Fraction Of Air Research Articles

Energy Conservation Potential of Economizer Controls Using Optimal Outdoor Air Fraction Based on Field Study

In commercial buildings, HVAC systems are becoming a primary driver of energy consumption, which already account for 45% of the total building energy consumption. In the previous literature, researchers have studied several energy conservation measures to reduce HVAC system energy consumption. One of the effective ways is an economizer in air-handling units. Therefore, this study quantified the impact of the outdoor air fraction by economizer control type in cooling system loads based on actual air-handling unit operation data in a hospital. The optimal outdoor air fraction and energy performance for economizer control types were calculated and analyzed. The result showed that economizer controls using optimal outdoor air fraction were up to 45% more efficient in cooling loads than existing HVAC operations in the hospital. The energy savings potential was 6–14% of the differential dry-bulb temperature control, 17–27% of the differential enthalpy control, 8–17% of the differential dry-bulb temperature and high-limit differential enthalpy control, and 16–27% of the differential enthalpy and high-limit differential dry-bulb temperature control compared to the no economizer control. The result of this study will contribute to providing a better understanding of economizer controls in the hospital when the building operates in hot-humid climate regions.

Fundamental study on chaotic transition of two-phase flow regime and free surface instability in gas deaeration process

Deaeration is a process of eliminating aspirated air from liquid in hydraulic reservoirs to avoid cavitation in the downstream pump blades. The complex fluid dynamics associated with deaeration is investigated. The three-dimensional buoyancy driven chaotic behavior of gas-liquid interfacial two-phase flow is studied. Parametric study is executed to understand change in internal flow physics (bubble coalescence, disintegration, horizontal spread, bubble velocity etc.), strength of accelerating Rayleigh-Taylor instability, turbulent kinetic energy, amplitude of upward velocity near free surface, and rise in free surface level with the variation of parameters like incoming mixture flow rate, incoming volume fraction of air, liquid fill depth, and Atwood number. The computations show increment in cavitation, wavenumber and amplitude of upward velocity towards oscillating free surface with incoming flow rate (Re). Cavitation and free surface instability show incremental trend with volume fraction of incoming air forming a kink (cavitation reduces) due to bubble coalescence in a threshold range of volume fraction of incoming air. With the variation of Atwood number, initially cavitation reduces. But after a critical value (A*) of Atwood number, effect of bubble disintegration, and rise of cavitation become prominent, which is formulated with respect to incoming flow rate (Re). With liquid fill depth, cavitation shows a slight decrement with almost equal deaeration and constant wavelength of free surface oscillation at an increasing buoyancy driven upward velocity. Some glimpse of design solution to reduce the cavitation and enhance the deaeration is also studied and formulated to get better understanding.

Production of algal oil from power plant algae

ABSTRACT Algae growing in the thermal power plant environment are considered as waste for the power industry. But the algal biomass could act as efficient CO2-bio-sequester as they are adapted to grow under high CO2 concentration and the algal oil extracted from those algae is a cheap source of bio-diesel or green energy, thus mitigating the environmental pollution and conversion of ‘waste-to-wealth’. The present study aims at the production of bio-oil from a macro-alga, Pithophora varia collected and identified from water bodies of a thermal-power-plant in India. The oil productivity of the alga can be correlated with the biomass growth. The alga was cultivated in Erlenmeyer-flasks with external CO2 supplementation of 0.15 mole fraction in air. The light intensity 10,897 lux was incident on the flask’s wall when placed under sunlight for 8 h. Simultaneously, oil yield of 18.7% has been measured before subjecting the alga to the growth and starvation phase. An increase in oil-yield was measured on day 9 for both growth (26.2%) and starvation phases (29.3%). During growth phase, initiation of conversion of reserve food materials to lipid granules advocates for the oil yield. But the increment in lipid productivity during the starvation phase might have resulted due to nutrient deficiency and initiation of the stimulation of lipid-synthetic pathways towards the formation of triacylglceride.

