Pressure Loss Characteristics Research Articles

Numerical investigation on the heat transfer and pressure loss characteristics of precooler under negative pressure

Precoolers have garnered considerable attention owing to their applications in aerospace and industrial fields. Nonetheless, there is a paucity of research concerning the performance of precoolers under conditions of extremely low pressure. This study conducts a numerical analysis of the heat transfer and pressure loss characteristics of a plate-fin precooler operating under negative pressure, considering the coupled heat transfer interactions among the hot fluid, solid wall, and cooling fluid. The comprehensive performance and flow field on each side of the precooler are investigated. Moreover, the impact of negative pressure on the heat transfer and pressure recovery performance of the hot fluid in the rectangle channel is evaluated. The results show that, even under operating conditions with pressures below 30 kPa and inlet temperatures exceeding 1100 K, the precooler attains a pressure recovery coefficient greater than 95.6 % and achieves a temperature drop exceeding 43.2 % for the hot fluid as the mass flow rate ranges from 0.205 kg/s to 0.564 kg/s. Additionally, the heat transfer coefficient of the hot fluid is less than 1/40 that of the cooling fluid, resulting in increased thermal resistance between the hot fluid and the wall. Consequently, a distinct thermal boundary layer develops between the hot fluid and the wall, which is not present between the cooling fluid and the wall. Furthermore, the performance of heat transfer and pressure recovery for the hot fluid exhibits considerable variability with changes in static pressure at a constant inlet velocity. However, a turning point is observed when these parameters are evaluated in terms of the inlet Reynolds number. At low Reynolds numbers, both the heat transfer coefficient and the friction factor remain relatively stable, notwithstanding fluctuations in static pressure. Conversely, at higher Reynolds numbers, a reduction in static pressure negatively influences these factors. For instance, when the static pressure is 10 kPa, the associated Reynolds number is 500. Nevertheless, the Reynolds number at which this turning point occurs escalates with an increase in static pressure.

Nusselt Number and Friction Factor Characteristics of Two Pass Solar Air Collector Provided with Double Sided Roughened Absorber Plate

Thermal efficiency of flat collector surface solar air heater (SAH) is relatively poor due to poor heat transfer coefficient. This article’s primary objective is to evaluate the heat transfer and pressure loss characteristics of counter flow SAH (CFSAH) by adopting novel discrete multi-V-shaped and staggered rib geometry. The experimentations are performed for various flow Reynolds number (Re) ranging from 3000- 21000 and rib parameters including relative gap distance (Gd /Lv) from 0.24 -0.69 and relative gap width (g/e) from 0.5-1.5 while other parameters are kept as constant. The study revealed that the maximum increment in heat transfer as 4.52 times and friction factor as 3.13 times as compared to non-roughened duct has been obtained. Further, the thermohydraulic performance parameter (TPP) has also been investigated to obtain the optimum parameters. The minimum and maximum value of TPP has been achieved as 1.94 and 3.88 corresponding to Re=2000 and Re=16000 respectively. Therefore, the present work can be fruitful for heating and drying application

Numerical simulation of pressure loss and flow characteristics in combined elbow pipes for solid-liquid two-phase flow.

The transport of solid-liquid two-phase flow is widely used in water conservancy, environmental protection, and municipal engineering. Accurate pressure loss calculation is crucial for hydraulic transport pipelines, particularly in the case of bends, valves, and other deformation parts. These factors directly impact the energy consumption and the investment of the system. This paper employed the Euler-Euler multiphase flow model to investigate the characteristics of solid-liquid two-phase flow in vertically positioned combined elbows. The model was initially validated using data from the literature. Subsequently, based on the validated model, an investigation was conducted to determine the relationship between pressure loss and various factors, including flow velocity, combined angle, particle concentration, and particle size. Finally, the changes in velocity distribution, particle concentration, and turbulent kinetic energy were analyzed. The results indicate that the pressure loss increases with the flow velocity, tends to decrease with the combined angle, and increases with the particle concentration. The relationship between pressure loss and particle size is more complex. The velocity distribution, particle concentration, and turbulent kinetic energy exhibit the variations caused by different factors.

