Determine Process Heating
It is important to consider taking the following steps when a industrial heating process is determined.
1. System Description
The description includes all parameters like material to be heated, accuracy of temperature to maintain, cooling off time, maximum temperature, soaking time, and so forth. Consider also desired accuracy, system cost and power consumption. Read here a description of thermal design considerations.
2. Calculate Required Wattage
Watts required for Start-up, maintaining the temperature, replacing the heat loss and a safety factor need to be calculated. For example less wattage is needed if the start-up time could be prolonged.see also notes on calculating wattage.
3. Determine Appropriate Watt Density (WSI)
The heat source and / or the material (example flammable oil) can determine the maximum allowable Watt density (WSI) Here are guidelines for watt densities for various materials at different operating temperatures.
4. Select Heater Type
Choose between conduction (examples: cartridge-, band-, flexible-, immersion-, cast heaters), convection (examples: open coil-, tubular heaters) and radiant / infrared (examples: Halogen and Ultraviolet lamps, ceramic-, quartz-, flat panel heaters) heat sources. Yes, there are many, many different types of heat sources.
5. Select proper sheath material
Copper, Steel, Stainless Steel (common: 304, 316), Incoloy and Inconel are the main choices. The selection depends on max temperature, max Watt density, corrosion resistance, application and costs.
6. Select temperature sensor
The basic choice is contact or non-contact temperature sensing. Contact measuring devices like thermocouple, RTD or Thermister are commonly used and very often the most economic. However, contact measuring can not be used for moving targets, high temperatures or when very quick reaction times are needed like in induction heating. In these environments an infrared thermometer (aka Pyrometer) is the right choice.
7. Select Temperature control
The choice here is open loop or closed loop system. In an open loop system, the heat source will generate heat for a set time and may include a high temperature alarm sensor.
In a closed loop system, there is a constant temperature feedback from the heat source or material to be heated. This information is processed in a temperature controller (example: ETR 9090 or other PID controller) which adjust the power for the heater.