الفهرس 
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Abstract
This research work was directed to study the heat transfer through enclosures, or hollow blocks, with different boundary conditions. The homogeneous material was taken into consideration in order to show the difference in temperature distribution between the homogeneous material and enclosures. Hollow blocks are used for construction purposes.
Heat transfer through enclosures has had very limited previous studies . Previous work dealt with the effects of wall conductance on natural convection through the cavity. The explicit method was used through the wall, while the implicit method was used through the cavity.
The present research work deals with the heat transfer through horizontal enclosures heated from the top nd cooled at the bottom , with the vertical sides insulated. Dimensionless equations were established in that position . The explicit method was used through each wall and cavity of the enclosure. More than one value of convergence criterion and Biot number appeared in the present work.
Effects of the ratio of thermal conductivities of the solid and air and the void fraction on the rate of heat transfer were studied . Transient conduction was considered in the present study.
The hollow blocks in ceilings are exposed to solar radiation and room temperature, these were taken as boundary conditions. Energy equations at the top and bottom surfaces were established to predict temperature distributions at the two surfaces.
Numerical examples were considered . The two-dimensional enclosure is composed of two parts, solid and cavity. A solid slb was added on the upper surface of the enclosure. The present study included the enclosure with and without solid slab or plate which was added on that surface.
The energy equation was used for the homogeneous material. Also, energy equations were used at the solid wall, cavity, interfaces and reentrant corners when heat was transferred through the enclosure by condition. The mass and momentum equations, besides energy equations at the above positions, were used when the heat was transferred by conduction and convection.
The local Nusselt number at the four interfaces was represented graphically. Most of the cases studied were compared with each other, and compared also with previous work.
At two different climatic conditions at Cairo , the sol-air temperature was graphically represented , and the temperature distribution through each of the homogeneous sold and the enclosure were also graphically represented at certain time.