Parallel Flow Paths Research Articles

A study on the effect of channel structures on flow and heat transfer performance of cold plate with double-layer serpentine microchannel

As the power consumption of electronic components continues to rise, liquid cooling technology has become the mainstream solution for cooling electronic devices. This study designs a double-layer serpentine microchannel cold plate with a ribbed structure and firstly investigates the effects of the flow path on thermal–hydraulic performance of the cold plate. Through orthogonal numerical tests, the impact of rib height, number of rib truncations, rib truncation gap, and rib end deviation distance on thermal–hydraulic performance of cold plate is analyzed, along with their significance. Based on the results of the orthogonal test, the optimal rib structure parameters are determined. Results show that the parallel flow path has a more uniform flow distribution and approximately 2.5 % lower thermal resistance of the cold plate than the series flow path. Higher rib height leads to a higher convective heat transfer coefficient, more uniform internal flow distribution, and lower thermal resistance. When the rib height increases from 0.3 mm to 3 mm, the convective heat transfer coefficient increases 18 %, and the thermal resistance of the cold plate decreases 12 %. Compared to the initial structure, the optimized structure at the highest PEC has total thermal resistance and pressure drop reduced by 5.5 % and 7.4 %, respectively, while the structure with the lowest thermal resistance has a 7.9 % reduction in thermal resistance but a 27 % increase in pressure drop.

P13: Hemodynamic Study of an Implantable Artificial Kidney Device Using a Computational Model

Study: Gradual loss of kidney function is experienced by patients diagnosed with chronic kidney disease (CKD) and may escalate to a severe condition of end-stage kidney disease. A treatment approach alternative to hemodialysis could be the implantation of an artificial kidney that filters blood using the natural pressure drop in the systemic circulation. This study aims to investigate the hemodynamic performance of several variations of two previously reported implantable artificial kidney device (IAKD) designs using a computational hemodynamic model. Methods: An in-house custom hemodynamic lumped parameter model was developed to analyze the implantation of an IAKD on the combined patient-device hemodynamics. The time-varying hemodynamic model (HM) consisted of all four cardiac chambers, systemic and venous circulations and included the implantation of an IAKD in parallel with the systemic circulation (Figure 1a). Two major IAKD configurations were analyzed: (i) a serpentine configuration (series flow path through the device) and (ii) a parallel configuration (parallel flow path through the device). For each configuration, several variations of the internal device resistance were analyzed to investigate the resulting pressure drop across and flow through the device, in order to investigate the customization of IAKD designs depending on a perceived patient-specific need. Results: We tested 8 variations of the serpentine IAKD and 6 variations of the parallel IAKD. For each case, the virtual patient characteristics were maintained constant (i.e. all cardiac, systemic and pulmonary circulatory parameters) and only the device resistance was varied. Preliminary data indicated that for the serpentine configuration, the flow through the IAKD reduced by over 50% as the resistance was increased, also causing an increase in the pressure drop across the IAKD for each variation (Figure 1b). This behavior was similar for the variations in the parallel configuration (Figure 1c), with an increase in flow up to 35% through the IAKD due to the overall reduced flow resistance of the parallel design in comparison to the serpentine design. Interestingly, as the device resistance was decreased, the patient MAP was reduced by more than 11% due to the shunting of more flow through the IAKD, and thereby less flow available to pass through the systemic circulation – this behavior was seen for both configurations. Conclusions: The HM developed in this study is capable of investigating several clinically-relevant scenarios to tailor an IAKD for patients with renal failure. Our analysis suggests that there is a complex interplay between the patient’s systemic circulatory network and the IAKD, necessitating detailed hemodynamic analysis such as that performed in this study. Depending on the patient’s needs, it is possible to tailor an IAKD, potentially with variable resistance configurations, that can best serve to maintain hemodynamic stability and hemodialysis efficiency.

