Transient, time-dependent or unsteady laminar natural convection flows occur in many technological and
industrial applications such as in nuclear reactors, rapid cooling process, motion of fluid in computer equipments,
radiators, storage devices, cooling of electronic equipment inside computers, furnaces, the growth of crystals for
semiconductor industry etc.. In the natural convection process, the buoyancy forces appear due to density variation and
this can affect the heat transfer mechanism. Therefore, it is significant to understand the heat transfer characteristics of
natural convection in an enclosure or cavity. The transient response of a fluid towards the steady state via a transient
natural convection flow has been extensively examined in the literatures under a variety of theoretical, numerical,
experimental methods and boundary conditions. The idealized problem of steady laminar natural convection in an
enclosure with different boundary conditions has been extensively studied in various works. Recently, in many of the
fields of application listed above, the convective flows may be in a transient or unsteady state in an enclosure.
Recognizing this fact, much attention has been focused to study the nature of the flow in the transient regime and the
manner in which this flow evolves into the final steady state. To author s knowledge, no review paper has been
published in the literature up to date related with transient laminar natural convection flows. For this reason, this paper
is devoted to help the researches to summarize most published papers in the transient laminar natural convection flows
in enclosures and gives them an excellent overview to develop and extend these published papers. We think that this
review paper is very necessary to the heat transfer community. The reviewed papers are grouped into various categories
in order to be useful for both researches and readers and arranged in each category according to the time of publication
to give a coherent overview about the research development in each specific category.