Constant Volumetric Flow Rate Research Articles

Additive Manufacturing of Liquid-Cooled Ceramic Heat Sinks: An Experimental and Numerical Study

With recent advances in power electronic packaging technologies, liquid-cooled ceramic heat sinks have been considered as a promising solution for further improving the performance of power electronic devices. In this study, several aluminum oxide heat sinks were fabricated and tested using the digital light processing-based additive manufacturing method, to verify their practical performance. The results showed that the complex cooling structures inside the heat sinks can be completely formed and exhibited high surface quality. The experimental thermal and hydraulic performances of the heat sinks were consistent with the numerically modeled predictions. Furthermore, by exploiting the advantages of additive manufacturing, a direct manifold microchannel (MMC) configuration was designed to reduce the vertical flow of the traditional MMC configuration and achieve an improved cooling efficiency. At a constant volumetric flow rate of 1 L/min, the direct MMC configuration achieved a 19.8% reduction in pressure drop and an 11.8% reduction in thermal resistance, as well as a more uniform temperature distribution.

Strategies to improve the thermal performance of solar collectors

Abstract The paper evaluates a passive method for heat transfer improvement in heat exchangers, which implies the use of nanofluids. All calculations were carried out with a constant volumetric flow rate. The study examines three fluids with 0–4 % volume concentrations of CuO, MgO, and Al2O3 particles. The results indicate an increase in the heat transfer coefficient with increasing temperature. An Al2O3 nanofluid (4 % concentration) contributed to the best thermal performance. The incorporation of a 4 % content of MgO yielded an augmentation in heat transfer ranging from 15 % to 22 %, whereas an analogous concentration of CuO led to a more substantial enhancement of 25 %. Notably, the introduction of nanoparticles of Al2O3 produces a remarkable augmentation in heat transfer performance, with potential improvements of up to 36 %. The Nusselt number increases with increasing particle volume fraction and Reynolds number, according to results obtained for several nanoparticles (Al2O3, CuO, SiO2, and ZnO) with volume percentages in the range of 1–4 % and nanoparticle diameters of 25–70 nm. For all nanofluids, the time-averaged Nusselt number rises with a solid phase volume fraction increase of less than 5 %.

Strategies to improve the thermal performance of solar collectors

Abstract The paper evaluates a passive method for heat transfer improvement in heat exchangers, which implies the use of nanofluids. All calculations were carried out with a constant volumetric flow rate. The study examines three fluids with 0–4 % volume concentrations of CuO, MgO, and Al2O3 particles. The results indicate an increase in the heat transfer coefficient with increasing temperature. An Al2O3 nanofluid (4 % concentration) contributed to the best thermal performance. The incorporation of a 4 % content of MgO yielded an augmentation in heat transfer ranging from 15 % to 22 %, whereas an analogous concentration of CuO led to a more substantial enhancement of 25 %. Notably, the introduction of nanoparticles of Al2O3 produces a remarkable augmentation in heat transfer performance, with potential improvements of up to 36 %. The Nusselt number increases with increasing particle volume fraction and Reynolds number, according to results obtained for several nanoparticles (Al2O3, CuO, SiO2, and ZnO) with volume percentages in the range of 1–4 % and nanoparticle diameters of 25–70 nm. For all nanofluids, the time-averaged Nusselt number rises with a solid phase volume fraction increase of less than 5 %.

Development of an airfoil-based passive volumetric air sampling and flow control system for fixed-wing UAS

This study aims to develop a concept of a passive volumetric flow control system for gas sampling applications onboard fixed-wing UAS based on the pressure field around airfoils. The passive flow control system utilizes the aerodynamics of a UAS to create a vacuum pump effect that ensures constant gas sampling, which can be used to facilitate airborne aerosol and gas measurements. The pump effect is achieved by short-circuiting the pressure field’s minima and maxima points around an airfoil through pipes and 3D printed structures that could function both as a pump system and a gas measurement chamber. The design of this structurally integrated functionality brings many advantages for scientific applications, especially onboard small research UAS, which would dispense entirely with complex active pump systems, thus reducing weight and ensuring gas sampling at a constant volumetric flow rate independent of altitude and atmospheric variance. In favor of developing further applications, this paper outlines the development steps of the passive pump concept starting from the theory and numerical modeling of the effect to the implementation on board a fixed-wing UAS. Finally, possible improvements based on numerical models and flight measurements are discussed.