Oscillatory behavior with fiber orientation in the flow–vorticity plane for fiber suspension under large amplitude oscillatory shear flow

In fiber suspensions, fibers with three-dimensional orientation states are dramatically flow-oriented in the flow–flow gradient plane when the flow starts. In contrast, large strains are required for flow orientation in the flow–vorticity plane. Under oscillatory shear flow, when the strain amplitude is small, the flow orientation in the flow–vorticity plane is weakly induced, unlike that in the flow–flow gradient plane. The orientation in the flow–vorticity plane increases with the strain amplitude. At large strain amplitudes, fibers are oriented in the flow–flow gradient plane; thus, the rotational motion of fibers in the flow–flow gradient plane is dominant, i.e., fibers are almost flow-oriented in the flow–vorticity plane. However, contributions of the oscillatory behavior of fiber orientation in the flow–flow gradient and flow–vorticity planes to complex viscosity are unclear. In this study, the objective is to determine the contributions of fiber orientation in each plane to complex viscosity with the two initial orientation states (random and flow-oriented states) for the strain sweep test. The two initial orientation states were controlled by manipulating the upper disk of the parallel disk flow path. The initial random state was induced by sliding the upper disk up and down. The initial flow-oriented state was induced by rotating the upper plate. Furthermore, phase transition behaviors from the random to flow-oriented state in the flow–vorticity plane with increasing strain amplitude were qualitatively estimated as the orientation angle via visualization. Consequently, when the initial orientation was random, the fibers gradually vibrated in a medium strain amplitude region, and complex viscosity was higher than that of the initial flow-oriented state. In the conclusion, we divided the complex viscosity behavior of the strain sweep test into five strain amplitude regions and clarified the dominant orientation state in each region. It is conceivable that this result will help in understanding the relationship between fiber orientation and dynamic viscoelastic properties of fiber suspension like fiber-reinforced thermoplastics.

Semi-quantitative detection of inflammatory biomarkers using a laser-patterned multiplexed lateral flow device

Inflammatory markers including C-reactive protein (CRP) and procalcitonin (PCT) have been shown to be useful biomarkers to improve triage speed and prevent the inappropriate use of antibiotics for infections such as pneumonia. Here, we present a novel and exciting solution to guide the administration of antibiotic treatment via rapid, semi-quantitative and multiplexed detection of CRP and PCT using an advanced lateral flow device (LFD) designed to have multiple parallel flow-paths, produced via the precise laser-based partitioning of the single flow-path of a standard LFD. Each flow-path within this multiplexed LFD has a unique detection capability which permits tailored detection of CRP within a predefined cut-off range (20 μg/mL - 100 μg/mL) and PCT above a pre-defined threshold (0.5 ng/mL). We demonstrate the use of this LFD in the successful detection of CRP and PCT semi-quantitatively within spiked human serum samples. This multiplexed near-patient assay has potential for development into a rapid triage and treatment of patients with suspected pneumonia.

Development and validation of a numeric tool for partially degraded core quenching under low injection rates

Quenching of reactor core has been studied numerically with the help of several numeric tools reported in literature. These tools have been developed to simulate core quenching under design basis conditions. Hence, most of these tools make use of classical homogeneous equilibrium model of two phase flow which are reported to perform better under high pressure conditions with relatively small temperature gradients. System codes such as RELAP5 make use of two fluid model. Such system codes can simulate core quenching under design basis injection rates (1 g/s per unit length of single fuel pin) prescribed under Emergency Operating Procedures (EOPs). However, because of possibilities of flow path breakage under Severe Accident conditions, the injection rate reaching the core is expected to be lesser than the typical injection rate used for Severe Accident Management Guidelines (SAMG). A numeric tool ‘Program for Degraded Reactor Core Reflood’ (PDRCR) has been developed to simulate quenching of partially degraded reactor core under low injection flow rates. PDRCR has specific modules to tackle issues such as water packing, high temperature gradients in the fuel and simulation of parallel flow paths to account for flow re-distribution in partially ballooned fuel pin condition. This paper presents validation results for PDRCR. The predictions of PDRCR for SEFLEX and DRCRE test facilities and comparison with the experimental results are presented. The predictions of PDRCR are found to be better than RELAP5 for low injection flow conditions.

