Flow Resistance Research Articles

Development of a liquid metal subchannel code applied to ocean conditions and study on the effect of core geometry parameters and ocean motions on flow and heat transfer characteristics

The Generation IV International Forum (GIF) proposes a type of liquid metal reactor, due to its thermal properties and efficient heat transfer in a relatively small system. This special heat transfer characteristic allows the liquid metal reactor to be modular in design and flexible in installation on a nuclear-powered ship. Accurate prediction of the coolant temperature and flow distribution between subchannels is important to ensure nuclear safety in the complex ocean environment. In this study, an ocean version of subchannel code is developed by adding the motion terms in the momentum equations for the liquid metal reactor core based on the previously land-based subchannel code. Since the research on the characteristics of flow resistance and heat transfer mechanism under ocean conditions is not mature, the original empirical model is still used in the ocean version code. The constitutive models of the liquid metal are analyzed and incorporated into the ocean code. The code has been verified and validated by comparing with Computational Fluid Dynamics (CFD) simulation results, and experimental data. The effect of geometric parameters such as rod Pitch to Diameter ratio (P/D), Rod to Wall gap (RTW) is studied in the liquid metal lead 7 rod bundles. In addition, the effect of heaving start-up and shutdown motions between liquid metal lead and water is discussed in the 5 × 5 bare rod bundles. In general, the modified subchannel analysis code can well complete the calculation of liquid metal reactor under ocean conditions, as well as provide support for the design and safety analysis of a liquid metal cooled fast reactor.

One-dimensional consolidation analysis of layered unsaturated soils: An improved model integrating interfacial flow and air contact resistance effects

Layered unsaturated soils exhibit complex mechanical and physical properties. Owing to the roughness between unsaturated soil interfaces and the presence of irregularly distributed micro-pores, this study explores the laminar flow of pore water and counter-cyclonic flow of pore air through these channels at low velocities. In response to the complex consolidation behavior of unsaturated soils influenced by the flow and air contact resistance, an improved model is developed. The model incorporates the flow contact transfer coefficient (Rω), flow partition coefficient (ηω), air contact transfer coefficient (Ra) and air partition coefficient (ηa). Semi-analytical solutions for pore water pressure, pore air pressure and settlement in layered unsaturated soils are derived by employing the Laplace transform and its inverse transform. The rationality of the model is validated through comparative analysis with existing solutions. Analysis of the improved model yields critical insights: the presence of flow and air contact resistance leads to the development of relative pore pressure and air pressure gradients at interfaces, which diminishes the influence of the permeability coefficients of the water phase (kω) and air phase (ka) on the consolidation process. Moreover, neglecting the flow and air contact resistance effects may lead to an overestimation of settlement.

Enhanced heat transfer performance in vapor chambers via fabrication of novel regular composite porous wick structures using selective laser melting

The composite structure wick has been proven to significantly enhance the heat transfer performance of vapor chambers. Aluminum vapor chambers offer advantages such as being lightweight and cost-effective, meeting the requirements for lightweight cooling in fields like aviation. This study presented two novel composite porous wick structures with regular-shaped pores, designed and controlled via selective laser melting (SLM): the vertical square pore composite wick structure and the round-vertical square pore composite wick structure. A water-cooling test platform was built to investigate the effects of parameters such as wick structure thickness, round pore diameter, and round pore depth on the heat transfer performance and thermal resistance of the vapor chambers. The results indicate that the optimal thickness for the vertical square pore composite wick structure was 1.5 mm, yielding a minimum thermal resistance of 0.04 K/W. When the thickness was below 1.5 mm, it caused a reduction in the density of the vaporized core and insufficient liquid transport capacity. Conversely, when the thickness exceeded 1.5 mm, the primary limiting factor for heat transfer shifts to vapor-liquid flow resistance. Furthermore, the round-vertical square pore composite wick structure can provide further improvements in vapor-liquid transport within the structure.

