Design Improvements in a 30,000 kcal/h Air Furnace, Assisted by CFD and Infrared Thermography

The design of low-end, oil or natural gas-fired air furnaces is currently carried out using traditional methodologies. On the other hand, the use of modern computational tools can be promising also in this category of equipment, especially if assisted by modern, non-intrusive experimental techniques of low operational cost. In this paper, we report on the use of commercial computational fluid dynamics (CFD) software, assisted by infrared thermography, to predict and improve the flow and heat transfer in a 30,000 kcal/h air furnace. The infrared thermography was employed in the determination of temperature boundary conditions in the heat exchanger surfaces. The 3D flow and heat transfer in the main control volume of the air furnace, at steady state (nominal operation point) is computed and presented by means of 3D streamlines and velocity and temperature fields at characteristic cross sections. The numerical results were checked by means of energy balances in the inlet and outlet sections of the control volume enclosing the heated air stream. In this way, the air furnace efficiency can be computationally predicted. Significant improvements in the traditional design process are demonstrated by means of this procedure. Thus, a promising design methodology for air furnaces, which is assisted by modern computational and experimental tools, can be formulated.