Air Mass Flow Research Articles

3D CFD modelling of dust deposition characteristics and influences on building-mounted photovoltaic system

Airborne dust deposition on the solar photovoltaic panels can significantly decrease the photovoltaic efficiency performance. Dust deposition characteristics and influences on building-integrated photovoltaic panels were studied by shear stress transfer k-ω turbulence model with inlet profiles and discrete particle model. The influences of dust size, wind velocity, and building roof inclination on the dust deposition behaviors were studied carefully. The air flow fields, the dust particle trajectories, the deposition rate on solar photovoltaic panels and the photovoltaic efficiency decrease by dust deposition were obtained and analyzed in the study. The three-dimensional simulation has great difference on the wind flow structures compared with two-dimensional simulation. The size of the separation vortex in the three-dimensional simulation is significantly smaller than that in two-dimensional simulation. The secondary flow structures become more significant in the rear of the building. The dust deposition rate is firstly increased and then decreased with the increasing of dust diameter. The maximum deposition rate is 2.54% for 150 μm particles. The minimum deposition rate is just 0.03% for 500 μm particles. The maximum deposition rate is 1.39%, 2.54% or 3.74% for the roof inclination angle of 16.7°, 22.6°or 36.9°, respectively. When particle size is 150 μm, the dust motions are determined by the air flow fields, mass inertia and gravitational settling. The photovoltaic efficiency reduction is significantly higher with increasing of dust size. The present model can conveniently estimate the photovoltaic efficiency decrease by dust deposition in realistic engineering application.

Investigation of cross-stream spray injection and wall impingement in a circular channel for SCR application

A parametric study of cross-stream pulsed spray injection and wall impingement characteristics in a circular channel has been carried out with an objective to investigate performance improvement in selective catalytic reduction (SCR) systems for exhaust gas after-treatment in diesel engines. The spray computations are performed based on a combined Eulerian and Lagrangian based modeling approach for the continuous and the discrete phases respectively. The simulation results are validated using the in-house experimental data for water injection in both open atmospheric and channel flow conditions. The spray structure, penetration, and droplet size are compared and good agreement between the experiments and simulations is demonstrated. Though the focus of the present work is on studying the influence of liquid preheating on post-impingement spray and wall-film characteristics as well as evolution of species mass fraction, the effect of air mass flow rates, and temperature, and the choice of the working liquid (water or Urea Water Solution (UWS)) are also investigated. While the mass flow rate of air and the selection of the above liquids for spray injection are found to have marginal influence on the results, the liquid preheating is shown to strongly affect the droplet evaporation and thus, the spray impact process. Especially, the liquid injection temperature that leads to flash evaporation results in reduced wall filming, higher ammonia generation rate and spatial uniformity of NH 3 across the channel. This paper demonstrates preheating as a promising approach for the improvement of SCR performance. • Spray injection and wall impingement in a duct air flow relevant to SCR systems is numerically investigated. • The predicted post-impingement droplet size and spatial distribution compared well against the in-house experiments. • Marginal influence of air mass flow rate and choice of the liquid (water or UWS) is observed. • Preheating the injected liquid is a viable alternate for performance optimization of the SCR systems. • Especially, the flash evaporation condition ensures reduced wall filming and, higher rate of NH 3 and its spatial uniformity.

Experimental performance evaluation of date palm fibers for a direct evaporative cooler operating in hot and arid climate

This paper presents an experimental investigation of a direct evaporative cooler, DEC, designed and installed in the hot and arid region of Biskra, Algeria. Date palm tree fibers are used as a novel evaporative cooling material. Different performance parameters are experimentally tested to assess the thermal performances of the DEC system. Results show that the cooling capacity, cooling efficiency and total cooling capacity of the pad improve by increasing the pad thickness and air mass flow rate in extreme ambient conditions. Besides, operation duration has no remarkable effect on the DEC performance. The operating parameters (pad thickness, air mass flow rate, ambient conditions, quantity and temperature of water) are the determinant factors to reach the optimum operating conditions of DEC. Finally, a comparison with the usual cooling systems shows that the date palm fibers pad is an effective material compared to the conventional pads in hot and arid zones.

