Hydrodynamic Analysis of Direct Steam Generation Solar Collectors

Abstract

Direct steam generation collectors are considered with the aim to improve the performance of a parabolic trough collector leading to a reduction of operating costs of solar electric generation systems. In this study a hydrodynamic steady state model is developed and linked with a thermal model to optimize the performance of once-through direct steam generation solar collectors. The hydrodynamic model includes flow pattern classification and a pressure drop model. Flow pattern maps for typical DSG collectors with horizontal and inclined absorber tubes are generated to investigate the variation of flow conditions with radiation level, tube diameter, tube length and flow rate. Two-phase flow frictional pressure drop correlations for the range of operating conditions in a DSG collector are selected from the wide range of published correlations by comparison with experimental data for typical steam-water flow conditions in a DSG collector. Pressure drop is calculated for different operating conditions for both horizontal and inclined solar absorber tubes. Alternative operational strategies are evaluated to achieve optimum performance of a direct steam generation collector at different radiation levels. [S0199-6231(00)00101-5]

Heat Transfer Fluids

“…29 Figure 7 shows the pressure drop variation with flow rate in DSG and oil-based collector tubes [28]. The flow rate in DSG collector tubes determines the two-phase flow patterns and the contribution of each phase to the total pressure drop.…”

“…Previous studies [27][28][29] have suggested a model for predicting flow transitions in horizontal two-phase flow, considering stratified flow with a wave existing on the surface. As the gas accelerates, the pressure in the gas phase decreases and the wave grows.…”

“…Methods for predicting the pressure drop in two- Friedel's correlation was determined to be best for DSG applications from the data obtained during the DISS project [21,28,44].…”

“…To increase the portion of annular flow, a small degree of inclination of the absorber tubes has been suggested [28,29]. Downward inclinations can decrease the stratified and intermittent flow region by increasing the liquid velocity and decreasing the liquid level.…”

A Direct-Steam Linear Fresnel Performance Model for NREL’S System Advisor Model

“…Benefits to the OT de sign are elimination of the steam separation and transport equip ment, though this arrangement introduces the possibility of flow and heat transfer instability. OT flow has been proposed for linefocus CSP [21][22][23], but has not yet been demonstrated because of control complexity [24].…”