ABSTRACT This experiment was conducted to evaluate and study the performance of the shell and tube heat exchanger heat load and heat balance, LMTD, overall heat transfer coefficient ,Reynolds shell side and tube side, heat transfer coefficient and pressure drop at shell side and tube side. The experiment will run in 2 with 3 sets each. Each 2 runs will be using different nominal flow rates for CW and HW. We carried out for Run III and IV only. The QC/QH that close to 1.00 will be chosen to use for U calculation. Every run will be using different flow rate. From the result, the pressure drop depends on the flow rate not the temperature. As we can see that the pressure drop for Run III which used 10USGPM and 15USGPM was higher than pressure at Run IV which used 10USGPM. From the calculation, we conclude that the number of QC is decreasing from Run III to Run IV and same pattern goes to QH and 0.5(QC+QH).Other than that, U is also decreasing from RUN III to Run IV. The overall heat transfer coefficient, U, Reynolds number and flow rates of hot water are also decreasing from Run III to Run IV.
INTRODUCTION Shell-and-tube heat exchangers are commonly used in oil refineries and other largescale chemical processes. A heat exchanger is a device that is used to transfer thermal energy between transfer thermal energy between two or more fluids, between a solid surface and a fluid a fluid, or between solid particulates and a fluid at different temperatures and in thermal contact In this model, two separated fluids at different temperatures flow through the heat exchanger: one through the tubes (tube side) and the other through the shell around the tubes (shell side). Several design parameters and operating conditions influence the optimal performance of a shell-and-tube heat exchanger. The main purpose of this model is to show the basic principles for setting up a heat exchanger model. It can also serve as a starting point for more sophisticated applications, such as parameter studies or adding additional effects like corrosion, thermal stress, and vibration. The heat exchanger is made of structural steel. The participating fluids are water flowing through the tube side and air flowing through the shell side. The baffles introduce some crossflow to the air and such increasing the area of heat exchange. Another advantage is that baffles reduce vibration due to the fluid motion.(Comsol,2013).
Figure 1: Geometry of shell and tube heat exchanger
The scope of shell and tube heat exchanger Maximum pressure
Shell 300 bar (4500 psia)
Tube 1400 bar (20000 psia)
Temperature range
Maximum 600oC (1100oF) or even 650oC
Minimum -100oC (-150oF)
Fluids
Subject to materials
Available in a wide range of materials
Size per unit 100 - 10000 ft2 (10 - 1000 m2) However shell and tube heat exchanger can be extended with special designs and materials. Heat Exchangers are classified according to Transfer process Number of fluids Degree of surface contact Design features Flow arrangements Heat transfer mechanisms
Shell and tube heat exchanger is the most common type of heat exchanger in industrial applications.It contain a large number of tubes (sometimes several hundred) packed in a shell with their axes parallel to that of the shell. Heat transfer takes place as one fluid flows inside the tubes while the other fluid flows outside the tubes through the shell. Shell-and-tube heat exchangers are further classified according to the number of shell and tube passes involved.(Cengel,2011).
Figure 2: Schematic shell and tube heat exchanger(open shell pass and one tube pass).
Regenerative heat exchanger: Involve the alternate passage of the hot and cold fluid streams through the same flow area.
Dynamic-type regenerator: Involve a rotating drum and continuous flow of the hot and cold fluid through different portions of the drum so that any portion of the drum passes periodically through the hot stream, storing heat, and then through the cold stream, rejecting this stored heat.
Condenser: One of the fluids is cooled and condenses as it flows through the heat exchanger.
Boiler: One of the fluids absorbs heat and vaporizes.
OBJECTIVE To evaluate and study the performance of shell and tube heat exchanger at various operating condition. To evaluate and study the heat balance, LMTD and overall heat transfer coefficient. To calculate Reynolds’s number at the shell and tube heat exchanger. To measure and determine the shell and tube side pressure drop.
THEORY In most heat exchangers, two fluids are exchanging their heat without direct physical contact to avoid mixing. This is called indirect heat transfer. Cooling water temperature in a hot area is normally above 25 degrees centigrade, and it depends on the atmospheric and climate condition. To reach the range of 1 to 5 degrees centigrade, we need to use chilled water, which is already cooled by a refrigerant. For heating purposes, the mechanism is similar to the cooling. We can use hot intermediate fluid such as hot water or steam and even other hot process streams. To proceed on the heat exchanger theory we need to know that the meaning of the following terminologies: The overall heat transfer rate in a heat exchanger The overall heat transfer coefficient can be used to calculate the total heat transfer through a wall or heat exchanger construction. The overall heat transfer coefficient depends on the fluids and their properties on both sides of the wall, and the properties of the wall and the transmission surface.
Q = U A ∆T
U
= Overall heat transfer coefficient
A
= Area of the tube
∆T
= Logarithmic mean temperature difference
Heat load and heat balance
Q This part of the calculation is to use the data in Table to check the heat load Q H and C Q and to select the set of values where C is closest to QH . Hot water flow rate (
HW ) QH = F Cp ( t1 t2) H H
Cold water flow rate (
CW )
QC = F Cp ( T T ) C C 2 1 where: Q H = Heat load for hot water flow rate
QC
= Heat load for cold water flow rate
FH Hot water mass flow rate
FC
Cold water mass flow rate
t1 Hot water inlet temperature t 2 Hot water outlet temperature T1 Cold water inlet temperature T2 Cold water outlet temperature
Log mean temperature difference (LMTD) ( t T) ( t2 T ) 1 LMTD 1 2 ( t T ) ln1 2 ( t2 T ) 1 (t T) R 1 2 (t2 t1) (t t ) S 2 1 (T 1t1)
The corrected LMTD= FT x LMTD calculated above
Overall heat transfer coefficient, U Overall heat transfer coefficient at which equivalent to U D can be calculated by using equation
Q U A LMTD Where: Q Heat rate with respect to the flow rate of water Q H or QC
Q Theoretically Q above is equal to Q H or C If there any error in temperature collected, it is recommended to calculate Q 0 .5 (Q Q ) C H equation of that will give an average value.
U ave
value based on
Reynolds Number Shell-side Re(s) for CW
De .Gs Re( s)
De
de 12
2
do 4 ( 1 / 2 PT 0 . 86 PT 1 / 2 . ) 4 de 1 / 2 . do
Where:
PT Pitch = 0.81inch do Tube outside diameter, inch
Viscosity, taken at average fluid temperature in the shell, lbmft-1hr-1 (lbmft-2hr-1) Ws Flow rate in (lbmhr-1)
Tube-side Re (t) for HW
D .Gt Re( t)
Where:
Viscosity, taken at average fluid temperature in the tube, lbmft-1hr-1
Gs
Ws As
Heat Transfer Coefficient Both values of internal heat transfer coefficient, hi and outside heat transfer coefficient, ho obtained from equation below:
jH . k k 1 . 3 W 0 . 14 ho .( ) .() De Cp .
And
jH . k k 1 . 3 W 0 . 14 hi .( ) .() D Cp .
Where: k Thermal conductivity at mean temperature with respect to fluid position
Fluid viscosity at mean temperature with respect to fluid position W Fluid viscosity for different value of hot and cold water stream jH Energy being transfer in the system
Therefore, the dirt factor, Rd value : U U Rd C D U U C. D
Where:
UC
Clean overall heat transfer coefficient from both individual inside and outside fluids U D Overall heat transfer coefficient obtained from calculation in part 1
From the equation before, UC value is calculated from heat transfer coefficients, the Reynolds number (i.e flow rates), the flowing fluids properties and the Heat Exchanger diameters.
U D value however is determined from actual heat transfer experiments at the Heat Exchanger
diameters. It is the dirty or design heat transfer coefficient. Fouling phenomenon would reduce U D value. Fouling may get worse with operation, resulting in reduced heat transfer and increasing pressure drop (and loss of flow).
Pressure drop This part would determine the following:
HW :
The measured tube-inside pressure drop DP (tube) which will be corrected and is expected to be more than calculated tube-side pressure drop.
CW :
The measured shell-inside pressure drop DP (shell) which will be corrected and is expected to be more than calculated tube-side pressure drop.
Pressure drop measurement The shell and tube-side pressure drop (DP) are measured using the differential pressure transmitter (DPT) and then indicated digitally at the panel DP (DPI*). A selector switch with a set of 5 solenoid valves allows both the shell and tube-sides pressure drop i.e. DP (shell), DP (tube), to be measured one at a time.
APPARATUS
Summary List of Instrumentation Field-Mount FT (H)
:
Flow Transmitter for HW. Vortex flow meter, 0-30 USGPM
FT (C)
:
Flow Transmitter for CW. Magnetic flow meter, 0-30 USGPM.
DPT
:
Differential Pressure Transmitter for Shell/Tube side Pressure drop, 0-5000 mm H2O.
TE1 to TE5
:
Temperature Element Resistance Temperature Detector (RTD), for t1, t2, T1, T2 TIC5 respectively, 0-1000C.
PG-H, PG-C
:
Pressure gauges, 0-60 psig.
TG2
:
Temperature gauge, 0-1000C.
TSV3A, TSV3B :
Temperature Solenoid Valve.