Analysis of polishing waste ceramic foam packing in evaporative cooling

This paper proposes the use of ceramic polishing slag to make fillers for evaporative coolers. The experimental tests on the heat transfer performance of the ceramic foam packing are carried out by using the independent test bench, focusing on the effects of the packing's flow channel form, drench density, the inlet air volume and pressure drop on the heat, and the mass transfer performance of the packing. The experimental results show that the optimum drench density of the ceramic foam packing in the form of a folded runner and a linear runner is 10.0 and 6.7 kg/(m·h), respectively. The direct evaporative cooling efficiency of the ceramic foam packing in both runners tends to decrease with the decrease in the dry and wet bulb temperature difference of the inlet air and the increase of the air mass flow rate. Under the same experimental conditions, the direct evaporative cooling efficiency, optimum inlet air velocity, and pressure drop of the packing in the form of a folded flow channel are higher than those of the linear flow channel. The optimal inlet air velocities of the packing in the form of a folded runner under the conditions of Urumqi, Xi'an, and Guangzhou are 1.6, 1.4, and 1.0 m/s, respectively, and the direct evaporative cooling efficiency can reach 83.01%, 70.74%, and 66.41%. In comparison, the optimal inlet air velocity for all three conditions under the linear runner is 1.0 m/s, and the direct evaporative cooling efficiencies are 73.78%, 68.56%, and 63.28%, respectively.

Experimental study on propagation mode of rotating detonation wave with cracked kerosene gas and ambient temperature air

In order to obtain propagation characteristics of a rotating detonation wave (RDW) of cracked kerosene gas (CKG) and ambient temperature air, a series of experiments were carried out at different cracking kerosene and air mass flow rates. The propagation mode of RDW was analyzed in detail, and the ignition range of CKG and air was evaluated. In the experiment, the propagation modes of rotating detonation mainly include the single rotating detonation wave (SRDW) mode, reversed single rotating detonation wave (RSRDW) mode, and mixed mode. In the mixed mode, SRDW and two-counter rotating detonation wave modes alternate. Combined with high-speed photography and pressure curve, the mechanism of mode transition of rotating detonation propagation is analyzed. The RSRDW mode is considered to be a transitional mode in the process of equivalence ratio change. The mixed mode is an unstable RDW propagation state due to the improper ratio of fuel and oxidizer. Based on a substantial number of experimental data, the ignition ranges of CKG are summarized. Under the experimental conditions in this paper, the equivalence ratio range of CKG that can be detonated is 0.63–0.99. RDW is favorable to be formed in the lean oil state. When the equivalence ratio is 0.99, the maximum RDW velocity is 1077.79 m/s. When the mass flow rate of cracking kerosene is 42 g/s, the ignition initiation range is widest. As the mass flow rate increases or decreases, the initiation range is gradually reduced.

Changes in the frequency and temperature of air masses over east‐central Europe

AbstractThe study specifies the circulation conditions, the frequency of occurrence, long‐term changes, and thermal characteristics of air masses over east‐central Europe in the years 1951–2020. The division of air masses utilized by The Polish Institute of Meteorology and Water Management was used, where, based on the geographical location of the source areas, Arctic (A), Polar maritime fresh (mPf), Polar maritime old (transformed) (mPo), Polar maritime warm (mPw), Polar continental (cP), and Tropical (T) air masses are distinguished. It has been shown that western circulation dominates in this area (60% of days on average), during which the advection of maritime air masses occurs. The share of Arctic air mass flowing from the north (about 12% of days a year) and Tropical air mass from the southern sector (4% of days) is clearly smaller. The results of the research have shown that the frequency of the majority of the analysed air masses was subject to short‐term changes in the studied period. On the other hand, long‐term changes in this frequency concerned two air masses flowing from lower latitudes (mPw and T). In the case of mPw, in the period 1951–2020 there was a significant increase in frequency, not only on a yearly basis, but also in all seasons. In the last two decades, the frequency of Tropical air mass has also increased significantly, while the increase took place only in the summer period. Therefore, the increase in air temperature recorded in east‐central Europe since the 1990s, mainly in the warm half of the year, should to a large extent be attributed to both the greater frequency of the inflow of air masses from lower latitudes (mPw and T) and the increase in temperature in virtually all separated air masses, which in turn is a result of progressing global warming.

