Test 2, Spring 2013 Thermal Fluid Sciences
Name ______(100/110 points)
Closed book, one page of notes one side in your own hand writing.
Casio: All fx-115 models. Any Casio calculator must contain fx-115 in its model name. Examples of acceptable Casio fx-115 models include but are not limited to the following:
- fx-115 MS
- fx-115 MS Plus
- fx-115 MS SR
- fx-115 ES
- fx-115 ES Plus
Hewlett Packard: The HP 33s and HP 35s models, but no others.
Texas Instruments: All TI-30X and TI-36X models. Any Texas Instruments calculator must contain either TI-30X or TI-36X in its model name. Examples of acceptable TI-30X and TI-36X models include but are not limited to the following:
- TI-30Xa
- TI-30Xa SOLAR
- TI-30Xa SE
- TI-30XS Multiview
- TI-30X IIB
- TI-30X IIS
- TI-36X II
- TI-36X SOLAR
- TI-36X Pro
By my signature below, I hereby swear that I have neither received aid from any other student, nor have I given aid to any other student on this exam.Moreover, I swear that I have not committed any form of academic dishonesty and have maintained ethical integrity in accordance with the UTEP Handbook of Operating Procedures, the UTEP Civil Engineering Honor Code, and the ASCE Code of Ethics.
Signature: ______
By my signature below, I swear that I have not witnessed any other student commit any form of academic dishonesty with regard to this exam.
Signature: ______
1. (10 points = 3 for answer, 2 for proper properties, 3 for equation, 2 for calculating relative rates)
Explain it in words but also show appropriate equation, properties, and numbers to prove your point.
Answer:
The thermal conductivity for brick is 0.72 W/m/K, 0.17 for wood, Q-dot/A = - K (T2-T1)/(X2-X1);
change in temperature is the same for a fair comparison so the rate is determined by K/thickness of wall
Brick = K/thickness = 0.72/0.25 = 2.88 W/K/m2 wood = 0.17/0.1 = 1.7 W/K/m2 so brick loses more than wood
2. (10 points = 5 for answer, 5 for equation)
Show an equation to prove your point
Answer: head loss doubles according to hloss = V2/2g ( f L/D), only the pipe length changes so the head loss changes in the same ratio as the pipe length – it doubles
3. (25 pts) Water at 10 degrees C is flowing steadily in a 20 cm diameter cast iron pipe with an average velocity of 8.5 m/s. Find the friction factor. Clearly show all the steps you take and clearly show how you calculated each intermediate dimensionless number. Also give:
Kinematic viscosity with units, ν = 1.31E-6 m^2/s, they calculate it is mu/density which they have in the tables
Relative roughness with units = 0.26/1000/0.2 = 0.0013, dimensionless
Reynolds Number with units, Re = 1.3E6, dimensionless
Discharge with units, V-dot = 0.27 m3/s
f = 0.021 (allow some reasonable slop, say: 0.02 to 0.022) for chart reading error
4. (15 points) Show direction of holding force. The density of water is 62.4 lbm/cubic foot.
The mass flow rate in, m-dot =
The force to hold it in place =
5. (10 points) The flow rate in a 10 inch diameter pipe is 16.17 ft/s and the friction factor is 0.02. The entrance loss coefficient is 0.5 and the exit loss coefficient is 1.0. Find the minor loss of head at the entrance.
0.5 * V^2/2 g = 2.03 (as shown right on the figure above) 5 pts for head loss equation, 5 pts for answer
6. (10 points) Hot air at 70 degrees C is blown over a 2-m x 3-m flat surface with a temperature of 25 degrees C. If the average heat transfer coefficient is 45 W/(m2-K), determine the rate of heat transfer in kW.
Answer:
Q-dot = h A (T – Tinfinity) = 45 * 2*3 *(25-70) = 12.15 kW
7. (5)
8. (10) Circle and label:
Highest pressure in figure, system with greatest flow rate, system with lowest flow rate.
Highest P is bottom of right tank in B
Greatest flow rate is D
Lowest flow rate is B (no flow)
9. (5) What is the flow rate in this pipe system with a pump?
Where system and pump curves intersect, about 4.2 m3/s
10. (5) Is momentum a vector?
yes
11. (5 extra credit) Show that the velocity head, pressure head, and elevation head all can be expressed as J/N, show your work
V2/2g = reduces down to m then multiply by 1: m*N/N = N*m/N = J/N
Note: I forgot to erase the answer so everyone gets 5 points
P/rho g = same
Z = m * N/N = J/N