Introduction to Heat Transfer

1. Introduction to Heat Transfer 1 Kausar Ahmad Kulliyyah of Pharmacy http://staff.iiu.edu.my/akausar

2. Contents • Introduction • Methods of heat transfer PHM3133 Dosage Design 1 2010/11

3. Transfer of Heat Heat transfers from a region of high temperatureto a region of low temperature. PHM3133 Dosage Design 1 2010/11

4. Examples: Simple Heat Transfer Processes Cooking Drying clothes under the sun Drying clothes in a dryer Boiling water on stove Boiling water using electric kettle Ironing PHM3133 Dosage Design 1 2010/11

5. Examples: Heat Transfer Equipment At home • Air-conditioner • Solar water heater • Water heater • Gas stove • Baking oven • Microwave oven Industrial • Cooling tower • Evaporator • Heat-exchanger • Liquid-liquid • Boiler PHM3133 Dosage Design 1 2010/11

6. Heat exchanger PHM3133 Dosage Design 1 2010/11

7. Boiler House PHM3133 Dosage Design 1 2010/11

8. Examples:Equipment in Pharmaceuticals • Drying • Fluidised bed • Oven • Spray drying • Milling • Fluid energy mill PHM3133 Dosage Design 1 2010/11

9. Methods of heat transfer The mechanisms involved are: • Conduction • Contactive • Convection • Radiation PHM3133 Dosage Design 1 2010/11

10. Conduction • 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 PHM3133 Dosage Design 1 2010/11

11. Collisions in Solids two substances at different temperatures separated by a barrier which is subsequently removed. barrier PHM3133 Dosage Design 1 2010/11

12. Transfer of energy in conductive heat transfer 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. PHM3133 Dosage Design 1 2010/11

13. Thermal conductivity • Different materials transfer heat by conduction at different rates • this is measured by the material's thermal conductivity. PHM3133 Dosage Design 1 2010/11

14. What is the thermal conductivity? • Suppose we place a material in between two reservoirs at different temperatures PHM3133 Dosage Design 1 2010/11

15. Conductors and insulators • Material with high thermal conductivity is a conductor • E.g. copper • Material with low thermal conductivity is an insulator • E.g. concrete PHM3133 Dosage Design 1 2010/11

16. 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. PHM3133 Dosage Design 1 2010/11

17. Radiation • 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? PHM3133 Dosage Design 1 2010/11

18. Example: Heat transfer by radiation • light (visible or not). • from the sun to the earth through mostly empty space • cannot occur via convection nor conduction PHM3133 Dosage Design 1 2010/11

19. References 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. PHM3133 Dosage Design 1 2010/11