Oxygen Transport Parameter in Plasma Membrane of Eye Lens Fiber Cells by Saturation Recovery EPR.

A probability distribution of rate constants contained within an exponential-like saturation recovery (SR) electron paramagnetic resonance signal can be constructed using stretched exponential function fitting parameters. Previously (Stein et al. Appl. Magn. Reson. 2019.), application of this method was limited to the case where only one relaxation process, namely spin-lattice relaxations due to the rotational diffusion of the spin labels in the intact eye-lens membranes, contributed to an exponential-like SR signal. These conditions were achieved for thoroughly deoxygenated samples. Here, the case is described where the second relaxation process, namely Heisenberg exchange between the spin label and molecular oxygen that occurs during bimolecular collisions, contributes to the decay of SR signals. We have further developed the theory for application of stretched exponential function to analyze SR signals involving these two processes. This new approach allows separation of stretched exponential parameters, namely characteristic stretched rates and heterogeneity parameters for both processes. Knowing these parameters allowed us to separately construct the probability distributions of spin-lattice relaxation rates determined by the rotational diffusion of spin labels and the distribution of relaxations induced strictly by collisions with molecular oxygen. The later distribution is determined by the distribution of oxygen diffusion concentration products within the membrane, which forms a sensitive new way to describe membrane fluidity and heterogeneity. This method was validated in silico and by fitting SR signals from spin-labeled intact nuclear fiber cell plasma membranes extracted from porcine eye lenses equilibrated with different fractions of air.

Study on the Oxygen Enrichment Effect of Individual Oxygen-Supply Device in a Tunnel of Plateau Mine.

Complex characteristics of the plateau environment such as low oxygen content seriously restrict the exploitation of abundant mineral resources in plateau areas. To regulate the hypoxia environment and improve the comfort of workers engaged in intense physical labor like tunnel excavation operations in plateau mines, an individual oxygen-supply device for tunnel of plateau mine was proposed to create local oxygen enrichment in the area around the human nose. The Computational Fluid Dynamics (CFD) method was used to judge the application’s effect of the individual oxygen-supply device in plateau mine, revealing the oxygen diffusion law under the influence of different oxygen enrichment factors. The orthogonal design and range analysis were used to measure the degree of influence of major factors such as oxygen-supply velocity, oxygen-supply concentration, and tunnel airflow velocity. The results demonstrate that the oxygen mass fraction of the air inhaled by the human had a positive correlation exponential function, a positive correlation linear function, and a negative correlation exponential function, respectively, concerning oxygen-supply velocity, oxygen-supply concentration, and tunnel airflow velocity. The range analysis revealed that the major influencing factors of oxygen enrichment in the tunnel of the plateau mine were, in a descending sequence, as follows: oxygen-supply concentration, tunnel airflow velocity, and oxygen-supply velocity, and the corresponding ranges were 2.86, 2.63, and 1.83, respectively. The individual oxygen-supply device achieved the best oxygen enrichment effect when the oxygen-supply velocity was 5 m/s, the oxygen-supply concentration was 60%, and the tunnel airflow velocity was 0.2 m/s, which increased the oxygen mass fraction of air inhaled by the human to 30.42%. This study has a positive guiding significance for the improvement of the respiration environment in the tunnel of plateau mine.

Performance Simulation and Analysis of Occupancy-Based Control for Office Buildings with Variable-Air-Volume Systems

Variable-air-volume (VAV) systems are used in many office buildings. The minimum airflow rate setting of VAV terminal boxes has a significant impact on both energy consumption and indoor air quality. Conventional controls usually have the terminal’s minimum airflow rate at a constant (e.g., 30% or more of the terminal design airflow rate), irrespective of the occupancy status, which may cause problems, such as excessive simultaneous heating and cooling, under ventilation, and thermal comfort issues. This paper examines the potential of energy savings from occupancy-based controls (OBCs). The sensed occupancy information, either occupant presence or people count, is used to determine the airflow rate of terminal boxes, the thermostat setpoints, and the lighting control. Using EnergyPlus, a whole-building energy modeling software, the energy savings of OBC strategies are evaluated for representative existing medium office buildings in the U.S. The simulation results show that the conventional OBC, based on occupant presence sensing, can save 8% of whole-building energy use in Miami (hot climate) for systems without air-side economizer and about 13% in both Baltimore (mixed climate) and Chicago (cold climate). Comparatively, the advanced OBC, based on people counting, can save 8% in Miami to 23% in Baltimore for systems with economizers. The outdoor-air fraction of the supply air from air-handling units significantly affects the potential energy savings from the advanced OBC strategy. In addition to energy savings, the advanced OBC satisfies the zone ventilation during all occupied hours over the whole year.

