Cooling with Liquid Nitrogen & Melting Aluminum Cans: Energy Calculations

In summary, there are two problems being discussed. The first one involves calculating the amount of energy needed to remove from 1.4 kg of gaseous nitrogen at 77 K to completely liquefy it, assuming the latent heat of liquid nitrogen is 2.01 *10^5 J/kg. The second problem is about determining the energy needed to melt 2200 aluminum cans, each with a mass of 14.1 g, with an initial temperature of 26.8 degrees C. The specific heat, latent heat, and melting point of aluminum are given as 899 J/kg * degrees C, 3.97*10^5 J/kg, and 660.4 degrees C respectively. The answers are expected
  • #1
mustang
169
0
Problem 2. Liquid nitrogen, which has a boiling point of
77 K, is commonly used to cool substances to
low temperatures.
How much energy must be removed from
1.4 kg of gaseous nitrogen at 77 K for it to
completely liquefy? Assume the latent heat
of liquid nitrogen is 2.01 *10^5 J/kg Answer
in units of J.

Problem 4.
You have collected exactly 2200 aluminum
cans for recycling, each with a mass of 14.1 g.
How much energy is needed to melt them if
their initial temperature is 26.8 degrees C? Assume
the specific heat, the latent heat and the
melting point of aluminum are 899 J/kg * degrees C,
3.97*10^5 J/kg and 660.4degreesC respectively. An-
swer in units of J.
 
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  • #2
Mustang,

You've been here long enough to know you should post what you've tried when asking for help.
 
  • #3
how much homework have you done...
 
  • #4
1600J and 3200J

The answers reflect how much effort you put into trying to solving your homework :tongue2:
 

1. How does cooling with liquid nitrogen work?

Liquid nitrogen is a cryogenic liquid that has a temperature of -196 degrees Celsius. When it comes into contact with objects that have a higher temperature, it rapidly absorbs the heat and evaporates. This causes the object to cool down quickly.

2. Can liquid nitrogen be used to cool down aluminum cans?

Yes, liquid nitrogen can be used to cool down aluminum cans. The rapid evaporation of the liquid nitrogen will cause the cans to cool down quickly, making them cold to the touch.

3. How much energy is required to melt an aluminum can?

The amount of energy required to melt an aluminum can depends on its size and thickness. On average, it takes about 1.8 kWh (kilowatt-hours) of energy to melt a regular-sized aluminum can.

4. How does the energy needed to melt an aluminum can compare to the energy used to cool it down with liquid nitrogen?

The energy needed to melt an aluminum can is significantly higher than the energy used to cool it down with liquid nitrogen. This is because the melting process requires a constant input of heat energy, while the cooling process only requires a one-time transfer of heat energy.

5. Is cooling with liquid nitrogen and melting aluminum cans an efficient way to use energy?

It depends on the purpose. If the goal is to quickly cool down a large number of aluminum cans, then using liquid nitrogen may be more energy-efficient than traditional methods. However, if the goal is to melt the cans for recycling purposes, then it would be more energy-efficient to use a furnace or other high-temperature methods.

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