Large Pressure Loss Research Articles

Swirl flow analysis in a helical wire inserted tube using CFD code

An analysis on the two-phase flow in a helical wire inserted tube using commercial CFD code, CFX11.0, was performed in bubbly flow and annular flow regions. The analysis method was validated with the experimental results of Takeshima. Bubbly and annular flows in a 10 mm inner diameter tube with varying pitch lengths and inserted wire diameters were simulated using the same analysis methods after validation. The geometry range of p/ D was 1–4 and e/ D was 0.08–0.12. The results show that the inserted wire with a larger diameter increased swirl flow generation. An increasing swirl flow was seen as the pitch length increased. Regarding pressure loss, smaller pitch lengths and inserted wires with larger diameters resulted in larger pressure loss. The average liquid film thickness increased as the pitch length and the diameter of the inserted wire increased in the annular flow region. Both in the bubbly flow and annular flow regions, the effect of pitch length on swirl flow generation and pressure loss was more significant than that of the inserted wire diameters. Pitch length is a more dominant factor than inserted wire diameter for the design of the swirl flow generator in small diameter tubes.

Experimental investigation of convective heat transfer and pressure loss in a round tube fitted with circular-ring turbulators

This paper presents the effect of the circular-ring turbulator (CRT) on the heat transfer and fluid friction characteristics in a heat exchanger tube. The experiments were conducted by insertion of CRTs with various geometries, including three different diameter ratios (DR = d/D = 0.5, 0.6 and 0.7) and three different pitch ratios (PR = p/D = 6, 8 and 12). During the test air at 27 °C was passed through the test tube which was controlled under uniform wall heat flux condition. The Reynolds number was varied from 4000 to 20,000. According to the experimental results, heat transfer rates in the tube fitted with CRTs are augmented around 57% to 195% compared to that in the plain tube, depending upon operating conditions. In addition, the results also reveal the CRT with the smallest pitch and diameter ratios offers the highest heat transfer rate in accompany with the largest pressure loss.

An Experimental Study on the Design of Miniature Heat Sinks for Forced Convection Air Cooling

An experimental study is performed on one of the smallest commercially available miniature fans, suitable for cooling portable electronic devices, used in conjunction with both finned and finless heat sinks of equal exterior dimensions. The maximum overall footprint area of the cooling solution is 534mm2 with a profile height of 5 mm. Previous analysis has shown that due to fan exit angle, flow does not enter the heat sinks parallel to the fins or bounding walls. This results in a nonuniform flow rate within the channels of the finned and finless heat sinks along with impingement of the flow at the entrance giving rise to large entrance pressure losses. In this paper straightening diffusers were attached at the exit of the fan, which resulted in aligning the flow entering the heat sinks with the fins and channel walls. Detailed velocity measurements were obtained using particle image velocimetry, which provided a further insight into the physics of the flow in such miniature geometries and in designing the straightening diffusers. The thermal analysis results indicate that the cooling power of the solution is increased by up to 20% through the introduction of a diffuser, hence demonstrating the need for integrated fan and heat sink design of low profile applications.

The role of ventilation frequency in airway reopening

Inhomogeneously compliant lungs need special treatment during ventilation as they are often affected by respiratory insufficiency which is frequently caused by a regional collapse of the airways. To treat respiratory insufficiency atelectatic areas have to be recruited. Beside conventional mechanical ventilation, high-frequency oscillatory ventilation (HFOV) is an efficient method for airway reopening. Using a transparent in-vitro model of the human lung the influence of varying frequencies on the reopening behavior of atelectatic regions is investigated for volume controlled ventilation. The experiments show that higher ventilation frequencies at constant tidal volume enhance the probability of successful reopening of collapsed lung regions and thus, lead to a more homogeneous distribution of air within the lung. This effect can be attributed (i) to larger flow velocities and thus larger pressure losses in the free pathways as the ventilation frequency increases and (ii) to higher inertia effects. In consequence, the static pressure in the branches above the atelectatic regions increases until it reaches a level at which recruitment is achieved.

