| Closed cooling water pipe network is an important part of the central air conditioning system,the deviation between each terminal branch flow and design value will directly affect the living environment of people's thermal comfort.It is meaningful to study on the operation stability and the interaction of each branch of the system.Moreover, excellent pipeline design and reasonable branch control will be less energy consumption. The start and stop transient process of centrifugal pump will lead to pressure fluction, which is related to the security of the system.This thesis discussed three different water systems, dynamic concentration system whose most unfavorable branch is controlled constant pressure difference, distributed power system whose most unfavorable branch is controlled constant pressure difference and the same process system whose most unfavorable branch is controlled constant pressure difference. Point out the method to identify the most unfavorable branch.The system is divided into the full load, part load, small load of three working conditions,use numerical simulation to find out hydraulic maladjustment degree of each condition.Compare the three systems' hydraulic stability and energy consumption with the traditional sytem whose most unfavorable has no control.The numerical simulation of centrifugal pump start and stop is to simulate different pump rated speed, start time and end resistance.Find out the effect of the three factors on the impact of impact head during centrifugal pump start process,analysis the causes of impact head theoretically.Discuss the inlet pressure of three pumps in parallel when they staggered start time, know the staggered start can reduce the risk of negative pressure of the pump entrance;When the valve opening changes, see the import and export pressure transient change of the vavle, the valve opening decreases more, the peak pressure value of the entrance is more large, the valley pressure value of the exportsis smaller, the pressure difference is bigger between transient state and steady state.The experiment of centrifugal pump start and stop, when the system adoptes automatic water expansion tank and diaphragm type pressure tank as two different pressure device, compare the time they need to stabilize pressure;Control the pump start and stop time of the inverter, monitor the inlet and outlet pressure of pump real-time, obtain the relationship between the transient pressure change with time when the centrifugal pump starts and stops in different ways. Ball valve closed fast and quick opening experiment of main pipe, collecting valve import and export pressure changes, find out the reasons of pressure mutation changes trend. The experiment of closed water system who has double constant pressure point and single constant pressure point, talk about pressure distribution difference in the pipe network,study the influence of the stability of the system operation when the system uses double constant pressure point. The experiment of centrifugal pump start and stop,which is very helpful to provides a reasonable methods to reduce overpressure and negative pressure risk in the closed water system. |
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