Pressure Drop Resistance Research Articles

Thermal Performance Improvement of Microchannel Heat Sink for Electronic Device Cooling System Using Numerical Analysis

The increasing miniaturization of technology has intensified thermal challenges, particularly concerning the cooling of small components like ICs and CPUs. Microchannel heat sinks offer a common solution, but optimizing their configurations remains a subject of interest. This study addresses multiple thermal enhancing factors that is position of the inlet and outlet and integrating pin-fin configurations. The objectives of the study are to improve the thermal uniformity of the heat sink and to analyse the thermal performance across the different geometry of pin-fin using Ansys. The thermal performance parameters focused on this study are the maximum temperature and pressure drop. The results gathered that hexagon shaped pin fin yield better thermal performance as compared to the other geometry as it shows the lowest maximum temperature, lowest thermal resistance and lowest pressure drop. This proves the significance of geometry selection for the pin fin as it affected the thermal performance of the microchannel heat sink with cross flow effects.

Selection of an oxygen injector for waste oxygen enrichment incineration with dual carbon targets

Abstract Waste incineration is one of the most effective means of achieving harmlessness, minimization, and resource utilization. As environmental problems become more and more prominent, the more stringent environmental standards will greatly limit the development of conventional waste incineration technology. Therefore, the development of a new type of clean and efficient waste incineration technology will be the inevitable development trend of the waste incineration industry. Oxygen-enriched injector sizing study was carried out based on Computational Fluid Dynamics (CFD) techniques for the oxygen-enriched incineration technology used in waste grate incinerators. The application of CFD method is applied to different types of oxygen injection device velocity fields, temperature fields, concentration fields, etc. The results show that the ring-type oxygen injector can achieve a good mixing effect, and the resistance pressure drop is minimized, which is better than the nozzle-type oxygen injector to meet the actual needs of the project.

Comparative analysis of performance of different types of Tesla valves

Abstract The Tesla valve is a valve with no moving parts. Its special configuration also allows the pressure drop of fluid passing through the Tesla valve from the reverse inlet to be much greater than the pressure drop of fluid passing through the Tesla valve from the forward inlet. Therefore, the Tesla valve has a certain degree of single pilot connectivity and pressure reduction capability. This article selected 8 common types of Tesla valves, By using numerical calculation method through Fluent simulation, the differences of resistance coefficient, pressure drop and Di value of 8 types of single-stage Tesla valves under three different working conditions were compared. In order to explore the performance of 8 kinds of Tesla valves under the three working conditions. At the same time, the relationship between the flow state and the structure of each part of the fluid before and after passing through the distributary pipe is analyzed. The simulation results show that due to the different structure of various Tesla valves, the flow rate, pressure and turbulent kinetic energy of the fluid inside the valve also have different changes. At the same time, there are many similarities in the flow state of some Tesla valves with similar structural types. Finally, according to the calculation results, the advantages and disadvantages of various types of Tesla valves and their applications are analyzed.

A Novel Piezoelectric Nonwoven Fabric for Recoverable High-Efficiency Filters.

Serious haze pollution, mainly caused by fine and ultrafine particulate matters (PMs) and aerosols, poses a significant threat to the public health, especially when the aerodynamic diameter is less than 2.5 μm. Electrostatic capture techniques, such as polymer electret filters and kinetic plasma processes, are widely used instead of mechanical filtration with high removal efficiency and low wind resistance (pressure drop). However, the inability to recharge, coupled with the generation of ozone byproducts, makes it challenging to meet the requirements for both recoverability and highly efficient filtration. Here, we propose an electrostatic filter as an alternative to conventional polymer electrets, aiming to achieve an ultrahigh removal efficiency, long-term performance stability, and reusability. Piezoelectric LiNbO3 (LN) particles are integrated into the polypropylene (PP) matrix through the melt-blown strategy to fabricate the LN/PP nonwoven fabric. Benefiting from the employment of piezoelectric LN particles, the LN/PP nonwovens exhibit an ultrahigh removal efficiency of 99.9% for PM0.3 to PM10. The airflow facilitates the sustained regeneration of piezoelectric charges on the surface of LN/PP nonwovens, thereby maintaining a removal efficiency of approximately 95% for continuous filtration over 11 days. Even after eight cycles of washing, the removal efficiency of the LN/PP nonwovens remains at nearly 90%, demonstrating the excellent reusability. Our proposed strategy offers an ingenious combination of high-efficiency and recoverability for filters, holding great promise for reducing plastic pollution.

