Comparative study of thermal efficiency of flat spiral vs. conical spiral in a parabolic solar collector

Compare the thermal efficiency of two kind of heat by radiant energy concentrated by a parabolic solar collector. Methodology: became two spirals with 1.3 m length and diameter 3/8” copper pipe, which were controlled water flow from one step and recirculated making temperature measurements to water in container return and readings taken every 5 minutes. These coils were placed at the focal point of a parabolic solar collector of 77 cm in diameter and concavity of 6.6 cm. both proved to be very efficient in heat absorption and transmission to the water into itself, which showed greater heat loss but was the conical, although it wasn't exposed to air currents and that it had an aluminum housing. Meanwhile the flat spiral showed greater uniformity in the behavior of temperatures despite being exposed to air currents.The maximum temperature reached, at a flow rate of 0.15 l/min, was 97.5 ° C in 30 minutes from the initial temperature. Lower flows did not allow to make a reliable temperature reading since the water was going into its vapor phase.