Minimum Cooling Time for Metallurgy Applications

1
Minimum Cooling Time for Metallurgy Applications

• Satyän Chandra
• Jordan Walser

2
Introduction Description

• Problem Focus Cooling of Heated Metals.
• Heated Aluminum cylinder left to cool
  experiences
• Conduction
• Free Convection
• Forced Convection
• Radiation
• Experimental and Analytical results compared.

3
Introduction Motivation

• Our goal in doing this project is
• To Validate Heat Transfer Principles and Theories
  learnt in this class by comparing experimental
  results to those obtained analytically using
  equations and correlations of Heat Transfer.
• To Support Safety and Safety Precautions by
  identifying the minimum time needed for Aluminum
  heated to its annealing temperature to cool down
  to a level safe for direct contact. (This
  objective is derived from several months of
  working in the Materials Lab and observing
  students burn their hands by touching Aluminum
  that is very hot)

4
Problem Set Up
Tsur 22 C 295 K
T8 20 C 293 K
Surrounding Room Wall
At t 0 s Tcylinder 250 C 523 K
Cylinder
Air
qconvection
Safe to Operate Temperature for Humans 50 C
323 K T
qradiation
qconduction
Resting Table of Fire Clay Brick (K lt 1 W/m.
K)). Flux consists of Conductive, Convective and
Radiative components.
Cylinder on Table
5
Experimental Results

• Used K Type Digital Thermometer for measurement
  of Cylinder Surface Temperature
• Initial Cylinder Temperature 250 C
• Desired Cylinder Temperature 50 C
• Time (250 C 50 C) 1Hr. 40 Min

6
Analytical Results I
Dimensions
Aluminum
Air (359 K)
7
Analytical Results II

Find htot
8
Analytical Results III

Check Lumped Capacitance
Lumped Capacitance Satisfied
Solve for time to cool from 250 ? to 50
9
Conclusion of Experiment
Experimental Result Analytical Result Difference
14000 24521 40
1 Hour and 40 Minutes and 0 Seconds 2 Hours and 45 Minutes and 21 Seconds

• It takes almost 1 hour more theoretically for an
  Aluminum Cylinder to cool that it does
  experimentally.
• The Experimental and Analytical methods compare
  closely. Although the difference is 40, the
  results are in the same range.

10
Analysis of Results

• The Experimental and Analytical Results vary
  considerably. The following are reasons for the
  disparity
• Cylinder approximated as uniform. Actual Cylinder
  was not uniform in Diameter.
• Thermal Conduction through resting table ignored
  due to ltlt thermal conductivity of Fire Brick.
• The extent of Forced Convection was higher in
  reality during heating of the room (Air gushing
  into the room from vents).
• Approximate Properties used at average
  temperature (250 C 50 C)/2
• The Emissivity co-efficient did not consider
  surface smoothness/ roughness of Al sample
  cylinder.

11
Appendix Cylinder Pictures