# 5 Design Factors that Determine Heater Element Efficacy

When choosing a heater element, emphasis should be placed on the element’s efficiency above all else. Various factors can determine a heating element’s effectiveness, but they can easily be overlooked. This post will examine key design factors that influence the efficacy of heater elements and weigh them into your purchasing decision.

1. ## Electrical resistance

Heating elements perform when the tape or wire resists the flow of electricity, resulting in a transfer of electrical energy into heat. We measure the electrical resistance of a metal by a “unit length of unit cross-sectional area.”

We can also calculate the linear resistance of a tape or wire from its electrical (cross-sectional) reactivity. Resistance can be calculated with the following factors:

ρ = Electrical Resistivity (μΩcm)

R = Element Resistance at 20 °C (Ω)

d = Wire diameter (mm)

t = Tape thickness (mm)

b = Tape width (mm)

l = Tape or wire length (m)

a = Tape or wire cross-sectional area (mm²)

Most metals maintain the same resistance regardless of temperature, but there are times when temperature changes lead to changes in resistance. In such cases, designers of the heater element must find the element’s resistance at room temperature. To obtain that measurement, designers will have to divide the resistance at operating temperatures by the following resistance factor:

F = Temperature-Resistance Factor

Rt = Element resistance at operating temperature (Ω)

R = Element resistance at 20°C (Ω)

Designers can create heating elements that come in various sizes to provide a desired wattage or power density per unit area. However, this could lead to the load on the surface of the heating element getting too high, resulting in overheating and failure if heat transfer is too slow.

Designers must build a heating element that’s low enough to allow the heat transfer mechanism to work fast enough to prevent premature failure. The ideal setting for heating elements depends on the type of heater and industrial application for which it’s being used.

1. ## Design envelope

The design envelope of heating elements simply refers to its dimensions. They include its overall size, length, diameter and also its lead length. Of course, these factors are crucial because they influence the design limitations of the heating element. For example, particular dimensions may determine the maximum watt density and operating temperature for a given heater element.

Additionally, specific design envelopes are more suitable for certain heaters and heating applications. That makes the design envelope an essential factor in heating element construction.

1. ## Terminations

Terminations can be considered a fundamental consideration for heater elements, but we’ll draw some added attention to them. They’re important because they affect the longevity of the heating element, for better or worse, depending on where they’re positioned.

Ideally, the bulk of a heater element should be placed in close contact with the termination. That maximizes heat transfer and prevents energy waste. Of course, certain conditions may require a special setup and protection against hazards like chemical corrosion or oxidation.

1. ## Lead styles and consideration

Determining the type of electric leads and exit/termination methods is just as important as carefully selecting a heating element type. In industrial heating, leads maximize the transfer of energy converted to heat.

### Considerations for electrical leads in heating elements

• Needed abrasion resistance
• The temperature of the lead area
• The flexibility of the lead