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sample questions + solutions

PEPEprinciples and practiceof engineering

mechanical: THERMAL and FLUIDS SYSTEMS

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Copyright ©2011 by NCEES. All rights reserved. All NCEES sample questions and solutions are copyrighted under the laws of the United States. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means without the prior written permission of NCEES. Requests for permissions should be addressed in writing to [email protected]. NCEES PO Box 1686 Clemson, SC 29633 800-250-3196 www.ncees.org ISBN 978-1-932613-61-2 Printed in the United States of America November 2010 First printing April 2013 Second printing


iii

CONTENTS

Introduction to NCEES Exams ................................................................ 1

About NCEES

Updates on exam content and procedures

Exam-day schedule

Admission to the exam site

Candidate Agreement

Scoring and reporting

Exam Specifications .......................................................................... 3

Sample Questions and Solutions

Morning Sample Questions ................................................................. 9

Afternoon Sample Questions ............................................................. 27

Morning Solutions .............................................................................. 51

Afternoon Solutions ........................................................................... 67

Psychrometric Chart ....................................................................... 89


1

About NCEES NCEES is a national nonprofit organization dedicated to advancing professional licensure for engineers and surveyors. It develops, administers, and scores the examinations used for engineering and surveying licensure in the United States. It also facilitates professional mobility and promotes uniformity of the U.S. licensure processes through services for its member licensing boards and licensees. These services include the records program, study materials, credentials evaluations, exam administration, and more. NCEES is composed of member licensing boards from throughout the United States and its territories. Updates on exam content and procedures NCEES.org is our home on the Web. Visit us there for updates on everything exam-related, including specifications, exam-day policies, scoring, and corrections to published study materials. This is also where you will register for the exam and find the additional steps you should follow in your state to be approved for the exam. Exam-day schedule Be sure to arrive at the exam site on time. Late-arriving examinees will not be allowed into the exam room once the proctor has begun to read the exam script. The report time for the exam will be printed on your Exam Authorization. Normally, you will be given 1 hour between morning and afternoon sessions. Admission to the exam site To be admitted to the exam, you must bring two items: (1) your Exam Authorization and (2) a current, signed, government-issued photo identification. Candidate Agreement The NCEES Candidate Agreement describes references and other personal materials allowed in the exam room. It also describes other exam policies designed to protect exam content. This document will be printed in your exam book. It is also available for download at NCEES.org. If you register to take an NCEES exam, you are strongly encouraged to review this document prior to exam day, as you will be asked to affirm that you abide by the policies and procedures it describes. Scoring and reporting NCEES typically releases exam results to its member licensing boards 8–10 weeks after the exam. Depending on your state, you will be notified of your exam result online through your My NCEES account or via postal mail from your state licensing board. Detailed information on the scoring process can be found at NCEES.org.


9

MECHANICAL

MORNING SAMPLE QUESTIONS

A psychrometric chart (normal temperature at sea level) is provided on page 89 for your possible use. Unless

stated otherwise, assume sea level conditions.


MECHANICAL MORNING SAMPLE QUESTIONS

Copyright 2011 by NCEES 10 GO ON TO THE NEXT PAGE

101. Poisson's ratio is a term that arises in:

(A) heat transfer

(B) HVAC

(C) mechanical behavior

(D) vapor power cycles 102. Which of the following is used as a measure of energy efficiency of refrigeration systems?

(A) COP

(B) Hydraulic head

(C) Latent heat

(D) SHR 103. A system with an initial cost of $90,000 has an operating cost of $2.50/hr and is operated

16 hr/day for 300 days/year. After 10 years, the system has a salvage value of $10,000. Assuming the interest rate is constant at 10%, the total annualized cost over the 10-year life is most nearly:

(A) $12,000 (B) $14,000 (C) $20,000 (D) $26,000

104. You manage a manufacturing production department that operates 80 hr/week. The process has a

production rate of 60 units/hr, with a scrap rate of 1 out of 120 units. With a 10% lost production time allowance, the number of good units that can be made per week is most nearly:

(A) 4,284 (B) 4,320 (C) 4,760 (D) 4,800


MECHANICAL MORNING SAMPLE QUESTIONS


2,500 lbf

2

1

3

4

119. Which of the following factors is least likely to affect the fatigue life of a steel spring?

(A) Alternating stresses

(B) Cycle period

(C) Primary stresses

(D) Surface roughness 120. The 2,500-lbf load shown in the figure is supported by a beam that is secured by six 3/4-in.-

diameter bolts in a hexagonal array with neighboring bolts 3 in. apart. The shear stress is greatest in which bolt?

(A) 1 (B) 2 (C) 3 (D) 4


27

THERMAL AND FLUIDS SYSTEMS

AFTERNOON SAMPLE QUESTIONS

A psychrometric chart (normal temperature at sea level) is provided on page 89 for your possible use. Unless

stated otherwise, assume sea level conditions.


THERMAL AND FLUIDS SYSTEMS AFTERNOON SAMPLE QUESTIONS


ATMOSPHERE

GAS

P = 19.4 psia

35.0 in.

