Thermal Engineering Basic Concepts.pptx

Basic Concepts of thermodynamics,

1. Subject:- Thermal Engineering (ME3403) Topic :- 1.1. Basic Concepts ( Concept of pure substance, types of systems , properties of systems, Extensive and Intensive properties, flow and non-flow processes, specific volume, temperature, density, pressure. Processes and cycles. Gauge pressure, Absolute Pressure, Atmospheric pressure, Vacuum pressure and their relation. Simple numericals . )

2. Concept of pure substance:- Pure substance is defined as, “the substance which remains homogeneous and its chemical composition does not change, even though, it undergoes change of phase”. Example:- Liquid or water

3. Systems:- Thermodynamic system is defined as “a region in space, upon which, attention is focused for understanding the concept of transfer and conversion of energies like heat and work” Surrounding:- Everything outside the system is called as surrounding. Boundary:- Boundary is defined as the envelope, enclosing the system. It separates the system from surrounding. Universe:- The system and surrounding together is called as universe.

4. Types of Systems:- Closed system:- When there is transfer of energy, i.e. heat and work, across the boundaries, such system is called as the closed system. Examples:- Piston in a cylinder. Thermal Power plant. Open System:- When there is transfer of mass and energy across the boundaries, such system is called as the open system. Examples:- Gas turbine power plant. Air compressor.

5. Isolated System:- When there is no transfer of mass and energy across the boundaries, such system is called as the isolated system. Examples:- 1) Gas enclosed in the insulated container. 2) Thermos.

6. S.N. Comparative Point Open System Closed System 01. Mass Mass of the system does not remain constant. Mass of the system remains constant. 02. Concept It can be explained with the concept of control volume and control surface It can be explained with the concept of boundaries. 03. Mass and energy transfer Mass and energy may transfer across control volume Only energy transfer take place across the boundary of the system Properties of Systems:-

7. Thermodynamic properties Thermodynamic properties are the characteristics (identifiable and observable) of a system by which it can be specified. For example mass, volume, temperature. Thermodynamic properties can be divided into two groups : Extensive properties and intensive properties

8. Extensive Thermodynamic Property Extensive properties are those properties which depend on the extent of the system. That means extensive properties are directly related (directly proportional) to the mass. Examples of extensive properties: volume, internal energy, mass, enthalpy, entropy etc.

9. Intensive Thermodynamic Properties Intensive properties are those properties of the system which do not depend on the extent of the system. That means intensive properties are not related to the mass. Examples of intensive properties:

10. FLOW AND NON FLOW PROCESS Non Flow process The processes occurring in closed system which do not permit the transfer of mass to and from the system, are known as flow processes.

It may be noted that in non flow processes, the energy crosses the system boundary in the form of heat and work, but there is no mass flow in to or out of the system.

11. FUNDAMENTAL OF THERMODYNAMICS Flow process:- 1.The processes occurring in open system which permits the transfer of mass to and from the system. Are known as flow processes. O It may be noted that in a flow process, the mass

2.enters the system and leaves after enhancing energy.
3.The flow processes may be steady flow or non steady flow processes.

4.Steady flow processes e.g. Flow through nozzles, turbines compressors etc.

5.Non steady flow processes are filling or
evacuation of vessels.

12. Specific Volume:- Specific volume is the volume occupied by one kg of gas. It is denoted by V s . It is measured in m 3 /kg. Mathematically:- Vs= Volume Mass Density:- Density is the ratio of mass to the volume. It is measured by p. It is also called as mass density. Mathematically:- p= Mass Volume Unit: kg/m 3

13. Temperature:- Temperature is a thermodynamic property, which shows the degree of hotness or heat intensity of the body. It is measured with the help of thermometer, thermocouple, radiation pyrometer etc. In degree Celsius, Kelvin or degree farenhite (i.e. °C, °K or °F). Conversion of units: K= ‘t’ °C + 273

°F = 9 ‘t’ °C + 32
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For example, for temperature 25°C, its conversion is, (1) Kelvin 25°C + 273 = 298 K

(2) Farenhite 25°C + 32 = 77°F

14. Guage pressure:- Gauge pressure is defined as the pressure which is measured with the help of a pressure measuring instrument, in which the atmospheric pressure is taken as datum. The atmospheric pressure on the scale is marked as zero. Absolute pressure:- Absolute pressure is defined as the pressure which is measured with reference to absolute vacuum pressure. Vaccum pressure :- Vacuum pressure is defined as the pressure below the atmospheric pressure. Atmospheric pressure:- Atmospheric pressure, also known as barometric pressure, is the pressure within the atmosphere of Earth. The standard atmosphere is a unit of pressure defined as 101,325 Pa, which is equivalent to 760 mm Hg, 29.9212 inches Hg, or 14.696 psi.

15. Relationship between pressures

16. Thank You