Which of the following could be a hypothesis for the function of the thick waxy coating of a pine needle
A. If the thick, waxy coating is destroyed, the pine needle will turn
B. The thick, waxy coating prevents water loss
C. What happens to the needle if the thick, waxy coating is brown. destroyed?
D. The tree would feel cold without the thick, waxy coating
Answer: A. If the thick, waxy coating is destroyed, the pine needle will turn
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Water flowing at a rate of 10 kg/s through 50 tubes double-pass shell and tube heat exchanger heats air that flows through the shell side. The length of the brass tubes is 6.7 m and they have an outside diameter of 2.6 cm and an inside diameter of 2.3 cm. The heat transfer coefficient of the water and air are 470 W/(m2 K) and 210 W/(m2 K), respectively. The air enters the shell at a temperature of 15°C and a flow rate of 16 kg/s. The temperature of the water as it enters the tubes is 75°C. Calculate (a) the heat exchanger effectiveness, (b) the heat transfer rate to the air, and (c) the outlet temperature of the air and water.
GIVEN
• Shell-and-tube heat exchanger - one shell, two tube passes
• Water in brass tubes, air in shell
• Water flow rate ( m w)= 10 kg/s
• Number of double passes (N) = 50
• Tube length (L) = 6.7 m
• Tube diameters
? Do = 2.6 cm = 0.026 m
? Di = 2.3 cm = 0.023 m
• Heat transfer coefficient
? Water ( )ih = 470 W/(m2 K)
? Air ( )oh = 210 W/(m2 K)
• Air inlet temperature (Ta,in) = 15°C
• Air flow rate ( m a)= 16 kg/s
• Water inlet temperature (Tw,in) = 75°C
FIND
(a) Effectiveness (e)
(b) The heat transfer rate (q)
(c) Outlet temperatures (Ta,out, Tw,out)
ASSUMPTIONS
• Tube length includes both passes
SKETCH
OPERTIES AND CONSTANTS
the specific heat of water at 75°C (cpw) = 4190 J/(kg K)
the specific heat of air at 15°C (cpa) = 1012 J/(kg K)
the thermal conductivity of brass (kb) = 111 W/(m K)
A horizontal uniform meter stick supported at the 50-cm mark has a mass of 0.50 kg hanging from it at the 20-cm mark and a 0.30-kg mass hanging from it at the 60-cm mark. Determine the position on the meter stick at which one would hang a third mass of 0.60 kg to keep the meter stick balanced
a. 74 cm b. 70 cm c. 65 cm d. 86 cm e. 62 cm
Which of the following statements is true about the Maxwell speed distribution?
When ice melts, its temperature __________
Fill in the blank(s) with correct word