Energy Transfer How much energy is wasted Use

Energy Transfer How much energy is wasted? · Use the equation: % efficiency = useful energy (power) transfer X 100 Total energy (power) input · Thermal transfer of energy o Temperature differences lead to heat transfer: reduce difference to reduce heat loss o Conduction – transfer of heat through solids o Convection – transfer of heat through liquids and gases: warm air is less dense and rises. Cold air is more dense and sinks. Radiation – infra-red radiation: emitted by hot objects; waves move through vacuum; white, shiny surfaces reflect heat, absorbing little. Black, dull surfaces absorb and emit heat well. · Water is 1000 X denser than air – more energy for turning turbines and generating electricity. Seawater more dense than freshwater. o Density = mass g/cm 3 e. g. calculate volume of water volume required to turn turbine What is the formula for density? If a piece of metal has a mass of 1. 2 kg and takes up 0. 4 m 3, what is its density? Name three forms of energy transfer Explain how loft insulation reduces heat loss in a house: 3. 3 Making Use of Energy What is the pay back time for lagging a boiler, which costs £ 40 yet saves the owner £ 80 off their bill in a year? The payback time of an energy-saving solution is a measure of how cost-effective it is. Here is the equation to calculate payback time: payback time (years) = cost of installation (£) ÷ savings per year in fuel costs (£) The payback time will be shortest if the cost of installation is low compared to the savings made each year. Heat insulation in homes 1. Foil behind radiators: reflects IR radiation back; reduces heat lost through walls by conduction; improves efficiency of convection (air is warmed up quicker) 2. Double glazing: traps layer of insulating air; air is poor conductor of heat; air gap small so air can’t circulate so heat not lost by convection. 3. Draught proofing: heat not lost by convection through gaps where air circulates. 4. Foam to insulate tanks: foam traps air which is poor conductor; foam may have shiny inside surface to reflect IR radiation. Draw and label a convection cycle here: