Heat Transfer Lab report #3
Attached:
1- Follow the instructions carefully (Instructions)
2- Lab Manual (What was done during the lab).
3- Two sample papers. (Previous courses, but are downloaded on Turnitin system)
#Please make the sections clear, well written, and understandable.
Instructions:
The samples I attached is related to other groups in the same class, so mine should be different.
You should write from scratch (DO NOT PARAPHRASE THIS WITH THE SAME WORDS!) Everything should be understood and then it should be written from scratch, so basically this sample that is attached is to help you understand what is needed in each section and Please be careful to make this lab memo the best lab memo you have ever done. It worth a lot. Please this is really important try your best. You can’t take any sentences or copy anything because this will be tested by a very high quality turnitin system so please be careful not copy either from the sample or from the internet or any other sources (NOTHING CAN BE COPIED). Those samples were done by two other members in the same course, so if I copied from them then I will be caught easily. Off course, you could search and learn so that you become able to write a perfect memo but DON’T COPY! + Add any resources you have used in understanding the idea in the bottom of this paper.
All of the parts found in the sample are required to be written from scratch. Thank you,
IMPORTANT: there might be some more steps or missing stuff in the samples because I don’t know if they have the same exact things, so please to be in the safe side read the manual carefully to know what I have done in the lab. The manual will tell you exactly what we did and please I don’t want to get into troubles. Make this lab report perfect and be careful not to copy and not to put something just because you saw it in the samples, because we might did something different. Those samples are of previous semesters. Thank you,
Parts I need you to do:
1- Introduction & objectives
2- Theory & Nomenclature (In the theory part the professor said that it is difficult to understand the theory if you didn’t explain it in a good way so please explain it well+ he said that if possible you should draw a schematic to help me in understanding the equations or whatever you are talking about and don’t just take the pictures directly from the lab manual.) He said it is easy to draw a schematic that will help in the understanding of the theory.
3- Discussion (Please if you found any numbers that should be included just leave a bracket and write inside the bracket what kind of number should be plugged, so that my colleague who will do the results plug in the numbers.)
4- Conclusion
5- References

Steps (What you should do):
1- Read these instructions
2- Read the attached instructions (only for the parts I asked for(intro & obj., theory and nomenclature, Discussion, conclusion, and references).
3- look at the two attached samples, and search the internet if you wish to understand everything perfectly and become able to write.
4- Write the parts ordered.
Experiment 3: Forced Convection over Extended Surfaces

Introduction

The fundamental topic covered in this laboratory is to study heat transfer from an extended surface through forced convection. Heat transfer between a fluid and a solid happens through convection. The rate of convection heat transferred betweenthe solid object and the fluid is proportional to the temperature difference between solid surface and fluid, the shape of the solid object, the surface area exposed to the fluid, and fluid speed and properties. In this experiment students become familiar with forced convection heat transfer from a cylinder to the fluid. Furthermore, the setup is in the form of an extended surface that gives the student the abilityto verify the analytical equations derived for extended surface in heat transfer class.

Theory

Forced convection happens when fluid at a given temperature is moved on a surface with a different temperature. The heat transfer depends on Reynolds number, geometries, temperatures, and fluid properties. Within this laboratory we are specifically looking at forced convection over a non-infinite heated circular cylinder that may (to be verified) be considered as fin.

Convection heat transfer coefficient is often calculated and expressed in the non-dimensional form called the Nusselt number:

Nu_D=hD/k (1)

Where D is the diameter of the cylinder and k is the conductivity of air. For a cylinder placed in a cross flow the Nusselt number can be obtained from Hilpert equation that is a correlation between the Nusselt number and Reynolds and Prandtl numbers when Pr>0.7.

Nu_D=CRe_D^m ?Pr?^(1/3) (2)

Where Re is the Reynolds number, Re=?VD/µ, and Pr is the Prandtl number, Pr=v/a. The coefficients for C and m have been empirically determined for the cylinder in cross-flow depending on the Reynolds number. See Table 7.2 in Incropera. (Pg. 426.)

For the case of this experiment the heating is only from one end of the cylinder with length L where L/D is relatively large. This case may be analyzed using extended surface, or fin, theory. Assuming a fin of uniform cross section, such as a cylinder, the temperature variation across the cylinder can be ignored compared with its variations along its length. In this case a differential equation can be derived as (see your text book for more details):

(d^2 T)/(dx^2 )-hP/(kA_c ) (T-T_8 )=0 (3)

Where P is the perimeter of the fin. ‘h’ is the heat transfer coefficient. Depending on the tip condition (convective heat transfer, adiabatic (insulated), fixed temperature, or infinite length) the solution to the temperature gradient along the axis changes. In this case, convective heat transfer at the tip, the temperature distribution across the fin can be defined as:

(?(x))/(?(b))=(cosh?(m(L-x) )+(h/mk)sinh?(m(L-x))/(cosh?(mL)+(h/mk) sinh?(mL) ). (4)

Here

?(x)=T(x)-T_8 (5)

and

m^2=hP/(kA_c ) (6)

Where P is the perimeter of the fin and k is the conductivity of the meta, and h is the convection heat transfer coefficient. We define ?(b) as ? at the base of the pin fin. The total heat transfer for the fin, q_f, can be determined as follows:

q_f= M ( sinh?(mL)+(h/mk)cosh?(ml))/(cosh?(mL)+(h/mk)sinh?(mL)) (7)

Where M is defined as:

M=v(hPkA_c ?_b ) (8)

And k is the conductivity of the metal. Fin efficiency is defined as the ratio of the heat transfer from the fin to the maximum possible heat transfer from the fin, which is when all the fin is at base temperature.
It can be computed as:
?_f=q_f/(hA_f ?_b ) (9)

For more details refer to MEEN 461 course materials and Incropera pg. 147-150.The fin effectiveness, characterized as the ratio between the energy dissipated by the fin, q_f, and the energy that would have been dissipated if the pin fin were not in place (i.e. if the surface were perfectly devoid of fins). It can be expressed as follows:

e_f=q_f/(hA_(c,b) ?_b )
(10)
Laboratory Objectives

The specific reportable objectives of this experiment are to:

Collect and normalize the experimental temperatures across the fins. Determine the axial temperatures using the theory.Normalize and Plottheoretical and experimental temperatures for both specimensat each wind speed on the same figure. (Three plots for three different speed).
For each specimen, plotthe normalized experimental temperatures at three different speeds on the same figure. (Two plots for the two specimens)
Choose one of the experimental tests (one of the test rods and one wind speed) and model the temperature distributions across the fin as if the tip was adiabatic (see Table 3.4, in Incropera). Present the results as you choose (graph or table). Discuss the differences. Determine how long the length of the fin would have to be in order for the tip condition to be negligible.
Determine the fin heat transfer rates for each experimental test and compare it with the actual heat generation at the base. Discuss differences.
Calculate the fin efficiency and performance for each case.
Discuss some methods which would decrease the amount of time required for the system to reach steady state.

Experimental Materials

The experimental materials for the Forced Convection over Pin Fins Experiment are:

(1) Engineering Laboratory Design Wind Tunnel
(2) Test heated circular pin fins: One Copper and one Brass.
EightT-type thermocouples each
Thermocouples spacing and other dimensions and properties given in appendix
(1) Pitot tube and TSI VelociCalc Hand Held Tester
(1) Labview System with NI PXIincluding DAQ input board and thermocouple cards.
5. Experimental Apparatus and Procedure 1-d Conduction

The Forced Convection over Pin Fins experiment consists primarily of the Engineering Laboratory Design wind tunnel, two different test specimens, and a LabView system. A FUJI variable frequency drive allows adjustment of the motor in the wind tunnel.

Each test specimen is made up of a 12mm diameter cylindrical stock of Copper and Brass approximately 21 cm in length, (figure 1). Each test specimen has eight Thermocouples embedded approximately half way into the rod. One of these thermocouples measures the temperature of the heated base, the rest measure the axial temperature distribution. The thermocouples are set 3 cm apart from each other. An Omega cartridge heater (CSH-101100/120V) is embedded in the base of each test specimen. The base of surface area 136 cm2, is insulated with cotton and then placed inside a small acrylic box.

Figure 1: Two test specimens inside wind tunnel

Figure 2: Pitot tube Figure 3: Brass fin

Startup Procedure for Forced Convection over Pin Fins
Ensure that the 3-phase to the wind tunnel VFD is connected and turned on.
Turn on and enable output on the two Agilent power supplies.
Ensure that all wind tunnel hatches are closed and sealed.
Operating Procedure for Forced Convection over Pin Fins
Create the LabView VI and run it. Name and save the data file appropriately.
Set the Heater power supply to 25 Volts.
Set the VFD power supply as directed by your instructor.
During the start of the experiment use the TSI Velocity meter to measure the wind speed and temperature. Record this information in the Appendix.
Wait until steady state temperatures have been reached. This may take between 30-45 minutes depending on the settings and test specimen.
Once steady state has been reached let the system run for approximately 5 more minutes to collect steady state temperature data.
Repeat steps 3-6 for two different wind speed.
Shutdown Procedure for Forced Convection over Pin Fins
Press the stop button inside the VI.
Turn off all Agilent power supplies unless directed otherwise.
Save data to USB key.
Data Charts for Experiment 3

Material Diameter (mm) ± (mm) Sensor Spacing (mm) Conductivity (W/m-K)
Brass 12 0.05 30 110
Copper 12 0.05 30 400

Wind Speed (m/s) Tunnel Temperature (°C)
Run 1
Run 2
Run 3