Thermal Flashcards
What is conduction?
Conduction occurs when two objects of different temperatures are in direct contact(Touching).
Heat is transferred from one particle to another when those particles collide.
What is natural convection?
Natural convection describes the motion of a fluid that is caused by natural forces within it.
The most common cause is buoyancy: hotter parts of the fluid are less dense so they float upwards.
As the fluid flows around, it forms a convection current which carries thermal energy throughout the fluid.
Forced Convection
Forced convection is the motion of fluids and gases that is caused by forces outside of it.
These forces often move the fluid faster then or in the opposite direction as natural convection.
Radiation
Radiation consist of electromagnetic waves which transmit energy from a source to an absorber.
This is the only form of heat transfer that does not involve the movement of particles.
The higher the temperature of the emitter, the greater the amount of radiation emits.
Radiation -emission and absorption
Objects can radiate and absorb radiation at the same time.
Objects with higher temperatures to their surroundings radiate more energy then they absorb so they can cool down.
Objects with a lower temperature to their surroundings radiate less energy and absorb more so they warm up.
Factors affecting Radiation
The surface of the body effects how efficiently it radiates and absorbs radiation.
Smooth surfaces don’t radiate or absorb much radiation, while rough surfaces do.
Reflective or white surfaces don’t radiate or absorb as much then dark and black surfaces.
Conductors
A thermal conductor is any material through which thermal energy flows quickly.
Metals such as copper and iron are good conductors.
Some conductors are better then others transferring energy more easily.
Insulator
A thermal insulator is any material through which thermal energy flows slowly.
Some insulators are better then preventing energy transfer than others.
What is Kinetic Theory:
All mater consist of tiny particles called atoms.
Electrical forces both attractive and repulsive, exist between these particles.
Particles move constantly and in a random manner.
Collisions between particles involve no loss of kinetic energy.
The distance between these particles in gas are large compared to the size of it particles.
Thermal Energy
Thermal energy is the sum of the kinetic and potential energies of all particles in that object.
The particles in a object all move by rotation, vibration, or from moving place to place. The kinetic energy of the particle determine how fast they are going
The particles can also attract or repel neighboring particles so they also have potential energy.
Temperature
Temperature measures the average kinetic energy of an objects particles. We experience this how hot or cold a substance is.
Heat
Heat describes thermal energy being transferred between objects dur to a difference in temperature.
Heat is always measured in Joules.
Heat always flows from a body at a higher temperature to a body at a lower temperature.
Heat transfers between objects stops when the temperatures of both the objects are the same, reaching thermal equilibrium.
Absolute 0
Absolute 0 is when the particles are the slowest they can possibly be. It corresponds to -273.15 degree celcius.
Heat Transfer:
If two objects of different temperatures touch, thermal energy will move from hotter object to a colder object until they both reach the same temperature. The state of balance is called thermal equlibrium.
Engine Cooling in Cars - Pump
A pump pushes the coolant around the engine.
Engine Cooling Cars - Thermostat
This releases the coolant into the radiator once it reaches a high temperature.
A radiator - Engine Cooling cars
This is a set of tubes surrounded by thin pieces of metal called radiator fins. Heat from the coolant is transferred to the fins which then transfer it to the air moving past them.
Engine cooling cars - Fans
This pulls the air through the radiator as required to increase the rate of cooling.
Heat Pumps:
Heat pumps allow the flow of energy from a cold place to a hot place.
- Compressor pressurises the gas called a refrigerant, driving up its temperature.
- The refrigerant then travels through a set of tubes called the condenser. The condenser releases the heat to its surroundings which transforms the high temp high pressure gas to a high temp high pressure liquids.
3.The liquid then travels through an expansion valve where the high temp high pressure liquid is depressurized causing it to become a low temp and low pressure liquid.
4.The now-cool refrigerant travels through an evaporator, absorbing heat from its surroundings and turning gas as it does so. It then re enters the compression valve repeating the cycle.
Passive Solar House Design: Positioning
Positioning of the Rooms: Place bedrooms that are used during the day in the north end of the house to make the most of the winter sun.
Bedrooms can be placed at the southern end of the house where they will be cool during summer.
Passive Solar House: Insulation
- Double glazed windows- made of two glass panels with a pocket of air between them. Because air is poor conductor it will slow down the flow of heat into the house.
2.Double brick walls.
Shades - trees and other sources of shade can prevent sunlight entering the house.
