 7551 & 11.11 to 48.54 for nanofluid. The enhancement of thermal efficiency found for 0% and 4.0% nanoparticle concentrations was 32.84% for the mass flow rate of 0.02 kg/s and 13.26% for the mass flow rate of 0.06 kg/s. Re and Nu of air depend on air velocity and ambient temperature. Re increased with the mass flow rate and decreased with concentration. Heat loss occurred by convection mode of heat transfer. Heat transfer coefficient and global efficiency increased with increased mass flow rate and volume fraction. The thermal efficiency of both 0% and 4.0% concentrations became equal for increased mass flow rate. It has been proven that at high mass flow rates, the time available to absorb the heat energy from the receiver is insufficient.

Thermodynamic evaluation and optimization of a flat plate collector operating with alumina and iron mono and hybrid nanofluids

This study presents a thermodynamic evaluation of a flat plate collector (FPC) operating with both mono and hybrid nanofluids. The performance of a collector operating with alumina-water, alumina-iron/water hybrid nanofluids, and water as its heat transfer fluids are evaluated. The two nanofluids were experimentally synthesized at nanoparticle concentrations of 0.05%, 0.1%, and 0.2%, their thermal properties were measured for varying temperature ranges and is used to create a correlation model for the thermal conductivity, specific heat, and viscosity of the nanofluids. A thermal model for the FPC was created on the engineering equation solver for both the first law and second law evaluation of the collector. Then a parametric study and optimization of the system were carried out for varying values of temperature, nanoparticle volumetric fraction and mass flow rate. The results show that the use of alumina-water at a concentration of 0.1% presented a thermal enhancement of 2.16% in the collector, while the hybrid nanofluids reduced the thermal performance of the collector by 1.79% when compared to water. Though the use of the hybrid nanofluids did not provide a better thermal option to water, it provided an exergetic efficiency enhancement of 6.9% as against 5.7% using the alumina-water nanofluids.

Regime Analysis in Ranque Tubes with Circular and Square Working Channels

This study compares detailed regime maps in the case of operation using the air of two Ranque tubes with circular and square working channels with identical inlet guides and identical outlets. The degree of air expansion and the fraction of a flow rate through a cold outlet vary in ranges of 2–8 and 0.2–0.8, respectively. It is observed for both tubes that, as the degree of expansion increases, the dependences of a volumetric flow rate and a cooling ratio on the fraction of a cold flow rate become invariant. It is revealed that the cooling ratio in a circular tube is 1.5–2.0 times greater than that in a square channel, with the volumetric flow rate therein being approximately 10% lower.

Numerical simulation of gas-liquid two-phase flow in gas lift system

The gas-lift system has a lot of significant advantages in sewage treatment, deep well oil recovery, liquid metal cooled reactor and magnetohydrodynamic power converters. The densities of different liquid media and gas media have great influences on the performance of gas lift system. Therefore, based on Fluent simulation software, using Euler model and <i>k</i>-<i>ω</i> SST (shear stress transport) turbulence model, the gas-liquid two-phase flow behaviors in nitrogen-water, nitrogen-kerosene, nitrogen-mercury and air-water, argon-water, nitrogen-water of gas lift system are studied. The rules of gas volume fraction and liquid flow rate at lifting pipe, liquid radial velocity at lifting pipe outlet, promoting efficiency are analyzed. The results are shown as follows. 1) In the nitrogen-water, nitrogen-kerosene and nitrogen-mercury system, the higher the density of liquid medium, the smaller the gas volume fraction in the lifting pipe is; the greater the flow rate of lifting liquid, the higher the promoting efficiency is. 2) In the air-water, argon-water and nitrogen-water systems, the higher the density of gas medium, the smaller the gas volume fraction in the lifting pipe is; the larger the flow rate of lifting liquid, the smaller the peak value of promoting efficiency is. 3) With the increase of gas flow rate, the liquid radial velocity at the lifting pipe outlet increases with overall fluctuation rising. Finally, the liquid velocity near the center of pipe axis is large, near the pipe wall is small. These research results provide the scientific theoretical basis for optimizing the gas lifting technology in applications such as sewage treatment, deep well oil recovery, liquid metal cooled reactor and magnetohydrodynamic power converters.

Numerical simulation of conjugated heat exchange in the turbulent motion of fluid in an oil well

The mathematical model of conjugate heat exchange is proposed for the turbulent movement of reservoir oil in a vertical well section. The motion of the medium is described using a two-dimensional axisymmetric stationary formulation and boundary layer equations. The movement of the turbulent flow of reservoir oil due to reservoir energy is presented. The liquid medium is a mixture of reservoir oil with dissolved gas and formation water. The results of the numerical modeling are presented in the form of dependences of the changing flow rate, temperature, and mass fraction of paraffin deposits that occur along the full vertical extent of the well. The results obtained describe the thermobaric state of the well under the condition of conjugate heat exchange between the fluid flow and the production pipe.

Система рекуперации тепловых потерь мобильной компрессорной установки на основе абсорбционной холодильной машины

The paper considers the heat loss recovery system of a compressor unit based on the absorption-refrigerating machine. The calculation of energy savings for driving the compressor based on the use of the mentioned system was performed. The energy saving amount is shown to be 14.86%. Besides the parametric analysis of the dependence of the power consumed by the compressor on the solution pressure after the pump, the refrigerant solution concentration and mass flow rate fraction of the phlegm returned to the generator from the dephlegmator was conducted.