Design of Draw Resistance of Pressure Drop Standards for Tobacco Products Based on the Flow Distribution

Summary Cigarette draw resistance and filter pressure drop are both critical physical indicators for the tobacco industry, which use testing equipment to measure the two parameters. Pressure drop standards are used as transfer standards to ensure the accuracy and reliability of the testing equipment. Pressure drop standards are generally cylindrical rods having a certain number of parallel capillaries. To address the issue of how to design and fabricate pressure drop standards quickly and conveniently, this paper proposes a design method for pressure drop standards based on structural parameters. The method uses a mathematical model of the internal airflow of the standard including the entrance effect into a circular capillary and uses an iterative calculation algorithm accordingly. By iterative calculation, the structural parameters of the pressure drop standard, namely, diameter and length of the capillaries, were obtained, along with the relationship between the draw resistance of the standard and the flow rate in each capillary. The accuracy of the mathematical model was validated by comparing and analyzing the experimental and theoretical draw resistance of standards with different structural parameters. The experimental results showed that the relative error between the measured draw resistance and the calculated draw resistance was below 8%, which proves the reliability and validity of the mathematical model, and provides theoretical support for the design and fabrication of pressure drop standards.

Pressure drop model of gas-liquid phase for Venturi scrubber in fog-annular flow

Venturi scrubber is widely used in wet dust removal. Its pressure drop performance determines the dust removal efficiency. The commonly used models, most of them are empirical ones, are hard to accurately predict the friction loss between the gas core and the liquid film near the wall, the proportion of the atomized droplets to the deposited liquid film, and the gas holdup, where the influence of the throat length on throttling and the local resistance formation mechanism were not discussed. Therefore, in this study, we established a pressure drop model for Venturi based on the theoretical derivation of two-phase flow and revision of local resistance pressure drop. It uses the similar theoretical method of straight pipe for Venturi, where the iterative method was employed to calculate the liquid-phase conversion coefficient which is related to the cross-flow ratio and the gas holdup. Meanwhile, the experiments and CFD simulations were carried out to validate the model and judge whether the local resistance should be considered. The results show that if the vena contracta extends out of the throat, the unconstrained expansion flow can cause the boundary layer separation, and the fluctuation of the two-phase flow in throat can induce Kelvin-Helmholtz instability, resulting in apparent energy loss. Accordingly, the critical throat length criterion was developed, and the pressure drop model was modified with the deviation less than 17.14%. It provides a scientific basis for establishing the universal two-phase theoretical pressure drop model of Venturi scrubber.

Turbulent forced convection flow of water-based nanofluids with temperature-dependent properties over backward-facing step channel with upwardly deflected downstream wall

The heat transfer performances of various water-based nanofluids (NFs) relative to the base fluid in turbulent forced convection flow within a 2-D backward-facing step (BFS) channel with an upwardly deflected downstream wall with a uniform heat flux are analyzed using the package OpenFOAM. The k-ω shear stress transport (SST) model based on the Euler-Euler single-phase framework is used. The performance evaluation criterion (PEC) is defined to assess the relative importance of the enhanced heat transfer and intensified resistance (pressure drop) caused by Cu/water NFs and MWCNT-Fe3O4/water hybrid NFs (low concentration NFs), Fe3O4/water NFs, and Cu-MWCNT/water hybrid NFs (high concentration NFs). At Re = 30215, the maximum enhancement of the average Nusselt number (ANN) is 7% when the copper NPs are added to the water. In addition, the increment of the deflection angle from 0.0 to 1.27 enhances the ANN values by 44 ∼ 45% concerning low-concentration NFs. At Re = 7940, the friction factor increases by 24.3% and 32.1% when copper and MWCNT-Fe3O4 hybrid NPs are dispersed in the base fluid, respectively. The highest PEC value (1.07) is achieved when the copper NPs with ϕ = 0.003 are used in configuration BFS1 at Re = 7940. Using MWCNT-Fe3O4 hybrid NPs is only proposed at lower Re numbers when the downstream wall is deflected and ϕ = 0.001. At Re = 30215, due to the addition of magnetic NPs, the ANN value abates by 28.5% and 30.7%, respectively, in the canonical case and configuration BFS2. Among the high-concentration NFs, the highest PEC (1.05) is obtained using Cu-MWCNT hybrid NPs with ϕ = 0.01 at Re = 30215 when the downstream wall is deflected upwardly. As Mouromtseff (Mo) number-based figure-of-merit (FOM) verifies, the worst scenario (PEC < 1.0) is substituting the base fluid with Fe3O4/water NFs. Cu-MWCNT/water hybrid NFs with ϕ = 0.02 become an effective coolant (PEC > 1.0) when the deflection angle and Re number increase simultaneously.

Photodynamic antibacterial micro/nanofiber composite membrane with high efficiency and low resistance filtration performance for medical protective materials

Bacterial infection is one of the major threats to human health worldwide, posing a great challenge to the development of medical protective materials with efficient filtration and long-lasting antimicrobial properties. In this study, electrospinning technology and non-woven fabrics were combined to construct a micro/nano-structured photodynamic rechargeable and storable antibacterial filtration composite membrane. The filtration efficiency of the composite membrane is as high as 99.99% for 0.5–5 μm particles, and the resistance pressure drop is 85 Pa. In addition, the release of OH and H2O2 from the composite film reached 5326.16 μg/g and 711.93 μg/g, respectively. After 7 cycles of quenching, the charging capacity retains more than 70 % of the original. It showed good antimicrobial properties even when stored under dark conditions for one month. The bactericidal efficiency of the composite membrane against E. coli and S. aureus exceeded 99% under both dark and light conditions. The development of this simple and clean micro/nanofiber membrane provides a new idea for exploring photoactive antimicrobial and filtration materials for medical protection.

Structural Improvement of Differential Motion Assembly in In Situ Pressure-Preserved Coring System Using CFD Simulation

In situ pressure-preserved coring (IPP-Coring) is one of the most efficient methods for identifying the scale of the oil and gas content. However, the differential motion assembly of the IPP-Coring system often undergoes ball and ball seat seal failure and sticking due to surface erosion, and a greater pressure drop may unexpectedly trigger the assembly. This paper addresses these issues by improving the hydraulic structure of an assembly based on a deep understanding of the flow characteristics in the assembly, thus increasing the success rate of the IPP-Coring. Computational fluid dynamics (CFD) was employed to investigate flows in a differential motion assembly. The effects of the diameter and outlet structure of the ball seat on the fluid status, velocity, and pressure distribution were thoroughly analyzed. When the ball seat diameter increased from 30 to 40 mm, the maximum velocity and pressure drop decreased to 0.55 and 0.2 times their original values, respectively. There was a severe vortex area in the differential motion assembly due to the presence of the ball seat, but changing the outlet structure in the ball seat to an arc structure decreased the length of the vortex area and the fluid velocity near the wall to 0.7 and 0.4 times, respectively, compared with those with the original right-angled structure. In addition, the pressure drop decreased to 0.33 times the original value. Thus, the hydraulic structure of the assembly was improved, and a 40 mm diameter ball seat and an arc-shaped ball seat outlet were selected. Particle trajectory and erosion calculation results showed that the improved structure has a lower particle velocity and less impact on the wall, and the average erosion rate is only 0.42 times the value of the original structure. Due to the better erosion resistance and smaller pressure drop, the improved structure shows promise for field performance.

