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Hampson, J 2013, Electrotechnology Practice: Section 6

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  • 1. PowerPoint to accompany Section 6 Electrical Heating
  • 2. Heating and heat energy  Heat is the energy transferred by virtue of a difference in temperature between a hot body (physicists use the term ‘systems’) and a cooler body. Heat can only be identified at the moment it crosses from one body to another. It is a momentary occurrence.  When a hot body is in thermal communication with a cooler body, heat energy is transferred until both bodies become stable or are in equilibrium at the same temperature. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 3. Heating and heat energy Heat as energy transfer  A refrigerator is an excellent example of heat transference. A refrigerator uses a liquid refrigerant that evaporates readily into a gas.  Rapid evaporation of the refrigerant in the evaporator (freezer) causes effective cooling thereby enabling the gas to remove large amounts of heat.  The heat energy from the food is transferred to the cold circulating gas. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 4. Heating and heat energy  A compressor is used to suck the gas from the evaporator and recycle the refrigerant through the system. The gas is compressed and discharged into a condenser (black tubes on the back of the refrigerator).  The condenser dissipates the heat energy gained by the gas in the evaporator to the surrounding air and allows the gas to return to liquid form. The liquid is then returned via a capillary tube back to the evaporator thereby completing the cycle. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 5. Heating and heat energy Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 6. Heating and heat energy  In SI units the unit of heat is the same unit that is used for other mechanical and electrical forms of energy, the joule (J).  The first law of thermodynamics is often called the Law of Conservation of Energy.  This law states that energy can be changed from one form to another but it cannot be created or destroyed.  The total amount of energy and matter in the universe always remains constant. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 7. Heating and heat energy  The second law of thermodynamics states that heat can never pass on impulse from a colder to a hotter body.  As a result of this fact, natural processes that involve heat energy transfer must have one irreversible direction. This law also predicts that the heat energy spontaneously disperses if not hindered.  The term given to the measurement of the dispersal (before and after effect) is called entropy. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 8. Heating and heat energy  The third law of thermodynamics states that if the thermal motion (kinetic energy) of molecules could be stilled a state called absolute zero would occur.  Absolute zero is a thermodynamic temperature of 0 Kelvin or –273.15 °Celsius. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 9. Heating and heat energy Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 10. Heating and heat energy Modes of heat transfer There are three modes of heat transfer:  conduction  convection  radiation. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 11. Modes of heat transfer Conduction  Conduction is the transfer of thermal energy between two solid materials in direct contact.  The rate of the transference depends upon the temperature difference of the two solid materials, the thermal conductivity of each material and the distance through which the heat is dissipated. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 12. Modes of heat transfer Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 13. Modes of heat transfer Convection  This is based on the principle that a hot fluid (liquids and gases) is less dense than a cold fluid.  When a cold fluid is heated the cool molecules gain kinetic energy and move away from each other. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 14. Modes of heat transfer Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 15. Modes of heat transfer  Radiation, unlike conduction and convection, does not need a transporting medium such as a molecule to exist. It is an electromagnetic wave like light but with a longer wavelength.  It is transmitted at the speed of light through any transparent medium including a vacuum.  It can be emitted from the source surface, reflected off a smooth surface or absorbed through the surface. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 16. Modes of heat transfer Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 17. Temperature  Temperature is a property of a substance and is not a holistic measurement of the substance’s internal energy.  It defines the direction of heat flow, which is always away from the body that is at the higher temperature and to the body that is at the lower temperature.  Temperature is the hotness or coldness of a substance and is the measure of the average kinetic energy of the molecules of a substance. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 18. Temperature Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 19. Temperature Temperature scale  The fundamental unit of temperature measure in the Système International d’Unités (SI) has been defined as the Kelvin (K). Zero K (0 K) is chosen as absolute zero (temperature at which no thermal activity occurs), while the freezing point of water is 273.16K and the boiling point is 373.15 K. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 20. Temperature Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 21. Temperature  The triple point of water is the most important defining thermometric fixed point used in the calibration of thermometers that accurately obey known laws.  The use of this defined point means that temperature standards around the world can be accurately equivalent. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 22. Temperature Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 23. Specific heat capacity  When the heat energy absorbed by a body increases, the temperature of the body increases.  The quantity of increase depends on the mass of the body.  The specific heat of a body is the amount of heat required per kilogram of the body to raise the temperature by one degree. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 24. Thermal conductivity  Thermal conductivity is the flow of internal energy from a region of higher temperature to one of lower temperature by the interaction of the adjacent particles, atoms, molecules, ions or electrons in the intervening space. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 25. Thermal conductivity There are four factors that affect the rate at which thermal conductivity occurs.  Temperature  Length  Cross-sectional area (CSA)  Type of material Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 26. Control of heating  In order to manage the thermal communication of a heating appliance some form of control device is required.  This control can be exercised via three forms of control—manual, automatic or programmable. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 27. Control of heating Manual control  There are several types of manual control devices and their choice depends upon the switching statement the control device executes.  The simplest form of a control device is a singlepole single-throw (SPST) switch. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 28. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 29. Control of heating Manual control  Another manual switch that was developed from the simple manual switch specifically to control two heating elements is the three-heat switch.  These switches have a four-position switching statement—off, low, medium and high. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 30. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 31. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 32. Control of heating Automatic control  There are two types of automatic temperature control—thermostatic and an energy regulator device called a simmerstat. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 33. Control of heating Thermostats  These devices are used whenever a heating system must be maintained within moderately accurate limits. They are designed to hold a thermal load continually at a set-point temperature with very little variation around the set point.  There are three main configurations of thermostats—bi-metal, strut and tube, and the bulb and capillary. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 34. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 35. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 36. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 37. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 38. Control of heating  The bi-metal, the strut-and-tube and the bulband-capillary thermostats are known as closedloop control sensors.  A closed-loop control senses the temperature of the load (called feedback) and opens or closes accordingly. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 39. Control of heating Simmerstat control (infinite switch)  The simmerstat is a bi-metal switch in which the bi-metal sensing element is activated by the current flow through its own resistance wire element.  This element is wrapped around the sensing bimetal element and is connected in parallel with the load that the simmerstat is controlling. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 40. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 41. Control of heating Programmable thermostat control  Programmable heat controllers are used when fine accuracy in temperature control is required.  These devices are based on microprocessors and thermistor sensors.  Most of these programmable heat controllers can store and initiate multiple daily temperature settings and they can adjust the turn on and off times of heating and cooling systems as the outside ambient temperature varies. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 42. Control of heating Programmable thermostat control There are five essential operating elements that relate with the programmable thermostat—  sensor  input  comparator  output  load. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 43. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 44. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 45. Control of heating Testing a thermostat  In order to maintain consistent quality of heat or cold production it is necessary to perform calibrations on process sensors such as thermostats.  A calibration is a matter of qualifying the sensor under test.  By knowing the limitations of the sensor it is possible to maximise the effectiveness of the heating or cooling process loop. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 46. Control of heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 47. Heating process  A water heater is a closed vessel used to supply hot water.  The heat generated by resistance elements heats the water.  The water heater includes all the controls and sensors necessary to prevent water temperatures from exceeding 60–70 °C.  Water heating processes fall into two categories—instantaneous and storage. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 48. Heating process Instantaneous heaters  Instantaneous or tankless water heaters are small cabinets that heat water on demand or instantly as it passes through the heater.  They contain no significant water storage, possessing only up to a 6 litre operating holding.  These water heaters only use energy when the hot water outlet is turned on and shut down immediately when the outlet is turned off. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 49. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 50. Heating process Storage water heaters  Storage tank water heaters or heat exchange units are very common.  They store and heat a large volume of water in an insulated (injected polyurethane) copper tank at a thermostatically controlled temperature.  The fully enclosed units are mounted at ground or floor level usually outside of the building. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 51. Heating process Mains-pressure water heaters  In the case of a mains-pressure unit the cold water mains pipe is connected directly to the copper storage tank via the cold water inlet.  On entering the unit the cold water is heated by an electric resistance element and then rises to the top of the tank.  Turning on a hot water tap allows the heated water to be delivered at the same pressure as the cold water. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 52. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 53. Heating process Mains-pressure water heaters  Mains-pressure storage heaters are normally attached to an off-peak electricity meter that usually operates between 10:00 pm to 7:00 am.  When a hot-water tap is opened, cold water enters the tank through the NRV and the PLV and the drop in temperature triggers the thermostat and element at the bottom of the tank.  When the tap is turned off, the heating element continues to carry current until the thermostats temperature setting is realised. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 54. Heating process Low-pressure water heaters  Low-pressure or gravity-fed vented (permanently open to the atmosphere) water heaters store water at a pressure lower than mains pressure.  The pressure is determined by the height (pressure = 10 kPa/m height) at which the unit is mounted with respect to the hot water outlets. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 55. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 56. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 57. Heating process Solar water heaters  In solar systems cold water travels through the roof-mounted solar collector where the water absorbs heat from the sun.  Water heating using solar energy occurs during the day and the solar involvement varies significantly throughout the year depending on the climatic conditions.  The apparatus of solar heaters includes the solar collector, insulated storage tank and, if required, pump and control valves. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 58. Heating process Flat-plate collectors  Flat-plate collectors are the most common collector for domestic water heating.  A typical flat-plate collector is an insulated rectangular-type metal box with a transparent cover (similar to a greenhouse) and a black absorber plate. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 59. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 60. Heating process Evacuated-tube collectors  The evacuated-tube collectors consist of rows of parallel transparent double glass tubes, each containing an electromagnetic energy absorber and covered with a solar-sensitive coating.  Sunlight enters the tube, strikes the absorber and heats the water flowing through the collector. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 61. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 62. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 63. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 64. Heating process Calorifiers  Calorifiers are cylinders with an internal coil which allows the use of any type of boiler for hot water production.  The calorifier can be either mains-pressure or low-pressure hot water storage systems.  A significant amount of heat energy can be transferred to the calorifier, allowing a large production of hot water from a relatively small cylinder. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 65. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 66. Heating process Heat pump  A heat pump water heater absorbs heat from the surrounding environment and pumps the acquired heat energy into a hot water storage tank.  The heat pump serves as a heater by absorbing heat from the surrounding environment and pumping it into a closed-system heat-exchanger water storage tank. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 67. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 68. Heating process Safety precautions  If the water heater’s thermostat, which controls the resistive heating element, malfunctions the pressurised water in the tank could continue to heat and superheat (beyond 100 °C). Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 69. Heating process This will cause two problems:  First, since water expands when heated, the water pressure in the tank will increase as the water is superheated.  If the pressure exceeds the vessels maximum pressure threshold the tank could rupture or even explode. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 70. Heating process  Secondly, the release of superheated water (water heated above 100 °C up to its critical temperature of 374 °C without boiling) causes the water to burst into steam (1 litre of water can produce about 3 litres of steam), causing a sudden increase in volume and release of energy.  Lowering the pressure of water lowers the boiling point. There is less pressure above the water to overcome. The superheated vapour plume expands until its pressure equals that of the surrounding atmosphere. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 71. Heating process Space heating  Commercial and industrial premises and even some residential premises can be cold, draughty and difficult to heat.  Poor insulation, high ventilation, excessive outside air filtration and poor draught control lead to chilly indoor environments and reduce work production.  Space heating offers direct, controllable and economic heat when and where it is required. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 72. Heating process Electrical heaters  Panel, column and architrave oil-filled convection-type space heaters provide a wide range of temperature variation with broad surface areas.  An oiled-filled column space heater that uses the convective movement of warm air for quick heating Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 73. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 74. Heating process Floor heating  Heating cables have been developed to meet the specific need for large-area space heating.  These cables have a high temperature capability and low electrical resistance values needed for long circuit lengths.  The cables are located under concrete, ceramic tiling or under soil. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 75. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 76. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 77. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 78. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 79. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 80. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 81. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 82. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 83. Heating process Process heating Heat plays an indispensable role in a wide variety of manufacturing processes:  cooking, softening  melting, drying  curing and fusing.  Electric process heating can be delivered in exact amounts at precise temperatures and has various methods of delivery. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 84. Heating process Resistance heating  Resistance heating has been the most economical means of supplying process heat in many applications.  Generally, resistance heating is an indirect method of heating which converts nearly 100% of the energy in the electricity to heat. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 85. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 86. Heating process  Resistance heating is the most simple and therefore the most widely used method of heat generation.  The most important advantages are wide temperature range, easy method of control, temperature uniformity, flexibility in positioning and design of electric heating elements and low cost. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 87. Heating process Induction heating  Induction heating occurs when a substance is heated from the inside out after being placed within an electromagnetic field.  Industries used induction heating for heat treatment, forging, annealing, soldering, pipe welding, thread rolling, removing electrical varnishes and surface coatings from electrical conductors and metal joining. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 88. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 89. Heating process Infrared heating  Infrared heating is produced by electromagnetic radiation that is generated in a heat source (425– 2200 °C) by vibration and alternation of molecules.  In industry infrared heating is used to warm food and bake bread and chickens, cure plastics and soften adhesives, dry water- and solvent-based paints and for space heating. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 90. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 91. Heating process Dielectric heating  Dielectric heating uses high-frequency electromagnetic waves such as microwaves and radio waves to stimulate molecules in nonconductive substances.  The stimulation causes rapid movement of the substance’s molecules that in turn causes heat to be produced. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 92. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 93. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 94. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 95. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 96. Heating process Cooking appliances  Many of today’s appliance manufacturers are striving to make the cooking process faster and more efficient by making available a wide variety of cooking appliances to the consumer.  Many appliances are particular in their application while others can be used for a wide variety of cooking functions. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 97. Heating process Tariffs  With hot water tariffs the purchaser of the energy can select any tariff in the residential, commercial and industrial category range that is appropriate to their requirements and user category. There are in general three types of tariffs:  on-demand  economy controlled  off-peak controlled. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 98. Heating process Causes of faults in heating equipment  Some faults that develop in heating devices result from loose termination screws which can generate heat and high temperatures at a small location.  The loose termination becomes a small heating unit itself. Insulation degradation with shorting between conductors or to earth is a possible result. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 99. Heating process Causes of faults in heating equipment  Ineffective and loose connections can be diagnosed by measuring the voltage across the connection point.  Mechanical scraped and nicked conductors can reduce the current-carrying effectiveness of a conductor, resulting in localised heating and eventual open-circuiting of the conductor. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 100. Heating process Wiring requirements of heating equipment  AS/NZS 3000:2007 Wiring rules  Areas of importance include electric duct heaters, heating cable systems, appliances producing hot water or steam, cooking appliances, under-carpet wiring systems and main switches.  Tables C1 and C2 of the Wiring rules should also be consulted with respect to maximum demand requirements. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 101. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 102. Heating process  To determine if an element is defective its resistance value needs to be measured.  The resistance can be determined from power and voltage ratings.  If the resistance measurement on the suspected element is proven to be sound then a check of the voltage is required.  A drop of 10% in voltage will reduce wattage by 20%. Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 103. Heating process Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition
  • 104. END Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition