Plasma-assisted ammonia synthesis in a packed-bed dielectric barrier discharge reactor: roles of dielectric constant and thermal conductivity of packing materials

In this article, plasma-assisted NH3 syntheses directly from N2 and H2 over packing materials with different dielectric constants (BaTiO3, TiO2 and SiO2) and thermal conductivities (BeO, AlN and Al2O3) at room temperature and atmospheric pressure are reported. The higher dielectric constant and thermal conductivity of packing material are found to be the key parameters in enhancing the NH3 synthesis performance. The NH3 concentration of 1344 ppm is achieved in the presence of BaTiO3, which is 106% higher than that of SiO2, at the specific input energy (SIE) of 5.4 kJ·l−1. The presence of materials with higher dielectric constant, i.e. BaTiO3 and TiO2 in this work, would contribute to the increase of electron energy and energy injected to plasma, which is conductive to the generation of chemically active species by electron-impact reactions. Therefore, the employment of packing materials with higher dielectric constant has proved to be beneficial for NH3 synthesis. Compared to that of Al2O3, the presence of BeO and AlN yields the 31.0% and 16.9% improvement in NH3 concentration, respectively, at the SIE of 5.4 kJ·l−1. The results of IR imaging show the addition of BeO decreases the surface temperature of the packed region by 20.5% to 70.3°C and results in an extension of entropy increment compared to that of Al2O3, at the SIE of 5.4 kJ·l−1. The results indicate that the presence of materials with higher thermal conductivity is beneficial for NH3 synthesis, which has been confirmed by the lower surface temperature and higher entropy increment of the packed region. In addition, when the SIE is higher than the optimal value, further increasing SIE would lead to the decrease of energy efficiency, which would be related to the exacerbation in reverse reaction of NH3 formation reactions.

ROOFTOP GARDENING A SOURCE OF ENVIRONMENT CONSERVATION AND CROP PRODUCTION WITH CHANGING CLIMATE FOR DHAKA CITY

The cities of the world are facing serious problems due to environmental hazards. The Department of Agricultural Extension has been implementing a pilot project on expansion of roof gardening in the Dhaka city since 2018 to reduce the increasing temperature, air pollution and for food production. However, no study has been conducted to find out the suitable technologies for producing fresh, safe and nutritious foods in the roof garden and to investigate the role of this roof garden on environment conservation for the Dhaka city dwellers with changing climate. Therefore, a research based roof garden model was developed at Sher-e-Bangla Agricultural University with the financial help of NATP-2 project. The experimental results showed that roof garden reduced upper surface temperature of roof more than 9°C and lower surface temperature of roof by 1.74°C and believe to reduce the electricity consumption for cooling the room of the top floor of the building during summer season. The oxygen and carbon dioxide percent were higher and lower, respectively in the garden than the bare roof. Therefore, the results suggest that urban crop production and environmental balance can be achieved to a certain extent by increasing the intensity of roof gardening in the Dhaka city

Effect of moisture buffering on surface temperature variation: study of different indoor cladding materials

The building materials used indoors constantly interact with the environment in which the occupants live. Recent studies have shown that natural materials, such as wood, can improve human well-being. In addition, the building materials facing the indoor air are able to adsorb and desorb water vapour from their surface and exchange it with the surrounding air. This mass exchange comes along with heat exchange, modifying their surface temperature, and thus the indoor environment. Therefore, in this article, we are investigating whether moisture buffering has an impact on comfort. For this purpose, room-scale numerical simulations have been carried out with WUFI Plus, comparing two types of interior cladding materials: painted plasterboards and a raw spruce panelling. The results show a slightly lower surface temperature and air temperature during the summer period when using spruce. A higher hygroscopicity of the spruce than the gypsum can explain this difference in behaviour between the two studied materials. Thus, spruce exchanges more latent heat with the surrounding air. However, only this thermal difference cannot explain the difference in comfort perception between the gypsum and the wood.

