Q1: For which of the following unit operations, Lewis number is of significance ?

ANS:D - Humidification

Humidification is the process of adding moisture or water vapor to the air to increase its humidity level. This process is commonly employed in various applications, including HVAC (heating, ventilation, and air conditioning) systems, industrial processes, agricultural settings, and controlled environments such as greenhouses and laboratories. The goal of humidification is to achieve and maintain a desired level of relative humidity (RH) in the air for comfort, health, or specific process requirements. Here's how humidification typically works:

1. Moisture Addition: In humidification, water is introduced into the air to increase its moisture content. This can be achieved through various methods:
   • Evaporation: Water can be evaporated directly into the air using devices such as evaporative pads, wicks, or spray nozzles. As water evaporates, it converts into vapor and mixes with the air, increasing its humidity level.
   • Steam Injection: Steam generated from boiling water is injected into the air stream. The steam condenses as it mixes with the air, releasing heat and moisture into the surrounding environment.
   • Ultrasonic Humidification: Ultrasonic humidifiers use ultrasonic vibrations to create a fine mist of water vapor that is released into the air.
2. Controlled Humidity Levels: Humidification systems are equipped with controls to maintain the desired level of relative humidity in the air. Sensors measure the humidity level, and the humidification system adjusts the moisture output accordingly to achieve and maintain the setpoint.
3. Distribution: Once moisture is added to the air, it is distributed throughout the space using fans or air circulation systems. This ensures uniform humidity levels in the entire area being humidified.

• Comfort: Maintaining proper humidity levels in indoor environments contributes to comfort and well-being. Low humidity levels can lead to dry air, which may cause discomfort, irritation of the respiratory system, and static electricity buildup. Proper humidification helps alleviate these issues.
• Health: Adequate humidity levels are beneficial for respiratory health. Dry air can exacerbate respiratory conditions such as asthma, allergies, and respiratory infections. Proper humidification helps keep mucous membranes moist, which can reduce the risk of respiratory issues.
• Industrial Processes: In industrial settings, humidification is often necessary to control moisture levels in manufacturing processes, storage facilities, and laboratories. Maintaining specific humidity levels is critical for product quality, process efficiency, and worker safety.
• Agriculture: Humidification is used in agriculture to create optimal growing conditions for crops, particularly in greenhouses. Controlling humidity levels helps regulate plant transpiration, reduces stress on plants, and promotes healthy growth.