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The significant increase in thermal efficiency and the rate of energy exchange used in fuel dynamics and automobile coolants are leading to a better understanding of nanofluids. This computational analysis explores the thermal conductivity performance for radiative cross-flow of a nanofluid across an expanding/constricting sheet with a suction effect as a result of its application. To compute or calculate the magnificent point of nanofluid flow, the entropy, and asymmetrical heat source/sink effects are also elicited. The boundary layers traverse a stream-wise procedure for expanding and contracting sheets. Additionally, the study examines the features of heat transfer and cross-flow of nanofluids using numerical simulations. By employing similarity variables, the basic PDE equations of the current model are transformed into ODEs, and they are subsequently evaluated using the bvp4c method. Therefore, the effects of embedded flow variables on drag force, heat transfer rate, and entropy generation profiles have been framed using parametric research. Multiple solutions are offered for a specific range of the contracting parameter as well as the mass suction parameter. In addition, the heat transfer rate accelerates due to the heat source and decelerates due to the heat sink. The literature that is already published has been compared favorably, and it reveals many commonalities. [ABSTRACT FROM AUTHOR]

The boundary layer's separation loss in compressor cascades constitutes a significant portion of profile loss, critically influencing aerodynamic performance optimization and control. This study employs Large Eddy Simulation (LES) to examine separation losses at varying attack angles, focusing on a rectangular compressor cascade. Specifically, it explores the long separation bubble at a 45% blade height cross-section under designed incidence. Analysis of the separation bubble's transition process revealed a notable surge in total pressure loss rate prior to transition, which stabilized following reattachment. The study thoroughly investigates the evolution of long bubbles, employing quadrant analysis of Reynolds stress, critical point theory, and an in-depth examination of individual vortex dynamics. The findings indicate that the peak of cross-flow within the separation bubble acts as the primary mechanism initiating the transition. This insight is corroborated by DNS calculations of natural transitions on flat plates. Building upon these findings, the study discusses the effects of varying attack angles on transition processes. Notably, increased incidence prompted the upstream migration of the long separation bubble, transforming it into a short bubble at the leading edge. This shift led to a fivefold increase in separation loss and doubled the frequency of transverse flow fluctuations. [ABSTRACT FROM AUTHOR]

The design of a supersonic combustor ramjet engine has gained significant attention for futuristic air-breathing engines. Achieving efficient fuel mixing and complete combustion within a short period poses a substantial challenge. This study has directed efforts towards improving mixing and minimizing total pressure losses across the supersonic combustor to enhance performance. Experiments were conducted to investigate the influence of fuel injection geometry in the supersonic combustor with an entry Mach number of 2. Two different fuel orifice geometries, inclined at 45°, were considered. The investigation covered four different momentum flux ratios: 0.8, 1.0, 1.2, and 1.4 respectively. Various measurements were conducted to observe flow phenomena inside the supersonic combustion, including wall static pressure measurement, Schlieren visualization, exit Mach number and total pressure loss measurement. Without injection cases exhibited weaker compression and expansion inside the combustor. During injection, the rise in wall pressure indicated that the bow shock formed in front of the arc injection was slightly weaker than that of the circular injection. The impinging bow shock on the opposite wall also exhibited higher strength, resulting in a static pressure rise. As a result, the lower total pressure ratio across the shock indicates a higher momentum exchange between the main flow and the orifice. Therefore, arc injection has proven more effective in exchanging momentum inside the supersonic combustor. Consequently, the Mach number at the exit of the combustor was higher for the arc injection.

The design of a supersonic combustor ramjet engine has gained significant attention for futuristic air-breathing engines. Achieving efficient fuel mixing and complete combustion within a short period poses a substantial challenge. This study has directed efforts towards improving mixing and minimizing total pressure losses across the supersonic combustor to enhance performance. Experiments were conducted to investigate the influence of fuel injection geometry in the supersonic combustor with an entry Mach number of 2. Two different fuel orifice geometries, inclined at 45°, were considered. The investigation covered four different momentum flux ratios: 0.8, 1.0, 1.2, and 1.4 respectively. Various measurements were conducted to observe flow phenomena inside the supersonic combustion, including wall static pressure measurement, Schlieren visualization, exit Mach number and total pressure loss measurement. Without injection cases exhibited weaker compression and expansion inside the combustor. During injection, the rise in wall pressure indicated that the bow shock formed in front of the arc injection was slightly weaker than that of the circular injection. The impinging bow shock on the opposite wall also exhibited higher strength, resulting in a static pressure rise. As a result, the lower total pressure ratio across the shock indicates a higher momentum exchange between the main flow and the orifice. Therefore, arc injection has proven more effective in exchanging momentum inside the supersonic combustor. Consequently, the Mach number at the exit of the combustor was higher for the arc injection. [ABSTRACT FROM AUTHOR]

Thermal comfort in openair situations is a difficult industrial task. In literature there were insufficient studies on how to control the external microclimate in a region, and there are many activities outside the house in open areas that require temperature control, such as the stadiums in hot humid countries, and tourism, and recreational areas in humid and hot climates. Openair conditioning requires huge amount of energy, that negatively affects the Global warming of the earth. To reduce energy consumption microclimate control is proposed. Isolation of the controlled area is performed to reduce the amount of air-conditioned load. In this project the air conditioning of an external open area will be studied. Wind tunnel with two air flows at different temperatures, relative humilities, angle of attach and velocities will be constructed. The two flows will be allowed to intersect to gather at different conditions (different wind speeds ranging from 1 to 7 m/s, as well as a jet flow about 1 m/s and angles 60 to 90 degrees) to construct an isolation Dom for the targeted outside open area. An open area with the use of cross flow that stops the local wind speed in the targeted area and allows to keep the conditioned air for a long time in the open space. This method allows to save huge energy used continuously for the air-conditioning purpose.