Comparison of experimental, empirical, and CFD pressure losses of lab-scale sampling cyclones

Significant efforts remain to be undertaken to achieve efficient separation of particulate matter. Devices widely used for this purpose are cyclone separators. This study investigates the pressure loss phenomena and flow structures within cyclone devices, aiming to elaborate and optimize their performance. Traditional cyclone models: (i) Muschelknautz, (ii) Stairmand, and (iii) PM1 Sharp Cut, are evaluated alongside the innovative vortex limiter cyclone (VL) to distinguish their advantages and limitations. The focus is on describing the relation between pressure loss and flow characteristics of the different cyclones with the same design separation diameter of 1μm. Empirical pressure loss correlations analyze how pressure losses vary within different cyclone devices. It was proven that predictions depend on cyclone size and operational parameters. Computational Fluid Dynamics (CFD) simulations further elucidate pressure loss mechanisms, highlighting the complexities inherent in modeling cyclonic behavior accurately. In conclusion, this study contributes to advancing the understanding of cyclone performance by elucidating the intricate interplay between pressure loss phenomena and flow structures. Such insights hold profound indications for optimizing cyclone separator design and operation in diverse industrial applications.

Experimental Investigation on Pressure Drops of Purge Gas Helium in Packed Pebble Beds for Nuclear Fusion Blanket

The flow characteristics of purge gas helium in the pebble bed of the tritium breeding blanket are important in analyzing the tritium purging process and optimizing the design of the solid breeder blanket. Therefore, the flow characteristics of helium gas in randomly packed pebble beds are investigated experimentally with a focus on the analysis of the pressure loss distribution. The results show that gas velocity, bed dimension, and pebble diameters have an obvious influence on the helium flow characteristics in pebble beds. With the increase in the inlet helium gas velocity, the pressure drop gradient of helium in the pebble bed gradually increased. With increases in the pebble bed dimension, the pressure drop gradient of helium in the pebble bed gradually increased. With the increase in the pebble diameter, the pressure drop gradient gradually decreased. In addition, the effect of temperature on the pressure drop of helium in the pebble bed was also preliminarily investigated. The pressure drop gradient of the helium through the pebble bed obviously increased with the increase in the helium and the bed temperature. The experimentally obtained pressure loss characteristics can be used for the validation of the simulation of a blanket pebble bed and as input parameters in the thermo-hydraulic analysis of solid-tritium breeder blankets.

Study of heat and mass transfer in a channel with fins based on a triply periodic minimal surface

Presents a methodology for studying heat and mass transfer in the channels of heat exchange devices, where fins made in the form of a Schwarz Primitive triply periodic minimal surface (TPMS) are used to intensify heat transfer. The solution of the heat and mass transfer problem is carried out using the finite element method in the Fluent module of the ANSYS software package. The work examines the influence of the initial flow velocity, as well as the thickness of the TPMS fins on the pressure loss and temperature characteristics of the flow. The study showed that TPMS fins enhance heat transfer and create turbulent flows in close to the TPMS frame. The pressure loss in the channel increases according to a power law with increasing initial flow velocity. The results obtained in this study demonstrate the potential of using TPMS in heat exchange devices and open many prospects for further research.

