Shumin Lin

Date of Graduation


Document Type



Augmented-system equations related to a subsystem of a multiple-fan ventilation system are established. It has been found that an augmented system has a unique solution curve and all the possible system solution points are located on the curve at the points where the augmented parameter has a zero value. The Quasi-Newton algorithm is then introduced and combined with the switching-parameter technique to form an effective and efficient numerical tool for identifying the solution curve and all the system operation points. Exemplary networks are analyzed using the new algorithm to demonstrate its superiority over all other methods available for analyzing ventilation systems. The algorithm is further applied to identify a subsystem characteristic curve that reflects the operating characteristics of a ventilation system with respect to a particular fan. Other related fundamental concepts such as a subsystem solution curve, and fan and system operating points are demonstrated as well. Detailed are the operating characteristics of multiple-fan systems (in comparison with those of a single-fan system), namely, a non-zero pressure at a zero quantity, non-monotonic quantity-pressure relation and multiplicity of fan operating points. Moreover, the influences on those operating characteristics from fan characteristics, system structures, branch resistance change, etc., are investigated. Laboratory experimental tests were carried out to obtain tangible information on the actual operating characteristics of tubing duct networks involving various structures and different number of axial-flow fans. The operating characteristics of basic ventilation components (i.e., a single branch and individual axial-flow fans) and simple networks (namely, a single-fan system and multiple fans in series and parallel structures) were systematically investigated. Emphasis was laid on the unstable system operation characterized by sudden or even drastic air quantity changes, which were caused by the unstable operating range of an axial-flow fan. Tests were specially designed to examine the influences on the system operation stability from various factors such as the operating characteristics of a fan, the system structure, number and resistance of intake branches, and fan speed change. Furthermore, the concept of a influence domain is introduced to analyze the operating characteristics and stability of complex systems based on those of simple systems (domains), which were found to be able to impact each other through link branches. Experimental tests also found that an axial-flow fan possesses two unstable operating ranges depending on the tendency of the air delivered by the fan to increase or decrease; and that the duality is responsible for the duality or even multiplicity of subsystem characteristic curves that depend on the sequence of fans' being put into operation. Systems involving multiple axial-flow fans were found to have multiple operating points, which also depend on the sequential order of fan operation. The finding (from experimental tests) of the unstable operating range of an axial-flow fan was then implemented into the Quasi-Newton algorithm to identify the feasible and the actual operating points of an example network at a given order of fan operation.