Heat Flux through Naturally Ventilated Building in Malaysian Climate

Roofs and walls are the main media for heat transfer for typical Malaysian buildings. In order to estimate the duration of uncomfortable periods, the environmental temperature of a building was determined over a period of time. A study of heat flux through a naturally ventilated was conducted by simulation. This study focused on heat transfer through the roof, ceiling and vertical walls. A Thermal Analysis Software was used for the modeling and analyses. A virtual test building model dimension 4m x 4m x 3m was created using conventional construction parameters for roof, ceiling, windows, door, walls and floor which meet the minimum requirement in Malaysian Standards. The results show that heat rate flux mostly peak at east wall before 12:00 hrs and west wall after 12:00 hrs. The heat rate flux through the roof is higher than that through the ceiling during daytime but lower at night as roof was the surface of most exposed to solar radiation. The proportion of heat through roof was 87% by radiation, 11% by convection and 2% by conduction. 97% of heat was transferred by radiation and 3% by conduction for ceiling and heat through wall was 88% by radiation, 8% by convection and 4% by conduction respectively.

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THE MECHANISM OF RAISING AND QUANTIFICATION OF SPECIFIC HEAT FLUX AT BOILING OF NANOFLUIDS IN FREE CONVECTION CONDITIONS

Energy Technologies & Resource Saving ◽

10.33070/etars.3.2017.03 ◽

2017 ◽

pp. 25-34

Author(s):

V.N. Moraru

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Capacity ◽

Specific Heat ◽

Chemical Properties ◽

Heating Surface ◽

Physical Models ◽

Superheated Liquid ◽

Two Phase ◽

Boiling Process

The results of our work and a number of foreign studies indicate that the sharp increase in the heat transfer parameters (specific heat flux q and heat transfer coefficient _) at the boiling of nanofluids as compared to the base liquid (water) is due not only and not so much to the increase of the thermal conductivity of the nanofluids, but an intensification of the boiling process caused by a change in the state of the heating surface, its topological and chemical properties (porosity, roughness, wettability). The latter leads to a change in the internal characteristics of the boiling process and the average temperature of the superheated liquid layer. This circumstance makes it possible, on the basis of physical models of the liquids boiling and taking into account the parameters of the surface state (temperature, pressure) and properties of the coolant (the density and heat capacity of the liquid, the specific heat of vaporization and the heat capacity of the vapor), and also the internal characteristics of the boiling of liquids, to calculate the value of specific heat flux q. In this paper, the difference in the mechanisms of heat transfer during the boiling of single-phase (water) and two-phase nanofluids has been studied and a quantitative estimate of the q values for the boiling of the nanofluid is carried out based on the internal characteristics of the boiling process. The satisfactory agreement of the calculated values with the experimental data is a confirmation that the key factor in the growth of the heat transfer intensity at the boiling of nanofluids is indeed a change in the nature and microrelief of the heating surface. Bibl. 20, Fig. 9, Tab. 2.

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