Inlet Flow Velocity Research Articles

The CPFD approach was used to investigate the particle flow characteristics and auxiliary air inlet in an ash transfer pipe

Numerical simulations for the air-solid two-phase flow in a horizontal pipe with a diameter of 125 mm and a length of 10 m were carried out using the Computational Particle Fluid Dynamics (CPFD) method. The deposition characteristics of particles in the pipe were investigated at various inlet flow rates and velocities, and the effect of the auxiliary inlet with different structural parameters on the evacuation of particles in the pipe after the auxiliary inlet was added to the horizontal pipe was compared. The results show that when the volume fraction of particles in the tube is less than 0.6, the flow of particles is relatively stable, and when the volume fraction of particles is greater than 0.8, the particles are seriously deposited and easily form a blockage; the auxiliary air inlet speed is proportional to the effect at the same tilt angle; when the air inlet speed is constant, the auxiliary air inlet angle increases from 35° to 55°, the effect of auxiliary air inlet increases and then decreases, and the effect of auxiliary air inlet reaches its peak at around 45°. The study's findings have implications for long-distance particle transport in horizontal pipelines.

Numerical investigation on falling film flow and heat transfer characteristics over corrugated plates

Falling film flow is commonly utilized in engineering applications. To explore the heat transfer process over falling film plates, the effects of structure and liquid inlet Reynolds number on flow and heat transfer characteristics are studied. The results indicated that corrugation amplitude and flow rate thicken the liquid film. As the corrugation amplitude increased, the critical inlet flow velocity for smooth flow gradually rose. The local heat transfer coefficient was great in the thin fluid film. The heat transfer performance of the optimum corrugated plate was 45%–77 % higher than that of a flat plate. An empirical correlation equation for Nusselt number was developed at Reynolds number of 149.28–398.09 and corrugation amplitude to wavelength ratio of 0.025–0.1. The deviation was less than ±21 %. These findings are significant for necessary temperature regulation in the CO2 capture packed column and also provide references for falling film equipment design and evaluation.

Numerical investigation of heat transfer characteristics of supercritical CO2 and water flow in 2D self-affine rough fractures

In recent years, efforts to maximize natural energy utilization have focused on harnessing energy from hot dry rocks (HDR) using supercritical carbon dioxide (SCCO2) or water as the heat transfer fluid. This study aims to enhance comprehension and evaluate the heat extraction performance of enhanced geothermal systems (EGS) by exploring the influence of various inlet velocities and fracture widths on the flow and heat transfer of SCCO2 and water within a rough single fracture in granite. This study utilized a 2D self-affine fractal function to create a rough-fractured rock with fractal properties in a φ50 × 100 mm granite sample. Investigating under 8 MPa conditions, we employed the thermophysical properties of SCCO2 and water to analyze the flow and heat transfer characteristics within the rough rock fractures. The results indicate the following: (1) Higher inlet velocities and wider fracture widths result in a broader temperature reduction range within the surrounding rock matrix for both SCCO2 and water. (2) Increasing the inlet flow velocity of SCCO2 and water leads to wider fracture widths, resulting in lower temperatures at the outlet end of the fracture. As the inlet flow velocity increases from 0.01 m/s to 0.04 m/s, the rate of temperature increase at the outlet can reach up to 19.8 % compared to water. (3) SCCO2, unlike water, exhibits significant reverse vortices at locations where the fracture surface morphology experiences substantial fluctuations. This behavior may be an indirect consequence of SCCO2’s higher velocity, with the direct cause being SCCO2’s lower viscosity and density than water. (4) Among the four conventional fluid thermodynamic parameters, specific heat capacity has the most significant impact on total energy flux rate (TEFR).

