Air Mass Flow Research Articles

Numerical investigation of mass flow rate effects on multiplicity of detonation waves within a H2/Air rotating detonation combustor

This paper presents results from numerical simulations of a non-premixed hydrogen-air rotating detonation combustor with radial injection. The fuel and air mass flow rate are varied in order to hold a unity global equivalence ratio. The calculations show that multiple detonation waves co-exist when the mass flow rate is increased. Conditional statistics of the detonation structure and combustion processes suggest similarities across co-existing waves. Quantification of the injection response to the rotation of a detonation indicates that at higher flow rate the refill time is short enough to allow for a quick and well mixed composition prior to the new front passage. Details of the combustion characteristics are analyzed. The results elucidate the correlation between initial injection conditions and detonation multiplicity on the overall physics within the combustor.

Effect of geometric parameters on spray characteristics of air assisted pressure swirl atomizer

In the present work, a modified Pressure Swirl Atomizer (PSA) was introduced to operate as an Assisted Pressure Swirl Atomizer (AAPSA). Different mass flow rates of assisted air were experimentally tested. The studied parameters are the orifice length to diameter ratio (L/Do), swirl chamber length/diameter ratio (Ls/Ds) and swirling passage size (width × depth). The spray characteristics were studied using water as the atomized liquid. The spray was photographed using a high-speed camera to determine the spray shape, the cone angle and the spray breakup length. Moreover, photos taken by the high-speed camera were processed using IMAGE J software to obtain the droplet size diameters. The spray concentrations were measured by the patternator tubes technique. The results indicated that the spray cone angle increased by increasing the value of the L/Do ratio or by decreasing the assisted air mass flow rate. The spray concentration maximum value is shifted inward with the assist air injection. The breakup length decreased by about 65% for the PSA and 77% for the AAPSA when the value of the Ls/Ds ratio is decreased from 1.163 to 0.664. With the injection of assist air at a rate of 2 g/s, the Sauter Mean Diameter (SMD) is reduced by about 64% compared to a PSA having the same geometry.

A 2E Analysis and Optimization of a Hybrid Solar Humidification-Dehumidification Water Desalination System and Solar Water Heater

This study presents an energy-exergy analysis of a Humidification-Dehumidification (HD) solar water desalination system. The extensive application of the HD system lies in its low energy consumption and ability to exploit solar energy to supply all the heat energy demands. The unsteady governing equations were solved until the system reached a steady state. The simulations were done with the Euler approach to solving the system of energy balance equations numerically. This study's main goal was to investigate the effect of different configurations of the hybrid system and various operating conditions on the performance of the solar HD water desalination system. The optimum configuration was selected based on thermodynamic and exergy analyses. The effects of important parameters such as inlet water and air mass flow rate in the humidifier and dehumidifier water temperature and mass flow rate on the system's operation were studied. This paper also explored the feasibility of the extra heat as a domestic water heater under various conditions. Based on exergy analysis, it is shown that the solar desalination system with air-water preheater with the power of 1057.9 W had the most exergy destruction in comparison with the two other systems (i.e., water preheater system and air preheater system with the respective exergy destructions of 901.3 W and 75.3 W). Comparing the values of freshwater production, exergy destruction, and exergy efficiency, the solar system with a water preheater was selected as the optimum one.

Experimental analysis of spray drying in a process intensified counter flow dryer

This research presents an experimental analysis of a counter flow spray drying process using water and skim milk as a feed. The study was performed by examining the droplet size distribution of sprays and the temperature profiles in the dryer. The influence of air inlet temperature, air mass flow rate, feed flow rate, and droplet size on air temperatures in the dryer was evaluated. The evaporation and deposition zones were found to be highly dependent on the droplet size. The obtained results show that it is possible to achieve efficient contact between hot air and spray in a small volume using a counter-current mechanism.

