SEN ANALYSIS OF STRATIFIED HOT WATER HEAT STORES WITH RESPECT TO AXIAL POSITION AND NUMBER OF CHARGING-DISCHARGING EQUIPMENTS

摘要

SEN analysis [Solar Energy, 2007, Vol. 81, pp. 1043-1054] is a robust characterization method for stratified thermal energy stores (TES). It integrates the concerns of the First and Second Law of Thermodynamics into single efficiency index. The First Law concern is incorporated into the definition of SEN efficiency index through energy response factor (E_R) and the Second Law concern through entropy generation ratio (R_(EG)). SEN analysis thus estimates the ability of a TES to store energy and exergy. In the current paper SEN analysis is utilized to characterize hot water heat stores (HWHS) with respect to the axial position and number of charging/discharging equipments they possess. Diffusers or flow-guides are used as charging-discharging equipments in view of reducing turbulent mixing within the HWHS, especially in the entrance and exit ports. For HWHS charging-discharging equipments are commonly positioned in the top-most and bottom-most regions of the HWHS in order to avoid development of dead volume, i.e., volume that does not take part in the charging-discharging process. Axially placed conical diffusers are observed to circumvent the issue of dead volumes. However, the effect of their axial position on the entropy generation is not yet studied. Further, one may use intermediate charging-discharging equipment in association with the original pair in order to feed or withdraw the working fluid into/from the HWHS at different heights. This paper provides a detailed analysis of the position and number of axially placed conical diffusers with zero diffuser angles inside a cylindrical HWHS. The thermal field information obtained from a computational fluid dynamic (CFD) analysis is subjected to the SEN analysis to achieve required design insights.