Condensation flow at the wet steam centrifugal turbine stage

This paper investigates spontaneous condensation of wet steam in a centrifugal turbine by means of three-dimensional computational fluid dynamics. The flow field and aerodynamic characteristics of the wet steam in the centrifugal turbine are compared and analyzed by using the equilibrium steam and nonequilibrium steam models, respectively, where the latter applies the classical droplet nucleation theory and neglects velocity slip between the liquid phase and the gaseous phase. The state parameters of wet steam are described here based on the IAPWS’97 formulation. It is concluded that under the design condition, the mass flow rate, wetness fraction, and flow angle of the wet steam centrifugal turbine in the nonequilibrium steam model all change compared with the equilibrium steam model, with values of 4.4%, 0.5%, and 10.57%, respectively. Then the performance variation of the wet steam centrifugal turbine is analyzed under different steam conditions and different outlet back-pressure conditions. The results show that the change law of the mass flow rate, shaft power, and wetness fraction in the centrifugal turbine are basically identical in both models, and the mass flow rate, shaft power, wheel efficiency, and entropy loss coefficient of the centrifugal turbine in the nonequilibrium steam model are all higher than those in the equilibrium steam model, whereas the outlet wetness fraction is lower than that in the equilibrium steam model.

Experimental investigation on heat and mass transfer in a vertical glass bubble absorber with R124-NMP pair

Abstract An experimental study on heat and mass transfer characteristics of R124-NMP in a vertical glass bubble absorber has been conducted under operating conditions of air-cooled absorption system. The key operation parameters, solution volumetric flow rate, temperature and mass fraction at the absorption tube entrance, vapor volumetric flow rate, orifice diameter and absorption pressure, are converted into dimensionless numbers. A sensitive study of the key operation parameters on overall heat and mass transfer coefficients and two-phase mass transfer coefficient has been performed. The overall heat and mass transfer coefficients and two-phase mass transfer coefficient increase as Rev and absorption pressure increase and decrease as orifice diameter increases. The overall heat transfer coefficient increases as Res increases and decreases as solution temperature and mass fraction increase. This trend is reversed for overall mass transfer coefficient. The increase of solution inlet mass fraction can improve the two-phase mass transfer coefficient while the solution inlet temperature affects the two-phase mass transfer coefficient slightly. On the basis of the experimental data, dimensionless empirical correlations for overall and two-phase Sherwood numbers are proposed with error bands of ±10% to calculate the volumetric mass transfer coefficient for R124-NMP bubble absorption process in a vertical bubble absorber.

A study on the optimal arrangement of tube bundle for the performance enhancement of a steam turbine surface condenser

A porous medium model was used for numerical and experimental investigations of a system that includes a tube bundle inside a steam turbine surface condenser. A condensation model was developed to predict the condenser performance using user-defined functions (UDFs) in the commercial computational fluid dynamics software FLUENT. The shell-side pressure drop around the tube bundle is an important indicator for the condenser performance and can be used to compare different condenser-tube arrangements. The condenser performance was analyzed using various numerical results, such as the absolute pressure, condensation mass flow rate, velocity magnitude, and air mass fraction. Detailed effects of the various parameters of tube bundle are discussed. These parameters had a great influence on the condenser performance. The numerical data were generally in good agreement with those obtained by experiments. An important practical finding from this study is that changing tube bundle can significantly improve the condenser performance by reducing the shell-side pressure drop. Consequently, the optimized model has approximately 40% better pressure drop performance than the base model, and the numerical results were verified with the experiments established by Donghwa Entec.

Potential failure analysis and prediction of multiphase flow corrosion thinning behavior in the reaction effluent air cooler system

The corrosion-thinning failure of tubes caused by ammonium salt remains a longstanding challenge in reaction effluent air cooler (REAC) systems and in other industries. During the quadrennial period of overall maintenance, the area of corrosion thinning is mainly found in the second tube side of the air cooler system, and the carbon steel in these pipes is in multiphase flow condition. Based on the relevant technological process flow, the inner flow field is simulated by using the mixture model and the discrete phase model, and its flow corrosion thinning regulation is revealed. The computational fluid dynamics (CFD) results indicate that the tube area with high liquid fraction and high particle mass flow rate is at higher risk of localized corrosion thinning, as the separated ammonium salt particles easily absorb moisture, deliquesce in the presence of water and form the corrosive environment. The potential failure analysis and prediction basically agree with the inspection results of eddy current testing instruments on the spot. Therefore, it verifies the CFD simulation can be utilized for predicting the multiphase flow corrosion thinning areas in REAC systems.

Simulation of Stratified Two-phase Flow Regime using Air-Water Model in ANSYS Fluent®

Two-phase flow has widely grown in importance in various fields of science and engineering system such as nuclear reactors, heat exchangers, transport system, chemical processing plants etc. One of the major issues faced by these sectors is the development of an accurate and reliable multiphase flow measurement system. At present there is no single system which could measure the two phase flow parameters irrespective of its incoming conditions. Characterization of the single phase flow parameter is easier when compared with two phase flow as the velocity distribution, mass flow rate and void fraction of each component phases are not easily measurable. The other factors that add to these difficulties are the prediction of flow regimes and the effect of pipe or channel orientation on the flow properties in the two phase flow. The hold-up of the individual phases and their relative velocity along with pressure drop needs to be taken care while dealing with these flows. Various researches have clearly shown that no correlation can be used for predicting the flow regimes in a two phase flow satisfactorily. By using volume of fluid multiphase flow model air water two phase flow was simulated for inlet velocities of water and air as 0.121 m/s and 6.56 m/s respectively. Stratified laminar flow was obtained from the CFD simulation. Variation in volume fraction of both air and water, mass flow rate and pressure drop with respect to change in time are investigated using the simulation.