5000kg of liquid A (?? 2.4 kJ/kg-deg) per hour is cooled from 90 C to 60 C through a counter flow heat exchanger. Liquid B (?? 1.7 kJ/kg-deg) is used as coolant, which is available at 35 C. The heat transfer surface area is 5 ?2 . If the flow of coolant is 4000 kg/hr. Determine: i) Outlet temperature of the coolant (3.5marks) ii) Overall heat transfer coefficient (3.5marks)
a. 5000kg of liquid A (?? 2.4 kJ/kg-deg) per hour is cooled from 90 C to 60 C through a counter
flow heat exchanger. Liquid B (?? 1.7 kJ/kg-deg) is used as coolant, which is available at 35
C. The heat transfer surface area is 5 ?2
. If the flow of coolant is 4000 kg/hr. Determine:
i) Outlet temperature of the coolant (3.5marks)
ii) Overall heat transfer coefficient (3.5marks)
b) Two well-known statements of second law of
energy, and the other about the transfer of heat appear to be unconnected at first sight, but in
fact, they are equivalent in all aspects. Write down the statements and establish their
equivalence. (5marks)
c) A nozzle is used to increase the velocity of steady flow stream. The parameters at inlet and exit
from the nozzle are given. (5marks)
PARAMETERS INLET EXIT
Enthalpy 3000 kJ/kg 2770 kJ/kg
Velocity 60 m/s ?
Area ?. ? ?? ?
Specific volume 0.185 ?. ??? ??
/??
Calculate velocity of fluid as it leaves the nozzle, rate of flow of fluid, exit area of the nozzle.
Assume the nozzle horizontal and neglect heat loss.
d) A magnetic circuit wound with 500 turns has a cross section area of 400 ??2
and a coil
resistance of 474Ω. If the diameter of the ring, relative permeability, current voltage are 10cm,
100 and 240V respectively, calculate the;
i) Current (2marks)
ii) Magnetic flux strength (4marks)
iii) Magnetic flux density (2marks)
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