Mechanical.knowledge

CFM to M3 conversion


CFM (Cubic Feet per Minute) can be converted to m³/min using:
1 CFM = 0.02832 m³/min

🔹 Formula:
m³/min = CFM × 0.02832

🔹 Example:
500 CFM × 0.02832 = 14.16 m³/min
👉 So, 500 CFM = 14.16 m³/min.

Difference between unit: CFM & M3


CFM vs m³ — Difference

CFM (Cubic Feet per Minute) is a flow rate unit. It tells how much air/gas flows in one minute.

m³ (Cubic Meter) is a volume unit. It tells the quantity/volume of space occupied by air or gas.

🔹 Example:
100 m³ = volume of gas
100 m³/min = gas flow rate
1 m³ = 35.315 ft³
1 m³/min ≈ 35.315 CFM

👉 Important: CFM and m³ are not directly comparable because CFM is flow rate, while m³ is volume.

Unit Conversion for AREA


Area conversion means changing the measurement of a surface from one unit to another.

1 m² = 10,000 cm²
1 m² = 1,000,000 mm²
1 ft² = 0.0929 m²
1 m² = 10.764 ft²
1 hectare (ha) = 10,000 m²
1 acre = 4,046.86 m²

🔹 Example:
5 m² = 5 × 10,000 = 50,000 cm²
Easy rule:
For area, the conversion factor is squared because area = length × length.

Evaporation Loss in Cooling Tower


Evaporation loss is the amount of circulating water that evaporates into the atmosphere while removing heat from the cooling tower.

Formula:
Evaporation Loss (m³/h) ≈ Circulating Water Flow × Cooling Range × 0.001 × 1.8

Example:
Water flow = 600 m³/h
Hot water = 35°C
Cold water = 30°C
Cooling Range = 5°C
Evaporation Loss ≈ 600 × 5 × 0.001 × 1.8
👉 ≈ 5.4 m³/h

So, approximately 5.4 m³ of water per hour is lost by evaporation.

Key Point: Higher water flow or higher cooling range (ΔT) → higher evaporation loss.

Unit conversion for LENGTH


1 km = 1,000 m
1 m = 100 cm
1 m = 1,000 mm
1 cm = 10 mm
1 inch = 25.4 mm
1 ft = 12 inches = 304.8 mm
1 yard = 3 ft = 0.9144 m
1 mile = 1.609 km
🔹 Example:
2.5 m = 2.5 × 1,000 = 2,500 mm
Easy rule: Bigger unit → smaller unit = Multiply
Smaller unit → bigger unit = Divide

Heat Load Calculation with Example


Suppose:
Water flow = 600 m³/h
Hot water = 35°C
Cold water = 30°C
ΔT = 35 − 30 = 5°C
Heat Load = 600 × 5 × 1.163
👉 Heat Load = 3,489 kW
Convert to TR:
TR = 3,489 ÷ 3.517 = ≈ 992 TR
✅ Cooling tower heat rejection ≈ 3,489 kW or 992 TR.

Heat Load Calculation


Heat load is the total amount of heat that must be removed by the cooling system to maintain desired temperature.

In simple words: How much heat your room / process / equipment generates, that your AC or chiller has to remove.

One-liner Formula
Heat Load (kW) = Mass flow × Specific heat × Temperature difference

For water: Q = m × cp × ΔT

COOLING TOWER TYPES — CLASSIFICATION & WORKING PRINCIPLE 💧


Cooling towers are classified based on airflow, air circulation, and construction design.

1. Based on Air Circulation
Natural Draft Cooling Tower: Uses natural air movement due to temperature and density differences. No fan is required.

Mechanical Draft Cooling Tower: Uses fans to circulate air.
Induced Draft: Fan is located at the top and pulls air through the tower.
Forced Draft: Fan is located at the air inlet and pushes air through the tower.

2. Based on Airflow Direction
Crossflow Cooling Tower: Air flows horizontally across the falling water.

Counterflow Cooling Tower: Air flows upward, opposite to the downward flow of water.

3. Based on Construction
Open Circuit Cooling Tower: Water directly contacts air for evaporative cooling.
Closed Circuit Cooling Tower: Process fluid flows through a coil, while spray water and air remove heat from the coil.

Key Point:
Most industrial cooling towers use mechanical induced-draft designs, as they provide effective heat removal with controlled airflow.

Working Principle of Cooling Tower


Working Principle of a Cooling Tower
A cooling tower works on the principle of evaporative cooling, where a small portion of hot circulating water evaporates and removes heat from the remaining water.

WHAT HAPPENS WHEN A DRY CORE FILTER GETS CHOKED? ⚠️❄️


When a dry core filter gets choked, refrigerant flow is restricted, causing a pressure drop across the filter.

⚠️ Effects:
❄️ Reduced refrigerant flow.
📉 Pressure drop across the filter increases.
🌡️ Evaporator cooling capacity decreases.
⚡ Compressor efficiency may reduce.
🚨 Low suction pressure and possible compressor trip.

🔧 Solution: Check the temperature difference across the filter and replace the clogged filter core if required.