Changes In Flow Rate Research Articles

Biochar colloids mobilization by consecutive fluid displacement in unsaturated condition

The theoretical narratives of transport and movement of biochar colloids (BCs) exist mostly for saturated zones or groundwater in the literature, while their corresponding mobilization mechanisms during drainage and imbibition in unsaturated systems have not been deliberated in detail. The main objective of this study is to quantify the BCs attached to the sand surfaces after passing the consecutive sequential fluid displacement cycles. The joint effect of change in flow rates and salinity of the solution was estimated in the artificially created unsaturated condition due to moving air-water interfaces over the BC deposited sediment. Initially, the synthesized BCs were deposited over silica sand. Then three flow rates (0.2, 1.0, 5.0 mL/min) and two salinity strengths (0.2 mM and 8 mM NaCl) were used to perform a series of unsaturated column transport experiments. The BC was also characterized by its elemental composition, functional groups, and surface morphologies. The results indicated that the BC could mobilize during the first sequential fluid displacement cycle while the salinity of the background solution was low. However, in a subsequent fluid displacement cycle, the BC was released while the salinity of the background solution was high. This phenomenon likely happened due to the attachment force between BCs and sand surfaces, as the primary energy barrier could be much stronger for higher salinity conditions. It is concluded that relatively smaller BCs could be detached from the sediment irrespective of flow rates or salinity strength used during the fluid displacement cycle. Based on these results, it can be inferred that BC present in the agricultural field effectively preserves the nutrients and supplies as a slow-release fertilizer in the event of intermittent rain during the monsoon season.

Effects of biventricular shunt on pump characteristics in a maglev total artificial heart.

Severe left ventricular failure can progress to right ventricular failure, necessitating alternatives to heart transplantation, such as total artificial heart (TAH) treatment. Conventional TAHs encounter challenges associated with miniaturization and hemocompatibility owing to their reliance on mechanical valves and bearings. A magnetically levitated TAH (IB-Heart) was developed, utilizing a magnetic bearing. The IB-Heart features a distinctive biventricular shunt channel situated between the flow paths of the left and right centrifugal blood pumps, simplifying and miniaturizing its control system. However, the impact of these shunt channels remains underexplored. This study aimed to investigate the effects of shunt flow on pump characteristics and assess the IB-Heart's potential to regulate flow balance between systemic and pulmonary circulation. At a rotational speed of 2000 rpm and flow rate range of 0-10 L/min, shunt flow exhibited a minor impact, with a 1.4 mmHg (1.3%) effect on pump characteristics. Shunt flow variation of about 0.13 L/min correlated with a 10 mmHg pressure difference between the pumps' afterload and preload conditions. This variance was linked to changes in the inlet flow rates of the left and right pumps, signifying the ventricular shunt structure's capacity to mirror the function of an atrial shunt in alleviating pulmonary congestion. The IB-Heart's ventricular shunt structure enables passive regulation of left-right flow balance. The findings establish a fundamental technical groundwork for the development of IB-Hearts and TAHs with similar shunt structures. The innovative coupling of centrifugal pumps and the resultant effects on flow dynamics contribute to the advancement of TAH technology.

Hplc Method Development and Validation for the Simultaneous Estimation of Pitavastatin and Telmisartan

