Help Needed with Fluid Dynamics Problems

[Aaron9890]

Fluid Dynamics help??

Homework Statement

A boiler is supplied with water at a rate of 0.5 kg/s through a pipe of diameter 80mm
a) Calculate the velocity of the water in the pipe
b) The velocity of the water just before it enters the boiler through a pipe and is raised by a means of a converging tapered section of pipe, calculate the smaller internal diameter of this tapered section of pipe calculate the velocity to be 2.5 times greater than the entry velocity calculated earlier.
c) Calculate the energy per second that must be supplied by the boiler, to raise the water temperature to 100C without superheating it when the water is supplied at 20C
d) If the input power supplied to the boiler is 1.45MW. Calculate the efficiency of the boiler and heat transfer process.

got a and b, not sure about c and don't have a clue about d...



The density of water - 1000kg/m^3
Specific heat capacity for water – 4200J/kgK
Latent heat of evaporation for water – 2260Kj/kg
Steam pipe outside diameter - 50mm
Steam pipe wall thickness – 3mm
Modudlus of elasticity for steel - 207gpa
Coefficient of linear expansion for steel - 15 x 10-3/C



answer to a = velocity = 0.1 m/s and to b = 50.46 mm

Homework Equations

I think the equation to c is something like Q = MCAO + MC
and for d = Thermal Efficency = Q in - Q out / Q in

The Attempt at a Solution

c) Q = MCAO + MC so
Q = 0.5 X 2260Kj/kg + 0.5
Q = 1,129.5 j/s? (really not sure what to do)

d) Thermal Efficency = Q in - Q out / Q in
Thermal Efficency = ?

 

[sacscale]

For c you would need the volume and amount of energy needed to raise the temperature 80°C and this would seem to be your Q out.