Air Mass Flow Research Articles

Thermal and Thermo-hydraulic Performance of Finned Double-Pass Solar Air Collector Utilizing Cylindrical Capsules Nano-Enhanced PCM

Double-pass solar air collector with a finned absorber and nano-enhanced PCM in the lower channel is one of the significant and attractive designs proposed to improve the performance. This research paper presents a novel mathematical model of steady-state equilibrium equations created and developed for two air streams: the glass cover, absorber plate, fins, nano-enhanced PCM capsules, and back plate. The influence of various operating parameters on thermal and thermo-hydraulic performance was presented and discussed. The simulations were conducted at air mass flow rates from 0.02 kg/s through 0.06 kg/s and solar irradiance levels ranging from 475 W/m2 to 1000 W/m2. The proposed collector has an optimal energy efficiency of 80%, an exergy efficiency of 18.2% at solar irradiance of 1000 W/m2, and a mass flow rate of 0.06 kg/s. The minimum and maximum improvement potentials for solar irradiance levels of 475–1000 W/m2 at an ambient temperature of 298 K are 163–237 W. The proposed collector's best findings in the current study are 1.0 m in length and a width of roughly 0.3 m for air mass flow rates of 0.02-0.06 kg/s.

Performance Analysis of a Novel Cross-flow Solar Air Heater with Square Perforated Absorber Plate: An Experimental Study

The current study introduces and analyzes a novel square cross-flow perforated solar air heater (SAH). Since the convection mechanism in SAHs is weak, numerous methods have been suggested to address this problem and improve thermal efficiency. Perforations and cross-flow configuration generate high turbulency and, consequently, high convection rate resulted. Hence these methods have been applied to enhance thermal efficiency. To achieve this goal, an experimental setup was fabricated and tested at outdoor conditions for two air mass flow rates (mair) of 0.015 kg/s and 0.03 kg/s while several sensors monitored the collector’s heat dynamics and ambient conditions. The obtained results illustrate that outlet temperature reaches the peak values of 38 oC and 34 oC, which is only 6 oC and 7 oC lower than the maximum absorber temperature. This crucial issue proves a high heat exchange rate in the fabricated SAH that causes the absorber temperature to approach the outlet temperature due to high turbulency. The strong convection mechanism in the fabricated SAH improves daily thermal efficiency, in which its value reaches nearly 78.6% for the mass flow rate of 0.03 kg/s. In conclusion, the square cross-flow perforated SAH is an economy, applicable, compact collector, ensuring high thermal efficiency.

Energetic and parametric studies of a basic hybrid collector (PV/T-Air) and a photovoltaic (PV) module for building applications: Performance analysis under El Jadida weather conditions

The photovoltaic thermal hybrid collectors represent one of the most used technologies in positive energy buildings, the device allows converting the available solar energy into heat and electricity at the same time. In this study, a comparative analysis is introduced between two different types of solar conversion devices: conventional hybrid solar air collector (PV/T-Air) and photovoltaic (PV) module. Also, a parametric study was performed to know the impact of different parameters related to the performance of both solar systems. A numerical system based on the fourth order Runge–Kutta iteration method, is used in this study, founded on a strong coupling between the heat balance equations and the different electrical and thermal parameters of both configurations that are included in this work. The energy performance evaluation was applied to the climatic conditions of El Jadida city, located in Morocco. The numerical results indicates that the estimated value of the daily average overall energy conversion efficiency attains: 30.22% for the PV module, and 52.14% for the examined hybrid air collector (PV/T-Air). These results are calculated with an air mass flow rate of 0.0215 kg/s, and these values are according to the meteorological data collected on the site of El Jadida city for a sunny day in July.

