# How to calculate heat load?

1. May 4, 2017

### Povilas

• Moved from a technical forum, so homework template missing
Hello everyone, I'm having problems understanding how to calculate heat load. Does anyone know what formula should i use?
I tried to calculate energy needed to cool the gases to 20 F but i need specific heat witch i don't know how to calculate.
Info in the picture.
Thank you for your time :)

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Last edited: May 4, 2017
2. May 4, 2017

### BvU

please post in homework. And use the template: what formulas do you have at your disposal ? What is your own attempt at solution ?

3. May 4, 2017

### Povilas

I'm sorry, this is not really a homework, this is for my bachelor. I'm in a situation where I took more then I can handle. I will edit my first post to include what I tried.

4. May 4, 2017

### BvU

It's hard work, I realize: coolant must
1. cool the whole gas stream to 20 F (the bulk of the work)
2. condense 90% of the styrene (a small extra term)
for a bachelor you should have formulas at hand for both of these tasks.

5. May 4, 2017

### Povilas

I don't have any formulas, because I'm going somewhat out of my filed (i study environmental engineering). Thank you for replying.

6. May 4, 2017

### BvU

Plenty formulas here, but I would advise to read some introductory thermodynamics first.

7. May 4, 2017

### Povilas

I will thank you.

8. May 4, 2017

### BvU

Read your edited first post: for the gas you indeed need the specific heat, which generally you look up (but that requires that you know what gas it is ... )

You can imagine heat needed is proportional to this $c_p$, proportional to the flowrate and proportional to the temperature drop:$$Q = c_p \, \dot m\, \Delta T$$

9. May 4, 2017

### Povilas

Is there any way to calculate specific heat of styrene? I've been looking for it few hours now... Thank you.

10. May 4, 2017

### Nidum

11. May 4, 2017

### BvU

You just look it up : google 'styrene gas heat capacity' and there you are. Point is that the styrene is only 1.3% of the stuff you are trying to cool down, so you still need to know what the remainder is ...

For the condensation you need the heat of condensation (e.g. from the same source)

12. May 4, 2017

### Nidum

A search on ' thermodynamic properties of styrene ' returns links for several books and papers dealing with this subject in detail . They are almost all behind paywalls but if you are at an accredited study centre you may be able to get free downloads .

13. May 4, 2017

### Povilas

Thank you, I will try some calculations
So lets say I have a mixture of two gases and styrene is 1.3% can i calculate Q like this:
Q=(m1*0.013*c1+m2*0.987*c2)(T1-T2) ?

14. May 4, 2017

### BvU

That's one way. Another is to dig up Purcell and Shareef (which wasn't all that difficult ) and in fact they do it all for you ! Formulas, phys props, the works ! Hideous units, but you can't have everything .

Spoiler: the 'other gas' is air !

15. May 4, 2017

### Povilas

Thank you kind sir, I will be forever in debt for you.

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