The boundary layer's separation loss in compressor cascades constitutes a significant portion of profile loss, critically influencing aerodynamic performance optimization and control. This study employs Large Eddy Simulation (LES) to examine separation losses at varying attack angles, focusing on a rectangular compressor cascade. Specifically, it explores the long separation bubble at a 45% blade height cross-section under designed incidence. Analysis of the separation bubble's transition process revealed a notable surge in total pressure loss rate prior to transition, which stabilized following reattachment. The study thoroughly investigates the evolution of long bubbles, employing quadrant analysis of Reynolds stress, critical point theory, and an in-depth examination of individual vortex dynamics. The findings indicate that the peak of cross-flow within the separation bubble acts as the primary mechanism initiating the transition. This insight is corroborated by DNS calculations of natural transitions on flat plates. Building upon these findings, the study discusses the effects of varying attack angles on transition processes. Notably, increased incidence prompted the upstream migration of the long separation bubble, transforming it into a short bubble at the leading edge. This shift led to a fivefold increase in separation loss and doubled the frequency of transverse flow fluctuations.

Relative permeability and capillary pressure are key parameters in multiphase flow modelling. In heterogeneous porous media, flow direction- and flow-rate dependence result from non-uniform saturation distributions that vary with the balance between viscous, gravitational, and capillary forces. Typically, relative permeability is measured using constant inlet fractional-flow—constant outlet fluid pressure conditions on samples mounted between permeable porous plates to avoid capillary end-effects. This setup is replicated in numeric experiments but ignores the extended geologic context beyond the sample size, impacting the saturation distribution and, consequently, the upscaled parameters. Here, we introduce a new workflow for measuring effective relative permeability and capillary pressure at the bedform scale while considering heterogeneities at the lamina scale. We harness the flexibility of numeric modelling to simulate continuum-REV-scale saturation distributions in heterogeneous rocks eliminating boundary artefacts. Periodic fluid flux boundary conditions are applied in combination with arbitrarily oriented, variable-strength pressure gradient fields. The approach is illustrated on a periodic model of cross-bedded sandstone. Stepping saturation while applying variable-strength pressure-gradient fields with different orientations, we cover the capillary-viscous force balance spectrum of interest. The obtained relative permeability and capillary pressure curves differ from ones obtained with traditional approaches highlighting that the definition of force balances needs consideration of flow direction as an additional degree of freedom. In addition, we discuss when the common viscous and the capillary limits are applicable and how they vary with flow direction in the presence of capillary interfaces. [ABSTRACT FROM AUTHOR]

Thermal comfort in openair situations is a difficult industrial task. In literature there were insufficient studies on how to control the external microclimate in a region, and there are many activities outside the house in open areas that require temperature control, such as the stadiums in hot humid countries, and tourism, and recreational areas in humid and hot climates. Openair conditioning requires huge amount of energy, that negatively affects the global warming of the earth. To reduce energy consumption microclimate control is proposed. Isolation of the controlled area is performed to reduce the amount of air-conditioned load. In this project the air conditioning of an external open area will be studied. Wind tunnel with two air flows at different temperatures, relative humilities, angle of attach and velocities will be constructed. The two flows will be allowed to intersect to gather at different conditions (different wind speeds ranging from 1 to 7 m/s, as well as a jet flow about 1 m/s and angles 60 to 90 degrees) to construct an isolation Dom for the targeted outside open area. An open area with the use of cross flow that stops the local wind speed in the targeted area and allows to keep the conditioned air for a long time in the open space. This method allows to save huge energy used continuously for the air-conditioning purpose. [ABSTRACT FROM AUTHOR]

AbstractThis article presents the results of numerical investigation on comparison between two different cooling techniques namely cross flow and jet impingement cooling techniques used in heat sinks for the electronic components. Pin fin heat sink with and without phase change material (PCM) are considered for the investigation. The main focus of this research is to reduce the peak operating temperature of electronic component and pressure drop and to increase the Nusselt number of the heat sinks. Computational fluid Dynamics (CFD) tool is used to model and investigate the heat transfer characteristics across the heat sink. It is found that the cross flow shows superior thermal characteristics compared to jet impingement method due to which the base temperatures of pin fins in cross flow is at an average temperature of 14.5° C lower than that of jet impingement. Furthermore, the use of PCM significantly reduces the operating temperature of the pin fins by an average temperature of 7.5 °C for cross flow and 6.1 °C for jet impingement flow techniques. [ABSTRACT FROM AUTHOR]

The significant increase in thermal efficiency and the rate of energy exchange used in fuel dynamics and automobile coolants are leading to a better understanding of nanofluids. This computational analysis explores the thermal conductivity performance for radiative cross-flow of a nanofluid across an expanding/constricting sheet with a suction effect as a result of its application. To compute or calculate the magnificent point of nanofluid flow, the entropy, and asymmetrical heat source/sink effects are also elicited. The boundary layers traverse a stream-wise procedure for expanding and contracting sheets. Additionally, the study examines the features of heat transfer and cross-flow of nanofluids using numerical simulations. By employing similarity variables, the basic PDE equations of the current model are transformed into ODEs, and they are subsequently evaluated using the bvp4c method. Therefore, the effects of embedded flow variables on drag force, heat transfer rate, and entropy generation profiles have been framed using parametric research. Multiple solutions are offered for a specific range of the contracting parameter as well as the mass suction parameter. In addition, the heat transfer rate accelerates due to the heat source and decelerates due to the heat sink. The literature that is already published has been compared favorably, and it reveals many commonalities.