Experimental Study of Primary Atomization Characteristics of Sonic Air-Assist Atomizers

The present study compares two twin-fluid atomizer concepts based on the airflow (shock waves) pattern obtained through shadowgraph imaging for atomization of water with a low air/water pressure supply. The research work was conducted using the backlight imaging technique for converging (sonic) and converging–diverging (supersonic) air-assist atomizers with a 3.0 mm (throat) diameter. An annular sheet of thicknesses 70 µm and 280 µm with a high-speed air-core was employed to study the breakup dynamics for different water mass flow rates (100–350 kg/h) and air mass flow rates (5–35 kg/h). Different sheet breakup patterns were identified as the function of the ALR ratio (air-to-liquid mass flow), liquid Weber number (WeL), and Reynolds number (Reg). Different breakup modes extend from canonical Rayleigh bubble breakup, ligament-type breakup, to the pure pulsating breakup via annular sheet disintegration. The sheet breakup dynamics were studied in terms of spray angle and breakup length. With higher ALR values, breakup length showed a decreasing trend, while spray angle showed an increasing trend in the converging and converging–diverging (CD) air-assist atomizers, respectively, owing to the drastic difference in the jet flow dynamics.

Spraying of Composite Liquid Fuels Based on Types of Coal Preparation Waste: Current Problems and Achievements: Review

This article discusses the atomization of composite liquid fuels. A large group of injectors is considered. A comparative analysis of the atomization characteristics (droplet sizes and velocities, jet opening angles) and the influence of the fuel characteristics (density, viscosity, component composition) and the process parameters (the ratio of the fuel–air mass flow rates, the features of the jet formation) has been carried out. Finally, the most effective types of injectors, which provide for the necessary characteristics of fuel atomization for its combustion, have been determined. The most favorable conditions for the applicability of each type of atomization have been formulated. Possible mechanisms of secondary fragmentation of droplets of composite fuels have been analyzed: those resulting from mutual collisions of droplets in the flux and from the interaction with a solid surface as well as those resulting from thermal overheating in the presence of a phase boundary or a large gradient of component volatility. A conclusion is made about the need of using a synergistic effect of primary and secondary atomization of fuel suspension droplets.

Integration of the Intelligent Optimisation Algorithms with the Artificial Neural Networks to predict the performance of a counter flow wet cooling tower with rotational packing

The present study investigated a counter-flow cooling tower performance by integrating the Artificial Neural Networks and Intelligent Optimisation Algorithms (ANN-IOAs). For this purpose, two scenarios were evaluated. In the first scenario, inlet air wet-bulb temperature (T aw), inlet air dry bulb temperature (T ad), water to the air mass flow rate ratio (mw /ma ), and rotor speed (υ) were the input parameters for the ANNs, while the output temperature (T wo) was the ANNs output. In the second scenario, the same input parameters applied for the first scenario were used as input variables and the tower efficiency (ε) was considered as an output parameter. The well-known IOAs methods, namely, Genetic Algorithm (GA), Particle Swarm Optimisation (PSO) and Bees Algorithm (BA), were used to optimise the ANNs for both scenarios. The obtained results showed remarkable accuracy for the proposed ANNs. The designed ANN model based on the BA method predicted the most efficient results. A sensitivity analysis was performed to study the most effective input parameters on the output temperature and the tower efficiency. Finally, for demonstrating the accuracy of the proposed ANN models for each case, a fair comparison is made between the proposed ANN models and regression models.

A predictive model for the industrial air-impingement drying of resin impregnated paper

Industrial drying lines of resin-impregnated paper are formed by contiguous furnaces where hot air jets impinge on the surface of the moving paper sheet. The number of production parameters that conditions the process is very high, making the final drying prediction, and the optimal adjustment of the production parameters, very complex tasks. A novel numerical tool for the fast prediction of this industrial drying is presented. The model, obtained from local mass and energy equations for the paper sheet, and fed with results from three-dimensional computational fluid dynamic simulations and thermo-gravimetric tests, determines the evolution of the paper weight along the line for any given combination of production parameters: paper velocity, furnaces air temperatures and mass flows, among others. The model is validated in an industrial line with 11 furnaces, 2 impregnation stages, and more than 150 adjustable operational input parameters, leading to relative errors in the predicted paper temperature evolution and final paper weight of less than 7% and 1%, respectively. Likewise, the model coupling with an optimization tool is also presented to show its capabilities on selecting the best production parameters for prescribed conditions, making the model a useful tool in the framework of the increasingly relevant role of mathematical models in industry.