Comparison of various structure designs of SO2-depolarized electrolysis cell

SO2-depolarized electrolysis (SDE) is the key step of the hybrid sulfur (HyS) process, which is one of the simplest thermochemical cycles for producing hydrogen by water splitting. Exploration and optimization of flow field/structure design is essential for improving the efficiency of SDE. In this work, graphite plates with different flow channels, together with porous graphite felts or carbon papers as diffusion layers are adopted to fabricate SDE cells with different structures. Evaluation of the cell structures is carried out, by comparing the SDE performance and taking into account the fluid resistance (pressure drop) of anode side. The effects of graphite felt compression ratio, hydrophilicity or hydrophobicity of carbon papers, anodic fluid flow rate, and operating temperature on the SDE performance are investigated. Square porous flow fields provided by graphite felts show excellent performance. Serpentine channel covered by hydrophobic carbon paper reveals advantages when adopted on the cathode side. Combination of above two flow fields and using them on anode and cathode sides respectively, could achieve excellent SDE performance. Under the condition of 40 °C and 360 mL/min anolyte flow rate, the current density could reach 760 mA/cm2 at the cell voltage of 1.19 V.

Research on Key Technologies to Improve Cementing Displacement Efficiency.

The annulus has a wide and narrow clearance due to casing eccentricity in the cementing process and due to the eccentricity of casing in the process of cementing. Because the flow resistance of the drilling fluid in the wide gap is less than that in the narrow gap, the phenomena of a delayed flow or even an overall nonflow occurs in the narrow gap. Based on the existing displacement efficiency calculation model, this paper establishes the cementing displacement efficiency model under the condition of oil-based drilling fluid, explores the residual layer thickness of drilling fluid on the casing side and the sidewall side, and then links the annular displacement efficiency to the injection displacement in combination with the circulating mode resistance pressure drop formula so as to explore the change in the cementing displacement efficiency under different displacements. Considering the change in the physical parameters of annulus fluid, the change in annulus displacement efficiency is obtained. On this basis, the relationship between the wellhead cement injection flow and the annulus retention layer is studied; then, the displacement is calculated. The reasonable cementing displacement is calculated by combining the displacement with annulus displacement efficiency. The results show that the thickness of the annular detention layer increases with the increase in the casing eccentricity in the same well depth, and the growth rate of the detention layer on the wellbore side is greater than that on the casing side at the same circumferential angle. The greater the displacement, the greater the annular circulation pressure drop and circulation equivalent density, thus increasing the cementing risk. The displacement is reasonably designed. The research results in this paper have a certain guiding significance for improving the displacement rate of isolation fluid under oil-based drilling fluid conditions.

Flow distribution in the air cooler of HTGR passive cavity cooling system

Passive Cavity Cooling System (PCCS) is an important safety related system for High Temperature Gas-cooled Reactor (HTGR). Air cooler is one of the key components of this system. The non-uniform flow distribution is a common issue encountered in similar Parallel Tube Heat Exchanger (PTHX). Improving flow uniformity is favorable for both thermal hydraulic performance and structure safety. In this work, the flow distribution characteristics of a compact parallel tube air cooler with U-type header arrangement are theoretically and numerically investigated. First, a theoretical discrete model is proposed for flow distribution in PTHX. It reveals that the static pressure distributions in the headers are influenced by static pressure recovery, friction resistance and local pressure drop, which is directly related with flow uniformity. Then, the flow uniformity of Z-type and U-type header arrangements is numerically investigated and compared in detail. Moreover, the effects of thermal hydraulic parameter and geometrical parameter on flow uniformity are successively evaluated. Numerical results show that the flow uniformity of PCCS air cooler with U-type header arrangement is more excellent than that of Z-type header arrangement. Thermal hydraulic parameters, such as tube-side water temperature and mass flow rate, have little impact on flow uniformity. Nevertheless, the flow distribution characteristics are very sensitive to the geometrical parameters, including the insertion angle configuration, the flow area ratio of header to parallel heat transfer tubes (AR) and the cross-sectional area ratio of distribution header to collection header (DCR). Reasonable insertion angle configuration and decreasing AR can effectively enhance the flow uniformity of PCCS air cooler. For header match, it should be avoided that the distribution header diameter below the collection header diameter. As a result, the optimal structure design determined in this work is an air cooler with U-type header arrangement, where the inlet insertion angle is 0°, the outlet insertion angle is 180°, and the diameters of distribution header and collection header are both 120 mm. Its flow uniformity is improved by more than 50% compared with present design. This work reports a promising design modification, as the potential structure optimization for HTGR PCCS air cooler.

