Study On Thermal And Dynamical Performance & Structure Optimization Of Oil-fired Air Heating Unit Applied To Different Altitude Zones

On key techniques in the development of plateau-type prototype and some problems of the unit structure, a series of theoretical and experimental studies on thermal and dynamical performances & structure Optimization of oil-fired air heating unit for the different altitude zone use were carefully carried out. The main results of the study are as follows:For applying the prototype to high altitude zones, the solutions to these key techniques are put forward. The design principles of firebox and convection surfaces are analyzed and concluded, the rule and means for a burner selection and its structure optimization are proposed, the method for the system resistance calculation and fan selection is determined.Since there is not sufficient fundamental theory for developing the unit, a thorough theoretical and experimental investigation upon thermal and dynamical performances of the unit was conducted carefully. The method of thermal system design and calculation is developed, and the thermal performance is shown. On the basis of heat transfer analyses, the mathematics model of the thermal system is established, the calculation program and software which was validated with experimental data is made, a set of theoretical basis and software is provided for the design and optimization for the unit of different heating capacity and different altitude zone use. By means of the proposed software, impacts of barometric pressure, surplus air coefficient, and supply air volume on heating efficiency of the unit are achieved. Especially the effect of different altitude on the unit thermal and dynamical performance is well understood.For the decrease of air flow resistance and the matching between air flow and heat exchange, numerical simulation of multi-channels air flow in the unit is carefully done. Numerical analyses on the influences of different altitudes, air supply volumes and air supply opening positions on the velocity field and pressure field of multi-channels air flow, the multi-channels flux ratio, the matching of flow and heat transfer, rational air supply opening position, the unit pressure drop are obtained. The research shows that multi-channels flux ratio is almost not varied with altitude and air supply volume, and does not match corresponding flow and heat transfer, therefore the current construction of multi-channel should be improved by reducing the flow flux area of annulus channel, outer space channel or increasing heat flux of annulus channel, outer space channel. The rationalposition of air supply opening is where the vertical distance from the center point of air supply opening to horizontal center line in firebox is 82.5mm.Upon difficult ignition and unstable combustion in high altitude zone, numerical simulation for the optimization of burner structure is conducted. The impacts of different altitude, angle and position of swirl plate, shape of blast tube has been analyzed on air velocity around an ignition electrode, a ratio of maximum tangential velocity in swirl zone to maximum axial velocity in center zone on outlet of blast tube, a ratio of maximum return velocity to maximum axial velocity in center transect of firebox, a pressure drop from inlet of blast tube to outlet of firebox. The optimization structure of burner were attained with an angle 20° of swirl plate, Az=14.5mm of position of swirl plate, a dilatation to shrinkage-type shape of blast tube. Based on these, numerical simulation of the mixing between air and oil spray in firebox is further conducted. In order to enhance the mixing between oil particle and oxygen species of air in firebox, the effects of different angle of oil spray, shape of blast tube, plain/plateau has been determined on a distribution of oil particles and air distribution, the rational structure of burner with an angle 50° of oil spray, a same shrinkage-type shape of blast tube.With regard to numerical simulation, a calculation mode selection, grid-making technique, two-grade calculation method have been investigated, some successful experiences on numerical simulation hav...