Air Mixing Research Articles

Fuel mixing enhancement of transverse coaxial air and fuel jet by upstream shock wave on in scramjet engines: numerical study

In this study, computational fluid dynamics (CFD) is used to disclose the impacts of upstream shock waves on fuel mixing of cross coaxial air and fuel jet at a scramjet engine. This study has tried to investigate the impact of three different lobe injectors (2-lobe, 3-lobe, and 4-lobe nozzle) on the fuel penetrations along the scramjet combustor. The supersonic air stream is M = 4 while cross hydrogen and air jet are released in sonic velocity. This study uses CFD simulations to analyze the effects of upstream shock waves on fuel mixing in the transverse coaxial jet and assess their potential for improving combustion efficiency. The results demonstrate that the usage of upstream shock waves significantly increases shock interactions and augments the vortex region downstream of the jet. Our results show that the impacts of shock waves on the penetration of fuel jet released from the coaxial lobe nozzle are substantial.

BIM and Computational Fluid Dynamics Analysis for Thermal Management Improvement in Data Centres

One of the most energy-intensive facilities requiring a comprehensive and well-optimised cooling system is the data centre. Air containment across the data centre is a key thermal management and energy-saving strategy that enhances the performance of data centres. The majority of modern energy-efficient data centres use some type of air containment. The primary advantage of aisle separation and containment is the decrease in the air temperature at the server inlet by reducing the mixing of hot air with cold air. In order to ascertain the volume of literature relating to corridor insulation, we conducted a literature review. Currently, there have been numerous articles regarding the application of computational fluid dynamics (CFD) analysis, however, publications delineating the integration of building information modelling (BIM) principles for corridor separation are still limited. Research specifically targeting data centre corridor insulation is somewhat limited. As a result of this analysis, the most common methods used to isolate hot or cold aisles within a data centre were identified. To determine the most effective type of corridor insulation, the BIM family was created in Autodesk Revit. The model includes 15 telecom cabinets containing information technology (IT) equipment, eight inter-row air conditioners, and one UPS. The model was used for the CFD analysis of the air temperature in different zones of the room. Visualisation of the results using gradient temperature distributions at different levels provides a complete picture of the microclimate formation in the room and allowed the advantage of the hot aisle isolation scheme to be demonstrated.

An Experimental Investigation On Converting Conventional to Supercharged CI Engine

Due to the increase in grounds performance of internal combustion engines, the diesel engine has become dominant forces in the power, propulsion, and energy. For domestic, industrial, and transportation applications, internal combustion engines are the more reliable and misogynist power source. Diesel engines rely on fluid Spritz dynamics for air-fuel mixtures and swirl plays a crucial role in the pattern of air motion as impacts fuel air mixing and combustion. Further-more, older studies have indicated that it affects heat transfer, combustion efficiency, and engine emissions. By varying air inlet pressure, this work demonstrates the presentation and production features of Compression Ignition engines. Using compressor, the inlet pressure of air is manipulated, and when compressed air is sent to engine at different pressures, performance parameters and heat balance sheets are calculated.

Nighttime ozone in the lower boundary layer: insights from 3-year tower-based measurements in South China and regional air quality modeling