Cooling performance of natural draft hybrid system with parallel air path

The flexibility of the dry cooling system in thermal power plant needs to be improved to suit the load undulation caused by the increased renewable energy power. For overcoming the weakness of conventional cooling system, a natural draft hybrid (dry/wet) cooling system (NDHCS) is proposed to fully take advantage of dry and wet cooling technologies, which comprises the wet and dry cooling sections with parallel air flow path. The three-dimensional numerical models are developed to investigate the thermal-flow performances of the NDHCS under various environment and operation conditions, by which the flow fields near the NDHCS as well as the heat and mass transfer between circulating water and cooling air are obtained. The results show that both the dry and wet cooling sections dominate the cooling capacity of the hybrid system but the performance of the former is inferior to the latter in most of the cases. Low ambient humidity, large spraying water flow ratio in the wet cooling section and small wind speed are of benefit to the thermal performance of hybrid cooling system. For the dry and wet cooling sections themselves, the cooling performance can be improved thanks to the ambient wind under specific conditions. Besides, NDHCS can effectively avoid visible plume especially under windy conditions.

Water vapor capturing using an array of traveling liquid beads for desalination and water treatment.

Growing concern over the scarcity of freshwater motivates the development of compact and economic vapor capture methods for distributed thermal desalination or harvesting of water. We report a study of water vapor condensation on cold liquid beads traveling down a massive array of vertical cotton threads that act as pseudo-superhydrophilic surfaces. These liquid beads form through intrinsic flow instability and offer localized high-curvature surfaces that enhance vapor diffusion toward the liquid surface, a critical rate-limiting step. As the liquid flow rate increases, the bead spacing decreases, whereas the bead size and speed stay nearly constant. The resulting increase in the spatial bead density leads to mass transfer conductances and hence condensation rates per volume that are almost three times higher than the best reported values. Parallel and contiguous gas flow paths also result in a substantial reduction in gas pressure drop and hence electric fan power consumption.

ERT, GPR, InSAR, and tracer tests to characterize karst aquifer systems under urban areas: The case of Quebec City

Urban infrastructures built over karst settings may be at risk of collapse due to hydro-chemical erosion of underlying rock structures. In such settings, mapping cave networks and monitoring ground stability is important to assure civil safety and guide future infrastructure development decisions. However, no technique can directly and comprehensively map these hydrogeological features and monitor their stability. The most reliable method to map a cave network is through speleological exploration, which is not always possible due to restrictions, narrow corridors/passages, or high water levels. Borehole drilling is expensive and is often only performed where the presence of karsts is suggested by other techniques. Numerous indirect and cost-effective methods exist to map a karst flow system, such as geophysics, geodesy, and tracer tests. This paper presents the outcomes from a challenging application in Quebec City, Canada, where a multidisciplinary approach was designed to better understand the groundwater dynamics and cave paths.Two tracer tests in groundwater flowing through the cave system indicated that water flows along an approximately straight path from the sinking stream to the spring. It also suggests the presence of a parallel flow path close to the one already partially mapped. This observation was confirmed by combining Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) techniques, and ultimately by observing voids in several boreholes drilled close to the main cave path. Lowering the water levels at the suspected infiltration zone and inside the karst, the infiltration cracks were identified and the hydraulic link between them was confirmed. In fact, almost no infiltration occurs into the karst system when the water level at the sinking stream drops below a threshold level. Finally, SAR interferometry (InSAR) using RADARSAT-2 images detected movements on few buildings located over a backfilled sinkhole intercepted by the karst system and confirmed the stability of the rest of the karst area. The knowledge of the flow system described in this paper is used by policy makers to assure civil security of this densely populated area.

Original article submission: Platelet stress accumulation analysis to predict thrombogenicity of an artificial kidney

An implantable artificial kidney using a hemofilter constructed from an array of silicon membranes to provide ultrafiltration requires a suitable blood flow path to ensure stable operation in vivo. Two types of flow paths distributing blood to the array of membranes were evaluated: parallel and serpentine. Computational fluid dynamics (CFD) simulations were used to guide the development of the blood flow paths. Pressure data from animal tests were used to obtain pulsatile flow conditions imposed in the transient simulations. A key consideration for stable operation in vivo is limiting platelet stress accumulation to avoid platelet activation and thrombus formation. Platelet stress exposure was evaluated by CFD particle tracking methods through the devices to provide distributions of platelet stress accumulation. The distributions of stress accumulation over the duration of a platelet lifetime for each device revealed that stress accumulation for the serpentine flow path exceeded levels expected to cause platelet activation while the accumulated stress for the parallel flow path was below expected activation levels.