Panel-Mount FI (H), FI (C)
:
Flow Indicator for HW, CW. Digital display, 0-30 USPGM
TI1, TI2, TI4
:
Temperature Indicator for TE1, TE2, TE4, displaying t1, t2 and T2 respectively. Digital display, 0-1000C
TI3 (T1)/TIC3 : Temperature Indicator with ON/OFF control for TE3 i.e. T1. Digital display, 0-1000C TIC5
: Temperature Indicator with ON/OFF control for TE5. Digital display, 0-1000C
DPI
: Differential Pressure Indicator for DP (Shell) and DP (Tube) of Heat Exchanger. Digital display, 0-5000 mm H2O
Portable FTDPR :
Flow, Temperature, Deferential Pressure Recorder, 12-
Channels, paperless and can be connected to PC-Data Acquisition System
PROCEDURE Preparation procedures Start the following preparation procedures step-by-step. i) Tanks T1 and T2 was filled with water to their maximum level define by their overflow drain pipes D. ii) At tank T1, the discharge valve (HV) was shut fully, but open fully its by-pass valve (BVH). The HW pump PH was start for the water to recirculate around its tank T1, via only BVH. The suction valve of pump PH must remained open at all times. The heaters at the front of the panel was switch on and the water was allowed in tank T1 to be heated to its maximum temperature 70℃ / 158℉ (see T1C5), which will took about 20 minutes. Whilst waiting, proceed to (iii) below. The heaters in tank T1 was automatically switch off by the on/off temperature controller T1C5 when the heated water temperature exceeds its preset High Limit (say 70℃), and when the temperature drops below switch them on again, say of its preset High Limit (i.e. below 69.5℃). iii) CW System : Heat Exchanger Shell side Meanwhile got familiar with the equipment, instrumentation, piping system and the various manual valves. The following preliminary procedures are recommended for farmilarization. a) All the CW pumps (PC1, PC2) by pass valves (BVC1, BVC2) and discharge valves (CV1, CV2) was checked that were opened. The suction valves of all the pumps (PC1, PC2 and PH) was noted that must remained opened at all times. b) The external water supply to tank T2 was checked that always available but was automatically shut by the mechanical float-level valve at high level in tank T2. The water availability was tested by pushing down the float-water must flow into tank T2 via the floatlevel valve to confirm water availability. c) Make sure the CW pumps PC1 and PC2 were off. The HW pump PH was noted that still recirculating HW around its tank T1 via its by-pass valve (BVH), but its discharge valve (HV) was still fully shut. d) Only one CW pump was switch on, say PC1 whose suction was from tank T2. Its by-pass valve BVC1 was still fully opened. PC2 was did not operated. CV2 was shut fully. The CW
recirculation was noted from PC1 back into tank T2 via mainly its by-pass valve BVC1 and the Heater Exchanger returned solenoid valve TSV3A. e) The by-pass valve ( BVC1) was parctise manipulated to set various flowrates of CW into the Heat Exchanger from PC1 as follows:
Remain fully opened the manual discharge valve CV1.
With BVC1 was fully opened, the CW flowrate {FC at FI(C*)} was noted,drop the pressure (PG-C) and shell-side (at DPI*). To read DP (shell), the signal to DPI* was selected used the DP Selector Switch provided at the panel, to the DP (shell) position and wait till the reading at DPI* was almost steady.
Manually adjusted BVC1 until FC at FI(C*) reads almost 10 USGPM. A DP (shell) and PGC was noted.
The by-passvalve ( BVC1) was shut fully and the increase in FC, PG-C and (shell) was noted. The CW temperatures was noted at the Heat Exchanger inlet (T1 at TI3*) oulet (T2 at TI4*). The Heat Exchanger pressure drop increases with flowrates was noted.
f) Pump PC2 was switch on whose suction was from tank T2. Opened fully its manual discharge valve CV2 and by-pass valve (BVC2). The CW flowrate {FC at FI(C*)} was note, pressure (PG-C) and shell-side pressured drop (at DPI*).
Gradually shut only BVC2 until the CW flowrate FC is about 200 USGPM. Fc, PG-C and DP(shell) was noted which increased with the flowrate FC.
g) BVC2 was opened fully but CV2 was shut fully so that pump PC2 now operates only as be mixing pump for tank T2. The drop in FC, PG-C and DP(shell)was noted. Only pump PC1 was now pumped through the Heat Exchanger. Shut BVC1 fully maximum flow from PC1 through the Heat Exchanger. Both the CW pumps PC2 and PC1 was swith off. The DP Selector Switch was switch to the equalising (vertical or ‘0’) position.
iv) Hw system : Heat Exchanger Tube side
a) TIC5 was noted to checked if the water temperature in tank T1 was about 70℃ (158℉) before proceeding to the next procedure (b). The discharge valve (HW) was noted, the
HW pump PH was still shut but its by-pass valve (BVH) was fully opened. b) The by-pass(BVH) was gradually shut fully and simultaneously opened its discharge valve (HV) sully so that the maximum HW flows into the Heat Exchanger and return into tank T1. The HW flowrate {FH at FI(H*)} was read, pressure (PG-H) and Tube-side pressure drop (at DPI*). Select the DP signal to DPI* to read used the DP Selector Switch provided at the panel, to the DP (Tube) position. Wait till the DP (Tube) reading at DPI* almost steady to took the reading. In tank T1, the temperature of HW will drop due to heat being transferred to the ‘metal’ body of the Heat Exchanger,even if there was no CW flow in the Heat Exchanger. The HW temperature at the Heat Exchanger inlet (t1 at T11*) and oulet (t2 at T12*) c) The HW pump PH was stopped and the drop in FH, PG-H and DP (Tube) ws noted. The DP Selector Switch to the equalizing (vertical ‘o’ ) position was switched. The heat from HW was noted and now ‘stored’ in the Heat Exchanger tubes. The heaters was switch off. d) Proceed to (C1) PLANNING THE EXPERIMENT. (C1) Planning The Experiment Refer to table 1 and plan out the experiment strategy as follows : i) RUN1 a) Run 1 was done at the following recommended nominl flowrates. It was not necessary to operated at exactly the recommended nominal flowrates below. Adeviation of ±5% was acceptable for tested purposes. CW, FC :110 USGPM
HW, FH : 25 USGPM
b) Please refered to table 1, Three (3) sets of readings were taken for every RUN.
