Total Pressure Drop Research Articles

Impingement heat transfer enhancement in crossflow by a skewed twisted rib pair for simplified leading edge structure

Impingement cooling is a widely used cooling technology with extremely high local heat flux dissipation, but its heat transfer is often destroyed by upstream crossflow. To improve the impingement heat transfer under crossflow condition, a skewed-twisted rib pair is proposed for simplified leading edge structure. The flow and heat transfer characteristics of Baseline and STRP cases are compared when the crossflow ratio varies from 0.2 to 0.4. According to the results, in both Baseline and STRP cases, increased crossflow ratio results in a decrease in impingement heat transfer, and it also leads to the peak value location of Nusselt number shift further downstream. Besides, with the increase of crossflow ratio, the total pressure-drop of jet decreases, but that of crossflow increases. Under the same crossflow ratio, the arrangement of STRP intensifies the turbulence level and induces an additional vortex pair whose centerline direction is same as jet, so the impingement heat transfer performance is improved effectively. Moreover, the effect of skewed-twisted rib pair height is considered, and it is found that the increased height makes the heat transfer enhancement effect get obvious, but it also leads to an increase in total pressure-drops of both jet and crossflow.

Experimental Studies of Hydraulic Losses and Carbon Dioxide Concentration in the Space Under the Face Mask Protecting Against COVID-19

Masks are the primary tool used to prevent the spread of COVID-19 in the current pandemic. Tests were carried out to determine the total pressure drop through the materials from which the masks are made and the correlation of these results with the concentration of carbon dioxide in the inner space of the mask. The results showed that a parameter representing hydraulic losses of the mask material has a significant influence on the concentration of carbon dioxide in the inner space of the mask. Masks with higher hydraulic resistances accumulated a higher concentration of carbon dioxide, and generated greater fluctuations of carbon dioxide as a function of time, which may be caused by compensation of the respiratory system. For example, in a two-layer mask (mask no. 3) the hydraulic resistance values are about three times higher than in a single-layer mask (mask no. 1). The study also noticed that the inscriptions and prints placed on the masks increase the hydraulic resistance of the material from which the masks are made, which may also contribute to the accumulation of carbon dioxide in the space between the mask and the face. To reduce the accumulation of carbon dioxide within the inner space of the mask, the results of this work suggest searching for mask materials with the lowest possible hydraulic resistance.

Influence of pleated geometry on the pressure drop of filters during dust loading process: experimental and modelling study

In this study, a pressure drop model was developed through numerical simulation and experimentation for optimizing the design of the pleated structure of the filter media to extend the service life of the filter and reduce the ventilation energy consumption. The effect of the Stokes number on the dust deposition on the pleated filter media was revealed through numerical simulation. On this basis, a pressure drop model during dust loading was developed. The model suggests that under the same mass of dust deposition per unit area (W), the greater the pleat ratio (α), the greater the dust cake thickness and the effective filtration velocity in the effective filtration area. In addition, for V-shaped and U-shaped filters, the relative mean deviations between experimental and modeling total pressure drops are 3.68% and 4.82%, respectively. In other words, the proposed model accurately predicts pressure drop during dust loading. Furthermore, under the same α and W, the total pressure drop of the U-shaped filter is lower than that of the V-shaped filter, demonstrating the superior filtration performance of the U-shaped filter.

Quantitative investigation of the evaporation and resistance characteristics of inlet jet precooling

Abstract A quantitative study is carried out to explore the air/mist-coupled cooling in the cooling section incorporating a spray device, aiming to conduct a comparative simulation on the effects of two radial spray arrangements (Apparatus A and Apparatus B) on the change of flow field. The results show that an even spray arrangement leads to improved flow performance owing to the large temperature drop in the cooling section. Compared with Apparatus A, Apparatus B enables a 1.60–2.25% higher temperature drop coefficient and a 1.1–3.0% higher water evaporation rate. Six high-altitude conditions are simulated to find that the spray device and water injection are the main factors causing flow loss, whereas the additional mass flow caused by water vapor reduces the amount of loss. The highest temperature drop coefficient is observed for Case 6 (27.3%), in which there is a more uniform nozzle arrangement. A slight difference in terms of total pressure drop coefficient between Apparatus A and Apparatus B is observed. Moreover, the highest total pressure drop coefficient (5.8%) at the location of the spray system is observed for Case 6, which has the largest injection rate and highest inlet air Mach number.