Development of an efficient membrane from waste resources has been receiving growing interest. The utilization of industrial waste coal fly ash (CFA) for the preparation of SiC based tubular membrane has reduced the raw material cost and sintering temperature, and hence beneficial in both economic and environmental points. In the present work, tubular membrane was prepared by extrusion of ceramic paste formulated using SiC powder, CFA, suitable dispersant, plasticizer and additives. The extruded green body was dried and then sintered at 850°C. The membrane was characterized by measuring porosity, morphology by scanning electron microscopy, linear shrinkage, mechanical strength. The membrane performance was evaluated using synthetically prepared oil-water emulsion, turbid water, kitchen wastewater and industrial wastewater. The membrane was found to remove 93-95% of oil depending on the oil concentration in the feed water. The oil rejection potential of the membrane was compared with other membranes reported in the literature and the results indicated that the membrane prepared in this study had a strong potential applications in wastewater treatment. [ABSTRACT FROM AUTHOR]

Analytical and numerical solutions for determining the dimensions of a cross-flow heat exchanger under different conditions have been developed in this study. The analytical solution using the ε-NTU method is used to find the initial dimensions of the cross-flow heat exchanger. The numerical solution is used to validate the analytical solution and optimise the cooling coil dimensions. The ε-NTU design results show the effect of water mass flow rate, air inlet velocity, and the outer tube diameter of the cooling coil. The distribution of air and water temperatures through the heat exchanger can be predicted by solving the basic Navier-Stokes equation and energy equation using numerical methods. [ABSTRACT FROM AUTHOR]

Port Fuel Injection (PFI) system in hybrid gasoline engines is frequently in cold condition due to use for electricity generation. Under cold condition, the fuel film forms on the intake port wall does not evaporate completely during the cycle, and the injected fuel spray impinges on it in the next cycle. In this paper, the process of fuel film formation under multi-cycle fuel injection condition is analysed by applying the Total Internal Reflection Laser Induced Fluorescence method. In addition, the particle size distribution of spray droplets was measured in quiescent conditions with Super High Spatial Resolution Photography method, which allows for whole spray imaging while maintaining the spatial resolution of small droplets. As a result, the fuel adhesion mass per injection increases as the critical Weber number increases with repeated fuel injections under quiescent conditions. Under cross flow conditions, fuel mass impinging on the wall is much smaller than under quiescent conditions. Accordingly, the fuel adhesion mass per injection is almost constant with repeated fuel injections because of the small increase in the critical Weber number. [ABSTRACT FROM AUTHOR]

This study presents a new strategy to strengthen the flow and thermal performance of gas-liquid tube bundle heat exchangers by combining oval tubes with variable-direction twist method. The effects of twist direction, twist angle and flow velocity on the overall performance were investigated. The variable-direction twisted oval tube enhances the mixing degree of the main stream and the tail vortex, thereby improving the thermal performance and reducing the pressure drop. Both heat transfer coefficient and pressure drop increase with the increase of twist angle, and the overall performance is negatively correlated. Twist period has little effect on overall performance. Convective heat transfer coefficient of the variable-direction twisted oval tube with a twist angle of 120° is increased by 5.8%–10.2%, pressure drop is reduced by 5.0%–7.8% and overall performance is increased by 7.4%–10.7%, as compared circular tube bundle. The proposed variable-direction twisted oval tube realizes the synergistic enhancement of thermal-hydraulic performance, and can directly replace the traditional circular tube. The work of this paper provides technical guidance for improving the processing technology of twisted oval tube and developing new heat exchangers.

Tube bundles of shell and tube-type heat exchangers often fail because of vibrations produced in tubes due to flow. The turbulence in the flow is the primary cause of vibrations in the tubes. In this study, a tube positioned in the third row of the tube bundle was considered to determine the vibrational response of the heat exchanger tubes. The tube bundle was parallelly arranged in a triangular (60°) configuration having a pitch to diameter (P/D) ratio of 1.44. The internal tube flow velocity ranges from 0 to 0.371 m/s and the shell side velocity ranges from 0.5 m/s to 2 m/s. The experimentation shows that the amplitude of vibration without flow inside the tube is less as compared to the amplitude with the flow. Furthermore, as the velocity of internal tube flow escalates; the amplitude of tube vibrations tends to escalate as well even when the shell side flow velocity is kept constant. The data points from experiments tend to reside in the unstable region of the stability map and particularly on the map’s left side, although the tube shows stable vibration behaviour as confirmed by the experimental results. Thus, further, development can be done by modifying the theoretical models to predict the realistic stability behaviour of tubes with internal tube flow.

In this study, copper foam was used as a porous medium in place of traditional aluminum fins. A comparison between the two heat exchangers—one with fins and the other with copper foam—was conducted under various conditions. The air inlet velocity ranged from 0.9 to 9.3 m/s, and the water inlet temperature ranged from 10°C to 18°C. Different water flow rates were tested. A comparison was made between the performance of copper foam and aluminum fins by calculating several parameters, including thermal resistance, heat exchanger effectiveness, Colburn factor, Nusselt number, friction factor, and area goodness factor (AG). The experimental results showed that at low air velocities, the heat transfer coefficient for both types of heat exchangers was almost equal. However, at high air velocities, the copper foam exhibited a higher heat transfer coefficient. The Colburn factor was higher for the heat exchanger with copper foam than in the conventional fins, where it was equal to 0.1959 for the copper foam and 0.1186 for the fins. On the other hand, the AG was higher in the case of fins than in the heat exchanger with copper foam. [ABSTRACT FROM AUTHOR]