Performance Evaluation of the Solar Air-water Heater Integrated with Triangle Obstacle According to Air and Water Mass Flow Rate

Performance Evaluation of the Solar Air-water Heater Integrated with Triangle Obstacle According to Air and Water Mass Flow Rate

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF A MICRO GAS TURBINE COMBUSTION CHAMBER

Micro gas - turbines (MGT) offer many advantages such as higher thermal efficiency and reduced noise, and are suitable sources for power generation due to their fuel flexibility, small sizes, and high efficiencies. In recent years, there has been an increase interest in developing MGT for transportation platforms such as Range Extender for Electric Vehicle (REEV), Unmanned Ground/Air Vehicles (UGV/UAV), Auxiliary Power Units (APU). For these applications, the MGT must meet essential requirements like reliability, reasonable price, ecological safety, low noise and vibration, multi-fuel, etc. This paper presents the numerical and experimental investigation of a newly designed annular type combustion chamber. This combustion chamber is part of a 40 daN micro gas turbine, destined to equip a small-scale multifunctional airplane. The combustion chamber is equipped with six innovative vaporizers, using Jet-A as fuel, patented by INCDT COMOTI. The experimental installation on which the combustion tests have been performed consists of: the fuel supply system, an air source, the combustion chamber assembly, a chimney for flue gas exhaust. During the combustion chamber testing campaign, the following parameters have been monitored and registered: air mass flow, air temperature, and pressure before the combustion chamber entrance, the temperature at the combustion chamber exit, the temperature before the pressure regulating valve placed on the exhaust pipe. After the testing campaign has been concluded the numerical simulations have been resumed. A three-dimensional RANS numerical integration of the Navier-Stokes equations has been carried out, using an Eddy Dissipation Combustion Model (EDM) and the k-ε turbulence model, implemented in a numerical simulation conducted using the commercial software ANSYS CFX. The computational domain has been modified in order to match the testing rig. Due to the complex geometry of the computational domain, an unstructured type computational grid has been used. The imposed boundary conditions have been changed in order to match the testing conditions and functioning regimes. A kerosene – air two steps reaction mechanism, with NO formation, has been used. The numerical simulation results have been compared with the parameters measured experimentally, thus validating the obtained results.

Impact of combustion chamber wall heat loss on the energy, exergy, ecology, NOx emission based performance and multiobjective optimization of the precooled scimitar engine

In this paper, the impact of the combustion chamber wall heat loss on the performance of the hydrogen-fueled precooled combined cycle Scimitar engine is investigated. Overall and exergy efficiencies, coefficient of ecological performance and coefficient of emission based ecological performance (CEEP) are considered as the performance indicators to analyze the effects of wall heat loss flux, chamber length, chamber contraction area ratio, throat area and nozzle convergent half angle. A multiobjective optimization is carried out to find the optimum values of hydrogen and air mass flow rates, cruise speed and altitude and core nozzle outlet area. It is found that a wall heat loss flux of 10 MW/m2 decreases the overall efficiency by 1.1% and causes an increase of 2 kJ/gNOx in CEEP. Multiobjective optimization revealed that increasing the hydrogen mass flow rate, decreasing the cruise speed and air mass flow rate improve the overall performance while the optimum values of cruise altitude and core nozzle outlet area are 23 km and 4.94 m2, respectively. The optimized design has a 20.35% better emission performance than the base design with a compromise of a 3.38% reduction in the overall efficiency.

Study on thermal performance of a new combined perforated Metallic/Asphalt solar air heater for heating Applications: An experimental study

Using accessible infrastructures and combining different solar air heater types is a novel approach that reduces environmental footprints. The current study investigates a new combined collector, including perforated metallic and asphalt air heaters. The asphalt heater utilizes accessible infrastructures and does not require extra space, while the perforated heater can be integrated with buildings composed of perforated metallic plates. Hence, a combined collector was constructed, and two scenarios were considered for air mass flow rates of 0.0085 kg/s and 0.014 kg/s. The acquired results illustrate that the asphalt heater preheated the flowing air to 61 °C and 58 °C, while the perforated heater continued heating to 85 °C and 76 °C. The asphalt heater started heating with a delay in the morning but continued heating in the afternoon using stored energy during daytime hours; however, the perforated heater started heating right after sunrise and stopped about in the afternoon. During diurnal hours, the asphalt heater gained 51 % of the total heat gain, while the perforated heater gained nearly 49 %. The introduced strategy causes the combined heater operates within a band of 5 % around the peak temperature for a long period, especially in the afternoon, when its efficiency reaches nearly 80 %.

