Week 2 - Thermal Systems Engineering, Heat Transfer and Heat Pumps Flashcards
What are the 4 basic laws involved in thermal heating systems?
-Conservation of energy(1st law of thermodynamics)
-the second law of thermodynamics
-Conservation of mass
-Conservation of momentum
What are the 3 modes of heat transfer?
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
3 types of combustion.
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
What is wet steam?
Mixture of steam and liquid water.
Contains more than 5% water
What is Dry Steam?
Steam at boiling point temperature
Contains no water.
What are the main properties of gases?
-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.
What are the three laws of gases?
-Boyles Law
-Charles Law
-Gay-lussacs
What is Carnot Efficiency?
-Carnot Efficiency - Max efficiency a heat engine can achieve.
How does a steam turbine power station operate?
-Burns fossil fuels to boil water
-Produces high-pressure steam
-Drives steam turbine that’s connected to generators
-Produces electricity
How does an internal combustion engine work?
-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
What is a heat pump?
System that extracts heat from environment and transfer heat indoors or to heat water through a condenser, where heat is exchanged
How are heat pumps used as alternative heating systems?
Air Source heat pumps - From Air
Ground Source heat pumps - From Ground
Ground Source Borehole -
What is the Kelvin Equivalent to 50 degrees Celsius?
273 + 50 = 323 Kelvin
Why are the 3 laws of thermodynamics important?
Provides principles in energy transfer and conversion
1st Law of Thermodynamics
Energy cannot be created or destroyed
Explain the process of energy transfer in a closed system.
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.
Name two types of convection.
-Forced Convection - Using fan/pump
-Natural convection - Arises from buoyancy forces from temperature change in fluid
Describe the process of thermal conduction.
Heat transfer within material due to temperature gradient.
Follows Fouriers Law - heat flux is proportional to temp gradient
3rd Law of thermodynamics
There is an absolute minimum temperature at which nothing can be cooled any further.
* Known as absolute zero (-273oC)
(Kelvin)
2nd Law of thermodynamics
If heat is the input energy source to a system then there will always be loses in the form of waste heat.
2 types of energy transfer in closed system
Energy transferred by heat and energy transferred by work.
What is energy transfer?
Energy relocated from one system to another.
Thermal Convection
Transfer of thermal energy in liquids and gases
Thermal Conduction
In any material heat transfer flows by conduction from hotter to cooler regions
-Direct contact with each other.
