Employing wavy structure to enhance thermal efficiency of spiral-coil utilized in solar ponds

Heat extraction is the main motivation in the design and fabrication of solar ponds. It is usually performed by using internal and external techniques. A heat transfer media is circulated through an internal heat exchanger located in hot zones and absorbed the heat. Then, the extracted heat is removed using an external heat exchanger. Spiral-coils can be utilized as core in these heat exchange systems. In this study, a passive technique is proposed to enhance the thermal efficiency of the spiral-coils thereby improving the performance of solar ponds. Wavy structure is introduced on side walls of spiral-coils for the first time, and six different enhanced models are created. The effects of the proposed technique on augmentations of both the heat extraction and the pumping power are examined. It is found the waving the side walls can noticeably enhance the heat extracted by the spiral-coils with a certain penalty in the pumping power. At the certain geometrical parameters, the heat extraction enhancements are in the range of 2.8-37.6%. Further, the simultaneous waving of both the upper and the lower side walls leads to the best overall hydrothermal performance. The results also show that increasing the wave-amplitude (a) and coil-diameters (d(i)-d(o)) enhances the heat extraction up to 58.5%, however, the best performance is achieved for the model with higher wave-amplitude and lower coil-diameters. At the range studied, the maximum performance index of 1.66 is obtained for the case of upper-lower with a = 2.4 mm and d(i)-d(o) = 50-70 mm.