Method validation of both the compounds was done on the basis of ICH guidelines. Validation by HPLC method the wavelength was selected at the isobestic point at which the two drugs can be detected using UV detectors. The selected wavelength was 250nm. Optimized liquid chromatographic condition was obtained by performing many trials for the selection of mobile phase and column, for the separation of Pitavastatin & Telmisartan. The method development was conducted with C18, 250 × 4.6 mm, 5µm particle size, Phenomenex with the flow rate of 1.0mL/min. the optimized mobile phase conditions were Acetonitrile and 10mM Ammonium acetate buffer containing 0.1% formic acid in the ratio of 65:35 v/v. Data of Simultaneous shows retention time for Pitavastatin 5.408 & Telmisartan was 7.183. The method found to be linear, accurate, rugged and robust for validated parameters. The linearity range was determined by external standard calibration method in the concentration range of 10μg/ml to 60μg/ml. The amount of recovery was calculated as 98% – 101% and it was observed that all the values are within the limits. Further the precision of the method was confirmed by the repeatable analysis of sample. The results were found to be precise due to low values of the %RSD. It indicated that the method has good precision. Limit of quantification for Pitavastatin & for Telmisartan 1.554μg/ml and 4.709μg/ml respectively. Similarly limit of detection for Pitavastatin & for Telmisartan 0.647μg/ml and 1.959μg/ml respectively. In the robustness study %RSD obtained for change of flow rate and wavelength and ruggedness for change of analyst was found to be below 2, which was within the acceptance criteria. So, simple, sensitive, accurate, precise RP- HPLC methods were developed and validated for the simultaneous estimation of Pitavastatin & Telmisartan.

An approach for optimization of controllable drilling parameters for motorized bottom hole assembly in a specific formation

This study focuses on optimizing drilling parameters when using Positive Displacement Motors (PDMs). In drilling operations involving mud motors, weight-on-bit (WOB) alterations lead to variations in the system's parasitic pressure drop. Consequently, this affects the optimum flow rate and the hydraulic power of the bit. Also, if the flow rate changes, the bit's rotations per minute (RPM) also change. In other words, using PDMs creates a link between the hydraulic system and the drilling speed, such that changing drilling parameters such as the WOB causes changes in the hydraulic system's performance. Therefore, one possible way to optimize the drilling parameters is to consider the drilling rate and hydraulic system simultaneously using a multi-objective approach. This study used an integrated approach encompassing data mining and mathematical modeling, employing a multi-objective framework to identify optimal parameters. The approach was applied to Dariyan Formation drilling data. The data mining approach revealed a well-distributed data set covering optimal and suboptimal zones suitable for optimization. In data mining, the identification of optimal conditions included a WOB of 11500 lb, a rotation speed of 105.8 rev/min, and a flow rate of 843 gpm, leading to an ROP of 44.23 ft/h. In multi-objective optimization, the optimal parameters consisted of a WOB of 14480 lb, a rotation speed of 115 rev/min, and a flow rate of 920.8 gpm, resulting in an ROP of 40.49 ft/h. Comparing optimal results with the drilling data shows a substantial MSE reduction of over 35 %. The results show the good performance of this approach in detecting the optimal and non-optimal drilling variables.

Toward tuning flow charecteristics in microchannel by nanotechnology and electrokinetic: Numerical simulation of heterogenous electroosmotic flow

Nanotechnology in recent years helps researcehers to design flow rate and profile in microsized channel via making surface charge heterogenous. This paper numerically simulates the electroosmotic flow inside a microchannel with non-uniform Zeta potential (ZP). The problem is a two-dimensional, incompressible, steady, and laminar channel flow between two parallel plates. The numerical results show that the flow rate changes compared to a constant ZP by ascending, descending, and parabolic modifications of the wall ZP at the mid-length of the microchannel. Results show that flow volume rate increases by microchannel width from 4 mm3/s to 6.5 mm3/s in best condition.

Multi-factor optimization of thermo-economic performance of coaxial borehole heat exchanger geothermal system based on Levelized Cost of Energy analysis

