Roman Kwidziński

Evaluation of the relaxation time of heat and mass exchange in the liquid-vapour bubble flow

The paper presents a method of evaluation of a time constant that describes relaxational heat exchange between vapour bubbles and superheated liquid. The Scriven equation of bubble growth solved in a numerical way is used to determine the temperature field in the surroundings of the growing bubble. However, initial and boundary conditions are different from those studied before. The heat transfer relaxation time is determined from variations of the average temperature of the superheated liquid surrounding the bubble. Calculations are performed in both Eulers and Lagranges descriptions. The relaxation time obtained in the present paper is compared with the relaxation time reevaluated from the Moby Dick experiment by means of the homogeneous relaxation model.

Analysis of application of feed-water injector heaters to steam power plants

Analysis of application of feed-water injector heaters to steam power plants Steam-water injectors are devices in which exchange of mass, momentum and energy between two fluids being in direct contact, occurs. They can operate as pumps, mixers or direct contact heat exchangers. In the last aspect their use as feed-water heaters in Rankine thermal cycle of steam power plants both in land and sea applications (to merchant and naval ships) is very interesting. This paper presents selected results of heat-and-flow investigations of a supercritical steam-water injector, obtained in Institute of Fluid Flow Machinery, Polish Academy of Sciences (IMP PAN). On their basis value of average heat transfer coefficient for mixing chamber was determined; the obtained values were even a few dozens greater than those for classical shell-and-tube heaters. In the theoretical part of this work is presented an original injector model based on balances of mass, momentum and energy, written for control volumes containing separately particular elements of injector. On the basis of the model flow parameters in characteristic cross-sections of injector were determined. The calulations were performed for two different injectors tested in IMP PAN (Gdańsk) and SIET (Piacenza, Italy), and their good compliance with experimental data was achieved.