High Volumetric Flow Rates Research Articles

Wear mechanisms and material deposition of high-performance polymer composites for hydrogen compression

The transistion to renewable energy production is a main component in achieving the climate targets defined in the 2015 Paris Agreement. Power-to-gas concepts, where electrical energy is stored as hydrogen gas, require the design and operation of state-of-the-art reciprocating compressor technology to realize high pressure ratios and high volumetric flow rates for gas supply demands. The main challenges in designing machines suited for these operating conditions are high thermo-mechanical stresses acting on the piston sealing rings. High shear loads and minimal ring gap sizes demand material pairings with excellent wear resistance and sliding properties. This work investigates the life cycle limiting wear mechanisms present in the piston compressor and develops advanced concepts for piston rings in cylinder tribo-contacts. PI and PPS polymers reinforced with carbon fiber were modified with dry lubricating PTFE to fulfil the requirements of this highly stressed tribo-system. Tribo-tests were performed against steel countersurfaces with a linear oscillating tribometer in pin-on-plate configuration. The failure mechanisms were analysed utilizing scanning electron microscopy on cross-sections cut into the depth of the countersurface material with focused ion beam milling. 2D scanning transmission electron microscopy mapping supported by energy dispersive X-ray spectroscopy were performed to analyze the depth profile of the deposited tribo-layer elements on the wear track.

Multi-objective topology optimization design of silicon carbide metal oxide semiconductor field effect transistors power module liquid-cooled heatsink for electric vehicles

Silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs) is gradually replacing silicon-based insulated gate bipolar transistor (IGBT) as the switching devices in electric vehicle power inverters due to its higher operating temperatures, switching speeds, and frequencyies. However, the high switching frequency of SiC MOSFETs can increase the losses of the power inverter, resulting in an increase in the temperature, which will limit the performance of power inverters. The improvement of power module performance is mainly controlled by optimizing its control methods during operation and improving its cooling system. Currently, the liquid-cooled heatsink used in power modules have disadvantages such as large flow resistance and poor heat dissipation performance. In order to enhance the performance of the heatsink, this study first established a three-dimensional finite element model of SiC MOSFETs power module based on a pin fin heatsink. The accuracy of the model was verified by numerical and experimental methods. Secondly, based on numerical analysis, a multi-objective topology optimization method for the power module liquid-cooled heatsink is proposed. This method takes heat exchange and fluid dissipation energy as the objective function and uses weight factors to adjust the influence of each on the objective functions. Additionally, the temperature distribution of the heatsink is considered to optimize its performance. Finally, the numerical results show that the topology-optimized heatsink exhibits better performance at high coolant volumetric flow rates. When the coolant volumetric flow rate is 14 L/min, the pressure drops of topology-optimized heatsink is reduced by 63.94 % and the junction temperature of the power module is reduced by 0.24 % compared with the pin fin heatsink. This topologically optimized heatsink could be helpful to improve the performance of existing power module heatsinks.

Quartz Dissolution Effects on Flow Channelization and Transport Behavior in Three‐Dimensional Fracture Networks

AbstractWe perform a set of reactive transport simulations in three‐dimensional fracture networks to characterize the impact of geochemical reactions on flow channelization. Flow channelization, a frequently observed phenomenon in porous and fractured subsurface rock formations, results from the spatially variable hydraulic resistance offered by a geological structure. In addition to geo‐structural features such as network connectivity, geometry, and hydraulic resistance, geochemical reactions, for example, dissolution and precipitation, can dynamically inhibit or enhance flow channelization. These geochemical processes can change the fracture permeability leading to increased flow channelization, which are localized connected regions of high volumetric flow rates that are seemingly ubiquitous in the subsurface. In our simulations, fractures partially filled with quartz are gradually dissolved until quasi‐steady state conditions are obtained. We compare the flow field's initial unreacted and final dissolved states in terms of flow and transport observations. We observe that the dissolved fracture networks provide less resistance to flow and exhibit increased flow channelization when compared to their unreacted counterparts. However, there is substantial variability in the magnitude of these changes which implies that the channelization strongly depends on the network structure. In turn, we identify the interplay between the particular network structure and the impact of geochemical dissolution on flow channelization. The presented results indicate that geological systems that have been weathering or reactive for longer times in older landscapes are likely to have increased flow channelization compared to their equivalent but younger counterparts, which implies a time dependence on flow channelization in fractured media.