The deep coaxial borehole heat exchangers (BHEs) are commonly employed for geothermal heating purpose. In this investigation, using the established thermo-economic model and fast algorithm for heat extraction prediction, the response surface approach was adopted for investigating the thermo-economic performance and optimizing the design parameters of the coaxial BHE system. The results show that the heat exchange rate is enhanced from 235 kW to 1,061 kW when the depth varies between 2,000 m and 4,000 m. A change in flow rate from 20 m3/h to 80 m3/h yields a 30% augmentation in heat exchange rate. However, increasing the depth will cause extra drilling costs. Extremely large or small flow rates and pipe diameter ratios result in additional equipment and operating costs. The system's levelized cost of energy (LCOE) is contingent upon the interaction among the depth, flow rate, and diameter ratio. The optimal design parameters to meet the minimum LCOE are 3912.8 m depth, 34.32 m3/h flow rate and 0.64 pipe diameter ratio. The optimized LCOE is $ 7.84/GJ with an improvement of 22.02–63.02%, demonstrating a competitive thermo-economic performance to traditional energy sources. This research will contribute to the parameter design of BHE and effective utilization of geothermal energy.

Intercomparison of marine tracer and catchment-based submarine groundwater discharge estimates for a karst aquifer

Submarine groundwater discharge (SGD) is a major source of solutes to the ocean. Consequently, the accuracy of estimates of the magnitude and seasonal variability of SGD is critical for the management of coastal marine ecosystems. However, very few intercomparison studies between different conceptual approaches have been made to assess the reliability and consistency of SGD flow estimates while simultaneously gauging the applicability of underlying models and budget assumptions in real-world scenarios. To date, intercomparison efforts have focused on homogeneous aquifers, and less so on highly heterogeneous aquifers such as karst systems. Here we compare the results of tracer-based (salt mass balance, tidal prism and radon mass balances) and catchment-based methods (water balance, semi-distributed karst network model) to assess SGD at a data-rich coastal location. All approaches tested here reveal a positive relationship between SGD fluxes and groundwater level measured close to the preferential groundwater flow pathways in the phreatic karst aquifer (e.g. water-saturated conduits or fracture network). We use this finding to derive site-specific relationships between groundwater level and SGD flow rates. We derive these relationships from least square fitting of Darcian and Non-Darcian models and regression analysis. The relationships validate the findings derived independently from hydraulic/hydrogeological modelling of the complex karst networks. By combining various estimates made with distinct assumptions, this method produces robust estimates of the SGD seasonal variability, essential to develop optimal management strategies of SGD resources in coastal karstic regions. Where direct measurements of SGD are not possible, monitoring of coastal groundwater level close to preferential phreatic groundwater pathways can be thus used as a useful indicator to compare past groundwater flow measurements and derive site-specific relationships, particularly in settings where large flow rate changes are present such as karst aquifers.

Suitable Analysis of Micro-Increased Capacity Model on Cold-End System of Nuclear Power Plant

The cold-end system of a nuclear power plant is a key complex node connecting the power generation system with the variable environmental conditions, and its operation, economy, and stability have become the main obstacles to further improving the performance of the first and second circuits. The current research on the interactions between the cold-end system and the thermal cycle of nuclear power mainly adopts the micropower model, while the existing condenser model does not take into account the influence of the turbine exhaust resistance and exhaust flow and other factors on the condenser vacuum change caused by the change in the circulating water flow rate and temperature in determining the optimal vacuum. This ignores the interactions between the equipment and the interconnections between the parameters, which results in the reduction of the model’s accuracy. This paper takes a nuclear power unit as an example, adopts the “constant flow calculation” method to calculate the heat balance of the two-loop thermal system of the nuclear power plant, and constructs an integrated simulation model of the reaction environment variables, the cold-end system, and the thermal cycle. Taking the circulating water temperature and flow rate as variables, the errors of the separate condenser model and the coupled model in circulating water parameter changes were obtained under the condition of satisfying the thermal system operation, and the circulating water temperature and flow rate change ranges applied by the separate condenser model were analyzed in order to reduce the amount of calculations when the unit power error was 1%. The results show that the circulating water temperature is 4 °C, the applicable range of the circulating water flow rate is 42 m3/s to the rated flow rate, the applicable range of the circulating water temperature is 20 °C, the applicable range of the circulating water flow rate is 32.12 m3/s to the rated flow rate, the applicable range of the circulating water temperature is 26 °C, the applicable range of the circulating water flow rate is 38.63 m3/s to the rated flow rate, the applicable range of the circulating water temperature is 30 °C, and the applicable range of the circulating water flow rate is 45 m3/s to the rated flow rate. At a circulating water temperature of 26 °C, the applicable range of the circulating water flow is between 38.63 m3/s and the rated flow; at a circulating water temperature of 30 °C, the applicable range of the circulating water flow is between 45.64 m3/s and the rated flow.

