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## Homework Statement

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Hi guys.

Been looking at this question for a while and can't figure it out.

An aluminium furnace is fuelled with propane gas. The furnace is loaded up with 4 aluminium ingots each of mass 22.5 kg.

The question is:

If 2.1 kg of propane is used to complete the melting process calculate the efficiency of the furnace’s heat transfer process.

## Homework Equations

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Calorific value for propane 49.93 MJ/kg.

## The Attempt at a Solution

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From an earlier question I worked out the following:

660 – 20 = 640

22.5 x 0.91 x 640 = 13,104 kJ

Melting point = 13,104 kJ

321 x 22.5 = 7,222.5

Boiling point = 7,222.5 kJ

Total energy = 13,104 + 7,222.5 = 20,326.5 kJ

So far I've played around with the values:

49.93 x 22.5 = 1,123.425 MJ or kg

49.93 x 2.1 = 104.853 MJ or kg

Do I have to replace the original melting point answer with one of the above answers?

I'm very new to physics so any help very much appreciated.

Thanks.