EXPERIMENTAL INVESTIGATION ON HEAT TRANSFER AND PRESSURE LOSS CHARACTERISTICS OF THE GROOVED HELICALLY COILED TUBE HEAT EXCHANGER

Helically coiled tube heat exchangers have long been a subject of intense research due to their compact structure and efficient heat transfer capabilities. To further augment their performance, this study proposes a grooved helically coiled tube heat exchanger and establishes an experimental platform for a comparative analysis against a conventional helically coiled tube heat exchanger. Through the utilization of water and steam as working fluids, a comprehensive series of experiments was conducted to investigate heat transfer and pressure drop characteristics. Applying the Wilson plot method, heat transfer coefficients were computed for both the tube and shell sides. The experimental results demonstrate that the maximum relative error of tube-side pressure drop in comparison with empirical correlations does not exceed 24%, while the average error for the tube-side heat transfer coefficient is approximately 13%. Moreover, heat transfer coefficients on the shell side can increase by up to 69%, albeit with a significant rise in pressure drop, reaching up to 96%. By employing heat exchanger effectiveness as a comprehensive criterion, the grooved helically coiled tube heat exchanger's effectiveness can increase by up to 23%. These outcomes suggest that the external grooves can effectively amplify the heat transfer efficiency of helically coiled tube heat exchangers.

Machine learning-assisted high precision predictive modelling of convective heat transfer in fluid channels fabricated by laser powder bed fusion

Laser powder bed fusion (LPBF) has proven to be an effective tool in fabricating heat transfer devices with improved efficiency. However, the accurate prediction of convective heat transfer in LPBF-fabricated fluid channels remains a challenge. The classical Gnielinski model is regarded as the most accurate correlation for predicting forced convective heat transfer in traditional pipes. However, whether it is applicable to LPBF-fabricated pipes is yet to be determined. To address this challenge, in this study, pipe samples with diameters of 3 mm, 4 mm, and 5 mm were designed and fabricated using LPBF along the building angles of 0°, 45°, and 90°. The pressure loss and heat transfer characteristics of these samples were experimentally measured. Results showed that there was a maximum prediction error of 72.1 % between the classical Gnielinski model and experimental results. To improve the prediction accuracy, a corrected Colebrook model with improved prediction accuracy of the friction factor was developed, introduced into the classical Gnielinski model, and reduced the maximum prediction error down to 36.8 %. To further improve the prediction accuracy, a gradient descent-based machine learning method was adopted to reconstruct the Gnielinski model, which achieved a high prediction accuracy with prediction errors of below 10 %. With the assistance of machine learning, a high precision predictive model of convective heat transfer in LPBF-fabricated fluid channels was established.

Numerical Study on Heat Transfer and Pressure Loss Characteristics of Swirl Cooling in Elliptical Tubes With Tangential Jet Inlets

Abstract The paper presents a numerical study of the heat transfer, pressure loss, and flow characteristics of swirl cooling in elliptical tubes, which are compared to the counterpart of swirl cooling in a circular tube with a diameter of D = 50.0 mm under equal passage Reynolds numbers and equal jet Reynolds numbers. The swirl tubes with two kinds of fixed tube length of 12D and 20D are compared, where there are sequentially arranged three tangential jet inlets over the leading tube length of 12D. The numerical results show that the swirl tubes with the tube length of 12D has a much better heat transfer performance. Under equal passage Reynolds numbers, the elliptical swirl tubes with the tube length of 12D show appreciably higher Nusselt numbers by up to 22.8% and lower pressure loss coefficients by up to 69.0% than the circular tube. Under equal jet Reynolds numbers, the elliptical tubes can reduce the global heat transfer performance modestly by up to 25.6%, but reduce the pressure loss much significantly by up to 70.6%. Mostly due to much less pressure loss, the elliptical tubes have remarkably higher thermal performance in terms of the obtained heat transfer coefficient per unit pumping power for both L1 = 12D and L2 = 20D. The numerical simulations indicate that the suppression of elliptical tubes on the swirling flow development reduces the heat transfer on the wall between the jet inlets, and decreases the wall shear force and the pressure loss in the tube.

