Transcript
Methods of Calculations
The objective of this experiment is to determine the overall heat transfer coefficients of a double pipe heat exchanger for saturated water and saturated steam in co-current and counter-current flow arrangements experimentally and comparing it to the theoretical values.
Inner Diameter for Outside tube (steam)
0.0573 m (measured)
Inner Diameter for Inside tube (water)
0.0222 m (measured)
Heat Exchanger Tube Length
0.285m (measured)
Inlet pressure of steam
10 psi (assumed)
Cold water flow rate
1 gal/min (assumed)
Note: Some values were measured last week, where the actual experimental values are estimated for the purpose of sample calculations.
For the purpose of conducting sample calculations, the following values for co-current and counter current flow at a given time are estimated.
Co-current Flow Heat Exchanger
Time
Cold Water (0C)
Steam (0C)
(min.)
TC #1 Ti
TC#2 To
TC#3 Ti
TC#6 To
0
10
25
110
85
Counter Current Flow Heat Exchanger
Time
Cold Water (0C)
Steam (0C)
(min.)
TC #1 Ti
TC#2 To
TC#4 Ti
TC#5 To
0
10
30
110
80
1. Calculating the experimental heat transfer co-efficient:
EXPERIMENTAL HEAT TRANSFER RATE
q = m Cp ?T [1]
where
q = the total rate of heat transfer between the hot and cold fluids (KJ/s)
m = the mass flow rate (kg/s)
Cp = is the specific heat capacity (4.18KJ/kg•K)
?T = the change in temperature of the fluid receiving the heat transfer (K).
Assumption: ambient temperature (Ta) =25° C and density of water (?) = 1000Kg/m3
Co-current Flow Heat Exchanger:
q =
Counter Flow Heat Exchanger:
q =
LOG MEAN TEMPERATURE DIFFERENCE
[1]
Where:
Th,i = Steam temperature in
Tc,i = Cold water temperature in
Th,o = Steam temperature out
Tc,o = Cold water temperature out
Co-current Flow Heat Exchanger:
=
=
Counter Flow Heat Exchanger:
=
=
OVERALL HEAT TRANSFER COEFFICIENT
q = UA ?T lm U= [1]
D = Inner Diameter for Inside tube (water) = 0.0222 m (measured)
L = Heat Exchanger Tube Length = 0.285m (measured)
A = ? D L A = 3.142*0.0222*0.285= 0.01987m2.
Co-current Flow Heat Exchanger:
U==
Counter Flow Heat Exchanger:
U==
SUMMARY OF EXPERIMENTAL OVERALL HEAT TRANSFER CO-EFFICIENT
Overall Heat Transfer Co-efficient
Co-Current Flow Heat Exchanger
Counter Flow Heat Exchanger
U
2. Calculating the theoretical heat transfer Co-efficient:
Type of Flow:
, where ?l = Kg/m.s (viscosity of water at 20oC, Perry’s handbook)
Laminar flow: < 2100
Turbulent flow: 2100< <4000
Hence Re =
Re =7.15 < 2300 ( Laminar flow)
Laminar fluid flow
Cold water heat transfer coefficient:
The heat transfer coefficient for cold water is given by the equation below:
[1]
Where,
h = Inside pipe heat transfer coefficient (J/s.m2.K)
Di = Inside diameter of pipe (m)
k = Thermal conductivity of water (J/s.m2.K/m), k= 0.58744 Watts (Perry’s)
V = Velocity of water (m/s)
= Viscosity (kg/m.s),
