Papers by Keyword: Two-Phase Flow

Abstract: This study experimentally investigated two-phase flow pressure drop of propane as refrigerant in horizontal small tube. Inner diameter and length of the tube were 7.6 mm and 1.07 m, respectively. In order to get pressure drop data, the experiment was conducted in various conditions of 10 to 25 kW m^-2 heat flux, 200 to 628 kg m^-2 s^-1 mass flux, and 4.0 to 11.7°C saturation temperature. This study clearly showed the effect of heat flux, mass flux, and saturation temperature on the pressure drop of propane. This study also investigated which fluid properties gave higher effect on the frictional pressure drop due to its change over the process based on the recent experiment data. The existing pressure drop correlations were evaluated against the experimental result.

Abstract: Substantial research has been completed with more on-going on the flow pattern and heat transfer associated with two-phase flows. Discrepancies reported may have been as much as agreements, due to the different models, approaches, flow regimes, correlations, and new working fluids being utilized. This paper reports the outcome of a study to look at the effects of applying two different friction factor correlations on the simultaneous minimization of the pressure drop and Martinelli parameter under optimized flow rate and vapor quality, using genetic algorithm. The homogeneous model is assumed with ammonia as the working fluid, the coolant being environmentally friendly and having recently discovered as a potential replacement for the current refrigerants in micro and mini-channels. Results show that significant differences in the frictional pressure drop and Martinelli parameter arise due to the different correlations used, and this is only the outcome from two different correlations currently being considered by researchers in pressure drop analysis for two-phase flows in mini-channels. Thus, absolute agreement is indeed not possible between theoretical, experimental, and numerical work in view of the many different available correlations being utilized today with differences between 10 to 100 percent that has already been established.

Abstract: Hydrate formation occurs in pipelines beyond sea water depth of 3000 ft. with uniform ocean temperature of 38-40^oF, and pressure as low as 100 psig. Plugged-up leads to pressure drop and decreased flow rate, disrupting crude oil transportation. This paper reported the detailed investigation of hydrates particles diameters and interfacial area density in relation to the hydrate deposition in deepwater pipeline. The work focused on the pipe bend section where there is an abrupt change of flow momentum. The flow was assumed isothermal and constant mean hydrate particle size. It was found that initial hydrate particulates’ diameter has the most significant impact on the deposition thickness, causing significant increase of thickness in comparison to other factors. It is concluded that the prevention of hydrate plugging should focus primary on controlling the hydrate’s mean particle sizes.

Abstract: The characteristics of two-phase flow boiling of R-290 are required for replacing R-22 that has been phased-out. The present study focuses on experimental pressure drop for R-22 and R-290. The experiment was run with heat flux of 5.09 kW/m² to 19.03 kW/m², mass flux of 114.91 kg/m²s to 751.74 kg/m²s and saturation temperature of 4.77°C to 18.12°C. The present result showed that pressure drop was affected by heat flux, mass flux and saturation temperature. Lower mass flux, heat flux and saturation temperature results in lower pressure drop. The pressure drop of R-290 is lower than that of R-22. Among the existing pressure drop prediction methods, Lokhart-Martinelli (1949) gives the best prediction for the present pressure drop data.

Abstract: Two-phase flow can have significance influence on exhaust plume of solid propellant, as well as the infrared radiation of the rocket. To show this influence, flow field of solid propellant rocket exhaust plume is simulated on different working conditions, where two-phase flow is involved using the DPM method. Comparing the flow filed results with or without two-phase flow considered shows that the existence of the condensed particles can decreases the velocity of the plume and increases the temperature. The influences of the flight height and Mach number on exhaust plume are also discussed.

Abstract: By changing a air flow rate of the two-phase (air-water) flow through a minichannel weidentified aggregation and partitioning of air bubbles and slugs of different sizes and air bubble arrangement into periodic patterns. The identification of these spatio-temporal behaviour was doneby digital camera. Simultaneously, we provide the detailed studies of these phenomena by using thecorresponding sequences of light transmission time series recorded by a laser-phototransistor sensor.To distinguish the instabilities in air slags and their breakups and aggregations we used the Fourierand multiscale entropy analysis.

Abstract: Established two-dimensional axisymmetric staggered tooth shape labyrinth seal grid model by GAMBIT software, simulated oil-air two-phase mixture flow field within labyrinth seal by fluent software, confirmed the best grid size of numerical calculation, studied the seal mechanism and influence of gap width variation on the leakage. The results show that when fluid flows through the narrow clearance, its velocity increases and pressure decreases. The optimized clearance width within 0.5mm to 1.0mm is preferable.

Abstract: We discuss the numerical modelling of two phase flow in porous media (see [1]). We consider a one-dimensional problem describing flow of two incompressible and immiscible fluids through a porous medium where the non-wetting phase (oil) is displaced by the wetting fluid (water). The used model is based on Darcy’s law and we consider either horizontal (neglecting the influence of gravity) or vertical flow. In case of horizontal flow, we compare our solution with analytical solution published in [2]. In case of gravity driven vertical flow, there is no known analytical solution and we propose our solution as a benchmark solution.Our numerical model is based on the modelling of interface separating zones where the water is present and where it is not. We semidiscretize the problem in space and obtain a mass preserving system of ODEs. We have moving grid points only on region where the water is present, and these move accordingly to the evolution of the interface. We can choose to have non-equidistant grid with more grid points in the neighbourhood of the interface. This guarantees very good approximation of sharp fronts during infiltration. Results obtained by our methods are compared with well-known result in [2] which was obtained by semi-analytical method and they are in perfect agreement.

Abstract: The header and the multiple microchannel tubes connected to the header compose a complicated fluid network with several circuits, and the refrigerant flow into the header and is distributed to the microchannels in parallel by the refrigerant pressure driving in the inlet. So all changed details of geometry, operating conditions and thermophysical properties of the fluids lead to nonuniform refrigerant flow distribution in the microchannels. In the present work, one 6-pass 40-tube microchannel condenser as the research objective was equipped in a window type air conditioner prototype with the cooling capacity 5200W for Middle East T3 climate. A mathematical model based on fluid network theory was developed to predict flow distribution and phase separation in 9 flat tubes and their connecting headers on the second pass of the microchannel condenser. In the assumption of homogeneous flow, the mesh current analysis was employed to solve the mass flow of the loop_i+1 by that of the loop_i upon two phase pressure drop. The simulated mass flow rate distribution in 9 tubes is parabolic and approaches to uniform distribution when inlet quality comes to the median 0.45 from both directions.

Abstract: An efficient numerical approximation for two phase flow in 1D is presented. Mathematicalmodel is based on two Richard’s type equations using Van Genuchten-Mualem (vG-M) model for capillarypressure-saturation and hydraulic permeability versus saturation of wetting liquid. The wettingand non-wetting liquids are incompressible and immiscible. The method is suitable for determinationof soil parameters (as a tunning parameters in vG-M model) via solution of inverse problem. Wettingliquid (-water) is injected into the sample originally saturated with non-wetting liquid (-oil) by gravitation,or centrifuge driving forces. In a series of experiments we discuss noninvasive (easy-to-measure)measurement scenarios which are satisfactory in a solution of inverse problem.