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Study on Dynamic Characteristics of HVAC Water Distribution Network Based on the Theory of Impedance

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Tutor: XieJunLong
School: Huazhong University of Science and Technology
Course: Refrigeration and Cryogenic Engineering
Keywords: Rigid pipe,inductance-resistance model,Dynamic characteristics,Buffertank,Hydrau
CLC: TU83
Type: Master's thesis
Year:  2013
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Abstract:
This paper studies the hydraulic characteristics of the closed water network in theHVAC system. The dynamic characteristics is mainly reflected in the transient changes ofpressure and flow over the time when the water system is running at the variable conditionsor when the pump start and stop. The dynamic characteristics of the pipe network is affectedby pump characteristic, network topology, network impedance distribution, constant pressurelevel, the special characteristics of equipment in the system and so on. The characteristicparameters in the hydraulic changing process, such as pressure fluctuations, flow changes,the system maximum pressure value, variable conditions stable time, is an important basisthat reflected Whether the system is operating safety, flow control is effective, fan coil unitand other equipment control strategy is feasible.Based on the theory of rigid pipe and drew on the electrical network theory, we dividedthe characteristics of the common elements of the pipe network into two major categories ofresistive and inductive, and put forward the method of simplifying the pipe network based onthe equivalent inductance-resistance model. By a combination of numerical simulation andactual experiments, we proposes to fit flow curve with S-shaped function during the pumpstart process, deduced the lift curve equation and put forward the method of exterminatinglift fluctuations and the value of the maximum pressure. We also study the buffer mechanismof the ideal inductance element. with the aid of CFD software,we analyze hydrauliccushioning properties of the buffer tank under variable flow conditions, puts forward theevaluation index of tank buffering capacity. Study the impact of buffering capacity affectedby tank structure, flow rate, import connection position and some other factors,in order toobtain the beneficial reference for the buffer tank structure design, type selection in theactual engineering.Another important research content of this article is to analyze the influence of the idealinductive components on the local system stability through the software simulation.Bysetting a certain source of disturbance, and increased inductance at special position of thepipe network to study flow fluctuations, judged the pros and cons of position to increase theinductive.Analysis of the stability flow rate affected by the distribution of the inductance, To get to the significant guidance for buffer equipment selection, the determination ofinstallation position in the actual engineering.
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