Browsing by Subject "pressure drop"
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Item Analytical and Experimental Study of Annular Two-Phase Flow Friction Pressure Drop Under Microgravity(2011-02-22) Nguyen, Ngoc ThanhTwo-phase liquid-gas flow has a wide variety of applications in space, including active thermal control systems, high-power communications satellites, heat pumps and space nuclear reactors. Two-phase systems have many potential advantages over current single-phase systems due to reductions in system size, weight and power consumption. The mechanisms of pressure drop, heat transfer coefficients, void fractions, and flow regimes must be well understood under microgravity conditions in order to design reliable two-phase systems. The main objective of this present research is to develop a new mathematical model that can accurately predict the annular two-phase friction pressure drop to optimize the design of two-phase systems. The two-phase flow tests were conducted aboard the NASA KC-135 aircraft by the Interphase Transport Phenomena (ITP) group from Texas A&M University. The two-phase flow pressure drops were measured across a single transparent test section 12.7 mm ID and 1.63 m long in annular regimes under microgravity conditions during two flight campaigns. Different from previous work, this was the first time both the void fraction and the film thickness were measured under microgravity conditions. The empirical correlations for the interfacial friction factor and void fraction were developed from 57 experimental data using a linear least squares regression technique. The annular two-phase friction pressure drop can be predicted by the new mathematical model requiring only knowledge of the length and diameter of the tube, liquid and vapor mass flow rates, and properties of the working fluid. In addition, the new mathematical model was validated using Foster-Miller & ITP data collected over twelve flights aboard the KC-135 with working fluid R-12 (77 data points), Sundstrand data collected aboard the KC-135 with working fluid R-114 (43 data points) and Zhao and Rezkallah data aboard the KC-135 with working fluid water and air (43 data points). Compared with the LockhartMartinelli model, Wheeler model, Chen model and homogeneous model, the new mathematical model is the optimal model for predicting the two-phase friction pressure drop in annular regimes. The majority of the data falls within +-20% of the proposed correlation and the average error is 12%.Item Static Pressure Loss in 12?, 14?, and 16? Non-metallic Flexible Duct(2013-08-01) Cantrill, David LeeThis study was conducted to determine the effects of compression on pressure drops in non-metallic flexible duct. Duct sizes of 12?, 14? and 16? diameters were tested at a five different compression ratios (maximum stretch, 4%, 15%, 30% and 45%) following the draw through methodology in ASHRAE Standard 120 -1999 ? Methods of Testing to Determine Flow Resistance of Air Ducts and Fittings. With the pressure drop data gathered, equations were developed to approximate the pressure loss at a given air flow rate for a given duct size. The data gathered showed general agreement with previous studies showing an increase in compression ratio leads to an increase in static pressure loss through the duct. It was determined that pressure losses for compression ratios greater than 4% were over four times greater than maximum stretched flexible duct of corresponding duct size. The increased static pressure losses can lead to decreased performance in HVAC systems. The findings of this study add to the existing ASHRAE and industry data for flexible duct with varying compression ratios.Item Theoretical study of cyclone design(Texas A&M University, 2005-08-29) Wang, LingjuanTo design a cyclone abatement system for particulate control, it is necessary to accurately estimate cyclone performance. In this cyclone study, new theoretical methods for computing travel distance, numbers of turns and cyclone pressure drop have been developed. The flow pattern and cyclone dimensions determine the travel distance in a cyclone. The number of turns was calculated based on this travel distance. The new theoretical analysis of cyclone pressure drop was tested against measured data at different inlet velocities and gave excellent agreement. The results show that cyclone pressure drop varies with the inlet velocity, but not with cyclone diameter. Particle motion in the cyclone outer vortex was analyzed to establish a force balance differential equation. Barth??s "static particle" theory, particle (with diameter of d50) collection probability is 50% when the forces acting on it are balanced, combined with the force balance equation was applied in the theoretical analyses for the models of cyclone cut-point and collection probability distribution in the cyclone outer vortex. Cyclone cut-points for different dusts were traced from measured cyclone overall collection efficiencies and the theoretical model for calculating cyclone overall efficiency. The cut-point correction models (K) for 1D3D and 2D2D cyclones were developed through regression fit from traced and theoretical cut-points. The regression results indicate that cut-points are more sensitive to mass median diameter (MMD) than to geometric standard deviation (GSD) of PSD. The theoretical overall efficiency model developed in this research can be used for cyclone total efficiency calculation with the corrected d50 and PSD. 1D3D and 2D2D cyclones were tested at Amarillo, Texas (an altitude of 1128 m / 3700 ft), to evaluate the effect of air density on cyclone performance. Two sets of inlet design velocities determined by the different air densities were used for the tests. Experimental results indicate that optimal cyclone design velocities, which are 16 m/s (3200 ft/min) for 1D3D cyclones and 15 m/s (3000 ft/min) for 2D2D cyclones, should be determined based on standard air density. It is important to consider the air density effect on cyclone performance in the design of cyclone abatement systems.