Drop Length Research Articles

Determination of the Effects of Aminoethoxyvinilglycine (AVG) and Gibberellic Acid (GA3) Applications on Pre-Harvest Fruit Drop Amount and Fruit Quality in Hakko Pear Cultivar

This study was conducted to determine the effects of pre-harvest Aminoethoxyvinylgylcine (AVG) and Gibberellic acid (GA3) applications on the pre-harvest fruit drop amount and fruit quality in the 'Hakko' pear (Pyrus pyrifolia) cultivar grafted on BA29 rootstock in a private orchard in the Bala district of Ankara in 2021-2022. It was conducted in an orchard belonging to a producer. 50-100-150 mg/l AVG and 25-50-75 mg/l GA3 were applied 4 weeks before the estimated harvest date. Fruits are harvested at full maturity date; Pomological properties such as cumulative drop percentage, yield, fruit weight, fruit width and length, fruit stem width and length, fruit flesh firmness, fruit color, and chemical properties such as soluble solids content (SSC), pH and titratable acidity (TA) were evaluated. It was observed that all doses of AVG and GA3 during the harvest period reduced the cumulative casting rate compared to the control application (6.78%). In general, the yield per tree was found to be high in GA3 applications. In both AVG and GA3 applications, its effects on fruit weight, fruit width and length, fruit flesh firmness, SSC and pH were found to be statistically significant. It was observed that in both AVG and GA3 applications, the amount of fruit drop pre-harvest decreased and fruit quality characteristics were better than the control.

Efficacy and Postoperative Infection following Super Mini Percutaneous Nephrolithotomy vs Flexible Ureteroscopy for Diabetic Nephrolithiasis: A Comparative Analysis and Risk Factors for Postoperative Infectious Complications.

Objective: To compare the efficacy and postoperative infection rate of super mini percutaneous nephrolithotomy (SMP) and flexible ureteroscopic lithotripsy (FURL) in patients with diabetic nephrolithiasis and to explore the risk factors associated with postoperative infection following these two procedures. Methods: The medical history and surgery details of 252 patients with diabetic nephrolithiasis who underwent lithotripsy in our hospital between January 2018 and May 2023, including 144 SMP and 108 FURL, were reviewed and compared. Perioperative outcomes were compared between the two groups. Logistic regression was performed to identify the significant risk factors for infection after each procedure. Results: SMP achieved a higher stone-free rate (SFR) on postoperative day 1 and postoperative day 30 compared with FURL (p < 0.05). The mean operative time was shorter in SMP (p < 0.01). FURL was associated with less hemoglobin drop (p < 0.01) and shorter length of stay (p < 0.01). The incident rate of systemic inflammatory response syndrome (SIRS) was higher after SMP (p = 0.019), while the incident rate of urinary tract infection (UTI) was higher after FURL (p = 0.021). Overall postoperative infection and sepsis rates were similar between the two procedures. Logistic regression analysis revealed that gender odds ratio [OR]: 0.225, 95% confidence interval [CI]: 0.079-0.639), HbA1c (OR: 3.516, 95% CI: 1.841-6.716), and operation time (OR: 1.037, 95% CI: 1.008-1.066) were independent risk factors for infection after FURL, while operation time (OR: 1.063, 95% CI: 1.022-1.106) and HbA1c (OR: 7.443, 95% CI: 2.956-18.742) significantly predicted SMP-associated infections. Conclusion: In diabetic patients, SMP demonstrated higher SFR and shorter operation time, whereas FURL was associated with less bleeding and shorter hospitalization. SMP had a higher incident rate of SIRS and FURL had a higher incident rate of UTI. Elevated HbA1c and prolonged operative duration increased infection risk after both procedures, while female gender was an additional risk factor for FURL-related infections.

