Week 2 - Thermal Systems Engineering, Heat Transfer and Heat Pumps

Question 1

What are the 4 basic laws involved in thermal heating systems?

Answer 1

-Conservation of energy(1st law of thermodynamics)
-the second law of thermodynamics
-Conservation of mass
-Conservation of momentum

Question 2

What are the 3 modes of heat transfer?

Answer 2

Convection - transfer of heat between two bodies by currents of moving gas or fluid

Conduction - transfer of energy between two objects by direct contact

Radiation - energy that is emitted by matter in the form of photons or electromagnetic waves

Question 3

3 types of combustion.

Answer 3

Perfect combustion - A very specific amount of Oxygen is used - heat
Good Combustion - additional oxygen is used - heat and o2
Incomplete combustion - excess oxygen is used - smoke only

See Diagram

Question 4

What is wet steam?

Answer 4

Mixture of steam and liquid water.
Contains more than 5% water

Question 5

What is Dry Steam?

Answer 5

Steam at boiling point temperature
Contains no water.

Question 6

What are the main properties of gases?

Answer 6

-Spaced molecules in rapid motion.

-Gas is pressurised due to collisions off the walls.

-Compressible

-Ability to fill the container and mix freely with each other.

Question 7

What are the three laws of gases?

Answer 7

-Boyles Law

-Charles Law

-Gay-lussacs

Question 8

What is Carnot Efficiency?

Answer 8

-Carnot Efficiency - Max efficiency a heat engine can achieve.

Question 9

How does a steam turbine power station operate?

Answer 9

-Burns fossil fuels to boil water

-Produces high-pressure steam

-Drives steam turbine that’s connected to generators

-Produces electricity

Question 10

How does an internal combustion engine work?

Answer 10

-Burns fossil fuels inside engine

-Does 4 strokes which are:
-induction - fuel and air let in through valve

-compression - Compressed 1/10th its original volume

-power - Spark plug ignites it, pushing piston down

-exhaust - exhaust valve opens and gas is let out

Question 11

What is a heat pump?

Answer 11

System that extracts heat from environment and transfer heat indoors or to heat water through a condenser, where heat is exchanged

Question 12

How are heat pumps used as alternative heating systems?

Answer 12

Air Source heat pumps - From Air

Ground Source heat pumps - From Ground

Ground Source Borehole -

Question 13

What is the Kelvin Equivalent to 50 degrees Celsius?

Answer 13

273 + 50 = 323 Kelvin

Question 14

Why are the 3 laws of thermodynamics important?

Answer 14

Provides principles in energy transfer and conversion

Question 15

1st Law of Thermodynamics

Answer 15

Energy cannot be created or destroyed

Question 16

Explain the process of energy transfer in a closed system.

Answer 16

Occurs around the boundaries, by either heat or work.

Heat - transfer of thermal energy due to difference in temperature.

Work - transfer occurs due to mechanical force acting on system.

Question 17

Name two types of convection.

Answer 17

-Forced Convection - Using fan/pump

-Natural convection - Arises from buoyancy forces from temperature change in fluid

Question 18

Describe the process of thermal conduction.

Answer 18

Heat transfer within material due to temperature gradient.

Follows Fouriers Law - heat flux is proportional to temp gradient

Question 19

3rd Law of thermodynamics

Answer 19

There is an absolute minimum temperature at which nothing can be cooled any further.
* Known as absolute zero (-273oC)
(Kelvin)

Question 20

2nd Law of thermodynamics

Answer 20

If heat is the input energy source to a system then there will always be loses in the form of waste heat.

Question 21

2 types of energy transfer in closed system

Answer 21

Energy transferred by heat and energy transferred by work.

Question 22

What is energy transfer?

Answer 22

Energy relocated from one system to another.

Question 23

Thermal Convection

Answer 23

Transfer of thermal energy in liquids and gases

Question 24

Thermal Conduction

Answer 24

In any material heat transfer flows by conduction from hotter to cooler regions
-Direct contact with each other.

Question 25

Thermal Radiation

Answer 25

Energy emitted by matter that is at a finite temperature

Question 26

What is Combustion

Answer 26

Exothermic reaction where substance reacting quickly with oxygen.
Original substance = Fuel
Source of Oxygen = Oxidizer

Question 27

What is Superheated steam?

Answer 27

Steam where temperature is higher than boiling point.

Question 28

Name 2 fossil fuel power generators?

Answer 28

-The Steam Turbine Power Station (Rankine Cycles)

-The Internal Combustion Engine