Performance optimization and scheme evaluation of liquid cooling battery thermal management systems based on the entropy weight method

Liquid cooling battery thermal management system (BTMS) is widely used in electric vehicles (EVs). A suitable liquid cooling BTMS scheme needs to be selected based on the magnitude of the weights for system performance. In this paper, thirty-six liquid cooling BTMS schemes involving the variables of cooling plate material types, flow channel layouts and inlet flow velocities are evaluated by using the entropy weight method (EWM) based on information theory. The weights and information entropies of the cooling performance, energy consumption performance and material cost of the system have been calculated and analyzed. The optimal scheme is selected considering global optimization based on the evaluation indicators. In addition, the cooling performance of the optimal scheme is examined under cyclic testing conditions (WLTC and US06). It is found that the flow channel layouts of the liquid cooling plate have a greater influence on the temperature control capability and temperature uniformity capability of the system. The liquid cooling system with a serpentine flow channel at an inlet flow velocity of 0.5 m·s−1, and aluminum as the cooling plate material exhibits the best cooling performance, energy consumption performance, and lowest material cost. The weights of material cost are 0.44, 0.32, and 0.34 under 1C discharge rate and cycle tests (WLTC and US06), respectively, which are the largest weight among the evaluation indicators. Material cost has the greatest degree of information dispersion because of the minimum information entropy, which plays a significant role in multi-attribute decision-making process. The temperature rise variation of the maximum temperature of the battery module under cyclic testing conditions is more reliable and dynamic compared with constant discharge rate conditions.

Tangential velocity and water vortex structure behaviour based on cylindrical-shaped basin’s design parameters for gravitational vortex power plants

The gravitational water vortex power plants (GWVPPs) have established in hydropower systems as a capable approach, generating micro-scale environment friendly electricity. In this system, energy is produced as a result of the interaction of water coming from an inlet canal with the turbine by creating a vortex in circular/conical-shaped structures. This interaction is based on an assumption that the water flow rate in a basin coincides with the tangential velocity on the turbine propeller. In this case, it is essential to investigate numerous geometric design parameters of the cylinder basin and their effects on vortex formation with the help of Computational Fluid Dynamics (CFD). Here, based on the CFD principles, the behaviour of various geometrical parameters on the vortex and tangential velocities in the basin are investigated separately with the help of Ansys Fluent, without using any turbine propeller. For a certain inlet flow velocity and head, different tunable geometric parameters for the gravitational water vortex plant with a cylindrical basin are inlet canal length, basin diameter, basin height and outlet diameter, respectively. The objective is to achieve an improved design configuration concerning factors such as tangential velocity, vortex arrangement, and the optimal placement of turbine propellers within this vortex.

NUMERICAL INVESTIGATION OF LIQUID-CARRYING AXIAL AND SWIRL FLOW IN A BENT PIPE

Water condensation occurs in the sloping sections of natural gas pipelines due to fluctuations in temperature and pressure. This event has a major effect on the efficiency and security of gas transportation. In this numerical study, the flow of water via a swirling flow in a wavy pipeline is examined using computational fluid dynamics. A 1-inch pipe is used to simulate a low-lying area of the pipeline, which is normally where the condensate water would gather. The effect of swirl on the flow patterns in the U-shaped pipe with previously published experimental results is studied and validated. In order to comprehend the change of static and dynamic pressure, results are extended in the doubly undulated pipe (w-pipe). According to the innovative analysis in this study, higher swirl flow could empty the water build-up faster than swirl flow inlet velocities below 11.2 m/s in a given amount of time. When the effusion volume increases and the water-carrying capacity is enhanced, several flow regimes, including annular flow, plug flow, slug flow, stratified wave flow, and stratified flow, are observed along with an increase in air velocity.

Analysis of hybrid active-passive prismatic Li-ion battery thermal management system using phase change materials with porous-filled mini-channels

The rapid expansion of electric vehicles (EVs) has created a significant demand for lithium-ion batteries (LIBs). However, ensuring safety and preventing thermal degradation of LIBs pose challenges to their overall performance and lifespan. Efficient battery thermal management systems (BTMS) are crucial in achieving long-lasting batteries with high energy density. Thermal management procedures are categorized into active and passive approaches. While active cooling methods are crucial, they consume power. Instead, passive cooling methods are not as influential in fulfilling all roles. This study examines a combination of active (mini-channel) and passive (PCM heat sink) techniques. The effects of employing a porous medium inside the mini-channel are also analyzed to enhance the heat exchange. Influences of different factors, including Darcy number, material, the thickness of porous media, and inlet velocity of mini-channel flow in multiple discharge rates (1C, 2C, 3C), are examined. Outcomes show the PCM heat sink itself can lessen the maximum temperature by about 4.2 to 5 K in different inlet velocities. The hybrid porous-filled channel and PCM heat sink can mitigate the maximum temperature by about 13 K in different inlet velocities and at the maximum discharge rate (3C) at the expense of about 14 % higher pumping power in different conditions.