Abstract. Nighttime ozone in the lower boundary layer regulates atmospheric chemistry and surface ozone air quality, but our understanding of its vertical structure and impact is largely limited by the extreme sparsity of direct measurements. Here we present 3-year (2017–2019) measurements of ozone in the lower boundary layer (up to 500 m) from the Canton Tower in Guangzhou, the core megacity in South China, and interpret the measurements with a 1-month high-resolution chemical simulation from the Community Multiscale Air Quality (CMAQ) model. Measurements are available at 10, 118, 168, and 488 m, with the highest (488 m) measurement platform higher than the typical height of the nighttime stable boundary layer that allows direct measurements of ozone in the nighttime residual layer (RL). We find that ozone increases with altitude in the lower boundary layer throughout the day, with a vertical ozone gradient between the 10 and 488 m heights (ΔO3/ΔH10–488 m) of 3.6–6.4 ppbv hm−1 in nighttime and 4.4–5.8 ppbv hm−1 in daytime. We identify a high ozone residual ratio, defined as the ratio of ozone concentration averaged over nighttime to that in the afternoon (14:00–17:00 LT), of 69 %–90 % in January, April, and October, remarkably higher than that in the other three layers (29 %–51 %). Ozone in the afternoon convective mixing layer provides the source of ozone in the RL, and strong temperature inversion facilitates the ability of RL to store ozone from the daytime convective mixing layer. The tower-based measurement also indicates that the nighttime surface Ox (Ox= O3+NO2) level can be an effective indicator of RL ozone if direct measurement is not available. We further find significant influences of nocturnal RL ozone on both the nighttime and the following day's daytime surface ozone air quality. During the surface nighttime ozone enhancement (NOE) event, we observe a significant decrease in ozone and an increase in NO2 and CO at the 488 m height, in contrast to their changes at the surface, a typical feature of enhanced vertical mixing. The enhanced vertical mixing leads to an NOE event by introducing ozone-rich and NOx-poor air into the RL to enter the nighttime stable boundary layer. The CMAQ model simulations also demonstrate an enhanced positive contribution of vertical diffusion (ΔVDIF) to ozone at the 10 and 118 m heights and a negative contribution at the 168 and 488 m heights during the NOE event. We also observe a strong correlation between nighttime RL ozone and the following day's surface maximum daily 8 h average (MDA8) ozone. This is tied to enhanced vertical mixing with the collapse of nighttime RL and the development of a convective mixing layer, which is supported by the CMAQ diagnosis of the ozone budget, suggesting that the mixing of ozone-rich air from nighttime RL downward to the surface via the entrainment is an important mechanism for aggravating ozone pollution the following day. We find that the bias in CMAQ-simulated surface MDA8 ozone the following day shows a strong correlation coefficient (r= 0.74) with the bias in nighttime ozone in the RL, highlighting the necessity to correct air quality model bias in the nighttime RL ozone for accurate prediction of daytime ozone. Our study thus highlights the value of long-term tower-based measurements for understanding the coupling between nighttime ozone in the RL, surface ozone air quality, and boundary layer dynamics.

A modified decay method based on a proposed uniformity index for measuring air change rates in non-uniform air mixed spaces

Building ventilation is essential during COVID-19 to reduce airborne viral transmission risks, while accurately estimating air change rates remains quite challenging. Due to the tracer gas method's assumption of uniform air mixing in a space, which is often not the case. However, the existing mixing models such as mixing factor (K) and zone distribution effectiveness (Ez) are limited to decrease the uncertainty of this assumption since their reported data are subjective, rough estimates, and inconsistent across different standards (e.g., ASHRAE and AIHA). Therefore, in this study, a novel modified decay method (MDM) is developed, where a proposed uniformity index (Ui) is integrated into the original decay method (ODM) to quantify the non-uniform air mixing and thereby improve the estimation of air change rates. We validated the proposed method in a real classroom using CO2 as a tracer gas. Wherein, the spatial variations of CO2 concentrations were measured at various locations using an automated system of a mass spectrometer with a 16-position valve. Later, the estimated air change rates using both the ODM and MDM were compared with the measured ones. It was found that the proposed Ui significantly decreased the error caused by the uniform-mixing assumption of estimated air change rates using ODM from 25.6 % to 3.4 % estimated by MDM at the outlet location. Similarly, the average concentrations of 16 distributed sensors at the breathing level also showed a decrease in error from 25.0 % to 2.5 %. This study can be applied to improve ventilation performance in buildings.

Positive Low Cloud Feedback Primarily Caused by Increasing Longwave Radiation From the Sea Surface in Two Versions of a Climate Model

AbstractLow cloud feedback in global warming projections by climate models is characterized by its positive sign, the mechanism of which is not well understood. Here we propose that the positive sign is primarily caused by the increase in upward longwave radiation from the sea surface. We devise numerical experiments that enable separation of the feedback into components coming from physically distinct causes. Results of these experiments with a climate model indicate that increases in upward longwave radiation from the sea surface cause warming and absolute drying in the boundary layer, leading to the positive low cloud feedback. The absolute drying results from decrease in surface evaporation, and also from decrease in inversion strength which enhances vertical mixing of drier free tropospheric air into the boundary layer. This mechanism is different from previously proposed understanding that positive low cloud feedback is caused by increases in surface evaporation or vertical moisture contrast.