4E Transient Analysis of a Solar-Hybrid Gas-Turbine Cycle Equipped with Heliostat and MED

The current study investigates a cogeneration cycle of power and freshwater integrated with a solar system. The solar system is of the heliostat type, which is considered to preheat the inlet air in the combustion chamber of a 25-MW gas turbine. The waste heat of the turbine output stream is used to produce freshwater. Parameters such as the ambient temperature and solar irradiance significantly affect the system’s performance; hence, all analyses, including those pertaining to energy, exergy, economics, and environment, were conducted transiently, with a one-hour time step throughout the year so that the impacts of these effective parameters could be examined. Besides the analysis assuming a constant mass flow rate for the air entering the compressor, the calculations were repeated with the assumption of a constant volumetric flow rate to evaluate the cycle in the same conditions as those of natural gas power plants. Given the constant volumetric flow rate, for every 10-degree increase in temperature, the compressor power consumption decreased by approximately 2%. Moreover, a sensitivity analysis of the cycle performance in terms of ambient temperature was performed, and the corresponding results are presented. Finally, some correlations are presented to estimate variations in compressor power consumption and net turbine power due to temperature variations. The results demonstrate that in Bushehr, Iran, every one-degree increase in ambient temperature leads to an approximately 0.67 percentage decrease in net-generated power. In the end, the performance of the cycle was investigated under climatic conditions and solar irradiation intensities in several cities in Iran and some cities in different countries in which heliostat power plants have already been established. The results obtained in these cities were compared; it was concluded that the lowest annual cost of electricity generation is related to Isfahan in Iran, which reduces the cost of electricity generation by more than 20% (2.32 Cents/kWh) compared to the base cycle.

Hydrogen production via supercritical water gasification of glycerol enhanced by simple structured catalysts

The supercritical water gasification (ScWG) technology is a promising alternative for H2-rich gas production from renewable sources, such as residual glycerol from biodiesel manufacture. Combined with heterogeneous catalysts, the ScWG process can achieve improved selectivity towards the desired products and high conversion efficiency in short reaction times. In this work, the efficiency of a synthesized Ni-based catalyst supported in cordierite (CRD) honeycomb structure on the ScWG of glycerol was evaluated and compared with two commercial automotive catalysts. Initially, to determine the best experimental conditions, the ScWG experiments were conducted in the absence of catalysts at constant conditions pressure (25 Mpa) and volumetric flow rate (10 mL min−1). The temperature range of 400–700 °C and glycerol feed composition between 10 and 34 wt% were evaluated. The catalysts evaluated were characterized by SEM-EDS, XRD, N2 adsorption/desorption, XRF, WDS and TGA. The liquid and gaseous products were analyzed by TOC and gas chromatography, respectively. Results indicated that Ni/CRD catalyst showed the highest H2 yield (5.38 mol H2 per mol of glycerol fed) and long-term stability. Additionally, a comparison between the experimental results on the ScWG of glycerol and simulated thermodynamic equilibrium data was also reported. Thus, results demonstrated the great potential of the prepared catalyst to improve H2-rich gas production from glycerol gasification.

Invasion of a porous domain by a fluid network, a constructal perspective

This paper presents a methodology to predict the growth of fluid networks within a porous domain. Tree-shaped networks are generated for minimum volume and constant volumetric flow rate, maximum flow rate at constant volume and minimum walls-fluid contact surface at constant volumetric flow rate. The constructal methodology relies on the development of an algorithm inspired by the Constrained Constructive Optimization technique combined to the Hess-Murray's law. It is shown that the fluid network reconfigures itself entirely while growing, but its average bifurcation angle remains constant regardless the number of outlets connected. Furthermore, our results show that the fluid networks tend to invade the entire space regardless the shape of the domain.

