Lesson 2 first law of thermodynamics .pptx

Thermodynamics

1. First Law of Thermo dynamics ENGR. SETH G. GREGORIO Instructor 1

2. WHAT IS THIS? LET’S PLAY A GAME “ FOUR PICS – ONE WORD ”

3. HEAT (Q) HEAT is the energy transferred from one object to another due to their temperature difference . Q = mCp ∆ T Where: Q = Heat in Joule, Calorie m = mass in grams Cp = specific heat capacity, J/g- ⁰C ∆T = Change in Temperature 1 cal = 4.184 Joule

4. WORK (W) WORK -The energy transferred when an object is moved against force. W = F x D Where: W = work in Joule F = Force in Newton D = Distance in Meter

5. First Law of 01 Conservation of Energy 02 Heat and Work 03 System-Surroundings 04 Internal Energy Thermodynamics

6. Conservation 01 States that the energy of an isolated system remains constant 02 Energy cannot be created or destroyed in an isolated system 03 It can only be transformed from one form to another o f Energy

7. KINETIC ENERGY (KE) Energy or stored capacity for performing work possessed by a moving body , by virtue of its momentum = F x d = N - m = Joule K E = ½ mV 2 kg – m 2 /s 2 = kg-m/s 2 - m Δ KE = K 2 – K 1 = ½ m ( V 2 2 – V 1 2 ) Where Δ KE = change in Kinetic energy m m V1 V2

8. POTENTIAL ENERGY (PE) Energy due to its position or elevation P E = mgh = kg-m/s 2 – m = N – m = Joule Δ PE = P 2 – P 1 = mg ( h 2 – h 1 ) Where Δ PE = change in potential energy

9. Q is positive (+) When head is added to the body Q is negative (-) When heat is rejected by the body HEAT (Q) HEAT is the energy transferred from one object to another due to their temperature difference.

10. UNITS OF HEAT C.G.S Calorie or Kilocalorie ( cal , kcal) S.I Joule or KiloJoule (J, kJ) F.P.S British Thermal Unit ( BTU) 1 cal = 4.184 J 1 BTU = 1055 J

11. CONDUCTION transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interaction between particles RADIATION transfer of energy due to the emission of electromagnetic waves or photons CONVECTION transfer of energy between a solid surface and the adjacent fluid that is in motion. It includes combined effects of conduction and fluid motion HEAT TRANSFER

12. TWO TYPES OF HEAT SENSIBLE HEAT LATENT HEAT

13. SENSIBLE 01 CAN SENSE 02 TEMPERATURE INCREASES HEAT

14. LATENT 01 CANNOT SENSE 02 NO CHANGE IN TEMPERATURE 03 PHASE CHANGE HAPPENS HEAT

15. Q =   Where: Q = quantity of heat m = mass L = latent heat of fusion or vaporization CALORIMETRY AND PHASE CHANGE Calorimetry – measuring heat Phase – state of matter

16. Latent Heat of Fusion- solid to liquid Latent Heat of Vaporization – Liquid to gas LATENT HEAT Is the heat needed by the body to change its phase without changing its temperature Latent heat of fusion of ice ( ) = 144 BTU/ lb = 334 KJ/kg=80 Cal/ gm Latent heat of Vaporization of boiling water ( ) = 970 BTU/ lb = 2257 KJ/kg = 540 Cal/ gm  

17. PHASE CHANGE

18. EVAPORATION Evaporation is a change of phase from liquid to gas. Cooling process Endothermic – heat is a bsorbed

19. CONDENSATION Change of phase from gas to liquid Warming process Exothermic = heat is released Steam burn is more damaging than a burn from boiling water

20. It is warm inside the shower room after taking a bath because condensation is a warming process.

21. W is positive (+) When work is done by the system W is negative (-) When work is done on the system WORK (W) Energy transfer associated with a force acting through a distance . W = F x d = Joules

22. W = = F x d ( N-m) Where P s pressure ( N/m 2 ) or Pascal and dV is differential Volume ( m 3 ) = W ( N-m ) or Joule  

23. SYSTEM W < 0 (-) W > (+) Q > 0 (+) Q < 0 (-) UNIVERSE SURROUNDINGS SYSTEM-SURROUNDINGS DIAGRAM

24. Universe – the observable, physical world. System – the limited, defined part of the universe Boundary -  the edge of a thermodynamic system across which heat, mass, or work can flow. Surroundings – all parts of the universe not included in the defined system. TERMS ON THE SUR-SYS DIAGRAM

25. INTERNAL ENERGY (U) It refers to energy contained within the system. The internal energy of a system can be changed by (1) heating the system, or (2) by doing work on it, or (3) by adding or taking away matter.

