How to calculate surface load heater?

In this article, you will understand what the surface load is and how to calculate it.

The surface load tells us about the force given per square centimeter of the heater’s surface.

To calculate the surface load of the heater, you must:

1. Calculate the length of the heater in its straight form (if the heater has any other shape than straight).
   The length of the heater on the bow can be calculated by the axis of the heating element: inner radius + half the diameter.

2. Subtract the length of the “dead spots” from both sides of the heater from the straight length.

3. Calculate the surface area of the side wall of the heater (excluding the bases), as it is shaped like a roller. Use the formula:
   Pb = 2πrH
   Where:

   • Pb = the side surface area of the heater (surface of the heater)
   • r = radius (half the diameter of the heater)
   • H = the length of the heater in its straight form (excluding the dead spots)

4. Divide the power of the heater (in watts) by the calculated surface area (Pb) measured in square centimeters (cm²).

The surface load is crucial for determining the suitability of a specific heater for a particular application.

Different materials used to create heating elements have different maximum heating capacities. The table below provides information about the maximum surface load for different conditions. For maximum heater lifespan, ensure the surface load does not exceed the values shown in the table below:

	Material: Tubes
	Copper	Regular Steel	Stainless Steel
stagnant water	10		10
water in motion	14		14
water flowing	25		25
steam generator	6		6
runny oil		3.5	3.5
thick oil		1.2	1.2
vegetable oil			4
tar			1
fuel oil		12	12
stationary air		1.7	5
moving air (v = 2 m/s)		2	5.5
moving air (v = 10 m/s)		5	10
alkaline bath			6
flooded aluminum		12	12

The above data is general and informative. The heater’s working conditions (e.g., in an open room versus a closed chamber) will affect the load.