Laser-based powder bed fusion is an additive manufacturing process in which a high-power laser melts a thin layer of metal powder layer by layer to yield a three-dimensional object. An inert gas must remove process byproducts formed during laser processing to ensure a stable and consistent process. The process byproducts include a plasma plume and spatter particles. An NC sensor gantry is installed inside a bespoke open-architecture laser-based powder bed fusion system to experimentally characterize the gas velocity throughout the processing area. The flow maps are compared to manufactured samples, where the relative density and melt pools are analyzed, seeking a potential correlation between local gas flow conditions and the components. The results show a correlation between low gas flow velocities and increased porosity, leading to lower part quality. Local flow conditions across the build plate also directly impact components, highlighting the importance of optimizing the gas flow subsystem. The experimental flow analysis method enables optimization of the gas flow inlet geometry, and the data may be used to calibrate the computational modeling of the process. [ABSTRACT FROM AUTHOR]

The cross‐flow heat exchanger involves a tractor moving between two fluids that flow in a direction perpendicular to each other, and one of the fluids is often a liquid and the other is a gas. This type of heat exchanger has been studied in many previous studies for its importance in air conditioning applications and many industrial applications. In this type of heat exchanger, the surface area for heat transfer is very large. Therefore, many techniques have been used to improve the thermal and dynamic performance of this type of heat exchanger. In this study, previous studies that used metallic foam as one of the ways to improve the performance of heat exchangers were reviewed. The most important techniques that were used in previous studies during the process of evaluating the thermal performance of a cross‐flow heat exchanger in the presence of different types of metal foam were clarified. The use of metal foam depends on important factors, including (1) the type of material, where copper and aluminum were used in most of the previous studies, due to their availability and ease of foam formation using these materials, in addition to the good thermal properties, (2) porosity, where the porosity value of metal foam ranged between 0.85 and 0.98 in the previous studies, (3) the density of pores, most of the studies ranged between 10 and 40 PPI. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The influence of the distance between two circular side-by-side cylinders in a cross flow on the surface distribution of temperature and static pressure is experimentally studied. The studies were carried out at free-stream Mach numbers M equal to 0.295 and 0.365 and Reynolds numbers ReD equal to 6.4 × 104 and 7.9 × 104, respectively. The surface distributions of the pressure coefficient and the temperature recovery factor for one of the cylinders are obtained. It is shown that, depending on the distance between the cylinders, the pressure coefficient and temperature recovery factor can be both higher and lower than the values obtained in the flow over a single cylinder with the same free-stream parameters. [ABSTRACT FROM AUTHOR]

The wall-impingement phenomenon significantly impacts mixture formation, combustible performance, and pollutant release in DISI engines. However, there is insufficient knowledge regarding the behavior of fuel adhesion. Thus, here, we examine adhesive fuel features at various injection pressure levels (5 and 10 MPa) in a cross-flow field (0 to 50 m/s). The RIM optical method was employed to track the expansion and distribution of fuel adhesion. As a result, adhesive fuel features such as area, mass, thickness, and lifetime were assessed. Postprocessing image analysis reveals that fuel adhesion was consistently thinner at the edge region. With increased injection pressure, the cross flow led to a rise in the fuel-adhesion area and mass; however, small changes in pressure did not affect adhesive thickness. Adhesive thickness significantly decreased in the cross flow, indicating enhanced evaporation potential. Furthermore, lifetime prediction was conducted to quantitatively evaluate the impact of cross flow and injection pressure upon fuel adhesion, which could be calculated by examining the decreasing trend in adhesive area. Results show that the lifetime was dramatically reduced with higher cross-flow velocity, and slightly decreased with lower injection pressure. Under injection pressure of 10 MPa, the adhesive lifetime in the cross-flow field of 50 m/s was reduced by 77.5% compared with the static flow field (0 m/s). The experimental results provide corresponding guidance for low-carbon fuel utilization and emission reduction in DISI engines. [ABSTRACT FROM AUTHOR]

The study confirms the feasibility of using information from flow-induced vibration generated by bluff bodies for measurement of flow. The proposed methodology is based on experiments conducted for recording acceleration signals from vibration sensors embedded along with bluff bodies in cross flow. The studies were undertaken in a wide Reynolds number range of 4700 to 5.655x105, with five different geometries of bluff bodies for shape optimization. Resonance and vortex shedding frequencies of samples are determined experimentally. The recorded acceleration signals are analysed using three different techniques such as frequency shift method, resonance amplitude method and overall acceleration estimation method. In this, the frequency shift method shows correlation at low flow velocities. In the resonance amplitude method and overall acceleration method, acceleration levels show a cubic relation with the flow rate. In the resonance amplitude method, obtained R2 values are from 0.93 to 0.99. Overall acceleration estimation method has shown better correlation with flow rate and its R2 values were above 0.99. The study confirms that application of all three methods together yields reasonably good estimation for a wide range of flow.

The investigation of nanofluid's cross flow, which is caused by a nonlinear stretching sheet within the boundary layer, is presented. The proper mathematical detail is provided for three distinct cross flow instances with the streamwise flow. A uniform transverse stream located far above the stretched plate, in one instance, creates the cross flow. Two further situations deal with cross flows caused by surface transverse shearing motions. Weidman's work was used to find a similarity solution by making the necessary changes. It has been found that two parameters, namely nanoparticle volume frictions ϕ and a nonlinear stretching parameter β , have a significant impact on the flow of fluids in cross flow scenarios. Graphical representations of transverse and streamwise shear stresses and velocity profiles are provided. From this study, we found that nanoparticle volume fraction ϕ reduces the momentum boundary layer in both streamwise and cross flow scenarios while increasing the temperature of the fluid and, hence, increasing thermal boundary layer thickness. The same is observed for the nonlinear stretching parameter β. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shanghai University / Shanghai Daxue Xuebao is the property of Journal of Shanghai University (Natural Sciences) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Inserting the jet plate between the bottom plate and absorber plate in a flat plate solar air heater has been proposed as an excellent option to enhance the performance of the conventional solar air heater. This research work presents an experimental study of flow and heat transfer in a jet plate solar air heater. Results are presented for the different mass flow rates of air 1 and 2, Reynolds number Reja2, streamwise pitch of the holes to jet hole diameter X/D, depth of upper channel to jet hole diameter Z2/D, fixed number of jet hole N and angle of tilt. In the present study, it is found that outlet air temperature, collector efficiency, heat transfer coefficient and Nusselt number are higher at lower jet hole diameter, D (6 mm) as compared to higher jet hole diameter, D (8 mm and 10 mm) irrespective of the mass flow rates, 1 and 2. The outlet air temperature decreases with increase of mass flow rates of air (1 and 2) and jet hole diameter. Based on the experimental data, the correlation for Nusselt number has been developed. [ABSTRACT FROM AUTHOR]

In this paper, a contemporary concept that is based on dividing, by means of multi-passages, the water flow rate of water-air cross flow heat exchangers (HXs) is proposed. The thermal performance of water-air cross flow heat exchangers varies through a rationale function when the water flow rate changes. The new concept is based on dividing high flow rates of water entering a water-flow heat exchanger into several passages. This fragmentation prevents keeping the thermal performance from being nearly constant at high flow rates which lead to increasing the thermal performance globally. The feasibility of this concept was examined and had been proven through calculations on a double passage heat exchanger using an in-house two-dimensional computational code that had been developed and validated to evaluate the thermal performance of Heat Exchangers (HX) using a prescribed set of parameters. It was observed that the thermal performance increases rapidly with the water flow rates at low flow rates and become nearly constant at high flow rates. Furthermore, results revealed that the implementation of the novel concept can increase the thermal performance of a standard water-air cross flow heat exchanger by up to 25.7 %. The enhancement is more significant at high mean air velocities and low water flow rates.

The application results of the method of digital image processing using smoke to visualize the gas dynamic picture of the flow by the image intensity parameter for such complex gas dynamic processes as a flooded laminar jet and a circular laminar jet in a transverse flow are presented. This method is based on obtaining image intensity matrices and their processing using receptor models. Its use makes it possible to determine with great certainty the position of any section (or a set of sections) of a gas flow with the assessment of its geometry and area with a given range of image intensity. It is shown that such an approach to the analysis of experimental data makes it possible to take a new look at the picture of gas flow mixing and to evaluate qualitatively and quantitatively the processes occurring in such jet flows. This technique is applicable to compare images obtained in different operating environments, and it allows determining the general patterns and differences in the flow of the gas. [ABSTRACT FROM AUTHOR]

This paper reports a parametric study’s experimental results based on the experiments’ design. No works in the literature have investigated parametrically experimental effects on electronic component cooling by combining an impinging jet and a channel flow configuration on the cooling of electronic components. This study analyzed five parameters experimentally to enhance the cooling process using statistical techniques. Additionally, the optimal configuration determined for the conventional cooling method using only the channel flow was compared. Three parameters are associated with the geometric configuration (height of the electronic component $h/H = 1/6, 1/3$ , 1/2, jet diameter $D/H = 0.3, 0.4$ , 0.5 and jet-component eccentricity $S/H = 0, 1/8$ , 1/4), and the other two are related to the fluid flow (the Reynolds number based on the channel height and mean velocity of the stream $Re_{H}= 3410$ , 4205, 5000 and the ratio between the jet and the channel mean velocities $U_{j}/U_{m}= 2.5$ , 3.75, 5). The results show that the main parameters are statistically significant relative to heat transfer, with $Re_{H}$ , $U_{j}/U_{m}$ and $h/H$ displaying the most significant amplitude of variation in response and increasing the Nusselt number by approximately 60%. The surface response models have shown a satisfactory fit with the experimental data, allowing, in a preliminary way, the minimum mechanical energy loss requirement to be identified to maximize up to 160% of the heat transfer. Specifically, the heat transfer enhancement is more significant for components of considerable height than other components. Heat transfer enhancement occurs at low mechanical energy loss when the velocity ratio decreases at the minimum channel Reynolds number at the maximum jet diameter and jet-component eccentricity.

This study investigated the burning rate and the flame geometry of gasoline pool fires under crosswinds in the context of bridge vehicle fires. A 1:4 scale bridge fire platform was established. A total of 45 fire experiments were conducted on 9 gasoline pool with 1–2.2 aspect ratios under 0–2 m/s cross-wind. The influence mechanism of aspect ratio n on the characteristic parameters of pool fires was investigated. The results showed that the burning rate of gasoline pool ranges from 0.028 kg‧m−2‧s−1 to 0.064 kg‧m−2‧s−1, which increases with wind speed and pool size. When the wind speed exceeds 1 m/s, the title angle of the flame on the windward side is greater than 45° and is less affected by pool size. The wall heat conduction at wind downstream increases with aspect ratio when placing the longer side facing to cross flow. The correction factor F r · n can be used to describe the competition between the air entrainment and the buoyancy in gasoline pool fire. A general model based on aspect ratio is proposed to quantify the burning rate and flame tilt characteristics of gasoline fires. The reliability and applicability of the model are compared with the existing experimental data. • The coupling effect of cross-wind and aspect ratio on gasoline combustion was investigated. • The aspect ratio was introduced to propose a general model of flame geometry. • A 1:4 scale bridge fire platform simulating vehicle fire was established. [ABSTRACT FROM AUTHOR]

