Image Credit: Minco | Chromalox

 

Flexible heaters are devices that can be molded to the shape of the heated object. Most products can be bent around a small radius, and can be bent more than once without damaging the internal heating elements. These properties of the heater are essential in order to provide an effective heat source in a myriad of applications including electronics, medical devices and industrial applications such as pipe, tank, vessel and drum heating. 

 

Drum Heaters (Flexible Jacket Type)

Video Credit: economyheaters1

 

 

Selection Criteria

Important parameters to consider when specifying flexible heaters are performance specifications, type of heating element, dimensions and sleeve or sheath material. Other considerations include RoHS / WEE compliance and various features.

 

Performance Specifications

Performance specifications for industrial heaters include maximum operating temperature, AC voltage, heating capacity and watt density. 

 

Maximum Operating or Sheath Temperature

Maximum operating temperature is the maximum temperature that the sheath covering the cartridge heater may reach. The materials of construction, voltage requirements and watt density are design factors affecting the operating temperature of the flexible heater.

 

AC Voltage

AC voltage is the minimum alternating current (AC) volts required to operate the cartridge heater.

 

Heating Capacity

Heating capacity is a measure of how much thermal energy the device delivers over a period of time, usually measured in kilowatts.

 

Image Credit: Spirax Sarco

 

Where:

= Mean heat transfer rate (kW (kJ/s)

 

m = Mass of the fluid (kg)

 

cp = Specific heat capacity of the fluid (kJ/kg °C)

 

ΔT = Increase in fluid temperature (°C)

 

t = Time for the heating process (seconds)

 

 

 

Watt Density

Watt density is the amount of wattage per square inch that a cartridge heater can deliver. High watt density heaters should not be used with extremely viscous materials, poorly-circulated materials, or explosive/volatile materials due to risk of fire.  High watt density heaters are required for higher operating temperatures.

 

Type of Heating Element

Flexible heaters use two types of heating elements: etched foil and wire wound.

 

Etched foil heating elements are resistive heating element etched out of a foil substrate. The elements lay flat with a low profile that exposes the effective heating area. Etched foil heating elements have a shorter warm-up time, distribute heated evenly and are more efficient than other heating elements used in flexible heaters.

 

Etched foil heating element

Image Credit: MINCO

 

 

Wire-wound heating elements use a wire shaped resistive heating element, most commonly Ni-Chrome, which is wound around a cord and then embedded in the effective heating area. They are durable and able to withstand repeated flexure without compromising the element. Although, wire-wound elements are not as efficient and take longer to warm-up they can be a cheaper alternative when heat needs to be applied over a larger surface.

Wire-wound heating element

Image Credit: Tempco

 

 

 

Dimensions

Length and width are important dimensions to consider when selecting flexible heaters. Heaters should be sized to fit their intended application.

 

 

Sleeve (Sheath) Material

Flexible heaters have a sleeve or sheath that encapsulates the heating element. The sheath serves two purposes; to provide electrical insulation and to provide a protective physical barrier. The heating elements needs to be insulated to prevent heater failure by short circuiting the load. A physical barrier is required to extend the life of the heater and to allow the device to operate in wet, corrosive or other aggressive environments. Material options for the sleeve or sheath include; Polyimide (Kapton®), Silicone Rubber, Fluoropolymer (Teflon®), Mica or other materials.

  

 

 

RoHS / WEEE Compliance


RoHS Compliant

 

Image Credit: Industrial Safety Solutions


Restriction of Hazardous Substances (RoHS) is a European Union (EU) directive that requires all manufacturers of electronic and electrical equipment sold in Europe to demonstrate that their products contain only minimal levels of the following hazardous substances: lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyl and polybrominated diphenyl ether. RoHS became effective on July 1, 2006.

 

WEEE Compliant

 

Image Credit: EPM Global Services 

 

Waste Electrical and Electronics Equipment (WEEE) is a European Union (EU) directive designed to encourage the reuse, recycling and recovery of electrical and electronic equipment. WEEE is also designed to improve the environmental impact and performance of this equipment. The WEEE directive establishes requirements and criteria for the collection, treatment, recycling and recovery of electrical and electronic equipment. It also makes producers responsible for financing these activities. Retailers and distributors must provide a way for consumers to return used or obsolete equipment without charge.

 

 

Features

Features common to flexible heaters include explosion proof, hazardous location and UL approved.

  • Explosion-proof heaters are designed to withstand explosions and protect the materials within. Some suppliers include heaters with housings that can withstand sparking and flames.
  • Hazardous location heaters are designed for use in places where there is a risk of fire or explosion. Underwriters Laboratories (UL) and other organizations rate these devices.
  • Heaters approved by Underwriters Laboratories (UL) have been tested and meet the requirements set by their published standards for safety. Products that receive UL approval bear a UL Mark. Typically, documentation of UL certification is available from the manufacturer.

 

Resources

 

Minco - Flexible Heaters Design Guide

 

Delta T - Introduction to Flexible Heaters


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