Effect of stocking rate and floor types on performance, skin temperature and leucogram in pigs raising

Objective. The aim of this study was to evaluate the performance, thermoregulatory characteristics and the leucogram of growing finishing pigs reared in different stocking rates kept on compact floor pens or with shallow pool pens. Material and methods. Thirty-six pigs were used in two steps (total of 72 animals were used). In the first step it was analysed performance pig (daily feed intake, weight gain and feed: gain ratio) and backfat thickness (P2). In the second step, the same analyzes were repeated, in addition, analysis of leucogram and skin temperature was performad in P2 and anal region, at the end of growing and finishing phase. Results. It was evaluated for differences between treatments and stocking. It was not found effect of floor type on growing phase, but the use of shallow pool had a negative effect on the gain and feed: gain ration in the finishing phase. Increasing linear effect on backfat thickness as the stocking rate was reduced, as well as lower surface temperature in the anal region on treatment with shallow pool in the finishing phase. No effect of treatments and type of floor on leucogram pigs. Allowing more space/animal decreased backfat thickness. The use of shallow pool affected negatively the performance in the finishing phase. Conclusions. The shallow pool uses impair the finishing pig performance, despite improving thermolysis, with no effect observed on cell immune response.

Incorporating Phase Change Materials to Mitigate Extreme Temperatures in Asphalt Concrete Pavements

The use of Phase Change Materials (PCMs) in asphalt pavement mixtures potentially offers a solution for regulating extreme temperatures that can cause thermally-induced rutting in pavement systems. The primary objective of this study is to fundamentally understand the effect on the heat transfer and maximum surface temperature in flexible pavement systems that includes PCMs. In particular, we consider a pavement structure in which PCM is embedded in the asphalt-concrete layer with varying volume fractions. Our simulation results show that the pavement system embedded with PCMs yield lower surface temperature values than systems without PCM (maximum temperature decrease is 1.5°C for the distributed PCM with a volume fraction of 30%). Further, we observe a higher temperature drop through the PCM-embedded asphalt layer compared to a pavement without PCM, and regions possessing temperature values less than 45°C that may help to reduce the thermally induced rutting problems. The simulation yields another interesting result: increasing PCM volume fraction beyond 60% results in higher surface temperature values. This increase in the maximum surface temperature may be explained by the fact that the PCM used in the simulation has a lower thermal conductivity than that of the asphalt-concrete that ultimately results in a lower effective thermal conductivity value for the system. Finally, we observe that an increase in the effective thermal conductivity yields lower surface temperature for the PCM embedded pavement system.

The Impact of Cool Roofs on Energy Consumption of Office Buildings in Chongqing of China

Cool roofs are characterized by high solar reflectance (SR) and high infrared emittance (E). When cool roofs are exposed to solar radiation, it will have a lower surface temperature compared to a similar surface with lower SR and E values, and this would result in decreasing the heat penetration into the building. Cool roofs offer significant cooling energy saving in buildings with air conditioning. In order to quantify the influence of cool roofs on the energy consumption of office buildings in Chongqing, the authors tested the electricity consumptions of air conditioners in two rooms on the top floor of an office building. One of the rooms was with cooling roof installed. The result shows that in summer, the room with cooling roof saved electricity 0.049kWh per square meter per day. However in winter, it increased electricity consumption by 0.012kWh per square meter per day.

Analysis on Thermal Measuring of Rooftop Farming Garden a Case Study of Julong Residential District in Zhongshan

Nowadays, many urban cities in the world are facing problems of urban heat island and lack of greenery space. Rooftop farming is a strategy for intensifying urban agriculture activities, which can not only improve nutrition and food security in urban neighborhoods, but also reduce the energy consumption of air-condition and ease the power shortage in urban area of metropolitan regions. In this study, a thermal experiment and an index of energy saving analysis were carried out in Zhongshan, Guangdong Province, China in August 2011, measuring external and internal surface temperatures of roofs with and without greening, using the same set of climate parameters. The experiment results show that the green roof with urban farming can contribute to the modulation of air temperature in the interior spaces of building. During the hot days in summer, the external surface temperatures of green roof are lower than the normal flat one. The result also reveals that external surfaces of vegetated green roof system could effectively lower surface temperature by 6 °C and save 18.7% electric power, comparing with the general flat roof of traditional building.

Research on Heat-Transfer Process of the Radiant Ceiling Cooling System

Physical and numerical models of the radiant ceiling cooling system were built and numerically simulated. The results showed that the lower the temperature of cooling water is, the lower surface temperature the ceiling has, and the bigger the cooling capacity is. The bigger the depth of tubes is, the higher the surface temperature and the smaller the cooling capacity. The differences are not evident. The bigger the distance of tubes is, the bigger the surface temperature is and the smaller the cooling capacity is. The diameter of tubes has a few influences on the surface temperature and the cooling capacity. Results in this paper can provide basis and guide for the design of the project, the selection of parameters and the feasibility of the system.