Laboratory 6: Thermal Insulation General Engineering Polytechnic University

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

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

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

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

Equilibrium The temperature at all points in a system are the same 65 o 73 o 125 o 50 o 39 o 25 o 80 o 95 o 90 o 58 o o TO 

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 HotCold Direction of Heat Now at equilibrium

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 HotCold Direction of Heat Now at equilibrium

Conduction Energy transferred from one solid body to another without passing through a medium Aluminum Iron q = kA  T  X k = coefficient of thermal conductivity A = cross-sectional area q = heat transfer  T = difference in temperature  X = length of bar

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) IronWaterSteel q = hA  T h = coefficient of convection A =cross-sectional area q = heat transfer  T = difference in temperature

Radiation Energy is admitted and absorbed by bodies in the form of electromagnetic waves Can travel through a vacuum q = e  AT 4 e = constant of emissivity  = Stefan-Boltzman’s constant A = cross-sectional area q = heat transfer T = temperature

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

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

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.

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”)

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

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

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

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

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

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?

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