I am familiar with using $\dot{Q}=c_p\cdot\dot{m}\cdot\Delta T$ to calculate the heat transfer rate of a fluid given a singular value for specific heat capacity (such as with water), but how do I go about calculating heat transfer rate for an aequeous solution such as $MgCl_2 (aq)$? Do I somehow use the heat capacities of both water and salt together?

  • $\begingroup$ I'd be amazed if there's no expermintal resarch into taht. What did you find so far? $\endgroup$ – mart Sep 29 '20 at 14:52
  • $\begingroup$ Check out solar systems - think some tried salt solutions but the disadvantage was corrosion iirc. $\endgroup$ – Solar Mike Sep 29 '20 at 18:46

The formula you are quoting is for estimating the heat exchange rate of a fluid that enters a control volume with rate $\dot m$ and has a change in temperature $\Delta T$.

If you know

  • the mass rate of the solution
  • the precise per weight ratio of your solution
  • the heat capacity of the elements
  • the temperature difference

And provided there are not endothermal or exothermal reactions, then its basically a pretty straight forward sum of the parts.

$$\dot{Q}_{total} = \dot{Q}_{water} + \sum _{i=1}^n \dot{Q}_{sub.1} $$ $$\dot{Q}_{total} = \dot{m}_{water}c_{p,water}\Delta T + \sum _{i=1}^n \dot{m}_{sub.i}c_{p,sub.i}\Delta T $$

However, you will find that in most cases, because $c_p$ of water is so much greater that most other substances and the weight percentage in most solutions is much greater, you probably don't need to bother.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.