Optimization Study of Cooling Channel for the Oil Cooling Air Gap Armature in a High-Temperature Superconducting Motor

With the continuous advancement of science and technology, the application of high-temperature superconductivity has developed rapidly. The high-temperature superconducting (HTS) motor replacing the copper coil in the traditional motor with HTS winding is increasingly used in power equipment, and the effective thermal management of HTS winding is vital in ensuring the life and effective operation of the HTS motor. In this study, five enhancement structures of indirect oil cooling channels were designed to improve the heat dissipation capacity of the HTS motor winding, and the enhancement effects of the different structures were comprehensively evaluated through numerical simulation using Fluent software 2022R1. The best enhancement structure was selected through structural optimization. The results showed that the Nusselt number of the gap-type enhanced structure was higher than that of the V- and staggered-type structures at the same flow velocity and 68% higher than that of the bare pipe. At the same inlet flow velocity and with a pressure drop limit of 30 kPa, the performance evaluation criterion value of the gap-type structure was 39% and 63% higher than that of the staggered- and V-type structures, respectively. The gap type is the optimal enhancement structure and can effectively improve the heat dissipation of the HTS winding coil.

Effect of leading edge and trailing edge serrations on a rotating Wells turbine

Wells turbine used for wave and wind power generation is known to generate loud noise during its operation. Aerodynamic noise reduction is an important issue in the design of the turbines. Since aerodynamic noise depends highly on behavior of the vortices around the turbine and the flow structure in the wake region, understanding of behavior of the unsteady flow past a rotating turbine plays important role. In this study, we modeled Wells turbine with normal (solid) blades and serrated turbine. To visualize the flow separation and vortex generation near the rotating turbine at its startup, LES simulations were performed by using moving mesh and transient inlet condition. In addition to the detailed flow structure around the turbine, the results show that the axial torque of the turbine increases with respect to the monotonically increasing inlet velocity. It is also found that positive axial torque generated for the normal and trailing edge serrated turbines as the inlet flow velocity increased, but no torque was obtained for the leading edge serrated turbine due to flow separation at the leading edge.

Study on static and dynamic characteristics of water-lubricated hydrostatic thrust bearings – Effect of feed hole inlet shape on bearing characteristics

Recently, water-lubricated hydrostatic bearings have been attracting attention. However, when water is used as the lubricating fluid, the flow velocity of the feed hole used as a restrictor is higher than that of conventional oil-lubricated hydrostatic bearings, resulting in a larger feed hole inlet flow velocity, making it difficult to analyze its characteristics using conventional hydrostatic bearing analysis methods. Therefore, in this study, a general-purpose fluid analysis tool has been used to numerically analyze the internal flow of two types of pocket-type water-lubricated hydrostatic thrust bearings with different feed hole inlet geometries and found that the pressure loss at the feed hole inlet is large for water-lubricated bearings and that the flow inside the feed hole is different from that of oil-lubricated hydrostatic bearings. The orifice effect at the feed hole inlet is found to account for most of the restrictor function. Furthermore, it was shown that the pressure loss at the feed hole inlet can be increased by adopting a right-angle inflow structure for the feed hole inlet geometry, which can improve the static and dynamic characteristics of the bearing.

