Cross-flow Channel Research Articles

Flow and Heat Transfer Behaviors of Impinging Spiral Jet Arrays in a Rectangular Channel Based on Battery Cooling Technique

Impinging spiral jet array cooling, an innovative concept, has been proposed as a way to enhance the thermal management of batteries in electric vehicles. The comprehensive flow and heat transfer behaviors of impinging spiral jet arrays in a rectangular channel with/without crossflow were numerically studied. In this study, the total spiral nozzle length was 290 mm under the helix generated at a slot nozzle thickness of 1.0 mm. The rectangular crossflow channel for the heated zone had length and width ratios of 18 and 12. The jet-to-target spacing was 1.0. The jet Reynolds numbers ranging from 5000 to 20000 were performed via the shear stress transport turbulence model. The results showed that the regional average Nusselt number increased with the increase in jet Reynolds number for all conditions. The average heat transfer rate in the case with crossflow was beyond 7.8% higher than in the case without crossflow due to the cumulative crossflow, the concentration of each impingement jet was deflected and bent downstream.

Energy mechanism of gas channeling channels in complex fracture networks for CO2 injection in ultra-low permeability reservoirs

The injection of CO2 into ultra-low permeability can enhance production as well as accomplish storage of carbon. However, the gas channeling phenomenon is serious and there is a lack of explanation of the energy mechanism. Based on the current state of CO2 gas channeling in the Y29-105 well group located in the Huang 3 block of Jiyuan Oilfield, this study utilises the ABAQUS finite element cohesion model to explore the mechanical evolution of the CO2 channel expansion process. And according to the size of the cross-flow channel, intra-fracture pressure, damage displacement and expansion pressure, it is divided into the unconnected stage, the inter-well connected stage and the well group connected stage. Furthermore, we also established energy judgment criteria for the expansion behaviour of gas channeling channels, including stopping at natural fractures, extending along natural fractures, and directly crossing natural fractures. Upon comparison with theoretical and experimental results, it was determined that the energy discrimination criterion is appropriate for expansion along natural fractures and cross natural fractures. It can be seen that our research results can offer energy mechanism support for preventing, controlling, and predicting large-scale CO2 injection in ultra-low permeability reservoirs.

Investigation of the Discharge Coefficient for Laidback Fan-Shaped Holes on Turbine Blades Under Internal Crossflow Condition

Abstract The discharge coefficient of laidback fan-shaped holes on turbine blades under internal crossflow conditions is investigated using experimental and numerical simulation methods. The study is conducted on a linear cascade, with single rows of film holes set on both the pressure and suction surfaces of the test blade, coolant supplied by an internal crossflow channel. The internal crossflow Reynolds number ranged from 39,100 to 78,200, and the pressure ratio ranged from 1 to 1.5. This research considered the effects of internal crossflow Reynolds numbers and hole length-to-diameter ratio on the discharge coefficient of laidback fan-shaped holes. The findings are as follows: internal crossflow increases the inlet loss of film holes and flow separation within the holes, leading to a significant reduction in the discharge coefficient of film holes. Meanwhile, film holes on the pressure surface of the blade exhibit greater sensitivity to crossflow. Under different hole length-to-diameter ratio conditions, the length of the cylindrical section is the primary factor affecting the discharge coefficient, and the magnitude of the discharge coefficient depends on the extent of flow separation within the cylindrical section. The sensitivity of the discharge coefficient to variations in the cylindrical section length decreases once the cylindrical section length exceeds 2.8D for the pressure surface and 2.0D for the suction surface, where the inlet separation region reattaches to the wall. Under plenum conditions, there are significant differences in the discharge coefficients of film holes between the suction surface and pressure surface, especially at pressure ratios below 1.05.