Numerical study of the influence of the micro pin fin arrangement on the thermal and hydraulic performance of a micro heat sink

In this project, a numerical study of the thermal and hydraulic performance in a micro pin fin heat sink is carried out. The micro heat sinks pin fins are used for cooling of electronic, due that every day a more powerful and smaller chips and electronic components are required. The geometric parameters to the build of the heat sink with micro pin fins are chosen in base of the geometric needs of the electronic chip, a circular geometry is used for the micro pin fin and inline and staggered arrangement for the micro pin fins distribution is used, different velocities in the inlet of the heat sink are used for development of the study. In the result section, the temperature contours and the thermal resistance of the different cases analyzed are reported, as well as the pressures distributions and the total pressure drop along the heat sink micro pin fin are reported too. Taken account the results, the optimal geometry for thermal and hydraulic performance of the heat sink micro pin fin is obtained.

The effect of plate size and corrugation pattern on plate heat exchanger performance in specific conditions of steam-air mixture condensation

The results of mathematical modelling and experimental study of plate heat exchangers (PHEs) in steam-air mixture condensation are presented. The mathematical model is validated by test data for PHE in the industry and for five experimental samples with corrugation angles, 30°, 45°, and 60° and corrugation heights 5, 7.5 and 10 mm. With no limited pressure drop in PHE, its heat transfer area can be decreased up to 4 times with the plate's corrugations angle of 60°. When pressure drop on the side of condensing stream is limited, at a small mass fraction of air, PHE with corrugated plates' heat transfer area can be smaller than in PHE assembled from flat plates about 1.5 times ± 11% at channels of different corrugations geometries. For commercially produced plate-and-frame PHE, the pressure losses at channel entrance and distribution zones should be accounted. For plates with a corrugations angle of 60°, their share in total pressure drop can be from 7% up to 39.3%, while at a corrugations angle of 30°, up to 59%. The final choice of corrugation angle and height for plates designed for specific duty can be made by solving a future optimisation problem with a developed mathematical model.

Flow characteristics in non-conventional combustion chamber configurations

Flow characteristics in combustion chambers of several non-circular cross-sectional configurations were numerically investigated. Different cross-sectional configurations, including annular and multi-sector annulus configurations with different fillets, were proposed, examined, and compared to the conventional circular arrangement. A numerical model was established and validated against other findings. The model was then used to study the effects of different design parameters, including convex and fillet radii, as well as some operational parameters, such as the angular velocity on the total pressure drop and the secondary flow characteristics like the swirl number, secondary vortex intensity, and helicity. The results revealed the optimum number of annulus sectors to be six, at which the highest hydraulic diameter was achieved for the same cross-sectional area. Optimum values of the inner and outer corner fillets were also obtained. Several valve arrangements were also investigated to achieve the highest possible valve area ratio for the proposed configurations. One of the proposed configurations, which incorporates six annular chambers with filleted corners with a hydraulic diameter ratio of 0.991 compared to the conventional circular design, denoted AFC4, achieved a more compact design while maintaining very comparable flow characteristics to those of the circular design. Although it needs more thorough investigations, it could present a viable alternative design option for the combustion chambers.

Comprehensive numerical investigations on the thermal performance of heat recirculating micro combustor with pin fins for micro-thermal voltaic system applications

Aiming at improving the relatively low energy output and energy conversion efficiency of the micro-thermal voltaic (MTPV) system, an innovative heat recirculating micro combustor with pin fins is designed. The effects of pin fins arrangement, hydrogen/air equivalent ratio on the energy output and performance of CHMC, HMCP and HMCI are compared and investigated. The result shows that when the Vin is 6 m/s and Φ is 1.0, the emitter power of CHMC is 72.76W, and that of HCMP and HCMI micro combustor are 75.99W and 76.35W. and the emitter efficiency of CHMC, HCMP and HCMI is 41.93%, 43.26% and 44.01%. HMCI has better energy output capability compared with CHMC and HMCP. Even though, HMCI brings a higher pressure drop, it is within the acceptable range. When the Vin is 6 m/s, the pressure drop from the pin fins only accounts for 26.4% of the total pressure drop for HMCI. Through the study of equivalent ratio, it is found that HMCI has good adaptability in different equivalent ratio range. This work provides new ideas for the development of MTPV system in the future.

