A Numercial Comparison of Single-phase Forced Convective Heat Transfer Between Round Tube and Round Microchannel Heat Exchangers

Abstract: Three dimensional simulations of the single-phase laminar flow and forced convective heat transfer of water in round tube and round microchannel heat exchangers were investigated numerically. This numerical method was developed to measure heat transfer parameters of round tube and round microchannel tube geometries. Then, similarities and differences were compared between different geometries. The geometries and operating conditions of those indicated heat exchangers were created using a finite volume-based computational fluid dynamics technique. In this article, at each Z-location variation of dimensionless local temperature, non-dimensional local heat flux variation and dimensionless local Nusselt number distribution along the tube length were compared between round tube and round microchannel heat exchangers. Consequently, averaged computational Nusselt number was obtained for those indicated models and then validation study was performed for round tube counter flow type heat exchanger model. Finally, all of these numerical results for both kind of geometries in counter flow heat exchangers were discussed in details

Numerical Investigation of Influence of Dilution in Air and Fuel Sides on MILD Combustion Burner

Abstract: Understanding of how and where NOx formation occurs is very important for efficient and clean operation of utility burners. FGR is a new method adopted to control NOx formation in combustion chamber. In this method flue gas decreases flame temperature and reaction rate, resulting in the diminish in thermal NOx emission. Recently, it has been accomplished that the entered flue gas in fuel stream, that named, FIR method, could increase a much improved reduction in NOx production per unit mass of recirculated gas, as compared to the conventional FGR in air. In the present study, the MILD combustion regime have been simulated, and result validated with experimental data. In order to modification, variations including, temperature and flow of air inlet are performed. Also the effect of FGR/FIR methods on NOx reduction by using CO 2 , H 2 O, and N 2 as diluents gases are investigated. Results show that FIR is more effective to reduce NOx emission than FGR in the same recirculation ratio of dilution gas, and H 2 O dilutor because of large specific heat, is more effective compared to CO 2 and N 2 gases, Also with increasing of velocity and flow of air inlet, the thermal NO X concentration decreases