Year

1999

Degree Name

Doctor of Philosophy

Department

Department of Mechanical Engineering

Abstract

Cavitation is a phenomenon that is manifest in a wide variety of liquid flow situations. Of particular relevance to this thesis is its appearance in industrial pumps and valves. Much of the early work proceeded in the form of fundamental research. The mathematical formulae coupled with and shaped by the experimental work done in cavitation laboratories established the foundations of this subject. In the early twentieth century, the relevance of this fundamental research to industrial problem areas such as short-lived valves and pumps was realised. Driven by the commercial advantage of providing cavitation resistant products, various companies established, within their existing research and development departments, sections which examined the impacts of and solutions to cavitation. Using the fundamental research as a springboard for their own, these industrial engineers undertook extensive laboratory and field test work. From this they developed products and the formulae and rules of thumb that enabled them to scale-up (or scale-down) these products to suit various industrial applications. Much of the knowledge produced by these companies remains private.

The situation at present shows a marked divergence in these two areas of research. However, this thesis contends that the current climate in academia and industry, where co-operative research projects in other fields of interest set a precedent, is well suited to the establishment of a combined effort in the area of cavitation. The establishment of such co-operative research is complex and varied when considered against the background of the many institutions, companies, products and test equipment involved. The approach adopted by the author has been to examine the history and current state of the two avenues of research (fundamental and industrial) with a view to establishing the broader bases for the seeding of links between them. This has been done by examining some examples in industry that display the nature of the problem that cavitation poses together with some of the solutions, which are often only means of mitigating the effects of cavitation. Some general test work with both Venturis and multiple orifice plate test rigs is presented where the problems associated with cavitation are discussed.

The terms of this examination have included a study of the products of industry as well as the basic experimental research tools adopted within institutions (orifice plate and venturi test rigs). It has been shown that there are grounds for work with such test rigs to develop industrial products whilst simultaneously leading to the furthering of our understanding of cavitation. Some phenomena (such as out of sequence, interstage cavitation) were discovered during testing that would lead to a re-examination of the mathematics currently being applied.

Within this thesis the author has developed a technique for examining the cavitation signatures of test items. This has been done by using a unique combination of tools such as high speed photography, image analysis and signal analysis software. This work is supplemented by a detailed study of multiple plate orifice arrays. The author presents means of overcoming the subjective nature of determining the points of incipient and desinent cavitation that have plagued researchers in the past. Finally, more detailed work, arising out of the practical need to protect valves and pumps from cavitation in severe service duties, has led to a method for designing multiple orifice plate arrays.

In addition to this, the author presents the concept for a device that performs high pressure letdown (as used in large power stations) without suffering cavitation.

The over-riding conclusion of this thesis is that whilst there is significant ground for establishment of c o m m o n efforts in cavitation research, there is both much merit in and momentum for continuing the current divergent streams. The development of the common ground, however, acts to enrich both the public knowledge domain and accelerate the development of solutions to industrial cavitation.

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