# FE Thermodynamics Review - PowerPoint PPT Presentation

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FE Thermodynamics Review. Dr. Omar Meza Assistant Professor Department of Mechanical Engineering. Topics covered. Thermodynamics Law 1 st and 2 nd law Energy , heat and work Availability and reversibility Cycles Ideal gases Mixture of gases Phase change Heat Transfer Properties of:

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FE Thermodynamics Review

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## FE ThermodynamicsReview

Dr. Omar Meza

Assistant Professor

Department of Mechanical Engineering

### Topics covered

• Thermodynamics Law

• 1stand 2nd law

• Energy , heat and work

• Availability and reversibility

• Cycles

• Ideal gases

• Mixture of gases

• Phase change

• Heat Transfer

• Properties of:

• enthalpy

• entropy

### Tips for taking exam

• Use the reference handbook

• Know what it contains

• Know what types of problems you can use it for

• Know how to use it to solve problems

• Refer to it frequently

• Work backwards when possible

• FE exam is multiple choice with single correct answer

• Plug answers into problem when it is convenient to do so

• Try to work backwards to confirm your solution as often as possible

• Progress from easiest to hardest problem

• Same number of points per problem

• Calculator tips

• Check the NCEES website to confirm your model is allowed

• Avoid using it to save time!

• Many answers do not require a calculator (fractions vs. decimals)

### Properties of Single-Component Systems

For a simple substance, specification of any two intensive, independent properties is sufficient to fix all the rest.

Handbook page:

### Properties of Single-Component Systems

A substance that has a fixed chemical composition throughout

is called a pure substance.

Handbook page:

### Properties of Single-Component Systems

A substance whose properties are uniform throughout is referred to as

A solid

An ideal substance

A pure substance

A standard substance

A substance whose properties are uniform throughout is referred to as

A solid

An ideal substance

A pure substance

A standard substance

### Properties of Single-Component Systems

T= 40oC

Tsat= 17.5oC

• Analysis:

• @ P = 2.0 kPa, Tsat = 17.5oC

• Tsat < T  “superheated vapor”

Given:Steam at 2.0 kPa is saturated at 17.5 oC. In what state will the steam be at 40 oC if the pressure is 2.0 kPa?

### Properties of Single-Component Systems

• At 0.4 MPa the Tsat=142oC approximately. It means that the steam is in the superheated region

Find the volume occupied by 20 kg of steam at 0.4 MPa, 400oC

### Properties of Single-Component Systems

Real gases exhibit ideal-gas behavior at relatively low pressures and high temperatures.

Handbook page:

### Properties of Single-Component Systems

When the volume of an ideal gas is doubled while the temperature is halved, what happens to the pressure?

Pressure is doubled

Pressure is halved

Pressure is quartered

All real gases deviate somewhat from ideal gas behavior: PV= mRT. For which of the following conditions is the deviation the smallest?

High temperature and low volume

High temperature and low pressures

High pressures and low volumes

High pressure and low temperatures

Handbook page:

Handbook page:

### First Law of Thermodynamics

• Formal sign convention:Heat transfer to a system and work done by a system are positive; heat transfer from a system and work done on a system are negative.

Wb is positive  for expansion

Wb is negative  for compression

Handbook page:

### First Law of Thermodynamics

During a process, 30J of work are done by a closed stationary system on its surroundings. The internal energy of the system decreases by 40 j. What is the heat transfer?

Handbook page:

### First Law of Thermodynamics

Calculate the work done by a piston contained within a cylinder with air if 2m3 is tripled while the temperature is maintained at a constant T = 30oC. The initial pressure is P1=400 kPa absolute.

### First Law of Thermodynamics

Polytropic process in a closed system

Handbook page:

Handbook page:

Handbook page:

Handbook page:

Handbook page:

### First Law of Thermodynamics

A steam coil operating at steady state receives 30 kg/min of steam with an enthalpy of 2900 kJ/kg. if the steam leaves with an enthalpy of 1600 kJ/min, what is the rate of heat transfer from the coil?

Handbook page:

Handbook page:

Handbook page:

Mollier Diagram

Handbook page:

Handbook page:

### Second Law of Thermodynamics

Part of the heat received by a heat engine is converted to work, while the rest is rejected to a sink.

• This is a law.

• It is always observed in real heat engines.

• One cannot derive it from first principles.

• No exceptions are known.

It is not just that we haven’t looked hard

enough and that future discoveries will make

it possible to convert heat completely to work.

### Second Law of Thermodynamics

The efficiency of a refrigerator is expressed in terms of the coefficient of performance (COP).

The objective of a refrigerator is to remove heat (QL) from the refrigerated space.

Can the value of COPR be greater than unity?

### Second Law of Thermodynamics

The work supplied to a heat pump is used to extract energy from the cold outdoors and carry it into the warm indoors.

for fixed values of QLand QH

• 1500-MW

• 600-MW

• 900-MW

• 2100-MW

• Yes

• No

• Not clear

• NA

• 2.82 kJ/K

• 6.86 kJ/K

• -8.10 kJ/K

• 8.10 kJ/K