Pressure Loss Measurements Research Articles

Investigations on heat and momentum transfer in CuO-water nanofluid

AbstractThis paper presents results of investigations on the application of CuO-water nanofluids for intensification of convective heat transfer. Performance of nanofluids with 2.2 and 4.0 vol.% CuO NPs (nanoparticles) content were examined with regard to heat transfer coefficient and pressure losses in case of turbulent flow in a tube. Negligible impact of examined nanofluid on heat transfer improvement was found. Moreover, measured pressure losses significantly exceeded those determined for primary base liquid. The observations showed that application of nanofluid for heat transfer intensification with a relatively high solid load in the examined flow range is rather controversial.

Validation of airway resistance models for predicting pressure loss through anatomically realistic conducting airway replicas of adults and children

This work describes in vitro measurement of the total pressure loss at varying flow rate through anatomically realistic conducting airway replicas of 10 children, 4 to 8 years old, and 5 adults. Experimental results were compared with analytical predictions made using published airway resistance models. For the adult replicas, the model proposed by van Ertbruggen et al. (2005. J. Appl. Physiol. 98, 970–980) most accurately predicted central conducting airway resistance for inspiratory flow rates ranging from 15 to 90L/min. Models proposed by Pedley et al. (1970. J. Respir. Physiol. 9, 371–386) and by Katz et al. (2011. J. Biomech. 44, 1137–1143) also provided reasonable estimates, but with a tendency to over predict measured pressure loss for both models. For child replicas, the Pedley and Katz models both provided good estimation of measured pressure loss at flow rates representative of resting tidal breathing, but under predicted measured values at high inspiratory flow rate (60L/min). The van Ertbruggen model, developed based on flow simulations performed in an adult airway model, tended to under predict measured pressure loss through the child replicas across the range of flow rates studied (2 to 60L/min). These results are intended to provide guidance for selection of analytical pressure loss models for use in predicting airway resistance and ventilation distribution in adults and children.

The Effect of Varying Fiber Characteristics on the Simultaneous Measurement of Heat and Momentum Transfer to Flowing Fiber Suspensions

Heat transfer and pressure loss measurements were obtained simultaneously for a range of wood pulp fiber suspensions flowing in a pipeline. Data were obtained over a selected range of flow rates and temperatures from a specially built flow loop. It was found that the magnitude of the heat transfer coefficient was above water at equivalent experimental conditions and at very low fiber concentrations, but progressively decreased until it was below water at slightly higher concentrations. Similar trends were obtained for the pressure drop measurements obtained simultaneously, showing good correspondence between the two sets of data. It was found that both heat and momentum transfer are affected in a closely similar way by varying fiber properties, such as fiber length, fiber flexibility, fiber chemical and mechanical treatment, the variation of fibers from different parts of the tree, as well as the different pulping methods used to liberate the fibers from the wood structure. Drag reduction increased and heat transfer coefficient decreased with increasing fiber flexibility as found by previous workers.

Heat Transfer and Pressure Loss Measurements of Matrix Cooling Geometries for Gas Turbine Airfoils

Matrix cooling systems are relatively unknown among gas turbines manufacturers of the western world. In comparison to conventional turbulated serpentines or pin–fin geometries, a lattice–matrix structure can potentially provide higher heat transfer enhancement levels with similar overall pressure losses. This experimental investigation provides heat transfer distribution and pressure drop of four different lattice–matrix geometries with crossing angle of 45 deg between ribs. The four geometries are characterized by two different values of rib height, which span from a possible application in the midchord region up to the trailing edge region of a gas turbine airfoil. For each rib height, two different configurations have been studied: one having four entry channels and lower rib thickness (open area 84.5%), one having six entry channels and higher rib thickness (open area 53.5%). Experiments were performed varying the Reynolds number Res, based on the inlet subchannel hydraulic diameter, from 2000 to 12,000. Heat transfer coefficients (HTCs) were measured using steady state tests and applying a regional average method; test models have been divided into 20 stainless steel elements in order to have a Biot number similitude with real conditions. Elements are 10 per side, five in the main flow direction, and two in the tangential one. Metal temperature was measured with embedded thermocouples, and 20 thin-foil heaters were used to provide a constant heat flux during each test. A specific data reduction procedure has been developed so as to take into account the fin effectiveness and the increased heat transfer surface area provided by the ribs. Pressure drops were also evaluated measuring pressure along the test models. Uniform streamwise distributions of Nusselt number Nus have been obtained for each Reynolds number. Measurements show that the heat transfer enhancement level Nus/Nu0 decreases with Reynolds but is always higher than 2. Results have been compared with previous literature data on similar geometries and show a good agreement.

