The investigation of natural convection in enclosures heated and cooled from walls

Improving thermal comfort and lowering energy consumption are the most significant concern fields of engineering carried out in buildings. Nowadays, in which efficient usage of energy increasingly gains importance, heating systems which use low temperature heating sources and natural convection problems that occur in enclosures have come forward. In this study, heating of living places by means of radiant heating panels from walls and the natural convection that occurs under this circumstance have been investigated and as result of the conducted experiments convection coefficients that occur in the rooms have been calculated. As heating and cooling source, one heater bath and a cooler bath have been utilized and also flow rates that pass through panels in hot and cold walls have been measured. T-type thermocouples were used to measure the surface and air temperatures. Furthermore, to investigate the natural convection behavior at different dimensions and heating conditions numerical studies have been implemented as well. For this purpose, different rooms were drawn in the program, Gambit. As in the experimental study, to create a real room situation, heating was implemented from one vertical wall, and cooling was implemented from the opposite wall of the room. The rooms have been divided into meshes and exported to CFD program, Fluent 6.3. Also, the results have been turned into independant from meshes. As holding room height same with the value at the experimental setup, at different values of floor dimensions Nusselt numbers and convective heat transfer coefficients were calculated via varying hot and cold wall temperatures. In addition, partial heat of the hot wall from floor level to different height values were simulated and results were scrutinized. From the obtained results, correlations that generalize the convective behavior in real-size rooms have been derived at various heating conditions and dimensions in which aspect ratio takes place as well. Also, deviations of produced correlations from real results were determined. Moreover, the convective heat transfer coefficient correlations which were derived experimentally and numerically have been compared with the correlations derived by other researchers and it has been seen that results were coherent with the literature. Also, temperature and velocity distribution that occur in the room were presented. From the figures that illustrate the temperature distribution, thermal stratification in the room has been observed and from the figures that illustrate velocity distribution in the room, it has been seen that air flows occur just at the sidewalls of the room. This demonstrates that when heating is realized by means of systems like radiant heating panels from walls, convection streams in the room decrease and thus convection coefficient decreases with respect to conventional heating systems as well.