Numerical analysis of indirect noise generated by compositional inhomogeneities using large eddy simulation

In the present work, indirect noises generated by compositional disturbances in a non-isotropic convergent nozzle are studied using Large Eddy Simulations (LESs). An in-house compressible LES code, Boundary Fitted Flow Integrator-LESc, is utilized to simulate the noise generation in the system. A non-reflective outlet boundary condition is used to eliminate numerical reflections and to ensure the reproduction of the operating conditions in the experiments. The experiments are designed to feature two configurations with different injection positions, which enable the separation of direct and indirect noises. Different operating conditions are investigated, including different injection gases and air mass flow rates. This present paper compares computational results with the experimental measurements. The results revealed that the processes of direct and indirect noise generation are successfully reproduced in the LES, with the noise magnitudes in good agreement with those in the measurements. Injection of gases with smaller (He) and larger (CO2) molar masses compared to air is found to generate negative and positive indirect noises, respectively, in the LES, which is consistent with the experimental findings. The effect of different air mass flow rates is also investigated and discussed, and the direct noise and indirect noise amplitudes are both found to be closely related to the air mass flow rate.

Transient experimental investigation of airside heat transfer in a crossflow heat exchanger

• Experimental analysis is performed to study the dynamic response of a heat exchanger. • Residence time is found to have a significant effect on the response time. • Transient air heat transfer coefficient is obtained by energy balance on the wall. • An empirical correlation of airside Nusselt number is developed. • The response time of both fluids was not instantaneous to the step imposed. The increase in energy consumption and the demand for effective thermal management systems necessitate the search for enhanced heat exchangers with high thermal performance, lower weight, and compact size. Crossflow heat exchangers are a key component in the thermal management system of many industries such as HVAC, automotive, etc. Transient analysis helps predict the behavior of heat exchangers when they experience variations in their operational conditions in terms of flow rate or temperature. This work experimentally studies the dynamic response of a cross flow heat exchanger to overcome the data scarcity in transient airside and presents the results for various cases of step changes in air mass flow rate. The effect of the step change on heat transfer is investigated and presented by airside Nu, fluids dimensionless temperature, airside Re, heat transfer rates, and Colburn j factor. Results show that the two fluids do not respond instantaneously to the step imposed. The magnitude of the step change has a dissimilar effect on the response time of each fluid. The response time increases with the increase in the step change. A generalized empirical correlation is obtained to predict the airside Nu. This study advances the control of heat exchangers by exploring their transient response due to step changes in one of the fluids inlet condition.

Hygrothermal simulations of timber-framed walls with air leakages

Air leakages can create substantial excess moisture loads into envelope structures and degrade their hygrothermal performance. Multiple previous research projects have studied the behaviour and modelling of air leakages in building physics applications, but it is still quite rare to see air leakages being considered in practical building design simulations. The purpose of this paper is to present the selection of input parameters for air leakage simulations, utilisation of a factorial design to manage simulation cases and the results for a timber-frame wall with and without air leakages. According to the results, the air permeability of mineral wool and the air pressure difference over the envelope were the two most important factors for the dry air mass flow through the structure, as opposed to gap width and leakage route. An ideally airtight structure had a better hygrothermal performance compared to leaky structure. However, when leakages were present, the exact yearly average air flow rate in the range 70…420 dm3/(m2h) did not have a strong correlation to the performance indicators. For the other studied variables, the existence of a 50 mm thick mineral wool insulation on the exterior side of the gypsum board wind barrier and the impacts from climate change had the biggest effect on the moisture performance of the structure.