A parametric assessing and intelligent forecasting of the energy and exergy performances of a dish concentrating photovoltaic/thermal collector considering six different nanofluids and applying two meticulous soft computing paradigms

In the present study, the application of six engine oil-based Nano fluids (NFs) in a solar concentrating photovoltaic thermal (CPVT) collector is investigated. The calculations were performed for different values of nanoparticle volume concentration, receiver tube diameter, concentrator surface area, receiver length, receiver actual to the maximum number of channels ratio, beam radiation, and a constant volumetric flow rate. Besides, two novel soft computing paradigms namely, the cascaded forward neural network (CFNN) and Multi-gene genetic programming (MGGP) were adopted to predict the first law efficiency (ηI) and second law efficiency (ηII) of the system based on the influential parameters, as the input features. It was found that the increase of nanoparticle concentration leads to an increase in ηI and a decrease in ηII. Moreover, the rise of both the concentrator surface area (from 5 m2 to 20 m2) and beam irradiance (from 150 W/m2 to 1000 W/m2) entails an increase in both the ηI (by 39% and 261%) and ηII (by 55% and 438%). Furthermore, it was reported that the pattern of changes in both ηI and ηII with serpentine tube diameter, receiver plate length, and absorber tube length is increasing-decreasing. The results of modeling demonstrated that the CFNN had superior performance than the MGGP model.

The CFD Modeling of Multiphase Flow in an SKS Furnace: The Effect of Tuyere Diameter and Bath Depth

CFD simulation using a multi-fluid VOF model on scaled-down SKS furnace multiphase flow was conducted, targeting the agitation performance under conditions of different tuyere diameters and bath depths, at a constant total gas volumetric flow rate. The results indicate that an increased bath depth contributes to the lateral movements of the matte and air phased, significantly promoting the agitation at the far side of the plumes. The characteristic of a deep bath allows larger tuyere diameters operated at a lower gas injection speed, to achieve comparatively smaller low velocity regions and dead zones. In addition, the wall shear stress was found to correlate with the distribution of low-velocity regions. Since the selections of tuyere diameter and bath depth are of major importance in the optimizing of flow fields, the results from this simulation offer good references for the future operation and design of SKS furnaces and other similar industrial vessels.

CFD Modeling of Multiphase Flow in an SKS Furnace with New Tuyere Arrangements

There has been a great deal of focus on the optimization of tuyere arrangements in SKS bottom blown copper smelting furnaces since the last decade, as the improved furnace operation efficiency of SKS technology has potential that cannot be ignored. New –x + 0 + x deg tuyere arrangements with 14 tuyeres are proposed in this research paper. Using a previously verified numerical model, CFD tests on the velocity distribution and wall shear stress for scaled-down SKS furnace models were conducted, with a constant total volumetric gas flow rate, and different operating parameters and furnace cross-section geometries. The results indicate that, at a relatively low gas injection speed compared with the previously optimized tuyere arrangement, although the –x +0 +x deg tuyere arrangements are unable to supply enhanced agitation in the typical round furnaces, they achieve better performance in elliptical furnaces. At a comparatively higher gas injection speed, the – x + 0 + x deg tuyere arrangements can improve the agitation performance in a round furnace while maintaining an acceptable wall shear stress on the bottom and side wall. The agitation enhancement with the − x +0 +x deg tuyere arrangements can essentially be attributed to stronger interactions between bubble plumes and furnace side walls. To further exploit the advantages of the new tuyere arrangements, an optimized tuyere angle was confirmed by a full-scale furnace model simulation.

Heat and Mass Transfer in an Adsorbed Natural Gas Storage System Filled with Monolithic Carbon Adsorbent during Circulating Gas Charging.

Adsorbed natural gas (ANG) technology is a promising alternative to traditional compressed (CNG) and liquefied (LNG) natural gas systems. Nevertheless, the energy efficiency and storage capacity of an ANG system strongly depends on the thermal management of its inner volume because of significant heat effects occurring during adsorption/desorption processes. In the present work, a prototype of a circulating charging system for an ANG storage tank filled with a monolithic nanoporous carbon adsorbent was studied experimentally under isobaric conditions (0.5–3.5 MPa) at a constant volumetric flow rate (8–18 m3/h) or flow mode (Reynolds number at the adsorber inlet from 100,000 to 220,000). The study of the thermal state of the monolithic adsorbent layer and internal heat exchange processes during the circulating charging of an adsorbed natural gas storage system was carried out. The correlation between the gas flow mode, the dynamic gas flow temperature, and the heat transfer coefficient between the gas and adsorbent was determined. A one-dimensional mathematical model of the circulating low-temperature charging process was developed, the results of which correspond to the experimental measurements.