Three‐dimensional simulation of dripping and jetting phenomenon in a flow‐focusing geometry

Abstract3D simulations have been achieved on a flow‐focusing geometry employing the VOF method to study the consequence of viscosity, surface tension, wettability, and geometry on drop generation for the dripping regime. Here the dispersed phase is the PDMS oil (polydimethylsiloxane), and the continuous phase is the water. Simulations were performed at different oil‐to‐water viscosity ratios of 3, 12, 27, and 50. The interfacial tension between PDMS oil and water is 0.0118 N/m. It has been abridged to 0.008 N/m, 0.005 N/m, and 0.002 N/m, and simulations were performed. The walls of the microchannel are considered to be PMMA surfaces. The contact angle of an oil droplet on the PMMA surface in the presence of water is 140°. The effect of wettability was shown at various contact angles (angle created by water droplet on the PMMA surface in the presence of oil) of 0°, 40°, 90°, 135° and 180°. The frequency of droplet generation (1/s), non‐dimensional droplet length (L/Wc), droplet volume (nl), and droplet velocity (m/s) have been calculated for each of the cases. A flow pattern map has been industrialized classifying the dripping and jetting regimes. A comparison between normal geometry and two constricted geometries (having different orifice lengths) based on the frequency of droplet, non‐dimensional drop length, drop volume, and drop velocity has been made for both dripping and jetting regimes. Prediction of simulated non‐dimensional droplet length has also been made using dimensional analysis.

Thermo-hydraulic performance evaluation through experiment and simulation of additive manufactured Gyroid-structured heat exchanger

Following the breakthrough of additive manufacturing in overcoming machining limitations, triply periodic minimal surface (TPMS), governed by mathematical implicit functions, has emerged as a highly promising configuration for heat exchanger. Current study evaluates the thermo-hydraulic characteristics of a 316L stainless steel Gyroid-structured heat exchanger, manufactured by selective laser melting (SLM), through experimental and numerical methods. The experiment was conducted on a single-phase test rig with water as the working medium. The measured performance is affected by surface roughness and other factors, resulting in deviations from the theoretical performance. Specifically, at a flow rate of 500 kg/h, the experimentally measured overall heat transfer coefficient and cold-side differential pressure exhibit a 9.70 % and 69.82 % increase, respectively, compared to their theoretical values. In comparison to various heat exchangers reported in the literatures, this experimental model possesses a notable advantage concerning the power density achievable per unit length of pressure drop consumed. In addition, a nonlinear regression method based on the least squares approach and the thermal resistance separation method is proposed to obtain the Nu ∼ Re correlation. The fitting effect is satisfactory, as all the points fall within the deviation range of (-7.5 %, 7.5 %). Moreover, this experimental model outperforms four conventional heat exchanger configurations in terms of performance evaluation criteria.

Slide electrification of drops at low velocities.

Slide electrification of drops is mostly investigated on tilted plate setups. Hence, the drop charging at low sliding velocity remains unclear. We overcome the limitations by developing an electro drop friction force instrument (eDoFFI). Using eDoFFI, we investigate slide electrification at the onset of drop sliding and at low sliding velocities ≤ 1 cm s-1. The novelty of eDoFFI is the simultaneous measurements of the drop discharging current and the friction force acting on the drop. The eDoFFI tool facilitates control on drop length and width using differently shaped rings. Hereby, slide electrification experiments with the defined drop length-to-width ratios >1 and <1 are realized. We find that width of the drop is the main geometrical parameter which determines drop discharging current and charge separation. We combine Kawasaki-Furmidge friction force equation with our finding on drop discharging current. This combination facilitates the direct measurement of surface charge density (σ) deposited behind the drop. We calculate σ ≈ 45 μC m-2 on Trichloro(1H,1H,2H,2H-perfluorooctyl)silane (PFOTS) and ≈20 μC m-2 on Trichloro(octyl)silane (OTS) coated glass surfaces. We find that the charge separation by moving drops is independent of sliding velocity ≤ 1 cm s-1. The reverse sliding of drop along the same scanline facilitates calculation of the surface neutralization time constant. The eDoFFI links two scientific communities: one which focuses on the friction forces and one which focuses on the slide electrification of drops.