Investigation of O atom kinetics in O2 plasma and its afterglow

We have developed a comprehensive kinetic model to study the O atom kinetics in an O2 plasma and its afterglow. By adopting a pseudo-1D plug-flow formalism within the kinetic model, our aim is to assess how far the O atoms travel in the plasma afterglow, evaluating its potential as a source of O atoms for post-plasma gas conversion applications. Since we could not find experimental data for pure O2 plasma at atmospheric pressure, we first validated our model at low pressure (1–10 Torr) where very good experimental data are available. Good agreement between our model and experiments was achieved for the reduced electric field, gas temperature and the densities of the dominant neutral species, i.e. O2(a), O2(b) and O. Subsequently, we confirmed that the chemistry set is consistent with thermodynamic equilibrium calculations at atmospheric pressure. Finally, we investigated the O atom densities in the O2 plasma and its afterglow, for which we considered a microwave O2 plasma torch, operating at a pressure between 0.1 and 1 atm, for a flow rate of 20 slm and an specific energy input of 1656 kJ mol−1. Our results show that for both pressure conditions, a high dissociation degree of ca. 92% is reached within the discharge. However, the O atoms travel much further in the plasma afterglow for p = 0.1 atm (9.7 cm) than for p = 1 atm (1.4 cm), attributed to the longer lifetime (3.8 ms at 0.1 atm vs 1.8 ms at 1 atm) resulting from slower three-body recombination kinetics, as well as a higher volumetric flow rate.

Oscillations and bistability of complex electrochemical reactions in 3D printed microfluidic devices

We investigate the kinetic features of complex charge transfer chemical reactions using a microelectrode integrated in a flow cell made with 3D printing technology. Thin layer electrochemical cells with 350 μm (height) × 1000 μm (width) channels were designed. Ferrocyanide oxidation on a 100 μm diameter Pt electrode using the printed cell showed mass transfer limiting current at large overpotentials. The variation of the limiting current with the flow rate (1 μL/min ≤ Q ≤ 100 μL/min) was interpreted with the superposition of a constant current due to radial diffusion and a Levich-type square-root relationship, indicating a mixed radial diffusion/thin layer mass transport condition. These findings were further supported by numerical simulation of a diffusion-convection equation in the flow channel. Experiments with copper electrodissolution in phosphoric acid electrolyte reproduced oscillatory behavior that was previously seen in macrocells and polydimethylsiloxane (PDMS) microchips. The 3D printed cell can accommodate multiple electrodes – to demonstrate this application we showed that the current oscillations with copper electrodissolution can exhibit frequency synhcronization with a dual electrode configuration. Finally, hydrogen oxidation on a Pt wire in the presence of Cu2+ and Cl− inhibitors displayed bistability at relatively large external resistance and oscillations at high volumetric flow rates. The results show that the 3D printed thin layer design is an alternative to studying nonlinear phenomena in electrochemical cells with distinct advantages to the traditional approaches of using macrocells and PDMS microchip flow cells.

Analysis of pulse electromagnetic electroosmotic flow of Jeffrey fluid through parallel plate microchannels under a constant pressure gradient