Effect of Channel Size on Air-Cooling Performance in Interior Permanent Magnet Motor Driving Aviation Fans at High Altitude

Abstract To enhance worldwide environmental conditions, the air transport industry must drastically reduce carbon dioxide emissions. Electrification of aircraft propulsion systems is one way to meet this demand. In particular, the focus is on obtaining single-aisle aircraft with partial turbo-electric propulsion and approximately 150 passenger seats by the 2030s. To develop a single-aisle aircraft with partial turbo-electric propulsion, an air-cooled interior permanent magnet (IPM) motor with an output of 2 MW is desired. One of the most difficult problems in air cooling is that air-cooling performance decreases with increasing altitude because the air density decreases. To investigate the effect of altitude on air-cooling performance in the IPM motor, the authors formulated mathematical system equations to describe heat transfer inside the target air-cooled IPM motor, and mathematical analytical solutions were obtained. The most severe condition is the top-of-climb condition. For this condition, a designer should choose cooling air mass flow rates that keep the temperature of the permanent magnets below the maximum temperature limit of 100 °C and the temperature of the coils below the maximum temperature limit of 250 °C. Here, the sizes of the air-cooling channels strongly affect air cooling with the IPM motor. In this paper, the authors briefly review the mathematical formulations and their solutions, investigate the effect of channel size on air-cooling performance in an IPM motor, and explore the optimum configuration and settings for the air cooling channels.

Effect of Mixing on the Anchoring and Combustion Regimes of Pure Hydrogen Flames in Sequential Combustors

Abstract In this work, we perform an experimental study of the combustion of pure hydrogen in the sequential stage of a generic combustor. This academic test rig is a simplified model of an industrial sequential combustor. The sequential fuel is injected using different injector geometries. The composition and temperature of the hot stream at the inlet of the sequential burner are defined by the mass flows of the hot combustion products from the first stage (30 kW natural gas–air flame with equivalence ratio of 0.7) and of the dilution air. This temperature is varied between 1100 K and 850 K by modifying the dilution air mass flow in order to study the different combustion regimes of the sequential hydrogen flame. High-speed imaging of OH radicals chemiluminescence is performed with optical emission spectroscopy to measure vitiated gas temperatures. In particular, we investigate the transition from a flame anchored in the sequential combustion chamber, to the situation where it stabilizes upstream into the mixing section, when the inlet flow temperature is increased. Of particular interest is the increasing rate of formation of auto-ignition kernels in this transition process. The underlying combustion regime change is analyzed with 0D reactor simulations, and the limitations of such a simplified low-order model of the flame location are discussed. The effects and importance of the mixing process between fresh fuel and the hot vitiated coflow are examined. Two different injectors are compared under the same operating conditions that create different flow structures along the mixing section. As a result of that, they provide different degrees of mixing between the hydrogen and the hot vitiated flow and allow to demonstrate the impact of mixing quality on the flame morphology.

Influence of effusion cooling air on the CO production in the primary zone of a pressurized single sector model gas turbine combustor

In this study, the influence of effusion cooling air on the CO production in the primary zone of a pressurized single sector model gas turbine combustor is investigated in a parametric study using a combination of laser-based diagnostics. Three species (OH, CO, CH2O) are probed using laser-induced fluorescence (LIF). In principle, this combination of probed species allows to derive the forward reaction rate of CO oxidation and the local heat release rate from the LIF signals. Based on simulations and measurements in a laminar flame, we show that the limited optical resolution of the intensified cameras severely limits the applicability of the method for pressurized flames. However, by employing a conditioning strategy, mainly using CH2O-LIF as a marker for low temperature chemistry, it was shown that effusion cooling air affects the structure of the premixed flame at large distances from the effusion cooled liner. At higher blowing ratios, samples measured in the primary zone during the CO production phase exhibit a higher CO concentration at a given level of OH concentration. Most likely, this is caused by the strong non-linear sensitivity of OH concentration to temperature, shifting the local equilibrium towards higher CO concentrations, when fractions of the effusion cooling air are recirculated towards the inlet nozzle. In the exhaust phase, dilution effects seem to dominate, as a higher effusion cooling air mass flow systematically lowers both measured OH and CO signals.