Numerical and experimental investigations on internal flow characteristic in the impact sprinkler

An integral 3D numerical model based on the structural characteristics of the impact sprinkler was constructed to simulate the relationship between flow rates and inlet pressures as well as the flow field distribution by computational fluid dynamics (CFD). A commonly used PY140 sprinkler in China with three different flow straighteners in lengths of 80, 140 mm and 200 mm respectively and without flow straightener was investigated under inlet pressures ranging from 300 kPa to 500 kPa numerically and experimentally. The simulation results obtained revealed that the predicted relationship of flow rates and inlet pressures was in good agreement with the measurements. Fixing a proper flow straightener can effectively improve the turbulent flow state inside the sprinkler and lead to a more uniform velocity at the nozzle outlet. The sprinkler with a flow straightener resulted in a larger pressure loss within the internal flow than the sprinkler without flow straightener. A longer flow straightener caused a smaller turbulent kinetic energy at the nozzle outlet, which indicated that the length of flow straightener had no significant effect on the flow rate. As well, it was found that reversed flow happened near the nozzle outlet with a diffused angle of 90° could be observed clearly. The decrease of the diffused angle from 90° to 60° can supply a larger flow rate, which was verified by an experiment.

Flow-Control-Enabled Aggressive Turbine Transition Ducts and Engine System Analysis

A methodology for designing flow-control-enabled aggressive transition ducts and evaluating their system level benefits is presented. The present methodology consists of a novel approach of coupling a parametric transition duct geometry with a flow control model to optimize aggressive transition duct shapes to reduce and/or eliminate flow separations and maximize system performance. Without boundary layer control, the flow through these aggressive transition ducts is characterized by large pressure losses due to massive flow separation resulting in low system performance. Flow control has the potential to eliminate flow separation in these aggressive transition ducts and was included in the present study as an enabling technology. A hierarchy of high and low fidelity models was utilized to include the relevant system effects, capturing not only the performance of the transition duct itself, but also the impact of the exit flow from the transition duct on the low pressure turbine and the engine and aircraft performance. The methodology was used to maximize range with minimum fuel burn by evaluating a system defined by families of transition duct geometries with large radial offsets coupled with a meanline representation of a low pressure turbine. In this example aircraft and propulsion benefits include the elimination of a low pressure turbine stage, which in turn translates into significant weight savings and compactness, while maintaining or improving overall propulsion system performance. The analysis also provides a direction for future studies aimed at defining what the required transition duct radial offsets and the corresponding flow authority levels to achieve aircraft range and total fuel burn benefits are.

Study of Interaction between Supersonic Flow and Rods Surrounded by Porous Cavity

In this paper, some preliminary experiments and the calculations were performed to clarify the flow field, in which the rods surrounded by a porous cavity were normally inserted into the main supersonic flow. As a result, it is found that the starting shock wave severely interacts with the rods, the bow shock wave, its reflections, and the porous wall, which are numerically well predicted under some conditions. In case of the single rod, the main supersonic flow is sucked in front of the rod and blown downstream of the rod. Furthermore, the suction mass flux through the porous holes depends on the number and the locations of the rods. On the other hand, the three rods aligned parallel to the flow make favorable suction area downstream of the rods and also generate as less total pressure loss as that for a single rod. In addition, the spanwised three rods cause the strongest bow shock wave making the large mass flux through the porous wall and also large total pressure loss downstream of the rods. The calculation also suggests that interaction between the bow shock wave and boundary layer along the upper wall results in the boundary layer separation.

Numerical prediction of concentration and current distributions in PEMFC

In this study, we present a rigorous 3-D mathematical model, to treat prediction and analysis of proton exchange membrane fuel cells (PEMFC) species concentration and current density distributions in different flow field patterns and operating conditions. The model is based on the solution of the conservation equations of mass, momentum, species and electric current in a fully integrated finite-volume solver using the CFDRC commercial code. The polarization curve of serpentine flow pattern is well correlated with experimental data. The cell performance with parallel straight, serpentine and interdigitated flow patterns are calculated and compared. The simulation results reveal that serpentine and interdigitated flow patterns show strong convection and high mass transfer. However, they also have larger pressure loss. In addition, the effects of operating temperature and relative humidity are also studied. Non-uniform distributions of concentration and current density appear at high temperature, high current density and low humidity operation, which could lead to an unstable cell performance.

