HVAC SMS # 24

[GR8 PLUMENG]

Am having issues with the correct method of calculating Q freezing for this question. 



The solution in the book calculated  Q (freezing) = 10,000lb (.73) (144 Btu/lb)



I used cp of 72.63% water content pork should from ASHRAE Refrigeration book, which was 104 Btu/lb.(2006  R-9.5)

and got Q freezing to be 1,040,000Btu. 

My solution was 619,300 Btu/h, which is different than their solution of 624,900 Btu/hr.

So what is the correct method for such a problem?

Thanks in advance.

 

[Slay the P.E.]

I used cp of 72.63% water 

I think you mean q_latent or h_fg... not cp. Correct?

Anyway, if you calculate q_latent per unit mass as w% x 144 Btu/lbm for w=0.7263 you get 104.6 Btu/lbm. So, its the same thing and the difference is a rounding error between using 73% or 72.63%

The difference between 619,300 Btu/h, and 624,900 Btu/hr is less than 1%

 

[GR8 PLUMENG]

Sorry. Cp of Pork with 73% moisture content.

 

[Slay the P.E.]

Sorry. Cp of Pork with 73% moisture content.

How are you using a specific heat to get a heat of fusion?

 

[GR8 PLUMENG]

I meant heat for fusion. Its been a long day. 

 

[Slay the P.E.]

I meant heat for fusion. Its been a long day. 

Ok, then it’s just a rounding “error”.