Casting a metal (Enthelpy of Fusion Question)

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Discussion Overview

The discussion revolves around the thermal interaction between molten aluminum and a steel mold during the casting process. Participants explore the heat transfer dynamics, specifically focusing on the final temperatures of both the aluminum and the steel mold, while considering the enthalpy of fusion and specific heat capacities.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents initial calculations for the heat transfer between aluminum and steel, questioning the final temperatures based on specific heat and enthalpy values.
  • Another participant challenges the initial approach, suggesting that the cooling of aluminum should be calculated from its melting point (660°C) to the final temperature, rather than from the initial temperature (700°C) to 20°C.
  • A subsequent reply confirms the need to adjust the temperature range for aluminum's cooling, proposing the use of (660°C - Tf) for the calculations.
  • Further clarification is provided that the aluminum should cool from its melting point to the final temperature, reinforcing the need for accurate temperature placement in the equations.
  • One participant revises their calculations and shares the results, indicating a final temperature of approximately 94.77°C, achieved through numerical methods.
  • A later comment raises concerns about potential chemical reactions between molten aluminum and stainless steel, emphasizing the importance of using dry molds despite the steel's higher melting point.

Areas of Agreement / Disagreement

Participants express differing views on the correct approach to calculating the final temperatures, with no consensus reached on the methodology or the final results. The discussion remains unresolved regarding the best way to model the heat transfer process.

Contextual Notes

Participants note the importance of considering the specific heat capacities and enthalpy of fusion in their calculations. There are indications of missing assumptions regarding heat losses and the potential for chemical reactions, which are not fully explored in the discussion.

360modina
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I want to take a liquid metal, Aluminum at 700oC and pour it into a steel mold starting at 20oC. For the purpose of the question let’s say that the heat transfer is 100% with no losses to the surroundings.

Here are some numbers:

Al
Mass = 200 g = 0.2 Kg
Ti, Al = 700oC
Cp = 900 J/Kg-K
ΔHf = 10.67 kJ/mol
Melting point of Al = 660oC

Steel
Mass = 3Kg
Ti, st = 20oC

So the liquid aluminum will cool once it hits 660, but the steel mold should never change state due to its higher melting point.

At this point I want to find the final temperatures of the Aluminum and the Steel mold.

Here's what I have so far can someone please check my theory/number placement:

(900 J/Kg-K)(0.2Kg)(700oC-660oC)+(200g)(1 mol/26.96g) + (900 J/Kg-K)(0.2Kg)(Tf, Al - 20oC)

= (486 J/Kg-K)(3Kg)(Tf, St - 20oC)

So my guess is both final temperatures will be the same, I just wanted to know if this work looks correct or if I need to change/move some numbers.
 
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This part (900 J/Kg-K)(0.2Kg)(Tf, Al - 20oC) is not correct. One is still cooling from Tmelt to Tf. The Al decreases in temperature while the Fe heats up.

At equilibrium Tf(Al) = Tf(Fe)
 
That's actually why I posted this, I had a feeling that using the 20oC on the Aluminum side didn't make sense, so I think the left hand side should be changed to (900 J/Kg-K)(0.2Kg)(Tf, Al - 660oC).

Is that correct, or am I still missing something else?
 
Try (660°C-Tf(Al)). The Al is cooling from 660°C to Tf, 660°C > Tf.
 
Ok, I reworked it again let me know what you link:

LHS (Aluminum)
(900 J/Kg-K)(0.2Kg)(700oC-660oC)+(200g)(1 mol/26.96g)(10.67 kJ/mol)+(900J/Kg-K)(0.2Kg)(660oC - Tf)

RHS (Steel)
(486 J/Kg-K)(3Kg)(Tf - 20oC)

I took the sum of the LHS and the RHS and put them both into excel

I set Tf as my variable on both sides of the equation and used goal seek to find Tf = 94.77oC

With that LHS=RHS=109019.9
 
It is my experience that molten Al can do nasty things to Stainless. Even though you are well below SS melting point reactions can still occur. The fact that your steel is cool should help.

Good luck and dry molds.
 

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