Measurements of a Parallel Channel Adjustable Inertance Tube

A recent modification to the cylindrical threaded adjustable inertance tube for pulse tube refrigerators links the two helical flow channels existing between the threads of the inner and outer screws in parallel. The phase shifting performance of an earlier design that was limited by fluid leakage occurring between the channels, was thought to be significantly improved by connecting the two channels in parallel. Measurements of the phase shift angle over the entire operating range of the adjustable device are compared with existing models. The models predict a total phase angle shift between pressure and flow waves of 105° with the new parallel flow path configuration. However, the experimental data only achieves a 28° phase shift angle.

Chip-Based Multicapillary Column with Maximal Interconnectivity to Combine Maximum Efficiency and Maximum Loadability.

On the basis of our previous work on the design of pillar array columns for liquid chromatography, we report on a new pillar array design for high-efficiency, high volumetric loadability gas chromatography columns. The proposed pillar array configuration leads to a column design which can either be considered as a packed bed with perfectly ordered and uniform flow paths or as multicapillary columns (8 parallel tracks) with a maximal interconnectivity between the flow paths to avoid the so-called polydispersity effect (dispersion arising from the inevitable differences in migration velocity between parallel flow paths). Despite our relative inexperience with column coating, and most probably (not supported by data) suffering from the same problem of stationary phase pooling in the right-angled corners of the flow-through channels as other chip-based GC devices, the efficiencies obtained in a L = 70 cm long and 75 μm deep and 6.195 mm wide chip for, respectively, quasi-unretained and retained components (k = 7) went up to N = 60 000 and 12 500 under isothermal conditions using H2 as carrier gas and a downstream restriction. Under programmed temperature conditions (Ti = 80 °C, Tf = 175 °C at 30 °C/min, and a H2 flow of 0.4 mL/min), a peak capacity of 170 was obtained in 3.6 min. For retained compounds, the optimal flow rate is found to be on the order of 0.4 mL/min, achieved at an operating pressure of 2.3 bar. Intrinsically, the column combines the efficiency of a 75 μm capillary with the volumetric loadability of a 240 μm capillary.

Flow investigation in an industrial-scale soaker using radiotracer technique

Flow dynamics of heavy petroleum residue in an industrial-scale soaker operating in a petroleum refinery was investigated. Residence time distributions (RTDs) of the residue were measured using radiotracer technique. Bromine-82 as dibromobiphenyl was used as radiotracer for tracing the petroleum residue. The measured RTDs were treated and mean residence times (MRTs) were determined. The measured RTD data was simulated using a combined model i.e. axial dispersion model in parallel with tanks-in-series with stagnant volume and exchange. The results of the model simulation fitted very well to the experimentally measured data and identified bypassing or existence two parallel flow paths within the soaker.

Serpentine and leading-edge capillary pumps for microfluidic capillary systems

Microfluidic capillary systems operate using capillary forces only and require capillary pumps (CPs) to transport, regulate, and meter the flow of small quantity of liquids. Common CP architectures include arrays of posts or tree-like branched conduits that offer many parallel flow paths. However, both designs are susceptible to bubble entrapment and consequently variation in the metered volume. Here, we present two novel CP architectures that deterministically guide the filling front along rows while preventing the entrapment of bubbles using variable gap sizes between posts. The first CP (serpentine pump) guides the filling front following a serpentine path, and the second one (leading-edge pump) directs the liquid along one edge of the CP from where liquid fills the pump row-by-row. We varied the angle of the rows with respect to the pump perimeter and observed filling with minimal variation in pumping pressure and volumetric flow rate, confirming the robustness of this design. In the case of serpentine CP, the flow resistance for filling the first row is high and then decreases as subsequent rows are filled and many parallel flow paths are formed. In the leading-edge pump, parallel flow paths are formed almost immediately, and hence, no spike in flow resistance is observed; however, there is a higher tendency of the liquid for skipping a row, requiring more stringent fabrication tolerances. The flow rate within a single CP was adjusted by tuning the gap size between the microposts within the CP so as to create a gradient in pressure and flow rate. In summary, CP with deterministic guidance of the filling front enables precise and robust control of flow rate and volume.

