in this thesis, first the notion of weak mutual associativity (w.m.a.) and the necessary and sufficient condition for a $(l,gamma)$-associated hypersemigroup $(h, ast)$ derived from some family of $lesssim$-preordered semigroups to be a hypergroup, are given. second, by proving the fact that the concrete categories, semihypergroups and hypergroups have not free objects we will introduce t...

In this study, thermal performance of the collector with analytic and quasi-dynamic method is evaluated based on energy balance equations for each part of the U-pipe evacuated tube solar collector. Using this approach, effect of different parameters such as tube size, overall heat loss coefficient, absorber tube absorptivity, mass flow rate and air layer thermal resistance on thermal performanc...