Explore the vast range of titles available.

In both centralized and decentralized air-conditioning systems, the performance, sustainability, and efficiency of the systems in delivering thermal comfort within a specific area are assessed as part of the air thermal management platform evaluation process. The evaluation of air thermal management platforms entails a thorough examination of numerous elements, customized to the unique features of these systems, such as system components, energy efficiency, control systems, maintenance procedures, and environmental concerns. The study considers mathematical modeling of energy-efficient techniques based on meteorological data of cooperative centralized and decentralized air-conditioning systems for external air recirculation treatment. Three systems were considered: an independently functioning central air conditioner, a central system functioning together with a local air conditioner, and a central system operating together with an adiabatic humidifier. Technological aspects of cycle performance are shown to be dependent on the acceptable design capacity of the air cooler and the adiabatic humidifier air wet-bulb temperature limit. Increasing the setting capacities of the air cooler to 0.00786 kg m −2  s −1 and the adiabatic humidifier to 0.03864 kWh, the air flow rate decreases from 0.0072 to 0.004 kg m −2  s −1 , and when the setting capacities of the air cooler are 0.01011 kg m −2  s −1 and the adiabatic humidifier is 0.04831 kWh, the air flow rate decreases to a minimum limit of 0.002 kg m −2  s −1 . Comparing the annual heating, cooling, and humidification load consumption without and with utilization of the second air recirculation, for the heating load 39.48 and 5.01 kWh, the costs increased by a factor of 7.9; for the cooling load 1850 and 1320 kWh, the costs increased 1.4 times; and for the moisture load 331.5 and 1245 kg m −2  s −1 , the costs decreased 3.8 times. The research conducted has led to the development of a methodology that combines the justification of energy-saving modes with formulated climatic tables and a probabilistic-statistical model. This methodology facilitates the selection of subsystem equipment’s AC setting capacities, the calculation of heating, cooling, and moisture load consumption at various times, and the technological scheme for heating and humidity air treatment. The refined AC can operate at peak efficiency and reduce energy loss thanks to this iterative approach. Moreover, this method's progressive design enables it to gradually increase in efficiency over time.

Nowadays, consumers are increasingly demanding processed food products with high levels of beneficial components. Bitter melon and apple are both nutritious foods rich in bioactive compounds. In this study, restructured bitter melon and apple chips were processed using four drying techniques: hot-air drying with/without exhaust air recirculation (EAR), and radio-frequency-assisted hot-air drying (RFHAD) with/without EAR. The drying characteristics, effective moisture diffusivity (Deff), specific energy consumption (SEC), total energy consumption (TEC), and some selected quality characteristics of the dehydrated chips were evaluated. The experimental results show that the application of radio frequency (RF) energy significantly facilitates water evaporation in the drying material, resulting in a significant (p < 0.05) reduction of drying duration by 31~39% over the experimental test parameters. The higher Deff values obtained from RFHAD and RFHAD + EAR were 6.062 × 10−9 to 6.889 × 10−9 m2/s, while lower SEC values ranged from 301.57 to 328.79 kW·h/kg. Furthermore, the dried products possessed better or fairly good quality (such as a lower color difference of 5.41~6.52, a lower shrinkage ratio of 18.24~19.13%, better antioxidant capacity, higher chlorophyll, total flavonoid, and total phenolic content, a lower polyphenol oxidase activity of 49.82~52.04 U·min−1g−1, smaller diameter and thickness changes, and a lower hardness of 27.75~30.48 N) compared to those of hot-air-dried chips. The combination of RF-assisted air drying and partial recirculating of dryer exhaust air achieved the highest saving in TEC of about 12.4%, along with a lower moisture absorption capacity and no deterioration of product quality attributes. This drying concept is therefore recommended for the industrial drying of several food materials.