The identification of normal to underpressured formations in the Southeastern Sichuan basin

The Sichuan Basin contains many overpressured formations with pore pressure coefficients as high as 2.3. However, in a Nanye 1 well found in the Southeastern (SE) Sichuan Basin, low-pore pressure coefficients as low as 0.9 have been recorded at a depth between 1544.3 and 1903.6 m, indicating the presence of underpressured formations. But the knowledge of normal and underpressured formations is not well studied in the SE Sichuan Basin. In this work, the normal to underpressured formations in the SE Sichuan Basin are identified, and their origins are discussed.We integrated the pore pressure measurement and estimation, pore pressure coefficient and pore pressure depth plot to identify the normal to underpressured formations. We also integrated basin modelling along with the faults system to determine the origins of underpressured formations. As a result, the Upper Permian Longtan and Middle Permian Maokou Formations (1906.5–2782.9 m depth) in the Nanchuan area, were identified as normal-to-underpressured gas deposits. Also, the study identified the Lower Silurian Longmaxi and Upper Ordovician Wufeng Formations (2072–2160 m depth) in the Pengshui area, SE of the Chongqing region as normal pressured gas formations. The study discovered a decrease in temperature, rock porosity rebound and gas migration out of the formations through faults as the reasons for underpressured formations in this area. The tectonic uplift and erosion resulted in a decrease in temperature and rebound of the rock porosity, which contributed to total pore pressure drop up to 46.62 MPa. The tight overlying seal rocks and underlying rocks helped to sustain the low pore pressures in these formations.

Study on non-monotonic pressure-drop of supercritical n-decane with pyrolysis in heated channels

The non-monotonic relation between pressure-drop and flow-rate leading to the flow instability of fuel with pyrolysis was investigated. A characteristic pressure-drop model of n-decane coupled pyrolysis reactions under supercritical pressure was established. The model includes one-dimensional flow control equation, species equation, RK-PR equation of state, high-pressure viscosity model and a reaction mechanism consisting of 10 species and 15 reactions. The non-isothermal friction factor formula with wall correction coefficient fitted by experimental data was used in the model. To verify the model, the pressure-drops at different flow-rates were measured in a horizontal stainless steel tube with the inner diameter of 1.93 mm under different back pressures (3, 4 and 5 MPa). The results show that the model can accurately capture the non-monotonicity of characteristic pressure-drop. Under 3 MPa condition, the characteristic pressure-drop curve of n-decane has a pseudo-critical negative slope (PCNS) region and a reaction negative slope (RNS) region caused by the pyrolysis. With the increase of pressure, the PCNS region disappears but the RNS region still exists. The high pressure makes the onset of RNS region appear earlier due to the accelerated initial reaction rate. The total pressure-drop is separated and analyzed based on the model mathematically. In the PCNS region, the derivative of acceleration pressure-drop to mass flux is negative, whereas the derivative of friction pressure-drop to mass flux is positive. In the RNS region, the two derivatives are both negative because of the sharp decrease in density and the increase in friction factor caused by the pyrolysis reaction. The two parallel channels’ instability with constant total mass flow rate is analyzed based on the characteristic pressure-drop curves for reacting and non-reactive flow. The results indicate that the fuel pyrolysis reaction not only expands the range where the flow excursion may occur but also makes it difficult for the flow-rate to reach stable state again after the flow excursion caused by pseudo-critical instability.