Emissions from a Euro 6 engine using polyoxymethylene dimethyl ethers: Chemical effects vs mapping strategy

New fuel technologies, such as electrofuels, are an attractive alternative to meet the energy demand and emission regulations, with sustainable electricity being the primary source of energy. Recently, there is increasing interest in using polyoxymethylene dimethyl ether (OME) as a diesel substitute. This study investigated the effect of a diesel fuel blend with 20% of OME (OME20) with 3–5 oxymethylene groups, on the performance, combustion characteristics, regulated emissions, particle number (PN), and particle size distribution in a compression ignition Euro 6 engine following the Worldwide harmonized Light vehicle Test Cycle (WLTC). Regulated emissions were measured downstream of the aftertreatment system, while PN emissions were measured upstream of the particulate filter. The results showed that OME20 increased the peaks of pressure and heat released rate, causing an increase in the combustion speed compared to diesel. OME20 reduced CO and THC accumulated emissions by 52% and 17%, respectively, and the PN exhibited a dramatic reduction close to 61%. Such reductions were influenced by both the fuel formulation and the engine settings induced by the fuel. With OME20, the engine requires higher fueling to maintain the same power output. Therefore, the accelerator pedal position was higher compared to diesel, leading a decrease in exhaust gas recirculation (EGR) rate to increase the air mass flow. Consequently, PN, CO and THC emissions were reduced, and conversely, accumulated NOx emissions increased up to 42%. OME20 decreased the peak number concentrations of accumulation-mode particles at all driving cycle phases and caused a slight shift of the particles toward smaller size compared to diesel fuel. From the results, it can be concluded that PN and regulated emissions, despite being strongly affected by the fuel properties, are very sensitive to the EGR rate and the equivalence ratio, which are established in the engine mapping.

Pressurised Chemical Looping Combustion (PCLC): Air Reactor design

Bioenergy combustion with Carbon Capture and Storage (BECCS) is a key technology to achieve carbon negative emissions power generation. This can be achieved by coupling the biofuels combustion with CO2 capture and storage (CCS). The lowest cost for CCS corresponds at the moment to the Chemical Looping Combustion (CLC) process. This can use biofuels which can be gaseous (biomethane, biogas or syngas etc.), liquid (biodiesel, bioethanol, biobutanol and pyrolysis oils etc.) or solids (wood dust, charcoal dust, wood chips, wood pellets etc.) While plant design with gaseous and liquid biofuels would be simpler, plants using solid biofuels and based on two couple fluidisd beds would need the use of a third reactor named carbon stripper. In the specific case if we plan to couple a CLC plant with a turbo expander (to achieve the high efficiencies of a combined cycle power plant) we have to work with pressurized reactors. However, there are some technical barriers to the coupling of a chemical looping combustor with a turbo expander, such as: the operation of the combustor in pressurised conditions; the inventory balance among reactors; elutriated particles reaching the turbo expander. This explaind why there is no commercial plant at the moment capable to do this. The aim of this paper is to present a model for the dimensioning of an air reactor to be coupled to a turbo expander of the power of about 12 MWe. Based on this, the air mass flow can be obtained and the geometric parameters can be calculated, to have an air velocity which is needed to achieve the fast fluidization regime and to ensure a high conversion rate as well as particles and heat exchage among air and fuel reactor.

A low‐energy approach to processing large‐scale airflow

AbstractA simplified solar updraft device adapted from the Trombe wall concept was built to process large‐scale airflow using only solar energy. The performances were systematically studied using experimental measurements and numerical models, with the focus of investigating whether this device can generate enough airflow under low solar intensities, and developing a fast‐analytical mathematical model to effectively and efficiently find design rules for further application. The experimental results prove that the air mass flow rate generated by solar updraft in a 0.9 m2 solar updraft device can be as high as 75.6 kg/h when the solar radiation is only 120 W/m2. A comparison of two numerical models shows that it is feasible to develop a fast‐analytical tool based on widely available MATLAB with low demand for computing resources and to provide guidance on how a future device should be designed for particular applications. The study also investigated the effects of a wider range of solar radiation intensities, air channel height and thickness on the updraft performances (e.g., air temperature, airflow velocity, and mass flow rate).

ACAES systems to enhance the self-consumption rate of renewable electricity in sustainable energy communities

This paper aims to evaluate the optimal configuration of an Adiabatic Compressed Air Energy Storage (ACAES) system designed to achieve the best matching between power production from non-programmable Renewable Energy Sources (RES) power plants and power demand from final users. The electrical energy demand of a small town, with a maximum power load of about 10 MW, has been considered as case study. The electrical energy can be supplied by both a photovoltaic (PV) power plant and the grid. For the ACAES system, different sizes for compressor, turbine, thermal energy storage (TES) system and air storage reservoir have been evaluated by varying the air mass flow rate of turbomachines and the charging and discharging duration times, to enhance the share of the PV energy supplied to the end user. The best performance is achieved with a PV power plant rated at about 35 MW and an ACAES section characterized by a compressor/turbine rated power of about 25-35% of the maximum power load of the end user, with a charging time of about 10 hours and a discharging time of about 20 hours. The average round-trip efficiency of the ACAES system is around 70%. On the overall, the integrated PV-ACAES system allows to cover 66% of the yearly electrical energy demand.