Performance monitoring of heat exchanger networks using excess thermal and hydraulic loads

Fouling in heat exchanger networks (HENs) affects thermal and hydraulic efficiencies resulting in economic penalties to the process industries. Conventionally, overall heat transfer rates of the heat exchangers in HENs are monitored to identify fouling. However, apart from fouling, these rates also vary with inlet conditions. Hence, estimating the degree of fouling accurately based only on heat transfer rates can fail. Previously, we had proposed the use of excess thermal and hydraulic loads as the basis for monitoring fouling in standalone exchangers (Patil et al., 2022). These are quantified as thermal and hydraulic performance indicators that can be easily tracked through suitably constructed charts. In this paper, we extend the approach to HENs wherein deviations in temperature drop across a heat exchanger vis-à-vis the clean condition also depends upon upstream heat exchanger(s). The network performance monitoring charts rely on normalized performance indicators and temperatures across heat exchangers and also have explicitly denoted normal, alert, and alarm regions. The proposed charts are applicable to HENs with or without temperature controllers. Two case studies comprising multiple scenarios of flow rate and setpoint changes are studied. The results show that the method can effectively identify the degree of fouling.

Characterization of Microbubbles Generated in a Venturi Tube via Image Processing: Effect of Operating Parameters

Context: This research developed a dissolved air flotation system using a Venturi tube to produce microbubbles. The Venturi tube replaces the saturation tank and the pressure-reducing valve of conventional systems. Method: The system has both suction and injection air inlets, regulates the recirculation flow of the liquid to the tank, and provides a high hydraulic load in a reduced size. Counting and measuring the microbubbles produced via digital image processing helps to characterize the system's performance. Results: The system with air suction produces smaller bubbles than that with air injection. A higher liquid recirculation pressure produces more bubbles and reduces their size in the case of air suction. Conclusions: In air injection, the change in flow rate influences the size of the microbubbles. Air injection and recirculation pressure do not influence the number of bubbles generated.

Rheological properties of polypropylene composites with calcium carbonate under high shear rates

The rheological properties of isotactic polypropylene (iPP) and its composites with unmodified and stearic acid-modified calcium carbonate (5, 10, 20, 30 wt.%) were investigated. The processability factor K of the composites was determined based on changes in the mass flow rate (MFR). The assessment of rheological properties was carried out at high shear rates, in the injection process, using a special on-line measuring head. Measurements were performed at a temperature of 230°C, in the range of apparent shear rate from 19,100 to 101,900 s-1, based on the Ostwald-de Waele power-law model. It has been shown that the behavior of polymer composites during processing (flow resistance, flow, and viscosity curves, MFR) depends on the degree of filling, the type of filler used and the range of shear rates.

A novel endogenous retention-index for minimizing retention-time variations in metabolomic analysis with reversed-phase ultrahigh-performance liquid-chromatography and mass spectrometry

Consistent retention time (tR) of metabolites is vital for identification in metabolomic analysis with ultrahigh-performance liquid-chromatography (UPLC). To minimize inter-experimental tR variations from the reversed-phase UPLC-MS, we developed an endogenous retention-index (endoRI) using in-sample straight-chain acylcarnitines with different chain-length (LC, C0–C26) without additives. The endoRI-corrections reduced the tR variations caused by the combined changes of mobile phases, gradients, flow-rates, elution time, columns and temperature from up to 5.1 min–0.2 min for most metabolites in a model metabolome consisting of 91 metabolites and multiple biological matrices including human serum, plasma, fecal, urine, A549 cells and rabbit liver extracts. The endoRI-corrections also reduced the inter-batch and inter-platform tR variations from 1.5 min to 0.15 min for 95 % of detected features in the above biological samples. We further established a quantitative model between tR and LC for predicting tR values of acylcarnitines when absent in samples. This makes it possible to compare metabolites’ tR from different tR databases and the UPLC-based metabolomic data from different batches.

