**3.3 Irregular geometries**

A variety of papers covering numerous geometries have been taken into consideration in this section. Narrow-spaced fuel element configuration in multichannel was modeled numerically [39]. Rhombus and ellipse shape ducts were studied using Galerkin integral method [40, 41]. The heat transfer in a pin fin at the end of the wall was investigated [42]. The heat transfer in a milliscale thrust nozzle was studied numerically [43]. Viscous flow convections and heat transfer were studied in corrugated ducts [44]. For square ducts a combined study was undertaken to understand the thermal characteristics in different shapes [45]. Experimental study was done with regard to two-pass internal coolant passages in gas turbines [46]. An increase in heat transfer due to rolling and pitching action in swirling ducts was found experimentally [47]. Flow and heat transfer for metal honeycomb geometry was inspected [48]. The effect of viscous forced convection in branching ducts was studied [49].
