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The wire is immersed in a fluid and can act both as an electrical heating element and a resistance thermometer. The transient hot wire method has advantage over the other thermal conductivity methods, since there is a fully developed theory and there is no calibration or single-point calibration.
The efficiency by which electricity is converted to heat depends upon on salt, water, and fat content due to their thermal conductivity and resistance factors. [13] In particulate foods, the particles heat up faster than the liquid matrix due to higher resistance to electricity and matching conductivity can contribute to uniform heating. [ 11 ]
The SI unit of absolute thermal resistance is kelvins per watt (K/W) or the equivalent degrees Celsius per watt (°C/W) – the two are the same since the intervals are equal: ΔT = 1 K = 1 °C. The thermal resistance of materials is of great interest to electronic engineers because most electrical components generate heat and need to be cooled.
In a suspended design, a resistance heater is attached at two or more points to normally either a ceramic or mica insulator. Suspended resistance heaters can transfer heat via convection and radiation, but not conduction as they are surrounded by air. In an embedded heating element, the resistance heater is encased in the insulator.
The thermal conductivity of a material is a measure of its ability to conduct heat.It is commonly denoted by , , or and is measured in W·m −1 ·K −1.. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity.
A heat exchanger brings the heat from the burner to the water. Its job is to bring heat to the water without having contact with the water, similar to boiling water in a pot. An exhaust stack takes the hot gases and transfers them away from the boiler. Boiler controls are there to make sure the hot water or steam is produced in a safe way. [5]