Investigation on preventive inerting approach of coal spontaneous combustion in gob considering adsorption effect.

Coal spontaneous combustion in the gob poses a significant threat to coal mining operations. Designing optimal process parameters for nitrogen injection to prevent and control fires efficiently is crucial. To achieve this, a multi-field coupling equation was established, considering the adsorption of coal to gas. The model's accuracy was verified on-site, and the effects of nitrogen injection at different locations and flow rates were simulated. The optimal injection parameters were determined by analyzing temperature and inerting time. The results showed that the coal spontaneous combustion hazardous zone in the gob tested on-site was consistent with the simulation from the perspective of physisorption. Nitrogen injection had three stages: gas expansion, rapid oxygen dilution, and complete inerting. The nitrogen injection effect presented a nonlinear change in injection location and flow rate. The optimal nitrogen injection location for the Tingnan Coal Mine in Shaanxi was determined to be 90 m behind the working face on the inlet side, with an optimal flow rate of 800 m3/min. This study focused on gas adsorption and offered valuable insights for creating high-efficiency fire-fighting techniques that involve inserting in the gob.

Possible Effects of Changes in Carbonate Concentration and River Flow Rate on Photochemical Reactions in Temperate Aquatic Environments.

In temperate environments, climate change could affect water pH by inducing enhanced dissolution of CaSO4 followed by biological sulphate reduction, with the potential to basify water due to H+ consumption. At the same time, increased atmospheric CO2 could enhance weathering of carbonate rocks (e.g., dolomite) and increase the total concentration of dissolved carbonate species. Both processes enhance phototransformation by the carbonate radical (CO3•-), as shown for the non-steroidal anti-inflammatory drug paracetamol, provided that the dissolved organic carbon of water does not undergo important fluctuations. Climate change could also affect hydrology, and prolonged drought periods might considerably decrease flow rates in rivers. This is a substantial problem because wastewater pollutants become less diluted and, as a result, can exert more harmful effects due to increased concentrations. At the same time, in low-flow conditions, water is also shallower and its flow velocity is decreased. Photochemical reactions become faster because shallow water is efficiently illuminated by sunlight, and they also have more time to occur because water takes longer to cover the same river stretch. As a result, photodegradation of contaminants is enhanced, which offsets lower dilution but only at a sufficient distance from the wastewater outlet; this is because photoreactions need time (which translates into space for a flowing river) to attenuate pollution.

Computational fluid dynamics analysis of flowmeters with elliptical gear pairs and evaluation of calculated flow rate by Taguchi method

Accurate determination of flowmeters' design and manufacturing parameters ensures that commercially available flowmeters' declared characteristics are reliable. In this study, nine different flow meters with elliptical gear pairs were manufactured at three different a/b ratios, three different modules, and three different tooth numbers, and the Computational Fluid Dynamics (CFD) models were prepared. CFD analysis forms the basis of the study's methodology, which seeks to statistically identify the most appropriate elliptical gear parameters according to the flow meters manufactured and what the most influential parameter that changes the measured flow rate is. As the pressure of the fluid increased, the measured and CFD-calculated flow rates decreased. According to the measured flow rates and CFD analysis results, it was found that the average flow rate change was −0.0102 %, the biggest change was in the flow meter coded Db-03 with 0.0855 % at 3.00 MPa pressure, and the least change was in the flow meter coded Db-02 with 0.0002 % at 4.50 MPa pressure. The CFD models developed for the manufactured flowmeters were suitable for all flowmeters according to the measured and calculated percent flow rate variations. Taguchi L9 analysis revealed that a/b = 1.40, m = 2.50 mm, and z = 40 teeth are the optimal manufacturing parameters for elliptical gear, according to the signal-to-noise ratio based on the largest, best analysis. According to the analysis of variance, the modulus value contributed the most to the calculated flow rate at 65.25%, whereas the a/b ratio contributed the least with 0.96%.

