NEED OF COMPENSATION FOR HEAT LOSS
A pipe system does not only consist of the pipe itself, it also includes pipe supports, ventilators, flanges, pumps and instrument. All these components contribute to heat losses and they have often a larger surface than the pipe itself. The heat loss is therefore bigger on these places than for the pipe in general.
For ventilators, pipe supports, pumps can the factors below be used to calculate increased heat losses on these. A pump has approximately the double heat loss than the ventilator as for example.
Supplementary factors for ventilators and mounting details:
|Key ventilator||1,3 x Q / m rör|
|Moving butterfly valve||0,7 x Q / m rör|
|Bullet valve||0,8 x Q / m rör|
|Mushroom valve||1,2 x Q / m rör|
|Flange||4 x Dflange – Dpipe|
|Pipe support||2 x width of the pipe support + 0,4 m|
Heat losses from a pump can also be calculated approximately as a barrel. The diameter of this barrel is the same as the distance between outlet flange and the base plate. The length is the same as the distance between the inlet flange and the opposite end of the pump. The heat loss from the shell of the pump can be determined by using this formula:
|Q pump =||k π D (0,5 x D + L) x Dt (W)|
Instrument included along the pipe is most often covered by the heating cable which runs on the piping are laid around the instrument. You must specially consider the electronically equipment which are used. They does in general not handle temperatures above 80 – 100°C due to incoming electronically component, solderings etc.
Projecting a heating cable application
Projecting can be divided into two directions which has their own:
a) Heating – heat loss compensation/frost protection
b) Heating up
Which information must be available as a minimum to be able to project?
- Type of insulation and thickness.
- Lowest ambient temperature
- Required temperature
- Pipe dimension
- Type of insulation and thickness (k-value)
- Maximum process temperature
Heating up – Supplement to keeping warm
- Pipe material and its thickness.
- The content of the pipe: Density, heat permittivity.
- Inlet temperature of the pipe/its content.
- Final temperature after heating
- Required heating up time
- At percolation even fluid volume
In both cases this is the absolute minimum demand which is required for a projection. To do a complete projection you also must take into consideration a couple of factors according to below:
- If the application is located within an Ex-rated area or not.
- Maximum operating temperature.
- Eventual steam bubbling (choose of cable).
- Available supply voltage.
- Which direction of the fluid (placement of transmitter).
- Type of control equipment (existing/required).
- If there is need of a limiting thermostat (temperature sensitive fluids, substances).
- Valves, pumps, instruments.
- Required special cable type.
- If the application is located indoors or outdoors.
- High gradients on pipes (chimney effect).
- Type of insulation (k-value)
- Suitable material to fix the heating cable.
- Surrounding environment (acids etc).