When a photon is scattered from an electron, there will be an increase in the photon's
A) energy.
B) frequency.
C) wavelength.
D) momentum.
E) speed.
C
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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
Suppose we compare the combined mass of a C atom and an O2 molecule, both at rest, with the mass of a CO2 molecule, also at rest. According to Einstein's theory, the combined mass of the C and O2 is
A) slightly less, by an amount so small that it hard to measure, than the CO2 molecule's mass. B) precisely equal to the CO2 molecule's mass. C) considerably more than the CO2 molecule's mass. D) considerably less than CO2 molecule's mass. E) slightly more, by an amount so small that it hard to measure, than the CO2 molecule's mass.
A charged particle (q = ?8.0 mC), which moves in a region where the only force acting on the particle is an electric force, is released from rest at point A. At point B the kinetic energy of the particle is equal to 4.8 J. What is the electric potential difference VB ? VA?
a. ?0.60 kV b. +0.60 kV c. +0.80 kV d. ?0.80 kV e. +0.48 kV
The threshold energy to initiate a certain nuclear reaction is 3.16 MeV and the Q for the reaction is -2.37 MeV. The stationary target is how many times as massive as the incident particle?
What will be an ideal response?