Technical Interview Questions related to Thermodynamics

[mejia198021]

Hi,

I am interviewing for a position at an energy plant and as of right now I am reviewing my old thermodynamics book. I was wondering if anyone can suggest any thermodynamic related technical questions or related to the overall mechanical engineering field. Any assitance would be much appreciated. Thank you

 

[DRWeig]

Hi Mejia,

My favorite thermo quiz during an interview was:

I have a cup of 150 degF coffee and an ounce of 40 degF cream. I won't be taking a sip for another 15 or 20 minutes, and I want my coffee to be at the highest possible temperature at that later time. Do I add the cream now, or just before I drink it?

Good on ya,

Goober Dave

 

[athomas236]

I was asked during one interview to develop the equation for the temperature profile through a thick tube from basic principles including the necessary integration.

I was never sure why anyone would want to do that when they could look it up in a textbook.

Regards,

athomas236

 

[SomptingGuy]

I was asked how I might estimate the heat flow through a specific (irrelevant here) metal component.

- Steve

 

[davefitz]

OK ,assume you are the assistant devil in charge of the heating system in Hades. You have the option of throwing in the fire (a) the governor of illinois (b) a hedge fund manager from palm springs Florida and (c) a subprim mortgage loan officer. Which one goes into the fire first?.

( this is a trick question)

 

[moltenmetal]

Funny that most of the thermo questions offered here are really heat transfer questions- you fail guys!

Some thermo questions?

I've invented a car which uses a 3000 psig vessel to store compressed air as an energy storage medium, and a single stage piston "engine" to run the wheels. Assuming I don't have a huge air-to-air heat exchanger under the car, about what percentage of the input mechanical energy I used to compress the air can I expect to get out to my wheels?

If the vessel is 100 gallons, the car weighs 2000 pounds, and I suddenly rupture the tank, how high in the air will the contents of the tank propel the car, neglecting friction?

I've got a machine which transfers heat from my beer to cook my eggs, without needing the input of mechanical work. What have I invented? More specifically, what KIND?

Best of luck!

 

[chicopee]

Are you referring to a steam power plant or a gas turbine power plant or a hydraulic turbine power plant. Be specific with your terms, don't be ambiguous as you would not impress those who will be interviewing you.
With regard to thermo, know your cycles, all of them.

 

[SomptingGuy]

moltenmetal: Closed questions. Interviews need open ones.

- Steve

 

[Unotec]

Moltenmetal,

If somebody asked me that type of questions in an interview, I'd be thanking them for their time and moving on.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[bk19702]

Part II of davefitz's question (extra credit):

Is Hades considered exothermic or endothermic?

 

[Unotec]

Hell did not freeze over

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[moltenmetal]

Hell, Michigan, freezes over every year!

unotec: then we wouldn't be hiring you...

We don't ask questions about thermo per se, nor do we typicaly ask anything that requires a numerical answer. We do ask technical questions which probe a candidates' understanding of applicable engineering fundamentals. They test whether a candidate guesses, reasons from what they know, or has the good sense to say, "I don't know, but here's what I do know- and I'd go to this book to get the piece I've forgotten that I need to give you an answer."

We've only ever had one candidate walk out.

The boss tried to give our test to a candidate as a written test once. The boss left the room and receptionist observed that the candidate promptly whipped out a cellphone and started calling his buddies...We didn't hire him...

The good ones actually perk up when we show that we care what they actually know, rather than asking them soft-pedal questions about what they want to do with the rest of their lives...

 

[willard3]

I have my PE and have had for years and have practiced for years.

I was interviewed once by a company that really wanted to hire me and they sat me down and gave me a simplistic engineering test. I told them that I had already passed the required PE test and left.

It's a mistake to patronize a licensed Engineer, you need them worse than they need you.

 

[rmw]

If you don't have previous experience in the type of energy plant to which you are applying, they will see that from your resume' (CV). What you should be prepared to do is be familiar with the cycles and processes that pertain to them (steam, gas, hydro???) and relate how whatever experience or education you have does pertain to the position that they are trying to fill.

You won't impress a steam plant guy spouting off about Brayton cycle stuff nor will you impress a CT plant guy with Carnot cycle stuff. Prepare yourself and know what they do and be prepared to be conversant about their process and how your qualifications will benefit them.

If you are newly graduated or changing career paths, don't try to bluff them. It will reflect badly on you. ONLY if you are coming from a similar background will you be able to stand there toe to toe with them and do battle over thermodynamics. Otherwise, your responses should be more like what moltenmetal has recommended.

They are probably looking for a variety of things and surely you must have some aspect of what they are looking for or they wouldn't be extending the invitation to interview in the first place.