Experimental Analysis of a Heat Pump Dryer with an External Desiccant Wheel Dryer

This study examines the performance of three heat pump dryers: the original reference design, a modified drying chamber, and an external desiccant wheel design. Unlike most existing studies that normally adopt organic products as the drying materials, in this study we used moist sodium polyacrylate (Orbeez) as the drying material for consistent characterization of the heat pump performance. R-134a was adopted as the refrigerant for the heat pump system. The experiments were performed subject to different weights of Orbeez (drying material) at a constant volumetric flow rate of 100 m3/h. During experimentation, different parameters like the coefficient of performance (COPHP), drying rate, heat transfer rate by the condenser, moisture extraction rate, and specific moisture extraction rate were calculated. The average COPHP, mass transfer rate, heat transfer rate, MER, and SMER of the system were calculated as 3.9, 0.30 kg/s, 0.56 kW, 0.495 kg/h, and 1.614 kg/kWh, respectively. The maximum COP for the refrigeration system was achieved at lower test loads with the desiccant wheel. The moisture extraction rate for a lower test loading was higher than that for a higher test load due to the higher penetration of drying air at the lower test load, although the maximum test load showed the maximum relative humidity at the dryer outlet. The desiccant wheel showed good performance in terms of moisture extraction rate and COPHP, but it showed poor performance in terms of the specific moisture extraction rate due to the high power consumption (around 2.6 kW) of the desiccant dehumidifier. The moisture extraction rate (MER) for all designs increased to a maximum value, followed by consistent decline. However, the maximum MER for the desiccant design exceeded those for the other designs.

Effects of local coronary blood flow dynamics on the predictions of a model of in-stent restenosis

Computational models are increasingly used to study cardiovascular disease. However, models of coronary vessel remodelling usually make some strong assumptions about the effects of a local narrowing on the flow through the narrowed vessel. Here, we test the effects of local flow dynamics on the predictions of an in-stent restenosis (ISR) model. A previously developed 2D model of ISR is coupled to a 1D model of coronary blood flow. Then, two different assumptions are tested. The first assumption is that the vasculature is always able to adapt, and the volumetric flow rate through the narrowed vessel is kept constant. The second, alternative, assumption is that the vasculature does not adapt at all, and the ratio of the pressure drop to the flow rate (hydrodynamic resistance) stays the same throughout the whole process for all vessels unaffected by the stenosis, and aortic or venous blood pressure does not change either. Then, the dynamics are compared for different locations in coronary tree for two different reendothelization scenarios. The assumptions of constant volumetric flow rate (absolute vascular adaptation) versus constant aortic pressure drop and no adaptation do not significantly affect the growth dynamics for most locations in the coronary tree, and the differences can only be observed at the locations where a strong alternative flow pathway is present. On the other hand, the difference between locations is significant, which is consistent with small vessel size being a risk factor for restenosis. These results suggest that the assumption of a constant flow is a good approximation for ISR models dealing with the typical progression of ISR in the most often stented locations such as the proximal parts of left anterior descending (LAD) and left circumflex (LCX) arteries.

Inertial-based Fluidic Platform for Rapid Isolation of Blood-borne Pathogens.

