Download - Resources Week01 SCIGAST 1.9
Radiation
• A process that does not require direct physical contact between heat source and the object.
• Thermal radiation: heat from the sun; Electromagnetic radiation: microwave
Principle of radiation
• All molecules are vibrating to some extent, → all matters emit thermal energy all the
time. • The hotter an object gets, the more energy it
radiates in higher regions of the spectrum.
Nina Paley [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Principle of radiation
Opensource Handbook of Nanoscience and Nanotechnology
Application of radiation in cooking
1. Grilling and broiling • These cooking methods all emit
visible light and also intense radiation of infrared energy.
By _BuBBy_ from USA (365 Days Project 188/365: Saturday Night Grilling) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
Grilling
Broiling
By Tomomarusan (This is the creation of Tomomarusan) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC-BY-2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons
Grilling and broiling
• Advantage: rapid and thorough browning of
the surface, and so produces intense flavors.
• Disadvantage: huge disparity between the rate of
heat conducted within the food.
Examples related to food handling and preparation - Radiation
• In an oven, the heating caused by radiation can be increased by moving food closer to the walls or reduced by wrapping the food with reflective aluminum foil.
By Joseph Zollo from Marietta, GA, United States of America (Flickr) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
Energy transfer can take place by phase change
Description of Phase Change
Term for Phase Change
Heat Movement During Phase Change
Temperature Change During Phase Change
Solid to liquid Melting Heat goes into the solid as it melts. None
Liquid to solid Freezing Heat leaves the liquid as it freezes. None
Liquid to gas Vaporization, which includes boiling and
evaporation
Heat goes into the liquid as it vaporizes.
None
Gas to liquid Condensation Heat leaves the gas as it condenses. None
Solid to gas Sublimation Heat goes into the
solid as it sublimates.
None
Energy transfer can take place by phase change
• Latent Heat of Condensation
– The amount of heat energy released to the environment when a gas changes its state to a liquid
– For one gram of water, the amount of heat energy released is 540 calories at a temperature of 100℃.
Energy transfer can take place by phase change
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Principle of vaporization/condensation
• When water boils, the change from liquid state to gaseous state require a large amount of energy –latent heat
• Conversely, a large amount of energy
is released when a gas condenses to become a liquid.
Phase Change of Water
By Cawang (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Application of vaporization in cooking
• Steaming – Impart energy of motion and energy
of vaporization.
Advantage: – especially quick in bringing the surface of
food to boiling point and keeping it there.
Disadvantage: – lower penetration power
Conclusion
• In cooking, heat energy can be transferred by conduction, convection, radiation and vaporization/condensation
• One kind of heat transfer usually predominates in a given cooking technique and, together with the cooking medium, has a distinctive influence on foods.