- Slides: 11
Minimum Cooling Time for Metallurgy Applications Satyän Chandra Jordan Walser
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.
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)
Problem Set Up Surrounding Room Wall Cylinder Air qconvection qradiation qconduction Cylinder on Table Tsur = 22 C = 295 K T∞ = 20 C = 293 K At t = 0 s: Tcylinder = 250 C = 523 K Safe to Operate Temperature for Humans: 50 C = 323 K = T Resting Table of Fire Clay Brick (K = < 1 W/m. K)). Flux consists of Conductive, Convective and Radiative components.
Experimental Results � Used K Type Digital Thermometer for measurement of Cylinder Surface Temperature � Initial Cylinder Temperature = 250 C � Desired � Time Cylinder Temperature = 50 C (250 C) = 1 Hr. 40 Min
Analytical Results: I Dimensions: Aluminum: Air (359 K):
: Analytical Results: II Find htot :
Analytical Results: III Check Lumped Capacitance: Lumped Capacitance Satisfied Solve for time to cool from 250 ℃ to 50
Conclusion of Experimental Result Analytical Result 1: 40: 00 2: 45: 21 1 Hour and 40 Minutes and 0 Seconds 2 Hours and 45 Minutes and 21 Seconds % Difference 40 % - 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.
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 << 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.
Appendix: Cylinder Pictures