Behind every syrup, extract, distilled water, and concentrated solution lies a carefully controlled heat process. Whether removing solvents, concentrating herbal extracts, or purifying liquids, heat transfer, evaporation, and distillation are fundamental to pharmaceutical manufacturing. UNIT 2 introduces these engineering operations that quietly ensure product quality, efficiency, and safety.
From steam-jacketed kettles to advanced molecular distillation units, these systems help transform raw materials into finished medicines.
Heat Transfer in Pharmaceutical Engineering
Objectives and Applications of Heat Transfer
Heat transfer is used to either supply or remove heat during processing.
Main Objectives
- Heating solutions
- Cooling products
- Sterilization
- Concentration of liquids
Applications include drying, pasteurization, evaporation, and distillation.
Heat Transfer Mechanisms
Heat moves from higher temperature to lower temperature through three basic mechanisms.
Conduction
Heat transfer through direct molecular contact, common in metal surfaces and solid materials.
Convection
Heat transfer by movement of fluids such as water or air. Stirring improves convection.
Radiation
Heat transfer through electromagnetic waves without direct contact, such as infrared heating.
Fourier’s Law of Conduction
Fourier’s law states that the rate of heat flow is directly proportional to the temperature gradient and area, and inversely proportional to thickness. This law helps engineers design walls and pipes for efficient heat exchange.
Heat Interchangers and Heat Exchangers
Heat exchangers allow heat exchange between two fluids without mixing.
Common Uses
- Heating syrups
- Cooling injections
- Energy conservation
Plate and tubular exchangers are widely used in pharmaceutical plants for safe and efficient thermal control.
Evaporation: Concentrating Pharmaceutical Solutions
Objectives and Applications
Evaporation removes solvent, usually water, to concentrate solutions.
Applications
- Herbal extract concentration
- Syrup preparation
- Waste solvent recovery
- Volume reduction
Factors Influencing Evaporation
Efficiency depends on:
- Temperature
- Pressure
- Surface area
- Nature of liquid
- Agitation
Higher temperature and larger surface area speed up evaporation.
Evaporation vs Other Heat Processes
Unlike boiling or drying, evaporation focuses mainly on removing solvent while retaining solute, preserving active ingredients.
Types of Evaporators
Steam Jacketed Kettle
Simple vessel heated by steam. Suitable for small-scale production.
Merits: Easy operation
Demerits: Slow, less efficient
Horizontal Tube Evaporator
Liquid flows outside heated tubes.
Advantages: Large heating surface
Limitation: Moderate efficiency
Climbing Film Evaporator
Liquid forms thin film inside tubes for rapid heating.
Benefits: Quick evaporation, suitable for heat-sensitive drugs
Forced Circulation Evaporator
Pump circulates liquid rapidly to avoid scaling.
Use: Viscous solutions
Multiple Effect Evaporator
Uses vapor from one effect to heat the next, conserving energy.
Advantages: High steam economy, cost-effective
Economy of Multiple Effect Evaporator
Steam consumption decreases significantly with each added effect. This system is widely preferred for large-scale pharmaceutical production due to energy savings.
Distillation: Purification by Vaporization
Basic Principles of Distillation
Distillation separates liquids based on differences in boiling points. The more volatile component vaporizes first and is then condensed.
Types of Distillation Methods
Simple Distillation
Used when boiling points differ widely. Commonly used for preparing distilled water.
Flash Distillation
Rapid vaporization by sudden pressure drop. Suitable for large volumes.
Fractional Distillation
Uses a fractionating column to separate close boiling liquids with better efficiency.
Distillation Under Reduced Pressure
Lower pressure reduces boiling point, protecting heat-sensitive substances like vitamins.
Steam Distillation
Steam carries volatile oils at lower temperatures. Used for essential oils and aromatic compounds.
Molecular Distillation
Operates under very high vacuum, allowing separation of thermally unstable compounds.
Applications in Pharmaceuticals
Distillation is widely used for:
- Water purification
- Solvent recovery
- Extraction of volatile oils
- Removal of impurities
These processes ensure high purity standards for medicinal products.