• Velocity and temperature field of cross flow over a tube bundle are discussed based on DNS results. • Flow field can be divided into the main flow region, recirculation region and the shear layer. • Reynolds stress, turbulent kinetic energy and their transport process are analyzed. • Temperature fluctuation variance, turbulent heat flux and their transport process are analyzed. Helical tube bundles are preferably utilized in high-temperature gas-cooled reactors (HTGRs) for steam generators (SGs) and intermediate heat exchangers (IHXs). However, to enhance their design, it is essential to understand the turbulent flow and heat transfer characteristics of cross flow over tube bundles. In this work, the convection of cross flow over an inline tube bundle with P / D = 1.875 is simulated using the Direct Numerical Simulations (DNS) method. Findings from the velocity spectrum and the drag/lift force variations show that the turbulent wakes swing at a main frequency corresponding to a Strouhal number (Sr) of 0.114. Based on the time-averaged velocity contour, the flow field has been divided into three parts: the main flow region, the recirculation region and the shear layer between the main flow and recirculation region. The flow field around the tube is symmetrical along the streamwise direction. Each half-tube surface (θ = 0°-180°) could be divided into three parts by the impinging point (θ = 40.5°), separation point (θ = 109.8°) and reattachment point (180°). Analysis of the Reynolds stress fields shows that large values of u ′ u ′ ¯ and u ′ v ′ ¯ are present in the shear layer, whereas v ′ v ′ ¯ dominate at the end of the recirculation region. Large w ′ w ′ ¯ mainly locates at the front side of the tube, where the main flow impinges on the tube wall. The convection terms are found to be non-zero while evaluating the transports of the Reynolds stress. The production and dissipation terms of turbulent kinetic energy (TKE) are found to be imbalanced, with pressure and turbulent diffusion terms playing key roles in balancing the TKE budgets. Similar to the flow field, the temperature field is also characterized by three regions: the main flow region (low temperature), the recirculation region (high temperature) and the shear layer (strong temperature gradient). The u ′ T ′ ¯ exhibits a clear distinction between positive and negative values near the shear layer. Positive values are concentrated within the recirculation region, while negative values are found outside this region. Both v ′ T ′ ¯ and u ′ v ′ ¯ show the same distribution patterns with larger magnitude present in the shear layer. The convection term of temperature fluctuation variance and turbulent heat flux budgets are found to be non-zero. For T ′ T ′ ¯ /2 budgets, the convection term is dominated by molecular diffusion in the near-wall region while it is dominated by turbulent diffusion in the main flow region. The turbulent diffusion has a significant influence on the balance of u ′ T ′ ¯ budget. [ABSTRACT FROM AUTHOR]

Laser-based powder bed fusion is an additive manufacturing process in which a high-power laser melts a thin layer of metal powder layer by layer to yield a three-dimensional object. An inert gas must remove process byproducts formed during laser processing to ensure a stable and consistent process. The process byproducts include a plasma plume and spatter particles. An NC sensor gantry is installed inside a bespoke open-architecture laser-based powder bed fusion system to experimentally characterize the gas velocity throughout the processing area. The flow maps are compared to manufactured samples, where the relative density and melt pools are analyzed, seeking a potential correlation between local gas flow conditions and the components. The results show a correlation between low gas flow velocities and increased porosity, leading to lower part quality. Local flow conditions across the build plate also directly impact components, highlighting the importance of optimizing the gas flow subsystem. The experimental flow analysis method enables optimization of the gas flow inlet geometry, and the data may be used to calibrate the computational modeling of the process.

The effects of cross flow and fluctuating cross flow on the aerodynamic performance of multirotor drone propellers were investigated by using wind tunnel testing and numerical simulations. Three hovering propellers were examined and were designed based on Adkins and Liebeck theory with modifications. Thrust coefficient CT and power coefficient CP of each propeller were experimentally measured and Figure of Merit FM was evaluated. From the cross flow experiments and numerical simulations, CT, CP and FM calculated were in reasonable agreement with the experimental results at high cross flow velocity. The results implicated that a stall might occur at near the root of the propeller as well as demonstrated that the starting point of the propeller design played a role in aerodynamic performance under the cross flow conditions. Moreover, from the fluctuating cross flow experiments, CT, CP and FM fluctuated in time and the propellers are more susceptible to cross flow and fluctuating cross flow at lower rotational speed in terms of the amount of change of aerodynamic forces.

The study confirms the feasibility of using information from flow-induced vibration generated by bluff bodies for measurement of flow. The proposed methodology is based on experiments conducted for recording acceleration signals from vibration sensors embedded along with bluff bodies in cross flow. The studies were undertaken in a wide Reynolds number range of 4700 to 5.655x105, with five different geometries of bluff bodies for shape optimization. Resonance and vortex shedding frequencies of samples are determined experimentally. The recorded acceleration signals are analysed using three different techniques such as frequency shift method, resonance amplitude method and overall acceleration estimation method. In this, the frequency shift method shows correlation at low flow velocities. In the resonance amplitude method and overall acceleration method, acceleration levels show a cubic relation with the flow rate. In the resonance amplitude method, obtained R² values are from 0.93 to 0.99. Overall acceleration estimation method has shown better correlation with flow rate and its R² values were above 0.99. The study confirms that application of all three methods together yields reasonably good estimation for a wide range of flow. [ABSTRACT FROM AUTHOR]

