Cooling tower terminology — The “cooling range” of a cooling tower refers to which temperature difference?

Introduction:
Cooling tower performance is commonly described using two key temperature differences: the cooling range and the approach. Knowing the exact definitions helps in specifying and evaluating tower duty and effectiveness.

Given Data / Assumptions:

• Hot water from process enters the tower; cooled water returns to the process.
• Ambient air provides evaporative cooling; its wet-bulb temperature sets a theoretical lower limit.
• Steady operation at a given load and ambient condition.

Concept / Approach:
The cooling range is defined as Range = T_hot,in − T_cold,out. It measures how much the process water is cooled across the tower. The approach is defined as Approach = T_cold,out − T_wb,air. Range reflects tower heat duty at given flow, while approach reflects proximity to the psychrometric limit and is a measure of tower size/efficiency.

Step-by-Step Solution:
Identify inlet hot-water temperature (to tower) and outlet cold-water temperature (from tower).Compute Range = T_hot,in − T_cold,out.Distinguish from Approach = T_cold,out − T_wb.

Verification / Alternative check:
Cooling tower specifications list both “range” and “approach”; example: range 10°C, approach 4°C at a given wet bulb—matching the definitions above.

Why Other Options Are Wrong:

• (a) and (b) incorrectly combine tower water temperatures with ambient wet bulb to define range (these correspond to approach variants).
• (d) Incorrect since a standard definition exists.
• (e) Dry-bulb minus wet-bulb defines the psychrometric depression, not cooling range.

Common Pitfalls:
Confusing range with approach; assuming smaller approach can be achieved without increasing tower size, airflow, or water distribution quality.

Final Answer:
Hot water entering the tower minus cooled water leaving the tower