Tunica Vaginalis Pedicle Flap Substitution Urethroplasty for Reconstruction of Anterior Urethral Stricture

Background: In long-segment urethral stricture, substitutional urethroplasty is the best option to get long-term good results. Though buccal mucosa is the most widely used tissue, it has limitations in some oral pathology. In several publications, there is evidence that Tunica vaginalis can be used as a graft or flap to reconstruct fibrotic urethra as well as to provide a vascularized covering to prevent subsequent urethrocutaneous fistula formation. This study evaluated the efficacy of the tunica vaginalis pedicle flap’s efficacy for managing anterior urethral stricture.Objectives: To evaluate the clinical efficacy of tunica vaginalis pedicle flap for reconstruction of anterior urethral stricture by assessing change in the maximum flow rate (Qmax), International prostatic symptom index (IPSS), postvoid residual urine (PVR) from baseline and the complication of surgery.Materials and Methods: This was a prospective clinical trial conducted in the Department of Urology, Bangabandhu Sheikh Mujib Medical University, Dhaka from July 2017 to June 2018. A total of 15 patients were selected from the study population according to inclusion and exclusion criteria. The standard operation technique of urethroplasty by tunica vaginalis flap was followed. Patients were followed up after 3 months & 6 months to evaluate IPPS score, Qmax, flow time, PVR, and complications.Results: The mean age and stricture length of study participants were 38.93±11.38 years and 3.55±1.05 cm. The maximum flow of urine was 15.844±3.80 ml/sec at the final follow up which showed statistically significant improvement from baseline. There was also a significant improvement in IPSS, and quality of life during follow-up. Flow time and post-void residue reduced significantly from preoperative measurement. A total of 4 patients developed complications after the substitution of urethroplasty with tunica vaginalis.Conclusion: Tunica vaginalis pedicle flap may be an effective choice in the reconstruction of anterior urethral stricture.KYAMC Journal Vol. 14, No. 02, July 2023: 79-82.

Model based process optimization of an industrial chromatographic process for separation of lactoferrin from bovine milk

Model based process development using predictive mechanistic models is a powerful tool for in-silico downstream process development. It allows to obtain a thorough understanding of the process reducing experimental effort. While in pharma industry, mechanistic modeling becomes more common in the last years, it is rarely applied in food industry. This case study investigates risk ranking and possible optimization of the industrial process of purifying lactoferrin from bovine milk using SP Sepharose Big Beads with a resin particle diameter of 200 µm, based on a minimal number of lab-scale experiments combining traditional scale-down experiments with mechanistic modeling. Depending on the location and season, process water pH and the composition of raw milk can vary, posing a challenge for highly efficient process development.A predictive model based on the general rate model with steric mass action binding, extended for pH dependence, was calibrated to describe the elution behavior of lactoferrin and main impurities. The gained model was evaluated against changes in flow rate, step elution conditions, and higher loading and showed excellent agreement with the observed experimental data. The model was then used to investigate the critical process parameters, such as water pH, conductivity of elution steps, and flow rate, on process performance and purity. It was found that the elution behavior of lactoferrin is relatively consistent over the pH range of 5.5 to 7.6, while the elution behavior of the main impurities varies greatly with elution pH. As a result, a significant loss in lactoferrin is unavoidable to achieve desired purities at pH levels below pH 6.0. Optimal process parameters were identified to reduce water and salt consumption and increase purity, depending on water pH and raw milk composition. The optimal conductivity for impurity removal in a low conductivity elution step was found to be 43 mS/cm, while a conductivity of 95 mS/cm leads to the lowest overall salt usage during lactoferrin elution. Further increasing the conductivity during lactoferrin elution can only slightly lower the elution volume thus can also lead to higher total salt usage. Low flow rates during elution of 0.2 column volume per minute are beneficial compared to higher flow rates of 1 column volume per minute.The, on lab-scale, calibrated model allows predicting elution volume and impurity removal for large-scale experiments in a commercial plant processing over 106 liters of milk per day. The successful model extrapolation was possible without recalibration or detailed knowledge of the manufacturing plant. This study therefore provides a possible pathway for rapid process development of chromatographic purification in the food industries combining traditional scale-down experiments with mechanistic modeling.

