# SMS-HVAC Second Editiom 3rd printing



## Pez1343 (Oct 10, 2010)

When i work the problem i get 51 lbm/hr

Even when you use the solution in the back you don't get the answer they have written down. Am i missing something?


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## jmbeck (Oct 12, 2010)

Pez1343 said:


> When i work the problem i get 51 lbm/hr
> Even when you use the solution in the back you don't get the answer they have written down. Am i missing something?


What is the problem? And what is the given answer? I'll see if I can help.


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## Pez1343 (Oct 14, 2010)

A steam boiler has a rating of 100 boiler horsepower. The boiler is operated at 15psig with water entering at 180F. The maximum rate of steam that can be generated is most nearly.

*A)3300 lbm/hr*

B)3340 lbm/hr

C)3350 lbm/hr

D)3540 lbm/hr

Solution:

Q=m(dot)Cp deltaT + m(dot)hfg

Q=100hp x 33475 btu/hr

Cp= 1

Delta T = 250-180=70

hfg= 945.6 Btu/lbm


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## HerrKaLeun (Oct 14, 2010)

it is more accurate and easier to calculate to use enthalpies, especially when you go from liquid to vapor.

Also consider pressure is given in psi*g*, which is gage pressure. Table values are absolute pressure.

I got 3297 or something like that.

It looks like you try to calculate energy required to heat up the water to boiling, and then to evaporate it (and then you should add heating up the steam even more). this gives you 3 equations to solve... good luck. Use the enthalpies from steam tables to rom the liquid low temp to vapor high temp state.

Let us know if you get stuck again.


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