Each set of temperature readings consists of four readings to be taken simultaneously : CW Temperature – inlet T1 at TI3* and outlet T2 at TI4*, HW temperatures – inlet T1 at TI1* and oulet T2 at TI2*
Each set of flowrate readings consists of two readings: CW flowrate {FC at FI(C*)} HW flowrate {FH at FI(H*)}
Each set of pressure drop readings consists of two readings : DP (shell) at DPI*, with the DP Selector Switch at the DP (shell) position. DP (Tube) at DPI*, with the DP Selector Switch at the DP (Tube) position.
Each set of Heat Exchanger inlet gauge pressure readings consists of two readings : PG-C of CW pipeline, inlet to the Shell side of the Heat Exchanger. PG-H of HW at the HW pipeline, inlet to the Tube side of the Heat Exchanger.
c) The HW temperature in tank T1 drops (note TIC5) was noted when the heater input was inadequate to meet with the heat (QC) removed by CW. Hence the second and third sets of temperature readings may be taken at decreasing heat load, but the water temperature at tank T1 must be at least 60℃. d) Concentrated on taking the three (3) sets of temperature, flowrate and pressure drop readings. The pressure drop readings DP( shell) and DP(Tube) were taken at the panel-mount DPI*, used the DP signal Selector Switch provided. The pressure drop depends on the flowrate and not on the temperature was noted. e) The above procedure for other RUNS (II, III, etc) was repeated at the following CW and HW recommended nominal flowrates. A deviation of ±15% was acceptable. A summary list of the recommended nominal flowrates.
RUN
CW, FC
HW, FH
III
10USGPM
15 USGPM
IV
10USGPM
10USGPM
(C2 ) Experimental Procedures With a good overview of the experiment plan detailed in C1, proceed with RUN I as follows: i)
All the pump suction valves (for PH, PC1, PC2) were checked and fully opened all the time.
Opened BVC2 fully but shut CV2 fully so chat that PC2 shall operated as a back-mixing pump for r tank T2 in the next experiment. CV1 BVC1 was opened fully. To pump CW into
the Heat Exchanger in the next experiment used PC1 shall. Did not switch on any CW pumps (PC1, PC2) yet.
Shut HV fully but opened BVH fully.
To circulate around tank T1 via only BVH was started pump PH for HW.
The heaters was started and noted TIC5. When the HW in tank T1 was almost 70℃/158℉ (see TIC5), opened HV fully. The HW flowrate was quickly adjusted to abouat 25 USGPM by regulating its by-pass valve BVH.
CW pumps PC1 and PC2 was switched on. The CW flowrate was quickly adjusted to about 10 USGPM by regulating the by-pass valve BVC1.
The DP Selector Switch to the DP (Shell) position was switched.
ii) a) First set of temperature and flowrate readings was took: CW: Temperature- inlet/oulet, TI3* (T1), TI4* (T2): Flowrate FC at FI(C*). HW: Temperature- inlet/oulet, TI1*(t1), Ti2* (t2): Flowrate FH at FI(H*) The CW inlet temperature (T1) was increased gradually was noted. The CW oulet temperature (T2) varies together with the HW inlet/oulet tenperature t1/t2. All the temperature and flowrate readings was important and be taken almost simultaneously. Readings appropriately in table 1 was recorded:
The respective inlet pressure and pressure drop of the CW and HW flow streams was recorded. For the pressure drop readings, DP (Shell), DP (Tube) at the panel-mount DPI*, used the DP signal Selector Switch appropriateky as explained below. CW: PG-C, DPI* for DP(Shell) with the DP Selector Switch at the DP (Shell) position. HW: PG-H , DPI* for DP (Tube) with the DP Selector Switch at the DP (Tube) position. To take the DP readings at DPI*, wait till they were fairly steady. Then took the DP reading at its highest reading (i.e. peak reading) just when it starts to decrease. `b)Continued and took the second and third sets of the above readings for RUN I consecutively. When all the temperatures were fairly steady, the last Set of temperature
readings should be taken.
iii)
RUN i was completed, with three sets of the above readings
All the CW pumps PC1 and PC2 was stopped.
Keep the Heaters on for the next RUN
With the HW pump PH still running, shut fully the discharge valve HV but opened fully the by-pass valve BVH.