Numerical Simulations on Combustion and Heat Transfer in Porous Medium with Different Gyroid Triply Periodic Minimal Surfaces Structures

ABSTRACT To investigate the influence of the porous medium with Triply Periodic Minimal Surfaces (TPMS) structures on lower concentration methane combustion. This study analyzed the flow field and heat transfer in the porous medium with three types, i.e. an axial gradual period type, a conical type and a uniform type, through the pore-scale simulation (PSS) approach. In cases of this study, the flashback equivalence ratio of the conical PMB is about 12.5% lower than that of the gradient PMB at the same inlet flow velocity, and the blow-off inlet flow velocity of the conical PMB is about 30% higher than that of the gradient PMB at the same equivalence ratio. Moreover, the flame shape is closely related to the local solid structure and flow velocity. The solid surfaces radiation heat transfer occurred mainly in regions with high solid temperature gradients. Additionally, the absolute value of the radiant heat flux is about 1/4 to 1/5 of the total heat flux, which reflects the proportion of thermal convection in the heat transfer on the solid surface. Convective heat transfer between solid and fluid occurred mainly in the areas of heat recuperation known as preheat zone, and higher inlet flow rates significantly increase the upstream convective heat transfer intensity.

Economic particulate transport performance analysis of k-epsilon models in highly concentrated slurry through pipelines

The paper analyzed the economic transporting performance of k-epsilon turbulence models using the Eulerian two-fluid approach in transporting highly concentrated fine particulate slurry through horizontal pipelines using Kaushal et al. (2005) experimental data of glass beads slurry of 125 μm mean diameter for volumetric concentration ranging 30%–52% and flow velocity ranging 2–5 m/s. The primary components of economical slurry transport are Specific Energy consumption (SEC) and pressure drop; both have been examined in the performance of different κ-ϵ models and are yet to be unlighted on these parameters. The CFD model found the excellent performance of all k-epsilon models with slightly more effectiveness in the case of the Realizable κ-ϵ model. The analyzed and validated CFD model was subsequently used in examining the parameters of slurry flow, such as the secondary phase velocity, concentration distribution, and SEC analysis for the range of fine particles 125, 150, and 212 µm. The plotted contours from CFD are useful in visualizing slurry flow parameters at intermediates inlet values for slurry inlet flow velocity ranging 2–6 m/s and inlet volumetric concentration ranging 30%–55% for fine particles. Analysis revealed that the highly concentrated fine particles slurry transported at optimum volumetric concentration range of 40–45% are economical slurry transport.

A Comparative Study of Flow Boiling Heat Transfer and Pressure Drop Characteristics in a Pin-Finned Heat Sink at Horizontal/Vertical Upward Flow Orientations

Abstract With the continuous development of power electronic devices toward miniaturization and compactness, it is necessary to develop more efficient flow boiling heat transfer technologies. In this work, the flow boiling heat transfer and pressure drop characteristics of Novec649 in a pin finned channel under two kinds of flow orientations (horizontal and vertical upward) are experimentally investigated. Heat flux, inlet flow velocity, and inlet subcooling are considered as the variable parameters. The results show that among all boiling operating conditions, the heat transfer performances between two orientations are basically consistent, while the pressure drop of vertical upward pin finned channel is relatively lower, indicating that the comprehensive flow boiling heat transfer performance of vertical oriented channel is better. Subsequently, a series of flow visualization experiments are performed in vertical upward pin finned channel. With the increase of heat flux, four kinds of flow pattern are discovered in the order of dispersed bubble flow, bubble flow, homogeneous flow, and annular flow. In the region of annular flow, although a vapor flow has already formed in the channel, there is still a large amount of liquid phase surrounding the wall and pin fins. Therefore, no obvious heat transfer deterioration was observed in the pin finned channel. Along the flow direction, the diameter of bubbles will increase first, and then present obvious oscillation. As the heat flux increases, both the average bubble detachment diameter and the frequency increase correspondingly. As the fluid velocity increases, the average bubble detachment diameter presents a downward trend, while the average bubble detachment frequency presents an upward trend.

