Low Pressure Loss Research Articles

Mixing improvement induced by the combination of a micro-ramp with an air porthole in the transverse gaseous injection flow field

A new injection strategy combined with a micro-ramp and an air porthole is proposed in this paper, and the properties of the transverse gaseous injection flow field with such injection strategy have been investigated simultaneously. The numerical approach employed in the current study has been validated against the two-dimensional and three-dimensional experimental data in the open literature, and it can be used with confidence to investigate the influence of the air porthole aspect ratio and the distance between the air porthole and the fuel orifice on the transverse injection flow field with the combination of a micro-ramp and an air porthole. The obtained results predicted by the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model show that the mixing performances of the transverse gaseous injection flow fields vary under different conditions, and a transverse injection flow field with short mixing length, low stagnation pressure loss and ideal fuel penetration depth has been achieved by adding the combination of an optimized micro-ramp with a proper air porthole, i.e. Case 6–8, and its mixing length decreases considerably by 14.26 mm on the basis of Case c, even shorter than the mixing length of Case a by 2.86 mm. However, its total pressure loss increases when compared with Case c, and its stagnation pressure loss is 2.7 percent smaller than Case a. Further, the hydrogen distribution on the flat plate of Case 6–8 is much less than that of Case a and Case b. Additionally, it is found that the mixing enhancement mechanism of the air jet is different from that of the micro-ramp. The micro-ramp enhances the mixing process between the fuel and air by inducing large-scale vortices, while the air porthole enhances the mixing process by seeding lots of air into the fuel boundary layer, as well as fuel plume.

Flow instability detected in ruptured versus unruptured cerebral aneurysms at the internal carotid artery

Flow instability has emerged as a new hemodynamic metric hypothesized to have potential value in assessing the rupture risk of cerebral aneurysms. However, diverse findings have been reported in the literature. In the present study, high-resolution hemodynamic simulations were performed retrospectively on 35 aneurysms (10 ruptured & 25 unruptured) located at the internal carotid artery (ICA). Simulated hemodynamic parameters were statistically compared between the ruptured and unruptured aneurysms, with emphasis on examining the correlation of flow instability with the status of aneurysm rupture. Pronounced flow instability was detected in 20% (2 out of 10) of the ruptured aneurysms, whereas in 44% (11 out of 25) of the unruptured aneurysms. Statistically, the flow instability metric (quantified by the temporally and spatially averaged fluctuating kinetic energy over the aneurysm sac) did not differ significantly between the ruptured and unruptured aneurysms. In contrast, low wall shear stress area (LSA) and pressure loss coefficient (PLC) exhibited significant correlations with the status of aneurysm rupture. In conclusion, the present study suggests that the presence of flow instability may not correlate closely with the status of aneurysm rupture, at least for ICA aneurysms. On the other hand, the retrospective nature of the study and the small sample size may have to some extent compromised the reliability of the conclusion, and therefore large-scale prospective studies would be needed to further address the issue.

A numerical model-assisted experimental design study of inertia-based particle focusing in stepped microchannels

Focusing methods based on fluid inertia have been demonstrated to be able to concentrate particles with a high precision and predictability offering great potential for practical application as manipulation of bodily fluids as blood for clinical diagnostics. However, to perform focusing to one single position at the center location of a channel with high focusing quality on the one hand and low pressure losses and shear stresses on the other hand still is a challenge in microchannel design. Three different stepped microchannels are analyzed via bright-field microscopy to investigate the impact of various geometric parameters on the focusing behavior of spherical particles. Reynolds numbers within a range of \( 8 \le Re \le 75\) are measured to evaluate the impact of flow conditions on the focusing characteristics. The microchannels show the ability to focus particles to a single stream with a maximum focusing efficiency of 97.1\(\%\) and purity of 99.1\(\%\). The focusing strongly depends on the channel geometry, that is, step length, step height, and settling length. A semiempirical model is developed to predict force-induced focusing ability at maximum shear stresses that are reduced significantly compared to previous systems. This model is demonstrated to be in very good agreement with experimental results and therefore can be utilized for future device design. Finally, guidelines for the design of stepped single-stream focusing devices at low pressure losses and low maximum shear stresses are derived based on experimental, numerical, and semiempirical data.

Numerical simulation of airflow around the evaporator in the closed space

The article deals with a numerical simulation of the forced airflow around a evaporator with the finned tubes in the electrotechnical box, by finite volume method in the program ANSYS Workbench. The work contains an analysis of the impact of forced airflow on the evaporator with the various seated the electrical components. The aim of the work is to find out the most effective way of heat dissipation by forced convection from the electrical components in the closed space with lowest pressure loss.