Developing characteristics of subsonic-supersonic shear layers induced by different lobed mixers in the RBCC

The rapid mixing of air and rocket gas is pivotal for enhancing combustion performance in the ejector mode of rocket-based combined-cycle engines. This study experimentally investigated developing characteristics of subsonic-supersonic shear layers induced by sinusoidal- and rectangular-lobed mixers using a subsonic-supersonic shear layer experimental system and an ice-cluster-based planar laser scattering technique. Both sinusoidal- and rectangular-lobed mixers evidently bolstered mixing through the promotion of transverse flow and vortex interactions. Under equivalent conditions, the sinusoidal-lobed mixer offered superior mixing effects. The mixing enhancement of a sinusoidal-lobed mixer exhibited a positive correlation with the wavelength, with excessively small wavelengths potentially impeding mixing. Based on the dimensionless wavelength ratio, a criterion was identified for evaluating the mixing enhancement of the sinusoidal-lobed mixer: a positive mixing enhancement occurred when the dimensionless wavelength ratio was at least 1. Notably, in this study, the shear layer thickness growth rate increased by 12 % when the dimensionless wavelength ratio was 1.905. These findings can offer valuable insights for improving combustion performance via enhanced mixing.

Enhancing indoor air quality and thermal comfort in indoor swimming pool facilities: investigating the impact of ventilation system configurations

This study focuses on enhancing indoor air quality and thermal comfort in indoor swimming pool facilities through the investigation of ventilation system configurations. Creating a comfortable and healthy environment in these facilities is crucial for the well-being of occupants and overall operational efficiency. The performance of the ventilation system significantly influences user comfort, energy consumption, and air quality. This research aims to analyze the impact of different ventilation system configurations on indoor air quality and thermal comfort parameters using computational fluid dynamics (CFD) simulations.To achieve the research objectives, CFD simulations were conducted using ANSYS Fluent ®, a widely used commercial CFD package. The simulations involved solving the governing equations for continuity, momentum, energy, and species transport, along with employing the k-epsilon turbulence closure model. A high-resolution mesh with over 5.6 million elements accurately captured the flow regimes and related phenomena.The study investigated various aspects of ventilation system configurations, including the placement and design of inlets and outlets, airflow rates, and distribution patterns. Evaluations were made based on key performance indicators such as indoor air quality parameters, thermal comfort indices, and energy efficiency metrics. Comparisons were made between different configurations to identify the most effective strategies for enhancing indoor air quality and thermal comfort.The findings of the study demonstrate the importance of ventilation system design in achieving optimal indoor air quality and thermal comfort in indoor swimming pool facilities. The results indicate that specific configuration choices, such as the use of circular inlets in the ceiling for improved spectator comfort and rectangular inlets in the side walls for better performance in the swimming pool area, can significantly impact thermal conditions and air distribution. Additionally, the study emphasizes the need for appropriate inlet grille height to ensure adequate air mixing and thermal comfort.The outcomes of this research provide valuable insights for architects, engineers, and facility managers involved in the design, construction, and operation of indoor swimming pool facilities. By understanding the impact of different ventilation system configurations, stakeholders can make informed decisions to optimize indoor air quality, thermal comfort, and energy efficiency. Ultimately, this research contributes to the development of sustainable and comfortable indoor swimming pool environments that cater to the needs of occupants and enhance their overall experience.

One dimensional approach to predict the performance of high pressure multi-stage axial turbine considering air cooling and diffuser performance

This paper provides an improved 1D mid-span program to quickly grasp the off-design characteristic of modern axial turbines. The improvements are mainly focused on cooling, diffuser and the calculation of choke condition. Disk cooling and blade cooling air mixing are considered in detail. A 1D diffuser model that considers the effects of area change, heat transfer, and friction is added so that a realistic boundary condition at the turbine outlet can be obtained. A choke routine that enables the assessment of choked flow up to limit load conditions is introduced to avoid the shortcoming that the calculation method fails to converge near or at the initial choking mass flow rate. Flexible modules for losses, deviation, and mixing models are built-in to increase the accuracy and versatility of the program. This work is of great value because few programs take cooling and diffuser into account in such detail when calculating turbine performance in the form of maps. The salient issues presented here deal first with the construction of the turbine performance prediction program. The validation of the code is first performed on public data for a five-stage low pressure turbine (LPT). The results show that the efficiency relative errors with the experimental value is in the range of −(0.11%−1.64%), which is within acceptable limits. Then, the performance of GE PG9351FA transonic axial turbine is estimated using this program. This industrial axial turbine is predicted for the first time in a form of turbine performance maps in open literature and the obtained performance map is very useful for the simulation of gas turbine.