Heat Transfer and Pressure Loss Measurements in a Turbulated High Aspect Ratio Channel With Large Reynolds Number Flows

AbstractExperiments to investigate heat transfer and pressure loss are performed in a rectangular channel with an aspect ratio of 6 at very high Reynolds numbers under compressible flow conditions. Reynolds numbers up to 1.3 × 106 are tested. The presence of a turbulated wall and the resultant heat transfer enhancement against a smooth surface is investigated. Three dimpled configurations including spherical and cylindrical dimples are studied on one wide wall of the channel. The presence of discrete ribs on the same wide wall is also investigated. A steady state heat transfer measurement method is used to obtain the heat transfer coefficients while pressure taps located at several streamwise locations in the channel walls are used to record the static pressures on the surface. Experiments are performed for a wide range of Reynolds numbers from the incompressible (Re = 100,000–500,000; Mach = 0.04–0.19) to compressible flow regimes (Re = 900,000–1,300,000, Mach = 0.35–0.5). Results for low Reynolds numbers are compared to existing heat transfer data available in open literature for similar configurations. Heat transfer enhancement is found to decrease at high Re with the discrete rib configurations providing the best enhancement but highest pressure losses. However, the small spherical dimples show the best thermal performance. Results can be used for the combustor liner back side cooling at high Reynolds number flow conditions. Local measurements using the steady state, hue-detection based liquid crystal technique are also performed in the fully developed region for case 1 with large spherical dimples. Good comparison is obtained between averaged local heat transfer coefficient measurements and from thermocouple measurements.

End Wall Loss Reduction of High Lift Low Pressure Turbine Airfoils Using Profile Contouring—Part II: Validation

The hypothesis, posed in Part I, that excessive end wall loss of high lift low pressure turbine (LPT) airfoils is due to the influence of high stagger angles on the end wall pressure distribution and not front loading is evaluated in a linear cascade at Re = 100,000 using both experimental and computational studies. A nominally high lift and high stagger angle front-loaded profile (L2F) with aspect ratio 3.5 is contoured at the end wall to reduce the stagger angle while maintaining the front loading. The contouring process effectively generates a fillet at the end wall, so the resulting airfoil is referred to as L2F-EF (end wall fillet). Although referred to as a fillet, this profile contouring process is novel in that it is designed to isolate the effect of stagger angle on end wall loss. Total pressure loss measurements downstream of the blade row indicate that the use of the lower stagger angle at the end wall reduces mixed out mass averaged end wall and passage losses approximately 23% and 10%, respectively. This is in good agreement with computational results used to design the contour which predict 18% and 7% loss reductions. The end wall flow field of the L2F and L2F-EF models is measured using stereoscopic particle image velocimetry (PIV) in the passage. These data are used to quantify changes in the end wall flow field due to the contouring. PIV results show that this loss reduction is characterized by reduced inlet boundary layer separation as well as a change in strength and location of the suction side horseshoe vortex (SHV) and passage vortex (PV). The end wall profile contouring also produces a reduction in all terms of the Reynolds stress tensor consistent with a decrease in deformation work and overall flow unsteadiness. These results confirm that the stagger angle has a significant effect on high-lift front-loaded LPT end wall loss. Low stagger profiling is successful in reducing end wall loss by limiting the development and migration of the low momentum fluid associated with the SHV and PV interaction.

Numerical Analysis of Fluid Flow Properties in a Partially Perforated Horizontal Wellbore

The pressure drops in horizontal wellbores, acceleration, wall friction, perforation roughness, and fluid mixing are analyzed in a partially perforated wellbore. It was demonstrated that the perforation inflow actually reduced the total pressure drop. The pressure drop due to perforation roughness was eliminated by the perforation inflow when the ratio of radial perforation flow to axial pipe flow rate reached a certain limit. Three dimensional numerical simulations on a partially perforated pipe with 150 perforations, geometrically similar with wellbore casing (12 SPF, and 60 phasing) were presented and analyzed. Numerical simulations by commercial code CFX were also conducted with Reynolds numbers ranging from 28,773 to 90,153 and influx flow rate ranging from 0 to 899 lit/hr to observe the flow through perforated pipe, measure pressure drops, friction factors and pressure loss coefficients. The acceleration pressure drop might be important compared with the frictional pressure drop. The numerically calculated results using k-ε model were compared with the experimental results. The numerical solutions agreed well with the experimental data.

