Error in MERM?

[bph]

In MERM 12th ed, page 33-6 (chapter 33 is refirgeration cycles), first sentance in secion 9;

"Any gas will cool when expanded."

I don't think this is correct, it depends on the Joel-Thompson coeficient and the inversion temperature of the gas.

See MERM 12th ed page 25-3.

Not a big deal really, but kind of distracting. I did not see this on the erratica.

BPH

 

[Sschell]

Not looking at MERM at the moment, but I have alot of experience with the J-T effect (and the reverse braton cycle), I agree with your conclusion... the statement "any gas will cool when expanded" should be modified to include proper temp and pressure conditions...

 

[Sschell]

good catch BTW.... it was tough for me to pay attention to details while reading MERM while studying.

 

[bph]

good catch BTW.... it was tough for me to pay attention to details while reading MERM while studying.

Thanks. I'm doing my depth in MD and worked all the MERM MD problems, but I figure reading the thermo / fluids / HVAC sections is as important as doing the problems for the morning breadth sections. I am moving through the material way faster than my comfort level, but still think reading is important and so sacrificing some problem solving time to do so.

The unqualified statement about "Any gas will cool when expanded" sounds like the type of thing they would ask in the morning breadth exam, or some variation of it. Now that I think of it, NCEES practice exam had a question just like this, it showed a very complex device and then asked what was the temperature of expanded gas after a throttling valve, but said earlier in the problem that the gas was ideal, and so the answer was no temp change. I missed this question not because I didn't know the answer, but did read carefully and note that the gas was ideal.

Bart

 

[Sschell]

So... did this come up at all on the test? (Remember not to post anything specific to an actual question)

 

[bph]

So... did this come up at all on the test? (Remember not to post anything specific to an actual question)

I don't want to say what did or didn't come up, but there are lots of questions on the exam that poke at basic understanding in different ways and I feel there is a Very high probability if someone goes into the exam thinking that "any gas will cool when expanded" will likely miss a question or two due to that inaccurate knowledge.

It's really one of those classic concepts that lots of engineers don't know. I may even classify it as one of the most common fundamental questions that an engineer would likely to get wrong if asked on the street.

BPH

 

[Sschell]

wow... so you came out with a good feeling overall?

 

[bph]

wow... so you came out with a good feeling overall?

I felt fantastic after the first 1/2 of the morning, and very good about the last 1/2 of the morning.

The afternoon I got off to a bad start, several of the hardest problems (for me) to start the session, so I fell behind a bit, got tunnel vision and started to get very sloppy; not writing out the whole solution, or drawing proper diagrams, or canceling units etc. I recovered at about the 1/2 way point and felt ok after that, but just ok.

Overall, I felt the exam was very passable for me, based on my preparation and experiance, However, I feel I may have made one too many dumb mistakes, I do that when I get tunnel vision, focus in narrowly and miss stuff. If I was given the exam as a practice exam, I'm 90% sure I would pass it, but when it's the real thing, and this was my first time, it's different. I (like many) feel there is a good chance I passed, but also a significant chance I didn't.

My prep was kind of short (~5 weeks) but very intense (averaged 5 hr/day every day). I hope I passed, I don't know if I can open up the time to study for 3-4 months?.

BPH

 

[Sschell]

based on the study hours you were most likely well prepared. The toughest part is waiting on results. Good luck!

 

[MikeR]

I felt fantastic after the first 1/2 of the morning, and very good about the last 1/2 of the morning.The afternoon I got off to a bad start, several of the hardest problems (for me) to start the session, so I fell behind a bit, got tunnel vision and started to get very sloppy; not writing out the whole solution, or drawing proper diagrams, or canceling units etc. I recovered at about the 1/2 way point and felt ok after that, but just ok.

Overall, I felt the exam was very passable for me, based on my preparation and experiance, However, I feel I may have made one too many dumb mistakes, I do that when I get tunnel vision, focus in narrowly and miss stuff. If I was given the exam as a practice exam, I'm 90% sure I would pass it, but when it's the real thing, and this was my first time, it's different. I (like many) feel there is a good chance I passed, but also a significant chance I didn't.

My prep was kind of short (~5 weeks) but very intense (averaged 5 hr/day every day). I hope I passed, I don't know if I can open up the time to study for 3-4 months?.

BPH

My experience was the reverse. I was down with the flu and got tanked up with medication for the exam. Turned up at 7:00 AM feeling like a thousand little goblins were sawing off my brain. Got off to to nightmare start but felt a little bit better about the last hour. After lunch I felt much better and felt that the afternoon went much better than I expected.

I am a little bit worried about the little traps that NCEES like spring on you (with units). As I was not feeling sharp I may have tanked some of these problems. Overall I must say that I did much better than I thought I would. Five days before the exam I was going to give it a miss because I could not even get out of bed.

I agree with you that if I took this exam at home as a practice test that I would pass. It was not very difficult but the exam pressure and situation tends to put you off your game.

We were informed by the proctor that the results take 13-14 weeks in CA. This SUCKS!

 

[Sschell]

yes cali is always the last to get results... by like a month.

 

[bph]

We were informed by the proctor that the results take 13-14 weeks in CA. This SUCKS!

MikeR,

Sorry to hear about you getting sick, after I saw you post about that (before the exam) I became very careful about hygiene so as not to catch anything, so I guess you cold say you took one for the team.

What's up with CA? Why are they so slow and why do they wait until just a couple weeks before the exam before informing people they can sit of it? I though CA was ahead of the country in most respects?

It's strange how different the test taking experience can be for each person on a given day, or for one person on different days; kind of gives a feeling that it's not as much under your control as one would hope.

Good luck,

BPH

 

[Kephart P.E.]

I had basically the same problem, I got sick on Sunday-Wednesday of the week of the exam. I started feeling better by Thursday night, but it did cut into my study schedule.

I felt really good about the morning session, but similar to bph, the afternoon started off bad and I got behind and did a little freak out for 20 minutes. I think I did o.k., but definitely not a stellar performance.

 

[MikeR]

MikeR,Sorry to hear about you getting sick, after I saw you post about that (before the exam) I became very careful about hygiene so as not to catch anything, so I guess you cold say you took one for the team.

What's up with CA? Why are they so slow and why do they wait until just a couple weeks before the exam before informing people they can sit of it? I though CA was ahead of the country in most respects?

It's strange how different the test taking experience can be for each person on a given day, or for one person on different days; kind of gives a feeling that it's not as much under your control as one would hope.

Good luck,

BPH

To be fair, I did notice at the exam site there were at least 400-500 people sitting for the PE in different disciplines. Also the next day there are about 600-700 people sitting for the FE and Civil Surveying/Seismic exam. Also when you add the Land Surveying exam folks there may be about 1200 over two days in one venue. I was in the Sacramento exam site. When you count in the Bay Area and Southern CA sites (with much larger numbers), I suspect there may be about 5000 examinees sitting for various exams. One of the main reasons for the delay is the Seismic and Surveying exam which delays the whole process.