Development of Inverse Greybox Model-Based Virtual Meters for Air Handling Units

Energy submetering at the equipment level provides a tool to identify energy use anomalies and detect operational inefficiencies. While physical meters can be costly and difficult to install, virtual meters (VMs) overcome practical issues associated with physical meters and provide insights into critical unmeasured quantities. This article introduces an inverse greybox model-based virtual metering method to estimate the energy in an air handling unit (AHU). Models that represent the components typically found in AHUs are formulated using a data set from a highly instrumented AHU and combined into an integrated greybox model. The use of the integrated model to create VMs is demonstrated by using a data set from an independent AHU located in a large office building in Ottawa, ON, Canada. Model parameters are estimated by using the genetic algorithm and used in creating VMs that can estimate the heat supplied/extracted at the AHU level. In addition, the model is used to estimate a monthly average outdoor air fraction used by the AHU. The potential of the component models and VMs to detect operational inefficiencies and support operational decisions is demonstrated through illustrative examples. Note to Practitioners-This article presents a novel virtual metering algorithm to estimate the heating and cooling energy at the air handling unit (AHU) level. This virtual metering algorithm fills a gap in the literature and provides a tool that will help detect and interpret energy use anomalies, identify operational inefficiencies, and guide on-going commissioning of building energy systems. Facility managers, operators, and other stakeholders can use the insights gained from virtual metering to improve building operational performance. Future planned research includes developing virtual meters to characterize energy flows at the zone level and visualization methods to make inverse modeling results more accessible to different building stakeholders.

A New Background Method for Greenhouse Gases Flux Calculation Based in Back-Trajectories Over the Amazon

The large amount of carbon stored in trees and soils of the Amazon rain forest is under pressure from land use as well as climate change. Therefore, various efforts to monitor greenhouse gas exchange between the Amazon forest and the atmosphere are now ongoing, including regular vertical profile (surface to 4.5 km) greenhouse gas measurements across the Amazon. These profile measurements can be used to calculate fluxes to and from the rain forest to the atmosphere at large spatial scales by considering the enhancement or depletion relative to the mole fraction of air entering the Amazon basin from the Atlantic, providing an important diagnostic of the state, changes and sensitivities of the forests. Previous studies have estimated greenhouse gas mole fractions of incoming air (‘background’) as a weighted mean of mole fractions measured at two background sites, Barbados (Northern Hemisphere) and Ascension (Southern hemisphere) in the Tropical Atlantic, where the weights were based on sulphur hexafluoride (SF6) measured locally (in the Amazon vertical profiles) and at the two background sites. However, this method requires the accuracy and precision of SF6 measurements to be significantly better than 0.1 parts per trillion (picomole mole−1), which is near the limit for the best SF6 measurements and assumes that there are no SF6 sources in the Amazon basin. We therefore present here an alternative method. Instead of using SF6, we use the geographical position of each air-mass back-trajectory when it intersects the limit connecting these two sites to estimate contributions from Barbados versus Ascension. We furthermore extend the approach to include an observation site further south, Cape Point, South Africa. We evaluate our method using CO2 vertical profile measurements at a coastal site in Brazil comparing with values obtained using this method where we find a high correlation (r2 = 0.77). Similarly, we obtain good agreement for CO2 background when comparing our results with those based on SF6, for the period 2010–2011 when the SF6 measurements had excellent precision and accuracy. We also found high correspondence between the methods for background values of CO, N2O and CH4. Finally, flux estimates based on our new method agree well with the CO2 flux estimates for 2010 and 2011 estimated using the SF6-based method. Together, our findings suggest that our trajectory-based method is a robust new way to derive background air concentrations for the purpose of greenhouse gas flux estimation using vertical profile data.

