Phase transitions Flashcards
3 components of Heat Transfer
- food
- heat source
- medium through which heat is transferred to the food
5 ways heat is transferred to food
- conduction
- convention
- radiation
- induction
- dielectric heating
Conduction
* A heat source transfers ____________
* Thermal energy is transferred _____________
* Molecules start to _____
* ________ molecules themselves begin to ______
* Heat passes through food via _____ _____
- heat through a medium directly to the food
- to the outer surface of the food
- vibrate
- Adjacent ; vibrate
- direct contact
Convection
* A heat source distributes _________________________
* ______ _____ (usually air) or _______ (usually oil or water) close to the heat source move towards _____ ___ or ______ further from the heat source
* This creates a _______ movement of _______
- thermal energy through movement
- Warmer gases (usually air) or liquids (usually oil or water)
; cooler gases or liquids - circular ; heat
Radiation
* Heat is _________ directly between objects without an ______ _____-
* Food absorbs ________ _______ which are _______ by a heat source
* The outer surface of the food _______ in ___________ as molecule begin to
_______
* Heat is _______ through the remainder of the food by ___________
Radiation
* transferred ; intervening medium
* electromagnetic waves ; emitted
* increases in temperature ; vibrate
* transferred ; conduction
Induction
* Use of ________ ________ for _____ generation
* A _________ _____ causes ____ _________ of the transfer medium’s molecules
* _____ is then created by ________-
Induction
* Use of electromagnetic forces for heat generation
* A magnetic field causes rapid vibration of the transfer medium’s molecules
* Heat is then created by movement
Dielectric heating
* _______ _________ ________ is used to generate ____ directly within the
food
* The food must have ______ molecules
* _____ molecule interact under the influence of ______ ________
* ______ molecules in food ______ and ______ heat which is generated by
________ ________
- Microwave electromagnetic radiation ; heat
- polar
- Polar ; oscillating microwaves
- Polar ; vibrate and distribute ;
intermolecular friction
9 Influences on Heat Transfer
- Temperature difference
- Food surface area
- Food thickness
- Food specific heat capacity
- Food thermal conductivity
- Cooking material specific heat capacity
- Cooking material thermal conductivity
- Cooking material thermal diffusivity
- Cooking material emissivity
Aluminium Key Characteristics
Heats quickly and evenly
Does not retain heat well
Reacts with food (can be lined or anodized)
Relatively cheaper
Emissivity low if shiny, high if anodised
Copper Key Characteristics
Heats quickly and evenly
Does not retain heat well
Reactive & toxic if diffuses into food in large amounts (often lined)
Oxidizes to a black tarnish so needs lots of
cleaning/polishing
Relatively expensive
Emissivity low if polished, high if coated
Stainless Steel Key Characteristics
Conducts heat poorly (Cu or Al plates can be inserted on
the base)
Retains heat well
Bright and long-lasting shine
Relatively expensive – especially if modified
Emissivity low if polished, high if dull
Cast Iron Key Characteristics
Heats moderately quickly and evenly
Retains heat better than Al and Cu
Reactive – needs to be treated and coated
Tendency to corrode
Cost varies – some very expensive
Moderate emissivity
Glass Key Characteristics
Conducts heat poorly
Not suitable for stove top use
Retains heat well
Non-reactive
Relatively cheap
High emissivity
CorningWare (pyroceram) Key Characteristics
Conducts heat poorly
Not usually suitable for stove top use – some ranges are
Retains heat well
Non-reactive
More resistant to temperature changes than standard
ceramics
High emissivity
Techniques for Ingredient & Food Preparation
Mechanical
Chemical
Heat Removal
Heat Addition