Hydrothermal performances of symmetric and asymmetric divergent-convergent microchannel heat sinks

The present work numerically studied the hydrothermal performance of symmetric and asymmetric divergent-convergent microchannel heat sink (DCMCHS) with the rectangular cross-section. Three different DCMCHS with fixed total channel volume were designed, the symmetric DCMCHS, the width-asymmetric DCMCHS with the fixed inlet-to-middle cross-sectional width ratio, and the width-asymmetric DCMCHS with the fixed middle cross-sectional width. Effects of the inlet-to-middle cross-sectional width ratio and channel height of the symmetric DCMCHS, and the outlet-to-inlet width ratio, the middle cross-sectional width and the channel height of the width-asymmetric DCMCHSs on the maximum temperature, overall thermal resistance, pressure drop, and the coefficient of performance (COP) of the DCMCHSs were analyzed. It was found that the symmetric DCMCHS with smaller inlet-to-middle width ratio has smaller thermal resistance but larger pressure drop. Moreover, the decreasing outlet-to-inlet width ratio can improve the thermal performance of the two width-asymmetric DCMCHSs and increase the pressure drop. The increasing middle cross-sectional width can reduce the thermal resistance of width-asymmetric DCMCHS with fixed channel height and fixed outlet-to-inlet width ratio by consuming more pressure drop. For the COP, all the proposed DCMCHSs in the present work have smaller COP compared with the conventional parallel MCHS.

The mechanism and solving measures for standpipe vibration of the circulating fluidized bed boilers

Standpipe vibration of circulating fluidized bed (CFB) boiler will threaten its safe and stable operation. In order to solve the standpipe vibration, the mechanism of standpipe vibration was discovered based on the type B choking theory in the CFB system and the Ledinegg instability criteria for the gas-liquid flow. And the influence of several factors on the gas-solid flow, especially the reverse flow in the standpipe, was qualitatively analyzed according to the pressure and mass balance in the whole loop. The standpipe vibration is caused by the mismatch between the driving pressure and the resistance pressure drop in the whole loop. To suppress the standpipe vibration, it is necessary to optimize the flow and pressure parameters under stable working conditions, which can be achieved by four main methods of reducing the resistance of the returning valve and cyclone, increasing the circulating rate and the solid height in the standpipe. In engineering application, these four methods can be realized by appropriately increasing the aerated air velocity and the sectional area ratio between the riser and the standpipe, reducing the length of the passage and the height of the weir, increasing the effective material fraction and the inlet area of the cyclone. This paper theoretically analyzes the mechanism of standpipe vibration and proposes corresponding engineering solutions to guide the operation and design of CFB boilers.

Characterization of performance and disinfection resilience of nonwoven filter materials for use in 3D-printed N95 respirators

The COVID-19 pandemic has caused a high demand for respiratory protection among health care workers in hospitals, especially surgical N95 filtering facepiece respirators (FFRs). To aid in alleviating that demand, a survey of commercially available filter media was conducted to determine whether any could serve as a substitute for an N95 FFR while held in a 3D-printed mask (Stopgap Surgical Face Mask from the NIH 3D Print Exchange). Fourteen filter media types and eight combinations were evaluated for filtration efficiency, breathing resistance (pressure drop), and liquid penetration. Additional testing was conducted to evaluate two filter media disinfection methods in the event that the filters were reused in a hospital setting. Efficiency testing was conducted in accordance with the procedures established for approving an N95 FFR. One apparatus used a filter-holding device and another apparatus employed a manikin head to which the 3D-printed mask could be sealed. The filter media and combinations exhibited collection efficiencies varied between 3.9% and 98.8% when tested with a face velocity comparable to that of a standard N95 FFR at the 85 L min−1 used in the approval procedure. Breathing resistance varied between 10.8 to >637 Pa (1.1 to > 65 mm H2O). When applied to the 3D-printed mask efficiency decreased by an average of 13% and breathing resistance increased 4-fold as a result of the smaller surface area of the filter media when held in that mask compared to that of an N95 FFR. Disinfection by dry heat, even after 25 cycles, did not significantly affect filter efficiency and reduced viral infectivity by > 99.9%. However, 10 cycles of 59% vaporized H2O2 significantly (p < 0.001) reduced filter efficiency of the media tested. Several commercially available filter media were found to be potential replacements for the media used to construct the typical cup-like N95 FFR. However, their use in the 3D-printed mask demonstrated reduced efficiency and increased breathing resistance at 85 L min−1.