Experimental study on the pressure drop characteristics of supercritical CO2 in horizontal rectangular microchannels

The pressure drop characteristics of supercritical carbon dioxide (S-CO2) are experimentally studied in horizontal rectangular microchannels with hydraulic diameters of 1 and 2 mm, which are used in printed circuit heat exchangers. The operating conditions include an operating pressure of 9–12 MPa, a mass flux of 290–1200 kg/m2 s, and a heat flux of 25–50 kW/m2. The four contributors to pressure drop in the S-CO2 microchannels were investigated. The results indicate that the total pressure drop decreases for lower operating pressures and mass fluxes, whereas the heat flux has little impact. The most significant contributor to the total pressure drop is the frictional pressure drop. The accelerational pressure drop increases with the heat flux. Eventually, a new frictional resistance correlation is proposed where the microchannel size and thermophysical property variations are considered.

A numerical study of microtube geometry effect on flow boiling using the volume of fluid method

Other than pursuing high heat flux, pressure drop also plays a key role in microtube applications as the power and efficiency of a pump are determined in terms of pressure drop. In the literature, only a few studies focus on how tube geometry influences pressure drop. This study numerically investigates the geometry effect on microtube flow boiling and pressure drop using the volume of fluid (VOF) method. Three types of geometries are used in this study: divergent, normal, and convergent microtubes with different lengths and hydraulic diameter ratios. The transient developments of vapor formation, heat flux, and pressure drops are presented within 200 ms. It is shown that the total pressure drop in the divergent microtube is the lowest. The heat flux is decreased as the massive vapor bubbles clog the tube. However, the shortened divergent microtube can increase the heat flux up to 38713.1 W/m2 and reduce the pressure drop down to 214.24 Pa, compared to the normal one under certain flow conditions, while the tube-clogging effect is not dominant. A larger inflow mass flux can delay the vapor bubble formation on the heated wall, which is beneficial to prevent the tube clogging and leads to a higher heat flux. On the other hand, higher heat flux can be achieved in the convergent microtube due to the increasing velocity inside the tube, although it induces the highest total pressure drop. This study provides a better fundamental understanding of the microtube geometry effect on flow boiling and relevant physical insight for the future design of microscale heat transfer applications.

Experimental thermohydraulic characterisation of flow boiling and condensation in additive manufactured plate-fin heat exchanger

In this paper, an experimental thermohydraulic characterisation of flow boiling and condensation in additive manufactured plate-fin heat exchanger was conducted. An original experimental setup was developed allowing the operation of the heat exchanger in both boiling and condensation modes. This heat exchanger mainly consists of two identical rectangular cross-section channels, each of hydraulic diameter 3 mm, with n-pentane and water used as refrigerant and heat transfer fluid, respectively. An experimental metrology, based on the infrared thermography, was implemented in order to determine the temperature distribution of the heat exchanger external walls. Based on this temperature distribution, the mean temperature profiles of the n-pentane and water were determined, allowing the identification of three main flow zones: the subcooled liquid zone, the two-phase (boiling/condensation) zone and the superheated vapour zone. These mean temperature profiles were then coupled to a developed thermal model in order to determine the local thermal parameters, such as heat flux, vapour quality and heat transfer coefficient. The total pressure drop in the two-phase zone was finally determined. All the obtained results were analysed and compared with data available in the literature.

NGHIÊN CỨU CÁC THÔNG SỐ ĐẶC TRƯNG CỦA BUỒNG ĐỐT NGƯỢC DÒNG DẠNG ỐNG HÌNH KHUYÊN CỦA ĐỘNG CƠ TUA BIN KHÍ TÀU THỦY BẰNG PHƯƠNG PHÁP MÔ PHỎNG CFD

Thisarticle presents the numerical study of combustor aerodynamic parameters of marine gas turbine engines to evaluate the actual characteristics. With the 3D model built from the upstream tube-annular combustor of DR76 engine, using CFD approach to evaluate the flow structure, determine the total pressure drop, the airflow distribution into the linner in primary, secondary and dilution zones. As aresult, the cold pressure loss in the combustor was 5.5% of the inlet pressure, the air mass flow through the swirl zone by about 29%, the primary orifices and cooling channels by 40.5%, and the dilution zone by 30% of the total combustor airflow.