The purpose of this work is to investigate the pulse electromagnetic electroosmotic flow (EOF) behavior of a Jeffrey fluid in parallel plate microchannels under a constant pressure gradient. Analytical solutions for the velocity and volumetric flow rate are derived by employing the Laplace transform method and the residue theorem. In particular, the electric double layer (EDL) effect is considered, and an analysis is conducted on both the near-center and near-wall velocities. The flow periodicity is also noted, and these velocities are evaluated during the first and second half-cycles, respectively. Moreover, both 3D and 2D graphics are simultaneously utilized to visualize the impact of relevant parameters on velocity and volumetric flow rate. Our analysis yielded the following key findings: The effects of relevant parameters, such as pulse width a¯, pressure gradient Ω, Hartmann number Ha, electric field strength β, electrokinetic width K, relaxation time λ¯1 and retardation time λ¯2, on the near-center velocity during the first half-cycle align with the results of previous studies. During the second half-cycle, higher values of variables Ha and β lead to reduced velocities. Interestingly, during any half-cycle, the near-wall velocity demonstrates similar characteristics to the near-center velocity in response to variations in certain parameters, including Hartmann number Ha, electric field strength β, relaxation time λ¯1 and retardation time λ¯2. It is worth mentioning that the influence of relaxation time λ¯1 and retardation time λ¯2 on the near-wall velocity is largely independent of the Hartmann number, especially for the retardation time. Regardless of the values of the parameters λ¯1 and λ¯2, a higher volumetric flow rate is observed with an increased electrokinetic width K. Additionally, the volumetric flow rate profile of the Jeffrey fluid exhibits a comparatively smoother trend over time compared to that of the Maxwell fluid. The remarkable similarity between Jeffrey fluid and blood suggests that the results presented in this paper hold immense potential as a crucial reference for studying blood transport within the field of microfluidics.

Donnan Dialysis for Recovering Ammonium from Fermentation Solutions Rich in Volatile Fatty Acids.

For the production of polyhydroxyalkanoates (PHA) using nitrogen-rich feedstocks (e.g., protein-rich resources), the typical strategy of restricting cell growth as a means to enhance overall PHA productivity by nitrogen limitation is not applicable. In this case, a possible alternative to remove the nitrogen excess (NH4+/NH3) is by applying membrane separation processes. In the present study, the use of Donnan dialysis to separate ammonium ions from volatile fatty acids present in the media for the production of PHA was evaluated. Synthetic and real feed solutions were used, applying NaCl and HCl receiver solutions separated by commercial cation-exchange membranes. For this specific purpose, Fumasep and Ralex membranes showed better performance than Ionsep. Sorption of ammonium ions occurred in the Ralex membrane, thus intensifying the ammonium extraction. The separation performances with NaCl and HCl as receiver solutions were similar, despite sorption occurring in the Ralex membrane more intensely in the presence of NaCl. Higher volumetric flow rates, NaCl receiver concentrations, and volume ratios of feed:receiver solutions enhanced the degree of ammonium recovery. The application of an external electric potential difference to the two-compartment system did not significantly enhance the rate of ammonium appearance in the receiver solution. The results obtained using a real ammonium-containing solution after fermentation of cheese whey showed that Donnan dialysis can be successfully applied for ammonium recovery from such solutions.

Optimization of a Developed Multi-Cyclone Using Response Surface Methodology (RSM) to Control Fine Particulate Emission

The effects of increasing volumetric air flow rate and inlet particulate loading on overall collection efficiency of MR-deDuster; a developed multi-cyclone system was investigated using various segregated sizes of palm oil mill boiler fly ash. The operating conditions of the fabricated pilot plant scale of the unit were predicted theoretically and screened experimentally. Increasing volumetric air flow rate theoretically will increase the overall collection efficiency, yet the experimental results during screening stage demonstrated contradict finding when the increment of volumetric air flow rate caused the overall collection efficiency to be decreased for a constant particulate loading. Subsequently, the optimization work was done to determine the optimum operating conditions of the system using Response Surface Method (RSM) with Box-Behnken design. The parallel arrangement of multi-cyclone units proved the ability of the system to uniformly disseminate the gas flow with high volume of gas carrier. Nevertheless, excessive pressure drops between each unit of multi-cyclone due to high volumetric air flow rate should be avoided as such condition may lower the overall collection efficiency by allowing dust re-entrainment from the hopper to circulate between the cyclones. Through statistical analysis of variance (ANOVA), validation and verification studies, it is suggested that the developed pilot scale multi-cyclone unit would be able to meet the targeted limit of 150 mg/m3 for solid fuel burning equipment industry in Malaysia by operating with optimized volumetric air flow rate of 0.27 m3/s, and maximum inlet particulate loading rate and size of 2 g/m3 and 1000 μm respectively.