Top-down holmium laser enucleation of the prostate (HoLEP) versus traditional HoLEP for the treatment of benign prostatic hyperplasia (BPH): 1-year outcomes of a randomized controlled trial.

The top-down holmium laser enucleation of the prostate (HoLEP) technique recently emerged as a safe and effective modification of traditional HoLEP. In our randomized controlled trial, we compared intraoperative and postoperative outcomes of traditional and top-down HoLEP for the treatment of benign prostatic hyperplasia (BPH) in patients with a prostate size ≥80 g. One-hundred patients with BPH and a prostate volume ≥80 cc participated in this prospective randomized controlled trial. Outcome measures were collected and compared, including IPSS, QoL, flow rate, PVR, IIEF-15, PSA, and TRUS prostate volume changes. Perioperative complications were also recorded. All patients were followed up at 1, 3, 6, and 12 months. There were no significant differences in preoperative baseline characteristics between the two surgical groups. The median prostate volume for the traditional and top-down HoLEP groups was 107 and 102 cc, respectively. The operative parameters and postoperative outcomes were comparable for both cohorts. The median enucleation time for traditional HoLEP was 60 min, which was not significantly longer than that of top-down HoLEP (52 min) (p = 0.07). At 3 months follow-up, there was no statistically significant difference in transient stress urinary incontinence (SUI) in the traditional HoLEP (4.1%) versus the top-down HoLEP group (2.2%), (p = 0.61). There were no significant differences in functional and sexual outcomes between the two groups at 12 months. The HoLEP procedure significantly improves patients' urinary functional outcomes and has comparable postoperative outcomes regardless of the technique utilized.

Influence of parallel and series U-loop configurations on the thermal behaviour of energy piles

Energy piles are foundation piles that have heat exchanger pipes installed in them for exchanging geothermal energy between buildings and the ground through the use of a ground source heat pump (GSHP). This is a cost-effective and environmentally friendly method to supplement heating and cooling of buildings. Heat transfer occurs between the piles and the ground through a heat transfer fluid circulating in the pipes. The heat exchanger pipes in the piles are commonly made from polyethylene pipes formed into U-loops [e.g., 1, 2, 3, 4, 5, 6, 7]. The U-loops are configured into series or parallel configurations to circulate water in the pipes. A number of studies have investigated the thermal and thermo-mechanical behaviour of energy piles with U-loop heat exchangers [e.g., 1, 2, 3, 4, 5, 6, 7]. Despite this widespread research, the fluid flow and temperature variations in the individual U-loops are not well understood for parallel and series U-loops in the piles. Given that the fluid flow behaviour varies between the two configurations [8], it can be hypothesised that the thermal behaviour of the energy piles may vary as well. 
 This study investigates the influence of series and parallel U-loop configurations on the variations in fluid temperatures and flowrates in the individual U-loops of energy piles, and the effects of these variations on the geothermal energy extracted by the piles. Heating experiments were conducted on a set of four field-scale energy piles installed below a 5-storey building in Brighton group sandy soils. The energy piles have a length of 15 m and diameter of 0.9 m, but different numbers of U-loops (1, 2, 3, and 4 U-loops in Piles 1, 2, 3, and 4, respectively). The fluid temperatures and flowrates were monitored in the individual U-loops of the piles that were connected to a plumbing manifold located in the monitoring room (Figure 1). A comparative thermal performance analysis of the two configurations was conducted to derive conclusions on the preferred configuration for improved thermal performance of the piles.
 The flowrate variations and change in fluid temperatures in the individual U-loops at Day 15 of group tests are shown in Figure 2. The flowrates were inconsistent between the U-loops in the parallel configuration but remained constant in the series U-loops. Heat exchange occurred in all the U-loops in parallel, whereas only the first few U-loops in the series configuration exchanged heat with the ground. The results suggest that all the energy piles in the group with parallel U-loops were thermally active and could improve the performance of energy pile systems compared to energy piles with U-loops in series.

