Pressure Loss Model Research Articles

Advanced Rayleigh Pressure Loss Model for High-Swirl Combustion in a Rotating Combustion Chamber

This paper considers the effect of excessive total pressure losses for heat transfer problems in fluid flows with a high circumferential swirl component. At RWTH Aachen University, a novel gas generator concept is under research. This design avoids some disadvantages of small gas turbines and uses a rotating combustion chamber. During the predesign of the rotating combustion chamber using computational fluid dynamics (CFD) tools, unexpected high total pressure losses were detected. To analyze this unknown phenomenon, a gas–dynamic model of the rotating combustion chamber has been developed to explain the unexpected high Rayleigh pressure losses. The derivation of the gas–dynamic model, the physical phenomenon related to the high total pressure losses in high-swirl combustion, the influencing factors, as well as thermodynamic interpretation of the Rayleigh pressure losses, are presented in this paper. In addition, the CFD results are validated by the gas–dynamic model derived. The results presented here are of possible interest for a wide range of applications, since these fundamental findings can be transferred to all heat transfer problems in fluid flows with a high circumferential swirl component.

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.

Cuttings-liquid frictional pressure loss model for horizontal narrow annular flow with rotating drillpipe

During oil and gas drilling operations, frictional pressure loss is experienced as the drilling fluid transports the drilled cuttings from the bottom-hole, through the annulus, to the surface. Estimation of these pressure losses is critical when designing the drilling hydraulic program. Two-phase frictional pressure loss in the annulus is very difficult to predict, and even more complex when there is drillpipe rotation. Accurate prediction will ensure that the correct equivalent circulating density (ECD) is applied in the wellbore to prevent formation fracture, especially in formations with narrow window between the pore pressure and fracture gradient. Few researchers have attempted to propose cuttings-liquid frictional pressure loss models, nevertheless, these models fail when they are applied to narrow wellbores such as in casing- while-drilling and slimhole applications. This study proposes improved cuttings-liquid frictional pressure loss models for narrow horizontal annuli with drillpipe rotation using Dimensional Analysis. Both Newtonian and non-Newtonian fluids were considered. The proposed model constants were fitted by generated data from a full-scale simulation study using ANSYS-CFX. The models showed improvement over existing cuttings-liquid pressure loss correlations in literature.

Mathematical Modeling of Dual Intake Transparent Transpired Solar Collector

Nowadays, in several types of commercial or institutional buildings, a significant rise of transpired solar collectors used to preheat the fresh air of the building can be observed. Nevertheless, when the air mass flow rate is low, the collector efficiency collapses and a large amount of energy remains unused. This paper presents a simple yet effective mathematical model of a transparent transpired solar collector (TTC) with dual intake in order to remove stagnation problems in the plenum and ensure a better thermal efficiency and more heat recovery. A thermal model and a pressure loss model were developed. Then, the combined model was validated with experimental data from the Solar Rating and Certification Corporation (SRCC). The results show that the collector efficiency can be up to 70% and even 80% regardless of operating conditions. The temperature gain is able to reach 20°K when the solar irradiation is high.

地下駅構内の列車風による冷房負荷推定に関する研究

The actual cooling load of underground stations in recent years has been much lower than the designed load thirty years ago. Therefore, it is important to estimate the actual load in the planning of cooling systems. In this study, the cooling load caused by train wind in an underground station was discussed and a field measurement and computational fluid dynamics (CFD) simulation were conducted. The main conclusions are as follows: (1) The measurement showed that air volume of the train wind was greatly affected by the train speed and the tunnel structure (single or double track). (2) In the CFD simulation, the train was modeled as a moving body to simulate train wind. The CFD simulation with a pressure loss model in the tunnel could reproduce the measurement. (3) The influence of train wind on the platform cooling system was examined by the CFD simulation in terms of an influence coefficient. In the Shin-Nihombashi station, the influence coefficient was approximately 0.38 in the area connecting to the tunnel while the coefficient was about 0.24 in the center area.

Modified pressure loss model for T-junctions of engine exhaust manifold

The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have focused on constant pressure models, constant static pressure models and pressure loss models. However, low model precision is a common disadvantage when simulating engine exhaust manifolds, particularly for turbocharged systems. To study the performance of junction flow, a cold wind tunnel experiment with high velocities at the junction of a diesel exhaust manifold is performed, and the variation in the pressure loss in the T-junction under different flow conditions is obtained. Despite the trend of the calculated total pressure loss coefficient, which is obtained by using the original pressure loss model and is the same as that obtained from the experimental results, large differences exist between the calculated and experimental values. Furthermore, the deviation becomes larger as the flow velocity increases. By improving the Vazsonyi formula considering the flow velocity and introducing the distribution function, a modified pressure loss model is established, which is suitable for a higher velocity range. Then, the new model is adopted to solve one-dimensional, unsteady flow in a D6114 turbocharged diesel engine. The calculated values are compared with the measured data, and the result shows that the simulation accuracy of the pressure wave before the turbine is improved by 4.3% with the modified pressure loss model because gas compressibility is considered when the flow velocities are high. The research results provide valuable information for further junction flow research, particularly the correction of the boundary condition in one-dimensional simulation models.

