10. Freezing Flashcards
What is the equation for heat loss due to conduction in ice?
q = - k dt/dx
Why is the variation in ice/water temperature often neglected when freezing calculations are made?
The latent heat of fusion is significantly larger than the specific heat of either ice or water. Furthermore the temp of the water at a freeze front is often close to 0 anyway.
What is the equation for convection at an air/ice interface?
q = α_0 (T0 - TA)
What is the equation for fusion heart required to change state?
q = -ρh_if dX/dt
Derive an equation for the time taken for a pond to form a layer of ice of thickness X, assuming a finite air-ice heat transfer coefficient and water temp at freezing.
t = [(2k+α_0X)/2k] [(ρh_if X)/((Tx-TA)α_0)]
What is permafrost
Soil or bedrock which remains frozen over a long time scale
What is the active layer?
The layer above permafrost which freezes and unfreezes as its temp varies ( Temp must be above zero at some point in the year)
Draw a graph of coldest and warmest temperature of permasoil against depth.
..c.c…c……………………………………|…..w…w…… active layer
……………….c………………………….w|……………….
………………………c……………..w……|……………….
……………………………c……..w………|……………….
………………………………..c.w………..|……………….
……………………………………c………..|………………
……………………………………….c…….|………………
…………………………………………..c…|………………
……………………………………………..c|……….. depth here (hp) is depth of permafrost
c = coldest, w = warmest | = 0degrees
Why is it much easier to change water’s temperature as opposed to changing its state
Energy required to freeze/melt (latent heat of fusion = 334 KJ/Kg) is much higher than the energy required to change its temperature (specific heat capacity of water = 4.2 KJ/kgK)
What is the active layer on permafrost
Thin layer close to the surface that can unfreeze if the air temp rises above 0 C
What is an ice age
A climatic epoch in which there are permanent continental ice caps reaching down near sea levels
What is a stadial
A cool interruption of an interglacial
What is an interstadial
A warm interruption of a glacial
