1. First Law Analysis of Closed Systems
Lecture 12
First Law Analysis of Closed Systems

2. Conservation of Energy
The First Law of Thermodynamics for a Closed System
Note: The 1st Law can also be written on a specific energy basis as well as a rate basis.

3. Alternate Forms: 1st Law for Closed Systems
The First Law over a finite period of time is (making a movie),
The First Law at an instant in time is (taking a picture),

4. Thermodynamic Problem Solving
1. Sketch System & Boundary 2. Identify Unknowns (put them on sketch) 3. Classify the System (open, closed, isolated) 4. Identify Processes/States 5. Write Governing Equations (including auxiliary eqns) 6. Algebraically Solve 7. Calculate Values (carrying units w/numbers) 8. Check Results (eqns, algebra, calculations, signs, units) 9. Reflect (on the problem, on the solution, and/or on the problem solving process)

5. Engineering Cycles
Deliver Work
Move Heat E R
Heat Engine
Refrigerator

6. Example 1 (for a cycle)
Given: A commercial refrigeration cycle used for making ice has a COP of ,000 Btu/hr are rejected by the condenser to ambient. Under these conditions, how much heat is extracted from the cold space and how much work is supplied by the compressor?

7. Example 2 (for a process)
Given: One pound of Refrigerant-134a is put into a piston-cylinder assembly at an initial pressure and temperature of 200. psia and 200. F. The R-134a is then slowly heated at constant pressure until the temperature reaches 300. F. Determine the work done on or the by the system and the heat transferred to or from the system.