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Laboratory 6: Thermal Insulation

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  1. Laboratory 6:Thermal Insulation General Engineering Polytechnic University

  2. Objective Heat Equilibrium Heat Transfer Conduction Convection Radiation Thermal Insulation Materials for Lab Problem Statement Guidelines Procedure Written Assignment Written Topics Recitation Topics Closing Overview

  3. Objectives • Understand the concept of heat as a form of energy • Learn how heat moves to different objects • Use your new knowledge to create a container that keeps an egg from cooling

  4. Heat • Energy transferred from one object to another due to a difference in temperature

  5. 125o 39o 70o 65o 70o 70 25o 90o 70o 70o 58o 70o 50o 70o 95o 70o 80o 73o 70o 70o Equilibrium • The temperature at all points in a system are the same

  6. Direction of Heat Heat Transfer • A result of all systems trying to reach equilibrium • Heat always travels from higher to lower temperature • There must be 2 or more substances in contact with each other • Three types of heat transfer • Conduction • Convection • Radiation Hot Cold Now at equilibrium

  7. q = heat transfer DT = difference in temperature DX = length of bar k = coefficient of thermal conductivity A = cross-sectional area Conduction • Energy transferred from one solid body to another without passing through a medium q = kADT DX Aluminum Iron

  8. q = heat transfer DT = difference in temperature h = coefficient of convection A =cross-sectional area Convection • Heat is transferred by mass transport of atoms • Typically when heat is transferred from a solid material to a fluid substance (or vice versa) q = hA DT Iron Water Steel

  9. q = heat transfer T = temperature e = constant of emissivity s = Stefan-Boltzman’s constant A = cross-sectional area Radiation • Energy is admitted and absorbed by bodies in the form of electromagnetic waves • Can travel through a vacuum q = esAT4

  10. Thermal Insulation • Prevents a system from quickly reaching equilibrium • Examples: • Clothing • Walls of houses • Refrigerators • Thermos bottles

  11. Foam chips Plastic wrap Tape Cardboard Aluminum foil Thermocouple and wire connectors Thermal LabVIEW program DAQ board Materials for Lab

  12. Problem Statement • Build an insulating container to accept a hard boiled egg that was just removed from the hot water. • The container should aid in reducing the loss of heat from the hot egg.

  13. Guidelines • All materials must remain inside the container • No external heat sources may be used • Start LabVIEW program when container cover is closed and egg is inside • The container may not be held or covered during temperature readings • The egg may not be returned to the water (i.e. No “restarts”)

  14. Procedure • Pre-Test • Brainstorm & sketch a suitable container to keep the egg warm • Include a written description of the dimensions and construction materials • Build the container according to the sketch • Pre-Test • Test • Post-Test

  15. Procedure • Test • Wait to receive boiled egg from instructor • Attach one end of thermocouple wire to the egg (They must remain in constant contact) • Quickly close the container • Connect thermocouple to pins 1 & 9 on the DAQ Board • Start the LabVIEW program • Pre-Test • Test • Post-Test

  16. Procedure • Post-Test • Once the time has finished the LabVIEW program will generate an Excel table • Use data on the table to create an Excel graph of Temperature vs. Time • Print out the graph and table • Present the Excel data to your instructor for his/her initials • Pre-Test • Test • Post-Test

  17. Written Assignment • Full Team Report (one report per team) • Use the guidelines on page 5 for help • Include original sketches with instructor’s initials • Include Excel table and graph • Include the topics found on the next slide • Remember to create a title page

  18. Written Topics • Address each of the following topics and place them in the proper sections of report • Describe the guidelines for this lab • Give reasons for your design • Find the slope of the last 5 minutes of the graph. Interpret how the slope and the graph describes the performance of your container • Why are some materials better than others for the purpose of the container? • What factors would affect the readings you recorded? • Describe how you would improve your container if you were to rebuild it

  19. Recitation Topics • Discuss the strategy employed by the team in the development of the design • Discuss the choice of materials and quantities used. Were some materials better than others? • Would this lab be a good competition? Why or why not?

  20. Closing • The egg is VERY hot, do not burn yourself • Clean up your workstation when finished • Throw the egg in the garbage after the lab • You may keep the cup for recitation, otherwise dispose of it properly