Calculation basis
Ohm’s law
- U
- = Voltage (V)
- I
- = Current (A)
- R
- = Resistance (Ohm)
- P
- = Power (W)
Calculation of the surface strain
- O
- = Surface strain (W/cm²)
- Ø
- = Diameter of the heating cartridge (cm)
- Lh
- = Heated length of the heating cartridge (cm)
Determination of the heating capacity
- P
- = Power in W
- m
- = Mass in kg
- c
- = specific heating capacity in Wh/kg K
- ΔT
- = Temperature difference in K
- Δt
- = Heating-up time in h
- η
- = Efficiency as decimal value (z.B. 80% = 0.8)
The heat losses are dependent on several factors, such as the flow of gases or fluids, carrier material, surface shape, heat insulation, draught, etc.
Properties of different media
| Medium | Density at 283.15 K [g/cm³] | Spec. heat (c) [Wh/kg·k] | |
|---|---|---|---|
| Fluids | Oil | 0.70-0.90 | ~ 0.6394 |
| Water | ~ 1.00 | ~ 1.1626 | |
| Gases | Air | 0.00129 | 0.2790 |
| Insulating materials | Glass | ~ 2.40 | ~ 0.2092 |
| Ceramic | 1.90-2.50 | ~ 0.2325 | |
| Metals | Aluminium | ~ 2.70 | ~ 0.2488 |
| Lead | ~ 11.34 | ~ 0.0360 | |
| Copper | ~ 8.93 | 0.1069 | |
| Steel | ~ 7.85 | ~ 0.1337 |