Calculation method for heating a volume of liquid
How do you determine the power required to heat a volume of liquid?
The power required to raise the temperature of a volume of liquid in a tank over a given period of time is the result of 2 calculations: the power required to raise the temperature of the liquid (Pch) and the heat loss (Pth).
Heating capacity calculation (Pch)
- Heating capacity: Pch (kW)
- Liquid mass: M (kg)
- Specific heat of liquid: Cp (kcal/kg .°C)
- Flow temperature: t1 (°C)
- Desired final temperature: t2 (°C)
- Heating time: T (h)
- Safety factor: 1.2
Calculating the mass of liquid to be heated (M)
- Liquid mass: M (kg)
- Volume of liquid to be heated: V (dm3 or liter)
- Liquid density: ρ (kg/dm3)
Density ρ of some liquids (kg/dm3)
- Water: 1
- Mineral oil: 0.9
- Bitumen: 1.1
- Acetic acid: 1.1
- Hydrochloric acid: 1.2
- Nitric acid: 1.5
Specific heat Cp of some liquids (kcal/kg.°C)
- Water: 1
- Mineral oil: 0.5
- Bitumen: 0.58
- Acetic acid: 0.51
- Hydrochloric acid: 0.6
- Nitric acid: 0.66
Calculating liquid volume (V)
Cylindrical tank
- Volume of liquid to be heated: V (dm3 or liter)
- Tank diameter: Ø (dm)
- Liquid height: H1 (dm)
Rectangular tank
- Volume of liquid to be heated: V (dm3 or liter)
- Tank length : L (dm)
- Tank width: l ( dm)
- Liquid height: H1 (dm)
Calculation of power required to compensate for heat loss (Pth)
- Heat losses: Pth (kW)
- Tank exchange surface: S ( m2)
- Desired final temperature: t2 (°C)
- Ambient temperature: ta (°C)
- Heat transfer coefficient: K (kcal/h.m2.°C)
- Safety factor: 1.2
Exchange coefficient (K)
The heat exchange coefficient is a physical quantity that quantifies the capacity of a fluid (liquid or gas) to transfer heat to a solid surface in a convective heat exchange .
Here are some values for the K exchange coefficient as a function of wind speed and insulation thickness:
| Tank location | Insulation thickness (mm) | |||
|---|---|---|---|---|
| Without | 25 | 50 | 100 | |
| Indoor tank | 9 | 1.7 | 1 | 0.55 |
| Outdoor tank - Wind ≤ 10 km/h | 12 | 2.1 | 1.1 | 0.59 |
| Outdoor tank - Wind ≤ 45km/h | 30 | 2.3 | 1.2 | 0.61 |
| Outdoor tank - Wind ≤ 90km/h | 49 | 2.4 | 1.3 | 0.62 |
Tank exchange surface (S)
Cylindrical tank
- Tank surface area: S (m2)
- Tank diameter: Ø (m)
- Tank height: H2 (m)
Rectangular tank
- Tank surface area: S (m2)
- Tank length : L (m)
- Tank width: l (m)
- Tank height: H2 (m)
