James Moore’s research while affiliated with University of Limerick and other places

Limited water supplies in proposed concentrated solar power (CSP) plant locations have instigated the need for air-cooling of the condensers in the Rankine cycle. The current industry standard for air-cooling in power plants is the A-frame air-cooled condenser (ACC), the installation of which has increased exponentially in the last 15 years. This has occurred despite the fact they suffer from significant inefficiencies and weather effects. This paper introduces a modular air-cooled condenser (MACC) design which seeks to minimise these inefficiencies. A thermodynamic analysis is carried-out to determine the outcome of installing this MACC design in a CSP plant. Firstly, a series of measurements performed on a full-scale prototype MACC under vacuum conditions representative of an operational ACC are presented. Condenser temperature and pressure were measured as fan speed was varied, for a range of steam flow rates, to determine the qualitative and quantitative relationship between fan rotational speed and condenser steam-side conditions. Results show that for a fixed steam flow rate and constant ambient temperature, condenser temperature and pressure decrease as fan speed increases. The relationships, developed from the measurements, between fan speed and condenser temperature-pressure were then used to evaluate the gross output from a 50 MW steam turbine and, ultimately, evaluate the net plant output. Results show that increasing fan speed leads to an increase in plant output up until a certain point, at which further increases in output are offset by larger fan power consumption rates. Thus, an optimum operating point exists. The effects of ambient temperature were also examined and were seen to have a significant impact on firstly, steam-side conditions and consequently, plant output. Increases in ambient reduce plant output. However, by varying the fan speed to achieve the optimum operating point for any given ambient, the losses can be minimised.

Diminishing fossil fuel reserves and a growing collective environmental awareness has led to the development of alternative methods of power generation such as Concentrated Solar Power (CSP). Although almost all existing CSP plants currently use water-cooled condensers, limited water supplies in the designated desert regions for such power plants, the high costs associated with providing cooling water and environmental considerations will all restrict the future use of water-cooled condensers. Air-cooled condensers (ACCs) are therefore proposed, despite evidence to suggest that they suffer from significant inefficiencies [1]. It has been suggested that a modular design, addressed in this paper, could offer solutions to issues with current ACC technologies. To fully characterise the modular ACC design it is necessary to quantify the steam-side characteristics. A series of tests were performed under vacuum conditions representative of an operational condenser. The condenser vacuum was measured for a series of incremental fan rotational speeds, to determine both the qualitative and quantitative relationship between fan speed and condenser pressure. Results indicate that for a given steam mass flow rate, the condenser pressure decreases with increasing fan rotational speed. Furthermore, the choice of vacuum pump, used to displace air leakages, was shown to have a significant influence on the steam-side response. Larger displacement-capacity vacuum pumps permit lower condenser pressures. The steam condensation pressure drop through the condenser tubes was also measured. Results for the measured pressure drop revealed a large level of momentum recovery, which is not uncommon in steam condensation processes. Experimental frictional pressure drops were determined and these compared favourably with certain two-phase frictional pressure drop correlations. In particular, the Lockhart & Martinelli correlation was found to be most capable of predicting the frictional pressure drop trends encountered during testing. The large level of agreement between the measurements and predictions provide confidence in future use of the Lockhart & Martinelli correlation to predict frictional pressure losses.

Limited water supplies in arid regions that have abundant solar resources eliminates the use of water as a feasible means of cooling condensers in a Concentrated Solar Power (CSP) plant condenser. This has triggered the need to optimise existing air-cooled condenser technology, which is currently extremely inefficient. This paper aims to investigate the influence of various fan parameters on the performance of a cross-flow heat exchanger. The study first focuses on the effect of varying the distance between the fan and the heat exchanger in order to establish if uniform airflow distributions can be achieved with acceptable axial spacing between the fan and the heat exchanger. This was achieved by mapping the velocity field at the outlet from the heat exchanger by means of a Particle Image Velocimetry (PIV) analysis. The analysis was carried out for two air flow scenarios; the fan mounted at the inlet to the heat exchanger (forced draught) and the fan mounted at the outlet of the heat exchanger (induced draught). An investigation into the effect of fan speed on velocity distribution was also carried out. The measurements which are presented show that uniform velocity distributions can be achieved with relatively small fan to heat exchanger spacing for the case of the induced draught, whilst for the forced draft, although increasing the fan to heat exchanger spacing resulted in increased flow uniformity, the flow was still highly non uniform at fan to heat exchanger spacing of up to 1.4 times the fan tip radius. The measurements also showed little effect of fan speed on normalised velocity distribution. Combining the fore mentioned measurements with an analytical calculation technique, the heat flux per unit area across the heat exchanger was calculated. The results highlight the limitations on heat transfer in various regions of the heat exchanger in both flow scenarios. These measurements and calculations will facilitate designers of air cooled heat exchangers in achieving the minimum fan to heat exchanger spacing which gives no further increase in total heat transfer.