i think it was enough time to do all 3 questions. the last one kind of threw me off and made me do some pointless shit, but i still got it done on time. hopefully, i won't be making stupid calculation errors.

10/19/2005 9:13:41 PM

yeh i needed more time, didn't finish part b of problem 3. i spent too much time writing all my units and showing equations. damned if you do, damned if you dont..

10/19/2005 9:15:51 PM

i fucked up problem 3 pretty bad

add that to the other mistakes i know i made and my grades not going to be good.

10/19/2005 9:18:48 PM

welcome to boles!

10/19/2005 9:25:57 PM

is he going to take off for not showing how you got Q-W=deltaU ??
I forgot

10/19/2005 9:39:02 PM

^no. i doubt it because i remember going to his office and writing that particular equation in front of him.

10/19/2005 9:42:38 PM

Anyone have any clue for prob 115, I found an equation for Heating value in the book where N_eff=Q_combustion/HV...
but I am stuck.
Anyone know any examples anywhere in the text

10/24/2005 11:19:24 PM

question 100

i get 4985 and 5785....

.744 for efficiency, 595.2 for Wout, COPr=8.375 gives me 4985...why does it say 4982? am i missing something here? not rounding gives an even higher answer

10/25/2005 7:07:44 PM

I'm having the same problem now looking back at it


Any help on 103?

[Edited on October 25, 2005 at 8:02 PM. Reason : ]

[Edited on October 25, 2005 at 8:03 PM. Reason : ]

10/25/2005 8:01:06 PM

^^ i got the same answer that was off by 3. i can't figure out 103 and 115.

10/25/2005 8:57:52 PM

yea i'm stuck with 103a&c and 115 as well
if you figure it out please help us

[Edited on October 25, 2005 at 10:54 PM. Reason : a]

[Edited on October 25, 2005 at 10:55 PM. Reason : and c]

10/25/2005 10:54:15 PM

last two for Ch 6?

[Edited on November 1, 2005 at 6:44 PM. Reason : asdf]

11/1/2005 6:44:19 PM

I'm having problems with those two as well.

With 54, I think if I could calculate Qh and Ql I would be ok but I'm having memory lapses from the last chapters. Any hints?

With 102, I'm really lost

11/1/2005 7:04:41 PM

To get Ql and Qh multiply the flow rate by the internal energy (u) for each, then use those to get the COP for a).

I'm not sure if that's how you're supposed to do it, but it gets me the right answer.

[Edited on November 1, 2005 at 8:31 PM. Reason : ]

11/1/2005 8:29:16 PM

for 54

a.)
Qh = mdot(h1-h2)

then COP = Qh/Win

for b)
Ql = Qh - Win

11/1/2005 8:51:06 PM

^^ nope, it's not. you're suppose to take a system of the condenser. it'll be a steady flow system, and the Qh would be the heat transfer out of the condenser.

^ yeah, like that.

for 102 a, take the system of the condenser. the condenser will be acting as a heat transfer system, so two exits and inlets: for water and r-134a. no work, no heat transfer. you should get the mass flow rate for r-134a.

for b, i've got through a really weird system equation by accident. i doubt it's the proper equation to use.

Ql_dot = Win_dot + [ m_dot (h2 - h1) ]_r-134a

use Ql_dot to find c. and for d, i don't know. i'll have to ask boles.

11/1/2005 11:32:07 PM

I'm doing 7.41 and I get 9.68 kW. I just assumed it was isentropic to get s1=s2 to get quality to solve for h2. I'm having problems determining when something is isentropic unless it specifically states that it is. I know that it is adiabatic, reversible...but how can you tell whether a process is reversible or not? Are we even supposed to assume this problem is isentropic?

11/7/2005 3:52:44 PM

Well for problem 41 you know that it should be reversible since it states that it wants what the minimum power should be. The minimum would occur when there are no friction losses, therefore being completely reversible.

11/8/2005 12:08:24 PM

there are too many problems this week and I need someone to work with
I only have 3 completely right....but work for all of them except I haven't started the last one yet

11/8/2005 7:52:55 PM

I got all of them but the last one. I can't seem to get the answer he's giving. Any tips? I'm kind of thinking his answer might be off again.

^ Which ones do you need help on. I agree that it's a lot of problems but many of them where real similar so I go through several farely easily.

11/8/2005 11:47:57 PM