1. Gentle Reminder
If you want to make up labs or standards from Term 1, contact me today.
If you do not contact me by today, your scores for the standards and labs from Term 1 will stay as they are now.

2. General Physics L04_engines.ppt forward and backward
Heat Engines
forward and backward
§ 15.8–15.10

3. Heat Engines
Divert heat flow

4. Heat Engine Qh = W + Qc Qc/Tc ≥ Qh/Th
Heat flow can be diverted to useful work
As long as entropy still increases

5. Heat Engine Th Qh Qc W Tc
e = W /Qh
Efficiency
One type of performance

6. Limits to Efficiency
e = W /Qh = (Qh–Qc)/Qh = 1 – Qc/Qh now Qc/Tc ≥ Qh/Th, so Qc/Qh ≥ Tc/Th thus e ≤ 1 – Tc/Th

7. Refrigerators and Heat Pumps
push heat upstream

8. Heat Pump or RefrigeratorTh
Qh = W + Qc
Qh/Th ≥ Qc/Tc Qh W Qc Tc
Heat flows uphill!
Still, entropy must increase

9. Performance of a Heat PumpTh Qh W Qc Tc
We want Qh
COP = Qh/W

10. Performance of a RefrigeratorTh Qh W Qc Tc
We want Qc
COP = Qc/W