This study aims to produce effectiveness from the development of learning tools through the concept of algebraic forms using Cognitive Conflict-Based Learning (PbKK) models for mathematical problem-solving abilities that are implemented in the Learning Implementation Plan (RPP) and Student Worksheet (LKPD) that are valid and practical. The method used is the Plomp design research model which consists of three phases, namely the preliminary research phase, the development phase (development or prototyping phase) and the assessment phase. The subjects of the study were the seventh grade students of junior high school. Data collection techniques used was posttest tests from two classes, namely the experimental class and the control class. Data analysis techniques are using the Independent-Sample T Test. The analysis shows that p-value = 0.034 <0.05 means that there are significant differences between the two classes. So, the development of Cognitive Conflict-based learning tools has a positive impact on students' mathematical problem solving abilities in algebraic form material.

Compressed natural gas (CNG) is a popular alternative fuel because of its more environmentally friendly properties than fossil fuels , including applications in diesel engines. However, supplying too much compressed natural gas fuel causes poor engine performance and emissions due to a decrease in the air-fuel ratio on the dual-fuel engine. The addition of air using electric superchargers was done to return the air-fuel ratio to ideal conditions. Lambda value (λ) was variation under low load (1.52 to 2.71), medium load (1.18 to 2.17), and high load (0.94 to 2.17) on a CNG-diesel dual fuel engine. The addition of pure air in each load can increase combustion stability in certain lambda, which was indicated by an increase in thermal efficiency, heat release rate, and a decrease in ignition delay, combustion duration, hydrocarbon, and carbon monoxide emissions.

Penggunaan compressed natural gas (CNG) sebagai bahan bakar utama pada mesin diesel menyebabkan penurunan performa mesin terutama pada efisiensi termal. Hal ini dikarenakan peningkatan daya mesin yang dikonversi melalui proses pembakaran tidak sebanding dengan penambahan jumlah bahan bakar yang masuk ke dalam ruang bakar seiring dengan penambahan beban mesin. Tujuan dari penelitian ini adalah bagaimana mengoptimalkan tekanan injeksi gas CNG yang diinjeksikan ke dalam ruang bakar melalui port (intake manifold) dapat menurunkan konsumsi bahan bakar dan meningkatkan efisiensi termal pada mesin diesel dual fuel (DDF). Metode penelitian ini dilakukan secara eksperimen pada mesin DDF Diamond DI 800 dengan putaran konstan (1500 rpm). Variasi yang dilakukan adalah mengatur tekanan injeksi gas CNG yang masuk melalui port sebesar 1,5 bar, 2 bar dan 2,5 bar. Hasil yang diperoleh adalah pada tekanan injeksi gas CNG 2,5 bar dapat memberikan persentase subtitusi gas CNG rata rata sebesar 57,59%, sedangkan pada tekanan injeksi gas CNG 1,5 bar dapat menurunkan konsumsi bahan bakar spesifik (SFCdual) hingga sebesar 0,196 kg/HP.jam dan meningkatkan efisiensi termal rata-rata sebesar 3,57% dibandingkan dengan variasi lain, meskipun masih di bawah kondisi operasi mesin single fuel.

A city car is needed to overcome congestion and parking spaces in urban areas. However, currently, the body design of the city car is still experiencing problems, namely the value of the large drag coefficient, which causes an increase in fuel consumption. This study aims to design a city car body with two passengers that is more aerodynamic so as to minimize fuel use. This research method is a numerical simulation model using the ANSYS fluent students version 2021. Parameters in the form of drag coefficient values, velocity streamlines and velocity contours on the city car are aerodynamic aspects that are analyzed. The results show that the dimensions of the designed city car have a length of 2.59 m, a width of 1.6 m, and a height of 1.52 m by considering the ergonomic parameters and comfort of the user so that it fits the character of the people in Indonesia. In addition, from the independence grid analysis performed, the value of the number of meshes that have the smallest error value is obtained, namely mesh C (the number of meshes is 129,635). Mesh C has an error of 7.2%. It was found that as the velocity increases, the value of the drag coefficient (CD) produced is relatively smaller. In a city car with a velocity of 10 m/s, the drag coefficient value is 0.599, at a velocity of 20 m/s, the drag coefficient value is 0.594, and a velocity of 30 m/s is a drag coefficient value of 0.591.

No abstract

This experimental study aims to investigate and analyze the performance of a Water-Air Heat Exchanger that functions as passive cooling in a building ventilation system in the tropics. Before being blown into the room, the high-temperature outdoor air will be passively cooled by the lower-temperature water. Air driven by an Inline Duct Fan with a constant mass flow rate of 4.68 cubic meters per minute flows through a PVC hose as a heat exchanger inserted into a full water reservoir with a diameter of 100 cm and a height of 110 cm. A heat exchanger hose with a diameter of 6.35 cm and a length of 4130 cm is installed in a spiral-circular manner with a total of 16 coils with a diameter of 80 cm to increase the heat transfer effectiveness between water and air. The passive cooling effectiveness is analyzed by decreasing the air temperature between the inlet and outlet of the ventilator after passing through the heat exchanger. The temperature, humidity, and daylight measurement data were carried out for 36 consecutive hours using a multichannel data logger at several locations; ventilator inlet, ventilator outlet, water in the tub, and outside air. The measurement results show that the designed water-to-air heat exchanger provides a significant passive cooling effect and can reduce air temperature to 6.88 °C. By utilizing the passive cooling effect, the cooling energy gain obtained during the measurement period in the ventilation system of this building is 8.3 kWh. The methodology and results of this research are expected to make a positive contribution to the development of the concept of energy-efficient buildings by using passive cooling techniques

No abstract

Many studies related with characteristics of fluid flow acrossing in a bluff body have been conducted. The aim of this research paper was to reduce pressure drop occuring in narrow channels, in which there was a circular cylindrical configuration with square cylinder as disturbance body. Another goal of this research was to reduce the drag force occuring in circular cylinder. Experimentally research of flow characteristics of the wind tunnel had a narrow channel a square cross-section, with implemenred of Reynolds number based on the hydraulic diameter from 5.21x104 to 1.56x105. Wind tunnel that was used had a 125x125mm cross-sectional area and the blockage ratio 26.4% and 36.4%. Specimen was in the form of circular cylinder and square cylinder as disturbance body. Variation of angle position was the inlet disturbance body with α = 200, 300, 400, 500 and 600, respectively. The results was obtained from this study was Reynolds Number value was directly linear with pressure drop there, it was marked by increasing of Reynolds number, the value was also increasing pressure drop. Additional information was obtained by adding inlet disturbance body shaped of square cylinder on the upstream side of the circular cylinder that could reduce pressure drop in the duct and reduce drag happening on a circular cylinder. The position of the optimum angle to reduce pressure drop and drag force was found on the inlet disturbance body with angle α = 300.