Particle Dynamics Study on Influencing Factors of Ice Slurry Flow Characteristics in District Cooling Systems

In district cooling systems, substituting the conventional cooling medium with ice slurry represents an ideal approach to achieve economical operation. During pipeline transportation, ice slurry exhibits heterogeneous flow characteristics distinct from those of pure fluids. Consequently, investigating the flow field characteristics of non-homogeneous ice slurry, quantitatively analyzing the rheological variations and flow resistance laws due to the uneven distribution of ice particles, and standardizing the comprehension and depiction of flow patterns within ice slurry pipes hold significant theoretical importance and practical value. This study analyzes the heterogeneous isothermal flow characteristics of ice slurry in a straight pipe by employing particle dynamics and the Euler–Euler dual-fluid model. Taking into account the impact of ice particles’ non-uniform distribution on the rheological properties of ice slurry, a particle concentration diffusion equation is incorporated to develop an isothermal flow resistance model for ice slurry. The flow behavior of ice slurry with initial average ice particle fractions (IPFs) ranging from 0% to 20% in DN20 horizontal straight and elbow pipes is examined. The findings reveal that the degree of heterogeneous flow in ice slurry is inversely proportional to the initial velocity and directly proportional to the initial concentration of ice particles. When the flow velocity is close to 0.5 m/s, the flow resistance of ice particles exhibits a linear positive correlation with changes in flow velocity, whereas the flow resistance of the fluid-carrying phase displays a linear negative correlation. As the flow rate increases to 1 m/s, the contribution of each phase to the total flow resistance becomes independent of the initial velocity parameter. Additionally, the drag fraction of the ice particle phase is positively associated with the initial concentration of ice particles. Furthermore, the phenomenon of “secondary flow” arises when ice slurry flows through an elbow, enhancing the mixing of ice particles with the carrier fluid. The extent of this mixing intensifies with a decrease in the turning radius and an increase in the initial velocity.

Comparative studies on heat transfer and flow resistance of nanofluid in microchannels with different sidewall micro-fins

Comparative studies on heat transfer and flow resistance of nanofluid in microchannels with different sidewall micro-fins

Design and experimental analysis of a novel thermal diode with asymmetric heat transfer inspired by feather

To overcome the limitation of isotropic heat transfer of traditional heat pipes, a novel thermal diode with asymmetric flow resistance vapor channel inspired by the goose feather fibers is proposed in this study. The thermal performance of novel thermal diode is experimentally investigated. Results show that under the wide range of operating conditions, the thermal resistance of one end surpasses the thermal resistance of the other end, indicating its excellent thermal rectification capability. Under the filling ratio of 10 % and heating power of 7.5 W, the maximum thermal resistance of the thermal diode is 5.23 times the minimum thermal resistance, demonstrating excellent asymmetric heat transfer performance. Experimental results demonstrate that the novel thermal diode proposed in this study can easily change its unidirectional heat transfer direction by simply adjusting the internal filling ratio, showing significant application potential in the fields of thermal control system.

Effect of CO2 Concentration on the Performance of Polymer-Enhanced Foam at the Steam Front.

This study examines the impact of CO2 concentration on the stability and plugging performance of polymer-enhanced foam (PEF) under high-temperature and high-pressure conditions representative of the steam front in heavy oil reservoirs. Bulk foam experiments were conducted to analyze the foam performance, interfacial properties, and rheological behavior of CHSB surfactant and Z364 polymer in different CO2 and N2 gas environments. Additionally, core flooding experiments were performed to investigate the plugging performance of PEF in porous media and the factors influencing it. The results indicate that a reduction in CO2 concentration in the foam, due to the lower solubility of N2 in water and the reduced permeability of the liquid film, enhances foam stability and flow resistance in porous media. The addition of polymers was found to significantly improve the stability of the liquid film and the flow viscosity of the foam, particularly under high-temperature conditions, effectively mitigating the foam strength degradation caused by CO2 dissolution. However, at 200 °C, a notable decrease in foam stability and a sharp reduction in the resistance factor were observed. Overall, the study elucidates the effects of gas type, temperature, and polymer concentration on the flow and plugging performance of PEF in porous media, providing reference for fluid mobility control at the steam front in heavy oil recovery.