Hierarchical Graphene/Metal-Organic Framework Composites with Tailored Wettability for Separation of Immiscible Liquids.

Membrane filtration is a promising technology for the separation of organic immiscible liquids. Surface topography has a direct impact on the wettability of membranes, and it remains largely unexplored. Here, we introduce on-demand liquid separation by coating porous graphene/metal-organic framework (MOF) composites with tunable wettability on porous substrates. Our results have shown that polydopamine (PDA) coating mediates the controlled growth of MOF nanostructures and subsequent fluorination on the porous graphene framework. Surface topography of the graphene frameworks strongly depends on the loading content of MOF nanostructures. The concurrent control of surface coverage of MOF and surface chemistry allows tailoring of the trapped air fraction underneath the porous graphene frameworks in the range of 0.97 to 0.8. As a result, the surface energy of the graphene/MOF coatings can be programmed to afford the change in surface properties from superamphiphobicity to lyophobicity and the selective penetration of low-surface-energy (SE) liquids and the interception of high-SE liquids were achieved. The tailored wettability of graphene/MOF coatings allows for the separation of liquid mixtures of different ranges of SE, making it a general strategy for complex liquid treatment and chemical purification.

Local multiphase flow characteristics of a severe-service control valve

For safety-critical industrial applications, severe-service valves are often used, and the conditions during operations can be either single phase or multiphase. The design requirements for valves handling multiphase flows can be very different to the single-phase flow and depend on the flow regime within valves. The variation in flow conditions during the operation of such valves can have a significant effect on performance, particularly in oil and gas applications where multiphase behaviour can rapidly change within the valve causing unwanted flow conditions. Current practices in designing and sizing such valves are based solely on global phase properties such as pressure drop of the bulk fluid across the valve and overall phase ratio. These do not take into account local flow conditions, as with multiphase fluids, the flow behaviour across the valve becomes more complex. In this work, a well-validated computational fluid dynamics (CFD) model is used to locally and globally quantify the performance characteristics of a severe service valve handling multiphase gas and liquid flow. Such flows are frequently encountered in process equipment found in vital energy industries e.g. process and oil & gas. The CFD model was globally validated with benchmark experiments. Two valve opening positions of 60% and 100% were considered each with 5, 10, and 15% inlet air volume fractions to simulate real life conditions. The results show that while the non-uniformity in pressure field is along expected lines, there is severe non-uniformity in the local air, water and void fraction distributions within the valve trim. To quantify the phase non-uniformities observed, an equation for the distribution parameter was defined and used to calculate its value in each localised quarter within the trim. Phase velocity and void fraction data extracted from the CFD results were also used to obtain relationships for the local void fraction distribution and flow coefficient. The detailed investigation that has been carried out allows for local flow characteristics to be determined and embedded in sizing methodology for severe-service control valve systems with multiphase gas and liquid flow.

Pressure Drop and Void Fraction in Horizontal Air–Water Stratified Flows with Smooth Interface at Atmospheric Pressure

This work presents and analyses the results of an experimental activity aimed at the characterization of stratified air–water flow conditions, which have been poorly analyzed in previous studies although they are significant for industrial applications. Tests were performed in a 24 m long, 60 mm inner diameter PMMA pipe; the superficial velocities ranged between 0.03 m/s and 0.06 m/s for the water and between 0.41 m/s and 2.31 m/s for air. The pressure gradient along the pipeline was determined and compared to the one obtained implementing two-fluid models available in the literature. Fair agreement with the models was found only at high values of the superficial gas velocities, i.e., above 1.31 m/s. Moreover, the void fraction was measured through a resistive probe and compared with the values predicted by available models. Since none of them was able to satisfactorily predict the void fraction in the whole range of superficial velocities, a drift flux model was successfully implemented. Eventually, with both the measured pressure gradient and the void fraction, a two-fluid model was implemented in order to determine the interfacial shear stress and to compare the outcome with the literature, emphasizing the influence of the operating conditions on the prediction performance.

