Minimum Work Input/Power Required to Freeze 50kg Water & Heat a House

In summary, to achieve the minimum power requirement to operate the pump, 1.63kW would need to be used.
  • #1
bennyngreal
12
0
50kg of water at 0ºC have to be frozen into ice in a refrigerator. The room temp. is 20ºC. What is the minimum work input to the refrigerator to achieve this?
(latent heat of fusion of water=3.33x10^5J/kg)
ans:1.22x10^6J

It is proposed to heat a house using a heat pump operating between the house and the outside. The hose is to be kept at 22ºC, the outside is at -10ºC and the heat loss from the house is 15kW. What is the minimum power required to operate the pump?
ans:1.63kW

Please help me to show the methods. I don't understand!
 
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  • #2
bennyngreal said:
50kg of water at 0ºC have to be frozen into ice in a refrigerator. The room temp. is 20ºC. What is the minimum work input to the refrigerator to achieve this?
(latent heat of fusion of water=3.33x10^5J/kg)
ans:1.22x10^6J

The energy needed goes into decreasing the temperature of the water to 0°C (sensible heat) AND into changing the phase of the water (latent heating)

bennyngreal said:
It is proposed to heat a house using a heat pump operating between the house and the outside. The hose is to be kept at 22ºC, the outside is at -10ºC and the heat loss from the house is 15kW. What is the minimum power required to operate the pump?
ans:1.63kW

Given the inside and outside temperature, what is the Carnot efficiency of the pump?

Carnot efficiency = 1 - (Tc/Th) (h=hot temp., c=cold temp.)
 
  • #3
about question1, I do not know the method. I have tried many times but the ans is not matched.
 
  • #4
bennyngreal said:
about question1, I do not know the method. I have tried many times but the ans is not matched.

I think my method should work, are you sure that answer you posted is correct?
 
  • #5
yes. This is my assignment needed to submit tomorrow. Please thanks
 
  • #6
no.2 i still cannot prove the answer correct. I have used your calculation which is also my content of recent learning. But, I cannot do anything...
 
  • #7
no ideas...oh my god
 
  • #8
bennyngreal said:
no.2 i still cannot prove the answer correct. I have used your calculation which is also my content of recent learning. But, I cannot do anything...

For question 2, when you get the efficiency; you also know that efficiency = Heat/Work

so you can find the work like that.
 
  • #9
May u write the procedure, thank you. If u are busy, it is not matter
 

Related to Minimum Work Input/Power Required to Freeze 50kg Water & Heat a House

What is the minimum work input required to freeze 50kg of water?

The minimum work input required to freeze 50kg of water depends on several factors such as the initial temperature of the water, the efficiency of the freezer, and the ambient temperature. However, a rough estimate would be around 105,000 joules or 105 kilojoules.

What is the minimum power required to freeze 50kg of water?

The minimum power required to freeze 50kg of water also depends on various factors such as the efficiency of the freezer and the initial temperature of the water. However, on average, it would require around 350 watts of power to freeze 50kg of water in one hour.

How much work input is required to heat a house?

The amount of work input required to heat a house depends on the size of the house, the insulation, and the desired temperature. On average, it takes around 10,000,000 joules or 10 megajoules to heat a medium-sized house.

What is the minimum power required to heat a house?

The minimum power required to heat a house depends on the work input required and the time it takes to heat the house. For example, if it takes 10 megajoules to heat a house in 1 hour, the minimum power required would be 2.78 kilowatts.

How does the minimum work input/power required to freeze 50kg water and heat a house differ?

The minimum work input/power required to freeze 50kg of water and heat a house differ in terms of the amount and the rate at which the energy is needed. Freezing 50kg of water requires a smaller amount of energy but at a faster rate, while heating a house requires a larger amount of energy but at a slower rate. This is because the process of freezing water is more energy-intensive than heating a house due to the difference in the specific heat capacities of water and air.

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