Substance A has a density of 3.0 g/cm3 and substance B has a density of 4.0 g/cm3. In order to obtain equal masses of these two substances, the ratio of the volume of A to the volume of B will be equal to
A) 1:3.
B) 4:3.
C) 3:4.
D) 1:4.
E) 4:1.
B
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In a shell of a shell and tube heat exchanger with two shell passes and eight tube passes, 12.6 kg/s of water is heated in the shell from 800C to 150°C. Hot exhaust gases having roughly the same physical properties as air enter the tubes at 340°C and leave at 180°C. The total surface, based on the outer tube surface, is 930 m2 . Determine (a) the log-mean temperature difference if the heat exchanger were simple counterflow type, (b) the correction factor F for the actual arrangement, (c) the effectiveness of the heat exchanger, (d) the average overall heat transfer coefficient.
GIVEN
• A tubular heat exchanger with 2 shell passes and 8 tube passes
• Water in the shell, exhaust gases in the tubes
• Exhaust gases have roughly the same physical properties as air
• Water flow rate m w= 12.6 kg/s
• Water temperatures
? Tw,in = 80°C
? Tw,out = 150°C
• Exhaust temperatures
? Te,in = 340°C
? Te,out = 180°C
• Surface are (A) = 930 m2
FIND
(a) LMTD if the exchanger is a simple counterflow type
(b) Correction F for the actual arrangement
(c) Effectiveness (e)
(d) The overall heat transfer coefficient (U)
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at the mean temperature of 130°C (cpw) = 4244.5 W/(kg K)
Water at 20°C enters a 1.91-cm-ID, 57-cm-long tube at a flow rate of 3 gm/s. The tube wall is maintained at 30°C. Determine the water outlet temperature. What error in the water temperature results if natural convection effects are neglected?
GIVEN
• Water flowing through a tube
• Entering water temperature (Tb,in) = 20°C
• Tube inside diameter (D) = 1.91 cm = 0.0191 m
• Tube length (L) = 57 cm = 0.57 m
• Mass flow rate (m) = 3 gm/s = 0.003 kg/s
• Tube wall surface temperature (Ts) = 30°C
FIND
(a) The water outlet temperature (Tb,out)
(b) Percent error in water temperature rise if natural convection is neglected
ASSUMPTIONS
• Steady state
• Tube temperature is uniform and constant
• The tube is horizontal
SKETCH
PROPERTIES AND CONSTANTS
for water at 20°C
Specific heat (c) = 4182 J/(kg K)
Thermal conductivity (k) = 0.597 W/(m K)
Kinematic viscosity (?) = 1.006 × 10–6 m2/s
Prandtl number (Pr) = 7.0
Absolute viscosity (?b) = 993 × 10–6 (Ns)/m2
Thermal expansion coefficient (?) = 2.1 × 10–4 1/K At 30°C ?s = 792 × 10–6 (Ns)/m2
What is the MOST important role that carbohydrates play in living organisms on Earth?
A) long-term energy storage and cell structure B) information storage C) basic functioning of living organisms D) short-term energy storage
Isaac Newton was able to estimate a value for G, the universal gravitational constant, from the following data: the radius of the Earth is about 6400 km, the average density of rocks is about 5.50 g/cm3, and g = 9.80 m/s2 near the surface of the Earth. What value did Newton obtain for G?
What will be an ideal response?