A CFD Investigation of a 2D Balanced Vane Pump Focusing on Leakage Flows and Multiphase Flow Characteristics

Vane pumps are often applied in automatic transmission systems of vehicles. Future applications require the oil pumps to be more efficient and to be able to handle multiphase flow pumping situations to a certain extend. To fulfill these requirements, efficient development tools are needed. Therefore, a less demanding computational 2D model of a fixed-type balanced vane pump was derived and numerically analyzed with the commercial computational fluid dynamics (CFD) software ANSYS CFX. The meshing of the rotating parts was done with TwinMesh, using a moving mesh approach. At first, a mesh convergence study was performed. It was shown that the resolution of the radial clearances in particular had a significant influence on the predicted leakages and the volumetric efficiency. The leakage was further investigated concerning the dependence on rotational speed and delivery pressure. In the next step, multiphase flows were considered. In a first setup, vapor cavitation was analyzed and the influence of the alignment of the suction ports on its onset was derived. In a second setup, the influence of different inlet volume fractions of free air was evaluated. The employed multiphase modeling approach was presented and a sensitivity analysis on modeling parameters was performed. Overall, it was shown that free air in the suction ports changed the pumping characteristic of the vane pump significantly. Pressure and flow ripple increased, and the volumetric efficiency and the mean power demand decreased significantly with an increasing inlet volume fraction.

Mechanisms governing the “gasification to char oxidation transition” in counter-current flame propagation in packed beds: insights from single-particle experiments

Mechanisms governing the gasification to combustion regime transition in counter-current packed bed biomass systems are investigated in the current work. Single-particle experiments are performed with different oxidizer streams (air, mixtures of O2/CO2) to bring out the role of the extinction of the envelope non-premixed “volatiles” flame and simultaneous volatile-char combustion at the stagnation point on the transition to char oxidation in packed beds. Results indicate that for O2 fractions lower than 23% (w/w), the transition is governed by the extinction of the envelope diffusion flame. At higher O2 fractions, typically >32% (w/w), simultaneous volatile-char oxidation at the stagnation point drives the transition to char combustion. The strain rates computed at “gasification to char combustion transition” from earlier studies with air and O2 fractions ≤23% (w/w) in the oxidizer streams coincide with the strain rates obtained at the transition from classical envelope flame to a wake flame with single particles. Velocities at which simultaneous oxidation of volatiles and char was observed at the stagnation point with single particles subjected to oxidizer streams with O2 ≥ 32% (w/w) matches with the velocities at transition in the packed beds from the earlier studies. Simultaneous volatile-char oxidation and decrease in reaction zone thickness from a few particles to one particle diameter observed post-transition in packed beds support the theory.

Additive manufacturing of Ti-alloy: Thermal analysis and assessment of properties

In this study, 3D printing of Ti6Al4V alloy is realized and the characteristics of the printed layer are examined. The morphological structures and metallurgical changes in the printed layer are assessed. Temperature and stress fields are simulated in line with the experimental conditions. Since the air gaps are present in between the loose alloy powders prior to the printing, the effective properties incorporating the air fraction are determined and the effective properties are used in the simulations. Thermal conductivity of the loose alloy powders with the presence of air gaps is determined by incorporating the virtual experimental technique. It is found that the printed layer is free from micro-cracks and large scale asperities; however, some small pores sites are observed because of the release of air around the loose powders during the printing. Microhardness of the printed surface is higher in the top surface of the printed layer than that of as-received solid alloy. In addition, the friction coefficient of the printed surface remains lower than that of the conventionally produced solid surface. The columnar structures are formed in the mid-section of the printed layer and slanted grains are developed in the region of the top and the bottom surface of the printed layer.

