The ____________ of a black hole is the radius from a black hole at which the escape velocity is approximately equal to the speed of light
a. Roche limit
b. Lagrangian point
c. Chandraskhar limit
d. Hubble radius
e. event horizon
E
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Water is heated by hot air in a heat exchanger. The flow rate of the water is 12 kg/s and that of the air is 2 kg/s. The water enters at 40°C and the air enters at 460°C. The overall heat transfer coefficient of the heat exchanger is 275 W/(m2 K) based on a surface area of 14 m2. Determine the effectiveness of the heat exchanger if it is (a) parallel-flow type or(b) a cross-flow type (both fluids unmixed). Then calculate the heat transfer rate for the two types of heat exchangers described and the outlet temperatures of the hot and cold fluids for the conditions given.
GIVEN
• Water heated by air in a heat exchanger
• Water flow rate m w= 12 kg/s
• Air flow rate m a= 2 kg/s
• Inlet temperatures
? Water (Tw,in) = 40°C
? Air (Ta,in) = 460°C
• Overall heat transfer coefficient (U) = 275 W/(m2 K)
• Transfer area (A) = 14 m2
FIND
(a) The effectiveness (e)
(b) The heat transfer rate (q)
(c) The outlet temperature (Tw,out, Ta,out) for: 1. parallel-flow 2. cross-flow
ASSUMPTIONS
• Steady state
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of dry air (cpa) = 1059 J/(kg K) at 400°C
the specific heat of water (cpw) = 4178 J/(kg K) at 50°C
The interior of a large mass of food in a microwave oven must be heated mainly by
a. radiation. b. conduction. c. convection. d. radioactivity.
Which of the following is not one of the three main categories of observation generally used by astronomers?
A) filtering to look at just a single color from an object B) time monitoring to track how an object's brightness varies with time C) spectroscopy to spread an object's light into a spectrum D) imaging to get a picture of an astronomical objects
The star Algol is
a. an astrometric binary. b. a spectroscopic binary. c. a visual binary. d. an eclipsing binary. e. both b and d