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# Important Questions and Answers: Basic Concepts and Thermodynamics First Law

Mechanical - Engineering Thermodynamics - Basic Concepts And Definitions

BASIC CONCEPTS AND FIRST LAW

1.  Define Zeroth law of thermodynamics?

It states, “When two systems are in th separately, then themselves are in thermal e

2.  Define Thermodynamic Equilibrium?

A system is said to be in thermodynamically equilibrium when there is no change in any macroscopic property of the system. i.e. the temperature and pressure at all points should be same, there should be no velocity gradient there should be no chemical reactions.

3.  Define Extensive Property?

Extensive Property is the thermodynamic properties depend upon the mass of the system. Example: Mass, Volume, Total energy etc..,

4.  What is meant by quasi-static process in thermodynamics?

A system passes through an infinite number of continuous equilibrium states and attains the original state when the process is reversed. This process is called as quasi-static process. This process follows a successive thermodynamic equilibrium process, thus it is reversible process. It is very low process.

5.List the limitations of First law of thermodynamics?

·        First law of thermodynamics does not specify the direction of flow of heat and mass

·        The heat and work are mutually convertible.

6.     What is PMMI? Why it is impossible?

PMMI is the first temperature delivers work continuously without any input. It violates first law of thermodynamics. It is impossible to construct an engine working with this principle.

7.  What is microscopic approach in thermodynamics?

A matter consists of myriads of molecules the properties of matter such as pressure, velocity, position and energy of individual molecules.

8.     Define Flow Energy?

It is the energy associated with the flow of mass across the boundaries of a system

Flow Energy = P x V (N-m)

9.     Distinguish between ‘Macroscopic energy’

Macroscopic Energy

Instead of studying parameters at molecular level, the behavior of total system in terms of properties.

Microscopic Energy

A matter consists of myriads of molecules, the properties of matter such as pressure, velocity, position and energy etc.,

10.                        Differentiate between point function and path function?

Point Function

The quantity which is independent on the process or path followed by the system.

Example:  Pressure,  Volume,  Temperature etc.,

Path Function

The quantity dependent on the process or path followed by the system.

Example: Heat transfer, work transfer etc.,

11.                        State the first law for a closed system undergoing a process and a cycle?

The first law of thermodynamics deals with this work and energy transfer and states that

“in any cyclic process the net heat supplie the net work done by the system on its surroundings”. i

12.                        Define the term Enthalpy?

The combination of internal energy and flow energy is known as enthalpy.

H = U x PV     (KJ)

13. What are the conditions for steady flow process?

In a steady flow process, the working fluid enters the system and leaves to atmosphere after doing work. In this system, both the energy and mass cross the boundary.

Example: Steady flow process applied to various systems like boilers, turbine, compressor etc.

14. Why does free expansion have zero work transfer?

A fluid is allowed to expand suddenly into a vacuum chamber through an orifice of large dimension, it is known as free expansion.

15. Distinguish between the term State and Process of thermodynamics?

State

It is condition of the system at an instant of Time

It is a fixed one

Process

It occurs when the system undergoes a change

It is variable one

16. Explain PMM 1.

There can be no machine which would continuously supply mechanical work without some other form of energy disappearing simultaneously. Such a machine is called perpetual motion machine of the first kind.

17.                        Name the different types of process.

a. Iso-choric process

b. Isobaric process

c. Isothermal process

d. Isentropic process

e. Polytropic process

18.                        Indicate the practical application of steady flow energy equation.

1. Turbine

2. Nozzle

3. Condenser

4. Compressor

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