Assessment of a hydrogen-fueled swirling trapped-vortex combustor using large-eddy simulation

In recent years, the study of hydrogen combustion has gained significant interest due to its exceptional lean blow-out (LBO) performance, high efficiencies, and almost negligible greenhouse gas emissions. The present study combines the advantages of hydrogen combustion with the beneficial characteristics of trapped-vortex combustion (TVC) and swirling flows. Large-eddy simulation (LES) is conducted to evaluate the performance of a swirling trapped-vortex combustor. LES sub-gird terms are described using k-equation subgrid model, while, turbulence-combustion interaction is modelled employing the PaSR (Partially Stirred Reactor) closure with a detailed 23-step chemical reaction mechanism for hydrogen/air. A radial vane swirler is incorporated to supply an annular mainstream and generate a wake region in front of the cavity leading edge to enhance cavity flow entrainment. To evaluate the performance of a hydrogen-fueled TVC under non-swirl and swirling conditions with varying swirl numbers (0.1–0.6), several flow and combustion characteristics are analyzed. These includes temperature distribution, vortical structure, combustion efficiency, NO emission, and flame shape. The results show that a large recirculation zone dominates the cavity for the all swirl numbers resulting in a strong fuel–air mixing and high combustion efficiency. It is demonstrated that the swirling motion effectively mitigates the negative impacts of pressure fluctuations arising from the interaction of combustion with cavity oscillations. A stable flame is observed inside the cavity and in the shear layer at the cavity lip in all cases, merging to form a distinctive C-shaped flame. Increasing the swirl number causes the second part of the flame to move to the wake region before the leading edge, enhancing combustion stability and efficiency. Combustion efficiency exceeds 98.5% for all cases, reaching 99.8% for a swirl number of 0.6. The temperature distribution is nearly uniform inside the cavity, with an improved distribution at the TVC’s outlet for higher swirl numbers. Under non-swirling conditions, the corrected NO concentration is below 5 ppm. Increasing the swirl number escalates the outlet NO emission, nevertheless, a maximum NO concentration of 19 ppm is observed for the swirling cases. Comparing these findings with existing data suggests that the swirling TVC offers advantages over other hydrogen-fired TVC’s.

Opposite Changes in Monsoon Precipitation and Low Pressure System Frequency in Response to Orographic Forcing

Abstract Monsoon low pressure systems (LPS) are synoptic-scale disturbances that form along the quasi-stationary trough of the larger-scale South Asian summer monsoon, producing a large fraction of total monsoon precipitation. Here, we use an Earth system model to investigate the influence of Tibetan and Himalayan orography (THO) on mean monsoon strength and LPS activity. The influence of THO height on LPS activity has not been investigated before. The model simulates decreased mean monsoon circulation and precipitation when THO is removed, but the number of LPS and the meridional extent of LPS activity increase; this is an unexpected, important finding given that LPS are principal rain-bearing systems of the monsoon. The decreased mean monsoon circulation and precipitation on removal of THO are attributed to enhanced mixing of dry extratropical air into the humid monsoon domain, as demonstrated by prior studies. The increase in LPS frequency and the meridional extent of LPS activity is attributed to the increase in magnitude and meridional extent of the low-level meridional shear of zonal wind, which previous work showed amplifies LPS through barotropic growth. Specifically, as monsoon precipitation decreases, the sensible heat-driven low-level trough intensifies and shifts equatorward; this strengthens the shear zone in which LPS grow. Conversely, increasing THO height decreases the magnitude and meridional extent of cyclonic shear over India, decreasing LPS frequency and the spatial extent of LPS activity while increasing total monsoon precipitation. These results demonstrate that LPS activity and total monsoon rainfall can undergo large, opposing changes in response to imposed forcings. Significance Statement Monsoon low pressure systems (LPS) are propagating atmospheric vortices that deliver a large fraction of seasonal-mean precipitation to agricultural regions of India. The influence of Tibetan and Himalayan orography (THO) on the South Asian monsoon is an active area of research, but its effect on LPS has remained unexplored. Here, a global climate model is used to simulate LPS characteristics for different heights of THO. Flattening the THO reduces total summer monsoon precipitation but increases the number of LPS and the spatial extent of LPS activity. We attribute these LPS changes to a decrease in the magnitude and meridional extent of the hydrodynamically unstable low-level cyclonic shear zone over South Asia that occurs when orography is flattened.

Investigations of the effects of two typical jet crushing methods on the atomization and dust reduction performance of nozzles

Single-fluid nozzles and dual-fluid nozzles are the two typical jet crushing methods used in spray dust reduction. To distinguish the atomization mechanism of single-fluid and dual-fluid nozzles and improve dust control efficiency at the coal mining faces, the atomization characteristics and dust reduction performance of the two nozzles were quantitatively compared. Results of experiments show that, as water supply pressure increased, the atomization angle of the swirl pressure nozzle reaches a maximum of 62° at 6 MPa and then decreases, but its droplet size shows an opposite trend with a minimum of 41.7 μm. The water supply pressure helps to improve the droplet size and the atomization angle of the internal mixing air–liquid nozzle, while the air supply pressure has a suppressive effect for them. When the water supply pressure is 0.2 MPa and the air supply pressure reaches 0.4 MPa, the nozzle obtains the smallest droplet size which is 10% smaller than the swirl pressure nozzle. Combined with the dust reduction experimental results, when the water consumption at the working surface is not limited, using the swirl pressure nozzle will achieve a better dust reduction effect. However, the internal mixing air–liquid nozzle can achieve better and more economical dust reduction performance in working environments where water consumption is limited.

A CFD-Based Design of S-Shaped Nozzle Attachment for Aircraft Cabin Gaspers

Cough has been the primary mode for transmitting airborne respiratory diseases as the droplets expelled are suspended in the air longer in closed environments like aircraft cabins. Air jets from personal gasper nozzles are studied using computational fluid dynamics (CFD) simulations to understand the flow pattern, which is of high velocity, very narrow, and susceptible to enhanced air mixing. An S-shaped nozzle attachment uses higher-order Bezier curves to spread the flow across the passenger’s face to form a shield to protect the breathing zone from foreign particles. The design of experiments theory, the Box – Behnken design, was employed to understand the influence of nozzle profile geometric parameters on the output criteria through CFD simulations. The numerical simulations were performed on the final design, which shows that the newly designed nozzle attachment can distribute the narrow jet from existing personal gasper nozzles into a curved air curtain across the passenger’s face.

Effect of Diesel Injection Strategy and Ammonia Energy Fraction on Ammonia-Diesel Premixed-Charge Compression Ignition Combustion and Emissions

The utilization of ammonia as a fuel is one of the effective measures to achieve decarbonization and carbon neutrality in internal combustion engines (ICEs). However, its slow laminar flame speed and high ignition energy limit the efficient application of ammonia-only in ICEs. In this study, based on a heavy-duty single-cylinder engine, the impact of ammonia energy fraction (AEF), start of diesel injection (SODI) timing, and diesel injection pressure (DIP) on combustion and emission characteristics of premixed-charge compression ignition mode under low load conditions was investigated. Combined with three-dimensional simulation, the mechanism of how AEF and diesel injection strategy regulation affected the in-cylinder equivalence ratio and reactivity distribution was analyzed. It was found that increasing the AEF and advancing the SODI timing can improve the homogeneity of mixture. However, the spatial distribution of the OH groups deteriorate continuously. Experimental results indicated that with the used of 50% AEF, 60 MPa DIP, and injecting diesel at −40°CA ATDC, a gross indicated thermal efficiency (ITEg) of 49.7% can be achieved. Compared to the diesel-only mode, the greenhouse gas (GHG) emissions reduced by 44%. To further improve the combustion of ammonia/diesel PCCI mode, the DIP was increased to 100 MPa, which optimized the in-cylinder fuel–air mixing process, improving the homogeneity of the mixture and enhancing the reactivity distribution before the ignition, and enabling faster combustion. As a result, an increase in ITEg to 51.4% with using 100 MPa DIP was achieved, and reduced the GHG emissions by 51% compared to the diesel-only mode.

Cyclic Analysis of In-Cylinder Vortex Interactions Based on Data-Driven Detection and Characterization Framework

Abstract The complex vortex flow interactions are critical to affect the fuel–air mixing and combustion stability in direct-injection engine. However, due to the strong cyclic variations inside engine, the multiscale swirl flow characteristics with cyclic details are difficult to be sufficiently revealed. Therefore, a vortex detection and characterization framework, including physical and data-driven methods, is implemented to elucidate the cyclic vortex interaction process. In this study, a high-speed time-resolved particle image velocimetry is applied to record the spatiotemporal flow behavior under three different swirl ratio conditions. First, the presence of vortex motion is detected at each crank angle for each engine cycle. Results show that the vortex interaction processes under different swirl ratio conditions exhibit distinctive characteristics. The presence of multiple vortices and their interactions are found to trigger dramatic changes and variations in swirl flow behavior. Then, the individual-cycle analysis of the vortex interaction effects on flow characteristics is conducted. The vortex characteristics including vortex location, strength, and size are examined with cyclic detail using data-driven unsupervised clustering. Results indicate that the vortex merging is the main source inducing the vortex characteristics variations. Furthermore, the occurrence and duration of the vortex merging process are found to be closely related to the intake swirl ratio and valve lift profile. Increased swirl ratio and valve lift cause vortex to merge earlier and reduce the merging duration. This finding provides a potential idea to alleviate the cyclic variation issue by controlling the vortex merging process.

Combustion characteristics of a dual-mode ramjet engine with a supersonic aerodynamic ramp injector

The combustion characteristics of a liquid-hydrocarbon-fueled dual-mode ramjet combustor with a new injector, including a cavity-type flame holder, were investigated under inflow conditions of M 1.8, total pressure of 590 kPa, and total temperature of 930 K. The newly proposed injector uses various injection methods, such as an aerodynamic ramp, pre-mixing chamber, barbotage gas, and supersonic nozzle. The aerodynamic ramp injection method consists of four injectors with inclination angles of 40° and 80° and toe-in angles of 30° and 60°. This was adopted to increase the penetration height of the fuel while minimizing the total pressure loss. A pre-mixing chamber with a barbotage gas injection device was employed to enhance atomization and fuel–air mixing. In addition, a contoured Mach 3 supersonic nozzle was used to obtain a higher momentum through acceleration. For performance comparison, a combustor with a pre-mixing chamber and barbotage gas was used in the same manner, but injected by a cylindrical nozzle with a 15-degree of transverse angle. The ignition was initiated by a torch ignitor installed on the cavity floor with hydrogen pilot fuel. Once combustion stabilized, only the main liquid fuel was supplied. The Mach number was calculated using quasi-one-dimensional analysis based on the measured wall pressures and inlet conditions. The results showed that the model combustor with two types of injectors operated in the ramjet mode, which was subsonic near the flame holder and supersonic at the exit of the combustor. At the combustor outlet, the total pressure according to the equivalence ratio of 0.25 to 0.56, the newly proposed injector case showed a higher pressure level, steep increase, and more uniform pressure distribution than the baseline injector from the measurement result of the pitot pressure rake at the combustor exit.

Experimental and Numerical Dynamic Investigation of a Swirling Jet: Application to Improve the Efficiency of Air Diffusion in an Occupied Zone

When reducing the energy prerequisites of buildings, the correct distribution of fresh air flows injected into the living rooms poses a problem. If the problem of mixing the injected air in the ambient air is not effectively solved, there will be a strong deterioration in air quality and comfort. In this research, a new design of swirling diffuser is investigated experimentally and numerically using large eddy simulations. The influence of fins is studied for the improvement of air diffusion and jet mixing with ambient air. The study was carried out for a fins angle of 30° with the jet's axis and 60° with the blowing orifice's plane with the condition of uniform heat flux of the air. The working fluid used is air. It has been validated that using fins leads to a greater spreading of the jet and good air mixing compared to those obtained from smooth tubes (circular nozzle). To enhance the accuracy of the turbulence models' predictions, three turbulence models are tested: the wall-adapting local eddy-viscosity turbulence model (LES/WALEVM), Smagorinski-Lilly (LES/S-LM) model and the kinetic-energy transport model (LES/K-ETM). It is worth highlighting that the LES/K-ETM model is well established in the prediction of swirling flows, which have been successfully compared with experimental results.

