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The temperature shown is the internal metallic element temperature. This would be the hottest point of the heater. The test heater was suspended horizontally in still air at a 70°F ambient temperature.
Watt densities of up to 35 watts/in2 are possible when heaters are bonded to a heat sink and controlled with a thermostat or electronic control.
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What is a Flexible Heater?
 A flexible heater is a device which can conform to the surface which requires heating. There are many
varieties of flexible heaters which include silicone rubber heaters, Polyimide Film heaters, heating tapes, heating tapes with thermostats,
rope heaters,wrap around tank heaters, gas cylinder heaters and custom sizes. Silicone Flexible Heaters are rugged, reliable,
accurate, and moisture and chemical-resistant. They can be easily bonded or adhered to other system parts. Flexible heating
elements have a wide range of industrial, commercial, and military applictions where reliability, cost of effectiveness, minimum
cross section, resistance to deterioration and basic flexibility are critical.
Important Formulas To Know
Ohms's Law
Ohm's law shows the relationship between voltage, wattage, amperage, and resistance. It is important to know Ohm's law in order
to calculate the load you will be switching with your thermostat or digital controller. For example if you select a flexible heater
which is rated 200 Watts and apply 120 Vac, the current will be 1.6 Amps
A is equal to W / V where: A = Amperes; W = Wattage; V = Voltage
Using our example above 200 Watts/120 Vac = 1.6 Amps
Some other variation of Ohm's Law:
Volts = Watts/Amperes
Volts = Amperes x OHMS
OHMS = Volts/Amperes
Amperes = Volts/OHMS
Watts = Volts x Amperes
Killowatt Requirement
To determine the kW required to be heat up a solid. The following formula is used.
kW = (WT x Cpx Δ T)/3412 x h
Where:
WT= Weight of Material, lbs
Cp=specific heat, BTU/lb-°F
Δ T = Temperature Rise, °F
3412= Conversion Factor, BTU/kWh
h = heat-up time, hrs
FLEXIBLE HEATER SELECTION
The key questions which need to be answered before selecting a flexible heater are:
How much wattage is required?
What voltage will be used?
If it is a flat surface, what size will be needed?
How long do the heater leads need to be?
Will you require a thermostat or a digital controller with sensor?
What is maximum temperature?
For flat surfaces will require wire wound or etch foil?
What is the time required to reach your temperature?
What is the ambient temperature?
Is insulation being used?
Temperature Controllers and Sensors for Flexible Heaters
There are a variety of temperature controllers and sensors one can use depending on the application. One of the more popular
sensor types for flexible heater applications are the surface mount temperature sensors. Thermocouple, RTD or Thermistors are available
with an adhesive backing or the ability to be cemented to the surface being heated. There also bolt on and magnetic surface mount type temperature
sensors available. Digital temperature controllers come in many different sizes with many output and input choices. Thermcouple and RTD inputs are the most
popular with a mechanical relay or dc pulse output. DC pulse ouputs allow the user to go to a larger relay to switch the heater load.
Thermostats are also available for the most basic applications.
Here is a typical combination of products:
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