Effects of Ribbed Crossflow Channel in a Turbine Blade on Film Cooling Performance of Diffusion Slot Holes with Various Cross Section Orientations

Abstract This paper investigates the influence of ribbed crossflow on the film cooling performance of a turbine rotor blade. A pressure-sensitive paint measurement technique was employed to measure the effectiveness of film cooling. The discharge coefficients were also measured to determine the flow resistance. A row of film holes was positioned at the pressure surface or suction surface with a spanwise hole spacing of 7.5D, which is half of the rib spacing. The experiments were carried out at a mainstream Reynolds number of 520,000, a turbulence intensity of 3.6%, and a density ratio of 0.97. The crossflow inlet velocity was 45% of the cascade inlet velocity. A fan-shaped hole with a 14 deg expansion angle (Fans-14), a horizontally oriented slot cross section diffusion hole with a 14 deg expansion angle (H1.7-14), and two vertically oriented slot cross section diffusion holes with 14 deg (V1.7-14) and 20 deg (V1.7-20) expansion angles were tested with/without crossflow. The results indicated that the slot cross-sectional orientation significantly changes the flow patterns inside the holes. H1.7-14 has stronger lateral expansion and better surface adhesion, while V1.7-14 and V1.7-20 yield more uniform lateral velocity distributions. Regardless of crossflow, H1.7-14 produces the highest film effectiveness and discharge coefficient on the pressure surface, while it changes to V1.7-20 on the suction surface. The ribbed crossflow increases the film effectiveness on both the pressure surface and suction surface, except for V1.7-20, as it is almost unaffected by the crossflow.

Evaluation of Adjoint-Optimized Holes—Part I Baseline Performance

Abstract With the advent of the use of additive manufacturing to build gas turbine components, the design space for new hole geometries is essentially unlimited. Recently, a computational adjoint-based optimization method was used to design shaped film cooling holes fed by internal co-flow and cross-flow channels. The associated Reynolds-averaged Navier–Stokes computations predicted that the holes optimized for use with cross-flow (X-AOpt) and co-flow (Co-AOpt) would significantly increase adiabatic effectiveness. However, only the X-AOpt hole was tested experimentally in this previous study. Though the experimentally measured performance for this hole was much less than computationally predicted, it still had a 75% improved performance compared to the conventional 7-7-7-shaped hole. In the current study, the X-AOpt and Co-AOpt-shaped holes were experimentally evaluated using measurements of adiabatic effectiveness and overall cooling effectiveness. Coolant was fed to the holes with an internal co-flow channel. For reference, experiments were also conducted with the baseline 7-7-7-shaped hole, and a 15-15-1-shaped hole (shown in a previous study to be the optimum expansion angles for a shaped hole). Furthermore, overall cooling effectiveness measurements were made with engine-scale models to evaluate the performance of additively manufactured (AM) X-AOpt and Co-AOpt holes with a realistic metal build. Results from this study confirmed that the X-AOpt hole had a 75% increase in adiabatic effectiveness compared to the 7-7-7-shaped hole. However, the Co-AOpt hole had only a 30% increase in adiabatic effectiveness, substantially less than had been computationally predicted. Measurements of overall cooling effectiveness for the engine-scale models and the large-scale models followed similar trends.

Experimental and numerical convective heat transfer performance analysis of a confined impinging round jet with triangular tabs under crossflow influence

In this study convective heat transfer performance of a confined impinging round jet with/without nozzle tabs under channel crossflow is investigated experimentally and numerically for a wall mounted heated module. Numerical investigations are carried out for different jet to crossflow velocity ratios (Vr) and compared to experimental data. Four different Vr values (5,6,8, and 10) are tested for single target plate distance to jet nozzle diameter ratio (H/D=8). ANSYS Fluent software is used for numerical simulations while infrared thermography is utilized for experimental investigations. Surface temperature values of the wall mounted module are obtained and presented along with complex flow structures obtained via numerical simulations. Results show that crossflow has decisive effect on temperature distribution on the component. By inserting triangular tabs to the nozzle exit, it is possible to further decrease the surface temperature of the module and minimize the crossflow caused jet deflection. The addition of triangular tabs resulted in a significant increase of up to 10% in the mean Nusselt number on the top surface of the module at Vr=10.

