Chemical Engineering Summary Of Heat Exchanger Report Individual Report:(2 pages double spaced + 1 page with figures, tables, and references) Each member m | Homework Answers
Chemical Engineering Summary Of Heat Exchanger Report Individual Report:(2 pages double spaced + 1 page with figures, tables, and references) Each member must prepare a summary report based on the team report.The purpose of this report is to evaluate your writing. Make the chart and table in each individual report different than those in the team report.The report is attached and a sample of a summary report is attached too Abstract
The objective of this experiment was to design a heat exchanger system and compare values of
experimental heat transfer coefficient to the theoretical heat transfer coefficient with and without
insulation. The system was designed to run steam and cooling water in co-current flow through a
vertically mounted double pipe heat exchanger. Water entering from tube side and steam
entering from shell side. Pressure gauges and thermocouples were placed at the inlet and outlet
of the heat exchanger to record data for pressure and temperature. The experiments were ran at
three different flow rates 2, 3, and 4 GPM. For each flow, three different pressures were used 5,
10 and 15 psi. For each run, the temperature should reach steady state before the readings were
taken and condensate were collected. This procedure was performed for both insulated and
uninsulated heat exchanger.
Experiment summary
In the first day of lab, piping and heat exchanger system were done to match the preplanned
piping and instrumentation diagram. In day two, leak test and pressure test were performed. three
leaks were found, one leak was found on the water side and it was due to a broken rotameter.
Two leaks were found on the steam side, one small leak was from one of the pressure gauges and
it was due to unwrapping the pipe with teflon tape. The other leak was found due to an old rusty
union. First thing was done in day three was calibrated the thermocouples, pressure gauges and
the water rotameter. The four thermocouples were calibrated by taking data for each
thermocouple in an ice bath (freezing temperature) and in a boiling bath. Pressure gauges were
calibrated using Precision Pressure Transfer Standard Machine, figure 1 shows the calibration
curve for the pressure gauges. Last calibration was for the water rotameter and it was done by
using bucket and stopwatch method, figure 2 shows the calibration curve.
Results
Nine different runs were performed for each uninsulated and insulated system. For the
uninsulated system, heat transfer coefficient for steam and water were found experimentally to
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??
be 1594 ??2 ??? and 5096 ??2 ??? respectively. On the other hand, the theoretical heat transfer
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coefficient for steam and water were found to be 4569 ??2 ??? and 30368
??
??2 ???
respectively.
For the insulated system, the experimental heat transfer coefficient for steam and water were
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??
equal to 1583 ??2 ??? and 5215 ??2 ??? respectively. However, the theoretical values for steam and
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??
water found to be 4598 ??2 ??? and 30368 ??2 ??? respectively. The theoretical heat transfer
coefficient for water was higher than the experimental and that due to the higher Reynolds
number was used in the correlation. Overall heat transfer coefficient was higher theoretically
than experimentally. However, the experimental overall heat transfer coefficient values were
within the same range of the typical overall heat transfer coefficient values, table 1 shows a
summary of the overall heat transfer coefficient values [1]. In the other hand, the overall heat
transfer coefficient in the insulated system was higher than the uninsulated system and that
because the insulated transfer more heat to the water than the uninsulated. Team Yellow
Submarine expected to see a difference in values between the theoretical and experimental for
various reasons. Theoretical U is calculated assuming there is no heat loss to the environment.
When calculating the experimental U, heat loss to the environment has to be included even if the
system is insulated.
Steam in
Steam out
PRESSURE READ [PSIG]
30
25
20
15
10
5
0
0
2
4
6
8
10
12
14
16
PRESSURE ACTUAL [PSIG]
Figure 1: Calibration curve for the inlet and outlet pressure gauges
0.3
FLOW RATE [KG/S]
0.25
y = 0.0667x
R² = 0.9781
0.2
0.15
0.1
0.05
0
1.5
2
2.5
3
3.5
4
4.5
ROTAMETER [GPM]
Figure 2: Calibration curve for the water rotameter
Table 1: Comparison between the measured Uoverall to the heuristics values
Overall Heat transfer coefficient [W/m^2*k]
Insulated
Uninsulated
Heuristics
U exp
U theo
U exp
U theo
U typical
1388
2614
882
2604
300 – 1200
Reference:
[1] Engineers Edge, Overall heat transfer coefficient table charts and equations
https://www.engineersedge.com/thermodynamics/overall_heat_transfer-table.htm
Abstract
Heat Exchangers are applied in industry to facilitate the transfer of heat from a hot fluid
to a colder fluid. Often, steam is utilized as the hot fluid due to large amount of energy
transferred associated with phase change. This experiment used steam and cold water to
test various parameters of a vertical double pipe heat exchanger system. The system
required design and piping to incorporate a three foot vertical heat exchanger with
necessary measurement devices. Pressure gauges were incorporated to measure steam
input and pressure drop across the system. Thermocouples were placed at each inlet and
outlet to determine temperature changes that were ultimately used for heat transfer
calculations. In order to ensure safety when running the experiment, pressure tests were
conducted to determine leaks.
After successful design of the heat exchanger and piping system, tests were conducted at
steam pressures of 5, 10, and 15 PSI with a constant cool water flow rate of 6 GPM.