Design and partial-load operation of a reversible Solid Oxide Cell system with molten salts thermal storage

The increasing penetration of renewable energy sources in the electricity mix requires efficient storage solutions on the seasonal scale. Reversible Solid Oxide Cell (rSOC) systems are receiving increased attention as viable options to fulfil this requirement. In this work, a MW-scale rSOC system capable of working over a large operating window is studied via modelling on Aspen Plus®. To ease the thermal integration, a molten salt thermal storage is coupled to the system, enabling heat recovery in fuel cell mode, which is then exploited for water evaporation in electrolysis mode. The rSOC stack is designed to operate exothermically in the electrolysis mode at nominal load. In both modalities, the air mass flow rate is regulated to control the stack temperature, while limiting the in-out gradients within 100°C. At nominal load, the system achieves an electrical efficiency of 52% in fuel cell mode and of 87% in electrolysis mode. The operation at low partial loads, due to the decrease of the air flow rate, requires an additional high-temperature heat source to guarantee the heat integration. In this regard, the adoption of an electrical resistance in electrolysis mode and a hydrogen-fed combustor in fuel cell mode are selected as viable solutions to amplify the operating range of the system. As a results, the system can be operated down to the 30% of the stack nominal power in both modalities, where the system achieves an electric efficiency of 44% and 80% in fuel cell and electrolysis mode, respectively.

Effects of Cooled Exhaust Gas Recirculation Combined With Prechamber Jet Ignition on the Combustion Characteristics in a Kerosene-Fueled Spark Ignition Engine

Abstract For security and logistical convenience, the single fuel forward policy hopes to use a single kerosene fuel to replace a variety of military fuels, especially the unsafe gasoline. However, the performance of kerosene-fueled spark ignition (SI) engines is severely restricted by knock, slow combustion rate, and poor combustion stability. This work innovatively applies cooled exhaust gas recirculation (EGR) combined with prechamber jet ignition (PJI) to a kerosene-fueled engine to suppress knock and improve performance. The results show that applying cooled EGR at a fixed throttle opening can suppress knock and improve fuel economy. However, the power decreased due to the decreased intake of energy. While applying EGR with constant fresh air mass flow makes the knock more prominent because of the microboosting effect caused by the increased throttle opening. This indicates that cooled EGR alone cannot improve the power output. Moreover, combustion instability was also caused due to the slower combustion rate. Therefore, PJI was introduced to compensate for the negative impact of EGR. As a result, a synergistic effect of cooled EGR and PJI was discovered, improving the IMEP by 5% and reducing the ISFC by 4.9% compared to the baseline. The PJI can shorten the combustion duration and improve the combustion stability because of the high kinetic energy jet and high turbulence flame. In addition, a novel two-stage heat release process which includes the unusual first-stage low-temperature heat release was discovered. Overall, EGR dominates the knock suppression, and PJI contributes to the combustion rate improvement.

Thermo-hydraulic performance of solar air heater with finned absorber plate forming multiple rectangular air flow passages in parallel under laminar flow conditions

The paper presents results of an analysis carried out using the governing equations to compare the heat transfer performance of a uniformly heated flat plate with longitudinal fins, which form multiple rectangular air flow passages in parallel below the plate and cover whole of the passage surface, with that of the low aspect ratio rectangular duct typical of conventional flat plate solar air heater at equal pumping power under laminar flow conditions. The heat transfer rate at equal pumping power for the plate with 1 mm thick steel fins at pitch of 25 mm and 40 mm is found to be about 2.7 and 2.5 times, respectively, over the duct without fins. The heat transfer study is followed by thermo-hydraulic performance study of the solar air heater with absorber plate having longitudinal fins forming multiple rectangular air flow passages in parallel. The finned solar air heater with low air mass flow rates has been found to provide 28–31 % better thermal efficiency than the conventional solar air heater at equal pumping power. The results of the study can be utilized for the development of enhanced performance finned solar air heater operating with low air mass rates to deliver high temperature air.