Experimental study on the flow characteristics of 7-pin hexagonal bundle assembly with grid spacers

Lead-cooled Fast Reactors (LFRs) are of great significance for future nuclear power systems. With the advantages of great neutronic properties and high passive safety, LFR has been selected as the reactor of China initiative Accelerator Driven System (CiADS), which has the potential to transmute long-lived nuclear waste into short-lived ones and enhance the utilization of nuclear fuel. The hexagonal bundle with grid spacers has been identified as a promising design of the CiADS fuel assembly. The new design of grid spacers has the advantages of reliable fixation, small flow resistance, and not easy to cause blockage. Flow characteristics in this fuel assembly model were revealed by the particle image velocimetry (PIV) method. The results showed the presence of cross-flow and high axial velocity areas around the grid spacers. The strongest cross-flow mixing was observed downstream of the grid spacers at a distance of approximately z/Dh = 7.5 (axial height/hydraulic diameter). Although the influence of the grid spacers was weak, it was still detectable downstream at a distance of z/Dh = 32. The axial velocity loss rates were obtained and they increased with Reynolds number. The highest axial velocity loss rate was in the edge subchannel. Measurements of axial pressure drop uncovered the pressure loss characteristics of grid spacers and a new correlation was proposed. This work contributes to the understanding of the flow and pressure drop characteristics of the CiADS fuel assembly and can facilitate the design of more efficient nuclear reactors.

Experimental investigation of pressure-reducing instabilities in perforated plates for compressible and cavitating flows

The pressure losses through sharp-edged, multi-orifice circular perforated plates with two different ratios of plate thickness to orifices’ diameter are experimentally investigated using both water and dry air as working fluids. The choice of a thickness for which fluid-dynamic instabilities related to flow reattachment are known to occur allows to investigate the effects of cavitation and compressibility on such instabilities. It is found that both cavitation and compressibility may be the cause of an early reattachment of the flow within the plate’s perforation, modifying the pressure loss characteristics of the device. Wall pipe pressure fluctuations measurements for subsonic air flows allow linking changes in whistling frequencies to changes in the pressure loss regime of the plate.

Experimental and Numerical Investigation on Finned Vortex Reducer in a Rotating Cavity with a Radial Inflow

In aero-engines, a secondary air system is used to cool the rotor discs and seal cavities between rotor and stator parts. The pressure loss caused by bleed air can be effectively reduced by setting the finned vortex reducer. Thus, the bleed system design can be optimized by researching the flow structure and pressure loss of each section in the cavity with a finned vortex reducer. In this study, the influence of different installation positions of a finned vortex reducer on the pressure loss characteristics was investigated through experimental and numerical simulation methods, focusing on the radial inflow of the secondary air system. The results indicate that the inlet and outlet positions of the fins affect the flow structure in the cavity. The aerodynamic parameters (rotational Reynolds number ReΦ and mass flow rate coefficient Cw), together with the inlet and outlet radii of the fins, influence the pressure loss in the cavity. Considering the swirl ratio β constrained by the fins, a pressure loss model was established, which showed good agreement with the experimentally measured pressure loss. This model reflects the impact of the inlet and outlet positions of the fins on the pressure loss characteristics.

Numerical investigation and benchmarking of heat transfer and pressure loss characteristics with two-sided rib-roughened and two-sided heat supply in narrow rectangular channels

Numerical investigation and benchmarking of heat transfer and pressure loss characteristics with two-sided rib-roughened and two-sided heat supply in narrow rectangular channels

Thermal performance and exergy analysis in a round tube with louvered trapezoidal winglets