Pulsatile pressure enhanced rapid water transport through flexible graphene nano/Angstrom-size channels: a continuum modeling approach using the micro-structure of nanoconfined water

Several researchers observed a significant increase in water flow through graphene-based nanocapillaries. As graphene sheets are flexible (Wang and Shi 2015 Energy Environ. Sci. 8 790–823), we represent nanocapillaries with a deformable channel-wall model by using the small displacement structural-mechanics and perturbation theory presented by Gervais et al (2006 Lab Chip 6 500–7), and Christov et al (2018 J. Fluid Mech. 841 267–86), respectively. We assume the lubrication assumption in the shallow nanochannels, and using the microstructure of confined water along with slip at the capillary boundaries and disjoining pressure (Neek-Amal et al 2018 Appl. Phys. Lett. 113 083101), we derive the model for deformable nanochannels. Our derived model also facilitates the flow dynamics of Newtonian fluids under different conditions as its limiting cases, which have been previously reported in literature (Neek-Amal et al 2018 Appl. Phys. Lett. 113 083101; Gervais et al 2006 Lab Chip 6 500–7; Christov et al 2018 J. Fluid Mech. 841 267–86 ; White 1990 Fluid Mechanics; Keith Batchelor 1967 An Introduction to Fluid Dynamics ; Kirby 2010 Micro-and Nanoscale Fluid Mechanics: Transport in Microfluidic Devices). We compare the experimental observations by Radha et al (2016 Nature 538 222–5) and MD simulation results by Neek-Amal et al (2018 Appl. Phys. Lett. 113 083101) with our deformable-wall model. We find that for channel-height Å, the flow-rate prediction by the deformable-wall model is 5%–7% more compared to Neek-Amal et al (2018 Appl. Phys. Lett. 113 083101) well-fitted rigid-wall model. These predictions are within the errorbar of the experimental data as shown by Radha et al (2016 Nature 538 222–5), which indicates that the derived deformable-wall model could be more accurate to model Radha et al (2016 Nature 538 222–5) experiments as compared to the rigid-wall model. Using the model, we study the effect of the flexibility of graphene sheets on the flow rate. As the flexibility α increases (or corresponding thickness and elastic modulus E of the wall decreases), the flow rate also increases. We find that the flow rate scales as for ; for ; and for , respectively. We also find that, for a given thickness , the percentage change in flow rate in the smaller height of the channel is more than the larger height of the channels. As the channel height decreases for the given reservoir pressure and thickness, the increases with followed by after a height-threshold. Further, we investigate how the applied pulsating pressure influences the flow rate. We find that due to the oscillatory pressure field, there is no change in the averaged mass flow rate in the rigid-wall channel, whereas the flow rate increases in the flexible channels with the increasing magnitude of the oscillatory pressure field. Also, in flexible channels, depending on the magnitude of the pressure field, either of the steady or oscillatory or both kinds of pressure field, the averaged mass flow rate dependence varies from to as the pressure field increases. The flow rate in the rigid-wall channel scales as , whereas for the deformable-wall channel it scale as for , for , and for . We find that both the flexibility of the graphene sheet and the pulsating pressure fields to these flexible channels intensify the rapid flow rate through nano/Angstrom-size graphene capillaries.