One of the most effective and simplest methods to maintain thermal stratification
of solar hot water storage tanks during charge and discharge is the use of a rigid porous
manifold. The same manifold design can be employed within a novel liquid desiccant
solar thermal storage tank to prevent destruction of chemically stored energy during
charge and discharge. This type of manifold does not require any moving parts or special
materials and thus is particularly appealing for solar thermal storage systems. It has a
series of vertical hydraulic resistance elements placed within a perforated tube. At the
design operating conditions, the manifold ensures that fluid entering the tank is delivered
to the vertical position where it is the same density as the tank fluid. In the present study
the utility of a rigid porous manifold is assessed over a range of operating conditions in
both a solar hot water and liquid desiccant storage environment.
The primary result is the development of a simple relationship between a
dimensionless performance indicator and a second dimensionless parameter that
represents the operating condition. A simulation model is used to define this relationship
between the operating condition and manifold performance and is applicable to manifolds
operating in both hot water and liquid desiccant storage tanks. A plug flow tank model is
used to approximate transient tank stratification. Initial modeling suggests off-design
operation results in low levels of mixing. Finally, a manifold was built and tested within
a prototype liquid desiccant tank. Results show that the design returns low density fluid
through the bottom of the tank at a significantly reduced mixing rate compared to free
discharge. The same manifold design is able to return high density fluid with minimal
University of Minnesota M.S. thesis. July 2011. Major: Mechanical engineering. Advisor: Dr. Jane H. Davidson. 1 computer file (PDF); v, 73 pages, appendices A-D.
Analysis of the rigid porous manifold as an effevtive device to stratify solar thermal storage tanks..
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