An experiment was performed to investigate the influence of inserting a louver-punched trapezoidal-winglet (LPTW) into a uniform heat-fluxed tube in order to create a longitudinal vortex generator. This research aims to maximize both the thermal performance to increase energy savings, and the relative Nusselt number (NuR) at the optimal performance to reduce heat exchanger sizes. Therefore, the experimental result was emphasized on the thermal and pressure loss characteristics including entropy, and exergy analysis of the turbulent tube flow for Reynolds numbers (Re) that extended from 4760 to 29,280. The LPTWs were arranged by letting V-tip direct downstream with three attack angles (α = 30°, 45° and 60°) and five louver angles (θ1 = 0°, 25°, 30°, 45° and 90°), all at a single relative winglet pitch (PR = 1.0) and height (BR = 0.25). According to the findings, it revealed that the friction factor (f) and Nusselt number (Nu) of the LPTW at α= 60° and θ1 = 0° are, respectively, up to 29.1 and 5.5 times above those of the plain tube. With decreasing Re and θ1, the entropy generation (S˙′gen) was reduced to a lower value and the maximum exergy efficiency (ηEx) was obtained for the LPTW at α = 60° and θ1 = 0° The peak thermal performance around 2.5 together with NuR = 4.68 was found at a= 60°, θ1 = 45° and the lowest Re. However, the optimal condition at α= 60°, θ1 = 30° was preferable because it provides the greatest NuR = 5.04 at TEF = 2.47. Additionally, correlations for f and Nu were derived and presented for the range of parameters that were taken into consideration.

A comparative numerical study on heat transfer and pressure drop characteristics of perforated ribs

Augmentation of heat transfer without increasing the pressure drop has been a challenge in turbine blade internal cooling. Ribs are commonly used to achieve this goal and it is imperative to keep the pressure loss as low as possible. In this paper, the thermohydraulic performances of a number of perforated ribs are examined and compared. Three geometrical features of the ribs include hole inclination angle (0°, 30°, and 45°), relative hole inlet height (0.2, 0.4, 0.6, and 0.8), and the variation of the cross-sectional area of the circular holes (convergent, straight, and divergent). The ribs are mounted in a rectangular channel (AR = 2:1) and flows with a range of Reynolds numbers (10,000 to 25,000) are examined. A validated SST Gamma-Theta model is employed to evaluate the turbulent heat transfer and pressure loss characteristics. It is found that the permeable rib labeled as Case #212, improves the performance between 4.35 and 6.39% for flows with Reynolds numbers between 10000 and 25000. Among the investigated configuration parameters, the hole inclination has the highest effect on the thermal performance enhancement.

Flow Field and Pressure Loss Characteristics at Rotary Drillstring Joints

A thorough understanding and accurate calculation of the annulus pressure losses are paramount to drilling design and construction. However, due to the influence of the drillstring rotation and the abrupt dimensional variation at the joint, it is difficult to calculate the pressure loss by theoretical analysis in the annulus at the drillstring joints. Considering the geometric nonlinearity of drillstring joints and the unsteady flow of annular fluid caused by pipe rotation, based on the turbulence model k − ε , the flow field characteristics demonstrate the annulus pressure losses at the drillstring joint are studied by numerical simulation. Simulation results indicate that drillstring rotation speed, annular gap, and eccentricity greatly influence flow field and pressure losses at drillstring joints. The annular pressure loss would increase with the decrease of the annular gap and eccentricity but decrease with the increase of the drillstring rotation rate. The investigation method and results would help guide the design of drilling hydraulic parameters.

Simulation and Field Studies on an Innovative Downhole Machine Designed for Ultrashort-Radius Horizontal Well Drilling Engineering

Ultrashort-Radius Horizontal Well (URHW) drilling engineering plays an important role in increasing the recovery factor of old oilfields. By sidetracking old wellbores at a very high build-up rate, the URHW can effectively exploit the residual oil near old wellbores. Currently, the main problem faced in URHW drilling engineering is the reduced torque received by drill bits owing to the increased friction between the flexible drilling assembly and wellbore as the horizontal section extends, which greatly limits oil production from a single trip. To tackle this problem, we proposed an innovative machine design, a Dynamic Flexible Drill Rod (DFDR), to provide extra torque near the drill bit to extend the horizontal section of the URHW. The interior structure and working principle of the DFDR were illustrated. The mechanical properties of the DFDRs critical load-bearing part were examined via simulation. The torque and pressure loss characteristics were analyzed using computational fluid dynamics. Corresponding modifications were made to optimize the design, with model machines produced accordingly. Field trials were carried out based on old wellbores in Chunliang District, Shengli Oilfield. The DFDR-based technique extended the URHWs horizontal section in this area by 13.38% on average.