Heat Transfer in Porous Graphite Foams

Measured values of heat transfer and pressure loss are presented for a variety of porous graphite foams in subsonic turbulent airflow. These foams were developed over the last decade to find combinations of high conductivity, porosity, strength, and low density suitable for application to rapid cooling of electronics and to corrosionless heat-exchangers. Measured maxima in the thermal performance that is the ratio of heat transfer to pressure loss, were correlated the pore structure obtained from scanning electron microscopy, to show a linear dependence of thermal performance on the average diameter of interpore windows representative of the cross-sectional area through which cooling air flows. For the same heat transfer, measured pressure losses were reduced by over two orders of magnitude by increasing pore and window diameters. However, the best thermal performance of porous graphite foams that were strong enough for industrial application, had measured pressure losses that were more than an order of magnitude greater than losses in conventional finned heat exchangers.

Methods for in-situ porosity determination of moving porous columns and application to horizontal slug flow pneumatic conveying

Two methods were developed to investigate the porosity of moving slugs in situ during horizontal slug flow pneumatic conveying. The first method consists in applying a permeability model in combination with measurements of pressure loss and fluid velocity along the slugs. A review of existing models describing the resistance of porous structures to fluid flow revealed that the semi-empirical model of Ergun is particularly suitable to investigate the porosity profile along moving slugs. The second method consists in a direct determination method involving a slug-catcher able to catch a moving slug in a fraction of a second and simultaneously separate it into three horizontal layers. Those two methods were applied to analyse the porosity of naturally occurring slugs during pneumatic transport of polypropylene pellets. It was found that in contrast to common belief, slugs are slightly fluidised structures that do not display any porosity gradient over the pipe cross-section height. The slug porosity appeared independent of the gas conveying velocity, all slugs displaying an average porosity around 0.41, which is slightly higher than the bulk porosity of 0.38. Most of the slugs displayed a rear that is denser than the front. However, some slugs had a front that is denser than the rear while other slugs displayed a relatively constant porosity over the entire length. Those unique results refuting the commonly used hypothesis that slugs are compact structures give a new incentive to the area of slug flow pneumatic conveying. While bulk solids mechanics can no longer be applied to explain the stresses induced by moving slugs, the validity of other theories that imply that slugs are fluidised structures should be investigated.

Impingement Heat Transfer From Jet Arrays on Turbulated Target Walls at Large Reynolds Numbers

Experiments to investigate heat transfer and pressure loss from jet array impingement are performed on the target wall at high Reynolds numbers. Reynolds numbers up to 450,000 are tested. The presence of a turbulated target wall and its effect on heat transfer enhancement against a smooth surface is investigated. Two different jet plate configurations are used with closely spaced holes and with angled as well as normal impingement holes. The test section cross-section is designed to expand along the streamwise direction maintaining the jet plate to target wall distance in order to reduce cross-flow effects. The jet plate holes are chamfered or filleted to minimize pressure loss through the jet plate. Heat transfer and pressure loss measurements are performed on a smooth target wall as well as turbulated target walls. Three turbulators configurations are used with streamwise riblets, short pins, and spherical dimples. A steady-state heat transfer measurement method is used to obtain the heat transfer coefficients while pressure taps located in the plenum and at several streamwise locations are used to record the pressure losses across the jet plate. Experiments are performed for a range of Reynolds numbers from 50,000 to 450,000 based on average jet hole diameters to cover the incompressible as well as compressible flow regimes. A target wall with short pins provides the best heat transfer with the dimpled target wall giving the lowest heat transfer among the three turbulators geometries studied. Addition of turbulators though does not significantly increase the pressure losses in the test section over the smooth target wall.

Study on the Resistance Loss Model of Slurry Pipeline for Iron Ore Concentrate with High Concentration

This paper introduces two models for calculating friction loss in slurry pipeline. Based on the comparison between the measured pressure loss of the highly concentrated iron ore concentrate slurry pipeline in Dahongshan, Yunnan Province, CHINA and the calculation outcomes of the two models, the model which can predict pressure loss in this kind of slurry pipelines has been found.

Study on the Resistance Loss Model of Slurry Pipeline for Iron Ore Concentrate with High Concentration

This paper introduces two models for calculating friction loss in slurry pipeline. Based on the comparison between the measured pressure loss of the highly concentrated iron ore concentrate slurry pipeline in Dahongshan, Yunnan Province, CHINA and the calculation outcomes of the two models, the model which can predict pressure loss in this kind of slurry pipelines has been found.