Effects of number of objective functions on the optimization of a hybrid building integrated photovoltaic/thermal-heat recovery wheel unit

The present study examines the effect of the number of objective functions on the optimal performance of an exhaust air heat recovery unit including a building integrated photovoltaic/thermal unit (BIPV-T) and a heat recovery wheel (HRW). The unit is able to precool/preheat the outdoor air and generate electricity. Four objective functions are introduced to optimize the performance of the system from energy, energy, economic and environmental perspectives and all the possible single-objective, two-objective, three-objective and four-objective optimizations are conducted and the results are compared. Seven geometrical and operating variables consisting of the width, depth, and length of the BIPV-T channel, air mass flow rate, and rotational speed, length, and depth of the HRW unit are chosen as the decision parameters. The outcomes revealed that if a designer expects the examined unit to supply the entire energy and exergy required by building and the production of extra energy and exergy is worthless, then the optimization of unit performance based on the maximization of the amount of undischarged CO2 (Scenario 2) will be the best and the most effective scenario for the single-objective optimization of the unit.

Performance Evaluation of PVT Air Collector Coupled with a Triangular Block in Actual Climate Conditions in Korea

This study experimentally investigated the performance of a PVT air collector coupled with a triangular block. The triangular block, newly suggested by the authors, is a triangular-shaped obstacle and was inserted at the bottom of the PVT air collector to enhance the heat transfer performance of the collector. The experiment was carried out in actual climate conditions in Korea with two air mass flow rate conditions: 0.03606 kg/m2 s and 0.06948 kg/m2 s. Results show the average values of electrical efficiency of the collector during the test period to be 16.15% and 16.43% for each air mass flow rate, while thermal efficiencies were 28.83% and 38.36%, respectively. The average values of total energy efficiencies were found to be 44.99% and 54.79%, respectively. The results show that air mass flow rate has a large impact on thermal and total energy efficiency, while it has a small impact on electrical efficiency. Furthermore, it was confirmed that the PVT air collector coupled with a triangular block can enhance the utilization of solar energy since the thermal performance was higher than that of the collector without a triangular block.

Aerodynamics of two-phase gas-solid flow in a flat suction nozzle during vacuum pneumatic transport

The paper reports the results of research on the effect of the design of a suction nozzle with a rectangular section under horizontal and vertical pneumatic conveying conditions in a pipe with a diameter of D = 30 mm. Five unmanned truncated pyramid-shaped suction nozzles were tested, which differed in height and cone opening angle 25°-120° while maintaining a constant ratio of the inlet to the outlet surface area of 8.5. The working media in the research were air and ten types of bulk materials commonly used in the industry with a variable equivalent particle diameter of ds = 0.2–2.4 mm and the specific density ρs = 495–6730 kg/m3. The materials used in the research were characteristic of bulk materials of type A, B and D defined according to Geldart's classification. The study was carried out at the superficial velocities of air ug = 2.8–46 m/s and solids us = 0.002–2 m/s. This ensured obtaining the mass concentration of the solid in relation to the mass flow of air in the range of μs = 0.6–290. As a result of the analysis of experimental data obtained by means of a high-speed camera and a computer system for archiving experimental data and image analysis, seven flow structures were identified and described. Also an original two-phase gas-solid flow map was developed. A new method has been proposed to calculate pressure drop ΔP2P during two-phase gas-solid flow for different geometries of rectangular suction nozzles with the accuracy mean relative error MRE = −0.83% and mean absolute error MAE = 29.5%. It is the first model of this type described in the literature.

PREDICTING OF REFRIGERANT LEAKAGE IN A CONDITIONED ROOM: A NUMERICAL STUDY LEAKS DISTRIBUTION R-32 REFRIGERANT IN A/C SPLIT UNIT

