In this example of a thick film heater applied to a 3/8" diameter tube, there is an almost instant transfer of heat to the water in the tube once current is applied (at time = 0).
There are a multitude of applications for applying heat to surfaces -- including pipes, tubes, covers, plates, grills, etc. Traditionally, the application of heat to these surfaces involved mechanically attaching a strip, tubular or ring heater to the work piece. Subsequently, laminate heaters were introduced to improve surface heating efficiency by reducing the size and mass of the heater.

The latest development in surface heating technology involves bonding thick film materials directly to the work piece surface. Thick film technology is a vast improvement over strip and laminate heaters due to its high watt-density performance, high thermal transfer, response time and increased reliability. Simply stated, thick film enables the direct monolithic application of a heater to the work piece.

One of the greatest advancements with thick film is its ability to pack a large amount of heat into a small area. Typical watt-density performance for thick film applications can reach as high as 385 to 500 W/in2. Bonding a palladium silver heater material directly to a stainless steel substrate eliminates a large percentage of the thermal resistance (qJ) inherent with traditional mechanically attached heaters. This results in a process that can transfer heat five to 10 times more efficiently than mechanical technologies and three to five times more than laminate technologies.

Thick film heaters also allow for rapid heating due to the bonded structure's high thermal conductivity and the minimal thermal mass. Visualize the difference in heat-up time between a 3/8" thick strip heater consisting of wire, magnesium oxide and metal sheath weighing one pound vs. a thin sheet of stainless steel with a heater layer of only 10 to 20 mils thick weighing a few ounces.

The table shows a general comparison of thick film watt density and response rate performance to laminate, strip and tubular technologies.

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Thick Film Benefits

With thick film technology's improved watt density and response-rate performance, the end-user's process benefits from smaller surface area, lower weight, lower input voltage and less consumed energy -- all aspects that lower heater cost. Thick film allows for extremely efficient heat to be applied selectively to areas of the work piece in a more economical manner.

Advanced thick film construction is emerging rapidly in the heater components business as more designers, engineers and product developers take advantage of the superior thermal efficiencies that this "direct contact" technology offers.

For more information

Contact Chromalox. Call (800) 443-2640 or visit www.chromalox.com.

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