Design and Development of Throttle Valve-based Hydrodynamic Cavitator for Food

Hydrodynamic cavitation is an emerging non-thermal technology in food sector. The existing methods are venturi meter, orifice meter, and high-speed homogenizer. The former two are economic, but susceptible to clogging as cavitation occurs close to the walls. High volumetric flow rate causes flow instability and super-cavitation that limit the use of venturi meter. The latter device performs well, but is expensive. The present research was undertaken for design and development of a throttle valve-based hydrodynamic cavitator to overcome above issues. The throttle valve for creating cavitation was fixed on the suction side of the pump. To avoid cavitation and to fully recover the downstream pressure, the minimum length between throttle valve and pump was found to be 1.25 m. Iodine liberation was studied as a function of cavitation number for performance evauation of the hydrodynamic reactor. It increased increased when cavitation number decreased up to 0.42, and super-cavitation occurred beyond that value.

Assessment of units vibration state and water supply path of Amuzang-2 pumping station

This article presents separate results of studies devoted to the study and analysis of vibrational phenomena occurring on pumping units and along the line of the pressure pipeline of the surveyed pumping stations, associated with flow pulsation in the water supply path and cavitation manifested on pumping units. As is known, the operation of pumps is accompanied by hydrodynamic oscillatory phenomena, which are expressed in the non-stationarity of the field of velocities and pressures of water at the outlet of the pump. This is especially typical for powerful centrifugal pumps with high volumetric flow rates and pressure drops on the impeller, which took place at Amuzang-2 pumping station. Thus, the analysis of the results of vibration tests of pipelines allows us to draw the following conclusions: 1. The vibration state of all pipelines is unsatisfactory. 2. The cause of increased vibration is an unfavorable combination of design, installation, and operational factors.

Dynamic stabilization of a hydrogen premixed flame in a narrow channel

Combustion of hydrogen can help in reducing carbon-based emissions but it also poses unique challenges related to the high flame speed and Lewis number effects of the hydrogen flame. When operated with conventional burners, a hydrogen flame can flashback at higher volumetric flow rates than a methane flame due to the difference in stabilization mechanisms of the two fuels. Due to these differences, conventional burners cannot offer similar operational ranges for hydrogen than that for hydrocarbon flames. An exploration into the unique stabilization behaviour of hydrogen flames is required which could help in envisioning non-conventional burner concepts for keeping hydrogen flames stable. Stability conditions, which describe the kinematics of premixed flames with spatially and temporally changing flow parameters, are crucial for such an exploration. Stability conditions are usually hypothesized for stable flames, where a flame upon perturbation is assumed to return to its original position. Alternatively, in the case of flashback/blow-off, it refers to a flame moving upstream of the burner or being convected out of the domain. However, it is also of interest to understand how and why a flame could move to a new location when the velocity and strain fields are varying with time and space at the original and the new location. In this paper, we investigate the flame stabilization by 1) observing the hydrogen flame’s upstream movement in a multi-slit configuration when a geometrical change is made, and 2) changing strain and velocity fields in a dynamic and periodic manner using numerical tools such that the unique behaviour of a hydrogen flame can be captured. We vary the location of high flow strain periodically in a channel by manipulating the boundary condition along a wall. It is found that a hydrogen flame follows this point in a periodic manner, also propagating against the inflow which is considerably faster than its unstretched burning velocity. Spatial and temporal stability conditions, that explain the mechanism behind the flame’s movement from its original position to a new position, are analyzed from the simulation data, advancing our knowledge on the flame movement in an unsteady setting and providing important insights into the stabilization mechanism of hydrogen flames.

Enhancement of liquid-solid mixing and particle hydrophobization by an impeller-less flotation pulp conditioning device

