Materi 4 Topik Aliran Kompresibel

Summary

This lecture on compressible flow focuses on isentropic flow, exploring critical properties and the behavior of fluids in steady-state conditions. It introduces the concept of critical properties, such as pressure, temperature, and density, at Mach number 1, specifically within converging-diverging or converging channels. The lecture also discusses the importance of the Mach number and its effect on fluid properties, highlighting the behavior of gases such as ideal gases, steam, air, and monoatomic gases like hydrogen and helium. Critical ratios of these properties are also derived and presented in the context of isentropic flow.

Takeaways

• 😀 The topic being discussed is compressible flow or aliran kompresibel, with a focus on isentropic flow.
• 😀 Previous discussions have covered relationships between total properties and static properties.
• 😀 The script explains how to calculate ratios of temperature, pressure, and density using specific equations.
• 😀 The concept of critical properties is introduced, particularly at a Mach number of 1 (Unity).
• 😀 The term 'krut' or throat is used to describe regions where the Mach number is 1 in converging-diverging or nozzle flows.
• 😀 Critical properties can be determined by applying the Mach number of 1 to the previous equations, yielding critical ratios.
• 😀 Critical ratios include pressure, temperature, and fluid density at Mach number 1.
• 😀 The script highlights that these relationships apply to one-dimensional, steady-state isentropic flow conditions.
• 😀 The table shows specific values of critical properties for different gases like superheated steam, exhaust gases, and air.
• 😀 The ideal gas constant (k) varies for different gases: 1.3 for superheated steam, 1.33 for exhaust gases, and 1.4 for air. For monoatomic gases like hydrogen and helium, the value of k is typically 1.67.

Q & A

What is the main topic of the lecture?

The main topic of the lecture is compressible flow, specifically focusing on isentropic flow in one-dimensional scenarios.

What is meant by 'isentropic flow' in this context?

Isentropic flow refers to a type of flow where entropy remains constant, which means there are no heat transfers or dissipative effects like friction in the system.

What does the script mean by 'critical properties' of a fluid?

Critical properties refer to the values of fluid properties (such as temperature, pressure, and density) that are associated with the flow condition where the Mach number is equal to 1, which is the speed of sound in the medium.

What is a Mach number and why is it significant in this context?

The Mach number is the ratio of the velocity of the flow to the speed of sound in the fluid. In this context, it helps define critical conditions, particularly when the Mach number reaches unity (Mach = 1), which is known as 'choking' or the 'throat' condition in a converging-diverging nozzle.

What is the significance of the critical point where Mach number equals 1?

The critical point, where the Mach number equals 1, is essential because it marks the condition of maximum flow speed in a converging-diverging nozzle, beyond which the flow cannot accelerate further. This is referred to as the 'throat' or 'krit' condition.

How is the critical pressure ratio derived?

The critical pressure ratio is derived by substituting a Mach number of 1 into the relevant thermodynamic equations for compressible flow, resulting in a ratio that defines the critical pressure at the throat of the nozzle.

What is the relationship between temperature, pressure, and density in isentropic flow?

In isentropic flow, temperature, pressure, and density are related through specific thermodynamic equations, with changes in one property affecting the others according to the adiabatic and reversible process conditions.

What are 'critical ratios' and why are they important?

Critical ratios refer to the ratios of properties like temperature, pressure, and density at the critical point (Mach number = 1). These ratios are crucial for understanding the behavior of the flow at the nozzle throat and are essential for designing and analyzing compressible flow systems.

What are the critical ratios for different gases mentioned in the transcript?

The critical ratios for different gases are: for superheated steam with a specific heat ratio (k) of 1.3, for exhaust gases with k = 1.33, for air with k = 1.4, and for monoatomic gases such as hydrogen and helium, which also have specific ratios depending on the substance.

How do these critical ratios apply to compressible flow in nozzles?

These critical ratios are used to calculate the fluid properties at the throat of a converging-diverging nozzle, where the Mach number is 1. These ratios help predict the conditions for optimal flow and performance in such systems.