Unitemp Blog

What is specific heat?

19.03.2015

The specific heat of a substance is the number of kilojoules (kJ) necessary to raise 1 kilogram (kg) of the substance 1°C compared with the number of kJ required to raise 1 kg of water 1°C.

Note: 1 kJ is almost the same as 1 Btu (1.055 kJ = 1 Btu).

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How is specific heat used in heat calculations?

19.03.2015

When the temperature of a substance changes, the heat gained or lost is found by multiplying the mass, or weight of the substance by the change in temperature (ΔT) and by the specific heat (sp ht).

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What do absolute pressure and gauge pressure mean?

19.03.2015

If a gauge measure pressure above atmospheric, then the atmospheric pressure of 1.013 bar (metric) or 14.7 (Inch-Pound) must be added to the gauge reading to determine absolute pressure.

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What is freeze protection?

19.03.2015

Freeze protection is a heat tracing application. Usually refers to maintaining water line temperatures at slightly above freezing (Tp = 40°F - 50°F).

Freeze protection design is simply a matter of selecting a heater to offset the heat loss through the thermal insulation. Freeze protection systems are characterized by relatively low heat delivery and by the fact that their use is generally seasonal during cold weather months.

“Freeze protection” is sometimes used to describe...

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Describe heat loss

19.03.2015

Heat loss is the rate at which process equipment heat flows to a cooler ambient, stated in either watts or BTU/hour.

The purpose of heat tracing is to replace that heat lost through the thermal insulation in order to maintain a desired temperature difference (ΔT or Delta T). Therefore, the first step in heat tracing system design is to calculate the heat loss.

Heat loss calculations always involve three factors: (ΔT or Delta T) or (Tp –Ta) Nominal Pipe Size or Vessel Dimensions...

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Explain the term watts per meter

19.03.2015

For pipe heat tracing it is convenient to think of the heat loss and respective heat required in Watts per unit length. Most pipe heat loss calculations are done with a per meter basis. Then it is only a matter of selecting a heating cable with this watt per unit output or higher.

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Can you splice two different watt cables together (i.e., 3 watt to a 6 watt)?

19.03.2015

Two different parallel watt density cables may be spliced together. Being parallel, the power out put in the two spliced sections will be different as rated. Care must be taken to not exceed the maximum circuit length and circuit breaker rating. The simple solution in this case is to use the maximum circuit length of the higher wattage cable.

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What is a "run-a-way" temperature?

19.03.2015

When the controller fails and the heating cable remains energized the pipe will increase in temperature to an equilibrium temperature. This is called “run-a-away” temperature. For stabilized designs in hazardous areas, the condition is used to determine the maximum heating cable sheath temperature.

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Do all thermal insulation have basically the same products?

19.03.2015

While thermal insulations have thermal conductivities, or k-factors, that reduce the flow of heat, the k-factors vary depending on the specific thermal insulation type. They also have different maximum temperature ratings. These factors must be addressed in a heat tracing design.

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A heat loss is based on a 25 mph wind. The specification is for a 50 mph wind. Is there a major increase in heat loss?

19.03.2015

Typically not, because most of the reduction in heat loss is through the thermal insulation. The increase for this change in wind speed may be only 2-5%.

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