An impeller-less device was proposed to employ opposite rotational jet flows conditioning pulp before flotation. The flow field characteristics and relevant effects on the liquid-solid mixing performance were investigated by the numerical simulation of computational fluid dynamics that was proved effective by the particle image velocimetry technique. The outcome of particle surface modification was clarified by variations in the contact angle and surface species of quartz particles. Results showed that the increase of turbulent kinetic energy induced by the opposite rotational flows remarkably improved the dispersion of mineral particles. Smaller particle size and larger circulation rate were conductive to a more uniform distribution of particles. In the case of a volume flow of 3.6 m3/h and a feed volume fraction of 7 % with an average particle size of −45 μm, nearly 4/5th of the whole device area exhibits a particle volume fraction within the range of 6 % and 7 %, and the coefficient of variation was as low as 0.151. Meanwhile, strong turbulence and high shear induced by opposite rotational flows provided favorable conditions for the collector adsorption and particle hydrophobization, which was responsible for the increase in contact angle under relatively higher volumetric flow rates. However, when the volume flow exceeded 3.0 m3/h, over-increasing shear stresses and excessive turbulence caused the desorption of adsorbed collectors, reflected as the decreased nitrogen content on quartz surfaces from 0.85 % to 0.51 %, thereby accounting for the declined contact angle of conditioned quartz particles. This study highlighted the dominant effect of turbulence and shear strain on particle surface modification, and the significance of proper parameter control.

Bioinspired Soft Bendable Peristaltic Pump Exploiting Ballooning for High Volume Throughput

Interest in bioinspired peristaltic pumps has grown in popularity among the scientific community in the last decade thanks to their extreme flexibility and their intrinsic compliance. In this paper, we propose a soft peristaltic pump exploiting ballooning. Our aim is to promote and propel forward the ballooned region by controlling the air pressure between the balloon and an external flexible containment tube, to achieve a peristaltic pumping motion with a simple design and using only one control signal. This paper describes the implementation of the pump and the inlet-pump-outlet system, provides an analytical model to predict the pump performance, and showcases experimental results. We also implement a computer simulation to further characterize the device. We show that it is possible to achieve high volumetric flow rates, up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.4\;mL/s$ </tex-math></inline-formula> , with only a single control signal, paving the way for more flexible and easy to manufacture peristaltic pumps.

Membraneless Electrolyzers for the Conversion of Brine into High-Value Products

Desalination offers an approach to address the shortage of fresh water, however, the main concern is the generation of reject brine or concentrated saltwater that contains organic compounds, metals, and contaminants. Membraneless electrolyzers present a viable solution to convert the reject brine into H2 and O2, while simultaneously splitting it into acidic (HCl) and base (NaOH). They transport ions through a highly conductive liquid electrolyte instead of a membrane. The lack of a separator allows for operation in a wide range of pH environments and inhibits degradation and fouling issues found in conventional electrolyzers. In this study, a membraneless electrolyzer was 3D printed and a Pt|porous electrode and planar Pt|Ti-foil were used as the cathode and anode, respectively. The electrodes are a key component since that is where the reactions of interest (hydrogen and oxygen evolution reactions) occur. Hence, the distribution of Pt onto a carbon foam substrate in a uniform and asymmetric pattern was studied. Kinetic overpotentials and mass transfer limitations decrease when Pt nanoparticles are in a uniform pattern since it increases active sites resulting in faster kinetics. However, asymmetric catalyst placement controls where gaseous bubbles are generated and therefore decreases product crossover. The device’s ability to generate acid and base at different applied current densities and volumetric flow rates was investigated whereby at high current densities and low volumetric flow rates, the pH differential of the effluent streams broadens. However, at this condition, product crossover increases. Future work involves using in situ high-speed videography to determine the critical Damköhler number to unravel the achievable maximum pH while minimizing product cross-over.

Application of a Sludge Blanket Reactor for Effluent Treatment: A Laboratory Study