Heat transfer and entropy production analysis of Casson nanofluid under cylindrical stretching motion in the existence of aggregates nanoparticles

This paper focuses on the heat transfer and entropy production of the Casson nanofluid under cylindrical stretching motion in the case of nanoparticle aggregation. Calculations derived from the BVP4C numerical solution were utilized in the study to verify the accuracy of the calculations in comparison with previous results. The results showed that when the nanoparticle volume fraction was increased from 1% to 3%, the heat transfer efficiency improved by 2.72% in the absence of nanoparticle aggregation, while the heat transfer efficiency improved by 12.42% in the existence of nanoparticle aggregation. It is also found that the existence of aggregation of nanoparticles significantly increased the heat transfer capacity and flow resistance of the Casson nanofluid compared to the absence of aggregation. The results of this study can provide important theoretical support for applications in thermal management of stretched cylinders, biomedical drilling, and other fields.

The Study of the Mechanical Strength of Polypropylene Filter Material for the Production of Disposable Respirators

Atmospheric air, which is a natural resource, significantly affects the health and disease level of the population [1, 2], as well as the quality of the environment [3, 4]. However, as a result of anthropogenic activity, the environmental condition of the air has a tendency of constant deterioration [5, 6]. The main anthropogenic source of atmospheric pollution is large industrial conglomerates, which include motor vehicles [7, 8]. Chemical pollution of the air on a global scale leads to the greenhouse effect, the appearance of acid rain [9, 10] and pollution of aquifers [11, 12], and as a result, an increase in diseases [13], pandemics [14]. The goal of the study is to investigate the relationship between the mechanical characteristics of polypropylene filter material and their deformation under external forces for stretching and determine the safe period of use of disposable respirators. Four types of samples have been used for experimental research. Operational properties were determined by three indicators: elongation from applied force, penetration coefficient by a test aerosol of paraffin oil, and air flow resistance in accordance with the requirements of the DSTU EN 149:2017 standard. The dependence of relative elongation on tensile force has been established for samples of Eleflen and Meltblown materials with an additional layer of coarse fiber material and without an additional layer. It has been shown that the presence of an additional layer increases the tensile force of the filter material sample by 1.5 times. It has been found that the longitudinal fibers of the filter material samples withstand 15 % more external force applied for stretching, allowing manufacturers to ensure the proper fit of respirator structural elements, which ensures a longer service life. Research results show that an additional layer of material increases the strength indicators of the main filter layer by 3 times. Scientific novelty lies in determining the relationship between the mechanical characteristics of polypropylene filter material for the production of disposable protective respirators and their protective properties and deformation under external forces by stretching. The practical value involves in determining the penetration coefficient, which ensures the appropriate protective efficiency of the respirator within the range of 0 to 10% elongation. The presence of an additional layer of coarse fiber material allows increasing this value based on the properties of the filter material (fiber thickness, packing density).

The use of patterned heating in controlling pressure losses within sloping channels

The effectiveness of utilizing heating patterns as a drag-reduction tool in sloping channels is analysed. The usefulness of heating is judged by determining the pressure gradient required to maintain the same flow rate as in the isothermal case. The key to reducing pressure loss is the formation of separation bubbles, although these bubbles are washed away at relatively large Reynolds numbers. The bubbles reduce the direct contact between the stream and the side walls, thereby reducing the friction experienced by the flow. Moreover, the fluid inside the bubbles tends to rotate, a motion provoked by longitudinal temperature gradients. This rotation also seems to reduce the resistance. On the other hand, the existence of the bubbles tends to obstruct the stream, increasing the flow resistance. In general, channels oriented close to horizontal experience a relatively small pressure loss, but this loss grows markedly as the channel inclines towards the vertical. When modest heating is applied, the pressure loss is approximately proportional to the square of the associated Rayleigh number. It is also shown that if the heating wavelength is too short or too long, the heating loses its effectiveness. In certain circumstances, it turns out that the theoretical pressure-gradient reduction achieved by judicious heating is so large that it exceeds the pressure gradient required to drive the flow in the isothermal problem. The conclusion is that in these instances, a pressure gradient of the opposite sign must be applied to prevent flow acceleration.

