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.

Abstract: This study investigates performance of a vertical solar chimney, which absorbs solar energy and induces airflow for natural ventilation and cooling of dwellings, under effects of walls neighboring to its air channel. A computational fluid dynamics model was developed to predict induced flow rate and thermal efficiency of a vertical solar chimney with four types of nearby walls: a vertical wall to which the solar chimney was attached, a horizontal plate above the outlet of the air channel, a horizontal plate, and a horizontal wall below the inlet of the air channel. Examined factors included the heat flux in the air channel, the chimney height, the air gap, the distance of the walls, and the location of the heat source in the air channel. The results showed that effects of the wall proximity were modulated by the location of the heat source and the ratio G/H between the air gap and the chimney height. Particularly, performance of the chimney was enhanced when the heat source was on the opposite side of the vertical wall and when G/H was large.

Abstract: Solar chimneys absorb solar radiation heat to create stack effect which induces airflow for natural ventilation of buildings. Solar chimneys have been studied mainly in two forms: vertical air channel and inclined one. In this paper, a solar chimney with a horizontal absorber surface was proposed. Its performance in term of the induced air flowrate through the channel and the thermal efficiency was predicted by a CFD (Computational Fluid Dynamic) model. Examined factors included the heat flux and major dimensions of the chimney: length of the absorber surface, gap of the air channel, and height and width of the inlet and outlet sections. The results show that increasing of all examined factors enhances the flowrate but has minor effect on the thermal efficiency. However, excessive large outlet width results in reduction of the flowrate and thermal efficiency due to appearance of reverse flow at the outlet.

Tóm tắt: Bài viết vận dụng lý thuyết ngữ pháp chức năng hệ thống của M.A.K. Halliday để khảo sát, phân tích các phương thức thể hiện ba siêu chức năng của ngôn ngữ trong đoạn trích "Đất Nước" của Nguyễn Khoa Điềm. Kết quả nghiên cứu của bài viết nhằm góp phần làm rõ hơn ba siêu chức năng của ngôn ngữ: chức năng kinh nghiệm, chức năng liên nhân và chức năng văn bản trong một diễn ngôn cụ thể - diễn ngôn thơ ca; đồng thời, bài viết cũng nhằm tìm ra những điểm mới lạ, thú vị của đoạn trích này khi tiếp cận từ cơ sở lý thuyết ngữ pháp chức năng hệ thống.

Tóm tắt: Sử dụng phần lời ca khúc “Tình ca” của Hoàng Việt làm ngữ liệu nghiên cứu, bài viết vận dụng lý thuyết ngữ pháp chức năng hệ thống của K. Halliday để phân tích chức năng liên nhân của ngôn ngữ trong lời bài hát. Cụ thể, thông qua hệ thống Thức với các cú nhận định, cú nghi vấn, cú mệnh lệnh, cú cảm thán cùng với các yếu tố tình thái và các cặp từ xưng hô để thấy được các quan hệ liên nhân mà tác giả muốn thiết lập trong lời bài hát.

Abstract: Experiential metafunction also known as reflective metafunction is one of the three metafunctions of language proposed by M.A.K. Halliday. This metafunction is used to convey new information or content unknown to listeners. Thereby, people's experience of the world around as well as in the speakers themselves is expressed. Based on the system function theory of M. A. K. Halliday, the modes of expressing experiential functions in the discourse of the Vietnamese revolutionary lyrics in the period from 1954 to 1975 are analyzed and investigated. This is to determine the authors linguistic strategies in organizing the messages through the transition system. Besides, the relationship between language and thought is also clarified.