Detailed numerical investigation of the drop aerobreakup in the bag breakup regime

Aerobreakup of drops is a fundamental two-phase flow problem that is essential to many spray applications. A parametric numerical study was performed by varying the gas stream velocity, focusing on the regime of moderate Weber numbers, in which the drop deforms to a forward bag. When the bag is unstable, it inflates and disintegrates into small droplets. Detailed numerical simulations were conducted using the volume-of-fluid method on an adaptive octree mesh to investigate the aerobreakup dynamics. Grid-refinement studies show that converged three-dimensional simulation results for drop deformation and bag formation are achieved by the refinement level equivalent to 512 cells across the initial drop diameter. To resolve the thin liquid sheet when the bag inflates, the mesh is refined further to 2048 cells across the initial drop diameter. The simulation results for the drop length and radius were validated against previous experiments, and good agreement was achieved. The high-resolution results of drop morphological evolution were used to identify the different phases in the aerobreakup process, and to characterize the distinct flow features and dominant mechanisms in each phase. In the early time, the drop deformation and velocity are independent of the Weber number, and a new internal-flow deformation model, which respects this asymptotic limit, has been developed. The pressure and velocity fields around the drop were shown to better understand the internal flow and interfacial instability that dictate the drop deformation. Finally, the impact of drop deformation on the drop dynamics was discussed.

Pressure drop and bubble length prediction for gas-non-newtonian fluid two-phase flow in a curved microchannel

The control mechanism of the pressure drop and bubble size has a guiding significance for selecting the micropump, the pressure resistance design, and the precise control of the microfluidics. In this study, single-phase flows and gas-non-Newtonian fluid two-phase flows are studied in a microchannel containing curved structures. Sodium carboxymethyl cellulose solutions are used as the non-Newtonian fluids; water and nitrogen are used as Newtonian fluid and gas phases, respectively. The pressure drop and the bubble length are measured. The influences of operating conditions are discussed. The non-Newtonian properties of the solutions are found to affect the parameters measured significantly. The experimental results are compared with the existing models, and the fanning friction factor is used to evaluate the pressure drop. The two-phase flow pressure drop can be predicted by the Lockhart-Martinelli method with a newly developed C-coefficient as a function of the fluid characteristic parameters and microchannel structure parameters. The new correlation for two-phase pressure drop prediction has an error within 18%, smaller than existing models. A new prediction method for the dimensionless bubble length containing the two-phase friction multiplier is also given with an error of 16%.

Pressure Drop Prediction Model of the Gas-Liquid Stratified Flow Development Section in the Horizontal Pipeline

Abstract The gas phase accelerating beyond the liquid phase caused by gas-liquid slippage cannot be ignored in short horizontal pipelines with undulation and inflow, and there is no method to calculate it. Therefore, a pressure drop prediction model for variable liquid holdup was developed in this paper. The theoretical model calculation results were validated using computational fluid dynamics. The effectiveness of the pressure drop prediction model has been demonstrated. The various pressure drop, liquid holdup, and development length laws were then examined. The findings indicate that: the pressure drop in the developed section of stratified flow is not only the friction pressure drop but also the acceleration pressure drop; the length of the stratified flow development section and pipeline pressure drop are more easily affected by the flowrate than the liquid holdup in the pipe inlet. Using the relevant data from coalbed methane horizontal wells as an example, the L/D of the development section is approximately 40–85 when the inlet flowrate is 0.8–1 m/s, and the inlet liquid holdup is 0.3–0.5. The pressure drop characteristics in the gas-liquid stratified flow development section are obviously different from those in the stable section. The development of a pressure drop prediction model for the stratified flow development section lays the theoretical groundwork for the investigation of gas-liquid two-phase flow in horizontal pipelines with short or undulating and inflow conditions.

PO-03-037 FEASIBILITY OF UNIPOLAR SIGNAL GUIDED ABLATION IN CREATING CONTIGUOUS LINES OF CONDUCTION BLOCK: A PROOF-OF-CONCEPT STUDY