Inhalation pressure distributions for medical gas mixtures calculated in an infant airway morphology model

A numerical pressure loss model previously used for adult human airways has been modified to simulate the inhalation pressure distribution in a healthy 9-month-old infant lung morphology model. Pressure distributions are calculated for air as well as helium and xenon mixtures with oxygen to investigate the effects of gas density and viscosity variations for this age group. The results indicate that there are significant pressure losses in infant extrathoracic airways due to inertial effects leading to much higher pressures to drive nominal flows in the infant airway model than for an adult airway model. For example, the pressure drop through the nasopharynx model of the infant is much greater than that for the nasopharynx model of the adult; that is, for the adult-versus-child the pressure differences are 0.08 cm H2O versus 0.4 cm H2O, 0.16 cm H2O versus 1.9 cm H2O and 0.4 cm H2O versus 7.7 cm H2O, breathing helium–oxygen (78/22%), nitrogen–oxygen (78/22%) and xenon–oxygen (60/40%), respectively. Within the healthy lung, viscous losses are of the same order for the three gas mixtures, so the differences in pressure distribution are relatively small.

Annular Frictional Pressure Losses During Drilling—Predicting the Effect of Drillstring Rotation

Controlling the annular frictional pressure losses is important in order to drill safely with overpressure without fracturing the formation. To predict these pressure losses, however, is not straightforward. First of all, the pressure losses depend on the annulus eccentricity. Moving the drillstring to the wall generates a wider flow channel in part of the annulus which reduces the frictional pressure losses significantly. The drillstring motion itself also affects the pressure loss significantly. The drillstring rotation, even for fairly small rotation rates, creates unstable flow and sometimes turbulence in the annulus even without axial flow. Transversal motion of the drillstring creates vortices that destabilize the flow. Consequently, the annular frictional pressure loss is increased even though the drilling fluid becomes thinner because of added shear rate. Naturally, the rheological properties of the drilling fluid play an important role. These rheological properties include more properties than the viscosity as measured by API procedures. It is impossible to use the same frictional pressure loss model for water based and oil based drilling fluids even if their viscosity profile is equal because of the different ways these fluids build viscosity. Water based drilling fluids are normally constructed as a polymer solution while the oil based are combinations of emulsions and dispersions. Furthermore, within both water based and oil based drilling fluids there are functional differences. These differences may be sufficiently large to require different models for two water based drilling fluids built with different types of polymers. In addition to these phenomena washouts and tool joints will create localised pressure losses. These localised pressure losses will again be coupled with the rheological properties of the drilling fluids. In this paper, all the above mentioned phenomena and their consequences for annular pressure losses will be discussed in detail. North Sea field data is used as an example. It is not straightforward to build general annular pressure loss models. This argument is based on flow stability analysis and the consequences of using drilling fluids with different rheological properties. These different rheological properties include shear dependent viscosity, elongational viscosity and other viscoelastic properties.

재생형 송풍기의 공력음향학적 성능 해석 방법

An aero-acoustic performance analysis method of regenerative blower is developed as one of the FANDAS codes. The aerodynamic performance of regenerative blower is predicted by using momentum exchange theory coupled with pressure loss and leakage flow models. Based on the performance prediction results, the noise level and spectrum of regenerative blower are predicted by discrete frequency and broadband noise models. The combination of the performance and the noise prediction methods gives aero-acoustic performance map and noise spectrum analysis results, which are well-agreed with the actual measurement results within a few percent relative error.

2018 1次元熱流路網解析を用いた相変化冷却装置の性能予測手法

In this paper, we propose a ID thermal-fluid network model of phase change cooling device and show how we can estimate the cooling performance of the device by calculating its maximum heat transfer based on the ID simulation. Our calculation is achieved based on Loop heat pipe (LHP) which is a typical model of phase change cooling device. Since evaporator wick and condenser are indispensable components of LHP for determining its cooling performance, we devise a new pressure loss model of wick and a new thermal conductance model of condenser fins. The proposed pressure loss model of wick can simulate how wick dries out accurately by introducing a wick pore inactivation equation to the wick permeability model which was proposed by Blake-Kozeny. For the condenser model, in order to simulate heat radiation of condenser fins, thermal conductance of condenser is defined as a function of temperature difference between working fluid and ambient air. By applying the LHP cooling devise to a server system, we show that the proposed ID model of the LHP cooling system predicts a precise cooling performance by calculating its maximum heat transfer in 3% error compared with the experimental value.

