Experimental Investigation on the Coupled Effects of Working Fluid Charging Amount  and Circulating Pump Behavior on System Performance in an Otec System

Abstract

Abstract：In ocean thermal energy conversion (OTEC) systems, the initial charging amount of the working fluid is critical, and as the circulating pump is the most direct and only means to regulate the working fluid flow, it is necessary to investigate the coupled effects of it and the working fluid charging amount on the system performance. In order to do this, an experimental facility which can control the working fluid charging amount and circulating pump behavior was established. The coupled effects were investigated by energy and exergy analysis under varying temperature difference as well. The results showed that varying working fluid charging amount changed the pressure of the cycle and the physical state of the working fluid, and the effect on the system varied under dissimilar temperature difference conditions. Compared to the standard charge (8 kg), 75% of the standard charging amount diminished the system thermal efficiency by 17% and exergy efficiency by 16% at small temperature difference (20°C), whereas a charging amount of more than 100% resulted in improved thermal efficiency by 14% and exergy efficiency by 13%. At large temperature difference (28°C), 75%, 125% and 150% of the standard working fluid charging amount all improved system performance (thermal efficiency by maximum 16%, exergy efficiency by maximum 21%). Besides, an increase in circulating pump frequency improved system performance regardless of the temperature difference and working fluid charging amount. In addition, the condenser always occupies the largest proportion of system exergy loss, which is more than 44%.

Keywords: Ocean thermal energy conversion, Organic Rankine cycle, Working fluid charging amount, Pump frequency；