A new electro-osmotic pump based on silica monoliths

A high-pressure electro-osmotic (EO) micro-pump fabricated by a sol–gel process is shown to be potentially effective as a fluid-driving unit on chip-scale analytical systems. A silica monolithic matrix with a morphology of micron-scaled through pores was synthesized within the 100 μm inner diameter (i.d.) fused-silica capillary of the micro-pump. The monolith bonds directly with the capillary wall such that frits with large pressure loss are unnecessary. This pump uses electro-osmotic flow to propel liquid solution with no moving parts. The Nafion ® housing design in the cathode chamber prevents flow leakage into the electrode reservoir from the flow channel and hence maximizes the pressure build-up. It also eliminates electrolytic bubble interference from the flow channels and provides ionic channels for current penetration simultaneously. As the monolith is silica-based, this pump can be used for a variety of fluids, especially for organic solvents, such as acetonitrile and methanol, without swelling and shrinking problems. The maximum flow rate and maximum pressure generated by the 100 μm i.d. monolithic pump are 2.9 μL/min and 3 atm for deionized water at 6 kV applied voltage. These results indicate that the pump can provide sufficient pressure and flow for miniaturized HPLC and micro-total-analysis systems (μ-TAS). A simple universal pressure pump curve collapses the data for a variety of working fluids and voltage.

Effects of Reynolds Number and Freestream Turbulence on Turbine Tip Clearance Flow

Tip clearance losses represent a major efficiency penalty of turbine blades. This paper describes the effect of tip clearance on the aerodynamic characteristics of an unshrouded axial-flow turbine cascade under very low Reynolds number conditions. The Reynolds number based on the true chord length and exit velocity of the turbine cascade was varied from 4.4×104 to 26.6×104 by changing the velocity of fluid flow. The freestream turbulence intensity was varied between 0.5% and 4.1% by modifying turbulence generation sheet settings. Three-dimensional flow fields at the exit of the turbine cascade were measured both with and without tip clearance using a five-hole pressure probe. Tip leakage flow generated a large high total pressure loss region. Variations in the Reynolds number and freestream turbulence intensity changed the distributions of three-dimensional flow, but had no effect on the mass-averaged tip clearance loss of the turbine cascade.

Studies of Heat Pumps Using Direct Expansion Type Solar Collectors

An aluminum roll-bond panel with a photovoltaic module on the surface was developed recently for use as an evaporator of a heat pump for residential hot water supply and room heating [Proceedings of the JSES/JWEA Joint Conference, Okinawa, pp. 305–308 (in Japanese)]. In the present study, the panel was modified to reduce the large pressure loss of the refrigerant flow at the evaporator. Total area of the panels was 1.9m2 and the rated capacity of the compressor was 250 W. A collector efficiency factor of 0.9 was obtained for the evaporator. The effect of the location of the feeler bulb on performance of the heat pump was also examined.

Characterizing Rheology of Fresh Short Fiber Reinforced Cementitious Composite through Capillary Extrusion

The rheology behavior of fresh short fiber reinforced cementitious composite (SFRCC) for extrusion purpose was investigated through capillary extrusion. It was found that the classical capillary theory for single-phase fluid was not appropriate to interpret the flow behavior of fresh SFRCC due to the large pressure loss occurring at the capillary entrance and the significant slip effect happening in the capillaries. By using a set of capillaries with the same diameter but different lengths, the true shear stress was derived on the basis of Bagley’s end correction while the slip effect was calibrated through a series of capillary extrusion tests with different capillary diameters. It was found that the slip velocity could be determined by the Jastrzebski model. Further studies showed that the intrinsic rheology behavior of fresh SFRCC could be modeled by the Herschel–Bulkley equation and the associated parameters could be determined through the experimental and the data interpretation method described in t...

