Nanoscience has shown that
A) a chemical occurs with the use of a scanning probe microscope.
B) the properties of a material can be different on the level of atoms then its properties when the material is analyzed in bulk.
C) a physical change can occur when using a scanning probe microscope.
D) DNA is the smallest molecule.
Answer: B
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In an industrial refrigeration system, brine (10 % NaCl by weight) having a viscosity of 0.0016 (Ns)/m2 and a thermal conductivity of 0.85 W/(m K) is flowing through a long 2.5-cm-ID pipe at 6.1 m/s. Under these conditions, the heat transfer coefficient was found to be 16,500 W/(m2 K). For a brine temperature of –1°C and a pipe temperature of 18.3°C, determine the temperature rise of the brine per meter length of pipe if the velocity of the brine is doubled. Assume that the specific heat of the brine is 3768 J/(kg K) and that its density is equal to that of water.
GIVEN
• Brine flowing through a pipe
• Brine properties
? Viscosity (?) = 0.0016 Ns/m2
? Thermal conductivity (k) = 0.85 W/(m K)
? 10% NaCl by weight
? Specific heat (c) = 3768 J/(kg K)
• Pipe inside diameter (D) = 2.5 cm = 0.025 m
• Brine velocity (V) = 6.1 m/s
• Heat transfer coefficient ( h c) = 16,500 W/(m2 K)
• Brine temperature (Tb) = –1°C
• Pipe temperature (Ts) = 18.3°C FIND
• Temperature rise of the brine per meter length (?Tb/m) if the velocity is doubled (V = 12.2 m/s) ASSUMPTIONS
• Steady state
• Fully developed flow
• Constant and uniform pipe wall temperature
• Density of the brine is the same as water density
SKETCH
PROPERTIES AND CONSTANTS
density (?) of water ? 1000 kg/m3
The force of Earth's gravity on a capsule in space will lessen as it moves farther away. If the capsule moves to twice its distance, the force toward Earth becomes
A) half. B) three-quarters. C) one-fourth. D) none of the above
Consider some water at 6°C. For a slight increase its temperature the water will
A) expand. B) contract. C) remain the same.
The astrology practiced by those who cast predictive horoscopes can be tested by
A) comparing how often the predictions come true to what would be expected by pure chance. B) asking astrologers if it works. C) polling people to find out what percentage believe their horoscopes to be accurate. D) counting how many times the predictions come true.