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Thermodynamics Lecture - 6

 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

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