The paper is concerned with water vapor condensation on vertical pipes. The vertical position of pipes in a condenser is not discussed very often. Its application has a number of particularities in terms of the numerical determination of heat transfer. In the first stage of this paper, the authors focus on the experimental identification of heat transfer during vapor condensation on vertical pipes with a diameter of 14.0 × 1.0 mm. The pipes are placed in a narrow channel and the steam flows around them in a perpendicular direction. Two channel widths were tested, i.e., 20.0 and 24.0 mm. In the second stage, numerical modelling (CFD) is used for a detailed identification of the vapor velocity fields near the pipes. In the third stage, the results of the experimental measurements and numerical modelling are compared with data published by various authors. There are studies in the literature dealing with axial flow around vertical pipes; however, the associated results are based on conditions which are distinct from those applied in our study. The outcome of this paper is the specification of the heat transfer coefficient and the calculation formulas precisely describing the studied condenser configuration. [ABSTRACT FROM AUTHOR]

To better understand the mechanism influencing the periodic lattice structures in gas turbine blade cooling, these numerical simulations present a systematic comparison of the effects in cases involving pin-fin, Kagome, and BCC lattice arrays on film-cooling effectiveness under three blowing ratios (i.e., M = 0.5, 1.0, and 1.5). The results indicate that the introduction of lattice array structures improves film-cooling effectiveness within the whole streamwise range, especially downstream of the film hole. With an increase in the blowing ratio, the superiority of lattice array structures relative to those without a lattice becomes increasingly evident. The local film-cooling effectiveness can be increased, to a maximum of about 100%, under a blowing ratio of 1.5. The secondary flow induced by the lattice array structure at the internal flow channel increases the TKE and accelerates the development of vortices in the film cooling hole. Using the lattice array model, the improvement of the Kagome and BCC lattice arrays in terms of film cooling is better than those of pin-fins. In addition, the effect of lattice arrays on film-cooling effectiveness is different at various blowing ratios, and the lattice array structures have little impact on the film cooling at a relatively low blowing ratio. [ABSTRACT FROM AUTHOR]

In the present study, a flow rig with optical access intended for spray investigations in exhaust system-relevant conditions was analysed in terms of flow and temperature in the spray area using numerical simulations. The operation of the rig was examined for a wide range of exhaust mass flow rates, temperatures and various forms of UWS (urea-water solution) spray plumes. The locations of the injector and thermocouple were verified. Both conventional and flash-boiling injections were considered to assess the effect of the interaction of sprays with a gas flow. The results showed a highly uniform flow in the visualisation area, with only minor fluctuations near the walls. A similar observation was carried out for the temperature distribution. It was found that the extreme operating conditions caused substantial deformations of the spray plumes. However, the selected injector location allowed us to properly observe the spray formation regardless of the flow conditions. The study showed that the examined test rig enabled reliable spray investigations for a wide range of operating points.

Effects of cross flow on the heat transfer and flow characteristics of a circular jet are numerically investigated. The numerical results are compared with the experimental results. Studies have been conducted in the range of Reynolds number (Re) 5100–23 000, dimensionless jet-to-plate spacing ($Z/D$) 2–8, and ratio of cross flow Reynolds number to jet Reynolds number ($\alpha $) 0–2. Heat transfer in the stagnation, transition, and wall jet regions is studied. At all Reynolds numbers, maximum heat transfer is obtained at $Z/D$ = 6. Without cross flow, at higher $Z/D$ and in the range of Reynolds number investigated, maximum heat transfer occurs at the stagnation point. At low $Z/D$ and high Reynolds numbers, there are secondary peaks in the transition region due to the high turbulent kinetic energy (TKE). In certain cases, the Nusselt number at the secondary peak is more than that at the stagnation point. In the wall jet region, the Nusselt number calculated using equivalent flat plate correlations is much lower than the actual values. Cross flow results in increase in peak Nusselt number at low $Z/D$ and $\alpha $. Furthermore, the heat transfer in the upstream region deteriorates and that in the downstream region improves. The degradation in heat transfer is more at smaller $Z/D$. [ABSTRACT FROM AUTHOR]

Aimed at vortex-induced vibration (VIV) of the submarine reconnaissance telescope lifting above the water surface, a theoretical model for VIV of a cantilever cylinder under the actions of two different cross flows, i.e. gas and liquid, was established. The effects of parameters such as the distribution ratio and the density ratio for these two fluids on VIV responses of the cylinder were studied. Based on the Galerkin technique and the Runge-Kutta algorithm, numerical results of the cylinder vibration responses were obtained. The results show that, the increase of the distribution ratio can widen the lock-in range of the cylinder. The peak amplitude of the cylinder increases first and then decreases with the distribution ratio. The amplitude reaches the maximum value with a distribution ratio of 0.5, and this maximum value will increase with the decrease of the density ratio. In addition, single-period and multi-period motions will occur with the change of the fluid distribution ratio. The present research provides a theoretical guidance for the design and analysis of the submarine reconnaissance telescope. [ABSTRACT FROM AUTHOR]