Hydrocarbon Refrigerant R-32 called difluoromethane is one alternative solution used for Air Conditioning (A/C) unit split, but the weakness is flame property. This study investigates and analyzes flammable refrigerant difluoromethane distributions in the room affected by the A/C unit's leakage. It discusses the distribution of flammable refrigerant R-32 (difluoromethane) in an air-conditioned room. The simulation uses three variations of mass flow rate (leakage) and three airflow rate variations: low, medium, and high cold airflow velocity. Numerical calculations are used in CFD ANSYS FLUENT software with a model developed by Species Transport, SIMPLE algorithm, solver using pressure-based, mesh type is the dominant quadrilateral (rectangle). Turbulent modeling uses K-Epsilon standards. CFD analysis in the transient system condition results from numerical simulation, indicating that the leak will run out after 180 seconds with 0.005 kg/s (0.5 m/s). The moderate leak rate of 0.002 kg/s for R-32 is 450 seconds (7.5 minutes). The slower 0.001 kg/s with 0.1 m/s airflows for the R-32 ends after 900 seconds (15 minutes). The air and flow mass flow can affect the distribution and directly difluoromethane to the conditioned room. The effect of airflow rates and positioning holes in the concentration leaks is also analyzed when the unit's refrigerant leak is indoors as the air conditioner works.

Experimental investigation on critical slowing down of premixed combustion in a backward-facing step combustor

Critical slowing down phenomena occur during the transition process of various dynamical states, such as bifurcations. The eigenvalues of dynamical systems can be regarded as an indicator of critical slowing down of impending bifurcation. Adaptive, locally linear models can extract local eigenvalues of the nonlinear dynamical system by segmenting a full-time series into multi-windows, and eigenvalue spectrum analysis is based on the eigenvalues. The state transition between different combustion states occurs through bifurcation processes. In this paper, we investigate critical slowing down in the bifurcation process of backward-facing step combustor. We performed a series of experiments by fixing the air mass flow and varying the fuel mass flow from the lean blowout condition to a thermoacoustic instability condition with a quasi-steady change, and the combustion state varying versus the change of the operation conditions exhibit a quasi-Hopf bifurcation process. The measured pressure fluctuations were treated by the local linear model to analyse the eigenvalue spectrum. The real parts of the eigenvalues approximate zero gradually when the equivalence ratio increases, and this tendency corresponds to the critical slowing down. Furthermore, the commonly used early warning signals were also used to support the analysis results of the eigenvalue spectrum.

Development and performance evaluation of a dual energy source solar dryer for tomatoes

Solar energy is the most promising of the renewable energy sources in view of its apparent limitless potential. A Dual energy Source Solar Dryer was developed under Bauchi weather at latitude 9°14′ N and longitude 12°26′ E using locally available materials and the performance was evaluated. The essence of the dryer was to achieve the effective method of tomato preservation and eliminate the drudgery and product deterioration associated with traditional methods of open sun drying of tomatoes. This is in view of alleviating the weather limitation experienced by farmers in crop drying especially for tomatoes. The solar dryer consists of tray, reflective walls and glass roof, a preheating air absorber plate, inner panels for removal of moisture and chimney through which air stream passes across the dryer. Evaluation of the dryer showed a raised temperature of about 47 ℃ attainable in the drying chamber. The dryer temperature and drying rate was found to be higher than the natural open sun drying method. The dryer was able to reduce moisture content of tomato from initial moisture content of 94% wet basis to 4% in three days with effective drying time of 24 h, efficiency of 64%, air mass flow rate of 0.025 kg s-1 and drying rate of 0.03906 kg h-1. The results showed a considerable advantage of solar dryer over the traditional open sun drying method in terms of drying rate and less risk for spoilage.

Predicting the energy and exergy performance of F135 PW100 turbofan engine via deep learning approach

In the present study, the effects of flight-Mach number, flight altitude, fuel types, and intake air temperature on thrust specific fuel consumption, thrust, intake air mass flow rate, thermal and propulsive efficiecies, as well as the exergetic efficiency and the exergy destruction rate in F135 PW100 engine are investigated. Based on the results obtained in the first phase, to model the thermodynamic performance of the aforementioned engine cycle, Flight-Mach number and flight altitude are considered to be 2.5 and 30,000 m, respectively; due to the operational advantage of supersonic flying at high altitude flight conditions, and the higher thrust of hydrogen fuel. Accordingly, in the second phase, taking into account the mentioned flight conditions, an intelligent model has been obtained to predict output parameters (i.e., thrust, thrust specific fuel consumption, and overall exergetic efficiency) using the deep learning method. In the attained deep neural model, the pressure ratio of the high-pressure turbine, fan pressure ratio, turbine inlet temperature, intake air temperature, and bypass ratio are considered input parameters. The provided datasets are randomly divided into two sets: the first one contains 6079 samples for model training and the second set contains 1520 samples for testing. In particular, the Adam optimization algorithm, the cost function of the mean square error, and the active function of rectified linear unit are used to train the network. The results show that the error percentage of the deep neural model is equal to 5.02%, 1.43%, and 2.92% to predict thrust, thrust specific fuel consumption, and overall exergetic efficiency, respectively, which indicates the success of the attained model in estimating the output parameters of the present problem.