Model of Heat Exchangers for Waste Heat Recovery from Diesel Engine Exhaust for Thermoelectric Power Generation

The performance and operating characteristics of a hypothetical thermoelectric generator system designed to extract waste heat from the exhaust of a medium-duty turbocharged diesel engine were modeled. The finite-difference model consisted of two integrated submodels: a heat exchanger model and a thermoelectric device model. The heat exchanger model specified a rectangular cross-sectional geometry with liquid coolant on the cold side, and accounted for the difference between the heat transfer rate from the exhaust and that to the coolant. With the spatial variation of the thermoelectric properties accounted for, the thermoelectric device model calculated the hot-side and cold-side heat flux for the temperature boundary conditions given for the thermoelectric elements, iterating until temperature and heat flux boundary conditions satisfied the convection conditions for both exhaust and coolant, and heat transfer in the thermoelectric device. A downhill simplex method was used to optimize the parameters that affected the electrical power output, including the thermoelectric leg height, thermoelectric n-type to p-type leg area ratio, thermoelectric leg area to void area ratio, load electrical resistance, exhaust duct height, coolant duct height, fin spacing in the exhaust duct, location in the engine exhaust system, and number of flow paths within the constrained package volume. The calculation results showed that the configuration with 32 straight fins was optimal across the 30-cm-wide duct for the case of a single duct with total height of 5.5 cm. In addition, three counterflow parallel ducts or flow paths were found to be an optimum number for the given size constraint of 5.5 cm total height, and parallel ducts with counterflow were a better configuration than serpentine flow. Based on the reported thermoelectric properties of MnSi1.75 and Mg2Si0.5Sn0.5, the maximum net electrical power achieved for the three parallel flow paths in a counterflow arrangement was 1.06 kW for package volume of 16.5 L and exhaust flow enthalpy flux of 122 kW.

J101041 回転円板と静止円板の間の旋回隙間流に起因する流体力の動特性

Axial self-excited vibration may be induced in a rocket turbopump by fluid with a tangential velocity component that flows into orifices of balance piston. To avoid such vibration, knowledge of the dynamic characteristics of fluid force induced by swirling leakage flow is required. In this research, the effect of axial rotation and swirl strength on the added fluid force coefficients is investigated by modeling the piston orifice as the combination of rotational and stationary disks, and deriving the unsteady fluid force generated by swirling leakage flow between the disks. As a result, in the case of a parallel flow path, with increasing swirl strength, the added mass and damping increase and the added stiffness decreases. The effect of rotation on the added fluid force coefficients depends on swirl strength. The effect of swirl strength and rotation on the added fluid force coefficients depends on the shape of the flow path.

A silicon-based micro direct methanol fuel cell stack with a serial flow path design

SUMMARY A 6-cell silicon-based micro direct methanol fuel cell (μDMFC) stack utilized the serial flow path design was developed. The effect of the structure of flow path on the performance of the stack was investigated using polarization characterization and electrochemical impedance analysis. Further, the voltage distribution for individual cells under different current density was discussed. The results indicated that the μDMFC stack with the serial flow path design exhibited better performance than that utilized the parallel flow path due to uniform mass transfer of methanol as a result of the use of the serial flow path. Such a μDMFC stack generates a peak output power of ca. 187 mW, corresponding to an average power density of ca. 21.7 mWcm-2, and exhibits a steady-state power output for more than 100 h. Copyright © 2011 John Wiley & Sons, Ltd.