I once went to an interview, one of multiple interviews at that same site thinking that I had applied for and was interviewing for one specific job (project related for mechanical rotating machinery) that I was well enough qualified for and when after the first (and primary) interview one of the subsequent interviewers spotted sone specific other type of experience on my CV (still related to thermodynamics) he took off down that path and the interview immediately went off in that direction-one I was totally unprepared for. Fortunately I did have plenty of that kind of experience, and I did go toe to toe with him/her/them and was immediately offered a job that didn't even exist and one that they had to later create a positon for after I had accepted. Turns out I had a kind of experience that they knew they needed but they hadn't specifically advertised for yet. It worked out well. Mind boggling, however.

rmw

 

[Powerman81]

Hi

I am a fairly a new higher at consaltant compnay for Nuclear generating plant and had an internship at a coal plant. If you are to work for a caol plant, I'd say worry less about answering any technical questions other than the basic concept of power generation. Look in your thermodynamic book and it should have a chapter on power plant. Don't be mr. know it all. make short answers or refer to a course you have taken that relates the the work or position you are applaying for. you can be a vibration specialist at a power plant!!

 

[moltenmetal]

willard3: good thing you walked out, because you wouldn't have fit in there anyway. Both you and they would likely have been unhappy.

I've met plenty of engineers, licensed and unlicensed, even with advanced degrees, all with excellent resumes, who couldn't function in our work environment due to a lack of necessary fundamental technical and practical knowledge. The boss has even hired a few without testing that we later had to fire due to incompetence- often after they cost us big money. I know licensed engineers in Canada who sell real estate, or who have been in managerial roles for so long that their engineering fundamentals are under a layer of dust and rust a foot thick- but that won't stop them from coming in for an interview if we invite them. So a license is no guarantee whatsoever here in Canada that a candidate is suitable for our technical job or even for ANY technical job. And it's clearly not a barrier to licensure, since only 25% of Canadian engineering graduates bother to go on to licensure.

Asking someone questions that test their knowledge AND their ability to reason before hiring them isn't patronizing- it's commonsense. And it's necessary at present, given the answers we've been receiving to some of the questions we've been asking. The results of these tests are appalling, actually!

In fact- far from it being considered patronizing, you should consider it a good sign when they test your knowledge. It's a sign that the company cares more about what you know and how you think than they do about the cut of your suit, your age, colour or whether or not you play golf- or any other criteria irrelevant to job performance.

 

[Unotec]

moltenmetal,

I think I can see your point (not that you would hire me anyway) and I would have to agree. Thinking of it, I'd actually appreciate if in an interview I am confronted with more hands-on, trouble-shooting, how-you-think approach questions than school-book type, which is the case for the PEng confirmatory tests, by the way.

The way the candidate approaches them not only shows their ability to reason but also speaks volumes of their personalities, which is also an important factor when assembling working teams.

However, I trust it is NOT HR doing these types of interviews, right?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[electricpete]

I don't think I have ever seen an "interview question" thread yet that hasn't degenerated into a debate about touchy-feely vs technical quesiton. For that debate, suffice it to say that most but not all companies stay away from technical questions. The closest you can get to a technical question is usually along the lines of: tell us about a project you've done... or tell us about a problem you've solved.

I can see the value of well-rounded questions and certainly a person's character, personality, work ethic, having-his-head-on-straight etc are important. The fact that it is so taboo to throw even a single technical questions into a mix is imo a reflection of the fact that H.R. weanies want to run the show and they have convinced everyone else that their's is the only way. I'm sure others disagree. That's just my opinion.

Moltenmetal - what are the answers to your 3 questions? I'm guessing the 3rd one is impossible?




=====================================
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[willard3]

Moltemetal

The company's test of your knowledge assumes that it is competent to test your knowledge. The company doesn't care a damn thing about anything but the bottom line, the function of a corporation.

Nothing more patronizing than the guy who interviews for a living.

 

[moltenmetal]

No, HR doesn't do these tests- we don't have the "luxury" of an HR department. An engineer does the test. And nobody here "interviews for a living"- we're all practicing engineers. When we hire we're looking for colleagues.

Our test questions are qualitative or semi-quantitative at most, and do tend to the practical. They test for the calibration of a candidate's commonsense, familiarity with the underlying fundamentals (ie. is it sharp or buried under rust and dust from disuse), their propensity to guess rather than reason etc.

We test our engineers' knowledge and ability to reason before we hire them because we've had poor results in past when we didn't do so- when we let the "boss" do the hiring. Resumes can be padded, and even good schools put out people who don't deserve their degrees. It's the same all over the world. And in Canada we accredit programs and schools rather than making every licensee candidate write a set of technical exams, so even a license is no guarantee of satisfactory knowledge of engineering fundamentals.

Yes, we care what they know and how they reason, because if they know little or reason poorly it will be bad for the company's bottom line- and that means ultimately it will be bad for OUR bottom lines too- the place has only one pocket!