Thermal Diffusion Performance of a Diffuser by various Guide Vanes configurations

The use of vane-less diffuser with large diffusion angle has shown a setback in the diffusion process of high temperature working fluids. The hot gas flow was characterized as a jet-like flow. This paper presents problem, encountered practically, using a vane-less diffuser with large diffusion angle and how the problem is solved by CFD simulation. The investigated thermal diffuser has a length of 0.3 m, an inlet to outlet crosssectional area ratio of 1:25 and diffusion angle of 115.44o. To resolve the jet-like flow problem and poor distribution of the flow temperature at the diffuser outlet, the study suggested the use of guide-vanes into the diffuser. The study employed CFD simulation by ANSYS-FLUENT software to analyze the flow and thermal process in the diffuser. Three different shapes of guide vanes; block-shaped, oval-shaped and airfoil-shaped were considered in this study and at different vanes diffusion angles, as well as vane-less case, which was adopted as the bench mark case. The simulation results of the velocity, temperature and pressure at the diffuser outlet were compared for all cases. It was found that the guide vanes with symmetrical airfoil profile provided the best performance with most uniform distribution at the outlet of the diffuser. Also, the airfoil-shaped guide vanes resulted in lower pressure losses compared to the block-shaped and oval-shaped guide vanes. According to the analysis results, the diffuser was redesigned to improve the diffusion and temperature distribution across the diffuser outlet.

Adjoint based topology optimization of conjugate heat transfer systems

AbstractThis paper presents a topology optimization method for coupled thermal problems. Heat transfer linked with the forced convection flow inside cooling channels is investigated using a conjugate model. This model includes both the full Navier‐Stokes equations for the fluid medium and the energy equations for both fluid and solid. In this present work, the adjoint method is extended to such conjugate heat transfer (CHT) systems to optimize their performance by the use of gradient based methods. This performance is usually a compromise between an increase in heat flux or temperature distribution at a surface and maintaining a low pressure loss within the system. To exemplify the method a uniform temperature distribution is chosen and evaluated numerically. For implementation the open source CFD Software OpenFOAM is used. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical analyses of pressure losses in organic Rankine cycles

The thermodynamic efficiency of Organic Rankine Cycle (ORC) obtained from experimental systems has been obviously lower than theoretical results. One of the reasons is that some elements affecting the efficiency, such as pressure losses in evaporator, condenser and pipes, have not been deeply discussed and optimized. The present manuscript detailed and examined the influences of pressure losses on ORC thermodynamic efficiency. Pressure losses in ORC system were divided into three categories: High Pressure Loss of the first category (HPL1), High Pressure Loss of the second category (HPL2) and Low Pressure Loss (LPL). A formula was developed to describe the relationships between three categories of pressure losses and ORC thermodynamic efficiency. Through analyses of the formula, it is found that the adverse impacts of pressure losses on thermodynamic efficiency are very different, mainly depending on the characteristic specific volume of working fluid in certain state. Because the very different specific volume, under a same value of pressure loss, LPL mostly leads to the largest thermodynamic efficiency drop of ORC system, HPL1 does less and HPL2 does the least. The influences of LPL are normally 3–21 times larger than that of HPL1, and 30–50 times larger than that of HPL2. The conclusions will serve as a guide for engineering applications of ORC system.

Experimental study of heat transfer performance of a tube with different shaped pin fins

The heat transfer performance of a tube with different pin fin shapes, including circular, elliptical and drop-shaped, were investigated experimentally in the range of Re 0.5×105–4.1×105. Naphthalene sublimation experiments were conducted to measure the local heat transfer on pin fins and on tube surfaces, as well as the pressure drop. The results showed that the local heat transfer performance on tube surfaces was higher than that on pin fins due to the larger heat transfer area under the certain conditions. And the heat transfer coefficients of pin finned tubes increased with the increase of Re for the given Re. Different shapes of pin fins caused different resistance, and drop-shaped pin fins exibited lower pressure loss due to the fairshaped geometry. Comparing the different shaped pin fins with the same cross-section areas, the drop-shaped pin fins showed a significant effect on the heat transfer, considering both the heat transfer improvement and the pressure drop limit.

Differences in Morphologic and Hemodynamic Characteristics for "PHASES-Based" Intracranial Aneurysm Locations.