Based on the rear-step flow reactor, the flashback characteristics of kerosene spray in cross flow under high temperature and high pressure are studied by means of thermocouple and optical test. The research focuses on the process and critical conditions of the spray flashback. The operating conditions are as follows: pressure ranging from 0.25 to 0.75 MPa, temperature ranging from 469 to 800 K, and inlet velocity 40 m/s. The results show that when flashback occurs, the flame is obviously unsteady with strong thermoacoustic oscillation; the starting point of flashback is located at the upper edge of the spray; with the increase of pressure and temperature, the starting point gradually increases in height; the local equivalent ratio of the starting point is about 1; The critical equivalent ratio of flashback increases with the increase of temperature and pressure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fluid flow and mass transfer in cross-flow across non-uniform bundles are studied. • A small and a large geometry made by low and high porosity regions are simulated. • In the small geometry friction coefficient is flat for Re ≤ 1, depends on θ for Re > 1. • In the large geometry friction coefficient depends on θ even at very low Re. • Non-uniformity strongly reduces Sherwood number for Re → 0, enhancing it for Re > 40. This study explores fully developed shell-side hydrodynamics and mass transfer past straight fiber bundles with non-uniform porosity in cross-flow. Simplified geometries made up by checkerboard arrays of alternately high and low porosity regions are considered. Simulations are performed for two domain sizes: a small geometry (26 fibers) and a large geometry (104 fibers). In the small geometry, the Darcy friction coefficient (f T) exhibits hydraulic isotropy at low transverse flow Reynolds numbers (Re T) but becomes dependent on the flow attack angle (θ) at higher Re T. In the large geometry, this dependency is observed at lower Re T. A non-uniform porosity reduces f T at almost all Re T and θ in the small geometry, with the large geometry exhibiting a more complex behavior. Regarding mass transfer, up to Re T ≈1-10 (depending on θ), a non-uniform porosity leads to lower Sherwood numbers compared to regular square arrays. However, at higher Re T , it enhances mass transfer. [ABSTRACT FROM AUTHOR]

Fuel leakage and spill fires often occur during storage and transportation of liquid fuels. And the spread and burning processes of spill fires are susceptible to cross-air flows. In this paper, spill fire experiments were conducted on a fireproof glass (with or without ignition) under different wind speeds (0–2 m/s). The effects of wind on the spread process and burning behaviors were analyzed. Results showed that, for the cases without ignition, the spread length could vary in a non-linear manner with wind speed. And a spread length model was developed based on force analysis. For spill fires under small wind speeds, the burning area increased firstly, followed by a decrease before stabilization. When the wind speed exceeded a critical value, the fuel layer spread rapidly in the upwind direction after the shrinking phase. The steady stage was observed for all tests. With the wind speed increase, the quasi-steady burning area changes from being circular to elliptic first, before it gradually became circular in the end. To explain this process, a detailed heat transfer analysis was conducted. Considering the fuel layer shape and the heat transfer characteristics of spill fires, an analytical burning rate model was developed. • Wind drag force shows a significant effect on the spreading process for non-ignition continuous leakage tests. • Three typical spill fire spreading behaviors can be observed under different wind speeds. • The variation of the convective feedback with wind speed is primarily responsible for the change in the fuel layer shape. • An analytical model is developed based on the stagnant layer theory to calculate the burning rate of liquid fires. [ABSTRACT FROM AUTHOR]

The investigation of nanofluid’s cross flow, which is caused by a nonlinear stretching sheet within the boundary layer, is presented. The proper mathematical detail is provided for three distinct cross flow instances with the streamwise flow. A uniform transverse stream located far above the stretched plate, in one instance, creates the cross flow. Two further situations deal with cross flows caused by surface transverse shearing motions. Weidman’s work was used to find a similarity solution by making the necessary changes. It has been found that two parameters, namely nanoparticle volume frictions ϕ and a nonlinear stretching parameter β, have a significant impact on the flow of fluids in cross flow scenarios. Graphical representations of transverse and streamwise shear stresses and velocity profiles are provided. From this study, we found that nanoparticle volume fraction ϕ reduces the momentum boundary layer in both streamwise and cross flow scenarios while increasing the temperature of the fluid and, hence, increasing thermal boundary layer thickness. The same is observed for the nonlinear stretching parameter β.

Polymer gel has been established as a water shut-off control agent for improved oil recovery. The role of the polymer gel in conformance control is to divert injected water from high permeability to low permeability zones of the reservoir. This paper presents a series of core flooding tests performed to investigate the propagation, blocking capability, permeability reduction and diverting performance of various mixtures of polymer gels at simulated reservoir condition. In this particular study, a core flooding scheme with crossflow effect using composite core has permeability contrast. Core flooding test with crossflow effect simulates reservoirs with communication between reservoir permeability layers. Experimental results show that PAM/PEI polymer gel reinforced with solid silica NP has been proven to provide satisfactory gel strength to divert water flow, thus recovering an additional 24% of oil. This reinforced PAM/PEI polymer gel tends to recover more trapped oil compared to weakened PAM/PEI polymer gel without solid particles. These results give better understanding and provide additional knowledge of strengthening gel by addition of solid particles, which could be the remedy for the weakened polymer gel. [ABSTRACT FROM AUTHOR]

The article presents the evolution of a novel configuration of tube placements in a shell and tube heat exchanger (HX). A CFD analysis on a double cross flow arrangement of tubes reveals improved mixing of the shell-fluid which is expected to increase heat transfer. This arrangement was modified for easier manufacture and maintenance, which led to the hybrid double cross flow (HDCF) arrangement. Experiments were carried out in the HDCFHX, for parallel and counter flows, to compare its performance against the conventional staggered arrangement. The HDCFHX comprises composite bundles of three and four tubes. The three-tube bundle is arranged in a staggered manner to themselves and orthogonal to the four-tube bundle. Ambient air at of 32 °C was used as the shell-fluid for Reynolds number ranging from 500 to 1000, for a fixed flow rate of 0.6 kg/min of water entering the tubes at 85 °C. This arrangement was observed to enhance the heat transfer with relatively lesser increase in pressure drop. The HDCFHX gave a significant improvement in heat transfer rate per pressure drop of 17 % to 38 %, vis-à-vis the conventional staggered arrangement in the parallel mode. The counter flow mode overly exhibited a similar trend, wherein the increase in this ratio varied from 8.5 % to 27.5 %. [ABSTRACT FROM AUTHOR]