Several lines of existing evidence support the possibility of airborne transmission of coronavirus disease 2019 (COVID-19). However, quantitative information on the relative importance of transmission pathways of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains limited. To evaluate the relative importance of multiple transmission routes for SARS-CoV-2, we developed a modeling framework and leveraged detailed information available from the Diamond Princess cruise ship outbreak that occurred in early 2020. We modeled 21,600 scenarios to generate a matrix of solutions across a full range of assumptions for eight unknown or uncertain epidemic and mechanistic transmission factors. A total of 132 model iterations met acceptability criteria (R² > 0.95 for modeled vs. reported cumulative daily cases and R² > 0 for daily cases). Analyzing only these successful model iterations quantifies the likely contributions of each defined mode of transmission. Mean estimates of the contributions of short-range, long-range, and fomite transmission modes to infected cases across the entire simulation period were 35%, 35%, and 30%, respectively. Mean estimates of the contributions of larger respiratory droplets and smaller respiratory aerosols were 41% and 59%, respectively. Our results demonstrate that aerosol inhalation was likely the dominant contributor to COVID-19 transmission among the passengers, even considering a conservative assumption of high ventilation rates and no air recirculation conditions for the cruise ship. Moreover, close-range and long-range transmission likely contributed similarly to disease progression aboard the ship, with fomite transmission playing a smaller role. The passenger quarantine also affected the importance of each mode, demonstrating the impacts of the interventions.

In order to solve the technical difficulties of SCR denitrification catalyst in the furnace activation baking process, a deactivated catalyst baking scheme is proposed in this study based on hot air recirculation of an electric heater. Additionally, numerical simulation methods are used to study the thermophysical characteristics and energy consumption characteristics of SCR denitrification catalyst in a furnace baking system of 300 MW thermal power uni. The results show that: the power of the heat source is 5.5～11 MW, the heating time is 5,000～11,000 s and the energy consumption is 15,534.7-20,931.3 kW·h, which fully meets the engineering needs. During the warming process, when the baking time of this system is 9,000 s (2.5 h), the temperatures of the two-layer catalyst center profiles are 453.55℃ and 447.05℃, with the relative standard deviations being 0.29% and 0.36%, meeting the requirements of temperature and temperature field for the activation in the furnace.

Although solar pyrolysis is a promising method for biomass energy extraction, traditional solar biomass pyrolysis utilises large-scale solar reflectors to meet the high-temperature demand, which limits its applicability at an industrial level. Hence, recirculation of the heat transfer fluid is proposed to reduce the scale of the solar reflector. This research designs a series of solar pyrolysis furnaces with solar parabolic dishes and compares the simulation results of those with compressed air recirculation to a benchmark. Results show that the recirculation can lead to a 30% reduction in the aperture diameter, a doubled thermal efficiency, and an 80% decrease in electricity consumption and related CO 2 emission. The change of the aperture diameter with a variation of the direct normal irradiance is insignificant. These multiple benefits can provide valuable insights into the scale optimisation method and promote its applicability in industrial sectors.

We explore the interaction of natural convection and mechanical ventilation in a room where fresh air is supplied at low level and stale air is extracted at high level. Turbulent buoyant plumes rising from heat sources interact with this upward airflow and establish a steady-state stratification with a warm upper layer above a layer of the cold supply air. Adapting the volume balance model used in natural ventilation (Linden et al., J. Fluid Mech., vol. 212, 1990, pp. 309–335) leads to the prediction that the upper layer will vent from the room when the ventilation volume flux exceeds the volume flux in the plumes at the ceiling. However, our new laboratory experiments establish that there is still a stable two-layer stratification beyond this point of critical ventilation. Motivated by our observations, we propose that the kinetic energy flux supplied by the plume leads to turbulent mixing in the upper layer. We propose a new model of this mixing which is consistent with our experiments in both the over- and under-ventilated regimes. This has important implications for air recirculation in buildings with large ventilation flows, particularly hospital operating theatres and clean rooms.

Recirculation and low-pressure regions associated to flow over bluff bodies such as circular cylinder have resulted in form drag dominance. Splitter plates attachment to cylinder has been found as a promising passive control technique to mitigate such effects. This study aims to examine the implications of splitter plates on the thermal aspects of the flow over a heated cylinder in cross flow, exploring experimentally the effects of wake splitter on the heat transfer coefficients. The experiment was carried out in the wind tunnel for three different Reynolds numbers around 7850, 13650, and 17500. The findings indicated that while the heat transfer performance improves with increasing Re , the addition of splitter plates has augmented the heat transfer coefficients by up to 34%, 77% and 153% for the respective geometry with rear plate, front plate and double plates incorporated to the circular cylinder. The results were explained from the perspective of boundary layer theory. Future work may investigate the local heat transfer coefficient variation with the azimuthal angle of the circular cylinder in cross flow.