Bacterial sepsis is a life-threatening disease and a significant clinical problem caused by host responses to a microbial infection. Sepsis is a leading cause of death worldwide and, importantly, a significant cause of morbidity and mortality in combat settings, placing a considerable burden on military personnel and military health budgets. The current method of treating sepsis is restricted to pathogen identification, which can be prolonged, and antibiotic administration, which is, initially, often suboptimal. The clinical trials that have been performed to evaluate bacterial separation as a sepsis therapy have been unsuccessful, and new approaches are needed to address this unmet clinical need. An inertial-based, scalable spiral microfluidic device has been created to overcome these previous deficiencies through successful separation of infection-causing pathogens from the bloodstream, serving as a proof of principle for future adaptations. Fluorescent imaging of fluorescent microspheres mimicking the sizes of bacteria cells and blood cells as well as fluorescently stained Acinetobacter baumannii were used to visualize flow within the spiral. The particles were imaged when flowing at a constant volumetric rate of 0.2 mL min-1 through the device. The same device was functionalized with colistin and exposed to flowing A. baumannii at 0.2 mL h-1. Fluorescent imaging within the channel under a constant volumetric flow rate demonstrated that smaller, bacteria-sized microspheres accumulated along the inner wall of the channel, whereas larger blood cell-sized microspheres accumulated within the center of the channel. Additionally, fluorescently stained A. baumannii displayed accumulation along the channel walls in agreement with calculated performance. Nearly 106 colony-forming units of A. baumannii were extracted with 100% capture efficiency from flowing phosphate-buffered saline at 0.2 mL h-1 in this device; this is at least one order of magnitude more bacteria than present in the blood of a human at the onset of sepsis. This type of bacterial separation device potentially provides an ideal approach for treating soldiers in combat settings. It eliminates the need for immediate pathogen identification and determination of antimicrobial susceptibility, making it suitable for rapid use within low-resource environments. The overall simplicity and durability of this design also supports its broad translational potential to improve military mortality rates and overall patient outcomes.

Experimental investigation of a cavitating Venturi and its application to flow metering

An experimental investigation has been carried out to evaluate the performance of a cavitating Venturi flow. For that purpose, a closed loop circuit with a centrifugal pump and a transparent asymmetric converging-diverging test section has been built which allows to set the pressure level and the flow rate. The system is instrumented with several pressure sensors and temperature probes that are continuously monitored during the tests. The experiments have consisted in generating non-cavitating and cavitating flows inside the Venturi under controlled conditions. The obtained results, which have been characterized as a function of the Venturi's discharge coefficient, pressure ratio and pressure loss coefficient, are in good agreement with previous studies carried out with standard Venturi geometries, specially under non-cavitating flows. The Venturi's performance under cavitation flows has been found to be dependent on the Venturi's inlet pressure and similar to a chocked flow condition with constant volumetric flow rate. On the basis of these observations and the analogous behaviour with compressible gas nozzles, a new flow coefficient has been derived which remains constant at any cavitating regime. Thus, this coefficient permits to use a Venturi as a flow meter on cavitation conditions.

Turbulent Bubble-Laden Channel Flow of Power-Law Fluids: A Direct Numerical Simulation Study

The influence of non-Newtonian fluid behavior on the flow statistics of turbulent bubble-laden downflow in a vertical channel is investigated. A Direct Numerical Simulation (DNS) study is conducted for power-law fluids with power-law indexes of 0.7 (shear-thinning), 1 (Newtonian) and 1.3 (shear-thickening) in the liquid phase at a gas volume fraction of 6%. The flow is driven downward by a constant volumetric flow rate corresponding to a friction Reynolds number of Reτ≈127.3. The Eötvös number is varied between Eo=0.3125 and Eo=3.75 in order to investigate the influence of quasi-spherical as well as wobbling bubbles and thus the interplay of the bubble deformability with the power-law behavior of the liquid bulk. The resulting first- and second-order fluid statistics, i.e., the gas fraction, mean velocity and velocity fluctuation profiles across the channel, show clear trends in reply to varying power-law indexes. In addition, it was observed that the bubble oscillations increase with decreasing power-law index. In the channel core, the bubbles significantly increase the dissipation rate, which, in contrast to its behavior at the wall, shows similar orders of magnitude for all power-law indexes.

Experimental and simulation study of forced convection in vertical eccentric annular space

In the petroleum production process, the tubing-casing annulus has been eccentric due to influence of gravity and thermal expansion, which complicates heat exchange. Forced convection heat transfer in vertical annulus with difference water-air ratios, eccentricities and radius ratios, has been experimentally studied with constant volumetric flow rate and temperature of hot fluid. The radius ratio that make Nu increase abruptly under operating conditions in this study is investigated numerically. The governing equations describing the heat transfer and flow are discretized using the Finite Element Method. Results indicate that the relation between Nu and radius ratio is non-linear. The radius ratios causing Nu to increase abruptly are 0.36 and 0.21 respectively. The coefficient of convection heat transfer increases as the radius ratios increase. For the eccentricity of 0.2, the decrease of water-air ratios enhances the heat transfer of eccentric annular space. For the eccentricity of 0.5 and 0.8, the heat transport first strengthens and then weakens with the decrease of water-air ratios. The effect of eccentricities on the Nu is affected by radius ratios and Re in the meantime. The empirical correlation is derived for the Nusselt number as a function of the Reynolds number, eccentricity and Prandtl number.

