Work & Heat_NEP.pptx thermodynamics3rdsembasics

Thermodynamics

1. Work and Heat

2. Energy Macroscopic form of energy System posses energy as a whole w.r.t some outside reference frame (K.E + P.E) K.E  system related to motion and influenced by some external frame.  possess energy result of motion relative to some reference frame K.E = ½ m v 2 (kJ) P.E  system possess energy as a result of its elevation in a gravitational field P.E = m g Z Magnetic, electric, surface tension are significant in some cases Total Macroscopic energy = PE + KE + EE + ME + STE + ……

3. Energy Microscopic form of energy Form a energy related to molecular structure of a system + degree of molecular activity and these are independent of external reference frame. Sum of all microscopic energy is called Internal energy IE (U) = Mole. Str + Mole. Activity + (K.E) m + (P.E) m + …….

4. SENSIBLE ENERGY Portion of I.E associated with K.E of molecular [V AV ]+ degree of molecular activity, directly proportional to temperature. As temperature increases, internal energy increases. LATENT ENERGY Portion of I.E associated with phase of system Binding force between atoms of molecule So molecules bind in some form Strong  solid Weakest  Gases If sufficient energy supplied then phase change will occur, that energy is Latent energy

5. Chemical E nergy Atom + e — bounded together with strong nuclear forces I.E associated with atomic bond of molecular is called chemical energy During chemical reaction  chemical bond destroyed + some other compound may formed H 2 C + O 2  H 2 O + CO 2 where H 2 C  bond destroyed & H 2 O-CO 2  another compound formed Total energy = Stored energy + Transit energy

6. Stored energy Transit energy Micro and macroscopic form of energy Energy in transit Energy con Stored in system Not stored in system View as static energy View as dynamic energy (due to variation of intensive property) Point – Point function state variable Path function State variables Recognized only at the boundary K.E + P.E + L.E + S.E + C.E where L.E + S.E = I.E Only when it cross the system boundary  Not exists at equilibrium During motion / transition state Work and heat

7. Closed system  System Interact with surroundings  Work transfer  Heat transfer Work (Closed system) Energy transferred without mass cross the boundary, only due to intensive property difference other than temperature  not be stored on a system

8. Mechanics Definition Work done by SYSTEM IS a force acts upon a body moving in the direction of force

9. Thermodynamic point view: In thermodynamics, work transfer is considered as occurring between system and surroundings Work is said to be done by the system, if the sole effect on things external to the system can be reduced to the raising the weight

10. Sign conversion for Work Transfer DKR 11 When work is done by a system, it is arbitrarily taken to be positive and when work is done on a system, it is taken to be negative. The symbol W is used for work transfer

11. Work done during Quasi – static process and Displacement work:  P 1 V 1  Initial values P 2 V 2  Final values Force acting on piston, F = PA Infinitesimal small work dw = F dz = P A dz dw = P dv  

12. Limitations of integral P dv Following conditions must satisfy System should be closed one Non Flow process Quasi – static process (Reversible process) Effect of gravity, magnetic, Viscous force are negligible All above conditions must satisfy simultaneously W = can be valid Hence work Workdone is path function Work is not a point function If differential is not exact Work is energy in transit Work transfer can take place change in intensive property other than temperature  

13. Forms of Work Displacement work Closed system Peddle wheel work Shaft work Flow work Open system Work is a path function Closed system Change state from 1 to 2 a & b are paths between 1 to 2 Work in 1 – a – 2 Work transfer in 1 – b – 2 Since below 1 – a – 2 is not equal to 1 – b – 2 Work transfer depends on path. Therefore, work is a path function  

14. P dv work in various Thermodynamic process (Reversible ) Constant pressure process (J) Constant volume process  

15. P dv work in various Thermodynamic process (Reversible)   Since   Constant temperature process ( Pv = C) Isentropic process / Reversible adiabatic process  

16. P dv work in various Thermodynamic process (Reversible) Displacement work dw = F dx = P A dx dw = P dv  

17. P dv work in various Thermodynamic process (Reversible) Flow work  Piston is force to move the element where Specific volume Pressure energy / Store energy  