Several recent prospective studies have found that unruptured intracranial aneurysms at various anatomic locations have different propensities for future rupture. This study aims to uncover the lack of understanding regarding rupture-prone characteristics, such as morphology and hemodynamic factors, associated with different intracranial aneurysm location. We investigated the characteristics of 311 unruptured aneurysms at our center. Based on the PHASES study, we separated and compared morphologic and hemodynamic characteristics among 3 aneurysm location groups: 1) internal carotid artery; 2) middle cerebral artery; and 3) anterior communicating, posterior communicating, and posterior circulation arteries. A mixed model statistical analysis showed that size ratio, low wall shear stress area, and pressure loss coefficient were different between the intracranial aneurysm location groups. In addition, a pair-wise comparison showed that ICA aneurysms had lower size ratios, lower wall shear stress areas, and lower pressure loss coefficients compared with MCA aneurysms and compared with the group of anterior communicating, posterior communicating, and posterior circulation aneurysms. There were no statistical differences between MCA aneurysms and the group of anterior communicating, posterior communicating, and posterior circulation aneurysms for morphologic or hemodynamic characteristics. ICA aneurysms may be subjected to less rupture-prone morphologic and hemodynamic characteristics compared with other locations, which could explain the decreased rupture propensity of intracranial aneurysms at this location.

Problems of Signal Processing in Ultrasonic Gas Flow Measurement

Vortex measuring methods with ultrasound are distinguished by small bluff bodies, low pressure losses and high sensitivity. The ultrasound wave is modulated by the vortices behind the bluff body. The modulation frequency represents the flow velocity and can be determined by well-known demodulation procedures.Cross correlation methods use the natural turbulences in a fluid. Because of the skewed density function of the velocity components the maximum of the cross correlation function does not represent the transit time of the turbulences between two ultrasonic barriers. Processing of the complex modulated signal is very difficult because the phase of the signal can reach very high values and can not be considered unambiguously. It is advantageous to simplify the signal processing by artificially generated vortices by a small bluff body. It results in a symmetric density distribution and symmetric cross correlation function. Furthermore, it results in a self-monitoring system. Alternatively, two different carrier frequencies can be applied to the two ultrasonic waves. In the cross correlation function the carrier frequencies are eliminated automatically.

Thermal performance in a rotating two-passage channel with various turning guide vanes

Generally, significant changes are observed in heat transfer and pressure distribution with respect to the turning area of a rotating twopassage channel. Thus, the achievement of high heat transfer and low pressure loss in the turning area of a rotating two-passage channel is an important goal in the design of a high-efficiency cooling passage. This study explored the use of various guide vane arrangements in the turning area to achieve this goal. The study investigated heat transfer and pressure loss in the turning area of a rotating two-passage rectangular channel with various guide vanes. A naphthalene sublimation method was used to determine detailed local Sherwood number ratios (which can be converted to the heat/mass transfer coefficient). The pressure loss in the rotating channel was measured to calculate the thermal performance. The channel aspect ratios is 5 and hydraulic diameter is 26.67 mm. Additionally the Reynolds number was maintained constant at 10000, and the rotation number corresponded to 0.1. The results revealed that the turning flow in the turning area was largely influenced by the rotation effect. Furthermore, the turning flow was deflected towards the outer wall, and the centrifugal force induced a large flow separation region around the inner wall. This was in contrast to the results typically observed for a stationary channel. Among the various observed patterns of a turning guide vane, the inner guide vane case exhibited the best thermal performance in the rotating two-passage channel. The inner guide vane in the rotating two-passage channel guided the turning flow and helped in reducing the flow separation. This increased the thermal performance of the rotating two-passage channel.

Theoretical Prediction of Longitudinal Heat Conduction Effects on the Efficiency of the Heat Wheel used for Ventilation in Powerhouse Building “Kjørbo” in Norway

The present study investigates effects of longitudinal heat conduction (LHC) on the heat recovery effectiveness of the heat wheel in the Powerhouse building “Kjørbo”. The effects LHC which are usually ignored in the heat wheel design play a relatively significant role in the heat wheel with high temperature efficiency and short depth in flow direction. The correlation developed by Shah, Kays and London is applied to predict the temperature efficiency and to investigate the impacts of the LHC. Good agreements have been observed between the theoretical predictions obtained from the correlation and experimental data collected from the field test at “Kjørbo”. The influence of the depth of the heat wheel, the airflow rates on the LHC and temperature efficiency were analysed. It was found that the heat wheel has difficulty to achieve a high temperature efficiency (85%) due to the effects of LHC. There is an optimal depth design for heat wheel in the flow direction to recovery maximum thermal energy with low pressure loss with considering the LHC effects. The present study provides preliminary analysis to optimize the heat wheel design and operation with the LHC being taken into account.

