Modelling and performance analysis of an electric heater

Electric heaters are used extensively in many industrial applications. There are several interacting parameters that affect heater performance and contribute to its cost. Such parameters are: coil length, coil diameter, helix diameter, coil pitch, number of turns, coil emissivity, heater wall emissivity, applied voltage, air flow rate, air temperature at the heater outlet, insulation thickness, and the heater dimensions. Three conical heater configurations were selected for preliminary optimization. A conical heater configuration with outer ring coils was found to give the highest heater efficiency, the easiest and least expensive to manufacture, and was selected for detailed modelling. In the simulation model, the heater wall was divided into four annular sections and the continuous heater coil was divided into four segments of four ring coils. Energy and heat transfer equations were written for each ring coil, each section of the wall, and the air past each ring coil. Equations for coil resistance and power, air properties, heater geometry, and configuration factors are added to form a system of 220 nonlinear equations. Engineering equation solver (EES) was used to solve the system of equations. The results were checked by comparing the heater efficiency based on the average inlet and outlet air temperatures, and the heater efficiency based on the heater losses. Both efficiencies matched well in all calculations. The effects of varying the identified heater parameters on the heater performance were studied and discussed. The results indicate that increasing the coil length and airflow rate, while reducing coil emissivity, wall emissivity, and wire diameter could improve heater performance. Copyright (C) 2004 John Wiley Sons, Ltd.