A study of heterogeneous nucleation and electrostatic charge in steam flows
This thesis describes two experimental investigations concerned with condensing flows of steam in a cascade of turbine blading. The first considers the effect of heterogeneous nucleation on the flow of condensing steam. The second is concerned with the measurement of electrostatic charges generated on first nucleation in steam. The facility used in this investigation is a blow-down steam tunnel constructed for the study of two-phase flows in a cascade of turbine blading. To carry out the first part of the investigation, substantial modifications were introduced to generate a supply of ultra-pure steam for admission into the blade cascade. This allowed a base line set of blade surface pressure measurements to be recorded in the absence of impurities. In subsequent tests the steam was dosed with known quantities of aqueous ammonia to investigate the influence of chemical impurities on the condensation process. To investigate electrostatic effects a Langmuir probe for operation in steam was developed. Charge distribution was recorded with the probe mounted upstream and downstream of the blade cascade. Observations were recorded over two pressure ratios, using ultra-pure steam and, in subsequent tests, steam dosed with known quantities of aqueous ammonia. Comparisons are carried out between the base line measurements using ultra-pure steam and the measurements using dosed steam. Both sets of results are compared with those of previous investigators. The electrostatic measurements are compared with similar measurements recorded by investigators working in LP steam turbines. The results are discussed and conclusions drawn.