FE Thermo Review

Fundamentals Exam

UNIVERSITY OF

FLORIDA

Fundamentals Exam Thermodynamics Review

Fundamentals Exam I assume you have applied?!? UNIVERSITY OF

Morning Session:

FLORIDAGeneral –  General – 120 120

questions, ½ pt each

Afternoon Session: General or Discipline Specific- 60 questions, 1 pt each

Fundamentals Exam I assume you have applied?!? UNIVERSITY OF

Morning Session:

FLORIDAGeneral –  General – 120 120

questions, ½ pt each

Afternoon Session: General or Discipline Specific- 60 questions, 1 pt each

Fundamentals Exam What to do in the afternoon? Your call...pass/fail is about the same.

UNIVERSITY OF

FLORIDA

Preparation easier for general.

Fundamentals Exam Morning Session: UNIVERSITY OF

FLORIDA

11 out of 120 thermo questions Afternoon General Session: 6 out of 60 thermo questions

Fundamentals Exam  NCEES Reference Handbook  UNIVERSITY OF

FLORIDA

Have you got it? Why not? How do you get it? How do you use it? www.ncees.org

Fundamentals Exam Morning session Generally unrelated. About 2 minutes  per question. FLORIDA UNIVERSITY OF

Fast recall essential. Use a marking system to keep track  of your progress. Afternoon: 4 minutes per question.

Fundamentals Exam Process of Elimination UNIVERSITY OF

Cross out wrong answers first.

FLORIDA Wrong

answers are sometimes easier  to find than right ones! Units on answer is sometimes a clue.

Answers are seldom given with more than 3 sig figs, your choice should be the closest to your solution.

Fundamentals Exam Guessing UNIVERSITY OF

 No penalty for guessing.

FLORIDA Leave

10 minutes for each session for  “educated” guessing.

Fundamentals Exam Hint: Write correct answer in the margin of  UNIVERSITY OF your test booklet beside the question FLORIDA and wait to you get to the end of the  page before transferring to the answer  key. Lookout for those long, drawn out questions… questions with four   paragraphs for answers!!

Fundamentals Exam Try working the following problem (you have two minutes for each type problem like this): I f a sample experienci ng a change of temperatur e f rom 23  deg C to 46 deg C al so experiences a chan ge in specif ic  UNIVERSITYenthal OF py of 120 kJ/kg, of what materi al i s the sample most  likely to be composed? You can use the data in the  FLORIDA NCEES Suppl ied Ref erence H andbook or the tables in the  back of your book. Better to practi ce these problems with   your NCEES handbook…..remember to be at one with this book!! 

Di d you get H eliu m?  There are sample tests on the NCEES website. Try these out. There are also sample tests in books like Barron’s How to Prepare for the Fundamentals of Engineering FE/EIT Exam. The  bookstores have books like this to help you review for the exam.

Fundamentals Exam Select the best response for an isolated system. a. The entropy of the system remains FLORIDA constant UNIVERSITY OF

 b. The heat transfer equals the work done c. The heat transfer equals the internal energy change d. The heat transfer is zero.

Fundamentals Exam Select the best response for an isolated system. a. The entropy of the system remains constant  b. The heat transfer equals the work done UNIVERSITY OF c. The heat transfer equals the internal energy FLORIDA change d. The heat transfer is zero. For a closed thermodynamic system: Q – w = DU + DKE + DPE, isolated implies Q = W = 0, (d) is the answer, (b) is close but not complete

Fundamentals Exam Two kilograms of air are contained in a cylinder. If 80 kJ of heat are added to the air, estimate the temperature rise if  UNIVERSITY OF FLORIDA the pressure is held constant. Cp = 1.0 kJ/kgK, Cv = 0.716kJ/kgK and k = 1.4. a. 56 deg C  b. 40 deg C c. 33 deg C d. 28 deg C

Fundamentals Exam Two kilograms of air are contained in a cylinder. If 80 kJ of heat are added to the air, estimate the temperature rise if the pressure is held UNIVERSITY OF constant. Cp = 1.0 kJ/kgK, Cv = FLORIDA 0.716kJ/kgK and k = 1.4. a. 56 deg C  b. 40 deg C c. 33 deg C d. 28 deg C Answer is (b) Q = mDh = m CpDT, 80 = 2*1.0*DT, DT= 40 deg C

Fundamentals Exam Steam at high temperature and pressure  passes through a half open globe valve. UNIVERSITY OF Select the property that remains FLORIDA constant through the valve. a. enthalpy  b. temperature c. pressure d. entropy

Fundamentals Exam Steam at high temperature and pressure passes through a half open globe valve. Select the  property that remains constant through the valve. UNIVERSITY OF a. enthalpy FLORIDA  b. temperature c. pressure d. entropy Answer is (a), energy equation q-ws = Dh + D pe + Dke, q = 0, ws = 0, D pe = 0, Dke=0 therefore Dh = 0, an isenthalpic process, enthalpy is constant

Fundamentals Exam For an isentropic process of an ideal gas (k= 1.4), with an initial pressure of 50 pounds per  square inch absolute, an initial specific UNIVERSITY OF volume of 8.2 cubic feet per pound mass, and FLORIDA a final pressure of 120 psia, what is the final value of the specific volume? a. 8.2 cubic feet/lbm  b. 3.42 cubic feet/lbm c. 19.7 cubic feet/lbm d. 4.39 cubic feet/lbm