A comprehensive numerical study based on topology optimization for cooling plates thermal design of battery packs

This article focuses on the problem of fluctuating cooling system flow caused by different working states such as acceleration and braking during the actual operation of electric vehicles, which prevents the system from effectively dissipating heat from the battery for a long time. In the past, liquid cooling heat dissipation schemes designed based on structural parameters often relied on the experience of CFD engineers. There is no in-depth study of the heat propagation characteristics. At present, research on the application of topology optimization method in cooling plate design mainly focuses on the relative positions of single inlet and outlet, objective functions, and constraint conditions. There are very few studies evaluating the adaptability of different cooling plate structures at different flow rates. In this perspective, this work proposes a two-dimensional topology optimization method for obtaining the cooling plates with different topological structures such as the series of cooling plate structures with dual entrances and exits. The method comprises of a comprehensive study on variations of the inlet flow rate under different average fluid volume fraction, outlet width, and temperature weight conditions. The results indicate that setting an excessive inlet flow rate can actually lead to an increase in the average temperature of the optimized cooling plate. Subsequently, the cooling plate structure obtained through topology optimization at inlet flow rates of 0.015 m/s, 0.02 m/s, and 0.025 m/s was selected, and a three-dimensional electrothermal fluid coupling model was established based on its two-dimensional channel structure. Its cooling performance, flow characteristics, and heat transfer characteristics were analyzed, and compared with two straight channel reference models. The results indicate that the optimized cooling plate structure under low flow conditions has better heat dissipation performance. At a flow rate of 0.56 × At 10-6m3/s, compared to traditional cooling plates(CASE D, CASE E), the highest temperature of the battery using topology optimized cooling plates (CASE A) decreased by 3.5 K and 1.79 K, respectively, and the standard deviation of temperature decreased by 48% and 14%, respectively. Under the same inlet flow velocity, the area of the fluid region increases with the increase of the mean fluid volume fraction, and the width of the flow channel increases gradually and the branches increase significantly, from the concentrated solid region to the dispersed isolated region. At a low flow rate, the normalized temperature of the cooling plate increases with the increase of the flow rate of the coolant inlet, and when the flow rate reaches a certain value, in order to reduce the power loss of the cooling plate, the flow path is gradually concentrated on both sides of the cooling plate. This leads to the decline of the normalized temperature of the cooling plate.

On the Effects of Flow Swirl on Static Stability Limits and Flow/Flame Characteristics of Premixed Oxy-Methane Flames: An Experimental Study

ABSTRACT An experimental study was performed to investigate the effects of flow swirl on flow/flame characteristics and stability of atmospheric premixed oxy-methane (CH4/O2/CO2) flames. The flames generated by two swirlers of 55° and 45° swirl angles were tested on a test stand for a dry low emission (DLE) model gas turbine combustor at constant inlet flow velocity of 5.2 m/s and over ranges of operating oxygen fraction (OF: 21% to 70% - by volume in the O2/CO2 mixture) and equivalence ratio (: 0.2 to 1.0). Combustor static stability limits (flashback and blow-out) were determined experimentally in the -OF domain to identify the operational ranges of the combustor while varying inlet flow swirl. To understand the mechanisms for flashback and blow-out, the lines representing the stability limits were displayed in the -OF domain against the contours of combustor power density (PD: MW/m3/atm), adiabatic flame temperature (AFT), and inlet flow Reynolds (Re). Comparison of flame macrostructure and measurements of local flame temperatures were performed for the two swirlers over ranges of , OF, and AFT to determine the effects of such operational parameters on flow/flame interactions and flame stability and to serve as a database for validating numerical models for such flames. The results show that, for both swirlers, the flames blow-out at a very similar AFT of ~1600 K indicating the dominant role of AFT in controlling premixed oxy-flame stability near the blow-out limit. Compared to the same combustor with a 55° swirler, the 45° swirler has a wider stable combustion zone. Comparing the flames of the same AFT, at fixed inlet flow velocity, shows almost identical flame macrostructure whatever the operating inlet flow swirl, OF and φ.