Possible power increase in a natural circulation Soluble-Boron-Free Small Modular Reactor using the Truly Optimized PWR lattice

In this study, impacts of an enhanced-moderation Fuel Assembly (FA) named Truly Optimized PWR (TOP) lattice, which is modified based on the standard 17 × 17 PWR FA, are investigated in a natural circulation Soluble-Boron-Free (SBF) Small Modular Reactor (SMR). Two different TOP lattice designs are considered for the analysis; one is with 1.26 cm pin pitch and 0.38 cm fuel pellet radius, and the other is with 1.40 cm pin pitch and 0.41 cm fuel pellet radius. The NuScale core design is utilized as the base model and assumed to be successfully converted to an SBF core. The analysis is performed following the primary coolant circulation loop, and the reactor is modelled as a single channel for thermal-hydraulic analyses. It is assumed that the ratio of the core pressure drop to the total system pressure drop is around 0.3. The results showed that the reactor power could be increased by 2.5% and 9.8% utilizing 1.26/0.38 cm and 1.40/0.41 cm TOP designs, respectively, under the identical coolant inlet and outlet temperatures as the constraints.

On the numerical assessment of flow losses and secondary flows in Pelton turbine manifolds

Different methods combining analytical guidelines, numerical simulations, and the manufacturer’s experience are employed to design and optimise the distributor manifold of a Pelton turbine. All these methods have in common to assume undisturbed straight inflow to the manifold, thus neglecting the upstream flow conditions. Our numerical simulations executed with the open-source code OpenFOAM v2012 show that the insufficient consideration of the upstream flow situation may lead to inaccurate predictions of the manifold flow. Five turbulence models were tested in our simulations, and the inflow turbulence intensity was varied from 1% to 10%. The flow quality was assessed by evaluating the head loss coefficient from total pressure drop, the head loss coefficient from the entropy production, the secondary velocity ratio upstream the injectors and the mass flow imbalances in the injectors. The study of turbulence models revealed that the k-ω Shear Stress Transport model predicted the head loss and secondary flows with reasonable accuracy. Also, the computationally less expensive model of Spalart-Allmaras leads to similar results and therefore emerges as an appropriate model for optimisation. The simulations with varying inflow turbulence intensity levels indicate a flow pattern change, if the specified inflow turbulence intensity is less than 4%. Below this value of inflow turbulence intensity, a significant increase of the secondary flow upstream of the injectors was observed.

Effect of back pressure on the separation performance of a hydrocyclone

In industrial process applications, to shorten the process flow and use the residual energy of hydrocyclone overflow, the overflow outlet is often directly connected to the subsequent equipment, and the back pressure of the subsequent equipment inevitably affects the normal operation of the front-end hydrocyclone. Therefore, this paper uses numerical simulation to study the effect of overflow back pressure on the internal flow field and separation performance of hydrocyclones. The results show that increasing the overflow back pressure increases the total pressure drop of the hydrocyclone, has no significant effect on the internal radial pressure gradient, and only increases the energy consumption of the hydrocyclone. With the increase in the overflow back pressure, the solid phase yield of the underflow increases, the content of fine particles gradually increases, the content of coarse particles decreases, and the separation accuracy of the hydrocyclone decreases. • The effects of back pressure on the flow field were investigated. • The influences of back pressure on the separation performance were studied. • The particle size distribution of the products were analysed.

MP-PIC simulation of dilute-phase pneumatic conveying in a horizontal pipe

Dilute gas-solid two-phase flows inside a pneumatic conveying pipe are simulated with the multiphase particle-in-cell (MP-PIC) method. To achieve high simulation accuracy, different particle-wall collision models, drag force models and turbulence modulation models have been tested. Simulation results including pressure drop, gas and solid mean velocities, fluctuating velocities are compared to experimental measurements. It is found that the particle-wall collision restitution coefficient, especially in the tangential direction, significantly influences the total pressure drop. The mean particle velocity and slip velocity are sensitive to the drag force and a much higher drag force can improve the simulation accuracy, whereas the mean gas velocity is not sensitive to the drag force. The fluctuating gas velocity is hard to be predicted with the currently available turbulence modulation modeling choices, implying more efforts are needed in understanding the turbulence in future. • Dilute-phase pneumatic conveying in a horizontal pipe was simulated by MP-PIC method. • Impact of different sub-models on simulation results has been investigated. • The sub-models include particle-wall collision, drag force and turbulence modulation models. • Special attention has been paid on the slip velocity prediction.