26. INTERNAL ENERGY (U)

27. INTERNAL ENERGY (U) Energy stored within a body or substance by virtue of the activity and configuration of its molecules and of the vibration of the atoms within the molecules. Δ U = U 2 – U 1 (m mass) Joule Experiment,1843

28. FIRST LAW OF THERMODYNAMICS ( U)   The change in the  internal energy of a closed system is equal to the amount of   heat  applied to the system (Q), minus the amount of  work(W) done by the system on its surroundings.  ∆U = Q - W

29. EXAMPLE

30. EXPLANATION TO THE GIVEN EXAMPLE 1. Heat (Q) is added to the system, therefore the system absorbs heat causing expansion within the system. (Q is positive) 2. Work (W) it expands while it is being heated. (W is negative) 3. ∆ U, the change in Internal Energy , if the heat added is 30kJ , and the Work done by the system is 15kJ , therefore, ∆U is 45kJ.

31. UNITS OF HEAT AND WORK Joule or KiloJoule (J, kJ) Calorie or Kilocalorie ( cal , kcal) BTU

32. APPLICATION Predict the convention signs of heat and work when A gas-filled balloon is heated over a flame Water is heated to the point of vaporization A hot iron bar is placed in cool water.

33. ANSWER Heat is positive and work is negative. Heat is positive and work is negative. Heat is negative and the work is positive.

34. APPLICATION Calculate ∆U for each of the following cases : Added heat of 51 kJ , Work of 15 kJ done by the system Added heat of 100 kJ , Work of 65 kJ done by the system Released heat of 65 kJ , Work of 20 kJ done on the system

35. ANSWER ∆U = +36 kJ ∆U = +35 KJ ∆U = -45 KJ

36. FLOW WORK ( W f ) Flow work or flow energy is work done in pushing a fluid across a boundary, usually into or out of a system. W f = FL = pAL W f = p V Δ W f = W f2 – W f1 = p 2 V 2 – p 1 V 1 Δ W f = change in flow work

37. STEADY FLOW 01 There is neither accumulation nor diminution of mass within the system 02 There is neither accumulation nor diminution of energy within the system 03 The state of the working substance at any point in the system remains constant ENERGY EQUATION

38. STEADY FLOW ENERGY EQUATION Energy entering System = Energy Leaving System P 1 + K 1 + W f1 + U 1 + Q = P 2 + K 2 + W f2 + U 2 + W Q = (P 2 - P 1 )+(K 2 - K 1 )+ (W f2 - W f1 )+(U 2 - U 1 )+ W Q = Δ P+ Δ K + Δ W f + Δ U + W Where Q = Heat P = Potential energy = mgh K = Kinetic energy = ½ mV 2 W f = Flow work or Flow energy = pV = FL = pAL U = Internal energy W = Work = F d = pAL

39. STEADY FLOW ENERGY EQUATION

40. ENTHALPY (H) It is a thermodynamic quantity equivalent to the total heat content of a system. H = U + pV Q = Δ U + W Q = Δ H = H 2 – H 1 The steady flow energy equation becomes P 1 + K 1 + ( W f1 +U 1 )+ Q = P 2 + K 2 + ( W f2 +U 2 )+ W P 1 + K 1 + H 1 + Q = P 2 + K 2 + H 2 + W Q = Δ P+ Δ K + Δ H + W

41. Being busy does not always mean real work. The object of all work is production or accomplishment and to either of these ends there must be forethought, system, planning, intelligence, and honest purpose, as well as perspiration . Seeming to do is not doing… WORDS TO LIVE BY.. .