Etiket Arşivleri: Examples of freezing in daily life

Freezing

• Examples of freezing in daily life

• Purpose of freezing

• Stages of freezing

• Effect of freezing on properties

• Types of freezers

• Freezing medium

• Shelf life and quality of frozen foods

• Equipment to characterize freezing

• Effect of solids on freezing point of solution

• Determination of freezing time

Examples in Daily Life

• Ice rink
– 9,000 gallons of ‐9 °C brine
– 5 miles of pipes
– 270 tons of cooling (1 ton of refrigerant = 3516.8 W)
– Humidity and temperature control needed
– Ice hockey versus ice skating (Load, impact)

• Earth’s surface
– 10.4 % is covered with ice
– 20% is permanently frozen
– Thickness of ice covering Antarctica (avg. temp. ~ ‐37 °C)

• Average: 2164 m; Max: 4785 m (> 10 times height of Sears tower)

• ~61 m rise in ocean level if all ice melted; add ~ 7 m for Greenland; not much in arctic

• Does the water inside animals living in extreme cold, freeze?

• Do hot water pipes burst before cold water pipes in winter?

• Can the engine coolant or fuel in our car freeze?

• Does Niagara Falls freeze?

• How does an ice maker work?

• How does a frost‐free freezer work?

• How does a snow‐maker at a ski slope work?

• How does a de‐icer (for cars and planes) work?

• Ice as an insulator
– Igloo
– Freezing of pond (do fishes survive? What does wind do?)

• Depression in freezing point
– Salting of roads during winter

• Freezing foods
– Blue ice, gel pack, dry ice, liquid nitrogen
– How is a popsicle made?

• Safety of using liquid nitrogen (in a room or car)
– 10 liter dewar spilt in a 17 x 17 x 8 room

• Reduces oxygen level to < 19.5% (need to use respirator)

• Freeze drying of milk/coffee powder
– Lower the temperature and use vacuum to sublimate ice

Freezing

• Purpose of freezing of foods

– To slow down rates of detrimental reactions by lowering temperature and water activity (aw)

• Microbial spoilage

• Enzyme activity

• Nutrient loss

• Sensorial changes
– Prolongs shelf life beyond that of refrigerated foods

Kaynak: https://projects.ncsu.edu/project/foodengineer/231/notes/freezing/Freezing-ppt.pdf