Solar energy is considered free and clean energy. Solar drying technology is adopted as a sustainable way of food preservation. In this research, the drying of mango and preparation of bread toast has been investigated through experiments. A baffled-type solar dryer with a feature for hot air exhaust recirculation has been used for the experimental analysis. The collector efficiency, drying efficiency, and drying rate have been calculated by creating turbulence and exhaust hot air recirculation with and without exhaust hot air circulation. Performance indicators such as drying rate, coefficient of performance, heat utilization factor, and drying efficiency have been evaluated. A satisfactory drying effect is produced by employing an electric coil at night to raise the temperature within the drying chamber to a maximum of 66.7°C. It is observed that the drying rate in the case of forced convection type hybrid solar dryer is higher when compared to natural convection type and open sun drying. Thus, solar drying is a hygienic process without negative environmental externalities and is most suitable in food processing industries.

The COVID-19 pandemic caused a paradigm shift in our way of using heating, ventilation, and air-conditioning (HVAC) systems in buildings. In the early stages of the pandemic, it was indeed advised to reduce the reuse and thus the recirculation of indoor air to minimize the risk of contamination through inhalation of virus-laden aerosol particles emitted by humans when coughing, sneezing, speaking, or breathing. However, such recommendations are not compatible with energy saving requirements stemming from climate change and energy price increase concerns, especially in winter and summer when the fraction of outdoor air supplied to the building needs to be significantly heated or cooled down. In this experimental study, we aim at providing low-cost and low-energy solutions to modify the ventilation strategies currently used in many buildings to reduce the risk of respiratory disease transmission. Measurements of the indoor air bacterial concentration in a typical office building reveal that ultraviolet germicidal irradiation (UVGI) modules added to the HVAC system are very efficient at inactivating pathogens present in aerosols, leading to indoor concentrations as low as outdoor concentrations, even with significant indoor air recirculation. Moreover, measurements of the CO2 and aerosol air concentration reveal that, with air supply vents placed in the ceiling, placing the air exhaust vents near the floor instead of on the ceiling can improve the ventilation capacity in terms of effective flow rate, with significant consequences in terms of energy savings.

There is ambiguity about the airborne transmission of the SARS-CoV-2. While a distance of 6 feet is considered a safe physical distance, new findings show that the virus can be transmitted more than that distance and cause infection. In hospitals, this may cause the virus to be transmitted from the treatment wards of COVID-19 patients to adjacent wards and infect medical staff, non-COVID-19 patients, and patient companions. The aim of this study was to investigate the presence of coronavirus in the air of ICU and adjacent wards. The low volume sampler (LVS) with two separate inlets for PM2.5 and PM10 was applied to collect indoor air of intensive care unit (ICU) with confirmed COVID- 19 patients and its surroundings. The samples were collected on 0.3μ PTFE filter fitted to the holder. Sampling was done at flow rate of 16.7 l/min for 24 h. The SRAS-CoV-2 virus was isolated using a SinaPure™ Virus Extraction Kit (SINACLON, Iran). The presence of SARS-CoV-2 genome was assessed using a commercially available SARS-CoV-2 Test Kit (Pishtaz-Iran), according to the manufacturer’s instructions using One Step plus Real-Time PCR system tool (Applied Biosystems, USA). A total of sixteen samples were taken, and the positive test rate for SRAS-CoV-2 was 12.5 % (2/16). All samples from surrounding (rest room and hallway) were negative, but two air samples from indoor of ICU (next to the patient bed and nursing station) were found to be positive. The results support the possibility of transmitting the SRAS-CoV-2 through the air at a greater distance than what is known as a safe physical distance. Therefore, in addition to maintaining a safe physical distance, other precautions including wearing a face mask, preventing air recirculation, and maximizing the use of natural ventilation should be considered, especially in crowded and enclosed environments. Graphical abstract