STUDIES OF VELOCITY FIELDS IN A WATER HEAT STORAGE WITH A VIDEO BASED PARTICLE TRACKING VELOCIMETRY TECHNIQUE

摘要

Thermal storage in water has become very common the last decades in many countries. Short term water heat storage systems play an important role in combined heat and power plants, in the process industry, in solar thermal systems and for domestic hot water production.The water volume must be thermally stratified to avoid degradation of heat quality. The temperature distribution in the storage is however the integrated result of a complicated process where many different phenomena act together. Only temperature measurements will not be sufficient to explain and evaluate the thermal behaviour of a storage, increased knowledge about the velocity field is needed.A video based Particle Tracking Velocimetry technique has been developed and used to document the non stationary velocity field in a water heat storage. An ordinary video camera is used to record the in plane movements of particles in a light sheet in seeded water.The technique offers a powerful method for studies of fluid flow and velocity field. The combination of particle traces and vector plots have proven to be an efficient tool in gaining knowledge about crucial phenomena.Velocity fields are presented, showing mixing near the inlet, natural convection at the wall and exchange of water between the boundary layer and the core, and their impact on the stratification in the storage.