Study on Particulate Accumulated Characteristics of Diesel Particulate Filter

The paper has carried out numerical simulation and experimental study on the pressure loss of filter. Based on pressure loss model of filter, research methods of particulate accumulated characteristics has proposed according to the exhaust flow, exhaust temperature and exhaust back pressure. Meanwhile, the model is important for the online calculation of accumulated particulate matters in the filters and failure monitoring of diesel particulate filter.

The development of natural circulation operation support program for ship nuclear power machinery

The existing simulation program of ship nuclear power machinery (SNPM) cannot adequately deal with the natural circulation (NC) operation and the effects of various ocean conditions and ship motion. Aiming at the problem, the natural circulation operation support computer program for SNPM is developed, in which the momentum conservation equation of the primary loop, some heat transfer and flow resistance models and equations are modified for the various ocean conditions and ship motion. The additional pressure loss model and effective height model for the control volume in the gyration movement, simple harmonic rolling and pitching movements are also discussed in the paper. Furthermore, the transient response to load change under NC conditions is analyzed by the developed program. The results are compared with those predicted by the modified RELAP5/mod3.2 code. It is shown that the natural circulation operation support program (NCOSP) is simple in the input preparation, runs fast and has a satisfactory precision, and is therefore very suitable for the operating field support of SNPM under the conditions of NC.

Combustion Engine Air Intake Theoretical Modelling, Model-Verfication & Application to Optimal Valve Actuation

AbstractA theoretical model for the air intake of a four stroke internal combustion engine is derived from first principles, the conservation of mass and the conservation of energy. Full valve actuation is taken into account: The opening angle of both the intake as well as the exhaust valve, as well as the variable valve lift are considered as plant inputs, which may be manipulated to maximize the air intake rate and hence the power, the engine delivers. The theoretical model is verified by comparing the model output to steady state data collected at an engine test bench. Therefor a formal connection between state-of-the-art mean value models and the crank angle resolved physical model must be established. The pressure loss in the intake valve is considered a disturbance of the ideal cylinder filling dynamics, which is estimated using non-linear optimization techniques. The intended purpose of physical model building for the cylinder air intake is prediction of the air intake rate and computation of optimal valve control action before a lot of effort is put into a real experiment at the engine test bench. A significant reduction of operating time and cost consumed by the real engine test bench can be achieved, if a small subset of steady state measurements are used to compute a meta-model for the pressure loss. The combination of the black-box pressure loss model and the air intake model allows for prediction of the air intake rate at unknown operating points of the engine with sufficient accuracy.

Experimental study and modeling of pressure loss for foam-cuttings mixture flow in horizontal pipe

In this study, we first sought to elucidate foam rheology to describe foam flow behavior, and then to experimentally investigate the pressure losses for both foam and foam-cuttings flow in a horizontal pipe by considering both varied foam qualities of 80%, 85% and 90% and foam velocities. Also, a two-layer numerical model to predict pressure loss was developed based on experimental observations of cuttings behavior. Results show that the foam behaves like a power-law fluid. Furthermore, and the pressure loss significantly increases as foam velocity increases, while the delivered cuttings concentration dramatically decreases. Moreover, results indicate that both the pressure loss and the delivered cuttings concentration increase with foam quality. Comparisons between the experimental results and numerical model predictions show satisfactory agreement.

An improved streamline curvature approach for transonic axial compressor performance prediction

An improved streamline curvature (SLC) throughflow analysis method is presented based on the predecessor's works to simulate the flow fields of a certain transonic axial compressor. The improvements of this method are embodied centrally in minimum loss incidence angle (MIA) model and total pressure loss (TPL) model that ensure accurate and reliable performance prediction at both design and off-design conditions. The improved MIA is set up as a function of inlet Mach number, solidity, thickness, camber angle, etc. according to low-speed minimum incidence angle. Therefore, TPL is divided into two parts, the first one is the minimum loss which considers the revise of Mach number and Reynolds number, and the second one is the additional loss when real incidence angle deviates from MIA. Finally, the internal flow field of a single-stage compressor is simulated. The characteristic curves and spanwise aerodynamic parameters distribution at design and off-design points are illustrated in this article. Compared to the experiment and computational fluid dynamics (CFD) data, this improved SLC method gives reasonable performance trends and generally accurate results, also the MIA and TPL models are demonstrated in this article.