Nanofluid cooling of a hot rotating circular cylinder employing cross-flow channel cooling on the upper part and multi-jet impingement cooling on the lower part

This study explores the convective cooling features of a hot rotating cylinder by using the combined utilization of cross-flow on the upper part and multi-jet impingement on the bottom part. The analysis is performed for a range of jet Reynolds number (Re) values (between 100 and 500), cross-flow Re values (between 100 and 1000), rotational Re values (between −1000 and 1000), cylinder size (between 0.25wj and 3wj in radius), and center placement in the y direction (between −1.5wj and 1.5wj). When the cylinder is not rotating, the average Nu increment becomes 102% at the highest jet Re, while it becomes 140.82% at the highest cross-flow Re. When rations become active, the impacts of cross-flow and jet impingement cooling become slight. As compared to a motionless cylinder, at the highest speed of the rotating cylinder, the average Nu rises by about 357% to 391%. For clockwise rotation of the cylinder, a lager cylinder results an increase in the average Nu by about 86.3%. At the lowest and highest cross-flow impinging jet Re value combinations, cooling performance improvement becomes a factor of 8.1 and 2, respectively. When the size of the cylinder changes, entropy generation becomes significant, while the vertical location of the cylinder has a slight impact on entropy generation.

Characteristics of planar buoyant jets and plumes in a turbulent channel crossflow from direct numerical simulations

AbstractThis paper is motivated by an interest in understanding the characteristics of buoyant fluids discharged from the bottom wall of channels, such as encountered during tunnel fires or in river effluent discharge. Direct numerical simulation is used to model the upward release of a planar buoyant jet or plume from the bottom wall of a channel into an incoming turbulent crossflow. The well-studied jet-in-crossflow with only a momentum source is simulated first, and subsequently, fixing the incoming Reynolds number, buoyancy source as heat flux is added alongside varying momentum source, with two cases where only a buoyancy source is present. Appropriate five non-dimensional parameters relevant for this flow are defined, of which three are fixed and two—source to channel momentum ratio and Richardson number—are varied. The changes in turbulence characteristics as the buoyant jet or plume evolves downstream are presented. In all cases with buoyancy, except for the pure jet case, the plume is initially confined to the lower half of the channel before it suddenly lifts to the top half, an effect that occurs at an increasingly smaller downstream distance with increasing buoyancy, and dividing the flow into a near and far field. The distributions of mean and Reynolds stresses in the near and far field of the source are reported, and it is found that the channel flow becomes more turbulent downstream of the source, and further, the turbulent vertical temperature flux switches sign from near to far field owing the a change in the mean temperature gradient sign. From the input parameters and using the integrated temperature equation a reasonable estimate of the far field mean channel temperature can be obtained by a reference temperature based on the heat conservation that includes the convective and diffusive source heat flux. A monotonic behaviour of the back-layering distance is also observed a function of this reference temperature, which was difficult to obtain with the two specified non-dimensional parameters.

On the aero-thermal performance of flat-plate film cooling hole with variable rib heights

This study conducted a numerical investigation into the impact of different cooling air feeding methods and structural parameters of the internal ribbed crossflow channel on the performance of cylindrical film cooling holes under varying blowing ratios. The considered flow conditions encompassed two feeding methods (plenum or crossflow channel), three different rib heights (h = 2–8 mm), three internal crossflow directions relative to the mainstream (θ = 0°–180°), and four blowing ratios (M = 0.5–2.0). In the case of crossflow, the external crossflow had a Mach number of 0.3, and the internal crossflow's Reynolds number was set at 2 × 105. The study delves into flow analyses of the hole and external flow field, discharge coefficient characteristics, aerodynamic losses, and heat transfer characteristics. The findings reveal that the presence of internal crossflow significantly alters the flow field and performance compared to the coolant plenum case. However, the effects of crossflow are attenuated when internal turbulence rib structures are introduced, and this damping effect is further pronounced as the rib height increases. The aerodynamic and cooling characteristics of the hole progressively approach those of a plenum supply form, a phenomenon aptly termed the “Plenum effect” of the ribbed crossflow channel.