Analytical models for adiabatic compressed air energy storage (A-CAES) systems in lined tunnels

Adiabatic compressed air energy storage (A-CAES) systems consist of an underground reservoir where compressed air is stored at high pressures. The ambient air is compressed by compressors located at the surface and the thermal energy is stored using thermal energy storage (TES) systems. The compressed air is stored in the subsurface reservoir (charge). Then, when the electricity is needed, the compressed air is released and expanded in gas turbines to produce electricity (discharge). In this paper, an analytical model has been developed to investigate the thermodynamic behaviour during air charge and discharge processes. Operating pressures from 4.5 to 7.5 MPa has been employed in lined tunnels in the compression and decompression stages. The model considers a 20 mm thick sealing layer, a 0.4 m thick concrete lining and a 1 m thick rock mass around the air. Air mass flow rates of 0.19 and 0.27 kg s−1 have been used in the charge processes for polymer material and steel, respectively. Finally, in the discharge processes the mass flow rate increases up to -0.38 and -0.45 kg s−1 for polymer and steel. The air temperature and pressure and the temperature and heat transfer in the sealing layer, concrete lining and rock mass have been analyzed for 100 cycles considering polymer material and steel as sealing layers. The heat transfer through the sealing layer reaches -150 and -95 W m-2 for steel and polymer, respectively. The results obtained show that the storage capacity increases when the heat transfer through the sealing layer increases.

Efficiency Enhancement in Double-Pass Perforated Glazed Solar Air Heaters with Porous Beds: Taguchi-Artificial Neural Network Optimization and Cost–Benefit Analysis

Analyzing the combination of involving parameters impacting the efficiency of solar air heaters is an attractive research areas. In this study, cost-effective double-pass perforated glazed solar air heaters (SAHs) packed with wire mesh layers (DPGSAHM), and iron wools (DPGSAHI) were fabricated, tested and experimentally enhanced under different operating conditions. Forty-eight iron pieces of wool and fifteen steel wire mesh layers were located between the external plexiglass and internal glass, which is utilized as an absorber plate. The experimental outcomes show that the thermal efficiency enhances as the air mass flow rate increases for the range of 0.014–0.033 kg/s. The highest thermal efficiency gained by utilizing the hybrid optimized DPGSAHM and DPGSAHI was 94 and 97%, respectively. The exergy efficiency and temperature difference (∆T) indicated an inverse relationship with mass flow rate. When the DPGSAHM and DPGSAHI were optimized by the hybrid procedure and employing the Taguchi-artificial neural network, enhancements in the thermal efficiency by 1.25% and in exergy efficiency by 2.4% were delivered. The results show the average cost per kW (USD 0.028) of useful heat gained by the DPGSAHM and DPGSAHI to be relatively higher than some double-pass SAHs reported in the literature.

The Effect of the Ratio of the Secondary and Tertiary Air on the Outlet Velocity Field of the New Swirling Pulverized Coal Burner

ABSTRACT The outlet velocity field of the pulverized coal burner is one of the important factors affecting its operating characteristics. In this article, cold tests were carried out for a new swirl burner with a pre-combustion chamber, and the influence of the air ratio on the outlet velocity field of the burner was studied. Through the cold single-phase test on the 1:3 model test bench, the burner outlet cold air velocities were obtained. The results shown that the formation of the central recirculation zone was mainly affected by the secondary air, a stable central recirculation zone could not be formed when the velocity of secondary air was too low. When the total air of the burner was fixed, the secondary air increased, the length of the central recirculation zone increased, and the mixing speed between different flows increased. When the ratio of the mass flow of the secondary air to tertiary air increased from 26:74 to 85:15, the reflux rate increases 5.5 times, which helped to keep the combustion stable.

