Thermal performance of annulus with its applications; A review

In addition, this study specifies the weakness points and the gap in this area of research which have not been investigated yet. These uninvestigated areas in annuli are still need more attentions investigations efforts from the researchers in order to get the optimum design for the annuli in different applications. Therefore, this article provides recommendations and hot topics require further investigational efforts to fulfill these gaps for more energy consumption and environment saving.