Contemporary ablation is guided by non-physiological surrogates such as Ablation indexTM (ABi). Dynamic changes in local atrial unipolar electrogram (Uni-EGM) with loss of the negative S component or “R-pattern” change during radiofrequency ablation (RFA) predicts a transmural lesion. To investigate the feasibility of generating contiguous, transmural lesions that result in conduction block, using ablation guided by Uni-EGM modification. This method was compared with ablation guided by standard ABi parameters. In a beating heart Yorkshire swine model, linear transcaval RFA was performed using an irrigated ablation catheter (Thermocool® SmartTouch Surround-Flow, Biosense Webster, Irwindale, CA) with power of 30W. RF delivery was turned off 3 seconds after a stable R-pattern change was seen on the unipolar EGM (Uni t+3). Inter-lesion spacing was directed by a 2nd operator, blinded to the electroanatomical map, and guided solely by Uni EGM morphology characteristic of viable myocardium as well as current of injury marking the contiguous location with ablated tissue (Figure 1A). Uni EGM signals were processed by the PureEP System (BioSig Technologies). Bidirectional block was demonstrated with standard EP maneuvers and histopathology. Uni EGM guided transcaval lines were compared to a historical cohort of ABi=400 guided transcaval lines. In 5 swine, transcaval ablation lines, guided by Uni EGM were performed. Bidirectional block was demonstrated in 4 of 5 lines (80%) and supported by postmortem histopathology (Figure 1B). Compared with transcaval lines with RFA guided by ABi, there was no difference in initial impedance, impendence drop, or mean length of the ablation line (Table). The Uni-t+3 lines were narrower (5.3±1.5mm vs 11.7±4.8mm, <0.001) and comprised of more closely spaced lesions (2.65±1.3mm vs. 3.4±0.5mm, p=0.001). RFA delivery time per lesion, guided by Uni-EGM modification, was substantially shorter (13.7±5.2sec vs. 21.9±5sec, p<0.001). While total RF delivery time did not differ between the groups [695sec (615-697) vs. 639sec (619-693), p=1). Monitoring changes in the local Uni EGM during ablation offers a real-time physiologic endpoint for titration of RF energy delivery. This study demonstrates that it is feasible to create a transmural line with bidirectional block using ablation that is guided by unipolar signals.Tabled 1Unipolar guided ablation lines Vs ABi linesParameterUt+3 LinesN=5Abi lines (control)N=4PImpedance (ohm)139±7.8131±8.50.3Impedance drop (ohm)14±6.816.1±5.10.1Ablation index333 (296-390)400<0.001Ablation time per lesion (sec)13.7±5.221.9±5<0.001Total RF time (sec)695 (615-697)639 (619-693)1Lesions per line49 (40-50)27 (26-31)0.01Inter-lesion distance (mm)2.65±1.33.4±0.50.001Line length (mm)70 (67-70)67 (66-75)0.62Line width (mm)5.3±1.5411.7±4.8<0.001Transmural80%100% Open table in a new tab

NUMERICAL SIMULATION STUDY ON THE REACTION PERFORMANCE OF A METHANOL STEAM REFORMING TO HYDROGEN MICROREACTOR

Hydrogen has received widespread attention as a new clean energy in order to reduce the carbon emissions of fuel vehicles. This paper studies a tubular microreactor based on methanol steam reforming. Methanol and steam are mixed in proportion and the chemical reaction takes place in a porous catalytic bed. For heating purposes, hot gas from the burner penetrates the reactor bed through heating tubes. Energy is supplied through the heating tubes to drive the endothermic reaction system. The microreactor is enclosed in an insulated jacket. In this paper, parameters such as methanol conversion and hydrogen concentration are evaluated by considering microreactor materials, heating gas temperature and flow direction, heating tube distribution, pressure drop and reaction channel length. First of all, choosing a microreactor material with a smaller thermal conductivity can avoid excessive heat loss, and improve heat transfer performance. Increasing the heating gas temperature leads to an increase in the temperature of the reaction zone, thereby increasing the CH3OH conversion rate and H2 mass fraction. Changing the flow direction of the heating gas affects the reaction rate, but has little effect on the reaction result. Through the research on the distribution of the heating tubes, the results show that the hydrogen production rate is higher when the contact area between the heating tubes and the reaction zone is larger. Secondly, through the comparison of the data under different pressure drops, the best parameter [Formula: see text][Formula: see text]pa is obtained, and the CH3OH conversion rate is 80.6% at this time. Finally, increasing the length of the reaction channel can make the reaction more complete. For example, when the reaction channel length [Formula: see text][Formula: see text]m, the CH3OH conversion rate is as high as 83.7%.