Numerical modelling of electrohydrodynamic airflow induced in a wire-to-grid channel

Electrohydrodynamic (EHD) airflows provide a means of generating air motion by a gas discharge across two electrodes without the need for moving parts. A two-dimensional numerical model for a wire-to-grid EHD air blower is developed, validated against previous data, and used to investigate the influence of key design parameters on blower efficiency, including the emitter wire diameter, the blower height, the locations of the collecting surfaces and grid wires, and the collecting grid density. The optimal locations of both collectors from the corona wire are determined based on blower efficiency at a fixed operating power, resulting in improvements in the average outlet velocity between 9% and 15%, depending on blower thickness. The presence of the grid has a strong influence on the electric field distribution and increases the blower performance, with higher flow, lower operating voltage and reduced blower size. An investigation into the effect of grid density reveals that using coarse collecting grids is generally beneficial, leading to higher efficiency with lower pressure losses.

Flow Characteristic and Heat Transfer for Non-Newtonian Nanofluid in Rectangular Microchannels with Teardrop Dimples/Protrusions

Abstract Porous cavity technology is one of the effective ways to improve local flow structures and thus the overall heat transfer of heat exchanging devices. In the present investigation, the flow characteristics and heat transfer in a microchannel heat sink with teardrop dimples/protrusions are studied with a numerical method. The working substances are Al2O3-water nanofluids, which are defined by power-law shear-thinning model. The relative depth and positive eccentricity of dimples/protrusions arranged in the microchannels are 0.2 and 0.3 respectively. The inlet velocity varies in the range of 1.41 m⋅s−1 to 8.69 m⋅s−1 and the volume fraction ranges from 0.5% to 3.5%. The effects of the flow and heat transfer characteristics are investigated by analyzing the limiting streamlines structures and temperature distributions. The overall thermal performance is evaluated by parameters of Fanning friction factor, Nusselt number and thermal performance. It is shown that the combination of teardrop dimple/protrusion structure and Al2O3-water nanofluids could effectively strengthen heat transfer with low pressure loss. Moreover, in order to obtain the best overall thermal performance, working substances with volume faction of 3.5% is preferred for the proposed microchannel structure.

Experimental Study on Flat Flame Combustion for Ultra Micro Gas Turbine Applications

ABSTRACTThe requirement for efficient power sources for portable electronics and miniature mechanical devices, such as laptops, micro robots, or micro aerial vehicles, has led to research on the ultra micro gas turbine (UMGT). The ultra micro gas turbine is one of the most promising power sources for small-scale applications due to its higher power and energy densities compared to currently used batteries. In order to realize UMGT as a viable power source, its individual components have to be developed, since downscaling introduces new problems for each component. Since the micro combustor is one of the key components of UMGT, it has to be improved. Until now, it has been very difficult for micro combustors to achieve wide flame stability, high combustion efficiency, and clean combustion with low pressure loss, due to the associated downscaling problems, such as high heat loss and small residence time. In order to achieve wide flame stability, the effect of preheating the reactants on flat flame stabilization was investigated experimentally on a 46-mm inner diameter quartz-walled flat flame combustor. The experimental results showed that preheating improves flat flame stabilization. Since preheating increases the burning velocity, flat flame can stabilize at higher incoming flow velocities as long as they are lower than the burning velocities. From the relationship between the incoming flow velocities and burning velocities, a correlation was obtained for flat flame micro combustors for micro power generation applications. With this correlation, it is possible to determine the minimum combustor diameter required for stable flat flame combustion. Also, in order to have a stable flat flame at higher mass flow rates, the correlation enables the calculation of the required reactants temperature, and is a major contribution to the design of micro combustors.

A Small Probe-Type Flowmeter Based on the Differential Fiber Bragg Grating Measurement Method

A small probe-type optical fiber flowmeter was proposed for fluid flow measurement. The hollow cylindrical cantilever was first used to measure the force caused by fluid. A couple of fiber Bragg gratings (FBGs) that were stuck on the inner wall were used to measure the strain of the cantilever. The flow rate can be obtained by monitoring the difference of the two shifted Bragg wavelengths. The cross-sensitivity problem of FBG sensors can be solved by the differential FBG measurement method. Theoretical relation between the Bragg wavelength shift difference and flow rate has been established by theoretical analysis. Meanwhile, experiments have been carried out to verify the feasibility and stability. The simulation and experiment results showed that the resolution of the proposed flowmeter was 0.81 $\text{m}^{3}$ /h and the accuracy was 3.6% in the region of 0–22.5 $\text{m}^{3}$ /h. Compared with the references existed, the proposed flowmeter in this paper was more compact with good sensitivity, wide measurement range, easy fabrication, and low pressure loss.