Contrasting Scale Dependence of Entrainment‐Mixing Mechanisms in Stratocumulus Clouds

AbstractThe apparent turbulent entrainment‐mixing mechanism between clouds and surrounding air is scale dependent; however, such scale dependence has been rarely studied, hindering development of scale‐aware entrainment‐mixing parameterizations. Here we extend our previous study on cumulus clouds to investigate scale dependence of entrainment‐mixing processes in stratocumulus clouds during Aerosol and Cloud Experiments in Eastern North Atlantic and Routine AAF (Atmospheric Radiation Measurement (ARM) Aerial Facility) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO). In contrast to previous studies, two opposite scale dependencies are found: Entrainment mixing can become more homogeneous or more inhomogeneous with increasing averaging scales, which is quantified by the difference between homogeneous mixing degree at the 100 and 10 m resolutions. A new heuristic model and two new quantities are introduced. The observations and model show that microphysical properties near and far away from droplet‐free air and relative humidity of entrained air determine both the sign and strength of scale dependence, while droplet‐free air fraction only affects the strength. The results shed new light on developing scale‐aware parameterizations of entrainment‐mixing mechanisms.

Low-pressure supersonic separator with finishing adsorption: Higher exergy efficiency in air pre-purification for cryogenic fractionation

Air fractionation in cryogenic plants demands a Pre-Purification Unit for air compression and removal of water, carbon dioxide and trace-species. The conventional Pre-Purification Unit – FULL-TSA – adopts temperature-swing adsorption (TSA) with an activated-alumina bed for dehumidification followed by a molecular-sieve bed removing carbon dioxide and trace-species. A novel scheme – SS-TSA – prescribes a Supersonic Separator abating ≈98.5% of moisture followed by a small single-bed molecular-sieve removing remaining impurities. SS-TSA-HI is a SS-TSA variant allocating compression heat for molecular-sieve regeneration. This work compares thermodynamic performances of FULL-TSA, SS-TSA and SS-TSA-HI via exergy analyses and discloses better utilization of resources. Exergy analyses are supported by HYSYS simulator running with unit-operation extensions for calculating the phase-equilibrium sound speed and simulating the supersonic separator. Since exergy rates depend on Reference Environmental Reservoirs, two Reference formalisms are employed at 1 atm and 25 °C. Reference#1 prescribes air with 60% relative humidity (the raw air feed), while Reference#2 adopts water-saturated air. It is shown that Reference#1 is appropriate for overall system analysis, while Reference#2 is better for sub-systems analysis as it dramatically lowers cooling-water exergy flows. SS-TSA has 61% less exergy losses than FULL-TSA in the purification step as the supersonic separator accomplishes bulk dehumidification drastically reducing steam and nitrogen for bed regeneration. Reference#1 exergy efficiencies of FULL-TSA, SS-TSA and SS-TSA-HI attained 57.9%, 60.0%, and 60.3%, respectively.

Measuring the air fraction and the gas temperature in non-thermal argon plasma jets through the study of the air influence on the collisional broadening of some argon atomic emission lines

Cold atmospheric argon plasma jets have shown to be very promising in medicine and they are being currently used for therapeutical uses such as the healing of wounds or the treatment of tumors. Because they run in the open atmosphere, they generate copious amounts of reactive oxygen and nitrogen species, which play an outstanding role in their biological action. But, in this kind of reactor, unknown amounts of air enter the plasma region depending on the experimental conditions, changing the chemistry in them, and eventually their effects. In this work, we propose a new spectroscopic method to measure the amount of air in argon non-thermal (including cold atmospheric) plasma jets through the collisional broadening of Ar I 840.86 and Ar I 842.46 nm emission lines. The method allows the simultaneous determination of the gas temperature. For validation purposes, it was applied to a microwave-induced plasma jet working at different operational conditions. Results were consistent with those obtained from the rotational temperature derived from simulations of N2 (2nd positive system) rovibrational band.