Comparative analysis of combustion stability and flow performance in micro combustor based on the synergistic action of slotted blunt body and front-baffle

Flame instability is a key problem that needs to be solved, and the existing improvement methods are still insufficient. Different from the traditional single structure improvement, a novel synergistic combustion stabilization method is proposed. In this paper, the conventional blunt body is slotted to achieve “graded combustion”, and the front baffle is embedded on the slotted blunt body to guide fuel flow, thus strengthening the combustion and improving the flame stability. With the help of simulation software Fluent, the combustion characteristics of conventional blunt body micro combustor (CMC), conventional slotted blunt body micro combustor (MCESB) and front-baffle slotted blunt body micro combustor (MCESB-FA) are compared, and further researched the flow characteristics and inlet velocity. According to the findings, the synergistic action of slotted blunt body and baffle is beneficial to improve combustion performance and flame stability, MCESB-FA demonstrates the highest combustion efficiency, the flame breaking limits of the MCESB-FA up to 80 m/s. Besides, the turbulent kinetic energy behind the blunt body is significantly increased, which is conducive to the heat transfer for the central combustion zone and the cold fuel on both sides, so as to achieve strengthening combustion. Interestingly, the backflow area disappears due to the slotting, but the front-baffle embedding breaks the original fuel flow balance and re-forms the backflow area to achieve steady combustion. Finally, as inlet velocity increase, the MCESB-FA and MCESB have better combustion performance and flow distribution, especially under the combination of slotted blunt body and front-baffle.

Design and Reliability analysis of energy pile using soft computing technique and a comparative study between the developed soft compu-ting models

Geothermal or energy piles, are environmentally friendly piles that extract heat energy from shallow depths of the earth surface to heat or cool the structures constructed over them, such as multi-storey residential buildings, industrial complexes, and shopping malls [1]. Through the energy piles, the heat is injected into the ground or extracted from the ground by the fluid circulating mechanism inside the heat exchanger pipes (HEP). The fluid is passed through the (HEP), which are attached to the reinforcement cage of the pile foundation element [2]. The use of energy piles to meet the thermal needs of the built structures has proven to be both environmentally and economically viable, as well as having significant social benefits [3]. A lot of uncertainties are associated with geotechnical engineering applications, which are unavoidable as they deal with natural materials. The reliability analysis of geotechnical structures has gained much attention in the last few decades [4]. Therefore, this paper aim is to study the reliability analysis of the ultimate group capacity) of energy piles along with the comparative study of the models developed using soft computing techniques. In the current study, cone penetration test (CPT) was carried out at Manali, Chennai (India), which falls in earthquake zone 3. Furthermore, () of piles was determined using CPT data by considering various parameters (such as pile length (), pile diameter (), cone resistance, average cone penetration resistance, an average of minimum cone penetration resistance ), Young’s modulus (), temperature change (), and coefficient of thermal expansion ()) and then the reliability analysis was performed. IS 2911 (Part 1): 2010 was followed to find out the . The total load (mechanical load and thermal load) coming on a single pile was computed by assuming mechanical load as 100 kN and thermal load as stated in [5]. The average annual temperature variation of the ground surface was considered as 21 and the average yearly ground temperature as 13 to determine the thermal load applied to piles through the heat-circulating fluid (HCF). A cast-in-situ concrete energy pile of M35 grade was considered in this work. Based on the total applied load and of the pile, the various parameters of the bored cast-in-situ concrete energy piles (9.0 m × 0.7 m) were determined. Two U shape copper pipes having a diameter of 40 mm, and a thickness of 3mm, were embedded and placed 250 mm apart in the energy pile to carry fluid, i.e., water [5] as shown in Figure 1. A laminar flow having a heat-carrying flow inlet velocity of 0.183 m/s and a flow rate of 0.326 m3/h was considered for this work[6]. The thermal conductivity and heat capacity of the steel and concrete materials used in this work are {44.4 (W/m K) and 475 (J/kg K) } and {1.8 (W/m K) and 880 (J/kg K)}, and Young’s modulus of steel and concrete are 200× (MPa) and 32× (MPa), respectively [7]. The reliability index (β) was calculated using equation 1 for reliability analysis. 
 β = ( 1 )
 where and are the standard deviation of capacity (C) and demand (D). After designing and selecting various parameters of the energy pile, 100 sets of data were generated randomly for,,

Distribution characteristics of non-Newtonian fluid swirling flow field in a vane-type separator

