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Abstract

Lysholm twin screw expanders are being developed to recover work from the two phase flash expansion of organic fluids. The work described in this thesis was carried out to maximise the efficiency of such machines by improving the inlet port design. To this end the flow in the inlet port was investigated both analytically and experimentally.

The theoretical analysis was carried out on the assumption of one-dimensional steady flow allowing for thermal non-equilibrium and relative motion between the phases with corrections to allow for boundary layer growth. The equations thereby developed were solved by means of a numerical procedure together with the calculus of variations to design the port as a circular cross section nozzle of optimum adiabatic efficiency. The resulting design was then modified to progressively transform its cross section from circular at the inlet to the characteristic irregular shape of a screw expander inlet port at the exit.

The experimental work involved the construction of both the circular and modified cross section port designs and their testing in a closed loop containing Refrigerant 113 as the working fluid. The loop was well instrumented and the void fraction distribution in the port exit plane was measured with a fibre optic probe whose tip position was varied by a specially designed computer controlled traversing system.

Predicted and measured values of void fraction differed on average by only 2.1% in the circular cross section design and 4.5% in the transformed design. The corresponding differences in pressure along the port length were well within 1.0%. The procedure developed for improved design therefore appears to be substantially validated.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses School of Science & Technology > Engineering

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