Transcript
(Data Recorder) CHE415 Unit Operations II
Chemical Engineering, Ryerson University
Pre-Lab Heat Exchanger- Steam to Water
Table 1: Raw data to be gathered during the experiment
Variables Measurement
Shell Outer Radius
Tube Outer Radius
Tube Inner Radius
Steam Input Pressure
Steam Outlet Pressure
Tube Length
Where, some of the data are given before:
Length of brass pipe: 10.92 ft ? 3.33 m
Outside diameter of brass pipe: 0.875 in ? 0.0222 m
Inside diameter of brass pipe: 0.745 in ? 0.018 9 m
Inside diameter of copper pipe: 2.07 in ? 0.052 m
Furthermore, it is require recording the inner and outer temperature of steam and water through co-current and counter-current fluid flow.
Table 2: Counter-Current Time Temperature Data
Time (min) Water Steam
In Out In Out
0
5
10
15
20
Average
Table 3: Co-Current Time Temperature Data
Time (min) Water Steam
In Out In Out
0
5
10
15
20
Average
Lastly, the total flow (USG) for initial and final have to be recorded for Co-current and counter current fluid. As well as, flow rate and velocity of fluid in pipe.
Table 4: Flow in Co-current and Counter-current conditions
Case Total Flow Initial (USG) Total Flow Final (USG)
Counter-Current
Co-Current
Case Flow Rate kg/s Velocity m/s
Counter-Current
Co-Current
Determination the experimental overall heat transfer coefficient:
The experimental overall heat transfer coefficient will be determined using equation 1(Incropera):
Where;
q is the heat transferred to the water by steam
A is the area of heat transfer
?T will be inlet and outlet temperatures
It is important to code that for co-current flow, ?T1 and ?T2 will be determined by;
?T1 = Thot,in-Tcold,in; ?T2 = Thot,out-Tcold,out
Bur for counter-current flow, ?T1 = Thot,in-Tcold,out; ?T2 = Thot,out-Tcold,in
Heat transferred to the water (q) will be obtained by using equation 2 (Incropera):
Where;
mc is the mass flow-rate of water
cp is the specific heat capacity of water
Tc,o is the outlet temperature
Tc,i is the inlet temperature of water
Determination the theoretical overall heat transfer coefficient:
The experimental overall heat transfer coefficient will be determined using the equation 3 (Incropera):
(3)
Where;
ro = outer process tube radius (m)
r i = inner process tube radius (m)
hi = water heat transfer coefficient (W/m2K)
k = is the thermal conductivity of the process tube (W/mK)
Furthermore, the water heat transfer coefficient can be calculated by using equation 4 (Incropera).
The equation 4 can be use if;
The equations 5 and 6 will be use to determine The Rynolds Number and Prandti Number, respectively (Incropera)
Where;
Di = the inside diameter of pipe (m)
k = the thermal conductivity of water (W/mK)
V = the velocity of water (m/s)
= the viscosity of water (Ns/m2)
s = surface viscosity of water (Ns/m2)
cp = the specific heat of water (KJ/Kg•K)
= the density of water (kg/m3)
Sample Calculation:
Calculation the experimental overall heat transfer coefficient for Co-current flow rate:
To determine the experimental overall heat transfer coefficient, several values has been assumed.
The average temperature of inlet steam (Thot,in) is 100oC
The average temperature of inlet water (Tcold,in) is 10oC
The average temperature of outlet steam (Thot,out) is 90oC
The average temperature of outlet water (Tcold,out) is 30oC
Flow Total Start=460000 USG
Flow Total End=450000 USG
Length of tube is equal to length of brass pipe: 3.33 m
Calculation the mass flow rate:
Flow = 31.54 kg/s
The average temperature is (30+10)/2 is 20oC
Thus,
Cp = 4.183 KJ/Kg•K
kwater = (Incropera)
kpipe =
Therefore,
q = mCp ?T
q = (31.54)(4.183)(30 – 10)
= 2638.636 KJ m2/s
Calculation the log-mean of temperature
Calculation the surface area of process pipe:
A = ?DL
=?(0.0189m)(3.33m)
= 0.20 m2
= (2638.636/(0.20)(73.989))
= 178.313
Calculation Theoretical Overall Heat Transfer Coefficient
Calculation the Reynolds Number:
In this equation, the velocity of fluid can be calculated by using the equation
V = Q/Across –sectional= (0.0006m3/s)/(pi*(0.00945)2)
V= 2.139 m/s
Reynolds Number is
=
= 6.095
Calculation of hi
= 8.196
= 0.2203
U = 4.539
Percentage Error =
Percentage error equal to 3828.46%
The high percentage error means the expected experimental value is not close to the theoretical value of overall heat transfer coefficient.
References
Incropera, DeWitt, Bergman, Lavine, 2007. Introduction to heat transfer. Hoboken: John Wiley & Sons Inc.
Department of Chemical Engineering (2010), Unit Operations II Lab Manual CHE 415, EXPT. 3: HEAT TRANSFER – STEAM TO WATER