Calibrated thermocouples recorded temperature changes that allowed for calculation of
overall heat transfer coefficients. Bare pipe heat loss was also determined in comparison to
an insulated adiabatic system with no heat loss to the environment. Also, correlations
between steam pressure and overall heat transfer coefficient were determined.
Experimental Summary
The heat exchanger system was assembled using a double pipe heat exchanger. The
inlet to the annular side of the exchanger was piped to the cold-water source with a
flowmeter to measure inlet water flow and a globe valve at the exit to ensure the exchanger
was flooded. The annular side exited to the sink. The inlet to the inner pipe connected to
the steam source with pressure gauges at the inlet and exit of the exchanger to measure
pressure drop. The steam side then exited to a metal bucket.
Testing of the double pipe heat exchanger was carried out by setting the cold-water
flow rate to 6 GPM and varying the steam pressure between 5, 10, and 15 PSI. For the first
run, the cold-water source was opened all the way to allow the maximum water flow rate of
6 GPM. One person was stationed by the steam inlet to adjust the regulator to the
appropriate steam pressure. Another person was stationed to watch the pressure gauges
and made sure that there was a pressure drop across the exchanger. A third person cycled
through the thermocouple temperatures until they reached steady state and then recorded
the final temperatures for both the inlet and outlet of the inner pipe and the annular side of
the heat exchanger. Each temperature was recorded along with the appropriate cold-water
flow rate and steam pressure.
For the heat exchanger system, both the thermocouples and the flowmeter were
calibrated. The thermocouples were calibrated before piping them into the system. The
thermocouples were attached to the box that transmitted the temperature readings and
were placed in ice-water, 0 C, and the temperature the thermocouples read were recorded
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as their respective zero. Then, the thermocouples were placed in boiling water to
determine a calibration curve to find the correct temperature for the thermocouples.
The flowmeter was calibrated using the bucket-and-stopwatch method. The
flowmeter, before being piped into the system was attached to the cold-water source and
the outlet flowed to a bucket on a scale. The GPM rate measured using the bucket-and-
stopwatch method was compared to the reading on the flowmeter and the reading was
accurate compared to the calculated flow rate.
Results and Discussion
The actual temperatures for the inlets and outlets of the double-pipe heat exchanger
were found using the calibration curve in App A.1.1. Temperature profiles for each run
were created by graphing the steam inlet and outlet as well as the cold-water inlet and
outlet versus the distance of where the temperatures were taken. All three temperature
profiles are included in App B.1.1, but since they all look similar, only one is included here
for comparison between textbook temperature profiles and experimental temperature
profiles for the double-pipe heat exchanger.
Figure 1. Temperature Profile for Run 1 of Double-Pipe Heat Exchanger with Cold-Water in
the Annular Space and Steam in the Inner Pipe, Co-Current Flow
Figure 2. Temperature Profile of a Co-Current Heat Exchanger with Condensing Vapor
1
For the double-pipe heat exchanger used, the temperature profile matches the theoretical
temperature profile for a co-current heat exchanger with condensing vapor, shown in
Figure 2. The temperature of the steam does not change much because most of the energy
being transferred to the cold-water is used to change the steams phase from vapor to
liquid, and not to change the temperature of the steam . The energy transferred does
1
greatly increase the temperature of the cold-water, as the temperature increases from
17.35 C to 81.05 C. The same temperature profile occurs in all three trials.
o
o
Condensate rate and overall heat transfer coefficients were determined for each steam
pressure at 6 GPM as shown below in Table 1.
Table 1.
Steam Pressure mcd
(psi)
(GPM)
5
0.021
Qcw
(kW)
Qcd
(kW)
Qloss
(kW)
33.086144 45.78 154.393856
10
0.022
34.040552 47.96 164.339448
15
0.023
33.881484 50.14 190.658516
Steam condensate rates were found by the bucket and stopwatch method. Each trial
was run for for 4 minutes. The steam condensate was placed at the outlet and weighed
after the total 12 minute period. How each rate was determined can be found in the log
book attached in the appendix. As displayed in the table, as water flow rate is held constant,
lower steam pressures yield lower steam condensate rates. Furthermore, high steam
pressures produced an increase of steam temperature, which resulted in an increased
temperature driving force. Some error in accuracy can be noted here because the steam
condensate was weighed after all three runs were completed. In order to yield more
accurate results, a scale could have been placed under the bucket, allowing for readings to
be taken after each 4 minute run. With insulation, theoretically, heat loss would be 0.
However, had the experiment been run with insulation, taking into account experimental
errors such as subcooling of steam, some heat loss would occur.
The equation used to solve experimentally obtained overall heat transfer coefficient
values shown in Table 2 is
U=mCpTATLM
Where m is the mass flow rate of water in kg/s, Cp is the specific heat capacity of water in
J/kg-C, ?T is the temperature difference, A is area in m2, and TLMis the log mean
temperature difference.
Theoretical and experimental U values are significantly different. Despite the
variance, the general trend of increasing pressure increases the overall heat transfer
coefficient is followed by both theoretical and experimental values. As stated previously,
increase in steam pressure produced an increase in temperature driving force ultimately
causing for increased experimental U values. According to the U value correlations shown
in Table 4 of Appendix C, experimental U correlations coincide with the expected range of
850-1700 W-m2K.
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