18. P dv work in various Thermodynamic process (Reversible) Electrical work       Current flows through register is a system Current can drive the motor Motor can raise the weight Work transfer into system W = VI (Rate of change) Where c  change in coulomb’s t  time is sec v  voltage   Shaft work     Shaft is considered as system and it rotates by a motor. Work transfer into the system Here, T = Torque Shaft work = W =  

19. P dv work in various Thermodynamic process (Reversible) Free expansion: is finite, but no work done.       Consider a vessel divided into two compartment One filled with gas and other evacuated Partition is removed expansion of gas takes place Gas is not restrained by an opposing force Other side is vaccum ; therefore Workdone = 0 Free expansion is irreversible process, therefore W = 0, W only for reversible process   Peddle work:     , But work is done Involving friction for work process No. volume change W = 0 ; W =  

20. Heat Mode of energy transfer, which cannot be accounted as work from Macroscopic point of view is called Heat. Energy transfer by virtue of temperature difference across the boundary of the system Heat is not property system Heat is energy in transit Its difference is in exact

21. Heat Mode of energy transfer, which cannot be accounted as work from Macroscopic point of view is called Heat. Energy transfer by virtue of temperature difference across the boundary of the system Heat is not property system Heat is energy in transit Its difference is in exact Sign convection       Expansion  + ve Compression  - ve Heating  + ve Cooling  - ve

22. Similarities between Heat and Work Both are Transient phenomena System never possess Heat and work May occur when the system undergoes a change of state. Both are boundary phenomena Both are path functions Both are in exact differentials. Work can be converted 100% into heat Heat cannot be converted 100% into work Their sign convection are opposite Heat is low grade & work is high energy Heat transfer due to temperature difference Work transfer due to other than temperature difference Difference:

23. Closed system  System Interact with surroundings  Work transfer  Heat transfer Work (Closed system) Energy transferred without mass cross the boundary, only due to intensive property difference other than temperature  was not be stored on a system Mechanics Definition Work done by a force acts upon a body moving in the direction of force

24. Thermodynamic point view: In thermodynamics, work transfer is considered as occurring between system and surroundings Work is said to be done by the system, if the sole effect on things external to the system can be reduced to the raising the weight

25. Work done during Quasi – static process and Displacement work:   P 1 V 1  Initial values P 2 V 2  Final values Force acting on piston, F = PA Infinitesimal work dw = F dz = P A dz dw = P dv  

26. Limitations of integral P dv Following conditions must satisfy System should be closed one Non Flow process Quasi – static process (Reversible process) Effect of gravity, magnetic, Viscous force are negligible All above conditions must satisfy simultaneously W = can be valid Hence work Workdone is path function Work is not a point function If differential is not exact Work is energy in transit Work transfer can take place change in intensive property other than temperature  

27. Mechanical Work Transfer Displacement PdV work Paddle Wheel work Flow Work Shaft Work DKR 29

28. Displacement PdV work DKR 30

29. Paddle Wheel work DKR 31

30. Flow Work DKR 32

31. Shaft Work DKR 33

32. Forms of Work Displacement work Closed system Peddle wheel work Shaft work Open system Flow work Work is a path function Closed system Change state from 1 to 2 a & b are paths between 1 to 2 Work in 1 – a – 2 Work transfer in 1 – b – 2 Since below 1 – a – 2 is not equal to 1 – b – 2 Work transfer depends on path. Therefore, work is a path function  

33. P dv work in various Thermodynamic process (Reversible ) Constant pressure process (J)   Constant volume process  

34. P dv work in various Thermodynamic process (Reversible) Constant temperature process ( Pv = C)   Isentropic process / Reversible adiabatic process Since  

35. P dv work in various Thermodynamic process (Reversible) Displacement work       dw = F dx = P A dx dw = P dv   Flow work  Piston is force to move the element where Specific volume Pressure energy / Store energy  

36. P dv work in various Thermodynamic process (Reversible) Electrical work       Current flows through register is a system Current can drive the motor Motor can raise the weight Work transfer into system W = VI (Rate of change) Where c  change in coulomb’s t  time is sec v  voltage   Shaft work     Shaft is considered as system and it rotates by a motor. Work transfer into the system Here, T = Torque Shaft work = W =  