Rheological properties of long glass fiber filled polypropylene

Long glass fiber-filled polypropylene (PP) composites are produced by pultrusion, and the extrudate is cut at different lengths producing composites containing long fibers of controlled length. The rheological properties of such composites in the molten state have been studied using different rheometers. A capillary rheometer has been constructed and mounted on a molding-injection machine. The shear viscosity of filled PP determined from the capillary rheometer, after corrections for entrance effects, was found to be very close to that of unfilled PP. However, large excess pressure losses at the capillary entrance were observed and these data have been used to obtain an apparent elongational viscosity. The apparent elongational viscosity was shown to be considerably larger than the shear viscosity for PP and filled PP, and it increased markedly with fiber length and fiber content. Rotational rheometers with a parallel-plate geometry were used to investigate the viscoelastic properties of these composites and their behavior was found to be non-linear, exhibiting a yield stress. A model is proposed to describe the shear viscosity from a solid-like behavior at low stresses to fluid-like behavior at high shear stresses taking into account fiber content and orientation. A modified model, proposed for elongational flow, describes relatively well the apparent elongational data.

High throughput screening for membrane process development

High throughput screening (HTS) is now a powerful tool for a variety of analytical and synthetic methods. The objective of this study was to examine the potential of using high throughput methods to rapidly screen a large number of process variables in the development of effective microfiltration processes. Data were obtained in 96-well plates, syringe filters, unstirred filtration cells, and small cartridge filters. The membrane resistance was very similar in the different formats, except for data obtained in the pleated filter which were influenced by large parasitic pressure losses in the cartridge. The specific resistance of baker’s yeast deposits was evaluated over a range of cake thickness, solution ionic strength, and in the presence or absence of a poly-cationic flocculant. The data obtained in 96-well filter plates were in good agreement with results from the larger filters, demonstrating the scalability of the results. Effective conditions for yeast microfiltration were identified, suggesting that high throughput screening techniques can be a useful tool for process development and optimization.

High throughput screening for membrane process development

High throughput screening (HTS) is now a powerful tool for a variety of analytical and synthetic methods. The objective of this study was to examine the potential of using high throughput methods to rapidly screen a large number of process variables in the development of effective microfiltration processes. Data were obtained in 96-well plates, syringe filters, unstirred filtration cells, and small cartridge filters. The membrane resistance was very similar in the different formats, except for data obtained in the pleated filter which were influenced by large parasitic pressure losses in the cartridge. The specific resistance of baker’s yeast deposits was evaluated over a range of cake thickness, solution ionic strength, and in the presence or absence of a poly-cationic flocculant. The data obtained in 96-well filter plates were in good agreement with results from the larger filters, demonstrating the scalability of the results. Effective conditions for yeast microfiltration were identified, suggesting that high throughput screening techniques can be a useful tool for process development and optimization.

Performance analysis of closed loop in a CCMHD single power generation system

AbstractResults of numerical study on performance of closed loop in the CCMHD single power generation system are presented. The small closed loop with thermal input of 2.3 MW was designed. The fluid‐dynamical and thermal performance of the closed loop was calculated for the first time by one‐dimensional numerical simulation. The result indicates that pressure loss and heat loss are large in the designed small closed loop. The large pressure loss was due to the wall friction or the pebble bed and it occurred at the supersonic nozzle, the MHD channel, and the regenerative heat exchanger used for argon cooling. The enthalpy extraction remained low (= 17.6%) owing to the large pressure loss and as a result, the thermal efficiency of the closed loop remained only 21.6%. The enthalpy extraction and the thermal efficiency became maximal at the optimal inlet total pressure of 0.60 MPa. At inlet total pressure lower than the optimal one, the electric conductivity, the flow velocity, and the electric efficiency became higher. However, the total pressure ratio (= exit/inlet) in the MHD channel became larger particularly at low inlet total pressure because of the increase in the pressure loss due to pebble bed and wall friction. These led to the existence of the optimal inlet total pressure. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(1): 27–38, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10118

A New Tailpipe Design for GE Frame-Type Gas Turbines to Substantially Lower Pressure Losses