A New Online Monitoring Method for Water-in-Oil Droplet Based Microfluidic Devices

The online water-in-oil (w/o) droplet monitoring is essential for the uniformity of the droplet based microfluidic devices. In this work, a contactless impedance detection (CID) method for online w/o droplet monitoring in microfluidic devices is proposed. In the proposed method, a new CID sensor, which can work at low working frequency and overcome the unfavorable influence of coupling capacitance, is developed to obtain the impedance information of the w/o droplet. Based on the obtained impedance information, measurement models are established to realize online measurement of drop length and dispersed phase holdup. Then the coefficients of variation (CVs) of the two measured parameters are calculated to evaluate the uniformity of the droplets for online monitoring. Online monitoring experiments of w/o droplet were carried out in a microfluidic device with a 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}\,\,\times $ </tex-math></inline-formula> 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> microchannel. The experimental results verify the effectiveness of the proposed droplet monitoring method. The developed CID sensor can realize impedance measurement at a working frequency lower than 50kHz. The drop length and dispersed phase holdup are useful parameters for online monitoring of droplets. With the established measurement models, the maximum relative error of droplet length measurement is less than 10% in the droplet length range of 1.5mm-3.5mm. And the maximum error of dispersed phase holdup measurement is less than 5% in the dispersed phase holdup range of 0.20-0.67.

Calculation Model of Bottom Hole Flowing Pressure of Double-Layer Combined Production in Coalbed Methane Wells

Bottom hole flowing pressure (BHFP) is the key factor to determine a reasonable working system and achieve long-term stable production of coalbed methane (CBM) wells. However, there is no special BHFP model for double-layer combined production (DLCP). Generally, the constant mass model (CMM) for single-layer production is applied to treat the double reservoirs as a whole, ignoring the changes of fluid mass in each section and the acceleration pressure drop in the reservoir section. The calculation results have great errors, and the BHFP of the lower reservoir is used to adjust the production system of the two reservoirs, which does not meet the requirements of the upper reservoir. In this paper, the expression of acceleration pressure drop assumed to be zero in CMM is decomposed and derived, the relationship between acceleration pressure drop and unit length radial flow is established, and then the pressure drop formula of reservoir section with radial inflow is obtained. The reservoir is divided into several sublayers, and the pressure drop equation for each sublayer is established. According to the water flow and gas flow in the reservoir and nonreservoir sections, the corresponding velocity equations of water phase and gas phase are derived. The above equations are combined to establish the variable mass model (VMM) for DLCP with three stages. The field data are substituted into the VMM and the CMM, and the accuracy of the new model is verified. The results show that in the stages of double-layer water production and double-layer gas production, the errors of the two models are less than 5%, while in the stage of gas-water coproduction, the error of the VMM is 2.75%-6.58%, and the error of the CMM is 7.15%-15.18%. The VMM is more accurate. In addition, in the stages of water production and gas-water coproduction during DLCP, the BHFP of the two reservoirs differs greatly, with a maximum difference of 49.1%. Therefore, the two reservoirs need to adjust the production rule according to their respective BHFP. To sum up, the VMM can accurately give the BHFP of each reservoir, which is more realistic. It also solves the problem that one BHFP cannot accurately adjust the production rule of the two reservoirs, so as to provide technical support for the formulation of optimal production rule and the realization of high production.

Investigation of the Effect of the Voltage Drop and Cable Length on the Success of Starting the Line-Start Permanent Magnet Motor in the Drive of a Centrifugal Pump Unit

The use of Line-Start Permanent Magnet Synchronous Motors (LSPMSM) improves the efficiency of conventional direct-on-line electric motor-driven fluid machinery such as pumps and fans. Such motors have increased efficiency compared to induction motors and do not have an excitation winding compared to classical synchronous motors with an excitation winding. However, LSPMSMs have difficulty in starting mechanisms with a high moment of inertia. This problem can be exacerbated by a reduced supply network voltage and a voltage drop on the cable. This article investigates the transients during the startup of an industrial centrifugal pump with a line-start permanent magnet synchronous motor. The simulation results showed that when the voltage on the motor terminals is reduced by 10%, the synchronization is delayed. The use of the cable also leads to a reduction in the voltage at the motor terminals in a steady state, but the time synchronization delay is more significant than that with a corresponding reduction in the supply voltage. The considered simulation example shows that the line-start permanent magnet synchronous motor has no problems with starting the pumping unit, even with a reduced supply voltage. The conclusions of this paper support a wider use of energy-efficient electric motors and can be used when selecting an electric motor to drive a centrifugal pump.