Experimental investigation of relative roughness height effect in solar air collector with convex dimples

This study focuses on the effect of dimple depth on improving thermal performance in a solar air collector (SAC) with huge convex dimples placed staggered on an absorber. In this regard, convex dimple absorbers with two different types of relative roughness heights, δ/D = 0.16 and δ/D = 0.32, and a flat plate absorber were tested for back-pass and front-pass applications at air mass flow rates of 0.013, 0.027, and 0.036 kg/s. The highest average energy efficiency of 37.9% and 53.5% were achieved for dimpled absorber plates in back-pass and front-pass, respectively, with δ/D = 0.32 at an air mass flow rate of 0.036 kg/s. The exergy efficiency ranged from 8.1% to 12.4% for the back-pass application, whereas it fluctuated from 14.6 to 19.7 in the front-pass application. In comparing δ/D = 0.32 with the flat plate in the back-pass application, Nud/Nuf varied from 1.2 to 1.48 with an increase in Re, while in the front-pass Nud/Nuf changed from 1.13 to 1.37. In the back-pass, Nud/Nuf/(fd/ff) achieved 1.24 in favor of δ/D = 0.32 at Re = 4000, on the other hand, it reached 1.15 in the front-pass. Similarly, the highest Colburn factor values in all Re numbers were obtained in the case of relative roughness height of δ/D = 0.32. As a result, a relative roughness height equal to 0.32 is the optimal geometry for this investigation of a dimpled collector. Accordingly, the results showed that SACs with convex dimples are more successful than the flat plates, thanks to the surface area expansion and turbulence generating ability, which significantly increases the thermal efficiency. This study also recommends the use of a front-pass application.

Deep Learning Model for Prediction of Air Mass Deviation Faults

Major Systems of an internal combustion Engine are Air System, Fuel system, and Exhaust system. Any malfunction in these systems increases emissions. OBD legislation mandates to monitor these systems for any faults and appropriate action should be taken in case of the any faults which increase vehicle emissions. The idea of the paper is to find the Air mass flow deviation faults using datamining and machine learning based approach. Detection of fault is classifying whether system is faulty or not. Objective is to create a deep learning model using the available vehicle data to classify the system for a fault. Three main inputs for the Air Mass flow in an internal combustion Engine are1) Fresh Air which measure using Mass Air Flow sensor2) Low Pressure EGR3) High Pressure EGRDuring vehicle lifetime, due to different real vehicle operating conditions and environmental conditions, deviation in the set point of air mass flow and actual mass flow are possible to an extent, which can affect vehicle emissions. Deviation in the Air Mass flow can be caused by intake Air mass, LP-EGR, HP-EGR. The Aim of the project is to create the deep learning model for Air Mass Flow Hi and Low faults using the available data, and associate the fault to the component in the Intake Air System.

Temperature variation inside a corridor-like enclosure under limited ventilation

This paper investigates the temperature variation inside a corridor-like enclosure (for example, high-speed train compartment) with persistent flame ejection through an opening (for example, window). The fire heat release rate and opening sizes are varied with 28 different experimental conditions. An exponential function is built and found to be able to describe the longitudinal temperature distribution, in which the decay rate has a power function with the window aspect ratio. The maximum temperature shows a considerable difference for various heat release rates (HRR), due to the mass flow rate of the fuel supply through the opening is comparable to or greater than the air mass inflow rate. A general model characterizing the longitudinal temperature distribution of various opening sizes and HRR is proposed with heat release to heat loss ratio inside the compartment, HRR and window aspect ratio, which shows a good agreement with the experimental results. This study provides important and new contributions over previous knowledge and has potential practical applications concerning the corridor-like enclosure fire safety and occupant evacuation.