501. A U-tube manometer containing an unknown fluid is connected to a tank containing a gas. The tank pressure is 19.4 psia, and atmospheric pressure is 14.7 psia. If the fluid height in the manometer is 35.0 in., the density (lbm/ft3) of the manometer fluid is most nearly:

(A) 1.6 (B) 19.3 (C) 62.4 (D) 232

502. Steam at 900,000 lbm/hr exits a low-pressure steam turbine at 2.0 psia with 7% moisture content

and a velocity of 300 fps. The required cross-sectional area (ft2) is most nearly:

(A) 56.3 (B) 135 (C) 145 (D) 156

503. An airplane is flying at a Mach number of 0.85. If the absolute ambient pressure is 20.64 kPa

and the ambient temperature is –56.7°C, the airplane velocity (m/s) is most nearly:

(A) 251 (B) 292 (C) 344 (D) 395


THERMAL AND FLUIDS SYSTEMS AFTERNOON SAMPLE QUESTIONS


REGENERATOR

Wout

Qout

QinQ = 0

120

100

80

60

40

20

0

FLOW (gpm)

HEAD(ft)

A

0 100 200 300 400 500 600

PUMP CURVE

SYSTEM CURVE

525. Known data for a closed regenerative gas turbine cycle are given in the figure. Carbon dioxide [cp = 0.203 Btu/(lbm-°R), cp/cv = 1.285, M = 44 lbm/lbmol] is the working fluid. Assuming constant specific heats throughout, the heat added (Btu/lbm) from an external source is most nearly: (A) 108 (B) 137 (C) 157 (D) 255

526. Given a hydronic piping system and a number of pumps, each having performance characteristics

as shown in the figure below, the minimum number of available pumps needed to supply the required flow at system operation Point A is:

(A) two

(B) three

(C) four

(D) Cannot be done with the available pumps


51

MECHANICAL

MORNING SOLUTIONS


MECHANICAL MORNING SOLUTIONS

53

CONSECUTIVE DAYS TASK AND DURATION PLANNED

REVISED-ACTUAL

A (2) B (2) C (7)

D (11) E (2)

E (2)

0 2 4

13 14 15

16

101. Poisson's ratio is a measure of how a material deforms when acted upon by a force. It is applied in situations where the mechanical behavior of a machinery component is important.

THE CORRECT ANSWER IS: (C)

102. The coefficient of performance (COP) is a measure of energy efficiency of refrigeration systems.

THE CORRECT ANSWER IS: (A)

103. Annualized purchase price over 10 years $90,000 (A/P, 10%, 10) = 0.1627

Annualized salvage value after 10 years $10,000 (A/F, 10%, 10) = 0.0627

Annual operating cost = (300 days/yr)(16 hr/day)($2.50/hr) = $12,000

Total annual cost = $90,000(0.1627) – $10,000(0.0627) + $12,000 = $26,016

THE CORRECT ANSWER IS: (D) 104. 80 hours – 10% lost production time = 72 hours

72 hours × 60 units/hour = 4,320 units 1 scrap/120 units × 4,320 units = 36 scrap 4,320 – 36 units = 4,284 units

THE CORRECT ANSWER IS: (A)

105. If Task C is delayed by 3 days, but has 2 days to spare while waiting on Task D, then the total

compensation delay will be 1 day of delivery time.

THE CORRECT ANSWER IS: (B)


67

THERMAL AND FLUIDS SYSTEMS

AFTERNOON SOLUTIONS


THERMAL AND FLUIDS SYSTEMS AFTERNOON SOLUTIONS

69

501. P = gL

psig psia atm

2 2

2 2 2

3

P = P P

= 19.4 psia 14.7 psia

= 4.7 psig

32.2 lbm-ftP lbf in sec 1 12 in.ρ = 4.7 144 ×gL 32.2 ft 35 in. ftin ft lbf-sec

= 232.0 lbm / ft

THE CORRECT ANSWER IS: (D)

502. m = AV = AV/v

From steam tables

At 2 psia: v L = 0.016230 ft3/lbm

v V = 173.72 ft3/lbm

X = steam quality = 1 – moisture content

= 1 – 0.07

= 0.93

v = vL + X(vV – vL)

= 0.01623 + (0.93)(173.72 – 0.01623)

= 161.56 ft3/lbm

m = AV/v

900,000 lbm/hr = A (300 ft/sec)(3,600 sec/hr)/(161.56 ft3/lbm)

A = 135 ft2 THE CORRECT ANSWER IS: (B)

503. V = Mach number speed of sound = 0.85 c = (0.85) [kRT]0.5

= 0.5

2J N m kg m(0.85) (1.4) 287 ( 56.7 C 273 K) 1

kg K J s N

V = 251 m/s THE CORRECT ANSWER IS: (A)


PE Sample Questions and Solutions Published by NCEES

Chemical

Civil: Construction

Civil: Geotechnical

Civil: Structural

Civil: Transportation

Civil: Water Resources and Environmental

Electrical and Computer: Computer Engineering

Electrical and Computer: Electrical and Electronics

Electrical and Computer: Power

Environmental

Mechanical: HVAC and Refrigeration

Mechanical: Mechanical Systems and Materials

Structural Engineering

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