LEARN - MECHANICAL ENGINEERING

  Properties of Pure Substances If any two independent intensive properties of a simple compressible system are defined, other properties automatically assume definite values.  These properties can be expressed in terms of charts, tables or equations. This chapter covers the charts and tables of properties of steam. Pure Substances Substances   of fixed chemical composition are known as pure substances    Example : Water, Helium, Nitrogen, Oxygen etc. Substances exist in any one of the three phases namely solid, liquid and gas. For example, H 2 O may exist in the form ice (solid), Water (Liquid) or Steam (Gaseous). In all these phases it will have the same chemical composition. A   Mixture of two or more phases of a pure substance should also be regarded as pure substance. If Water and Steam Co-exits in a container, the chemical composition of both the Vapour and liquid phases will be identical. Hence this heterogeneous system is also a pure substance. Phase Transform

  BASIC PROBLEMS OF FIRST LAW OF THERMODYNAMICS 1. During a Flow process 5 KW paddle wheel work is supplied while the internal energy of the system increases in one minute as 200 KJ. Find the Heat transfer when there is no other form of Energy Transfer Given Data: Workdone (W) = -5 Kw Internal Energy (U) = 200 KJ / Min (Need to Convert in Sec) = 200 / 60 = 3.33 KJ /s To Find : Heat Transfer (Q) Solution: First Law of Thermodynamics: Q = W+U = - 5+3.33 = -1.67 KW (“-” Sign Indicates that the heat is transferred from the system) 2. A liquid of mass 18 Kg is heated from 25 ° C to 85 ° C. How much is heat transfer is required? Assume Cp for water is 4.2 KJ/Kg.K Given Data: m = 18 Kg T1 = 25 ° C = 25 +273K = 298 K T2 = 85 ° C = 85 + 273 = 358 K To find : Heat transfer Q Solution: Q = m.Cp(T2- T1) = 18 x 4.2 x (358 – 298) = 4536 KJ

IMPORTANT FOR SOLVING PROBLEMS Heat (Q) Specific Heat Capacity (C) Relation Between The Cp, Cv and R Internal Energy (U) Enthalpy (H) Workdone (W) Pressure Unit Conversion Sign Convention Of Work and Heat   Relationship Between Temperature Scales Three Temperature Scales, Fahrenheit Celsius Kelvin Convert a temperature from its representation on The Fahrenheit ( F) scale to the Celsius (C) value: C = 5/9(F - 32) The Celsius (C) value to Fahrenheit ( F) scale : F = 9/5C + 32 Kelvin(k): 0°C = 273K Heat (Q) Q is the heat supplied to the system, m is the mass of the system, c is the specific heat capacity of the system and ΔT is the change in temperature of the system. Q=m×c×ΔT Or Q=W+ ΔU Specific heat capacity (C) In The Form Of Heat, To One Unit Of Mass Of The Substance In Order To Cause An Increase Of One Unit In Its Temperature. Unit - J/Kg.K Specific heat capacity at constant pressure (Cp ) Cp = 1.005 KJ/Kg.K Specific heat capacity at constant volume (Cv) Cv = 0.716 KJ/Kg.K Relation

 Laws of thermodynamics Zeroth law of thermodynamics First law of thermodynamics Second law of thermodynamics Third law of thermodynamics Zeroth law of thermodynamics If two systems are in thermal equilibrium with a third system, they must be in thermal equilibrium with each other. or In other words If a body C, be in thermal equilibrium with two other bodies, A and B, then A and B are in thermal equilibrium with one another. First law of thermodynamics Known as the law of conservation of energy. This states that energy can be neither created nor destroyed. However, energy can change forms, and energy can flow from one place to another. * The total energy of an isolated system does not change. The increase in internal energy of a closed system is equal to the heat supplied to the system minus work done by it. dUsystem=Q - W We can say Qsystem= W + dU Qsystem= W 100% Efficiency

 THERMODYNAMIC EQUILIBRIUM : a state of a physical system in which it is in mechanical, chemical, and thermal equilibrium and in which there is therefore no tendency for spontaneous change. THERMODYNAMIC PATH   is the path or series of states through which a system passes from an initial equilibrium state to a final equilibrium state and can be viewed graphically on a pressure-volume (P-V), pressure-temperature (P-T), and temperature-entropy (T-s) diagrams. PROCESS  The change of system from one state to other state is known as thermodynamic process. REVERSIBLE PROCESS   is one in which both the system and its environment can return to exactly the states they were in by following the reverse path. An IRREVERSIBLE PROCESS is one in which the system and its environment cannot return together to exactly the states that they were in. Heat Heat is the form of energy that is transferred between two substances at different temperatures. Heat is measured in units of energy, usually calories o

  Thermodynamic Process: Process which contains transformation of heat into work or work into heat  System:  If thermodynamics  Process carried in any space is known as System Types:  Closed System, Open system and Isolated system Surroundings:  Every thing apart from the system Boundary :  Separation of System and Surrounding Universe:  Everything outside of Surroundings  Types:  Closed System, Open system and Isolated system Closed System:  can exchange only energy with its surroundings, not matter.  Open system:  can exchange both energy and matter with its surroundings.   Isolated system:  cannot exchange either matter or energy with its surroundings. Closed System, can exchange only energy with its surroundings, not matter (mass). Open system can exchange both energy and matter (mass) with its surroundings.  Isolated system: cannot exchange either matter or energy with its surroundings.

  UNIT I BASIC CONCEPTS AND FIRST LAW Basic concepts -  concept of continuum, comparison of microscopic and macroscopic approach.  Path and point functions. Intensive and extensive, total and specific quantities.  System and their types.  Thermodynamic Equilibrium State, path and process.  Quasi-static, reversible and irreversible processes.  Heat and work transfer, definition and comparison, sign convention.  Displacement work and other modes of work .P-V diagram.  Zeroth law of thermodynamics – concept of temperature and thermal equilibrium Relationship between temperature scales –new temperature scales.  First law of thermodynamics – Application to closed and open systems –  Steady and unsteady flow processes. CONTINUUM means  The matter can be treated as continuously distributed without any void or hole. Macroscopic- This approach can be applied if continuum concept concept can be applied. In these approach matter can be treated as on an avg. Basis and individual behavior is neg

Thermodynamics , science of the relationship between  heat ,  work ,  temperature , and  energy . In broad terms, thermodynamics deals with the transfer of energy from one place to another and from one form to another. The key concept is that heat is a form of energy corresponding to a definite amount of mechanical work. Syllabus                               UNIT I BASIC CONCEPTS AND FIRST LAW Basic concepts - concept of continuum, comparison of microscopic and macroscopic approach. Path and point functions. Intensive and extensive, total and specific quantities. System and their types. Thermodynamic Equilibrium State, path and process. Quasi-static, reversible and irreversible processes. Heat and work transfer, definition and comparison, sign convention. Displacement work and other modes of work .P-V diagram. Zeroth law of thermodynamics – concept of temperature and thermal equilibrium– relationship between temperature scales –new temperature scales. First law of thermodynamics