The DO Selector Switch was switched to equalizing (vertical or ‘0’) position.
v) Analyst the data by computing the QC and QH values for each of the three(3) sets of readings for the previous RUN I whilst waited for the HW in tank T1 to be heated to about 70℃/158℉ (see TIC5) for RUN II as follows: a) For each set of readings in RUN I, the heat load QC and QH was calculated for the CW and the HW as per the formula in section (E) calculation. b) The three (3)b calculated values of QC and QH for RUN I was compared. Select the set of readings where QC was closest to QH and noted them down in table 1 and table 2, as the selected QC and QH for RUN I. At the same time, noted down their corresponding temperatures, flowrates and pressure drops as the selected datas for RUN I. The other two sets of data not selected can be rejected as they were of no further used. c) The above selected set od data i.e. QC, QH, temperatures, flowrates and pressure drops for RUN I shall be used to compute the LMTD, the overall heat transfer coefficient, Reynolds numbers, individual heat transfer coefficient and the pressure drop, for RUN I. d) Run IV,V at different recommended nominal flowrates of CW(i.e. FC) and HW(i.e. FH) was repeated,used the following procedures check list:
To continued with the next RUN The HW pump PH was running with BHV fully opened but HV fully shut was checked.
With the heaters on, the HW in tank T1 almost 70℃/158℉ (see TIC5) was heated Opened HV fully. The HW flowrate was adjusted until FH at FI (H*) was almost at the recommended nominal flowrate for the RUN. This was done by regulating the by-pass valve BVH with HV fully opened. (However, if the flowrate was still too high even when its by-pass valve was fully opened, gradually shut its discharge valve, HV, to got the required HW flowrate) The CW pumps PC1, PC2 with CV1/BVC1/BVC2 was started fully opened but CV2 fully shut. Fc at FI(C*) as noted. Fc was adjusted to the recommended nominal flowrates for the RUN by regulating the by-pass valve BVC1 with CV1 fully opened. (However, If the CW flowrate (FC) from PC1 was still inadequate even when its by-pass valve BVC1 was fully shut, used the second CW pump (PC2) by gradually opening CV2 and simultaneouslt shutting BVC2 to got the required cw flowrate) The DP Selector Switch to the DP (Shell) position was switched The various readings for the RUN was took. Refer to table 1 of the apptopriate RUN.
To end a RUN after got 3 set of readings All the CW pumps PC1, PC2 was stopped. The DP Selector Switch to the equalising (vertival or ‘o’) position was switched. The HW pump PH and the heaters still on, shut fully HV but opened BVH fully.
(C3) Plant Shut Down I)
The heaters was switched off
II)
Checked all the pumps (PH, PC1, PC2) were switched off
III)
The DP Selector Switch to the equalising (vertical ‘0’ ) position was switched
IV)
The main power supply was switched off to the plant at the front of the panel/cubical. All the pumps suction valves, discharge valves (HV, CV1, CV2) and bypass valves (BVH, BVC1, BVC2) was opened
RESULT Table 1 : experimental data for RUN III RUN III Nominal Flow, USGPM
SET 1 CW FC: 10
SET 3 CW
HW
10
15
15.3
9.9
15.2
DP:1454(TUBE 2.5 28.7 ) 621 T12: t2: 52.4 13.2 18.8 46.9
4.5 58.6
2.5 28.7
4.5 54.0
11.8 1477 48.1
16.1 632 46.9
9.9 1487 44.8
59.6
54.1
36.35 1.288
50.55
HW FH: 15
SET 2 CW
Actual Flow, USGPM Temp, °C, Inlet
10 15 FC: 9.8
FH: 15.3