Fundamentals Exam For an isentropic process of an ideal gas (k= 1.4), with an initial pressure of 50 pounds per square inch absolute, an initial specific volume of 8.2 cubic feet per pound mass, and a final pressure of 120 psia, what is the final value of the specific volume? UNIVERSITY OF a. 8.2 cubic feet/lbm FLORIDA  b. 3.42 cubic feet/lbm c. 19.7 cubic feet/lbm d. 4.39 cubic feet/lbm Answer is (d). P1v1k  = P2v2k , v2 = v1(P1/P2)1/k  = (8.2)*(50/120)1/1.4 = 4.39 ft3/lbm

Fundamentals Exam How much energy must be transferred through heat interaction to raise the UNIVERSITY OF temperature of a 4 kilogram sample of  FLORIDA methane in a closed system from 15 deg C to 35 deg C? a. 34.8 kJ  b. 45 kJ c. 139 kJ d. 180 kJ

Fundamentals Exam How much energy must be transferred through heat interaction to raise the temperature of a 4 kilogram sample of methane in a closed system from 15 deg C to 35 deg C? UNIVERSITY OF a. 34.8 kJ FLORIDA  b. 45 kJ c. 139 kJ d. 180 kJ Answer is ( c). Q- w = DU + DKE + DPE Closed system. Q = DU = mDu = mCvDT = (4kg)*(1.74kJ/kg K)*(35-15 deg C)= 139.2 kJ

Fundamentals Exam A tank contains 0.02m3 of liquid and 1.98 m3 of  vapor. If the density of the liquid is 960 3 and that of the vapor is 0.5kg/m 3, what kg/m UNIVERSITY OF FLORIDA is the quality of the mixture?

a. 5.2%  b. 4.9% c. 2.04% d. 1.01%

Fundamentals Exam A tank contains 0.02m3 of liquid and 1.98 m3 of  vapor. If the density of the liquid is 960 kg/m3 and that of the vapor is 0.5kg/m 3, what is the quality of the mixture? UNIVERSITY OF a. 5.2% FLORIDA  b. 4.9% c. 2.04% d. 1.01% Answer is (b). x = mg/(mg + mf ) = (1.98)*(.5)/((1.98*0.5)+(0.02*960)) = 0.049 or 4.9%

Fundamentals Exam Which of the following is an intensive  property? UNIVERSITYa. OF Pressure FLORIDA  b. Entropy c. Internal Energy d. Enthalpy Answer is (a) Pressure does not depend on mass , extensive properties are proportional to mass

Fundamentals Exam Which of the following devices is possible? a. A cyclic machine that will experience no other interaction than to produce energy through a work interaction, while transferring energy from a high -temperature reservoir to a low-temperature reservoir through heat interactions.  b. A cyclic machine that will experience no other interaction than to transfer to a thermal reservoir an amount of energy equal to the amount of energy it UNIVERSITY OF receives from a work interaction. c. A device that will change the thermodynamic state of a material from on equilibrium state to another without experiencing a change in the amount of  energy contained in the material, in the amount of material, or in the external forces placed on the material. d. A cyclic machine that will experience no other interaction than to accept from a heat interaction with a high-temperature reservoir an amount of energy equal to the amount of energy it receives from a work interaction. Answer is (a). Note that this problem takes about a minute to read!! You better  understand this one as you read it or you won’t do this in 2 minutes!! (b) is not right because entropy decreases continuously, (c) is not right because you can’t be in two equilibrium states, (d) is not correct because energy is increasing continuously

FLORIDA

Fundamentals Exam Energy is added in the amount of 50 kJ in a heat interaction to a closed system while 30 kJ of work is done by the system. The change of the internal energy of the system is: UNIVERSITYa. OF 80 kJ FLORIDA  b. 20 kJ c.  – 20kJ d.  – 80kJ Answer is (b). DE = Q-W = +50kJ-(+30kJ) = 20 kJ This is an example of how you need to know the first law and know the correct sign conventions for work and energy. Q into a system is + W done by a system is + (remember it is a positive thing to get work out of a student!!)

Fundamentals Exam Devices: Turbines UNIVERSITY OF Compressors FLORIDA Diffusers  Nozzles Throttling Devices Heat Exchangers

Fundamentals Exam Devices: Turbines UNIVERSITY OF Compressors FLORIDA mi’(hi +Vi2/2 + gzi) – me’ (he +Ve2/2 + gze)+Q’ –W’ = 0 Assume well insulated, assume Vi=Ve and steady flow mi’ = me’,and zi = ze Then: m’(hi – he) = W’ Compressors: W’ is –  Turbines: W’ is +

Fundamentals Exam Devices:  Nozzles and Diffusers UNIVERSITY OF 2/2 + gz ) – m ’ (h +V 2/2 + m ’(h +V FLORIDA i i i i e e e gze)+Q’ –W’ = 0 Assume well insulated, no shaft work, and steady flow mi’ = me’,and zi = ze Then: (hi – he +Vi2/2 -Ve2/2 ) = 0 Ve > Vi for nozzles and Ve