Feasibility study on using asphalt pavements as heat absorbers and sensible heat storage materials in solar air heaters: An experimental study

Asphalt pavements are affordable infrastructures exposed to solar irradiation for a long time a day, and they experience considerable high temperatures. Due to high thermal capacity, asphalt pavements can store high sensible thermal energy during daytime hours and release it when solar irradiation is negligible or absent. The current study investigates the heat dynamics and thermal efficiency of asphalt solar air heaters (SAHs) utilizing asphalt materials that function as both heat absorbers and sensible heat storage units. To this aim, a 1.2 m2 single-glazed baffled SAH prototype was constructed, and its heat dynamics were monitored on cold and mild winter days at two different air mass flow rates of 0.02 kg/s and 0.03 kg/s. The constructed SAH uses black stainless-steel baffles to produce a serpentine air passageway and improve turbulence and heat exchange rates. The acquired data illustrates that the maximum intake and exhaust air temperature difference reaches up to 14 °C and 24 °C on cold and mild winter days, respectively. When the solar irradiation was negligible in the evening, the asphalt pavement serves as sensible heat storage and heats the passing airflow up to 8 °C and 12 °C at sunset on cold and mild winter days, respectively. This issue causes the collector thermal efficiency to reach as high as 80%. Therefore, using asphalt materials is a feasible approach to simultaneously serve as heat absorber and sensible heat storage.

Numerical Evaluation of the Hydropneumatic Power of the Oscillating Water Column Wave Energy Converter Submitted to Regular and Irregular Waves

The purpose of this study is to computationally analyze the hydropneumatic power available in the air duct of an Oscillating Water Column (OWC) Wave Energy Converter (WEC) device when subject to realistic sea state data (irregular waves) and when submitted to the regular waves representative of this sea state. The OWC WEC is mainly composed of a hydropneumatic chamber and an air duct where a turbine and electric generator are coupled. The chamber is open below the free surface while the duct is open to the atmosphere. The oscillating movement of the water-free surface inside the chamber causes the air to flow, moving the turbine and generating electricity. To execute this study, a bi-dimensional computational model was considered and numerical simulations of wave generation were carried out using ANSYS Fluent, which is a Computational Fluid Dynamics (CFD) software based on the Finite Volume Method (FVM). The Volume of Fluid (VOF) multi-phase model was applied in the treatment of the water-air interaction. To evaluate the average hydropneumatic power available in the duct, the static pressure, velocity, and air mass flow rate were monitored. The results were analyzed, showing that the available power is 250% greater when the device is subject to realistic irregular waves rather than subject to representative regular waves.

Investigation of a Storage Type Solar-Driven Solid Desiccant Cooling System

Solar-driven solid desiccant assisted evaporative cooling could be an effective alternative to conventional vapour compression cooling systems due to its lower operating costs and lower environmental impact. This technology has been widely investigated for continuous operation through the use of desiccant wheels. However, the investigation of such technology for storing solar radiation in the form of coolth energy is missing in the literature. In that regard, primary objective of the present study is to investigate a fixed bed solar driven desiccant assisted evaporative cooling system, that uses vermiculite-calcium chloride composite sorbent, to be utilized as a coolth storage in hot-humid climate. To achieve this aim, a prototype unit was designed, developed and tested under real climatic conditions of North Cyprus. According to the results, over six hours of charging period, at regeneration temperature between 51 – 62 °C and air mass flow rate of 0.03 kg/s, average moisture desorption rate of 3.9 g/min was obtained. On the other hand, over four hours of discharging at air inlet temperature of 32 – 35 °C and mass flow rate of 0.06 kg/s, vermiculite-calcium chloride / wood chips couple provided average air temperature drop and cooling capacity of of 8.4 °C and 0.49 kW respectively. Hygrothermal efficiency of the system is also found 0.65. Additionally, the average wet-bulb effectiveness and average dew-point effectiveness were obtained as 121.6%, and 90.2% respectively. Furthermore average total and thermal coefficient of performance of 0.35 and 0.6 were achieved over the three consecutive cycles. These results suggest that the proposed system could be a potential technology for storing solar energy to be used in air conditioning applications in buildings.

