If I have one refrigerator (fridge A) that's set to 1 degree Celsius and one set to -5 degrees (an arbitrary number that's below freezing point- fridge B). I put one cup of water into fridge A and I put one into fridge B (waters are exactly the same). Will the water in fridge B freeze faster because the temperature is lower? Or will the waters reach 1 degree in the same amount of time but then the water in fridge B will decrease to -5 degrees (and become ice)?
2006-08-13 15:08:57 · 15 answers · asked by Max B 2 in Science & Mathematics ➔ Physics
The rate of heat transfer increases PROPORTIONAL to the temperature difference in most cases of convective/conductive cooling. A simple Newton's law of cooling probably applies in this case (heat transfer coefficients from boundary layer theory).
Q = hA(delta T)
Q = heat loss per unit time
h = heat transfer coefficient, depends on airflow and fluid type (air is the transfering fluid in this case)
A = heat transfer area
delta T = difference in temperature between the bulk water and the bulk air
The water in the colder fridge will cool faster to 1 degree.
The water in the fridge above zero C will not freeze.
Once the water in the colder fridge reaches zero Celcius, it will start to freeze and for a time the heat loss will be constant because the temperature will be zero everywhere until the whole block of ice is frozen.
I am making an assumption that the rate-limiting step in the process is getting heat from the water/ice to the cold air.
2006-08-13 15:23:11 · answer #1 · answered by Anonymous · 0⤊ 0⤋
If each refrigerator has reached its setpoint -5 and zero respectively. Then the water that is in the -5 degree refrigerator will cool down faster than in the refrigerator that is at zero degrees. Several factors come in to play in how fast heat is transferred. One factor is the driving force....that is the temperature difference.
The basic equation to describe the rate of heat transfer Q is
Q=UxAx temperature difference.
U is a combination of factors describing the material or environment that the heat must be transferred through. That environment can be a wall, or a piece of insulation, or the ambient air in a refrigerator. The units are in BTU/deg/unit time.
Area is square units.
So Q = BTU/deg/unit area.
The key qualifiers here is that
1. Both refrigerators have reached their setpoint when the water was put in.
2. The capacity to remove heat is the same for both refrigerators.
Now one qualification.
If both refrigerators are both at the same room temperature...say 20 degrees C, when the water is placed inside. And both refrigerators are the same, then the temperature of the water samples will decrease at the same rate. When the refrigerator set at 1 degree reaches setpoint, the water will not go below 1 degree. The other water sample will continue past 1 degree until it reaches the lower temperature of -5 degrees.
2006-08-13 15:23:45 · answer #2 · answered by richard Alvarado 4 · 0⤊ 0⤋
Water will turn to ice when it reach freezing point, which is 0 degree celcius. The fridge that was set to -5 degree will turn the water to ice faster, but when both fridge have turned each water to ice, both the ice will have the same temperature, and maintain that temperature, and when put to room temperature, both will melt at the same time.
2006-08-13 15:18:29 · answer #3 · answered by megalomanya 3 · 0⤊ 0⤋
If when you place the water inside if the temperature is different ( One fridge at 0 and the other -5) then the B will freeze faster. The amount of heat removed is proportional to the square of the temperature differences.
2006-08-13 15:10:19 · answer #4 · answered by Dr M 5 · 0⤊ 0⤋
Here is a fundamental question for heat transfer. This includes the amount of heat per second traveling out of a cup of water in a fridge.
Q=H*a*Delta( t)
Because it is all in capitols it means per unit time. Basically it breaks down to the amount of heat per second equal the conductivity times the surface area times the difference in temperature.
Because there is a greater difference in temperature in fridge B, it will cool faster than fridge A.
2006-08-13 15:21:24 · answer #5 · answered by eric l 6 · 0⤊ 0⤋
Practically,the water in fridge B will freeze faster.But,due to a concept called the Latent Heat both the water samples will reach the 1 degree mark at the same time.
2006-08-13 15:18:14 · answer #6 · answered by Stifmyster 1 · 0⤊ 0⤋
Assuming efficiency of both machines is same under identical conditions time taken to reach a given temperature will be same. The one set at neg 5 Deg. C will eventually become ice.
2006-08-13 15:15:09 · answer #7 · answered by rjbendre 3 · 0⤊ 0⤋
The water in fridge B will cool faster because the colder temperature will absorb the water's molecular energy faster. Did I win ?
2006-08-13 15:12:46 · answer #8 · answered by crownvic64 4 · 0⤊ 0⤋
the water in the colder fridge will freeze first...
here is why... the temperature transfer is larger when the temperature difference is greater...
think of it in reverse... does ice melt faster in 130 degree weather or in 78 degrees?
2006-08-13 15:13:09 · answer #9 · answered by ♥Tom♥ 6 · 0⤊ 0⤋
the will freeze at the same rate however the water in fridge B will solidify into ice more quickly becaus eit is at a lower temperature.
hey if this is homwork dont count me on this.
2006-08-13 15:12:45 · answer #10 · answered by University Girl 3 · 0⤊ 0⤋