Many GE frame gas turbines have a unique 90-deg tailpipe exhaust system that contains struts, diffusers, and turning vanes. As confirmed in a recent report by GE and other authors, it is known in the industry that this tailpipe design has large pressure losses. In this recent report a pressure loss as high as 60 in. of water (0.15 kgs/sqcm) was cited. Due to the flow separations they create, the report indicates that the struts can cause very high-pressure losses in the turbine. The report also states that these pressure losses can vary with different turbine load conditions. Cheng Fluid Systems and Cheng Power Systems have conducted a study aimed at substantially reducing these pressure losses. Flow control technology introduced to the refinery industry, i.e., the Cheng Rotation Vane (CRV) and the Large Angle Diffuser (LAD) can be used to mitigate the flow separation and turbulence that occurs in turns, bends, and large sudden expansions. Specifically the CRV addresses the flow separations in pipe turns, and the LAD addresses the flow problems that occur with large sudden expansion areas. The paper will introduce the past experience of the CRV and LAD, and will then use computer simulations to show the flow characteristics around a new design. First, the study meticulously goes through the entire GE exhaust system, starting with the redesign of the airfoil shape surrounding the struts. This new design has a larger angle of attack and minimizes the flow separations over a much wider operating range. Second, the pros and cons of the concentric turning vanes are studied and it is shown that they are more flow restrictive, rather than flow enhancing. Third, it is shown that the highly turbulent rectangular box-type exhaust ducting design, substantially contributes to high noise levels and pressure losses. In this paper a completed design will be shown that incorporates a new airfoil shape for the struts, and by using CRV flow technology in combination with the LAD flow technology, the pressure recovery can be enhanced. If the pressure losses could be reduced by 40 inches of water (0.10 kgs/sqcm), the turbine efficiency could be increased by 5%, and the power output could be increased by 6%.

Characteristics of Three-Dimensional Flow Field and Velocity Fluctuation Near the Rotor Tip in an Axial Flow Fan. Relation to the Noise Generation.

Three-dimensional vortical flow structures and velocity fluctuation near the rotor tip in an axial flow fan have been investigated by experimental analysis using a rotating hot wire probe and a numerical simulation. Both the experimental and the numerical analysis have been performed in the relative frame of reference rotating with the rotor. It is found that a tip leakage vortex is observed in the blade passage, which has a major role near the rotor tip. The tip leakage vortex formed close to the leading edge of the blade tip on suction side grows in the streamwise direction, and forms a local recirculation region resulting from a vortex breakdown inside the blade passage. It causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and large total pressure loss. High velocity fluctuation is observed in the interference region between the tip leakage vortex and the main flow. Near the casing wall, a discrete frequency is formed between tip leakage vortex center and rotor trailing edge.

フレームホルダ二段化によるラム燃焼器の小型化に関する研究

In order to carry heavier payloads and to fly longer distance, the compact engine is required. The ram combustor with the double-staged flameholders was introduced to shorten the ram combustor which is a major component of the ATR. An additional flamefolder is placed downstream of the conventional (single-staged) one to achieve quick flame expansion in the downstream direction. The ram combustion test was carried out in a 120 deg sector chamber for three cases of flameholder configuration to investigate the various effects on the combustion and aerodynamic performances. The ram combustor with the double-staged flameholders increased the combustion efficiency without large total pressure loss and therefore it was able to shorten 40% axial length of the ram combustor in comparison with the ram combustor with a conventional flameholder. In this study, for the compact ram combustor, the combustion efficiency is greater than 80% on sea level static condition where the air temperature and pressure at the combustor inlet is much lower than that of the supersonic flight condition.

Verification of Turbulence Models for Compressible Turbulent Wall Jets.

If separation occurs in a flow field, it makes a large pressure loss and thus aerodynamic performance is largely reduced. A wall jet (i.e. tangential blowing) is one of control techniques for such a flow field. However, the verification of turbulence models for a wall jet in compressible flow is insufficient. In the present study, we examine the predictive performance of five typical turbulence models (Spalart-Allmaras 1 eq. model, Lam-Bremhorst, Myong-Kasagi and Shimada-Nagano k-ε 2 eq. models and Craft-Launder-Suga k-ε-A2 3 eq. model) for 3 cases of wall jet. In the results, the k-ε models show a relatively good predictive performance and little difference of distributions among the models. On the other hand, Spalart-Allmaras and Craft-Launder-Suga models indicate the inclination to overestimate a separation region.