Sheath temperature
CALCULATION OF THE SHEATH TEMPERATURE OF THE HEATING CABLE
Determining sheath temperatures in application against the pipes
If the cable is free in air, the heat transfer will be poor, but if the cable is fixed with aluminium tape the heat transfer will increase considerably.
This gives us the following formula:
Ts = |
Q uA |
+ Tp |
Q |
= | W/m | The output of the heating cable per meter |
A |
= | m²/m | The surface of the heating cable/m cable |
u |
= | W/m²°C u = u = |
Heat transfer coefficient Loose cable against pipe 17 – 28 W/m²°C With aluminium tape 57 W/m²°C |
Ts |
= | °C | Sheath temperature |
Tp |
= | °C | Prozess temperature |
A |
stated according to following: | ||
A(m²) = p x D (m) |
|||
D |
= | The diameter of the heating cable (m) |
The determination of parallel resistive and series resistive heating cables sheath temperature is easy, since the output is constant which is is not for self-limiting heating cables.
To be able to determine the sheath temperature for a self-limiting heating cable you should go to the data sheet and in the output diagram read the emitted output at the required process temperature, i.e. the temperature that the thermostat/regulator of the heating cable is set on.
Example
Example
Series resistive cable TCT
Ts = | 20 0,009 x 57 |
+ 50°C = 87°C |
Heating cable 20W/m mounted with aluminium tape, process temperature 50°C
Series resistive cable TCTR
Ts = | 20 0,016 x 57 |
+ 50°C = 72°C |
Heating cable 20W/m mounted with aluminium tape, process temperature 50°C
Parallel resistive cable EST/CWM
Ts = | 20 0,024 x 57 |
+ 50°C = 65°C |
Heating cable 20W/m mounted with aluminium tape, process temperature 50°C
Self-limiting cable RSL
Ts = | 15 (SRL-10) 0,032 x 57 |
+ 50°C = 59°C |
The heating cable gives approx. 15 W/m at process temperature 50°C mounted with aluminium tape
Self-limiting cableRSM
Ts = | 20 (SRM-8) 0,032 x 57 |
+ 50°C = 61°C |
The heating cable gives approx. 20 W/m at process temperature 50°C mounted with aluminium tape