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Lect 8 – Thermo I – The First Law, Part A

• Able to summarize chapters 1-4 in terms of key concepts and terms

• Able to write down (math) and explain (words) the first law for a control mass going through a cycle

• Able to write down (math) and explain (words) the first law for

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• Able to write down (math) and explain (words) the first law for a control mass undergoing a process or change of state.

• Able to successfully apply the first law to control mass problems

Blueprint

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Modes of Heat Transfer

Modes of Heat Transfer ?

warm exhaust

cool exhaust

work input

work input

work input

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Example Problem – Fourier’s Law

Given: a power plan condenser that needs to exchange 100 MW. The fluids are steam and seawater. Assume the steelMW. The fluids are steam and seawater. Assume the steel piping is 4 mm thick, the conductivity is 15 W/m K and that a maximum of 5 C temperature difference between the fluids.

Find the req’d minimum area for heat transfer neglecting convective heat transfer in the flows.

Steam Power Plant

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Comparing Heat vs. Work

04_20Heat Crosses the Boundary Electricity Crosses boundary

Points to Ponder

"[Thermodynamics] is the only physical theory of universal content which, within the framework of the applicability of its basic concepts, I am convinced will never be overthrown." — Albert Einstein

" Y l d i thi h b th l f" Young lady, in this house we obey the laws of thermodynamics" – Homer Simpson

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Chapter 5 - Overview

Example – Control Mass Undergoing a Cycle

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Process 1 – Work Input Process 2 – Heat Exchange Outward

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Arbitrary Cycle or Processes

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USS George Bush – Steam Catapult Testing

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Total Energy is Constant

Work and Heat in Action

05_03

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Lect 9 – Thermo I – The First Law, Part B

1. Able to explain and calculate the internal energy of a simple substance

2. Able to explain and calculate the enthalpy of a simple substance

3. Able to successfully apply recommended solution

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techniques to 1st law problems.4. Able to define what specific heat is and how it can

be calculated and used

Solving Difficult Problems

“I think solutions come through evolution.

They come through asking the right questions.

It is the question that we have to define and discover”

Jonas SalkOctober 28, 1914 – June 23, 1995

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Rowan Power Plant - Cogeneration

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Rankine Cycle with a Thermal Process

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Car AC

Car AC

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Car AC

The viewpoint of Sonntag and Borgnakke

8 key questions

# Question CategoryQ g y1 What is the C.V.? Do you need more than one? Are all

flows labeled? ( energy and mass) 2 What do we know about the initial state?3 What do we know about the final state?4. How about the process?5. Would a diagram or sketch help?6. What property model should we use?7. What analysis is appropriate ( eg. focus on boundary vs.

internal behavior)?8. What is our solution technique: trial and error, EES, or

some other tool?

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Example problem

Given: R-12 in piston-cylinder at MPa, 150C with massless piston. At stops V = 0.5m^3. The side above the piston is connected to an open valve with air at 10C

d 450 kP Th h l t l t thand 450 kPa. The whole setup now cools to the surrounding temperature of 10C.

Find: the heat transfer and show the process on a P-v diagram

R-12Q

Internal Energy of Superheat steam

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Consider A Constant Pressure Heat Exchange Process

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