Hi i need you to paraphrase this word file. you don’t have to paraphrase too much just a simple paraphrasing.# for the prucedure part it would be preferred to combine the steps to make it shorter.I’ve attached the word document.
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In this experiment the Cross Flow Heat Exchanger was studied. The direction of one fluid
is perpendicular to the other. Heat is transferred via convection because of the temperature
difference in the two fluids. In the experiment the cross flow in cylindrical tubes arranged as
single tube, full row or full bank. Therefore, the velocity, Reynolds number, Biot Numbers and
Nusselt number were calculated. A thermocouple was used in the experiment it is used to
measure the temperature difference between the hot rod and the cold air stream. The inlet air
temperature is measured by a mercury-in-glass thermometer and by a thermocouple located in
the center of the duct. The convective coefficient for each configuration was obtained from the
slope of plots (1-12). Using the convective coefficient, from there the Biot number was
calculated. Since â??Biot number less than 0.1â? holds true for all cases, the assumption of a lumped
system is valid. The significance of this data is that this allowed the use of the Nusselt equation
This experimental apparatus includes a centrifugal fan driven by a 1-hp electric motor
and having its inlet connected to the working section. Air enters the experimental apparatus by
way of a bellmouth. After the working section, a transition piece leads to the fan inlet and is
fitted with a honeycomb flow straightener intended to prevent the transmission of swirl from the
fan back into the working section. The fan discharges to a graduated throttle valve, by means of
which the air velocity through the experimental apparatus may be regulated. One Pitot tube is
located at upstream before the rods and another downstream after the rods to measure dynamic
heads. A thermocouple is used to measure the temperature difference between the hot rod and the
cold air stream. The inlet air temperature is measured by a mercury-in-glass thermometer and by
a thermocouple located in the center of the duct.
A thermocouple is a temperature-measuring device consisting of two different conductors that contact
each other at one or more spots. Voltage is produced when the temperature of one of the spots differs
from the reference temperature at other parts of the circuit. By measuring the voltage directly,
temperature can be calculated.
Figure A shows the diagram of a thermo couple circuits which helps for a better understanding about
the thermal process. Letter a, is called hot junction. A junction of two different metals A and B. It is
placed at where the temperature ð??â?? needs to be measured. Both letters b and c are called cold junction.
They are both immersed in an ice bath therefore maintained at the same temperature ð??ð?. The
temperature difference between ð??â?? and ð??ð? causes voltage and current. The voltage between a, and b
can be expressed as the equation. Similarly, is the voltage between a, and c. Where E1 is the electric
potential at letter a, E4 is the electric potential at letter b and E3 is the electric potential at letter c. Since
temperature difference causes voltage, the magnitude of the voltage is a function of temperature. It can
be written as ð?? = â??ð¸ = ð¶ (ð??â?? â?? ð??ð?). The material property is also a function of temperature and it can be
referred as the letter C. C only depends on the material chosen. Consequently:
Where ð¶ð´ is a material property of metal A and ð¶ðµ is a material property of metal B. Letter b and d is
connected with material metal C. where d is usually exposed to the environment the temperature at d
can be assumed the same as environment temperature ð??â??. Since point b is maintained at , the
temperature difference between b and d again causes voltage which can be written as:
Where ð¶ is a material property of metal C. Similarly, between c and e:
ð??ð??â??ð?? is the voltage between d and e which can be directly measured by the voltmeter. ð¶ðµ and ð¶ð´ are
material properties and constants, ð??ð? is called reference temperature which in this case is 0 Â°C. It is now
can be seen that by measuring the voltage between d and e, the desired temperature ð??â?? can be
calculated from this above equation. A note regarding this equation: metal A and metal B cannot be the
same material, otherwise ð¶ðµ = ð¶ð´ which makes the denominator equal to zero. This is how a
thermocouple works. If an object is heated/cooled via convection and the temperature within the object
is the same everywhere, this object is considered lumped. In heat transfer, the developed equation for
this scenario is:
Therefore, the equation above can be rewritten as:
Where T is temperature of the object, T_inf is fluid temperature, T_i is initial temperature of the object,
h is convective heat transfer coefficient, m is mass of object and C_p is specific heat transfer. By plotting
y vs t and fitting data with a linear function, the slope a can be found and from a, therefore convective
heat transfer coefficient h will be able to be calculated. However it is extremely important to verify that
the rod can be treated as a lumped system. In order to be considered a lumped system, Biot number has
to be less than 0.1.