Experimental study on single-phase hybrid microchannel cooling using HFE-7100 for liquid-cooled chips

It is highly desired to efficiently dissipate the high heat flux generated in electronics. A novel hybrid microchannel heat sink combining manifold with secondary oblique channels (MMC-SOC) has been proposed and studied numerically in our previous work. The current study conducts the fabrication and experimental test of the hybrid microchannel heat sink using dielectric fluid HFE-7100. The volume flow rate qv ranges from 211 to 580 mL/min, with channel Reynolds numbers between 278 and 905 for heat fluxes q'' = 20, 25, 30 and 35 W/cm2. The results indicate that the MMC-SOC heat sink can simultaneously reduce the thermal resistance Rt and pressure drop ∆P. For heat sinks with channel height Hc = 60 μm, an 11% reduction in ∆P and a 24% reduction in Rt are obtained compared to conventional manifold microchannel (MMC) heat sink for qv = 580 mL/min and q'' = 20 W/cm2. As qv increases, the ratio (Rt/Rt0) becomes smaller and (∆P/∆P0) becomes larger, which indicates an enhanced ability of reducing Rt and a suppressed ability of reducing ∆P. For the maximum qv = 580 mL/min and q'' = 35 W/cm2, the MMC-SOC heat sink can maintain a maximum chip temperature of 53 °C with a pressure drop of only 3.77 kPa. Moreover, the proposed MMC-SOC heat sink has a lower pressure drop compared to MMC heat sink owing to a reasonable design, even though the Reynolds number of the MMC-SOC heat sink reaches up to 883. This provides a very promising scheme for safe and efficient single-phase microchannel cooling used in the thermal management of electronics with high heat flux. In addition, the ratio (Rt/Rt0) will increase with increasing heat flux and increasing the flow rate becomes an effective way to further reduce the chip surface temperature at operating conditions with higher heat flux.

Flow and thermal analysis of hybrid mini-channel and slot jet array heat sink

In this paper, experimental tests and numerical studies were performed for better understanding the flow and heat transfer characteristics of the hybrid mini-channel and slot jet array heat sink. The average heat transfer coefficients were experimentally obtained and compared with independent mini-channel heat sink and slot jet array heat sink with a dimension of 10 mm × 10 mm at a flow rate from 0.1 L/min to 1.2 L/min, heat flux of 35.74 W/cm2 and 62.22 W/cm2. The results showed that the hybrid scheme has a better heat transfer performance than other two heat sinks at the same flow rate. Numerical simulations were conducted to further analyze thermal-hydraulic performance of the hybrid heat sink at an inlet Reynolds from 230 to 2760. Compared with k-ε models, numerical results with transition SST flow model match better with the experimental results. According to the numerical results, we found vortexes in the channel of the hybrid heat sink and these vortexes are beneficial to the heat transfer. The influence of geometries on the overall thermal resistance and total pressure drop were discussed using numerical simulations. The results demonstrated that the base thickness, channel height, side wall to channel width ratio and channel number of the hybrid heat sink all have significant effect on the cooling performance and thermal resistance and pressure drop can be reduced obviously via geometry optimization.