Impact of V-shaped interrupted ribs in cross-flow channels on film cooling

This study primarily investigates the enhanced heat transfer of V-shaped ribs with?in an internal cross-flow channel and their impact on external film cooling per?formance. The aim is to assess the advantages of V-shaped ribs in the cooling of gas turbine blades. The research specifically discusses the internal heat transfer efficiency of smooth channels, channels with V-shaped ribs, and channels with intermittently placed V-shaped ribs at a blowing ratio, M, of 0.5 and three different Reynolds numbers. The results indicate that the vortices generated by the coolant passing through the positive V-shaped ribs and intermittently placed V-shaped ribs effectively impinge on the upper and lower surfaces, thereby enhancing heat trans?fer performance. Regarding film cooling, under low Reynolds number conditions, the film cooling efficiency of the positive V-shaped ribs is 9-20% higher than that of the smooth channel. Under high Reynolds number conditions, the film cooling efficiency of the negative V-shaped ribs significantly increases, reaching 29-120%. The study demonstrates that rib shape and inlet Reynolds number have a signifi?cant impact on the swirl intensity of the coolant in the film cooling holes, and fluid with a certain swirl intensity exhibits better film cooling efficiency.

Experimental pool boiling study on novel multistage cross-flow porous structure using FC-72 for high-heat-flux electronic applications

An experimental pool boiling study on multistage cross-flow porous structure was conducted under atmospheric pressure using saturated FC-72 as the working fluid. The novel design comprises two stages: each stage contains cross-flow rectangular channels of 1.5 mm in height and 1 mm wide connected by thorough circular pores 0.325 mm in diameter. The dimensions of the pores and channels in both stages were kept identical. Tests were conducted in three positions, enhanced surface horizontal position (EH), enhanced surface vertical position (EV-a), where upper stage channels were parallel to the buoyancy force, and enhanced surface vertical position (EV-b), where lower stage channels were parallel to the buoyancy force. The critical heat flux was significantly enhanced with an improved boiling heat transfer rate in all three positions using the multistage cross-flow porous structure. The highest heat flux of 107 W/cm2 was recorded in EV-b, followed by EV-a and EH with a wall superheat of 42 °C. The heat transfer coefficient was improved by 300% to 700%, and the critical heat flux was enhanced by 6.5 times compared to the plain surface. Improved performance is attributed to the cross-flow of multistage porous structure and orientation of the test section, which induced a breathing phenomenon and prevented the drying out of the test section by resisting the merging of large vapor bubbles for a longer period and decreasing its lingering time over the surface. Bubble behaviors were investigated utilizing a high-speed camera. Two separate modes of the boiling mechanism were observed. At low heat fluxes below 50 W/cm2, bubble discharge and liquid intake co-occurred at random pores and channels, whereas at high heat fluxes, volatile bubbles exhibited a breathing phenomenon.

The study of heat exchange processes during induction heating of the casing string in relation to the determination of behind-the-casing flows

One of the promising methods of geophysical survey of existing wells is active thermometry. The technology for conducting research using this method includes induction heating of a section of a metal casing string, registration and analysis of temperature changes in the range of induction exposure. As a result of heat exchange with the heated section of the column, a thermal disturbance is created in the fluid flow moving inside the column or in the behind-the-casing flow channel. The analysis of non-stationary temperature in the process of induction action allows solving actual practical problems, for example, determining the presence of fluid overflows in the space behind the casing string. In this work, on the basis of numerical simulation, the features of the formation of a temperature field in the process of inductive heating of the casing string are studied in relation to the determination of behind-the-casing fluid flows. Numerical simulation was performed using the Ansys Fluent software package. Fluid movement in the well is described by the Navier–Stokes equation in the Boussinesq–Oberbeck approximation, and its temperature is calculated taking into account forced and free convection. To calculate the temperature in the inductor, casing string, rocks and cement sheath, a non-stationary heat equation is used. The application of induction heating in diagnosing behind-the-casing flows in the sump, localized below the working perforated formations, in the annular space between the casing string and the cement ring is considered. The distribution curves of the cross-sectional average temperature in the casing string body in the induction heating interval at different flow rates in the casing cross-flow channel are plotted. It is shown that with an increase in the volume flow in the overflow channel, the maximum heating of the column decreases due to more intense heat transfer to the flow in the overflow channel. It has been established that the temperature curves show a “pull” of temperature (temperature disturbances in the body of the casing string propagate in the direction of flow in the overflow channel), the value of which increases with the flow rate in the overflow channel. It is shown that the temperature “pull” (the distance over which the thermal disturbance propagates) during upward flow exceeds the “pull” during downward flow, which is due to the influence of natural thermal convection in the fluid inside the casing string. On the example of the modeling conditions adopted in the work, it was found that up and down flows of more than 0.5 m3/day can be reliably determined from temperature measurements during the induction effect.

