Heat transfer processes in solar collectors

A New Low-Cost Plastic Solar Collector

“…The mean temperature in the grid collector is determined by the average between the inlet cold temperature ( ) and the exit ( ℎ ) hot temperature. Since the cooling flow is driven just by this temperature difference, Δ , it could easily rise to 40 ∘ C [10]. So, let us consider for illustrative purposes a standard collector in which = 10 ∘ C, = 30 ∘ C, and Δ = 40 ∘ C. Hence, ℎ = 70 ∘ C, and thus = 50 ∘ C, obtaining − = 40 ∘ C. On the other hand the mean temperature of the equivalent water pond is just 30 ∘ C since = ℎ = , and thus − = 20 ∘ C, half of the previous case.…”

“…Although this comparison can only be quantified by setting the right ( 0 , 1 ) parameters, it is clear that this trend will be greater for low-quality collectors (i.e., having higher 1 values) like the ones used in developing countries. Tables 1 and 2 show bibliographic values [10,11] of ( 0 , 1 ) for different collectors and water ponds, respectively, in which the efficiency is the merit figure.…”

The Vertical-Tube Solar Collector: A Low-Cost Design Suitable for Temperate High-Latitude Locations

“…On the other hand, a standard free-convection collector is driven by the buoyancy force caused by the temperature difference between both legs (cold and hot) of the cooling circuit, and ℎ , respectively, being = ( ℎ + )/2. Thus, a standard free-convection collector always works on a high ( ℎ − ) difference (typically around 40 ∘ C, [15][16][17][18]) that in turn implies that this collector works on a markedly higher than the storage tank or conversely having a lower efficiency than the previous design. For illustrating this key characteristic, let us consider a hose collector heated up to 30…”