A Simple Model for Two-Phase Flow in Liquid-Cut Gas Wells

This paper presents a simple two-phase flow model for liquid-cut gas wells, which considers phase slippage and can be applied to various flow patterns. The model is developed from 312 measured pressure losses of gas wells in China, covering a wide range of flow patterns: annular flow, churn flow, and slug flow. Unlike most available methods, this new model introduces a derivation factor, ψ, to modify the void fraction, which not only considers the phase slippage but also unifies the slip model with the homogenous model. Parameter, ψ, is obtained from test data using the regression analyses method. It is a function of gas velocity number, liquid velocity number and liquid viscosity number. Frictional factor is estimated using the simple homogeneous modeling approach. The evaluation results using 145 published data indicate that the new model performed better than the other models.

Flow of Newtonian and non-Newtonian fluids in a concentric annulus with a rotating inner cylinder

We examine the characteristics of helical flow in a concentric annulus with radii ratios of 0.52 and 0.9, whose outer cylinder is stationary and inner cylinder is rotating. Pressure losses and skin friction coefficients are measured for fully developed flows of water and a 0.4% aqueous solution of sodium carboxymethyl cellulose (CMC), when the inner cylinder rotates at the speed of 0∼62.82 rad/s. The transitional flow has been examined by the measurement of pressure losses to reveal the relation between the Reynolds and Rossby numbers and the skin friction coefficients. The effect of rotation on the skin friction coefficient is largely changed in accordance with the axial fluid flow, from laminar to turbulent flow. In all flow regimes, the skin friction coefficient increases due to inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, becomes smaller as the Reynolds number increases for the transitional flow regime, and gradually approaches zero for the turbulent flow regime. The value of skin friction coefficient for a radii ratio of 0.52 is about two times larger than for a radii ratio of 0.9. For 0.4% CMC solution, the value of skin friction coefficient for a radii ratio of 0.52 is about four times larger than for a radii ratio of 0.9.

Performance analysis of a new design of office diffuse ceiling ventilation system

This paper aims to document and analyse performance of a new design of diffuse ceiling ventilation system in a typical office room. A full scale measurement is carried out in a climate chamber with an office setup at the Technical University of Denmark. Indoor air temperatures, air speeds, wall surface temperatures, pressure loss of the ceiling and ventilation effectiveness are measured for an air change rate of 3.5h−1 and 5.1h−1 respectively. A computational fluid dynamics model of the office with the diffuse ceiling ventilation system is built and validated by the full scale measurement. The measurements of pressure loss across the ceiling show a low pressure drop between the plenum and the occupied zone. Ventilation effectiveness is measured to be close to 1 on average under the tested conditions. It is shown that the diffuse ceiling ventilation system is able to remove indoor pollutant in an efficient way. The draught risk is found to be insignificant by both experimental and theoretical investigations. A design chart based on “flow element” method is created for the diffuse ceiling ventilation system by calculations with the validated CFD model. The design chart serves as a guideline for design and dimension of the investigated diffuse ceiling terminals as an air distribution system.

Enhancement and Long-Term Testing of Optimised Post-Combustion Capture Technology –Results of the Second Phase of the Testing Programme at the Niederaussem Pilot Plant

In phase I of their joint development programme BASF, Linde and RWE Power have successfully tested an innovative post-combustion capture technology at the pilot plant in Niederaussem – commercialised under the trade mark “OASE® blue” by BASF – with a specific energy demand of 2.8 GJ/tCO2 and a solvent consumption of around 300g/tCO2. In April 2011, phase II of the project has started, which will run until the end of 2013. Corrosivity, long- term stability of the scrubbing agent and its impact on emissions and the need for reclaiming are being investigated in a long-term trial. At the beginning of phase II, the pilot plant was modified in order to test two optimisation measures. Firstly, a new high-performance structured packing was installed, aiming at a reduction in the absorber's cross- sectional area by more than 35%. Pressure loss measurements and parameter studies were carried out to assess the performance of the new packing. Secondly, an additional washing section was installed at the top of the absorber. Owing to the fact that standards for measuring emissions of large-scale capture plants are not finally defined yet, different process configurations for emission reduction are being tested and optimised. This paper summarises the achievements of the testing programme and presents the results of the performance tests for the new structured packing and operational experience regarding emission reduction.

