Maximizing Energy Efficiency Through Heat Transfer Dynamics

1. Heat transfer Evaporation Infrared Radiation Generating Electricity Particles Efficiency Heating/ Insulation Electrical Energy Red-shift EM Spectrum Waves Formulae Big Bang Interpreting graphs Checking answers How science works

2. Energy transfer by heating • 3 methods – conduction, convection, radiation • The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred by heating. • Rate of transfer of energy depends on surface area and volume, object materials, surfaces. Back

3. Infrared Radiation • All objects emit and absorb infrared • The hotter an object is, the more IR it emits in a given time(time is important!) • Dark, matt surfaces – good absorbers, good emitters (this means that a dark, matt object will heat up faster or cool down faster than a light, shiny one) • Light, shiny surfaces – poor absorbers, poor emitters, good reflectors. Back

4. Conduction All to do with particles banging into each other and passing on KE. Metals have free electrons which can also pass on KE, making metals excellent conductors. The arrangement of particles in a substance determine how good a conductor it is. Conduction, convection, evaporation and condensation all transfer energy, and all involve particles in their theories. Particles In an object, the more kinetic energy the particles have, the hotter the object is. Convection Takes place in liquids and gases. When a liquid or gas gets hotter, the particles have more KE  they move around more, making the liquid or gas less dense. Therefore, hot liquids or gases will rise above cooler liquids or gases. (HEAT DOES NOT RISE, HOT LIQUIDS AND GASES DO!!) Particle arrangements: Solid – fixed in place, least amount of KE but still some movement Liquid – some fixed arrangement, free to slide over each other, more KE than solid Gas – free to move about randomly, no fixed arrangement, lots of KE Back

5. Evaporation Particles can gain kinetic energy through heating but that energy has to come from somewhere The particles need lots of kinetic energy to overcome these forces Particles in a liquid are held together by forces So your skin is losing energy through heating the particles and it will feel colder. Liquids on your skin get the energy they need for evaporation from your skin. If particles are leaving the liquid on your skin through evaporation, they are taking kinetic energy with them. The average kinetic energy of the liquid on your skin has dropped. Back

6. Heating and Insulation Insulation materials aim to reduce energy transfer by heating – they may reduce conduction, convection, and radiation. New heating systems or insulation for a house cost money. The payback time of an investment tells you how long it will take to get your money back based on how much the investment saves you. Payback time = initial investment saving per year Liquids on your skin get the energy they need for evaporation from your skin. Insulation materials for homes (including double glazing) are often given a U-value. This is a measure of how effective the insulator is. The lower the U-value, the better the material is as an insulator. Solar panels sometimes contain water that is heated by the Sun. The pipes in a solar panel are often black. The hot water can be used for heating. Back

7. Efficiency • Two formulae (you’ll be given both) • Efficiency = useful energy out(x 100%) total energy in • Efficiency = useful power out(x 100%) total power in • You might need to rearrange these and put in the numbers. • Answers can be given either as a percentage (e.g. 30%) or as a decimal (0.3)  DO NOT combine these (e.g. 0.3%)

8. Efficiency • Sankey diagrams are often used to show efficiency • Efficient: • Not efficient: Most energy is transferred to a useful form. Most energy is transferred to a non-useful form – it is wasted. The ratio of useful energy transferred to total energy in gives you the efficiency of the machine represented by the Sankey diagram. Back

9. Generating Electricity Power stations heat water to make steam  steam turns a turbine  the turbine spins a generator • Heat can be generated by: • burning fossil fuels • nuclear fission • burning biofuels Water and wind can drive a turbine directly (no need for heating) At night, power stations still generate electricity. Fewer people use electricity at night (they’re asleep…) so the supply of electricity is much greater than the demand. Electricity companies can therefore sell electricity for less during the night. The Sun’s energy can be used to generate electricity (either by heating water or directly) Different methods of generating have different effects on the atmosphere Small-scale generation is useful in remote areas. National grid – a grid of cables and transformers transferring electrical energy around the country Step-up transformer  voltage up, current down  lower current means less heating in cables  less energy wasted in the cables Step-down transformer  voltage down, current up  voltage is stepped down to a level which is safe to use in homes, factories, etc. Back Back

10. Electrical Energy There are a few formulae you should be familiar with (some will be given to you in the exam). Energy transferred = power x time E (Joules) = P (watts) x t (seconds) Energy transferred in kWh = power x time E (kWh) = P (kW) x t (hours) Cost of using electricity = number of kWh x cost per kWh Electrical appliances are machines, they transfer energy from one form to another. For example, a light bulb takes in electrical energy and gives out light and heat; a hair dryer takes in electrical energy and gives out heat, sound, and kinetic energy. Back Back