Experimental study of H2/air rotating detonation wave propagation characteristics at low injection pressure

H2/air rotating detonation wave (RDW) propagation characteristics were studied under low injection pressure. A small air mass flow rate and wide air injection ring were used to obtain low injection pressure. The formation of RDWs and the influence of different injection pressures on the RDW propagation process were studied and analyzed. The experimental results show that the lower limit of injection pressure for H2/air to form an RDW with stable propagation is 2.21 bar for hydrogen and 2.32 bar for air. At these injection pressures, the longitudinal pulsed detonation (LPD) mode and the single rotating detonation wave (SRDW) mode occur successively in the rotating detonation combustor (RDC), and the RDW velocity is 1491.4 m/s. The reasons for the generation, persistence and transformation of the LPD are analyzed. When the air mass flow rate is 370 g/s, the minimum air injection pressure to produce RDC ignition in a wide equivalence ratio range is 3.0 bar. With an equivalence ratio of 0.57–1.54, the RDW velocity and pressure first increase and then decrease, the maximum RDW velocity and pressure occur with an equivalence ratio of 1.2–1.3. RDW velocity and pressure increase with the air injection pressure rises. Flame characteristics during steady RDW propagation were analyzed using high-speed photography.

Brush seal design and secondary air system modification of a heavy-duty gas turbine to improve the output power

The overall performance of heavy-duty gas turbines is strongly affected by the mass flow distribution of the secondary air system. Reducing the mass flow of the secondary air is a remarkable method to improve the performance of a gas turbine. The aim of this article is to implement a brush seal as an alternative to labyrinth seal. Based on the experiences gained from the integrity of brush seals into a gas turbine, installing a brush seal would not necessarily improve turbine performance. This is because of SAS mass flow redistribution, which may not lead to overall SAS mass flow reduction. Therefore, some other components in the SAS arrangement should be modified as controlling variables to overcome this problem. The effect of these modifications on the airflow distribution is investigated using an in-house network analysis code. To establish an optimum solution (optimized brush seal geometry and controlling variables), the network analysis code is coupled with an in-house optimization code that benefits from the Genetic Algorithms and Artificial Neural Networks. Some constraints including upstream and downstream cavity purge flow and vane cooling air are considered in the optimization process. The final network results show a 33.27% reduction in overall SAS mass flow. To ensure an improvement in the performance of the new three-stage turbine, a CFD analysis is conducted, which indicates 1.0% more power with respect to the original turbine. In the end, the aerodynamic and mechanical behavior of the brush seal is analyzed using CFD and FEM.

Combination of a v-grooved solar collector with a single slope solar still: Performance evaluation, mathematical modeling, and economic analysis

Solar stills are known as one of the best and most efficient methods for water desalination. Due to low production of solar stills, researchers have been using experimental and theoretical methods to come up with possible solutions for ameliorating freshwater production through these systems. This study aims to investigate the performance of a single slope solar still combined with a v-grooved solar air heater. Important parameters (height of the v-grooves, length of the collector, and air mass flow) affecting the performance of the proposed system were mathematically investigated using MATLAB software. The average deviation between the experimental and theoretical results was found to be about 7%. Furthermore, the results showed that the water production rate and the efficiency of the modified solar still were 150% and 44.20% higher than those of the conventional ones, respectively. Two new correlations were proposed based on the experimental results in order to predict the water production via solar stills, which are in good agreement with the results of the existing models. Based on the obtained results, the increase in the inlet air mass flow rate was not conducive to water production as the production rate was reduced by 60%. In addition, through the economic analysis, the cost per liter for the modified still was determined to be 0.03 [Formula: see text] with an interest rate of 10%.

A novel method for convective drying rate estimation in a deep fixed porous material bed

In this paper, we propose a novel approach to describe the convective drying process of deep fixed porous material beds during the constant-rate drying period, which is based on the equation describing the heat power conservation within the drying zone. In addition, we propose a novel iterative method to solve the equation, which evaluates the outlet air temperature and the drying rate for the bed with given inlet air parameters. The validity of the proposed approach is examined against experimental and CFD numerical modelling data for two cases of biomass beds, namely, sawdust and barley grain, which represent typical porous material drying problems. Furthermore, the analysis of the conservation equation shows that the drying rate of the bed is proportional to the inlet air mass flow rate and is a function of the initial moisture content of the bed; however, it is independent of the bed volume.