ABSTRACT
This paper describes the design, development and testing of a new design of heat exchanger for use in smaller low-flow solar heating systems. We call it a Spiral Small Tube (SST) heat exchanger. The SST can be mounted either inside or outside the tank. It is designed for forced convection on the primary (collector) side and natural convection on the secondary (tank) side. The design is described along with its advantages and disadvantages. It is also compared with other, more common, designs.
Development work has concentrated on the design concept and optimising of the geometry to produce the best results for a given specification. This specification is for low-flow (1–1.5 1/min) on the primary side, natural convection on the secondary side (with pressure drop < 100 Pa), and low material usage (< 3 kg copper tubing) with the goal of a heat transfer capacity of 750 W/K.
Several prototypes have been built and tested. Results from these tests are presented and are compared with theoretical calculations. Other heat exchangers have also been tested. These were units that the manufacturers thought would work well for the specified conditions. The results show that the SST prototypes performed much better than the other heat exchangers tested in low-flow applications.
