Specific heat help -- cooling down a metal bar

In summary, the conversation discusses cooling a 17-4 stainless steel bar from room temperature (70F) to 50F by immersing it in pure water. The surface area of the bar is 245 sq. inches and it weighs 6.9 lbs. The specific heat of the bar is 0.11 (BTU/lb/F) and the desired temperature change is 20 degrees. The time required to cool the bar depends on several factors, including the heat transfer coefficient and the shape/thickness of the bar. However, the amount of BTU's used can be calculated using the temperature change, specific heat, and mass of the bar.
  • #1
Don9of11
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0
I'm a design draftsman, I have bar of 17-4 stainless steel it weighs 6.9 lbs. The Product Data Sheet shows a specific heat 0.11 (BTU/lb/F (32-212F) (www.aksteel.com)

It's at room temperature or 70 degrees F. I want to cool the bar to 50 degrees F. The surface area of the bar is 245 sq. inches. The bar is then immersed in pure water and the water temperature is 50F.

How long will it take to cool and how many BTU's are used?

I'm trying to put the answer in simple terms and so I'm looking to get a simple equation that let's me say "it takes (X) amount of minutes or hours to cool and it takes (X) amount of BTU's".

Thanks
 
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  • #2
Welcome to PF, Don9of11!
Don9of11 said:
How long will it take to cool
Can't answer that without knowing the heat transfer coefficient between the bar and the water. That, in turn, depends on the conditions: is the water just a small tub, or is the cool water forced over the bar? Is the bar submerged completely? And so on. You could assume a very high coefficient to get a minimum time ("it will take at least XXX minutes"). The shape/thickness of the bar comes into it and you will need the density and the thermal conductivity values as well. Google "Heisler Charts" for a starting point on one way of doing the calculation.

how many BTU's are used
That you can calculate, its just the temperature change (70 - 50 = 20 degrees) times the specific heat, times the mass of the bar. That assumes that the entire bar reaches a uniform temperature and the water stays at 50 degrees somehow.
 

1. What is specific heat and how does it relate to cooling down a metal bar?

Specific heat is the amount of heat required to change the temperature of a substance by 1 degree Celsius. It is a property that is unique to each material and is important in understanding how it will respond to changes in temperature. In the case of cooling down a metal bar, the specific heat will determine how quickly the bar will lose heat and reach a lower temperature.

2. How does the specific heat of a metal bar affect the cooling process?

The specific heat of a metal bar determines how much heat energy is required to change its temperature. This means that a metal bar with a higher specific heat will require more heat energy to cool down compared to a metal bar with a lower specific heat. So, a metal bar with a higher specific heat will take longer to cool down.

3. What factors influence the specific heat of a metal bar?

The specific heat of a metal bar is influenced by several factors including the type of metal, its mass, and its temperature. Different metals have different specific heats due to variations in their atomic structure. The mass of the metal bar will also affect its specific heat as a larger mass will require more heat energy to change its temperature. Lastly, the specific heat of a metal bar will also change with temperature, meaning it will require more or less heat energy at different temperatures.

4. How can the specific heat of a metal bar be calculated?

The specific heat of a metal bar can be calculated by dividing the heat energy required to change its temperature by the mass of the bar and the change in temperature. This can be represented by the equation Q = m * c * ΔT, where Q is the heat energy, m is the mass, c is the specific heat, and ΔT is the change in temperature.

5. How can the cooling process of a metal bar be accelerated?

The cooling process of a metal bar can be accelerated by increasing the surface area of the bar, increasing the difference in temperature between the bar and its surroundings, or by using a cooling agent such as water or ice. These methods increase the rate at which heat energy is transferred from the bar, thus speeding up the cooling process.

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