Speeding up Ice Freezing in Backyard rinks with Fans for Convection Cooling

 Making a backyard rink involves making a large container to hold water, and then waiting for that water to freeze.

This year's rink is 28' x 48',  it has an average depth of probably 6-8"  Shallowest parts are just over 4" deep,  and the deepest part is around 14" deep.

Municipal water comes out of the tap at around 5C here,  that water holds heat.

"The specific heat capacity of water is 4,200 joules per kilogram per degree Celsius (J/kg°C). This means that it takes 4,200 J to raise the temperature of 1 kg of water by 1°C."

It takes a lot more energy  (or in this case a loss of energy in the water) to turn water into ice.

"An input of 334,000 joules (J) of energy is needed to change 1 kg of ice into 1 kg of water at its melting point of 0°C. The same amount of energy needs to be taken out of the liquid to freeze it."

from https://www.bbc.co.uk/bitesize/guides/zchgqhv/revision/4#:~:text=An%20input%20of%20334%2C000%20joules,the%20liquid%20to%20freeze%20it.

Once a layer of ice has formed on the surface of the water,  the ice continues to form along the bottom surface of the ice,  slowly getting thicker.  The ice itself traps some of the heat in the water underneath, slowing the cooling process.

Hypothesis:

If the air temperature is -5C,  and winds are calm, the surface of temperature of the ice will be above -5C if there is unfrozen water underneath the ice.  By using fans to push -5C air over the ice,  we can hopefully reduce the temperature of the ice to closer to -5C and cool the ice.

The water underneath the ice should cool faster, (ie lose more heat) and thus freeze faster, as it is also trying to get to steady state and get to -5C.....

Observations:

I am using a cheap infrared thermometer with laser pointer.  It was set outside to acclimatize to the outside air for 15 minutes before taking measurements.

Local weather station reports Air temperature to be -4.7C
Infrared Thermometer reports -17C (i said cheap, plus the surface you measure's reflectiviity affects the reading) for a piece of metal from the roof rake that is suspending in the air.

Ice temperatures were taking at about 3" above the ice surface,  pointed at a 90 degree angle to the ice surface.  The ice surface was cleared of any snow with my glove.

Ice temperature where the biggest fan was blowing measured -14.7C.
Ice temperature at about 24' from fan, not in fan's path  ~ -12C
Ice temperature on opposite side of the rink from the fan, but about the same ice/waterdepth ~ 9C

Interim conclusion,

The fan is helping to cool the ice more effectively than just the ambient temperature/wind conditions.

--updated infrared thermometer readings,  after acclimatizing for about 1hr and using the AVG setting on thermometer.

Air temp -8 C measured on a piece of paper printed 'gray'

Ice temp by fan ~ -7C
Ice temp 20' away from fan ~ -6C
Ice temp far side of rink ~ -5C

About a 2C difference with the fan on