Heat is a form of energy associated with random movement of molecules. For our purposes, it can be well understood with the help of an example in which a metal vessel containing liquid is heated, the molecules of the vessel will start vibrating with a higher energy and with the quest of coming to a lower energy state, will release their energy to the water molecules in contact. In this way, heat energy is transferred from more energetic molecules to those with lesser energy.

Temperature Gradient and Spontaneous Heat Transfer

The temperature of a material is an indication of its internal energy, the greater the molecular motion, the greater the internal energy, and higher the temperature. Therefore, at a particular temperature all the molecules will have some energy. It is only at absolute zero (0 K), that the substance will have no heat content. Temperature gradient gives rise to spontaneous transfer of heat and the rate of heat transfer indicates how quickly heat is exchanged. It is expressed in units Js⁻¹ or watts (W).

Pharmaceutical Applications Of Heat Transfer

Many pharmaceutical processes involve heat transfer. Some of the direct purposes of heat transfer include sterilization of the products using autoclaves and hot air ovens, evaporation of liquids for yielding concentrated products, drying of granules for tablet production, separation of mixture components using distillation, melting of substances, creating an elevated temperature during production of creams, suppositories or ointments, heating of the solvents to hasten dissolution processes, etc.

Evaporation, distillation and drying are the three direct applications involving heat transfer. The processes of evaporation, distillation and drying can be distinguished from each other based upon the desired product. Evaporation is carried out when a concentrated liquid residue is needed, distillation is done when condensed vapour is required and drying is done when a dried solid residue is required as the product.

Reference:

• Khar, R.,Vyas, S., Ahmad, F., & Jain, G. (2016). Lachman/Lieberman’s The Theory and Practice of Industrial Industrial Pharmacy. New Delhi, ND: CBS Publishers & Distributors Pvt Ltd.