Performance of a Water-in-Glass Evacuated Tube Solar Water Heater

There has been wide scale adoption of evacuated tubular solar water heaters in China and Europe. The performance of the water-in-glass evacuated tube solar water heater that has been commercialised in China has been evaluated using the ISO9459-2 test procedure. Factors limiting the performance of this type of product have been evaluated. A numerical model of the heat transfer and fluid flow inside a water-in-glass tube has been developed to investigate the heatextraction efficiency and the flow structure inside the tube. Initial investigations have shown that the natural convection flow-rate in the tube is high and that the storage tank is forced into a fully mixed state by the high flow rate produced by the 21 tube solar collector.