Experimental and numerical investigation on the thermal performance of linear LED housings under forced convection

This study aims to experimentally and numerically test the thermal performances of three different linear housings (Model 1-without fin, Model 2-with inner fin, and Model 3-with inner and outer fin) with medium power light-emitting diode (LED) arrays at 30 °C and 40 °C ambient temperatures under forced convection for 25 W and 35 W. Although the mass of Model-3 was reduced by 54.2% and 34.67% compared to Model-1 and Model-2, its surface area was increased by 46.3% and 9.11%, resulting in an improvement in junction temperature (Tj) up to 4.4 °C and 7.75 °C, respectively. Thermal resistance (Rth) for Model-3 is approximately 1.38–3.1% and 7.85–9.72% smaller than that of Model-1 for 25 W at ambient air temperature (Taa = 30 °C and Taa = 40 °C), respectively. The Rth for Model-3 is approximately 1.39–2.6% and 8.65–6.07% smaller than that of Model-1 for 35 W at the same Taa, respectively. The Model-3 offers lower junction temperature, lower cost, and safe operating temperature range by inner and outer fins compared to the others. The results demonstrated that all of the temperatures reduced with the increase in air mass flow rate; however, it was found that as the LED power and ambient temperature increased, the junction temperature increased. Experiment and simulation results show that adding a fan to the luminaire significantly lowers the LED junction temperature, in which case it provides a safe operating range and protects the luminaire against thermal shocks. The forced application allows using of comparatively smaller housing as it provides a lower junction temperature.

Heat transfer and performance analysis of SAH having new transverse finned absorber of lateral gaps and central holes

An experimental work is presented on the performance of solar air heater (SAH) has new designed absorber of finned transverse plate of lateral gaps and central holes. Moreover, a complete heat transfer analysis of the radiation and convection and SAH thermal performance are presented and discussed. The performance of this transverse SAH (TR_SAH) is compared with identical conventional flat plate SAH (FP_SAH) for single (SP) and double-pass (DP) airflow and air mass flow rates (AMFR) of 0.025, 0.05, and 0.075 kg/s. The experimental study is performed under hot climate conditions of Upper Egypt. The findings show that for all studied cases, TR_SAH has higher energy gain, output air temperature, thermal efficiency, and Nusselt number on the absorber plate, thermal-hydraulic performance parameter, and pressure drop compared to FP_SAH. The energy loss and radiation and convection Nusselt number on the TR_SAH glass plate is lower than that of FP_SAH. The maximum TR_SAH energy efficiency of value of about 89% is achieved in the case of DP airflow and high AMFR of 0.075 kg/s, with an enhancement of 24.2% compared to FP_SAH. The higher TR_SAH efficiency at these conditions reflects the optimal TR_SAH absorber design especially at high AMFR and using DP airflow. Despite TR_SAH air pumping power is greater than FP_SAH but it has a negligible effect on net energy gain.

Performance of an Indirect Packed Bed Reactor for Chemical Energy Storage.

Chemical systems for thermal energy storage are promising routes to overcome the issue of solar irradiation discontinuity, helping to improve the cost-effectiveness and dispatchability of this technology. The present work is concerned with the simulation of a configuration based on an indirect-packed bed heat exchanger, for which few experimental and modelling data are available about practical applications. Since air shows advantages both as a reactant and heat transfer fluid, the modelling was performed considering a redox oxide based system, and, for this purpose, it was considered a pelletized aluminum/manganese spinel. A symmetrical configuration was selected and the calculation was carried out considering a heat duty of 125 MWth and a storage period of 8 h. Firstly, the heat exchanger was sized considering the mass and energy balances for the discharging step, and, subsequently, air inlet temperature and mass flow were determined for the charging step. The system performances were then modelled as a function of the heat exchanger length and the charging and discharging time, by solving the relative 1D Navier-Stokes equations. Despite limitations in the global heat exchange efficiency, resulting in an oversize of the storage system, the results showed a good storage efficiency of about 0.7.