Abstract
Flow maldistribution represents a problem of particular interest in the engineering field for several thermal systems. In flat plate solar collectors, the thermal efficiency strongly depends on the flow distribution through the riser tubes, where a uniform distribution causes a uniform temperature distribution and therefore a higher efficiency. In this work, a Computational Fluid Dynamics (CFD) numerical analysis has been carried out using the commercial software FLUENT®, in order to determine the flow distribution, pressure drop and hence the thermal efficiency of a solar collector with distribution flow plates inside the manifolds. The obtained numerical solution for this type of thermal systems has been validated with experimental results available in literature for laminar and turbulent flow. Four distribution plate configurations were analyzed. Results show that using two distribution plates in each of both manifolds improves the flow uniformity up to 40% under the same operating conditions when distribution plates are not used. Besides, it is shown that there exists an increase in the overall pressure drop which is practically negligible for the tilt angles commonly employed in the installation of flat plate solar collectors in Mexico. The use of closed end distribution plates on the dividing and combining manifolds allows the thermal efficiency to become close to the ideal thermal efficiency which is obtained with a uniform flow distribution.
Highlights
A fundamental problem of particular interest to engineering is flow maldistribution, which is the non-uniform distribution of flow in a system or device in some industrial applications
The aim of this work consists on improving the flow distribution by using division plates in the manifolds of a flat plate solar collector in order to increase the thermal efficiency
A numerical analysis on the flow distribution and overall pressure drop has been performed for a flat plate solar collector in which the use of distribution plates was considered inside the manifolds
Summary
A fundamental problem of particular interest to engineering is flow maldistribution, which is the non-uniform distribution of flow in a system or device in some industrial applications. Dunkle and Davey [13] performed experimental analysis on the non-uniform flow distribution, demonstrating that unlike systems with natural circulation, this condition presents a stronger effect on forced circulation systems Their results show that there exist temperature differences up to 22 ◦ C from the center to the end sides of a bank of twelve collectors connected in parallel. Datta and Majumbdar [16] showed that for a U type configuration (Figure 1a) the larger amount of flow is present in the first riser tubes This behavior is attributed to pressure distribution through the manifolds; in the Z type, pressure increases along the dividing manifold and decreases along the combining manifold, which produce lower pressure drop in the risers close to the inlet, and higher pressure drop in the risers close to outlet. The development of a model with good accuracy for the prediction of the flow distribution is necessary for a complete characterization of a solar collector
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