Modeling of pressure losses for the slug flow of a gas–liquid mixture in mini- and microchannels

In addition to the previously constructed model of the hydrodynamics of a gas-liquid slug flow, a mathematical model is developed that describes pressure losses taking into account the rearrangement of a velocity profile in liquid slugs and energy losses on the formation and renewal of interfacial area during the motion of bubbles. The contribution of different forms of pressure losses in capillaries is analyzed. It is shown that in microchannels tangential stresses on the surface of a bubble substantially affect the total pressure losses. It is found that the length of bubbles does not affect the rate of surface formation and respective pressure losses if bubbles have the same velocity. The results of modeling are in satisfactory agreement with experimental data of other researchers.

A model for pressure loss, film thickness, and entrained fraction for gas–liquid annular flow

A two-component (air–water) annular flow model is presented requiring only flow rates, absolute pressure, temperature, and tube diameter. Film thicknesses (base film and wave height) are calculated from a critical film thickness model. Modeled pressure gradient is weighted by wave intermittency to compute average pressure gradient. Film flow rate and wave velocity are estimated using the universal velocity profile in the waves and a piecewise linear profile in the base film. For vertical flow, mean absolute errors for film thickness, wave velocity, and pressure gradient are 9%, 9%, and 19%, respectively. In horizontal flow, mean absolute errors for pressure gradient, base film thickness, and disturbance wave velocity are 17%, 10%, and 14%, respectively, on par with those from single-behavior models that require additional film thickness or other data as inputs.

Design of the Speed Regulating PIG with Butterfly Bypass-Valve

Foreign development regarding devices for speed regulating of in-pipe robot inspection has been commercially applied in gas pipeline this decade, however, the results of theoretical and structural research on bypass device were scaled in and abroad after the research of literature. First, this paper deals with the new structure of a butterfly bypass-valve, the basic parts and working principle on this speed regulating unit. The using of a butterfly disc in bypass-hole of PIG (pipeline inspection gauge) can achieve a speed regulating purpose in bypass-PIG. Next, the theoretical model of pressure loss and regulating feasibility or ability of PIG are introduced by the similar mathematical model with a throttle valve. Finally, give the conclusion.

Experimental studies of adiabatic flow boiling in fractal-like branching microchannels

Experimental results of adiabatic boiling of water flowing through a fractal-like branching microchannel network are presented and compared to numerical model simulations. The goal is to assess the ability of current pressure loss models applied to a bifurcating flow geometry. The fractal-like branching channel network is based on channel length and width ratios between adjacent branching levels of 2 −1/2. There are four branching sections for a total flow length of 18 mm, a channel height of 150 μm and a terminal channel width of 100 μm. The channels were Deep Reactive Ion Etched (DRIE) into a silicon disk. A Pyrex disk was anodically bonded to the silicon to form the channel top to allow visualization of the flow within the channels. The flow rates ranged from 100 to 225 g/min and the inlet subcooling levels varied from 0.5 to 6 °C. Pressure drop along the flow network and time averaged void fraction in each branching level were measured for each of the test conditions. The measured pressure drop ranged from 20 to 90 kPa, and the measured void fraction ranged from 0.3 to 0.9. The measured pressure drop results agree well with separated flow model predictions accounting for the varying flow geometry. The measured void fraction results followed the same trends as the model; however, the scatter in the experimental results is rather large.

Hydraulics of Drilling With Aerated Muds Under Simulated Borehole Conditions

Maintaining optimum circulation rates is important in aerated mud drilling operations. However, reliable predictions of the optimum rates require accurate modeling of the frictional pressure loss at bottom-hole conditions. This paper presents a mechanistic model for underbalanced drilling with aerated muds. Extensive experiments in a unique field-scale high pressure and high temperature flow loop were performed to verify the predictions of the model. This flow loop has a 150×89 mm2(6″×3.5″) horizontal annular geometry and is 22 m long. In the experiments, cuttings were introduced at a rate of 7.5 kg/min, representing a penetration rate of 15 m/h in the annular test section. The liquid phase flow rates were in the range of 0.30–0.57 m3/min, representing superficial liquid velocities in the range of 0.47–0.90 m/s. The gas liquid ratio (gas volume fraction under in situ condition) was varied from 0.0 to 0.38. Test pressures and temperatures ranged from 1.28 to 3.45 MPa, and 27°C to 80°C, respectively. Gas liquid ratios were chosen to simulate practical gas liquid ratios under downhole conditions. For all the test runs, pressure drop and cuttings bed height over the entire annular section were measured. Flow patterns were identified by visual observations through a view port. The hydraulic model determines the flow pattern and predicts frictional pressure losses in a horizontal concentric annulus. The influences of the gas liquid ratio and other flow parameters on the frictional pressure loss are analyzed using this model. Comparisons between the model predictions and experimental measurements show a satisfactory agreement. The present model is useful for the design of underbalanced drilling applications in a horizontal wellbore.