What Wattage Do I Need?
How do you calculate the size of an etched foil silicone rubber heater for your specific application? We know that etched foil heating elements laminated between two layers of silicone rubber has excellent heat transfer properties. The silicone rubber protects the etched heating elements. The design of the component promotes even heat distribution through the silicone to the surface to be heated. Joule’s law, is used in electricity, this is a mathematical description of the rate at which resistance in a circuit converts electric energy into heat energy.
How do you calculate the heat needed?
It isn't straightforward, and the physical sizes and wattage of the silicone heaters vary tremendously. Heat transfer from the surface of the silicone to the material heated is efficient, but without extensive testing in a laboratory setting, how will you know what the efficiency will be and how much heat transferred to the surface material or container.
You won't know, but some necessary calculations can get you closer to selecting the right size for your application. Etched silicone heaters are in all types of heating applications, so there is no one answer. You may be keeping a battery from freezing in the cold or maintaining oil or other liquid in a viscous state in an engine block or pipeline. A great example of this is certain chemicals manufacturers in colder climates tend to keep the chemicals from freezing with a flexible heating source.
Etched foil silicone heaters are known for their watt density. So what does watt density have to do with heat transfer or calculating the heat needed? The higher the watt density, the more efficient the heat transfer takes place, and the quicker the temperature will rise. The chemical etching of the flexible heating elements allows for precise placement of the heating pattern customized for a specific application.
Higher watt density and uniform heat transfer than resistive wire reduces the watt-hours required for heating. Fewer watt-hours less cost. Watt-hours are the number of hours the heating device needs to be powered to transfer the amount of heat necessary for the application.
Converting watts to heat
Calculating heat from watts requires first to calculate the energy produced by the watts over time. Watt-hours equals the amount of energy produced by the heating elements. Power or energy is measured in joules. One watt equals 3,600 joules per hour.
100 watts X 1 hour = 360,000 joules per hour
1055.06 joules = 1 BTU
360,000 / 1055.06 = 341 BTU
BTU or British Thermal Unit is the amount of energy needed to raise one pound of water 1 degree Fahrenheit at sea level. One watt is equivalent to 3.412 BTU per hour.
Specific heat capacity of a material to be heated
Chances are you need to heat a material other than water. Each substance has a specific heat capacity. In most cases, the material you are heating is enclosed within a pipe or other container when requiring a silicone pad type of heater. To calculate the heat needed for your equipment, you will need the specific heat capacity of that material.
Specific heat is the amount of heat energy required per unit of mass to raise the temperature on degree Celcius. The table shows capacity in Btu/(lb-F) and Btu/(lb-C) of metals. This table might apply to heat a die for extrusion or engine block.
There are specific heat capacity tables for oils, gases, and even sand. Knowledge of the specific heat capacity will provide a better understanding of how many watts and for how long of a time.
You can save yourself some time by consulting with DBKUSA engineers that have experience with similar applications and how to size the heating elements.
Do you need temperature controllers?
The need for temperature controllers is dependent on the application. It is possible to size the flexible heater such that it maintains continuous heat to the surface materials without needing temperature sensors or controllers. A barrel warmer may never transfer enough heat to the contents of the barrel to require temperature controllers.
Other applications may need a temperature sensor to turn off the heater after warming up the material. Yet others may require constant control over the temperature. It is best to check with our experienced engineers on your application for the correct monitors or controls.
What size of heater do I need?
DBK's etched foil silicone heaters come in a variety of sizes and shapes. Custom shapes and sizes are also available. To maintain heat transfer efficiency, the size of the silicone pad should not be larger than the surface that requires heating. Heating the air around the device isn't of much value.
If you need to attach or conform, the heater to the surface of an object ensures that the surface is flat without protruding fastener or connections. Direct contact with the surface makes for effective heat transfer.
Can I get help selecting the right kind of etched foil silicone heater?
Please request a quotation or investigate our other heating options for your specifications and application. Call 1-864-607-9047 and talk to an engineer, not a salesperson. Leverage our experience and knowledge to help you make the right decision on the best heater.