Optimization of thermal energy storage by the thermocline technology

It has received an increasing attention because integrated TES systems can largely enhance the reliability and the dispatchability. Low-cost single storage tank based on the thermocline technology becomes an alternative to commonly used two-tank system. However, the improper inlet/outlet manifolds may cause the strong mixing of hot and cold fluids and disturb the temperature stratification, resulting in reduced thermal performances of the storage tank. An original CFD-based optimization algorithm is developed to determine the optimal flow distribution and restricted thermocline propagation manner using a SMT tank at high temperature as an example. A practical method for homogenizing residence times of the thermal front in order to flatten the thermocline zone is proposed, based on the insertion of a geometrically optimized perforated The feasibility of optimization algorithm is then validated experimentally by testing of a lab-scale cylinder SMT storage tank at low temperature, by measuring the local temperature evolutions of the fluid during both the charging and discharging operations. Results show that optimized Ring opening plate distributors can significantly improve the energy and exergy efficiencies under large range of operating conditions. After that, the mechanism of dynamic mixing and the jet entrainment phenomenon are particularly addressed by measuring the flow profiles inside a rectangular SMT tank using Particle Image Velocimetry (PIV) method. The local competing relation between the convection and diffusion heat transfer mechanisms on the degradation of temperature stratification is particularly explored. (author)