Maximum energy loss in a vertical drop equipped with horizontal screen with downstream rough and smooth bed

Abstract Screens are one of the recent energy dissipator structures that can be used downstream of small hydraulic structures. In this study, screens were used horizontally at the brinks of the vertical drop with downstream smooth and rough bed to investigate the energy loss of the drop. Experiments were performed on two porosities of screens, a relative critical depth of 0.13–0.39 and a median size of 1.9 cm aggregates. The results showed that for a relative critical depth of more than 0.3 in a vertical drop equipped with a screen with a rough bed, the drop length with respect to smooth bed increases. Compared to applying a Type I stilling basin, a vertical drop equipped with a screen with downstream smooth and rough bed reduces the drop length by approximately 50%. Although a rough bed increases air entrainment, it has no effect on the energy loss and pool depth of a vertical drop equipped with a horizontal screen with smooth bed. The use of horizontal screens at the brinks of the vertical drop causes maximum energy loss in the downstream of drop. Equations were provided to estimate the flow parameters with a R2 value of more than 0.925 and a normalized root mean square error of less than 0.04.

Numerical and experimental investigation on thermal performances of quartz tube gravity-driven solid particle solar receiver based on linear-focused solar furnace

This paper reported a novel quartz tube gravity-driven SPSR. A test platform of the receiver with a drop length of 4 m based on a linear-focused solar furnace was built. The optical performances of the linear-focused solar furnace were measured by a direct method. Solid particles were heated to a temperature of 156∼308°C after a single pass with an averaged irradiance of 14.9∼21.7kW/m2. A three-dimensional mathematical model with the wavelength dependent radiative properties integrated is built and discretized in OpenFOAM, which is later verified by experimental results. Lastly, the influences of several pertinent parameters on thermal performances of the receiver are studied using the proposed model. It was observed that the green-house effect of the quartz tube could reduce the radiative heat losses by a percentage from 2.1% to 9.4%. Wind speed surrounding the quartz tube has a positive effect on the green-house effect since high wind speed is helpful to decrease the outer surface temperature of the tube. An optimal thermal efficiency of 57.2% was obtained when heating particles from 27 °C to 800 °C by circulating particles for four times. The proposed model could be used for the design and optimal operation of the quartz tube gravity-driven SPSR.

Oil drop stretch and rupture behavior at throat and pore junction during imbibition with active nanofluid: A microfluidic approach

Imbibition is an effective method to recover oil from small pore and throat. Here we report the formation of oil drop at pore and throat junction during spontaneous imbibition with active nanofluid. A T-channel microfluidic model combined with high-speed camera was used to observe the stretch and rupture process of oil discharged from throat to pore. When oil drop was discharged from throat gradually, its width/length was kept deceasing before rupturing. With more active content in the aqueous phase, the interfacial tension decreased from 33.8 to 8.7 mN/m, and the oil recovery increased by 12.4% by spontaneous imbibition. The oil drop rupture frequency increased by 3.0 times, but the length and width of the oil drop decreased by 32.2% and 28.0%, respectively. The reduced size of the oil drop would benefit the oil transportation in porous media. Higher flow rate in pores and throat would all intensify rupturing of the oil drop. Moreover, small throat could further reinforce the rupturing process. From combination of fluid flow rate, interfacial tension, and viscosity, higher capillary number reduced the maximum dimensionless width and length of the oil drop by 44.3% and 42.7%, respectively. The reduced size of oil drops ruptured at pore and throat junction contributes to the transportation of oil in porous media. Overall, this study provides a basic theory for active nanofluid to enhance imbibition oil recovery in tight reservoirs.

Performance evaluation of a wrapped around condenser for heat pump water heater applications