Rotating Detonations in Hollow and Flow-Through Combustors

This paper focuses on rotating detonation combustor (RDC) experiments involving two configurations, a hollow and flow-through RDC, using hydrogen–air and ethylene–air mixtures. Two air injection areas with gaps of 1.778 and 3.81 mm were used at different air mass flow rates of 0.2, 0.3, 0.4, and 0.5 kg/s and equivalence ratios from 0.6 to 2 in 0.2 increments. Results show repeatable detonations for hydrogen–air mixtures in both configurations; however, the detonative range is wider, stronger, and faster in the hollow configuration. Speeds exceeding the Chapman–Jouguet velocity and pressures matching the ideal model were observed. Sustained detonations for ethylene–air mixtures were not attained with the flow-through configuration. Installing a back plate to convert the configuration into a hollow combustor promoted rotating detonations with the ethylene–air mixture at select operating points. The results of this study showcase the strong promise of producing and sustaining rotating detonation in nonannular RDC configurations.

Optimizing model parameters of artificial neural networks to predict vehicle emissions

This paper presents a novel approach to predict carbon dioxide (CO2), nitrogen oxides (NOx), and carbon monoxide (CO) emissions of diesel vehicles using artificial neural network (ANN), which offer high degrees of accuracy and practicality. Six operating parameters (velocity, engine speed, engine torque, engine coolant temperature, fuel/air ratio, and intake air mass flow) collected through on-board diagnostic interface were used as predictors of exhaust emissions. The importance of each parameter to the emission predictions were comprehensively analyzed by comparing the coefficient of determination, root mean square error, cumulative emissions, and instantaneous emission rates. The emission prediction accuracy of ANN tends to increase as more parameters were considered as model inputs at the same time. However, the level of accuracy improvement depends on the input parameters. For CO2 emissions, engine torque and fuel/air ratio were good predictors for achieving high prediction accuracy. The relative importance of intake air mass flow rate and fuel/air ratio was high for NOx and CO predictions, respectively. In addition, the emission prediction accuracy of ANN depends on the vehicle type (Euro 5, Euro 6b, Euro 6d-temp). The emission prediction accuracy of vehicles equipped with after-treatment devices (selective catalytic reduction and lean NOx trap) was lower than that of vehicles without after-treatment devices.

Rainwater chemistry composition in Bellsund: Sources of elements and deposition discrepancies in the coastal area (SW Spitsbergen, Svalbard)

Discrepancies in rainfall chemistry in Bellsund were found to be influenced by the orographic barrier and related to the variability in the inflow of air masses as well as to the distance of sampling sites from the sea and thus the extent of sea spray impact. This study covers measurements of rainfall (P) and air temperature (T), physicochemical parameters (pH, specific electrolytic conductivity (SEC), major ions (Cl−, NO3−, SO42−) and elements (Na, Ca, Mg,K), as well as trace elements (i.a. As, Cd, Cr, Fe, Co, Pb, Ni, Zn) and dissolved organic carbon (DOC) in 22 rainfall samples collected in August on the Calypsostranda marine terrace and in the forefield of a land-terminating glacier (NW Wedel Jarlsberg Land). The comparison of chemical parameters in the samples revealed major discrepancies, including statistically significant higher rainwater pH and SEC, and the levels of Ag, As, Bi, Ca, Co, Fe, Li, Mn, Mo, Ni, Pb, Sb, and V, deposited near the seashore (Calypsostranda) than in the glacier forefield. Cluster analysis (CA) showed that elements deposited in lower concentrations at the glacier forefield site came from predominately anthropogenic sources. Conversely, CA results of metals and metalloids deposited on the Calypsostranda marine terrace indicate both natural and anthropogenic sources. A correlation matrix and principal component analysis (PCA) permitted identifying two primary factors affecting rainfall chemistry at each of the study sites. In Calypsostranda, these were the inflow of relatively unpolluted cold air (F1 = 35.1%) and sea spray (F2 = 27.6%), while in the glacier forefield the factors were an orographic barrier (F1 = 37.3%) and the inflow of polluted warm air (F2 = 25.2%).