11. Waves Waves transfer energy Transverse Vibrations are perpendicular to the direction of energy transfer Longitudinal Vibrations are parallel to the direction of energy transfer. Compressions – where the lines are close together. Rarefaction – where the lines are spread out. • Electromagnetic waves are transverse. • Sound waves are longitudinal. • Mechanical waves can be either. Waves can be reflected, refracted (light changing direction), and diffracted (spread out – much greater diffraction when the obstruction or gap is a similar size to the wavelength) angle of incidence = angle of reflection Back Wave speed (m/s) = frequency (Hertz) x wavelength (metres) v = f x λ

12. Electromagnetic Spectrum Electromagnetic waves form a continuous spectrum – the EM spectrum Decreasing wavelength, increasing frequency, waves transfer more energy All EM waves travel at the same speed in a vacuum. Some of these EM waves can be used for communications: Radio waves – TV and radio (these can be diffracted by mountains) Microwaves – mobile phones and satellite TV Infrared – remote controls and optical fibres Visible light - photography Back

13. The Big Bang theory states that… Everything in the known Universe was contained at a very hot, very dense initial point. A rapid expansion took place around 13.7 billion years ago in which space, time and all matter were created. There are 2 key pieces of evidence for this theory – CMBR and Red-shift. Big Bang Theory Other theories: There are other theories for the origins of the Universe. The Steady State theory suggests that the Universe has always been huge and is expanding because matter is entering the Universe through white holes. However, there is very little evidence for this theory. Cosmic Microwave Background Radiation(evidence for Big Bang theory) If you look into space with your eyes, you will see a lot of emptiness. But if you use microwave detectors you will see a lot of cosmic microwave background radiation (CMBR). The existence of this radiation can only be explained by the Big Bang theory. Red-shift is another piece of evidence that the Universe is expanding because it shows us that galaxies are moving away from each other. Back Back

14. Red-shift Doppler  an object making a sound is moving away from you, the sound waves stretch out  wavelength increases, frequency decreases Doppler can also be applied to light, but the object emitting the light needs to be moving very fast and huge distances  this is called Red-shift Absorption spectra: These show which colours of light are absorbed by, for example, the atmosphere of a planet or the contents of a galaxy. The absorbed light is shown by dark lines on a colour spectrum. For a galaxy moving away from us, these lines are shifted towards the red end of the spectrum. Red-shift is one piece of evidence for the theory that the universe started through a very rapid expansion (the Big Bang) and is continuing to expand (CMBR is another piece of evidence). The faster a star or galaxy is moving away from us, the bigger the red-shift will be. Blue-shift is the opposite to red-shift. If a galaxy is moving towards us the wavelength of light reduces and the spectrum of light is shifted towards the blue part of the spectrum. Back Back

15. Formulae • The formulae you need to use will (probably) be given to you • You should be able to rearrange the formulae when asked • After that, all you need to do is put in the numbers Y = X Z Z = X Y If X = Y x Z Back

16. How science works • Bias – if research is funded by a company (e.g. a mobile phone company) there is the possibility that the results could be biased, or even not published if they do not favour the sponsoring company. • Reliability – Results are reliable if they are repeatable by others. Results can be compared with others to check reliability. Reliability of data can be improved through collecting lots of data and calculating an average. • Sample size – experiments should use as large a sample of people as possible to get a good representation of a population.

17. How science works • Control groups – Used in investigations to allow a comparison to be made. • Issues: Ethical – using people (particularly children) or animals in scientific researchEconomic – research being funded by companies, governments, etc.Social – how the results of scientific research affect peopleEnvironmental – research projects can have a negative impact on an environment even if there is some benefit (e.g. wind farms) Back

18. Interpreting graphs • Use numbers from the graph to back up any conclusions • Use terms and units given to you in the graph • Use numbers from the graph as well • If there is more than one plot on the graph, compare the plots in your answer • The graph might show a relationship between X and Y – i.e. directly/indirectly proportional

19. Interpreting graphs What does this graph tell you? Temperature (oC) Time (s) • Red starts at a higher temperature than blue. • The temperature of red decreases more rapidly than blue. • Blue maintains a constant temperature for longer. Back

20. Checking your answers • After you’ve calculated an answer, have a good look at it and compare it to the question  does it look right? • E.g. A student is asked to calculate the mass of some water being heated in a beaker. She gets a result of 2.3 x 1012 kg… • Make sure you use a calculator if you’re not confident doing it by hand! Back