• A model has been developed to predict the performance of a HPWH condenser in two wrap patterns. • The impact of condenser design on the heat transfer to the storage tank has been established. • Optimization of the spacing for two wrap patterns shows little difference in performance. • Charge amount, as well as subcooled, saturated and super-heated lengths have been determined for the condenser. Accurate performance evaluation of a wrapped-around condenser for heat pump water heaters (WHPWH) is critical since the COP of the system depends heavily on thermal stratification and condenser design. An analytical, quasi-steady state heat balance method has been developed to determine the optimal spacing between adjacent channels, tube diameter, tube shape, and total refrigerant charge amount for the condenser. The heat transfer rate is compared among three approaches: the refrigerant thermodynamic model, the condenser-wrap fin model, and the analytical natural convection model on the inside of the tank for the three regions based on the refrigerant phase (e.g., super-heated, saturated, or subcooled). The heat transfer rate was predicted by a combination of slug-plug and annular flow for a D-shaped helical tube. Experimental data were used as boundary conditions for validating the model. The rate of heat transfer based on tube shape and tank wall temperatures was compared by CFD analysis. Parametric analysis indicates a tradeoff between refrigerant mass, pressure drop, tube diameter, and tube length to maximize the heat transfer rate. The model suggests the saturated region length can be extended by 400%, and the condenser pressure drop can be reduced by 23% with an optimal spacing pattern.

Numerical investigation of an aggressive s-shaped compressor transition duct with boundary layer suction

Aggressive s-shaped compressor transition ducts are important components in the connection between upstream boosters and downstream high-pressure compressors. The flow path is an s-shaped channel with struts and a large radial drop length ratio, which breaks through the limitations of traditional design and has a large aerodynamic loss. Therefore, this paper considers an aggressive s-shaped compressor transition duct in a geared turbofan engine and creatively proposes a method for controlling the flow separation through boundary layer suction. The results show that hub suction reduces the losses of the aggressive s-shape transition duct. As the mass flow rate of hub suction increases, the total pressure loss coefficient decreases and the rate of reduction in the total pressure loss slows down. Combined boundary layer suction reduces the total pressure loss to a greater extent. On the premise that the location of blade suction remains unchanged, the optimal location for the circumferential slot of hub suction is at 20% of the axial chord length of the strut, whereby the total pressure loss coefficient decreases by about 30% compared with the case of no suction. When the mass flow rate of suction is fixed at 3% of the inlet mass flow rate, a distribution of 0.5% from blade suction and 2.5% from hub suction reduces the total pressure loss by 1.6% compared with the case where all 3% comes from hub suction. The distribution of the mass flow rate for combined boundary layer suction has an optimal ratio.

The Investigation of the hydrodynamic drag of a slit microchannel with a textured wall

The results of numerical investigation of the hydrodynamic drag of a slit microchannel with a textured wall surface, as well as of the pressure drop in such a channel and the effective slip length on the wall for various Reynolds numbers, are presented. The channel height was 10 μm, and the length varied from 25 to 500 μm. It was found that the pressure drop in the textured microchannel was less than in a conventional one at any length. The dependences of the relative pressure drop, friction factor, and effective slip length on the Reynolds number were obtained for various channel lengths. A correlation that describes the dependence of the relative pressure drop on the Reynolds number for small channel lengths was proposed. The friction factor was described by a correlation expressed as 20 / Re. Keywords: microchannel, textured wall, wall slip, numerical simulation

Numerical study of microfluidic emulsion dynamics under the influence of heterogeneous surface wettability

Surface wettability plays a vital role in various natural phenomena and technical applications, such as coating, printing, membrane technology, microfluidic devices, and porous media flow. We numerically investigate the dynamics and stability of liquid–liquid dispersion flowing in a microfluidic channel with heterogeneous surface wettability, using a conservative phase-field lattice Boltzmann method. First, we validate the implementation of the wetting boundary conditions. We then perform three-dimensional simulations of a single drop motion immersed in another immiscible liquid in a square microchannel with alternating surface wettability: hydrophilic, hydrophobic, and again hydrophilic sections. The viscosity of the dispersed liquid (oil) is ten times higher than that of the continuous one (water), while the two liquids have equal densities. Depending on the drop length and Capillary number, calculated based on the drop velocity and the dynamic viscosity of the continuous phase, four different flow patterns are observed when the drop passes through the hydrophobic section. The distinct flow patterns include passing without any changes in drop shape or dynamics, adhesion of the dispersed liquid to the walls, phase inversion (i.e., water becomes the dispersed phase), and drop breakage. These outcomes are in close agreement with the experimental data. A detailed explanation of the choice of the numerical parameters is presented. The critical aspect of capturing the observed drop behavior is introducing an intervening thin-film of the continuous phase of at least three diffuse interface thicknesses (between the drop and channel walls).