Most of the fluids encountered in the oil and gas exploitation process exhibit non-Newtonian fluid characteristics, which presents new challenges for the treatment of produced liquid. In this paper, the Eulerian multiphase model and the power law model were coupled to simulate the distribution characteristics of non-Newtonian fluid swirling flow fields in a vane-type separator. Larger oil droplets are able to migrate to the pipe center at relatively weak vortex intensities, which helps to accelerate the formation of the oil core. Due to the rapid decay of the vortex strength, the tangential velocity of the oil droplets drops more rapidly than that of the axial component, thereby reducing the axial energy loss. As the volume fractions of inlet oil increase, the oil core becomes more pronounced, but the convergence of the oil phase gets worse. During the migration, the interaction between dense oil droplets increases the viscosity of the non-Newtonian fluid and decreases the tangential velocity, leading to a maximum apparent viscosity at the center of the pipe. A higher vortex intensity tends to stabilize the vortex core, whilst higher flow velocities, which increases rotational velocities at the exit of the deflection section, deforms the vortex more severely. Moreover, higher inlet flow velocities contribute to better convergence of the oil cores. All these factors are important to better understand the smooth characteristics of non-Newtonian fluids and to provide a theoretical basis for future design and optimization of efficient separators.

Joint effect of air flow and substrate wettability on evaporation of a sessile droplet on a solid surface

We study the evaporation of microliter droplets of water on hydrophilic, hydrophobic, and superhydrophobic substrates subjected to airflow around them. While there is a large body of literature on diffusion-limited evaporation, evaporation in the presence of external convection is not fully-explored. We use side-view imaging and a custom-built flow channel to record the evaporating droplets from the side and develop an analytical model for evaporation in the presence of convection. Based on the droplet’s inlet flow velocity and wetted diameter, the maximum Reynolds number is 203. We quantify the time-variation of droplet volume, wetted diameter, and dynamic contact angle as a function of substrate wettability and airflow velocity. We found that the droplet lifetime decreases with the airflow, which is explained by the larger contribution of the convective mass loss rate compared to the diffusive mass flow rate computed by the model. Interestingly, the droplet lifetime is longer on a hydrophobic substrate due to the smallest area of liquid-gas interface among the three substrates for a given airflow. In general, evaporation occurs at constant contact radius (CCR) mode for hydrophilic surface in case of without flow and for all cases of airflow velocity. The CCR followed by constant contact angle (CCA) mode is observed for hydrophobic surface, and CCA followed by mixed mode is reported for superhydrophobic surface. The theoretical model reasonably predicts the measurements of different cases of airflow velocity and substrate wettability.

Acoustic attenuation analysis of expansion chamber mufflers with non-uniform cold and hot flow

In the presence of flow, the acoustic field and the flow field inside mufflers will interact with each other. In order to capture this phenomenon, the frequency-domain linearized Navier–Stokes equations (LNSEs) are employed to investigate the vortex-sound interaction inside expansion chamber mufflers. The calculations are performed in three steps: (1) to obtain the background mean flow variables by using the steady-state CFD simulation, (2) to map CFD results to acoustic meshes, and (3) to calculate the acoustic perturbation by using the finite element method based on LNSEs. Primarily, the transmission loss of single expansion chamber with inlet/outlet extensions is predicted in the presence of cold flow and the numerical predictions of LNSEs showed consistent agreements with measurements published in the literature. With the increase of inlet flow velocity, transmission loss in the low frequency range is obviously influenced by the vortex-sound interaction, which is attributed to the energy transfer between the fluidic and acoustic scales inside the muffler. Further, the acoustic attenuation performance of dual-chamber mufflers with flow is investigated numerically and experimentally, and the LNSEs predictions agree well with measurements. In the presence of cold flow, the transmission loss curves of the mufflers in the low frequency range is disturbed by the acoustic dissipation and amplification, while the effect of hot flow on the acoustic attenuation behavior of the mufflers is almost the same as that of cold flow, except that the non-coaxial mufflers with side-inlet is remarkably influenced by temperature. The studies demonstrated that the background mean velocity gradient is the most important impact factor for acoustic attenuation performance of the dual-chamber mufflers in low frequency range, whether in the presence of cold or hot flow.