Consider a moon that orbits one of our most distant planets in an elliptical path. The distance that the moon covers each day is
A) greatest when closest to the planet.
B) greatest when farthest from the planet.
C) the same everywhere.
D) need more information
Answer: A
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Water flowing at a rate of 12.6 kg/s is to be cooled from 90 to 65°C by means of an equal flow rate of cold water entering at 40°C. The water velocity with the such that the overall coefficient of heat transfer U is 2300 W/(m2 K). Calculate the heat-exchanger surface area (in square meters) needed for each of the following arrangements: (a) parallel flow, (b) counterflow, (c) a multi-pass heat exchanger with the hot water making one pass through a well-baffled shell and the cold water making two passes through the tubes, and (d) a crossflow heat exchanger with both sides unmixed.
GIVEN
• Warm water cooled by cold water in a heat exchanger
• Both flow rates ( m c) = 12.6 kg/s
• Water temperatures
? Th,in = 90°C
? Th,out = 65°C
? Tc,in = 40°C
• Overall heat transfer coefficient (U) = 2300 W/(m2 K)
FIND
The transfer area (A) for (a) Parallel flow (c) Tube-and-shell; 1 hot shell pass, 2 cold tube passes (b) Counterflow (d) Crossflow–both unmixed
ASSUMPTIONS
• The specific heat is constant
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water in the temperature range of interest (cp) = 4187 J/(kg K)
When we see Venus in its full phase, what phase would Earth be in as seen by a hypothetical Venetian?
A) waning crescent B) new C) third quarter D) first quarter E) full
According to the first law of thermodynamics, the sum of the heat gained by a system and the work done on that same system is equivalent to which of the following?
a. entropy change c. temperature change b. internal energy change d. specific heat
A 25. meter long wire, of diameter 0.30 mm, connected to 3.00 volts draws 0.499 A
(a) What is the resistance of the wire? (b) What is its resistivity? (c) What is its conductivity?