A novel pulse liquid immersion cooling strategy for Lithium-ion battery pack

Ensuring the lithium-ion batteries’ safety and performance poses a major challenge for electric vehicles. To address this challenge, a liquid immersion battery thermal management system utilizing a novel multi-inlet collaborative pulse control strategy is developed. Moreover, different cooling methods (cooling structures, immersion coolants and pulse control method) are numerically investigated to assess their impact. Compared with other structural schemes, the battery module using baffles with fish-like perforations for the 5-in and 5-out scheme demonstrates superior cooling capability while reducing external power consumption. Furthermore, the utilization of FC-3283 exhibits better comprehensive performance compared to AC-100 and mineral oil. Notably, in terms of pulse cooling, when the output ratio reaches 50 %, the battery pack temperature can not only be maintained within a reasonable range, but also the time-averaged pump power consumption decreases by 87.6 % compared to the bottom inlet and top outlet scheme. At the same average flow rate, the liquid immersion battery thermal management system with output ratio of 25 % is the optimal choice for the trade-off between cooling performance and flow resistance, and compared with the bottom inlet and top outlet scheme, the maximum temperature and maximum temperature difference decrease by 23.7 % and 13.9 %, respectively.

Interplay between endothelial glycocalyx layer and red blood cell in microvascular blood flow: A numerical study.

The endothelial glycocalyx layer (EGL) plays a crucial role in regulating blood flow in microvessels. Experimental evidence suggests that there is greater blood flow resistance in vivo compared to in vitro, partially due to the presence of the EGL. However, the complex relationship between EGL deformation and blood cell behavior in shear flow and its quantification remains incompletely understood. To address this gap, we employ a particle-based numerical simulation technique to examine the interaction of the EGL with flowing red blood cells (RBCs) in microtubes. We examine changes in EGL deformation in response to variations in shear rate, EGL graft density, and contour height. Our results indicate that the alterations in EGL height are influenced by the mechanical properties of the EGL, flow conditions, and the RBC-EGL interaction. The flowing RBC compresses the EGL, causing a notable reduction in EGL height near the RBC flow. Additionally, we find that the presence of the EGL in the microtube results in increased RBC deformation and a wider gap between the RBC and tube wall due to spatial occupancy. The significant impact of the EGL on RBC flow is particularly evident in microtubes with diameters ranging from 7 to 10µm, a range consistent with notable differences in vascular flow resistance observed between in vivo and in vitro experiments. The simulation results shed insight on the dynamic interplay between RBC and the EGL in microvascular blood flow.

Soft Micropneumatic Touchpad

Soft tactile sensors outputting fluidic signals have many potential applications in soft microfluidic devices and soft robots. However, existing systems have been limited to a single or a few sensors in parallel, so they are not comparable to the state‐of‐the‐art electrical resistive and capacitive touchpads, which can detect rich tactile information, including touch location, pressure, area, and even multiple touches simultaneously. This work reports a soft micropneumatic touchpad. The touchpad consists of 32 pneumatic channels inside soft elastomer, with 16 channels aligned row‐wise and 16 column‐wise. The flow resistance of each channel is measured using a pressure divider. When the pad is touched, the cross‐sectional area of the channels close to the contact location deforms, which changes the flow resistance of those channels. With 32 sensing channels, the location, depth, area of the contact, and even two simultaneous touches can be detected. Letters hand‐written on the touchpad can be reconstructed from the measured data. With the assumption of sparsity, a tactile pressure map, with a value at each 16 × 16 grid point, can also be reconstructed. This work opens a path to replace electronic tactile sensors in soft devices with all‐fluidic alternatives.

Scaling up magnetocaloric heat pump for building decarbonization initiatives

Building decarbonization necessitates renewable heating and cooling solutions such as heat pumps. Magnetocaloric heat pumps (MCHP) offer environmental and efficiency advantages but face challenges when scaling up from existing active magnetic regenerator configurations. This study highlights uneven flow resistance, porosity, and refrigerant magnetocaloric effects as key obstacles to MCHP performance in parallel multi-bed setups. To address these effects, two control strategies for the fluid flow control system were investigated: measurement feedback control and model predictive control. Results show a 36.9 % heating power improvement with measurement feedback control, though with extended control convergence times. Model predictive control achieved approximately seven times faster control convergence compared to the measurement feedback control strategy, despite exhibiting minor overshooting. Utilization factor-based model predictive control increased the heating capacity by 1.6 %–30.9 % and the COP by 1.2 %–10.7 % in scenarios with uneven flow resistance and porosity, offering computational efficiency but assuming even magnetocaloric effects between regenerators. This assumption can be addressed by outlet temperature-based model predictive control, albeit at a higher computational cost using genetic algorithm. The findings emphasize the importance of advanced control methods to scaling up MCHP in renewable energy building systems.

Innovative flow field design strategies for performance optimization in polymer electrolyte membrane fuel cells

This study introduces an innovative flow field design methodology that departs from traditional approaches, aiming to simplify design variables and ensure an efficient, automated design process. This methodology integrates topology optimization, the Gray-Scott reaction/diffusion system, and Murray's law to design the flow field layout. We applied this methodology to the flow field design of Polymer Electrolyte Membrane Fuel Cells (PEMFC) bipolar plates. Specifically, the optimal two-dimensional pattern of the PEMFC cathode flow field was achieved by merging topology optimization with the Gray-Scott reaction/diffusion system. Applying Murray's law, an optimal three-dimensional flow field with an unpredictable new pattern was established. The design emphasizes efficient fuel diffusion and reduced flow resistance, validated through experiments. Quantitative comparisons with serpentine and parallel flow fields showed performance differences of approximately 60 mV and 120 mV at a current density of 1.43 A/cm2, respectively. These metrics reflect the impact on mass transfer efficiency under high-power PEMFC operations, serving as critical indicators of flow field effectiveness. Additionally, simulations confirmed an 18-fold reduction in pressure drop compared to the serpentine design. This innovative design process offers advantages that could be incorporated into diverse research areas in the future.

Heat transfer performance of a multiport mini-channel loop thermosyphon for cooling miniaturized electronic devices

Multiport mini-channel thermosyphon with hydraulic diameters less than 2 mm undergoes a severe entrainment problem both in vapor and liquid regions, impeding the flow and affecting the performance characteristics. To address this issue, a novel multiport mini-channel loop thermosyphon (MPMC-LT) design is proposed. This design separates the vapor and liquid flow paths, reducing entrainment and enhancing the performance characteristics. Tests are conducted with heat loads ranging from 5 to 45W at four inclinations (0°, 30°, 60°, and 90°) relative to the horizontal plane. Results revealed that the MPMC-LT design extends the entrainment limit by 10.6 times compared to conventional designs, reducing the interaction between the vapor and condensed working fluid. Additionally, the total entropy and thermal resistance drops by 20.7 % and 19.9 %, respectively at an optimum inclination angle of 30°. It is also noted that the effective thermal conductivity at the optimal inclination is 5.8 times higher compared to the conventional multiport thermosyphon designs. The design effectivity uses the buoyancy, inertial and surface tension forces to reduce resistance in the fluid flow, thereby enhancing the heat transfer characteristics. These results highlight that MPMC-LT is a suitable thermal management device for power electronic systems.

Obstructed Branching Networks: A Constructal Approach in Fluid Flow Investigation

Tree flow networks are common in both natural and manufactured systems. The organization of the flow hierarchy passes through the dimensional evolution of the form that is linked to the function. Thus, the objective of comparing bifurcated tube networks obtained by the constructal design method, where part of the structure is obstructed, aims to understand the effects on fluid flow and the prediction of evolutionary deviations in its function. This study compares designs of 3D tree networks with various homothety reduction factors for sizes, having tubes obstructed in some locals of the network. In this computational fluid dynamics study, the geometric constraint applied to these networks is the equal total volume of tubes at each branch level. The evaluation is based on the flow resistance of the networks. This study shows, among other things, that the performance of tree designs is highly dependent on geometric characteristics and the branching level where the obstructions are applied. The effect of the number and position of tubes obstructed in the network, as well as the alignment of the tubes across the network branching levels, on the asymmetry of fluid flow through the network is also studied. It is recommended that the results presented be considered when designing networks for engineering systems.

