KAUSAR AHMAD KULLIYYAH OF PHARMACY Introduction to Heat Transfer 1

KAUSAR AHMADKULLIYYAH OF PHARMACY

Introduction to Heat Transfer

http://staff.iiu.edu.my/akausar

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http://staff.iiu.edu.my/akausar

Contents

PHM3133 Dosage Design 1 2010/11

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Introduction

Methods of heat transfer

Transfer of Heat


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Heat transfers from

a region of high temperature to

a region of low temperature.

Examples: Simple Heat Transfer Processes


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Cooking

Drying clothes under the sun

Drying clothes in a dryer

Boiling water on stove

Boiling water using electric kettle

Ironing

Examples: Heat Transfer Equipment


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At home

Air-conditioner

Solar water heater

Water heater

Gas stove

Baking oven

Microwave oven

Industrial

Cooling tower

Evaporator

Heat-exchanger

Liquid-liquid

Boiler

Heat exchanger


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Boiler House


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Examples:Equipment in Pharmaceuticals


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Drying Fluidised bed Oven Spray drying

Milling Fluid energy

mill

Methods of heat transfer


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The mechanisms involved are:

Conduction

Contactive

Convection

Radiation

Conduction


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Solids Transfer of vibrational energy.

Occurs via collisions between atoms and molecules in the substance

and the subsequent transfer of kinetic energy.

E.g. cooking on electric stove/hot plate

Collisions in Solids


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two substances at different temperatures separated by a barrier which is subsequently removed.

barrier

Transfer of energy in conductive heat transfer


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When the barrier is removed:fast/hot atoms collide with slow/cold ones. faster atoms lose some speed and slower

ones gain speed; fast ones transfer some of their kinetic

energy to slow ones. This transfer of kinetic energy from the

hot to the cold side is called a flow of heat through conduction.

Thermal conductivity


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Different materials transfer heat by conduction at different rates

this is measured by the material's thermal conductivity.

What is the thermal conductivity?


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Suppose we place a material in between two reservoirs at different temperatures

Conductors and insulators


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Material with high thermal conductivity is a conductor

E.g. copper

Material with low thermal conductivity is an insulator

E.g. concrete

Heat transfer by convection

Applied to most fluids Movement in natural convection

is caused by buoyancy forces, induced by variations in the density of the fluid, due to temperature difference.

E.g. boiling water: Hot water at bottom rises due to

buoyancy Dense cold water at top falls

down A current is created.

In forced convection, a pump is used.


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Radiation


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All bodies at temperature above absolute zero can radiate heat.

Radiation may be transmitted, reflected or absorbed.

The amount absorbed is transformed into heat.

E.g. nuclear power, food irradiation to kill bacteria and lengthen shelf-life

In pharmacy?

Example: Heat transfer by radiation


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light (visible or not).

from the sun to the earth through mostly empty space

cannot occur via convection nor conduction

References


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Aulton, M. E. (1988). Pharmaceutics: The Science of

dosage form design. London: Churchill

Livingstone.

Llachman, L, Lieberman, H. A. and Kanig, J. L.

(1986). The theory and practice of industrial

pharmacy (3rd ed.). Philadelphia: Lea & Febiger.

Note:I got some of the materials from the internet and books but I lost the information on the sources. I acknowledge the authors’ contribution to science. Thank you.

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KAUSAR AHMAD KULLIYYAH OF PHARMACY Introduction to Heat Transfer 1