Heat Transfer Coefficient for Phase Change

In summary, the problem is about determining how long it takes for a 100 gram sphere of ice at 0 C to melt in a liter of water at 30 C. Assuming uniform mixing and insulation from surroundings, the ice will absorb 8000 calories to melt and cause the final water temperature to be 20 C. Using the heat transfer coefficient and surface area of the ice, the initial rate of heat transfer is calculated to be 0.162 cal/sec. However, the decrease in surface area and temperature make this calculation not entirely accurate in the real case.
  • #1
morrobay
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Homework Statement


One liter of water at 30 C (30000 calories )
A 100 gram sphere of ice at 0 C in center of water volume .
The ice will absorb 80000 calories melting, and final water temperature
= 22000 cal/1100g = 20 C.
Assume mixing and uniform water temp during melting and water vessel
insulated from surroundings. How long for ice to melt ?

Homework Equations


Heat Transfer Coefficient
h =q/A delta T
q = cal/sec
h = cal/sec/M2 C for ice , .523 cal/sec ( converted watts to cal/sec )
A = surface area. for approx 100 cc ice = .01034 M2 ( initial)
delta T 30 C ( initial )

The Attempt at a Solution


This is difficult since both Area and delta T are decreasing
For initial conditions only: q = ( .523 cal/sec/ M2 C ) ( .01034 M2(30 C
q= .162 cal/sec. so 8000 cal/ .162cal/sec. = 13.7 hrs
But in the real case this is not correct as A and delta T are decreasing
 
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  • #2
morrobay said:

Homework Statement


One liter of water at 30 C (30000 calories )
A 100 gram sphere of ice at 0 C in center of water volume .
The ice will absorb 80000 calories melting, and final water temperature
= 22000 cal/1100g = 20 C.
Assume mixing and uniform water temp during melting and water vessel
insulated from surroundings. How long for ice to melt ?

Homework Equations


Heat Transfer Coefficient
h =q/A delta T
q = cal/sec
h = cal/sec/M2 C for ice , .523 cal/sec ( converted watts to cal/sec )
A = surface area. for approx 100 cc ice = .01034 M2 ( initial)
delta T 30 C ( initial )



The Attempt at a Solution


This is difficult since both Area and delta T are decreasing
For initial conditions only: q = ( .523 cal/sec/ M2 C ) ( .01034 M2(30 C
q= .162 cal/sec. so 8000 cal/ .162cal/sec. = 13.7 hrs
But in the real case this is not correct as A and delta T are decreasing

1. That should be 8000 calories melting: ice heat of fusion (80 cal/g) (100g)
Can anyone do this problem or should something else be applied in place of
Heat Transfer Coefficient ?
 

1. What is the heat transfer coefficient for phase change?

The heat transfer coefficient for phase change is a measure of how efficiently heat is transferred between two phases of matter, such as from a solid to a liquid or from a liquid to a gas. It is typically denoted by the symbol 'h' and has units of watts per square meter per kelvin (W/m2K).

2. How is the heat transfer coefficient for phase change calculated?

The heat transfer coefficient for phase change can be calculated using the formula h = Q / (A * ΔT), where Q is the heat transferred, A is the surface area, and ΔT is the temperature difference between the two phases. It can also be determined experimentally by measuring the heat flux and temperature gradient during the phase change.

3. What factors affect the heat transfer coefficient for phase change?

The heat transfer coefficient for phase change can be influenced by a variety of factors, including the type of material undergoing phase change, the temperature difference between the two phases, the surface area of contact, and the presence of any barriers or insulating materials.

4. Why is the heat transfer coefficient for phase change important?

The heat transfer coefficient for phase change is an important parameter in many engineering and scientific applications. It is used to design and optimize heat exchangers, refrigeration systems, and other devices that involve phase change. It also plays a crucial role in studying the behavior of materials during phase transitions and can impact the efficiency and performance of many industrial processes.

5. How can the heat transfer coefficient for phase change be improved?

The heat transfer coefficient for phase change can be improved by increasing the surface area of contact between the two phases, reducing the temperature difference between them, using materials with higher thermal conductivity, and minimizing any barriers or insulating layers. Additionally, optimizing the design and operation of heat transfer systems can also lead to improved heat transfer coefficients for phase change.

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