Tailored directional porosity in ceramic matrix composites (CMCs) for hypersonic applications

AbstractIn the field of hypersonic systems and their missions, the occurring flows impose extreme mechanical and thermal loads on the materials used. At the German Aerospace Center (DLR), extensive research is conducted in this area, ranging from design and specification to the development of suitable materials concluding with the proof of concept under realistic conditions in wind tunnels. In recent years, ceramic matrix composites (CMCs) have been investigated for specific aspects of hypersonics. These materials exhibit consistent mechanical behavior over a wide temperature range (up to 1600 °C), coupled with high damage tolerance and thermal shock resistance, distinguishing them from metals and superalloys. Particularly, special porous C/C–SiC ceramics (carbon-fiber-reinforced carbon with silicon carbide) enable innovative material applications for components in transpiration cooling, fuel injection, or boundary-layer transition control. The work presented focuses on the next generation of porous C/C–SiC ceramics currently in development. By deliberately modifying the textile preform, the resulting microstructure and pore morphology are influenced, allowing for control over both the total volume and the orientation of the pores. Relevant parameters influencing porosity have been determined based on the results, and an initial characterization has been conducted. It has been demonstrated that there is a preferred direction of porosity within the sample thickness (Z-axis), and in terms of hypersonic-relevant properties, an absorption coefficient of 0.58 for an acoustic wave at 500 kHz (static pressure of 15 kPa), as well as a length-specific flow resistance of 3.4 MPa s/m2 and an overall porosity of 12.25% were determined. Building upon these promising initial findings, the goal is to further expand the understanding of the parameters influencing porosity and to generate a tailored material for different application scenarios by correlating them with hypersonic properties.

Characterization of Geopolymer Masonry Mortars Incorporating Recycled Fine Aggregates

This study evaluates the characteristics of geopolymer masonry mortars (GMMs) made with slag–fly ash binder and up to 100% recycled fine aggregates (RFAs). For each RFA replacement rate, two types of GMMs, namely N and S types based on ASTM C91, were proportioned and tested for mechanical, physical, and durability properties. Results revealed that using geopolymeric binder enhanced the flow, water retention, compressive strength, sorptivity, and abrasion resistance of GMMs compared to cementitious counterparts but reduced the initial setting time by up to 75%. Subsequent RFA additions negatively affected the flow, setting time, density, water absorption, porosity, and bulk resistivity but enhanced the water retention, sorptivity, and abrasion resistance of GMM. It also reduced the compressive, pull-off, and flexural strengths by 36, 44, and 27%, respectively. Furthermore, S-type mortars exhibited improved bulk resistivity, sorptivity, and abrasion resistance compared to N-type counterparts. A multifunctional performance index deduced that the GMM mixes incorporating 100% RFAs were superior to geopolymeric or cementitious masonry mortars made with natural fine aggregates (NFAs). Such findings emphasize the sustainability of GMMs made with RFAs in masonry construction, eliminating the need for water curing while maintaining comparable or even superior properties compared to cement-based mortars made with NFAs.

Study of microfluidic heat transfer in 2D hydrophobic walls with different slip mechanisms

Numerous studies have shown that the gas at the solid-liquid interface in microflow can increase the slip length, reduce the flow resistance. However, the relationship between nanobubbles and fluid boundary slip is complicated, and the impact of nanobubble morphology must be considered. To investigate the combined effect of the bubble model on slip and heat transfer, we investigated the drag reduction and heat transfer effect of microfluidic flow on a 2D hydrophobic wall by theoretical derivation combined with numerical simulation. The comparison of the results revealed good agreement between the analytical solution and the numerical simulation results. It was shown that the gas slip generated by the rarefied gas significantly affected the flow heat transfer effect. Further analysis of the bubble meniscus shape revealed that minimizing the protruding angle of the meniscus is crucial for enhancing drag reduction. In addition, the simulation results also revealed that increasing the gas coverage fraction effectively reduces flow resistance while maintaining heat transfer performance. At the same time, the higher pressure enhanced the heat transfer effect while maintaining the stability of the drag reduction effect.