Temp, °C, Outlet
9.9 T13: T2.5 1: 28.6 PG-C:
Pressure, psig, Inlet
DP: 597 (SHELL)
T14: T2: 52.3 *Pressure Temp change, °C H2O 23.7 drop, mm
* Average Temp, °C QC/QH
HW
40.45 1.168
PG-H: 4.7 T11: t1: 65.4
37.7 1.122
Select QC/QH nearest to SELECTED NOT SELECTED *Q, Head load, BTU/HR SELECTED QC:209472.97 QH:179385.92 NOT 162502.54 144888.63 162403.33 126120.30 1.0 Selected set, 194429.45 0.5(QC+QH), BTU/HR
Table 2: experimental data for RUN IV HW
SET 3 CW
HW
10
10
10
10
9.8
10.4
9.8
10.4
2.5 DP: 605 (SHELL) DP: 564(TUBE) 29.4 620 T14: T2: 50.4 T12: t2: 50.7 *Pressure Temp change, °C H2O 21.1 16.1 16.6 drop, mm 46.0
2.0 61.2
2.5 29.4
2.0 58.8
14.1 673 47.1
15.2 627 44.6
13.0 578 45.8
* Average Temp, °C QC/QH
54.15
37.00 1.101
52.3
RUN IV Nominal Flow,USGPM
SET 1 CW FC: 10
HW FH: 10
Actual Flow, USGPM Temp, °C, Inlet
FC: 9.8
SET 2 CW
FH: 10.5
Temp, °C, Outlet T13: T2.5 1: 29.3 PG-C:
T11: : 66.8 PG-H:t12.0
Pressure, psig, Inlet
39.85 1.22
58.75
37.7 1.109
Select QC/QH nearest to SELECTED QH:152464.50 NOT SELECTED SELECTED 121935.53 *Q, Head load, BTU/HR NOT QC:186492.81 146719.47 132253.15 134345.53 1.0 Selected set,
128140.53
0.5(QC+QH), BTU/HR Table 3 : calculated value for heat load, LMTD and U RUN
QC (BTU/hr)
QH (BTU/hr)
0.5(QC+QH) (BTU/hr)
LMTD*FT (°F)
U(
III
209472.97
179385.92
194429.45
20.14
504.81
IV
134345.53
121935.53
128140.53
25.50
332.70
)
℉
Table 4: calculated Reynolds number Actual Flow (USGPM)
RUN
Re (s)
Re (t)
389.31
12833.12
364.46
7753.94
FC: 9.8 III FH: 15.3 IV
FC: 9.8 FH: 10.4
Table 5: Calculated Heat Transfer Coefficient and Dirt Factor ho RUN
(
hi ℉
) (
hio ℉
) (
Uc ℉
) (
Ud ℉
) (
Rd ℉
) (x10-3)
III
1598.82
721.68
571.57
421.05
504.81
3.94
IV
1620.18
604.95
479.12
263.63
332.70
0.664
Table 6: Calculated Pressure Drop Pressure Drop RUN
Shell-side (mmH2O)
Tube-side (mmH2O)
Calculated
Measured
Corrected
Calculated
Measured
Corrected
III
4937.73
560
65.05
89.891
1093
353.72
IV
4484.88
564
69.05
18.79
563.32
191.88
CALCULATION Sample calculation RUN III, Set 1 Heat Load and Heat Balance FC= 9.8 USPGM m3/Hr
FC= 9.8 USGPM x
× 1000 Kg × 2.20462 Ibm
4.4 USGPM
m3
kg
FC= 4910.29 Ibm/hr CP= 1 Btu/Ibm oF QC= FC × CP × (T2-T1) Convertion unit of temp. T2 = 44.6 oC = 44.6(1.8) + 32 = 112.28 oF T1 = 29.4 oC = 29.4(1.8) + 32 = 84.92 oF
= 4910.29 Ibm/hr x 1 Btu/Ibm oF x (112.28 – 84.92 oF = 209472.97Btu/hr
FH = 15.3 USPGM m3/Hr
FH = 15.3 USGPM ×
4.4 USGPM FH = 7666.065Ibm/hr CP= 1 Btu/Ibm oF QH= FH X CP X (t1 - t2)
× 1000 Kg × 2.20462 Ibm m3
kg
Conversion unit of temp. t2 = 45.8 oC = 45.8(1.8) + 32 = 114.44 oF t1 = 58.8oC = 58.8(1.8) + 32 = 137.84 oF =7666.065 Ibm/hr x 1 Btu/Ibm oF x (137.84 – 114.44) oF = 179385.92Btu/hr Ratio QC/QH =
= 1.168
Calculations above were repeated for each set in RUN IV. The set which gives the ratio of QC/QH nearest to 1 is then used for the next part of the calculation for each respective RUN.
LMTD (RUN III, Set 1)
LMTD =
(
) ( ( (
) ) )
= 25.33
Correction factor, FT is obtained from figure 18 (appendices) based on the value of R and S, where FT = 0.795
LMTD (true)
= 0.795 x 25.33 = 20.14
Overall Heat Transfer Coefficient, U (RUN III, Set 1) The total heat transfer area of the Heat Exchanger, A = 31.5 ft 2 Q = 0.5(QC+QH) Q = 0.5 (209472.97 + 179385.92) Q = 194429.45(BTU/hr) (
)
5(
℉
5
)
(
)
℉
All calculations involving LMTD and U were repeated again for the selected set on RUN IV. The results of calculation are tabulated in table .
