Tiếp cận đoạn trích "Đất nước" của Nguyễn Khoa Điềm từ lý thuyết ngữ pháp chức năng hệ thống

Abstract: Using solar chimneys in buildings can enhance the thermal insulation of the building envelope and provide sufficient ventilation and cooling. The performance of a solar chimney is strongly affected by its configurational factors. This work examines the effects of the opening heights on the flow field in the cavity of a wall solar chimney with a Computational Fluid Dynamics (CFD) model. Both cases of equal and unequal opening areas were considered. The results show that the induced flow rate increases with the opening height and gradually becomes constant as the opening height is about 2.0–3.0 and 5.0–6.0 times the air gap for heating the left wall (HLW) and the right wall (HRW) of the air cavity, respectively. Particularly, using equal inlet and outlet heights that are equal to the air gap reduces the flow rate of 27% for HLW and 85% for HRW compared to the maximum ones. The optimal design of a wall solar chimney to achieve maximum flow rate is proposed for two cases of heating, that is, (a) for HLW, equal opening heights which are twice the air gap, and (b) for RHW, the inlet height equal to the air gap, and the outlet height equal to five times the air gap.

Abstract: Solar chimneys can help to reduce solar heat gain on a building envelope and to enhance natural ventilation. In this work, we proposed three configurations of two solar chimneys combined with a heated wall for the natural ventilation of a room: (I) the chimneys are connected serially, (II) the chimneys are parallel and exhaust air at two separate outlets, and (III) the chimneys are parallel, but the outlets are combined. The airflow rate achieved with each configuration was predicted with a Computational Fluid Dynamics model. The results show the effects of the heat flux in each channel and the geometries of the channels. Configuration (II) shows the highest flow rate. Particularly, the proposed configurations enhance the flow rate significantly and up to 40% when compared to the typical setup with a single channel solar chimney. The findings offer a novel design option for building façades for reducing solar heat gain and enhancing natural ventilation.

Abstract: This paper reports effects of the opening areas of a wall solar chimney on the flow rate and heat transfer performance. Previous studies showed that the opening size is among the most important factors which affect the performance of solar chimneys. However, such effects for a wall-attached solar chimney whose openings are vertical have not been reported in the literature. The performance of a wall solar chimney was simulated with a Computational Fluid Dynamics (CFD) tool in this paper. The induced flow rate and Nusselt number were compared for various inlet and outlet areas. The results show that the most influencing factor is the ratio of the inlet and the outlet areas. Particularly, the heat transfer coefficient and flow rate approach constants as the inlet or outlet area is above twice the channel gap. The findings suggest that the optimum opening height is equal to the channel gap.

Abstract: Aquaponics is a method that helps to cure the scarcity of food and serves as an excellent solution to environmental problems. It is horticulture between aquaculture (farming of fish) and hydroponics (growing plants without soil). Through these techniques, it reduces the use of pesticides and fertilizer. Since the interest in aquaponics is rapidly increasing, one of the significant problems is monitoring the time, plants, and fish. This study aimed to improve the residents' long-term sustainability by offering continuous greenery supplies and fresh fish. Smart Aquaponics system is consisting of different sensors and devices. The sensor is used to monitor the consistent pH level, water level, and water temperature data. Other features also include the ability of the system to feed the fish automatically and deliver an image of the desired greenery at a set time using an Esp32 Cam. All the data gathered from the sensor will be relayed to the Blynk cloud and sends the information to the Blynk application through the IoT module. For a moment, homeowners can easily monitor and control IoT-based aquaponics remotely. The experiment results show that the system uses Esp32-Cam to successfully detect the image of the lettuce plant and upload it into Blynk App. In the water temperature, the system had a variation of temperature reading and is being shown in LCD Display together with the pH level and water level. This system reduces the amount of effort required by humans to maintain and produce healthy greenery and fresh fish.

Abstract: Thermal insulation of walls is important in green or energy-efficient buildings. To increase the thermal resistance of walls, solar chimney can be used, as it helps to release solar heat gain on the wall. In previous studies on wall solar chimneys in the literature, simulations with the Computational Fluid Dynamics (CFD) are among the common methods. One of the influencing factors of the reliability of the CFD simulations is the size of the domain size. In this work, we tested effects of the dimensions of the computational domain on the air flow rate through and Nusselt number of a wall solar chimney with a CFD model. Two types of the domain were considered. The small one included only the cavity of the air channel while the large one was extended from the small one to cover ambient air. The results show that to achieve solutions with less than 1.0% change with the domain, the extension should be more than 3.0G above the top and to the side, and 1.5G below the bottom inlet of the air channel of the solar chimney. The findings in this study offer a good reference for determining the computational domain for wall solar chimneys.