Energy is required in all societies worldwide. This led to a dependency of fossil fuel. During uncertain times fossil fuel supply become highly politically and used as an influencing source. This requires establishing a more environmentally friendly processes to decrease dependency. To produce biogas from municipal, agricultural and industrial waste a laboratory benchtop up-flow sludge blanket reactor with a operating volume of 2850 ml was designed build, started up, and operated using prepared municipal wastewater and separated liquid cow manure at a hydraulic retention time of 1 day, 3 days and 6 days after an 120 h adjustment time prior to testing.&#x0D; While using wastewater as influent, the laboratory benchtop up-flow sludge blanket reactor system was not able to reduce the chemical oxygen demand content significantly. Especially at a high volumetric flow rate for the 1-day hydraulic retention time. The produced gas amount decreased from 0.59 ±0.07 (ml/h)/L at a hydraulic retention rate of 6 days to 0.042 ±0.04 (ml/h)/L. The fluctuating influent chemical oxygen demand of 25 ±1 mg/L to 74 ±15 mg/L resulted in a stable effluent concentration of 39 ml/L and 45 ±11 mg/L respectively.&#x0D; The laboratory benchtop up-flow sludge blanket reactor system with separated liquid cow manure showed a higher chemical oxygen demand degradation capability but resulted in higher chemical oxygen demand in the effluent. The influent chemical oxygen demand of 308 ±42 mg/L was broken downs to 59 ±1 mg/L at a hydraulic retention time of 6 days and to 114 ±5 mg/L for 1 day retention time. The biogas production result in a stable gas production rate of 0.27 ±0.02 (ml/h)/L through all three hydraulic retention times. For both the wastewater and separated liquid cow manure operation the biogas without carbon dioxide was between 55 and 65%.&#x0D; The results show that the laboratory benchtop up-flow sludge blanket reactor system can reduce high chemical oxygen demand in wastewater and separated liquid cow manure. However, a minimum feed level having a minimal chemical oxygen demand above 36 mg/L is needed, otherwise, the active bacterial mass contributes to the effluent level as seen for the influent level below 36 mg/L and 25 mg/L which resulted in a minimum effluent level of 39 mg/L for a hydraulic retention time of 3-days and 6-days.

Two phase (water/air) suction performance of turbopump inducer

Abstract In the present study, the gas-liquid two-phase flow performance of a turbopump with an inducer has been experimentally investigated. In the performance evaluation test, the air bubbles is released from dissolved air at the upstream valve to realize two-phase flow. By this method, a homogeneous bubbly flow is expected just after the valve. The amount of dissolved oxygen (DO) is an important parameter, and the experiment is carried out under the conditions of DO≅50%, 100%, 200%, where DO[%] indicates the relative amount of DO against the saturated value at the atmospheric condition. Under each DO condition, the experiment is performed at various water flow rates. As a result, a clear trend that the higher DO is, the worse the performance becomes, is observed. It is found that the mechanism for the head drop of the pump differs between at high and low flow rates. At the high flow rate, the performance does not deteriorate up to relatively high volumetric flow rate ratio of air and water. The cause of performance deterioration seems to be the increased number and/or size of bubbles released at the upstream valve. On the other hand, at the low flow rate, the performance deteriorates at relatively low air-water flow rate ratio. Although the air water volume flow ratio is low, the bubbles can precipitate in inlet flow recirculation and back flow vortices, which seems to cause the performance deterioration.

Confined Shear Alignment of Ultrathin Films of Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) are a naturally abundant nanomaterial derived from cellulose which exhibit many exciting mechanical, chemical, and rheological properties, making CNCs attractive for use in coatings. Furthermore, the alignment of CNCs is important to exploit their anisotropic mechanical and piezoelectric properties. Here, we demonstrate and study the fabrication of submonolayer to 25 nm thick films of CNCs via solution-based shear alignment. CNC solution is forced through a sub-millimeter tall channel at high volumetric flow rates generating shear. The half-width at half-maximum of the spread in CNC alignment significantly improves from 78 to 17° by increasing the shear rate from 19 to 19,000 s-1. We demonstrate that the film thickness is increased by increasing the volume of CNC solution flowed over the substrate and/or increasing the CNC solution concentration, with a degradation in film uniformity at higher (≥7 wt %) concentrations, likely due to CNC aggregates in the solution. Deposition of ultrathin aligned CNC films occurs within seconds and the technique is inherently scalable, demonstrating the promise of solution-based shear for the fabrication of ultrathin aligned CNC films, thereby enabling the future study of their inherent material properties or use in high-performance coatings and applications.