Capillary-driven multiparametric microfluidic chips for one-step immunoassays

Here we present a capillary-driven microfluidic chip for “one-step” immunoassays. The chip allows for easy modification of several assay parameters such as the flow rates of sample, the volumes of samples for tests, and the type of reagents and receptors for detecting analytes. We therefore term such a chip a multiparametric chip and illustrate this concept with the integration and release of anti-C-reactive protein (CRP) detection antibodies (dAbs) together with splitting flow of samples containing CRP across lines of anti-CRP capture antibodies (cAbs). The microfluidic chip is fabricated in Si and is sealed with polydimethylsiloxane (PDMS) patterned with cAbs. The microfluidic chip is ∼1.7 × 3.4 cm 2 and is capable of analyzing 20 μL of human serum in 6 parallel flow paths with a range of flow rates from 3.3 nL s −1 to 0.46 nL s −1. An inkjet spotter was used to deposit 10.6 nL of dAb solution in a structure vicinal to the main flow path of the chip. The consequent asymmetric release of dAbs in a stream of human serum is compensated by a Dean flow mixer having 9 mixing loops and a footprint of 2.8 mm × 0.78 mm. The quantity of dAb present in the half of the flow path close to the spotting region decreases from 83% at the entrance of the mixer to 52% in the region after the mixer. The sample is then equally split into 6 reaction chambers and proceeds via connecting channels to 2 μL capillary pumps. The hydraulic resistance of the connecting channels is designed to vary flow rates, and therefore the kinetics of capture of CRP-dAb complexes, from 10 min to 72 min. The increased incubation time leads to a fourfold increase in detection signal in the reaction chamber with the longer incubation time. The concept presented here is flexible and suited for implementing various surface fluorescence immunoassays on a capillary-driven microfluidic chip.

Investigation of parallel heat flow path in electro-thermal microsystems

Due to the miniaturization seen in the last decades, several macro models that neglect parameters have to be revised in order to evaluate the behavior of different types of microsystems. In this paper we present the analysis of one such parameter which affects the thermal functionality, namely, the convection of natural gases. In macro scale this parameter is usually neglected, because the conductivity of gases is several magnitude smaller than that of the base materials. With the advance of microfabrication really good thermal isolation can be achieved and so their values can be evenly compared and the models have to be revised. This effect can be easily modeled on microstructures whose thermal resistance can be compared to the thermal conductivity of natural gases and whose output is temperature dependent. For this purpose different types of cantilevers with embedded thermopiles and heating resistors were used. The modeling and experimental results show that in microsystems that are sensitive to temperature change, the parallel heat flow created by the surrounding gases have significant impact on the operation.

Thermo-hydraulic testing and integrity of ITER Test Blanket Module (TBM) First Wall mock-up in JAEA

Fluid flow and heating tests on the full-scale Test Blanket Module (TBM) First Wall (FW) mock-up under the TBM-relevant operating condition were carried out in an ion beam irradiation system with a pressurized high temperature water loop in JAEA to verify the fabrication process and design of the TBM First Wall and demonstrate its heat removal capability. The TBM FW mock-up is made of reduced activation ferritic/martensitic (RAFM) steel, F82H, and its parts such cooling channels and plates were assembled with Hot Isostatic Pressing (HIP) method. In the fluid flow test, the cooling water at room temperature is supplied to 15 parallel flow paths in the mock-up. The flow distribution in each path inside the First Wall mock-up is compared with a numerical simulation. This result shows that no severe cross-sectional deformation of the entire flow path in the mock-up takes place during the fabrication process. In the heating test, the mock-up was exposed to repetitive hydrogen ion beam irradiation with the maximum heat flux of 0.5 MW/m 2. No indication of joint defect of the HIP joint like a hot spot was observed during 80 irradiation cycles.

Analysis and Design of a Single-Stage Parallel AC-to-DC Converter

In this paper, a single-stage (S <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) parallel ac-to-dc converter based on single-switch two-output boost-flyback converter is presented. The converter contains two semistages. One is the boost-flyback semistage, which transfers partial input power transferred to load directly through one power flow path and has excellent self-power factor correction property when operating in discontinuous conduction mode even though the boost output is close to the peak value of the line voltage. The other one is the flyback dc-to-dc (dc/dc) semistage that provides the output regulation on another parallel power flow path. With this design, the power conversion efficiency is improved and the current stress of control switch is reduced. Furthermore, the calculation process of power distribution and bulk capacitor voltage, design equations, and design procedure for key parameters are also presented. By following the procedure, an 80 W prototype converter has been built and tested. The experimental results show that the measured line harmonic current at the worst condition complies with the IEC61000-3-2 class D limits, the maximum bulk capacitor voltage is about 415.4 V, and the maximum efficiency is about 85.8%. Hence, the proposed S <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> converter is suitable for universal input usage.