Fine spherical powder production during gas atomization of pressurized melts through melt nozzles with a small inner diameter

A pressure-gas atomizer was developed, in which the melts were pressurized through melt nozzles with a small inner diameter, aiming for a small mass median diameter (MMD, d50,3) and high productivity of fine spherical powders. The maximum melt flow resistance in a melt nozzle, defined as the sum of the capillary resistance and viscous pressure drop, was analyzed by varying the inner diameter of the melt nozzle (D0). The calculation results indicate that the maximum melt flow resistance increases quickly with the decrease of D0, and varies in an order of 100–102 kPa for different metal melts when D0 reduces from 4.0 mm to 0.5 mm. Atomization runs with three kinds of aluminium (Al) alloys were accomplished using melt nozzles with different inner diameters in a pilot plant whereby an over-pressure in a range of ∆pl = 30–45 kPa can be maintained on the melts to enhance the melt flowing in the melt nozzle. The experimental results indicate that the atomization efficiency can be well improved by reducing the inner diameter of the melt nozzle, which resulted in a small MMD, narrow particle size distribution and high fine powder yield. For Al-I alloy powders, when the inner diameter of the melt nozzle reduces from D0 = 3 mm to D0 = 1 mm, the particle MMD reduces from d50,3 = 86.13 μm to d50,3 = 40.42 μm, and the powder yield <53 μm increases from 27.60% to 62.57%. For Al-III alloy powders, when the inner diameter of the melt nozzle reduces from D0 = 4 mm to D0 = 2 mm, the particle MMD reduces from d50,3 = 120.10 μm to d50,3 = 54.82 μm and the powder yield <53 μm increases from 20.70% to 48.20%. Moreover, the satellite particles and lamellae sticking on the particle surface were reduced when a melt nozzle with a small inner diameter was employed in a gas atomization process.

Numerical study on flow and heat transfer of a hybrid microchannel cooling scheme using manifold arrangement and secondary channels

The flow and heat transfer characteristics of a novel hybrid microchannel heat sink with manifold arrangement and secondary oblique channels (MMC-SOC) are numerically studied. Through the relationship between the total thermal resistance ratio (Rt/Rt0) and pressure drop ratio (ΔP/ΔP0), we define a region named Design Optimization Area (DOA), where the pressure drop ΔP and the total thermal resistance Rt can be both reduced due to the secondary channels. The numerical results show that the best heat sink can reduce ΔP by 1.91%, and simultaneously decrease Rt by 19.15% compared to the original MMC heat sink at Re = 295. In addition, the effects of secondary channel on ΔP are dependent on both the geometrical parameters and Reynolds numbers. On the one hand, it can reduce the pressure loss at small Reynolds numbers for most heat sinks. However, it can also increase the pressure loss at high Reynolds numbers for most heat sinks. As Re increases, the ratio (Rt/Rt0) becomes smaller and (ΔP/ΔP0) becomes larger, indicating a better thermal performance and a worse hydraulic performance. The secondary flow field analyses visually show the hydraulic and thermal performance enhancements due to thermal boundary layer re-development and flow mixing.

Influence of triangle tube structure with twisted tape on the thermo-hydraulic performance of nanofluids in heat-exchange system based on thermal and exergy efficiency

An experiment is carried out to research the thermo-hydraulic performance of TiO2-H2O nanofluids in triangle tubes while taking the effect of twisted tapes into consideration. The theories of thermal and exergy efficiency are applied to estimate this system. The influence of mass fractions of nanoparticles (0.1 wt%, 0.3 wt% and 0.5 wt%), Reynolds numbers (Re = 800–9000), different structures of triangle tubes (isosceles right triangle tube (tube 1), isosceles 45° triangle tube (tube 2)) and twisted tape on the Nusselt number, Nusselt number ratio, resistance coefficient, resistance coefficient ratio and pressure drop are experimentally studied respectively. Results show that there are three positive factors for heat transfer performance including large nanoparticles concentration, large Reynolds number and existence of the twisted tape. Compared with the smooth tube, tubes (tubes 1 and 2) with twisted tape can enhance heat transfer, but that without twisted tape can deteriorate heat transfer, for heat transfer performance, tube 2 is better than tube 1. Tube 2 with twisted tape has the biggest value of comprehensive performance index R3. A better exergy efficiency performance can be obtained when Reynolds number is greater than 5000 and the exergy efficiency reaches the best when Re = 8000.