Numerical investigation on the performance of PEMFC with rib-like flow channels

An innovative flow channel inspired by the physical structure of the human rib was developed in this paper. The performance of a proton exchange membrane fuel cell (PEMFC) with the proposed rib-like flow channels under different flow patterns and relative humidity of anode (RH_a) was investigated. Compared with the conventional interdigitated flow channel (CIFC) and cross-flow channel (CRFC), the maximum current density of the counter-flow channel (COFC) was 1.06 A/cm2 at 0.4 V, with enhancements of 4.95% and 2.91%, respectively. In addition, the quantity referred to as non-uniformity N was introduced to quantify the concentration distribution of oxygen, the minimum non-uniformity N of 0.17 was obtained for CRFC, and the COFC exhibited a more uniform concentration distribution of temperature as compared with the CIFC and CRFC, indicating that the COFC would prevent the occurrence of local hot spots. The maximum net power density of COFC was 6.0% and 3.0% higher than that of the CIFC and CRFC. Finally, the maximum current density of RH_a = 30% was 1.06 A/cm2, which was 3.9% and 7.1% higher than that of RH_a = 60% and RH_a = 100%. The temperature with RH_a = 100% was more uniform in comparison with RH_a = 30% and RH_a = 60%, and the mass fraction of H2 decreased with the increase of values of RH_a. The proposed rib-like flow channel can further enrich PEMFC flow channel design and afford novel insights into the application of bionics in fuel cells.

Multi-scale visualization of incipient CaCO3 scaling on the polyamide layer of reverse osmosis membranes

Although robust models on water transport across reverse osmosis (RO) membranes exist, detailed mechanistic insights of mineral scaling in the active polyamide (PA) layer, especially through visual investigations, are still lacking. Herein, a holistic approach of imaging the onset of mineral scales in the PA-layer is detailed at different length scales. BW30 RO membranes were scaled by running CaCO3-rich feedwater in a narrow, spacer-filled crossflow channel for 120 min. Then, microscopy and spectroscopy-based characterization tools were applied to investigate the CaCO3 scaling in the PA-layer. The vaterite phase of CaCO3 dominated at the incipient stage and was amplified at higher flux. TEM imaging, followed by digital staining with unsupervised K-means clustering, demonstrated incipient scaling primarily on top of the intricate folds of the PA-layer. Scales with a characteristic size between 1 and 6 nm were also identified deep inside the randomly distributed microvoids formed by those folds, hinting at heterogeneous crystallization of CaCO3. Thus, membranes designed to limit the complex folding of the PA-layer could show more scale resistance. The improved visualization of PA-layer via TEM–K-means and resulting insights can be broadly used in designing novel scale-resistant membranes and evaluating the efficacy of membrane cleaning operations.

Conjugate heat transfer investigation of impingement cooling for ribbed internal passage of a turbine vane

In this study, the effect of internal cooling configuration on overall cooling effectiveness of gas turbine vane is investigated using conjugate heat transfer approach. The C3X turbine vane with internal cooling and a turbine vane leading edge model with combined impingement and film cooling scheme are used as primary cases. An impingement cooling configuration is designed in order to enhance cooling effectiveness on the leading edge of the internally cooled C3X vane. In an attempt to further improvement, two rows of ribs are added on regions where impingement jets do not cover. In the leading edge model, the effect of modification for internal cooling channel and within film cooling holes are investigated by adding different rib configurations in those regions. The SST model is adopted for turbulence modeling in fluid zones. In the C3X vane, overall cooling effectiveness is generally enhanced using impingement cooling configuration. Furthermore, span wise distribution of overall cooling effectiveness becomes uniform in the leading edge of the vane. In the leading edge model, it is found that overall cooling effectiveness is varied due to the change in distribution of coolant flow in internal cooling channel and on external surface of the vane by adding ribs in internal cooling channel. The case with ribs perpendicular to the internal channel cross flow provides higher overall effectiveness. The results also indicate that cooling performance of the film cooled vane is sensitive to the location of ribs installed within film holes. The interaction between coolant flow and hot gas flow and its contribution in cooling performance of the vane are elaborately discussed for the leading edge model.