37. P dv work in various Thermodynamic process (Reversible) Free expansion: is finite, but no work done.       Consider a vessel divided into two compartment One filled with gas and other evacuated Partition is removed expansion of gas takes place Gas is not restrained by an opposing force Other side is vaccum ; therefore Workdone = 0 Free expansion is irreversible process, therefore W = OW only for reversible process   Peddle work:     , But work is done Involving friction for work process No. volume change W = 0 ; W =  

38. Heat Mode of energy transfer, which cannot be accounted as work from Macroscopic point of view is called Heat. Energy transfer by virtue of temperature difference across the boundary of the system Heat is not property system Heat is energy in transit Its difference is in exact

39. Heat Mode of energy transfer, which cannot be accounted as work from Macroscopic point of view is called Heat. Energy transfer by virtue of temperature difference across the boundary of the system Heat is not property system Heat is energy in transit Its difference is in exact Sign convection       Expansion  + ve Compression  - ve Heating  + ve Cooling  - ve

40. Similarities between Heat and Work Both are Transient phenomena System never possess Heat and work May occur when the system undergoes a change of state. Both are boundary phenomena Both are path functions Both are in exact differentials. Work can be converted 100% into heat Heat cannot be converted 100% into work Their sign convection are opposite Heat is low grade & work is high energy Heat transfer due to temperature difference Work transfer due to other than temperature difference Difference between Heat and Work

41. Gas from cylinder of compressed helium is used to inflate an inelastic flexible, balloon originally flated completely flat to a volume 0.6m³. If the Barometer reads 760mm of Hg. what is the amount of work done upon the atmosphere by the balloon. Sketch the system before & after the process. A piston & cylinder machine containing a fluid system has a stirring device in the cylinder. The piston is frictionless, & it is held down against the fluid due to the atmospheric pressure of 101.325kPa. The stirring device is turned 10,000 revolutions with an average torque against the fluid of 1.275 mN . Meanwhile the piston of 0.6m diameter moves out 0.8m. Find the network transfer for the system. To a closed system 150kg of work is supplied If the initial volume is 0.6m³ & pressure of the system changes as p = 8 - 4V, where, p is in bar, v is in m³, determine the final volume & pressure of the system. A gas system has mass m, occupies a volume V at a pressure of p & temperature T. these properties are related by the equation (p + ) (V - b) = mRT , where, a; b&R are constants obtain an expression for the displacement work, done by this gas system during a constant temps process for long of gas expanding from 1m³ to 10m³ at a temperature of 293k, assume a=15.7X10 Nm4, b=1.07x10² m³, R=0.278kJ/ kgK .  

42. A Spherical balloon of diameter 0.5m is initially having an inside pressure of 100kpa, due to heating the pressure inside the balloon increases to 400kpa during which the inside pressure various inversely proportional to square of diameter of balloon. Determine the displacement -work during this process . A fluid is heated reversibly at a constant pressure of 1.013 bar until it has a specific volume of oil m³/kg. It is then compressed reversibly according to a law PV=C to a pressure of 4.2 bar, then allowed to expand reversibly according to a Law PV 1.3 =C to the initial conditions. The work done in the constant pressure process is 515 Nm & the mass of the fluid present is 0.2kg. Calculate the net work done on or by the fluid in the process & Sketch the cycle on a P-V diagram. The following data defer to a 12 cylinder single acting, two-stroke marine diesel engine speed-1500pm, cylinder diameter -0.8m, Stroke of Piston -1.2m, Area of indicator diagram - 5.5 × 10 -4 m², length of diagram - 0.06m, Spring value -147 mpa /m. Find the net rate of work transfer from the gas to the piston in KW. A copper vessel of 2kg contains 10 kg of water at initial temperature of water is 20 o C & final temperature is 80°C. Find the heat added to the system. The specific heat capacity of the system during a certain process is given by C n = (0.4 +0.004T) kJ/ kg°c . If the mass of the gas is 6kg & its temperature changes from 25°C to 125°C.