Lab 3_Prelab_Fall2023

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University of Notre Dame *

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334

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Mechanical Engineering

Date

Dec 6, 2023

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pdf

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2

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Name: Section (day/time): ME139L-Experimental Heat Transfer Prelab Assignment for Lab 3 (Your team should bring one computer to the lab session that meets in ETC 1.204) NOTE: In the Lab 3 folder on Canvas, your team will find a template that you will build upon to assist in lab data analysis. This template is named “ Lab 3_ Data Processing Template.xlsx ”. Download, modify, and validate this template as per the guidelines below: In this lab you will examine convective heat transfer from a flat plate positioned in a wind tunnel. Selected specifications for this experiment are as follows: Free-stream flow velocity: 12 to 16 m/s (each session will be given a different velocity) Length of the plate: 0 . 633 m Width of the plate: 0 . 204 m Power into the heater is determined using the measured electrical resistance of the heaters, and the measured voltage in the electrical outlet. This power is dissipated into the plates and is used to determine the heat flux from the surface: Typical resistance of the front heater: 58 ohms Typical resistance of the back heater: 56 ohms Voltage of the power outlet: 119 V (rms) Power dissipated into the plates: to be calculated Heat flux from both surfaces: to be calculated Assuming that the film temperature is 300K, and assuming that transition occurs at Re x = 5 x 10 5 , modify the Lab 3 Data Processing Template to calculate the following. Download Lab 3 working conditions_ F2 023.xlsx ” on Canvas , to find the velocity in your session . You will need the calculated results during your lab session, so remember to bring the pre-lab with you to the lab. a. Location (in meters) of the expected transition from a laminar to turbulent boundary layer at the given velocity for your lab session? Validate your spreadsheet calculations with a hand calculation. b. Expected boundary layer thickness at 25 cm and at 50 cm from the leading edge of the plate for your session velocity under the following two conditions: (i) if a laminar boundary layer exists along the entire flat plate (ii) if a turbulent boundary layer exists along the entire flat plate Validate your spreadsheet calculations with a hand calculation. c. In your lab session, you will take at least 15 measurements in both the velocity and thermal boundary layers, until you find the thickness (velocity or temperature does not change any more). Calculate the thermal boundary layer first based on the results in (b) for both locations and both laminar and turbulent cases (4 cases in total), and then evaluate the approximate increment sizes for velocity and thermal BL in both millimeters and inches (divide the thickness by 15), which you will use during your lab session. d. For the typical resistances and voltage indicated above, calculate the surface heat flux (W/m 2 ) and treat this as constant (remember, there are two sides to the plate). If the measured local surface temperature is 32 o C and the room air temperature is 25°C, what is the local convective heat
Name: Section (day/time): coefficient when the radiation loss is ignored? It is not necessary for you to structure your template to perform this calculation. However, you should realize that this is precisely the calculation that you will be doing with your actual lab data. You should use the free time you might have in the lab to further develop your spreadsheet.
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