Development of tin-plated regenerator material

To improve the efficiency of a cryocooler, it is vital to improve the regenerator. In general, the heat capacity of materials decreases as temperature decreases. Thus, when temperature is below 50 K, lead spheres are often used as a regenerator material. However, the pressure drop through a sphere regenerator is larger than that through a screen regenerator. To overcome this dilemma, a new, low pressure loss tin-plated screen is proposed. A comparison test was performed with a two-stage GM cryocooler by replacing part of the first stage regenerator material, bronze screens with tin-plated screens. Compared to a regenerator filled with bronze screens, the cooling capacity of the first stage increased by about 14% at 40 K and 90% at 30 K with such tin-plated screens. The ratio of the wire diameter before and after the deposition was also optimized. An optimum cooling capacity of 53.5 W at 40 K was obtained at a diameter ratio of about 1.4. The detailed experimental results are reported in this paper.

Integrated Separate Layer Injection Technology on ASP Full Term Flooding for II and III Kind Formation in Daqing Oilfield

With the development of ASP flooding in Daqing oilfield, the II and III formation with low permeability and apparent interlamination contradictory has been developed as the main target. Due to the worse technology adaptation, the big difficulty of testing, the low successful ratio of running and fishing, the high cost of changing the strings for water flooding and ASP flooding, the original separate layer ASP injection failed to be applicated extensively. In order to resolve the problems mentioned above, the integrated separate layer injection technology on ASP flooding was researched in this paper. The eccentric injection regulator, the pressure regulator with low viscosity loss ratio and high pressure choke, the molecular weight regulator with high viscosity loss ratio and low pressure loss are designed, the injection of high permeable interval and the molecular weight of medium and low permeable interval can be controlled at the same time. The separate injection string is compatible with water flooding technology and it can be satisfied the requirement of the blank water flooding、ASP flooding and sequent water flooding, the investment and operation cost are dropped. The field application of 56 injection wells shows that the running and fishing, the verifying sealing and the flowrate allocation technology can be operated by production company by themselves, the average testing time of single well is about 2-3 days. The Daqing oilfield practice shows that [1, 2]: ASP flooding compare with water flooding can be more increased the oil recovery over 20 percent. At present, Daqing Oilfield totally have 728 ternary production wells and 625 injection wells, the oil production maintain keeps more than one million tons for three consecutive years, the cumulative oil production of 6.135 million tons. With the deepening of the development of ASP flooding, permeability differences, second and third grade reservoirs with much interlayer difference has become the main development of the object. Original ASP flooding stratified injection technology, has poor process adaptability, difficulty of throwing-in and pulling test and low success rate, the water flooding turning into ASP flooding and ASP flooding turning into subsequent water flooding due to high cost, it needs to replace the string, and is unable to scale application. In order to solve the above problems, this paper researches the ASP flooding integration separate layer injection technology, to achieve the dual control of the Injection volume of the high permeability interval and the molecular weight of the low permeability interval, researches the pressure regulator with low viscosity loss ratio and high pressure choke, the molecular weight regulator with high viscosity loss ratio and low pressure loss. The separate injection string is compatible with water flooding technology and it can satisfy the requirement of the blank water flooding, ASP flooding and sequent water flooding, the investment and operation cost are dropped. Integrated separate layer injection technology has the scale application conditions, and plays an important effect on continued stable and high yield for Daqing Oilfield 40 million tons crude oil.

New Ceramic Substrate with Gas Flow Control Functionality to Realize High Purification and Low Pressure Loss, Compact Catalyst Volu

New Ceramic Substrate with Gas Flow Control Functionality to Realize High Purification and Low Pressure Loss, Compact Catalyst Volu

A conceptual design of shock-eliminating clover combustor for large scale scramjet engine

A new concept of shock-eliminating clover combustor is proposed for large scale scramjet engine to fulfill the requirements of fuel penetration, total pressure recovery and cooling. To generate the circular-to-clover transition shape of the combustor, the streamline tracing technique is used based on an axisymmetric expansion parent flowfield calculated using the method of characteristics. The combustor is examined using inviscid and viscous numerical simulations and a pure circular shape is calculated for comparison. The results showed that the combustor avoids the shock wave generation and produces low total pressure losses in a wide range of flight condition with various Mach number. The flameholding device for this combustor is briefly discussed.