An experimental investigation on pressure loss and local heat transfer characteristics in additively manufactured ribbed cooling configurations

Pressure loss and transient heat transfer measurements are performed on real-scale turbine cooling configurations at engine-relevant flow conditions. To determine the influence of rib turbulators and surface roughness on heat transfer and pressure loss, five additively manufactured models and one milled model were investigated, which distinguish in their manufacturing-related surface roughness and/or rib turbulator configurations. The experimentally determined friction factors are compared with data from a computed tomography (CT) scan, which was carried out for one of the additively manufactured models. An inverse discrete volume approach is applied, where the temperature response of the accessible outer wall caused by a sudden change in the temperature of the fluid flowing through the channel is measured. This allows the determination of locally resolved heat transfer coefficients on the non-accessible inner surface and provides information about the internal heat transfer processes. From the variety of experiments performed on the six models, the influence of surface roughness, one-sided high-blockade ribs, combination of these two, and the Reynolds number on friction factor and heat transfer coefficient is determined. The effects of roughness and rib configuration are separated from each other, and the expected measurement uncertainties are estimated by means of a sensitivity analysis.

Heat transfer and pressure loss characteristics of an offset fin with oblique waves

An offset fin with oblique waves (OFOW) which is a combination of offset fin (OSF) and V-shaped oblique wavy fin (OWF) has been proposed to further enhance heat transfer in single phase laminar flows. The heat transfer and pressure loss characteristics of different configurations of the OFOW are investigated numerically. The 3D unsteady periodic model with the H1 thermal boundary condition is adopted to explore the effects of V wave pointing direction, phase angle and wave amplitude. The local distributions of velocity, secondary flow, wall shear stress and heat flux as well as friction factor f and Colburn factor j are presented and compared with those of the plain channel, OSF and OWF with the same aspect ratio and hydraulic diameter. It is found that the OFOW can further enhance heat transfer than the OSF and OWFs, i.e., at Re ≈ 400 with wave amplitude of A = 0.3, the Colburn factor j is around 4.2 times of that of the plain channel. It is shown that opposite V wave pointing directions in the successive offset plates cannot induce long-range counter-rotating vortices, and V wave amplitude A is the most dominant parameter, where wave pointing direction and phase angle in the successive offset plates have minor effects.

Design and power calculation of HLFC suction system for a subsonic short-range aircraft

Hybrid laminar flow control (HLFC) can be a possible solution for future sustainable energy-efficient aviation. The current study proposes a MATLAB-based numerical tool for the design of the suction system for an airfoil optimized for a subsonic short-range HLFC application. Considerable energy losses may occur when the air passes through the perforated metallic outer surface and the inner structure of the suction system. A semi-empirical approach is used to design a layout that provides a target suction velocity based on measured pressure losses through porous medium and substructures. Flowbench measurements were performed on 3D-printed internal core test samples to quantify the pressure losses that can be used to create a lower pressure below the porous sheet matching the target suction velocity. The actual suction realized on the airfoil using this substructure concept has a discrete nature that increases with the distance between two adjacent walls. Finally, the suction system’s power requirement is calculated. The power requirement for distributed suction accounts for the pressure loss characteristics of the porous material, the internal core structure, and throttling holes. However, the study does not include the ducting losses from the substructure to the compressor. Approximately 80% of the total suction power is utilized to eject the sucked air back to the freestream conditions for a system with a compressor and propulsive system efficiency equal to one. The study analyses the performance of the designed internal core layout to different flight conditions and addresses the suction power requirement variation with lift coefficient and flight altitude.