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BACKGROUND
Heat transfer is a major unit operation in pharmacy. Heat flows from a region of high temperature to a region of low temperature. Heat may flow by one or more of three mechanisms.
Conduction:-It is a process in which heat flow in a body is achieved by the transfer of the momentum of the individual atoms or molecules without mixing.1,2
Convection:-It is a process in which heat flow is achieved by actual mixing of warmer portions with cooler portions of the same material.
Radiation:-It is process in which heat flows through space by means of electromagnetic waves.
A freely suspended body looses heat by conduction, convection and radiation until it reaches room temperature. This is an equilibrium condition. In this system, the heat loss through convection is neglected, since movement of molecules is negligible. As the metal cylinder is freely suspended without any contact with the metal the heat loss through conduction is minimum. For this reason, the metal cylinder is placed on a glass tripod stand. Thus heat loss by radiation is highlighted.3,4
Stefan- Boltzmann law gives the total amount of radiation emitted by a body.
q = bAT4
Where q = energy radiated per sec w or j/s
A = area of the radiating surface
T = absolute temperature of the radiating surface.
B = constant, w/m2.k4
The radiation constant is (α) is calculated using the following formula
αA[ {4]+
Where M= mass of metal cylinder
S = specific heat of metal
dq/dt = Rate of heat loss by metal cylinder
T1 = Temperature of the metal body
T2 = Room temperature
α = Radiation constant,
A= Surface area of heat transfer
Aim:
The aim of the experiment was to determine the radiation constant of the given iron cylinder at 800 and 1200c.
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REQUIREMENTS
Apparatus: Metal cylinder
Glass tripod stand
Thermometer (3600c)
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PROCEDURE
An iron cylinder was cleaned and weighed thrice and the average weight was noted. The diameter and height were measured. The metal cylinder was heated using a Bunsen burner. After reaching a constant maximum temperature, the hot body was transferred to the glass tripod stand using long tongs. The thermometer (3600c) was placed in the central hole of the cylinder and fixed to a standard using a thread. Slowly the temperature of the hot body decreases. The decrease in temperature was noted every 5 minute interval. The data was recorded in the table. A graph was plotted taking time on X- axis and temperature on y-axis. Depending on the temperature at which the radiation constant is to be determined, a tangent was drawn at that temperature. The slope was determined which represents the rate of fall of the temperature. Radiation constant was determined.
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CONCLUSION
The radiation constant of the given iron cylinder was found to be ________
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REFERENCES
- Subrahmanyam CVS, Setty JT, Suresh S. Laboratory manual of pharmaceutical engineering (Unit operations). Delhi Vallabh Publications.
- Pharmaceutical Engineering by Sanbamurty K. (New Age International, New Delhi)Cooper and Gunn’s Tutorial Pharmacy Edited by Carter SJ. (CBS Publishers, Delhi)
Pharmaceutical Dosage forms by Aulton; Churchill Livingstone, Edinburg.
- Chemical Engineering by Badger and Banchero; Mc Graw Hill, New Delhi.