8.2 Reynolds Number Shell side Re(s) for CW (RUN III, Set 1) ( ) (
Given,
)
do
= 0.625 ins
Pt
= 0.8125 ins
Ws
= 4910.29 lbm/hr
As
= 0.029 ft2
µ
= 1.584 lbm/ft.hr
Gs
= 4910.29 /0.029 = 169320.34 lbm/hr.ft2
de
= 0.537838 ins x 0.08333 = 0.0443 ft
De
= 0.0443/12 = 0.003642ft
Re (s) = 0.003642 x(169320.34 / 1.584) = 389.31
Tube side Re (t) for HW (RUN III, Set 1) ( ) Given,
Re(t)
D
= 0.04125 ft
Wt
= 7666.065 lbm/hr
At
= 0.02139
µ
= 1.152 lbm/ft.hr
Gt
= 7666.065/0.02139 = 358394.81 lbm/hr.ft2
= 0.04125 x (358394.81 / 1.152) = 12833.12
8.3 Heat Transfer Coefficient, hi and ho, Uc, Ud and Rd Calculation of ho for shell-side (CW) (RUN III, Set 1) Given, De Cp
= 0.003733 ft 1.001 btu/lbm.F
k
= 0.36462 btu/hr.ft2. F/ft (at Tavg = 40.45°C)
µ
= 1.584 lbm/ft.hr
Twall
=( 40.45+59.6)OC/2=50.030C
µwall
= 2.412lbm/ft.hr (at Twall)
From figure 28(appendices), when Re (s) = 389.31, jh = 9.85 (
9.85
)(
ho = 1598.82 (
)
)
℉
Calculation of hi for tube-side (HW) (RUN III, Set 1) Given, D
= 0.04125 ft
Cp
1.001 btu/lbm.F
k
= 0.37871 btu/hr.ft2. F/ft (at Tavg = 59.6 °C)
µ
= 1.152 lbm/ft.hr
From figure 28(appendices), when Re (t) = 12833.12, jh = 61 (
61 =
)
)
hi = 721.68(
℉
Calculation of ‘Clean’ Overall Heat Transfer Coefficient, Uc (RUN III, Set 1) = 571.57 = 421.05
℉
℉
Calculation of Dirt Factor, Rd (RUN III, Set 1) Ud
= 504.81
Uc
= 421.05
℉
℉
Rd
= = 3.94x 10-4
8.4 Pressure Drop Conversion:
1 psi = 2.3088ft = 27.72 ins = 703.72 mmH2O at 60°F (SG=1.0)
Shell side pressure drop (RUN III, Set 1) (
ΔPs = Given, Ds
ΔPs =
)
= ID = 6.065ins = 0.50541 ft
N
= 23
g
= 4.17 x 108 ft/hr2
ρ
= 62.0348 lbm/ft3 (at Tavg = 40.45°C)
De
= 0.003733 ft
Gs
= 169320.34 lbm/ft2.hr
SG
= 0.9931 (at Tavg = 40.45°C)
Øs
= 1.01167
ƒ
= 0.0052 (at Re(s) = 389.31)
( (
)
)
= 9.2550 psi
Since SG = 0.9931, 1psi = 703.72 x 0.9931 = 698.86 mmH2O ΔPs = 9.2550 psi x 698.86 mmH2O / 1 psi = 4937.73 mmH2O
Correction to the measured pressure drop for Shell side, CW (RUN III, Set 1) Pressure drop read at 560 mmH2O and flow rate CW of 9.8 USGPM, Calculated piping pressure drop DP(s) = 494.95 mmH2O
ΔP (corrected) = 560-494.95 = 65.05mmH2O
Tube side pressure drop, HW (RUN III, Set 1)
ΔP’t = Given, D
= 0.04125 ft Lxn
= 12
ρ
= 61.392 lbm/ft3 (at Tavg = 59.6°C)
Gt
= 358394.81 lbm/hr.ft2
SG
= 0.98671(at Tavg = 59.6°C)
Øt
= 0.9893
ƒ
= 0.00012 (at Re(t) = 12833.12)
ΔP’t =
(
= 0.1295 psi
)
Since SG = 0.98671, 1psi = 703.72 x 0.9871 = 694.14 mmH2O
ΔP’t = 0.1295 psi x 694.14 mmH2O / 1 psi = 89.891 mmH2O
ΔPr =( ) ( Where ( ΔPr = (
)( )(
( )
), )= 0.02 (at Gt = 358394.81 from figure 27 in appendices)
) 0.02 = 0.1622psi x 694.14 mmH2O / 1 psi = 112.56 mmH2O
= 89.891+ 112.56= 202.45mmH2O
Correction to the measured pressure drop for Tube side, HW (RUN III, Set 1) Pressure drop read at 1093 mmH2O and flow rate CW of 15.3USGPM, Calculated piping pressure drop, DP (t) = 739.28 mmH2O
ΔP (corrected) 1093-739.28 = 353.72 mmH2O
DISCUSSION The objective of the experiment is to evaluate and study the performance of shell and tube heat exchanger at various operating condition. Besides that, evaluate and study the heat balance, LMTD and overall heat transfer coefficient. We need also calculate Reynolds’s number at the shell and tube heat exchanger and measure and determine the shell and tube side pressure drop. During the experiment, we carried out Run III and Run IV experiment. Every run consist of three set of data which need to be considered. Firstly, set up equipment according to the variable we need to investigate which are pressure and temperature. The ideal temperature for this heat exchanger is between 50 0 C and 70 0 C. So that, experiment run when the ideal temperature is achieve. For run III the flow rate is set to the 10 USGPM cold water (CW) and 15 USGPM for hot water (HW).The experiment was run until the value of flow rate was stable. Then, all the data was record for set 1.The experiment were repeated three times to get best result. The calculation was made from data recorded to identify which set of Run III have better result. The heat load was calculated for all sets of data. The ratio of Q C/QH which nearest to 1.0 is selected to continue the calculation. Then, for RUN III, set 1 is selected. The QC is 209472.97 Btu/hr ,QH is 179385.92 Btu/hr and 0.5(QC+QH) is 194429.45 Btu/hr. Next, the corrected LMTD was 20.14 0F while the overall heat transfer coefficient is 504.81 (
). The Reynolds
℉
number for shell is 389.31 and for tube is 12833.12.Other than that, for part III value ho, hi and ), 721.68(
hi0 are 1598.2( 421.05 (
℉
) and UD is 504.8(
℉
) and 571.57(
℉
) respectively. For UC the value is
℉
).The value of RD is 3.94 x x10-3 .Next, for the pressure
℉
drop at shell-side the calculated value, measured and corrected are 4973.73 mmH 2O,560 mmH2O and 65.05 mmH2O respectively. For the pressure drop at tube-side the calculated value, measured and corrected are 89.891 mmH2O,1093 mmH2O and 353.72mmH2O respectively.
