The objective of the lab is to calculate the time constant of the aluminum cylinder cooling in air, using the methods discussed in the lecture. Based on the time constant, the convective heat transfer coefficient (natural convection) is to be estimated using the lumped capacitance method.
The raw data for the heat-up and air cooling of the aluminum cylinder, provided in Excel Format, is available on TITANium.
Cooled by natural convection in still air.
Based on the simulated raw data provided, complete a memo report for the following:
· Report the time constant of the aluminum cylinder, cooling in air, using the “37% method” discussed in the lecture.
· Plot the temperature vs time data in terms of ln[(T-T∞)/T0-T∞)] versus seconds.
T∞ -- measured air temperature.
Determine the time increment it takes the logarithmic temperature to drop one integer value. This will be approximately one time constant.
· Follow the steps outlined in the lecture to determine the time constant using a manual linear regression analysis. Confirm your results with a computer-based linear regression analysis.
· Calculate the free convective heat transfer coefficient of the cylinder cooling in air using the time constant obtained above from linear regression analysis. Calculate the Rayleigh number of the cylinder cooling the air. Use Equation (9.33) from your heat transfer textbook [1] to calculate a predicted heat transfer coefficient. How does the experimentally determined value differ from the empirical value? If the difference is significant, greater than 10 to 20 percent, why might the measured value be different?
Each student needs to submit an individual memo report for this laboratory.
Include step-by-step sample calculations in the attachments.
1. Bergman, T. L. Lavine, A. S. Incropera, Dewitt, D. P., 2011, Introduction to Heat Transfer, 6th Edition, John Wiley & Sons, New York.
EGME 476B
ENERGY AND POWER LABORATORY
LAB # 1
–
T
hermal
T
ime Constant
Introduction
The objective of the lab is to calculate the time constant
t
of the aluminum cylinder cooling in air
,
using
the
methods
discussed in the lecture
. Based on the time constant, the convective heat transfer
coefficient (natural convection)
is to be estimated
using the lumped capacitance method.
Raw Data
The raw data
for the heat
-
up and air cooling of the aluminum cylinder,
provided in Excel Format
,
is
available on TITANium.
The aluminum cylinder properties are as follows:
Diameter = 0.375 inch
C
p
= 875 J/kg.K
r
= 2770bkg/m
3
Cooled by natural convection in still air
.
Simulated Results
Based on
the simulated raw data provided, complete a memo report for the following:
·
Report the time constant
t
of the aluminum cylinder, cooling in air, using the “37% method”
discussed in the lecture
.
·
Plot the temperature vs time data in terms of ln[(T
-
T
8
)/T
0
-
T
8
)
] versus seconds
.
Here,
T
–
time dependent cylinder temperature
T
0
–
initial temperature of cylinder
T
8
--
measured air temperature.
Determine the time increment it takes the logarithmic temperature to drop
one integer value.
This will be
approximately one time constant.
·
Follow the steps outlined in the lecture to determine the time constant using a
manual
linear
regression analysis. Confirm your results with a
computer
-
based
linear regression analysis.
·
Ca
lculate the free convective heat transfer coefficient of the cylinder cooling in air using the
time constant obtained above from
linear
regression analysis. Calculate the Rayleigh number of
the cylinder cooling the air. Use Equation (9.33) from your heat
transfer textbook [1] to
calculate a predicted heat transfer coefficient. How does the experimentally determined value
differ from the empirical value? If the difference is significant, greater than 10 to 20 percent,
why might the measured value be diff
erent?
EGME 476B
ENERGY AND POWER LABORATORY
LAB # 1 – Thermal Time Constant
Introduction
The objective of the lab is to calculate the time constant of the aluminum cylinder cooling in air, using
the methods discussed in the lecture. Based on the time constant, the convective heat transfer
coefficient (natural convection) is to be estimated using the lumped capacitance method.
Raw Data
The raw data for the heat-up and air cooling of the aluminum cylinder, provided in Excel Format, is
available on TITANium.
The aluminum cylinder properties are as follows:
Diameter = 0.375 inch
C
p
= 875 J/kg.K
= 2770bkg/m
3
Cooled by natural convection in still air.
Simulated Results
Based on the simulated raw data provided, complete a memo report for the following:
Report the time constant of the aluminum cylinder, cooling in air, using the “37% method”
discussed in the lecture.
Plot the temperature vs time data in terms of ln[(T-T
8
)/T
0
-T
8
)] versus seconds.
Here, T – time dependent cylinder temperature
T
0
– initial temperature of cylinder
T
8
-- measured air temperature.
Determine the time increment it takes the logarithmic temperature to drop one integer value.
This will be approximately one time constant.
Follow the steps outlined in the lecture to determine the time constant using a manual linear
regression analysis. Confirm your results with a computer-based linear regression analysis.
Calculate the free convective heat transfer coefficient of the cylinder cooling in air using the
time constant obtained above from linear regression analysis. Calculate the Rayleigh number of
the cylinder cooling the air. Use Equation (9.33) from your heat transfer textbook [1] to
calculate a predicted heat transfer coefficient. How does the experimentally determined value
differ from the empirical value? If the difference is significant, greater than 10 to 20 percent,
why might the measured value be different?
Evengrowth
thermal_lab.docx
0