Effects of crossflow-fed-shaped holes on the adiabatic film cooling effectiveness

The effects of internal crossflow-fed-shaped holes on the unsteady behavior of the adiabatic film cooling effectiveness were extensively investigated using high-resolution fast-response pressure-sensitive paint (fast-PSP). During the experiment, coolant (DR ≈ 1.0) was fed into either plenum chamber or crossflow channel at coolant to mainstream velocity ratio of VRc = 0.4-1.6, channel to mainstream velocity ratio of VRch = 0.4-0.7, and channel to coolant (hole-inlet) velocity ratio of VRin = 0.25-1.75. The mean and unsteady effectiveness were presented in the near-hole region (9D), where the significance of the internal crossflow was captured. The results affirmed the asymmetrical coolant deterioration behind the crossflow-fed-shaped holes compared with the plenum feed. The unsteadiness was originated from the hole entrance (i.e., in-hole counter-rotating vortex-pair (CRVP) and the in-hole vortex-tube structures for plenum and crossflow, respectively). The vortex-tube formed a swirl-vortex, which interacted with the CRVP at the windward side, leading to asymmetric CRVP and declined effectiveness. Meanwhile, the coolant spreading behind the crossflow-fed-shaped holes was sensitive to the hole-inlet velocity (VRin), showing symmetric spreading at VRin ≈ 1.0, biased to the windward at VRin < 1.0, and biased to the leeward when VRin > 1.0. The combined results insight our understanding into the coolant unsteadiness of the shaped-holes in-flow conditions, recommends modifying the hole-inlet shape in order to enhance the effectiveness and damp the corresponding unsteadiness.

Numerical investigation of impingement heat transfer on the crossflow channel with vortex generators

• A new vortex generator with downstream common-flow-down configuration is obtained. • The counter rotating vortex pair is extruded by a recirculation behind the jet. • The maximum enhancement of area averaged Nusselt number can reach up to 69.7%. • The additional increase of friction coefficient is lower than 10%. Vortex generators (VGs), as novel measures for suppressing a crossflow, have been used for the promotion of jet impingement heat transfer. In this study, to explore more VGs’ benefits, numerical simulations are investigated for the comparisons of a jet in crossflow with four VGs, considering the heat transfer performances and the flow interaction mechanisms. VGs with common-flow-up or common-flow-down configurations are arranged in the upstream or downstream of the jet hole. Parameter studies are carried out by varying the crossflow-to-jet ratio from 0.19 to 0.32, VG heights from 1/8 H to 1/2 H ( H is the jet-to-wall distance), and spacings between the jet and the VGs from 0 d to 2 d ( d is the jet hole diameter). Results show that a new VGs with downstream common-flow-down configuration (DCFD) is obtained with favorable enhancement of heat transfer, which is competitive to the upstream common-flow-up configuration (UCFU) studied in previous work. With the DCFD configuration, the extrusion of the counter rotating vortex pair is caused by a recirculation region generated behind the jet, which gives more blockage to the crossflow. In addition, the heat transfer for the DCFD case is promoted with the increasing height of the VGs, and decreasing the spacing between the VGs and the jet. The maximum enhancement in area averaged Nusselt number for DCFD case can reach up to 69.7% with a small increase in the friction coefficient of lower than 10%. This study will present much more possibilities for the heat transfer enhancement in more complex system, such as jet array system and nonuniform crossflow system.

