HW Set No. 1

Homework Set No. 1
ChE 317
Fall 2014
R.B. Eldridge
1. Work Textbook Problem 2.9 (Student Workbook)
2. The Reynolds Number (NRE) for flow in a pipe is a dimensionless parameter which you
will encounter frequently as a chemical engineer. Determine the NRE for the flow of
liquid propylene (propene - C3H6) in a 2 inch nominal diameter pipe (inside diameter of
2.067 inches) at 30 °C.
 DV 
 where D = pipe inside diameter, V = fluid velocity (5 ft/s)
  
NRE = 
Physical properties for propylene should be obtained from Physical Property Database
on the class web site: http://utwired.engr.utexas.edu/eldridge/che317/resources.html
3. The following empirical equation correlates the values of variables in a system in which
heat is transferred from the walls of a heated pipe into a cooler flowing liquid stream:
 Cp  
hD

 0.023 
k
k


 Cp  
 and
 k 
Both 
1/ 3
 DV 


  
0.8
 DV 

 are dimensionless groups; h is a coefficient that expresses
  
the rate at which heat transfers from the wall; and the coefficients 0.023, 1/3 and 0.8 are
dimensionless constants obtained by fitting experimental data covering a wide range of
equation variables and experimental conditions.
The value h is needed to design a heat exchanger. Since this coefficient is difficult to
determine directly, values of the other variables are measured or estimated and h is
calculated for the given correlation. The variable values are as follows.
D = 2.5 cm
k = 0.60 W/ m °C
Cp = 1.0 cal / g °C
 = 1.00 X 10-3 N·s / m2
 = 1000 kg /m3
V = 10.0 m/s
a) What is the estimated value of h (Give its value and units)
b) Create a spreadsheet in which the corresponding values of h are calculated. Test
your program using the following variable sets: (i) the values given above, (ii) as
above, only double the diameter D (making it 5.0 cm), (iii) as above only double the
thermal conductivity - k, (iv) as above, only double the viscosity (v) as above,
only double the velocity -V. Report all five calculated values of h.
4. Work Textbook Problem 2.25 (Student Workbook)
5. Convert the following:
a)
b)
c)
d)
4 g mol of MgCl2 to g.
2 lb mol of C8H18 to g
16 g of O2 to lb mol
3 lb of C3H8O to g mol
6. A mixture is 10.0 mole % methyl alcohol (methanol), 75.0 mole % ethyl acetate
(C4H8O2) and 15.0 mole % acetic acid. Calculate the mass fractions of each compound.
What is the average molecular weight of the mixture ? What would be the mass (kg) of a
sample containing 25.0 kmol of ethyl acetate ?
7. At 25° C an aqueous solution containing 35 wt% H2SO4 has a specific gravity of 1.2563.
A quantity of the 35 % solution is needed that contains 195.5 kg of H2SO4
a) Calculate the required volume (Liters) of the solution using the given
specific gravity.
b) Estimate the error that would have resulted if pure-component specific
gravities of H2SO4 (sg = 1.8255) and water (sg = 1.0) had been used for the
calculation instead of the given specific gravity of the 35 wt% mixture.
8. The Fred and Barney Oil Company has just run their tanker full of 45 °API crude oil
aground in 60 F ocean water. What is the specific gravity of the crude oil and will it float
on the water ?
9. A gas mixture of isobutene and air is capable of being ignited only if the mole percent of
isobutane is between 1.8 % and 8.5 % (therefore you can travel to Colorado and smoke
in a room containing 10 % isobutane and not blow up or be arrested). A mixture
containing 6.0 mole % isobutane in air flowing at a rate of 700 kg/hr is to be diluted with
pure air to reduce the isobutane concentration to the lower flammability limit (1.8%).
Calculate the required flow rate of air in mol/hr and the percent by mass of oxygen in the
product gas. (NOTE: Air may be taken to consist of 21 mol % O2 and 79 mol % N2 and
to have an average molecular weight 29.0)

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