Modified Convergent Flow Tracing Method for Evaluating Advective Velocity and Effective Porosity in Fractured Rock Aquifers

This study presented the analysis of the modified convergent flow tracing method, which is a modified virtual solute transport approach to retrieve tracer masses from a pulse image (virtual) well to an extraction well. In the convergent flow tracer test, approximate analytical solutions were extended for the pulse image well using a single-well tracing method. This method transformed the drift-and-pumpback conditions of the single-well tracing method. The method requires a prior information of the effective porosity. Using sodium chloride as a tracer mass, the tracer data sampled through field-scale tests were used to obtain breakthrough curves. This modified method was different from the pre-existing single method because it considers both the ambient groundwater movement (the two classes of drifts) and the constant volumetric flow rate during the pumping phase. The method was applied to the tracer test at underground research tunnel for verifying the theory inductively derived from the single tracing method. Through field tests, the values of velocity and porosity were compared to the results of the drift-and-pumpback equations of the single-well test, and the several different equations related to breakthrough curves of the two-well tests conducted on a field scale.

Experimental and Numerical Investigation of Gas-Focused Liquid Micro-Jet Velocity

Compressible multiphase numerical simulations of gas-focused micro-jets are compared with the experimental data obtained with the dual pulse imaging laser-induced fluorescence drop velocimetry. Such jets, originating from a 3D printed gas dynamic virtual nozzle into a low-vacuum (150 Pa) environment, are increasingly being used for sample delivery in serial femtosecond crystallography. The distance traveled by a detaching drop from the jet is measured between the two consecutive illumination pulses with a known time delay at the positions 200 µm and 450 µm from the nozzle. Additionally, the high-speed camera images are used to analyze the shape of the jet. An axisymmetric, compressible, Newtonian two-phase helium-water mixture model is numerically solved within the framework of the volume of fluid and the finite volume method. The experimental and the computational studies are performed with a constant volumetric liquid flow rate of 14 μl/min and the gas mass flow rate in the range from 4.6 mg/min to 20 mg/min. The related jet Reynolds number ranges from 120 to 220 and Weber number from 30 to 150. The maximum difference between the measurements and the results of the numerical model in terms of the droplet velocity and jet diameter is within 10 %. The study provides new information on the jet velocities for micron-sized gas-focused nozzles. The validated numerical model can be used as a design tool for the nozzles dedicated to the specific needs of the femtosecond crystallography experiments.

Microfluidic solvent extraction of Cd(II) in parallel flow pattern: Optimization, ion exchange, and mass transfer study

Micro solvent extraction of cadmium ion from nitrate solution with a cationic extractant (MDEHPA) was performed in parallel flow pattern utilizing Y-Y microchannels. At first, the effects of the operating parameters on the extraction efficiency were studied. The optimum condition was determined using response surface methodology based on the central composite design (extractant concentration 6% (v/v), feed phase pH 6.3 and residence time 20 s). Additionally, for the first time, a correlation for the estimation of the aqueous phase Sherwood number in liquid–liquid parallel flow in the microchannels was developed. In this correlation, the aqueous phase Sherwood number was defined as a function of the aqueous phase Reynolds and Schmidt numbers. This model was able to predict the aqueous phase Sherwood number precisely with an average error of 9.91%. The influence of microchannel dimensions on the extraction efficiency was also examined. The increase in the channel length and the decrease in the channel width enhanced the extraction efficiency. Using the microchannel with optimal dimensions, the extraction percentage was obtained 99.3% at residence time 8 s. Moreover, the overall volumetric mass transfer coefficient (KLa) decreased with increasing residence time, channel width, and also channel length at a constant volumetric flow rate but increased with raising the channel length at an equal residence time. The KLa of the microfluidic system was much higher than the batch extractor.