Pressure Losses across Multiple Fittings in Ventilation Ducts

The accurate prediction of pressure losses across in-duct fittings is of significance in relation to the accurate sizing and good energy efficiency of air-delivery systems. Current design guides provide design methods and data for the prediction of pressure losses only for a single and isolated fitting. This study presents an investigation of pressure losses across multiple interactive in-duct fittings in a ventilation duct. A laboratory measurement of pressure losses across one fitting and multiple fittings in a ventilation duct is carried out. The pressure loss across multiple interactive fittings is lower than that across multiple similar individual fittings, while the percentage decrease is dependent on the configuration and combination of the fittings. This implies that the pressure loss across multiple closely mounted fittings calculated by summing the pressure losses across individual fittings, as provided in the ASHRAE handbook and the CIBSE guide, is overpredicted. The numerical prediction of the pressure losses across multiple fittings using the large-eddy simulation (LES) model shows good agreement with the measured data, suggesting that this model is a useful tool in ductwork design and can help to save experimental resources and improve experimental accuracy and reliability.

Effect of Trailing Ramp Angles in Strut-Based Injection in Supersonic Flow

Experimental and numerical studies are conducted on supersonic mixing of air injected from struts of various trailing ramp angles with freestream air at Mach number 1.63. By providing an alternate trailing ramp on the strut, streamwise vortices in spanwise row configuration are generated. In the present study, various alternate trailing ramp struts were examined and their capability to enhance supersonic mixing was evaluated. Numerical simulation of the flow field with struts of various trailing ramp angles such as 2.86, 5.71, 8.53, 11.31, 14.04, 18.43, and 26.57 deg is also carried out. From the numerical results, it is seen that mixing enhancement is better only for the strut with a 14.04 deg ramp angle compared with a plain strut. Three types of struts are considered for the current experimental investigation: plain strut, two relieved ramp struts 2RRS-14.04 deg, and three relieved ramp struts 3RRS-14.04 deg. Diagnostic methods employed are Mie scattering combined with image processing, time-averaged schlieren and time-resolved high-speed shadowgraph images, velocity measurement using laser Doppler velocimetry, and total pressure loss measurements. Numerical simulation of the flowfield is performed using the commercially available software Fluent.

Pressure drop and void fraction during flow boiling in rectangular minichannels in weightlessness

An experimental investigation has been carried out on flow boiling in a minichannel to explain heat transfer enhancement observed experimentally under the conditions of weightlessness. The analysis is based on the local void fraction and frictional pressure loss measurements. Frictional pressure loss in two-phase flows in minichannels under terrestrial gravity is described by several well-known correlations. In weightlessness, however, few experimental results are available on the void fraction and the frictional pressure loss. The experiments for this study have been performed at constant heat flux supplied to the minichannel with inlet liquid mass velocity ranging between 30 and 248 kg s−1 m−2. The influence of hypergravity (gravity level of 1.8g) and microgravity (gravity level of ±0.05g) on the frictional pressure loss is observed and explained using the flow patterns visualization and experimental void fraction determination through image treatment. Pressure drops for two-phase flow in microgravity are found to be significantly higher than for single-phase flow under similar conditions; possible explanations for the difference are discussed. The experimental thermal measurements have been previously analyzed using inverse techniques which led to evaluation of the local heat transfer coefficient. The heat transfer enhancement observed during weightlessness is explained in the present work by investigating the differences in flow patterns and void fraction under different levels of gravity.

A Static Pressure Reset Control System with a New Type of Flow Damper for Use in Low Pressure Ventilation Systems

The control strategy for mechanical ventilation systems has significant impact on the performance of the system, in terms of energy consumption and correct air distribution. This paper presents a static pressure reset control system employing a new type of flow damper with lower pressure loss for use in low pressure ventilation systems. The flow damper has a droplet shape that minimizes turbulence generation and the resulting pressure loss. The performance of the damper was examined by making measurements of pressure loss and airflow. These were used to determine the required pressure loss for operation and the airflow accuracy. Results were compared to similar tests carried out with conventional flat plate dampers. A static pressure reset control algorithm was programmed and analyzed on a test system consisting of three dampers, representing three office rooms. The comparison of the dampers shows that the droplet shaped damper resulted in an airflow of 234 L/s at 30 Pa pressure loss, more than twice the airflow past a flat-plate damper at the same pressure loss (114 L/s). Also the droplet shaped damper could operate precisely down to 5 Pa pressure loss. The programmed control algorithm ensured that one damper was always fully opened, based on the flow demand to the zone, and that this reduces the static pressure loss under partial load by up to 53%. However, as the maximum static pressure during the tests was 15 Pa, the reduction was only 8 Pa, so it was not possible to document any significant fan power saving compared to a fixed static pressure control. A maximum static pressure of 15 Pa is a reduction of more than 50% compared to flat-plate dampers that required at least 30 Pa to operate precisely; this is expected to yield fan energy savings in practice.