Study on two microchannel coolers with different coupling mechanisms of distributed J-T effect and heat transfer

As a typical characteristic of the microchannel Joule-Thomson (J-T) coolers, the distributed J-T effect significantly impacts the cooling effect. To investigate the coupling mechanism of distributed J-T effect and heat transfer, two micro-coolers are fabricated by Printed Circuit Board (PCB) technology in this study. The throttling device is removed from the micro-cooler with staggered etched pillars (Cooler-Pillars), resulting in an entire coupling of heat recovery and throttling processes. The heat recovery and throttling structures are preserved in a micro-cooler etched with rectangular microchannels (Cooler-REC), and the two processes couple partly. The performance of the two micro-coolers is investigated experimentally and numerically at the inlet pressure of 2.02∼5.12 MPa. The experimental results show that the mass flow rate and total pressure drop of Cooler-Pillars are higher than Cooler-REC at the same inlet pressure. Compared with Cooler-REC, Cooler-Pillars can reach a lower cold end temperature and has a cold-end temperature of 190.6 K in steady-state operation at 5.03 MPa. A steady-state mathematical model is developed and compared favorably with the experimental results. The simulation result shows that at the same inlet pressure, the overall distribution of J-T coefficients and the total temperature drop caused by distributed J-T effect of Cooler-Pillars are higher. It is also found that the overall Nu distribution of Cooler-Pillars is higher than Cooler-REC, and heat transfer is enhanced, leading to an increase of 64.5% in average unit heat transfer at 5 MPa.

Parametric design analysis of a multi-level 3D manifolded microchannel cooler via reduced order numerical modeling

Waste heat flux from power dense electronics is expected to reach > 1 kW/cm2 in the next few decades, and they will require novel cooler designs with low thermal resistance, that can simultaneously dissipate large levels of heat and have high coefficient of performance (COP). 2D straight microchannel cold plates (CP) are an industrial go-to solution for active heat dissipation needs, but they suffer from a major drawback – very high pump pressure is required to force large quantities of fluid through miniscule channels in the CP and thus these coolers are very inefficient, achieving low COP. Recently, manifolded micro-coolers (MMC) have become popular which use a second manifold layer to distribute the fluid in 3D within the CP, thus shortening fluid travel length within the miniscule CP channels and significantly reducing the total device pressure drop. In this study, we first introduce a novel two-level manifold design which boasts a potential of > 2x improvement in COP compared to conventional single-level manifold concept without affecting the thermal performance. Recognizing the difficulty in simulating large area full MMCs, we then aim to simplify the 2-level MMC geometry into reduced order models to bring down simulation cost at an expense of accuracy. Two models were considered, the widely popular and convenient to use Single Cold Plate U-bend Channel (SCPUC) model which only simulates the CP channels, and the slightly more complicated Single Manifold Channel (SMC) model which also considers the effect of the manifold. The SMC model simulations were first validated against full device simulations for different heater footprint sizes (25, 100, 400 mm2) to establish accuracy and it was found that the SMC model could predict thermal performances of all device sizes with a nominal inaccuracy of 5%. In contrast, the widely accepted SCPUC model produced highly inaccurate (as high as 25–45%) predictions for thermal performance of the MMCs. The two models were then used under an extreme heat flux load of 800 W/cm2 and 0.2 liter per min (lpm) device flow rate, to simulate 54 different 2-level MMCs obtained by varying important geometric parameters on the manifold and cold plate side. Detailed analysis was performed to explain the trends in thermal performance and pressure drop with different geometric parameters. Finally, two pareto curves were reported, one between thermal resistance and pressure drop, and the other between COP and device size. It was seen that the proposed 2-level MMC showed record high COP as compared to state-of-the-art single-level MMCs. We hope that this study will act as a design guide for MMCs as well as act as a performance repository for a wide range and combinations of geometries of 2-level manifold structures.