Liquid-cooled structure design and heat dissipation characteristics analysis of cross-flow channels for lithium batteries

A detailed three-dimensional thermal model is developed to examine the thermal behaviour of a lithium-ion battery. This model is a cross-flow liquid cooling model, which can make the heat dissipation of lithium-ion battery pack achieve higher safety. Two kinds of fluids are used for cooling, and the polynomial fitting function is used as the heat source term of lithium battery pack. The battery temperature distribution under the conditions of different Reynolds numbers, different numbers of micro-channel and different micro-channel radii are studied for this model. The simulation results show that the maximum battery temperature is 295.84 K, the minimum battery temperature is 293.14 K, and the maximum temperature difference of the battery pack is 2.7 K. The maximum temperature and temperature difference of the battery under the model are in line with the reasonable operating temperature range of lithium-ion battery pack. The maximum temperature of battery pack decreases with the increase of Reynolds number, but the effect of Reynolds number on heat dissipation of lithium-ion battery pack has a critical value. As the number of micro-channels increases, the maximum temperature of the battery string decreases. However, when the number of micro-channels increases to a certain value, the maximum temperature of the battery pack decreases slowly. The maximum temperature of the battery pack does not decrease monotonically as the radius of the micro-channel increases. Orthogonal analysis results show that the Reynolds number has the greatest influence on the cooling effect of the model, followed by the size of the micro-channel radius, and the number of micro-channels has the least influence. The optimized liquid cooling model can effectively reduce the maximum temperature of lithium-ion battery in theory, and the maximum temperature of lithium-ion battery decreases by 26.24 K in comparison with that of single battery at 2C discharge rate. The reliability of the cross-flow channel model is proved by numerical analysis, and it is also proved that the cross-flow channel has an equilibrium point between the perturbation gain and the flow retarding effect. The heat dissipation effect of lithium- ion battery pack is correlated with the number and radius of micro-channels, but not a single positive correlation. Reasonably increasing the number and size of micro-channels can effectively enhance the heat dissipation effect of battery pack.

A circular gradient-width crossflow microfluidic platform for high-efficiency blood plasma separation

Separation and collection of blood plasma are required steps for broad ranges of clinical diagnostic assays. Here, we introduce a continuous-flow blood plasma separation microfluidic device based on size exclusion cell separation in crossflow microchannels. A gradient-width crossflow microchannel structure is utilized to minimize blood cell leakage into the plasma collection channel while maximizing the flow rate for higher throughput. Additionally, the crossflow channels are placed at the corner of the blood channel to enhance Fahraeus effects, resulting in reduction of the concentration of blood cells around the entrance of the crossflow channels. Combined with a circular geometry that minimizes the footprint of the device for point-of-care diagnosis applications, the developed device significantly improves the performance of blood plasma separation in terms of separation efficiency, degree of hemolysis, and microchannel clogging by blood cells. At a relatively high flow rate of 2000 µl/h for a passive blood separation device, a plasma extraction ratio of 22% and red blood cell separation efficiency of 97% could be achieved using undiluted whole human blood, where such separation efficiency is about 28% higher compared with that of a conventional crossflow design. The effect of channel height and flow rate on the degree of hemolysis was also investigated, where the optimized device could achieve very little hemolysis (0.01–0.5%), demonstrating that the device can produce high-quality blood plasma. Integration of this high-performance, compact, and passive blood plasma separation microdevice with on-chip blood biomarker sensing elements can create a point-of-care diagnosis system with reduced cost, test time, and sample/reagent volume.

Film cooling performance for the cratered film-cooling holes with various coolant crossflow orientations

The present study investigates the influence of the coolant crossflow orientation on the cooling performance for the cratered film-cooling hole. It is well known that the quiescent coolant plenum is mostly adopted in the laboratory for convenience. In the present article, the coolant crossflow channels with three possible orientations in practice are further considered. The flow fields for the film-cooling are solved with the RANS method with the SST turbulence model at blowing ratios of 0.5, 1.0, and 2.0. The numerical results show that the coolant crossflow orientation significantly alters the coolant flow at the hole exit, further the downstream vortex structure and the cooling effectiveness. The symmetric flow and cooling effectiveness distribution occur for the quiescent plenum case, in-line parallel crossflow case, and the counter parallel crossflow case provide, but the asymmetrical flow and cooling effectiveness distribution for the perpendicular crossflow. The in-line parallel crossflow case gives almost considerable cooling effectiveness as the common quiescent plenum case. On the other hand, the counter-parallel crossflow case provides the worst cooling performance due to the opposite flow direction of the coolant supply relative to the mainstream flow. At the high blowing ratio of 2.0, the cooling performance is higher for the perpendicular crossflow feeding despite its asymmetrical distribution of the cooling effectiveness.