Hydraulic analysis of flow intake conditions for cooling tower pumps

Magistrsko delo obravnava eksperimentalno raziskavo vtočnih razmer na črpališču za hladilne stolpe v Nuklearni elektrarni Krško. Nastajanje površinskega vrtinca tipa 6 v vtočnem bazenu ni bilo sprejemljivo za obratovanje CT1 črpalke in hladilnega sistema nasploh. Za ustrezno ukrepanje je bilo treba podrobno poznavanje tokovnih razmer. Opravljene so bile terenske meritve in zasnova fizičnega hidravličnega modela v merilu 1:16 v laboratoriju. V teoretičnem delu so na splošno opisani črpalni sistemi, vtočne zgradbe in centrifugalne črpalke. Poleg tega je predstavljeno teoretično ozadje vodnega toka z ohranitvenimi zakoni, črpalnega sistema, toka s prosto gladino, dimenzijske analize s poudarkom za tok s prosto gladino ter merilna negotovost. V nadaljevanju je podan pregled raziskav obravnavane problematike. Predstavimo izkustven pristop ter priporočila standarda ANSI/HI za načrtovanje vtočnih zgradb ter za načrtovanje fizičnega hidravličnega modela z merilno tehniko in meritvami. V eksperimentalnem delu je predstavljen dejanski primer z analizo razmer, terenskimi meritvami in modelnimi preizkusi v laboratoriju. Preizkusi so bili narejeni za različne obratovalne režime CT črpalk. Rezultati so pokazali dobro ujemanje med modelom in prototipom, saj so bile dobljene podobne tokovne razmere s pojavljanjem površinskega vrtinca tipa 6 na enakem območju. Z namestitvijo dodatnih elementov in ovir v vtočni bazen smo skušali preprečiti nastajanje vrtinca. Ukrep s podaljšano vmesno steno je zagotovil ugodne tokovne razmere v sprejemljivih mejah po kriterijih standarda ANSI/HI.This master\u27s thesis deals with an experimental research of the intake flow conditions on cooling towers pumping system in the Nuclear Power Plant in Krško. Formation of the free surface vortex type 6 in the pump sump was not acceptable for the operation of the CT1 pump and the cooling system in general. Detailed flow conditions in the intake structure were needed. Field measurements as well as a design of the physical hydraulic model with a scale factor 16 were conducted in the laboratory. Pumping systems, intake structures and centrifugal pumps are described in the theoretical part of this paper. This section provides a theoretical background in describing the flow through conservation laws pumping systems, free surface flow, dimensional analysis, with an emphasis on free surface flow and measurement uncertainty. The chapter is followed by an overview of research dealing with the issues of intake structures. The empirical approach and recommendations of Standard ANSI/HI for pump intake design and for designing a physical hydraulic model are introduced. At the end of the theoretical part, measurement techniques and measuring procedures are included as well. The following experimental sections presents an example of the analysis of a CT pumping station, providing field measurements and model tests in the laboratory. The model tests were made for different operational conditions of pumps. Comparison between the model and the prototype showed a good agreement with the formation of identical free surface vortex type 6 in the same area of the sump. In order to prevent the formations of an unfavorable free surface vortex, the geometry of intake structures with the additional elements and obstacles were modified. The model test which included an installation of an extended intermediate wall provided favorable flow conditions in the acceptable criteria of Standard ANSI/HI