In this subsection, the flow distribution through an absorber is analysed. The absorber has 327 riser tubs with a diameter of 6 mm and a length of 1m which are connected to two manifolds with a diameter of фм. The riser tubs are mounted with no separation (no fins) between them. Therefore, the width of the absorber is in the range of 2 m. The risers will be numbered from 1 upwards, where the riser 1 is the one next to the inlet. The absorber has a z-configuration: the water enters the absorber through one ending of the inlet-manifold and is distributed through the different risers; after passing through the risers, water is collected in the outlet-manifold, and exists the absorber from the ending closer to the riser number 327. Investigated is the flow distribution in the risers for different diameters of the manifold, фм, and for two different total mass flow rate through the whole absorber: 25 l/hrn2 and 50 , using water as thermal fluid. Results are shown in figure 2. Given are the mass flow rates through each riser і, йц. These values are normalised by the ideal flow rate m0 which will result from a uniform distribution of the fluid flow through the riser, i. e fn0 = m/n, where n is the number of riser tubs.

iii= 25 1/hm2 m= 50 1/hm2

Figure 2: Numerical results with the intermediate model: flow distribution through a absorber with a z-conflguration, with two manifolds of a diameter of and 327 riser tubs (riser 1 = riser next to the inlet). Given is the mass flow rate through each riser i, , normalised by tha mass flow rate for a uniform distribution of the flow, . Two different total mass

flow rates, m, are analysed: a) m = 25 l/hrn2; b) .

Studies like this are of major importance in order to assure an appropriate flow distribution through the absorbers in order to obtain best thermal performance of the collector, [20].