Study of the geometry of open channels in a layer-bed-type microfluidic immobilized enzyme reactor

This paper aims at studying open channel geometries in a layer-bed-type immobilized enzyme reactor with computer-aided simulations. The main properties of these reactors are their simple channel pattern, simple immobilization procedure, regenerability, and disposability; all these features make these devices one of the simplest yet efficient enzymatic microreactors. The high surface-to-volume ratio of the reactor was achieved using narrow (25–75 μm wide) channels. The simulation demonstrated that curves support the mixing of solutions in the channel even in strong laminar flow conditions; thus, it is worth including several curves in the channel system. In the three different designs of microreactor proposed, the lengths of the channels were identical, but in two reactors, the liquid flow was split to 8 or 32 parallel streams at the inlet of the reactor. Despite their overall higher volumetric flow rate, the split-flow structures are advantageous due to the increased contact time. Saliva samples were used to test the efficiencies of the digestions in the microreactors.Graphical abstract

Blood flow changes in the forearm arteries after ultrasound-guided costoclavicular brachial plexus blocks: a prospective observational study

BackgroundAn increase in blood flow in the forearm arteries has been reported after brachial plexus block (BPB). However, few studies have quantitatively analysed the blood flow of the forearm arteries after BPB or have studied only partial haemodynamic parameters. The purpose of the present study was to comprehensively assess blood flow changes in the distal radial artery (RA) and ulnar artery (UA) after BPB performed via a new costoclavicular space (CCS) approach using colour Doppler ultrasound.MethodsThirty patients who underwent amputated finger replantation and received ultrasound-guided costoclavicular BPB were included in the study. The haemodynamic parameters of the RA and UA were recorded before the block and 10 min, 20 min, and 30 min after the block using colour Doppler ultrasound to determine the peak systolic velocity (PSV), end-diastolic velocity (EDV), mean velocity (Vmean), pulsatility index (PI), resistance index (RI) and area. The volumetric flow rate (VFR) was calculated using the formula Q = area×Vmean. The aforementioned parameters were compared not only before and after the BPB but also between the RA and UA.ResultsCompared with those of the respective baselines, there was a significant increase in the PSV, EDV, Vmean, area, and VFR and a significant decrease in the PI and RI of the RA and UA 10 min, 20 min, and 30 min post-block. The increase 30 min post-block in EDV (258.68 % in the RA, 279.63 % in the UA) was the most notable, followed by that in the Vmean (183.36 % in the RA, 235.24 % in the UA), and the PSV (139.11 % in the RA, 153.15 % in the UA) changed minimally. The Vmean and VFR of the RA were significantly greater than those of the UA before the BPB; however, there was no significant difference in the VFR between the RA and UA after the BPB.ConclusionsA costoclavicular BPB can increase blood flow in the forearm arteries. The RA had a higher volumetric flow rate than the UA before the BPB; however, the potential blood supply capacity of the UA was similar to that of the RA after a BPB.Trial registrationThis study was registered at the Chinese Clinical Trial Registry (http://www.chictr.org.cn/searchproj.aspx, clinical trial number: ChiCTR 1900023796, date of registration: June 12, 2019)

Thermodynamic Assessment of Using Water as a Refrigerant in Cascade Refrigeration Systems With Other Environmentally Friendly Refrigerants

Abstract For current and future sustainability, refrigerants with high global warming potential (GWP) are being phased out and replaced with environmentally friendly refrigerants. To this end, research into the current and possible future low-GWP refrigerant alternatives in cascade refrigeration systems has caught much attention. In this paper, a mathematical model is developed to assess the optimum energetic, exergetic, and operational parameters of a cascade refrigeration system using water as a refrigerant in the upper cycle with R744, N2O, R41, R717, R290, and R1270 in the lower cycle for a cooling load of 10 TR (35.2 kW). Multiple studies have been conducted for evaporator temperatures between −25 and 5 °C. Results show that R41 and R717 as low- and intermediate-temperature refrigerants, respectively, are recommended for the bottom cycle. Furthermore, R717-water showed improved coefficient of performance (COP) compared to other top cycle refrigerants, with a COP improvement of 2.9% to 8.6%. This study demonstrates the thermal feasibility of using water as a refrigerant in low-temperature cascade systems. Using water as a refrigerant in the top cycle showed promising results in low-temperature applications without the risk of solidification. However, the drawbacks are the high volumetric flowrate and compressor discharge temperature, requiring high capacity water injected compressor.