4.21 Look up (a) the total degree-days for heating and (b) the total degree-days for cooling for
your university town or city (or hometown).
Solution:
Students’ responses will vary.
4.22 In Section 4.2.4, we worked out a problem where the combined heat loss from a
hypothetical 3,000 sq. ft. building was 1,053 Btu/degree-days. Determine the total energy
requirements (in Btu) to heat that hypothetical building for the locations in the following table.
Location
Heating Degree-Days
Anchorage, AK.
541
Winslow, AZ.
70
Yuma, AZ.
0
Rochester, NY.
237
Pittsburgh, PA.
106
Rapid City, SD.
193
Solution:
4.23 Go to the Weather Channel Web site (www .weather.com), and look up the monthly
average temperature for a major metropolitan area and nearby rural area anywhere in the world
over a 12 mo. period. Use the data you looked up to estimate the magnitude of the urban heat
island effect for that city. Graph your data in two figures, and determine the temperature
differences in each month.
Solution:
4.24 Identify an urban core of a major metropolitan area that you are familiar with or that is close
to your college or university. Calculate the magnitude of the maximum urban heat island impact
in the urban core. Provide some detailed alternatives for reducing the urban heat island in this
core area, and relate them to specific items in the energy balance performed on the urban canopy.
Solution:
Students’ responses will vary. They will need to select an urban core and make some
Energy Balance
Term
Feature of an Urban
Environment That
Alters the Energy
Engineering Modifications That Reduce Intensity of
Urban Heat Island
4.25 Assume a small downtown area has two 12 ft. travel lanes with 6 ft. sidewalks on each side.
This is all surrounded by buildings that are 25 ft. tall. What is the maximum urban heat island
impact that can be expected?
Solution:
4.26 Using the systems thinking approach, draw a systems diagram for urban heat islands,
including feedback mechanisms for increased energy demands for cooling and refrigeration,
increased air pollution from these increased energy demands, and other effects such as global
warming and public health.
Solution:
Students’ responses will vary, the following is an example.
4.27 The concentration of a pollutant along a quiescent water-containing tube is shown in Figure
4.28. The diffusion coefficient for this pollutant in water is equal to 10-5 cm2/s. (a) What is the
initial pollutant flux density in the x–direction at the following locations: x = 0.5, 1.5, 2.5, 3.5,
and 4.5? (b) If the diameter of the tube is 3 cm, what is the initial flux of pollutant mass in the x–
direction at the same locations? (c) As time passes, this diffusive flux will change the shape of
the concentration profile. Draw a sketch of concentration in the tube versus x–axis location
showing what the shape at a later time might look like. (It is not necessary to do any calculations
to draw this sketch.) Assume that the concentration at x = 0 is held at 3 mg/L and the
concentration at x = 6 is held at 1 mg/L. (d) Describe, in one paragraph, why the concentration
profile changed in the way that you sketched in your solution to part (c).
Solution:
4.28 The tube in problem 4.27 is connected to a source of flowing water, and water is passed
through the tube at a rate of 100 cm3/s. If the pollutant concentration in the water is constant at 2
mg/L, find: (a) the mass flux density of the pollutant through the tube due to advection; (b) the
total mass flux through the tube due to advection.
Solution:
4.29 The following conditions exist downstream of the point where treated effluent from an
advanced wastewater treatment facility has removed the phosphorous concentration to 1 mg P/L.
The river characteristics just downstream of the discharge point are cross sectional area equal to
20 m2 and a volumetric flow rate of 17 m3/s. Determine the average flux density of phosphorus
downstream of the discharge point.
Solution:
4.30 Calculate the settling velocity of a particle with 100 µm diameter and a specific gravity of
2.4 in 10°C water (µ = 1.308 × 10-3 N-s/m2 and the density of water equals 999.7 kg/m3).
Solution:
4.31 Calculate the settling velocity of a particle with 10 µm diameter and a specific gravity of
1.05 in 15°C water. (µ = 1.140 × 10-3 N-s/m2 and the density of water equals 999.1 kg/m3).
Solution:
4.32 One type of pathogen commonly found in the developing world are helminths (i.e.,
parasitic intestinal worms). These worm species are generally transmitted in a soil (or biosolids)
environment, directly from one human host to another. The eggs of helminths develop into their
infective state in a soil environment. (a) Determine the settling velocity for Ascaris
lumbricoides in a wastewater stabilization lagoon which have a diameter of 50 µm, density of
1.11 g/cm3 and assumed spherical shape. (b) Determine the settling velocity for hookworm eggs
which have a diameter of 60 µm, density of 1.055 g/cm3 and assumed spherical shape. Assume
the wastewater is 15°C. (µ = 1.140 × 10-3 N-s/m2 and the density of water equals 999.1 kg/m3).
Solution: