What is a Surface Heater?
Postado por Adelle Webber em
What is a PTC Surface Heater?
A surface heater comprises a heating element designed to conduct heat directly to the surface of an object or material. Contact heater is also a term used when referring to a heating element in direct contact with a surface.
“Surface refers to the outer face, outside, or exterior boundary of a thing; outermost or uppermost layer or area. Or any face of a body or a thing.”
“Contact as a noun refers to the act or state of touching, immediate proximity, or association. As a verb to bring into contact.”
The purpose of a surface heater is to raise the temperature of an object that the heating device is in direct contact with or attached to. Direct contact is one of the most effective ways for heat conduction into solid matter.
(A surface heater is not a gun lying on a surface!)
What are the kinds of surface or contact heaters?
While users and manufacturers have no total agreement on the naming conventions for heating devices that raise the temperature of object surfaces, here are some of the more common devices.
- Drum heaters
- Bottom heaters
- Surface heaters
- Flexible silicone heaters
- Cartridge heaters
- Induction heaters
- Etched foil heaters
These devices come in direct contact with the surface or material to be heated.
Where are surface heaters used in industry?
- Space exploration
- Weapons and aerospace
- Ships at sea
- Trains, boats, and planes
- Electrical Vehicles
- Medical Equipment
- Vending machines
- 3D printing
- Plastic molding and extrusion
- Commerical food delivery systems
- Food packaging sealing
- Home appliances
- Manufacturing processes
- Traffic cameras
So how does a surface heater work? Conductive heating.
The surface heaters referenced here are electrical, while other surface heaters using close cycled oil and water exist for numerous applications. How heat is transferred from the heating element to a surface involves understanding the heat transfer characteristics of metals.
A surface heater transfers heat via conduction directly to the surface of an object. Objects can be heated by indirect heat, radiant heat, heat pipes, liquids, and other means but the devices for indirect heat transfer is not surface heater by our definition.
For true surface heating, the heating elements are mounted directly with a heat transfer medium such as aluminum or silicone rubber that can be attached firmly to the material. Heat can be transferred through the air and other materials but not efficiently as when the heating element is in direct contact with the surface to be heated. Any air space or multiple materials the heat must travel through to the surface inhibits the effective conduction of the heat. Additional materials, including air impact the consistent application of heat to the surface.
Surface heating elements come in all sizes and shapes
A surface heater for electronics, medical devices, aerospace, or small enclosures might be as small as 1.5 inches square. Barrel heaters are designed to wrap the circumference of a 55-gallon drum will being 6-8 inches in width.
This small size is ideal for coffee vending machines, security cameras, packaging process lines, and even the International Space Station.
PTC surface heaters are popular for small-sized surface heaters because of their self-regulating properties and high watt densities. With preset temperatures, the device maintains desired temperature without the requirement of external temperature sensors and controls. These are ideal for use in small areas or surfaces of containers that need to be kept at a precise temperature.
The surface itself is kept at a constant temperature but it is the continents of the container that needs to be maintained at the desired temperature for correct operation. Materials could be a die or nozzle for 3D printing or a vessel that contains pharmaceuticals for testing.
It may also be a simple as sealing film or plastics for packaging in food processing or other products. Size or number of the surface heating devices is dependent on the application and number of surfaces to be heated.
What is an example of a small PTC electronic heater?
DBK USA has a series of PTC heaters made of the PTC ceramic disk heating element embedded into an aluminum housing. The aluminum housing can be attached directly to a flat surface of the material to be heated by fasteners.
The conductive heating of the material is enhanced further by applying heat transfer silicone or similar past between the heating device and the surface to be heated.
These devices, as small as 1.58 inches X 1.38 inches can be powered by 12-24 volt circuits or 100-240 volt circuits. They have a surface temperature range of 104 degrees to 392 degrees F. View the actual specifications of these unique PTC surface heaters.
Because of the self-regulating effect of the device the temperature raises quickly when power is applied but slows as the set-point temperature is reached. Resistance to current in the element is low at low temperature but increases rapidly to reduce current flow through the heating element. Even with the high watt density of efficient heat conductance, the temperature inside the vessel will be less than the setpoint temperature.
Calculations or testing can determine the actual heat conductance of the surface materials.
Conductive heat transfer coefficient
Where
q = heat transfer (W, J/s, Btu/hr)
k = thermal conductivity of material (W/m K or W/m°C, Btu/(hr°F ft2 /ft))
s = material thickness (m, ft)
A = heat transfer area (m2, ft2)
U = k/s Coefficient of heat transfer
dT =t1 - t2 Temperature Gradient
Need more answers about surface heat transfer and devices?
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