An Experimental Study omn Evaporative Condenser in Air Conditioning Systems Using R744

Nowadays, the use of refrigerants has low GWP and zero ODP applying refrigeration and air conditioning systems is an important concern. There has been a lot of research taking about refrigeration systems using R744. In this study, we focus on the use of the mix of water and air for an evaporative condenser through an experiment to study the heat transfer efficiency between water and the R744. The results of this study show that it is feasible to use water to cool down R744 to a subcritical state. The data obtained show that the R744 temperature at the outlet condenser gradually decreases with each change in the number of tube layers, the condensing pressure is stable at 73 bar with a pressure drop of 0.4 bar. The water temperature is stable between 26oC and 28oC, and the air outlet temperature from the indoor unit gradually decreases from 28oC to 16.8oC. With the 3 configurations of the condenser, the coefficient of performance gradually increases from 3.6 to 4.5 respectively.

Efficacy of green infrastructure in reducing exposure to local, traffic-related sources of airborne particulate matter (PM)

One aim of roadside green infrastructure (GI) is to mitigate exposure to local, traffic-generated pollutants. Here, we determine the efficacy of roadside GI in improving local air quality through the deposition and/or dispersion of airborne particulate matter (PM). PM was collected on both pumped air filters and on the leaves of a recently installed ‘tredge’ (trees managed as a head-high hedge) at an open road environment next to a primary school in Manchester, U.K. The magnetic properties of PM deposited on leaves and filters (size fractions PM10 and PM2.5) were deduced from hysteresis loops, first-order reversal curves (FORCs), and low-temperature remanence measurements. These were complemented with electron microscopy to identify changes in magnetic PM concentration downwind of the tredge/GI. We show that the tredge is permeable to airflow using a simple CO2 tracer experiment; hence, it allows interception and subsequent deposition of PM on its leaves. Magnetic loadings per m3 of air from filters (PM10 saturation magnetisation, Ms, at 5 K) were reduced by 40 % behind the tredge and a further 63 % in the playground; a total reduction of 78 % compared to roadside air. For the PM2.5 fraction, the reduction in magnetic loading behind the tredge was remarkable (82 %), reflecting efficient diffusional capture of sub-5 nm Fe-oxide particles by the tredge. Some direct mixing of roadside and playground air occurs at the back of the playground, caused by air flow over, and/or through gaps in, the slowly-permeable tredge. The magnetic loading on tredge leaves increased over successive days, capturing ~23 % of local, traffic-derived PM10. Using a heuristic two-dimensional turbulent mixing model, we assess the limited dispersion of PM < 22.5 μm induced by eddies in the tredge wake. This study demonstrates that PM deposition on leaves reduces exposure significantly in this school playground setting; hence, providing a cost-effective mitigation strategy.

Size-resolved inhalation intake fractions for particles released from human activities in residential indoor environments

Inhalation exposure to elevated concentrations of airborne particulate matter is a public health concern. Assessment of exposure can be enhanced through better knowledge of source-receptor relationships, which can be characterized through the inhalation intake fraction metric. This case study provides new insights on variations in particle inhalation intake fractions for indoor sources associated with common human activities in residential buildings. In a controlled climate chamber (air temperature: 24 ± 1 °C, relative humidity: 50 ± 5%), we investigated size-resolved intake fractions for particles in relation to four scripted activities performed by a human volunteer: sitting, walking, cooking, and vacuuming. We measured size- and time-resolved particle number concentrations at the volunteer's breathing zone to characterize intake fractions. In addition, we measured particles at four different stationary locations across the climate chamber to assess the degree of spatial heterogeneity in particulate matter concentrations. The results show that particles released from human skin and clothing during sitting were associated with the highest total inhalation intake fraction (13‰), followed by cooking (9‰), vacuuming (5.7‰), and walking (3.9‰). These results highlight how breathing zone proximity to localized emission sources and low indoor air mixing can enhance inhalation exposure to particles. Sitting and cooking caused a maximum inhalation intake fraction in the size range of 1–3 μm. Findings also show that the assumption of a perfectly mixed environment could lead to an underestimation of the inhalation intake of particles by up to 3.2-fold. The results of this case study provide a basis for achieving more accurate personal inhalation exposure assessment and improved indoor air quality management.