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Hello. FYI, we don't have (yet) products targeted to the HVAC&R exam; only TFS. There is some overlap, but we also cover a LOT of stuff you don't need.

That would be a poorly crafted problem. Can you share the problem statement (don't reveal the source)?

See this post  http://engineerboards.com/topic/34191-pe-thermal-and-fluids-system-study-pal-october-2019/?do=findComment&comment=7569055

We just received the 3rd successful entry, so the contest is now closed. Thanks!

Great question. For ideal gases it can be shown that both internal energy, u, and enthalpy, h depend on temperature only (you can find this proof in any Thermo textbook).  Since u and h depend only on temperature for an ideal gas, the specific heats Cv and Cp also depend on temperature...

A rigid tank with an internal volume of 100 gallons contains saturated water at 50 psia and 50% of the mass of water inside the tank is liquid. The tank is fitted with a pressure relief valve (PRV) set to open if the pressure ever reaches 150 psia. In one occasion, a process upset caused the...

Check your private messages for the feedback. Since this contest is ongoing, we will not discuss the solution here.

y is defined as the fraction of steam that gets extracted from the high pressure turbine. Hence y = m2/m1 but m7=m1 so y = m2/m7 y is NOT also equal to m3/m7. m3 is what remains in the turbine after extraction, so m3 = m1 - m2. Divide this by m1 and you get m3/m1 = 1 - y

Perform an energy balance on the feed water heater; energy in = energy out m2 h2 + m6 h6 = m7 h7 but, from a mass balance m2 + m6 = m7 so the energy balance becomes: m2 h2 + (m7 - m2) h6 = m7 h7 Now, divide this equation on both sides by m7 and note that y=m2/m7: y h2 + (1 - y) h6 = h7...

Yes, be careful. Throttle devices are isenthalpic. It just happens that for ideal gases, isenthalpic = isothermal (regardless of the magnitude of pressure drop). That is not generally the case. For example, look at the throttle device in the vapor compression refrigeration cycle. It is constant...

Thanks Mike. @Buckley if you perform an energy balance around the throttle device you’ll get h7 = h8 Since (for ideal gases) the enthalpy changes only with temperature, then if there is no enthalpy change, there is no temperature change, hence T8 = T7.

The water enters as a compressed liquid at 70F, so that is the inlet temperature of the water. So, for the water, the enthalpy at the inlet is calculated with the saturated liquid approximation for compressed liquids: h(70F, 50psi) = h_f(70F) and NOT h_f(50psi) so you have to change that in...

This problem is discussed in pages 2 and 3 of this thread (click the link below). However, we can talk about it here, absolutely. Can you show your work?

Thanks @Audi driver, P.E. for this endorsement! 👍 @MecEng we don't offer a course with lectures (yet). However, our practice problems book presents the solutions to each problem in such detail and extensive discussions and tips that a lot of our customers have not really needed lectures...

Also recommend “reverse” combustion analysis, in which the composition of combustion products is provided (given the composition of combustion products of a known hydrocarbon fuel, do you know how to calculate, say, the air-fuel ratio?) Also, something like the attached (we consider this...

@MikeGlass1969 can tell you Combustion was actually an important part when he took the HVAC exam. He doesn’t seem to be active on the boards anymore, but search his old posts. At a minimum, do some problems where you have to figure out air-fuel ratios, (or alternatively, fuel-air ratios). Also...

Hi all! We are offering a special prize to the first 3 people who correctly answer the following problem. Please do not post the solution here. Send it to us (work it by hand and take a picture or scan to pdf) via private message. PROBLEM: An industrial ice-making machine operates on the...

Oh, OK then. At this point there's not much else you can do. Have you checked out the "practice problem of the week" thread? There's like 8 or 9 problems there as well as lively discussion among EB users on the solutions and techniques. Highly recommended: 

I’m grateful that you’ve tried our exam and that you’ve found it useful. I assume you’ve also worked the NCEES practice exam. That being said, I don’t think I’ve ever encountered anyone who only used those two resources for their exam prep. There’s a lot more you can do; although at this point...

Excellent.