For RUN IV, the flow rate was set up to 10 USGPM for both cold water (CW) and hot water (HW).The instrument is run for a while until the ideal temperature is achieved. For RUN IV, set 3 is selected. This is because the ratio of QC/QH is nearest to 1.0 which is 1.101. The QC is 134345.53 Btu/hr ,QH is 121935.53 Btu/hr and 0.5(QC+QH) is 128140.53 Btu/hr. Next, the corrected LMTD was 25.5 0F while the overall heat transfer coefficient is 332.7(
). The
℉
Reynolds number for shell is 364.46 and for tube is 7753.94.Other than that, for part III the ho, hi ), 604.95(
and hi0 are 1620.18( value is 263.63(
℉
) and UD is 332.70(
℉
) and 479.12(
℉
) respectively. For UC the
℉
). The value of RD is 0.6604 x x10-3 .Next, for
℉
the pressure drop at shell-side the calculated value, measured and corrected are 4484.88mmH2O,564mmH2O and 69.05 mmH2O respectively. For the pressure drop at tube-side the calculated value, measured and corrected are 18.79mmH2O,563.32mmH2O and 191.88mmH2O respectively. From the result above, the pressure drop depends on the flow rate not the temperature. As we can see that the pressure drop for Run III which used 10USGPM and 15USGPM was higher than pressure at Run IV which used 10USGPM. From the calculation, we conclude that the number of QC is decreasing from Run III to Run IV and same pattern goes to QH and 0.5(QC+QH).Other than that,U is also decreasing from RUN III to Run IV. The overall heat transfer coefficient, U, Reynolds number and flow rates of hot water are also decreasing from Run III to Run IV.
CONCLUSION The objective is achieved for Run III and Run IV. Based on evaluate and study the performance of shell and tube heat exchanger at various operating condition was determined. Besides that, the heat balance, LMTD and overall heat transfer coefficient also determined. The Reynolds’s number at the shell and tube heat exchanger was identified. Moreover, the shell and tube side pressure drop also determined. From the result , the pressure drop depends on the flow rate not the temperature. As we can see that the pressure drop for Run III which used 10USGPM and 15USGPM was higher than pressure at Run IV which used 10USGPM. From the calculation, we conclude that the number of QC is decreasing from Run III to Run IV and same pattern goes to QH and 0.5(QC+QH).Other than that,U is also decreasing from RUN III to Run IV. The overall heat transfer coefficient, U, Reynolds number and flow rates of hot water are also decreasing from Run III to Run IV.
RECOMMENDATION
The water to the tube side should be the first and last flow rate to be turned on. The steam should be turned on only after the water is flowing through the tube side and the water should be turned on only after the steam has been turned on.
Fully drain system after each use of water on tube side and steam condensate on shell side in order to avoid corrosion build-up during down-times.
The eye position should be perpendicular to the meniscus and the scale. Avoid any leakage of the instrument, the instrument should be working properly Avoid direct contact with water because it is hot
REFERENCE Comsol.(2013).Shell and tube heat exchanger. Retrieved from: https://www.comsol.com/model/download/177045/models.heat.shell_and_tube_heat _exchanger.pdf Yunus A. Cengel, Afshin J. Ghajar.(2011). Heat and Mass Transfer: Fundamentals & Applications Fourth Edition McGraw-Hill. http://www.inspection-for-industry.com/heat-exchangertheory.html#sthash.z1rLpGBV.dpuf http://www.engineeringtoolbox.com/overall-heat-transfer-coefficients-d_284.html http://iitkgp.vlab.co.in/?sub=35&brch=107&sim=1174&cnt=1
APPENDIX
Appendix Data: Approximated data for water TEMP °C
71.1 65 60 54.5 48.9 48 40 35
SG (1.0 at 60°F)
DENSITY lbm/ft3
DENSITY lbm/USG
61.00 61.30 61.38
0.9872 0.9901
61.71
8.156 8.182 8.207 8.227 8.253
0.995
61.94 62.06
8.289 8.296
0.985
VISCOSITY lbm/ft. sec
2.6947 x 10-4 2.9272 x 10-4 3.1503 x 10-4 3.430 x 10-4 3.7565 x 10-4 3.8223 x 10-4 4.4083 x 10-4 4.8572 x 10-4
HEAT THERMAL CAPACITY CONDUCTIVITY BTU/lbm. BTU/hr.ft2. °F °F/ft
1.00
0.3840 0.3830 0.3790 0.3710
0.999
0.3605