Where k_c is the thermal conductivity of copper and L_c is the characteristic length. Therefore the Biot
number can be calculated by:
Biot number has to be less than 0.1 in order for the lumped system assumption to be valid.
Nusselt Number, k_c is the thermal conductivity of the fluid air and L_c is the characteristic length. The
Velocity can be represented as:
The Reynolds Number equation used for this experiment is:
Upstream dynamic pressure head measurement and cooling curve
â?¢ R1C1SR: Row 01, Column 01, and Single rod
Step 1: Place the Pitot tube in the upstream position in the test section.
Step 2: Move the plastic tubing connecting the upstream static pressure port.
Step 3: Connect the static pressure port to one end of the manometer and stagnation pressure port to
the other end of the manometer.
Step 4: Fully open the slide throttle valve.
Step 5: Cover all of the slots with caps except Row 01 and Column 01.
Step 6: Start the fan. Step 7: Set the throttle valve to a 10% opening.
Step 8: Heat up the copper rod to about 60â?¦C.
Step 9: Insert the copper rod to Row 01 and Column 01.
Step 10: Enable the data acquisition system by hitting the Run button in the LabVIEW vi. This will record
temperature of the rod, air temperature, and time.
Step 11: While waiting for the rod to cool down, record the height difference in the two taps of the
manometer as the dynamic pressure head h.
Step 12: Move the Pitot tube from 3 to 11 cm in increments of 2 cm and at each position record the
height difference in the two taps of the manometer as the dynamic pressure head h.
Step 13: Stop the DAQ system when the rod temperature is equal to the air temperature, end of the
Step 14: Save the data as an Excel spreadsheet and name it R1C1SR01. Note: R1 indicates row number,
C1 indicates column number, SR stands for single rod, and 01 indicates 10% throttle opening.
Step 15: Repeat Steps 7 through 14 for throttle openings of 40%, 70% and 100%. Name the
corresponding Excel spreadsheets as R1C1SR04, R1C1SR07, and R1C1SR10, respectively.
Step 16: Shut off the air.
â?¢ R2C3FR: Row 02, Column 03, and Full row Repeat Steps 1 to 16 with the copper rod inserted into Row
02, Column 03 and plastic dummy rods inserted to the other open slots within the same row. This trial is
called FR which stands for Full Row.
â?¢ R2C3FB: Row 02, Column 03, and Full bank Repeat Steps 1 to 16 with the copper rod inserted into
Row 02, Column 03 and plastic dummy rods inserted to the other open slots. This trial is called FB which
stands for Full Bank.
Downstream dynamic pressure head measurement
Step 1: Place the Pitot tube in the downstream position in the test section.
Step 2: Move the plastic tubing connecting the downstream static pressure port.
Step 3: Insert plastic dummy rods to every slot so it is a full bank.
Step 4: Fully open the slide throttle valve.
Step 5: Start the fan.
Step 6: Set throttle valve to 10% opening.
Step 7: Set the Pitot tube height to 2 mm above the bottom surface facing the fluid direction.
Step 8: Record the height difference in the two taps of the manometer as the dynamic pressure head h.
Step 9: Move the Pitot tube from 2 to 122 mm in increments of 2 mm and at each position record the
height difference in the two taps of the manometer as the dynamic pressure head h.
Step 10: Repeat Steps 6 through 9 for throttle openings of 40%, 70% and 100%.
Conclusion and discussion:
The natural log of the change in temperature was calculated and plotted against the time at all four
throttles, 10%, 40%, 70%, and 100%. The main point of this experiment was to determine how heat
transfer phenomena works. The experiment had three configurations and a changing throttle. The first
configuration was the single rod configuration and the configuration went through four throttles, 10%,
40%, 70%, and 100%. The calculated values from this configuration were the convective heat coefficient
which was used to find the Biot number. The Biot numbers was found to be less than 0.1 at 10%, 40%,
70%, and 100%. This means that all the Biot numbers obtained are valid for obtaining the Nusselt
number. The Same calculations were done for the full row configuration and the full bank configuration.
The Nusselt number and the Reynolds number of the three configurations were graphed and the graph
shows that as the Reynolds number increased, so did the Nusselt Number, which matches the equation
in the theory. The configuration of the experiment also had an impact on the graph. The maximum
velocity was found at 10mm, 35mm, 60mm, 90mm, and 110mm from the bottom of the duct. The
velocity at the 40% throttle was double the velocity at the 20% throttle.
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