Effect of viscosity and shear regime on stability of the air-void system in self-consolidating concrete using Taguchi method

Achieving suitable air-void characteristics in self-consolidating concrete (SCC) can be a difficult task due to the various influencing factors, including rheology and shear history. The effect of viscosity and shear regime on air-void system (AVS) of different SCC mixtures was evaluated using Taguchi method. The investigated SCC mixtures were proportioned with various high-range water-reducer (HRWR) and viscosity modifying admixture (VMA) combinations. Three different shear regimes, corresponding to static, semi-static, and dynamic were evaluated. These regimes simulate the concrete at rest, transportation, and casting processes, respectively. The characteristics of AVS were investigated immediately after mixing and up to 60 min after the first contact between water and binder using the ASTM C231 and air-void analyzer (AVA) test methods. Test results showed that the viscosity and shear rate regime are key factors affecting the AVS in SCC. High viscosity SCC mixtures exhibited better stability of air bubbles and spacing factor, regardless of the shear regime. On the other hand, the maximum size of aggregate showed the lowest contribution. Based on the statistical analysis, the optimum levels of control factors to minimize the variation in air volume (up to 60 min) and spacing factor are quantified. This consists, by order of importance, of the static shear regime and high viscosity of the mixture. Under these conditions, a high effective air fraction can be secured. Indeed, greater effective fraction of air bubbles is observed in high viscosity SCC compared to that of low viscosity mixtures.

Pressure drop, void fraction and flow pattern of vertical air–silicone oil flows using differential pressure transducer and advanced instrumentation

New data for pressure drop, void fraction and flow pattern in a vertical riser using air–silicone oil as the system fluid are reported in this work. A differential pressure cell (DP cell) was used to measure the pressure drop. Also, void fraction data were recorded simultaneously by an electrical capacitance tomography (ECT) and wire mesh sensor (WMS). The observed flow patterns are the spherical cap bubble, slug and churn flows. However, only the slug flow without the presence of churn flow is seen within the transition line as predicted by the map. The characteristic probability density function (PDF) derived from void fraction data was used to determine the flow patterns. A comparison between present experimental results and the air–water data reported in the literature was carried out and various levels of agreement were achieved. The PDFs obtained from the DP cell signals for spherical cap bubble and slug flows significantly differ from those derived from the ECT and WMS outputs. Current void fraction and pressure gradient results were compared with the values predicted by ten empirical correlations selected from the literature. Statistical tools such as Mean Square Error (MSE), Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE) were applied in the comparison. The Greskovich and Cooper correlation gave the least MSE, RMSE and MAPE values of 0.0007908, 0.013 and 3.05%, respectively for slug flow.

A constraint multi-objective evolutionary optimization of a state-of-the-art dew point cooler using digital twins

This study is pioneered in developing digital twins using Feed-forward Neural Network (FFNN) and multi objective evolutionary optimization (MOEO) using Genetic Algorithm (GA) for a counter-flow Dew Point Cooler with a novel Guideless Irregular Heat and Mass Exchanger (GIDPC). The digital twins, takes the intake air characteristics, i.e., temperature, relative humidity as well as main operating and design parameters, i.e., intake air velocity, working air fraction, height of HMX, channel gap, and number of layers as the inputs. GIDPC’s cooling capacity, coefficient of performance (COP), dew point efficiency, wet-bulb efficiency, supply air temperature and surface area of the layers are selected as outputs. The optimum values of aforementioned operating and design parameters are identified by the MOEO to maximise the cooling capacity, COP, wet-bulb efficiencies and to minimise the surface area of the layers in four identified climates within Köppen-Geiger climate classification, namely: tropical rainforest, arid, Mediterranean hot summer and hot summer continental climates. The system monthly and annual performances in the identified optimum conditions are compared with the base system and the results show the annual improvements of up to 72.75% in COP and 23.57% in surface area. In addition, the annual power consumption is reduced by up to 49.41% when the system is designed and operated optimally. It is concluded that identifying the optimum conditions for the GIDPC can increase the system performance substantially.