Penyelesaian Soal Termodinamika 9-34, 9-56, dan 9-95

Summary

This video covers the detailed explanation of three thermodynamic cycles: the Otto cycle, the Diesel cycle, and the Brayton cycle. It explains the step-by-step process to solve various problems related to these cycles, including calculating pressures, temperatures, work done, efficiency, and other key parameters. Using formulas, tables, and interpolation, the script provides insights into how to approach real-life engineering problems in thermodynamics. The cycle specifics are demonstrated with calculations and examples, ultimately leading to the determination of net work and thermal efficiency for each cycle.

Takeaways

• 😀 The presentation covers the explanation of three thermodynamic cycles: Autocycle, Diesel Cycle, and Brayton Cycle.
• 😀 The Autocycle section involves calculations of pressure, temperature, and energy at various states, with specific formulas for each thermodynamic state.
• 😀 For the Autocycle, key values such as temperature (300K) and pressure (95 kPa) were used to calculate properties like energy and volume ratio for the cycle.
• 😀 Interpolation is used to determine the energy and temperature at certain states for the Autocycle when values are missing in the provided table.
• 😀 The work done (Wnet) in the Autocycle is calculated by subtracting the energy lost (Qod) from the energy input (Qin), resulting in a net work of 495.6 kPa.
• 😀 Autocycle efficiency is calculated as the ratio of Wnet to Qin, yielding an efficiency of 52.3%.
• 😀 The Diesel Cycle calculations involve determining temperature, pressure, and volume using initial conditions like 95 kPa pressure and 15°C temperature.
• 😀 In the Diesel Cycle, the compression ratio and energy calculations are derived, with key results like the efficiency of 51% and net work (WN) of 102.1 kW.
• 😀 For the Brayton Cycle, key parameters such as temperature (313K at the start) and pressure (100 kPa) are used to calculate mass flow and thermal efficiency.
• 😀 The Brayton Cycle involves the calculation of temperatures at various states, with an efficiency of 37.5% and a calculated power output of 6,379.6 kW.

Q & A

What is the purpose of the first part of the script, and what does it cover?

The first part of the script introduces the speaker, Valen Rayity Bakti, a student of Mechanical Engineering from Universitas Andalas. It outlines the three thermodynamics cycles to be discussed: the Otto cycle, Diesel cycle, and Brayton cycle. The script includes detailed calculations and explanations for each of these cycles, including steps for finding pressures, temperatures, work, efficiency, and other thermodynamic properties.

How is the temperature at state 1 converted from Celsius to Kelvin in the Otto cycle?

The temperature at state 1 is given as 27°C. To convert it to Kelvin, the formula is T(K) = T(°C) + 273.15. Therefore, 27°C is converted to 300 Kelvin.

What is the process to find the energy and specific volume at state 2 of the Otto cycle?

At state 2, the specific volume is determined using the given volume ratio (VR) between state 1 and state 2. The formula for specific volume (v2) is used, and interpolation is then applied to find the temperature and internal energy at state 2, since these values are not directly available in the tables.

What formula is used to calculate the work (Wnet) in the Otto cycle, and how is it determined?

The net work (Wnet) is calculated as the difference between the heat input (Qin) and the heat output (Qod). Qin is given, while Qod is determined by the difference in internal energy between state 4 and state 2. The final Wnet is used to calculate efficiency.

What is the efficiency of the Otto cycle, and how is it calculated?

The efficiency of the Otto cycle is calculated using the formula: Efficiency = Wnet / Qin * 100%. In this case, the calculated efficiency is 52.3%.

How is the mean effective pressure (MEP) calculated in the Otto cycle?

The mean effective pressure (MEP) is calculated using the formula: MEP = Wnet / (V1 - V2). The initial volume (V1) is determined using the equation PV = RT, and the final volume (V2) is derived from the volume ratio.

What are the key steps involved in solving the Diesel cycle problem presented in the script?

The Diesel cycle problem involves finding the volume at state 1, using the given piston diameter and stroke, determining the compression ratio, and calculating the pressures and temperatures at each state. For state 2, the temperature is derived using the compression ratio, and further steps involve determining the energy at each state and the work output of the cycle.

What formula is used to calculate the compression ratio in the Diesel cycle?

The compression ratio in the Diesel cycle is calculated as the ratio of the maximum volume (Vmax) to the minimum volume (Vmin). In the script, this ratio is calculated as 20.

How is the heat input (Qin) and output (Qod) determined in the Diesel cycle?

In the Diesel cycle, Qin is calculated using the change in internal energy from state 1 to state 3. Qod is determined by the difference in internal energy from state 2 to state 4. The net work (Wnet) is then calculated by subtracting Qod from Qin.

What is the efficiency of the Brayton cycle, and how is it calculated?

The efficiency of the Brayton cycle is determined by calculating the work output (Wnet) and comparing it to the heat input. The net work is calculated based on the temperatures and pressures at each state, and the efficiency is found to be 37.5%.