The heat transfer from window affects indoor environment. It is important to evaluate the characteristics. In the case of window with shading devices such as screens, curtains, and Venetian blinds, thermal properties are affected by ventilation between the cavity, which is formed between the glazing surface and the shading device, and the room.
There are many studies about the heat transfer from the window with internal blinds. In some previous studies the calculation model is presented based on the assumption that the ventilation was occurred by the stack effect depending on thermally-driven pressure. However, the model could not describe well our previous experiment results probably because the shape of blinds effects the airflow and thermal properties. There are also the studies on predicting the convective heat transfer coefficient from the viewpoint of temperature difference between the glazing surface or the blinds surface and air by experimental and numerical study. However, these research has focused mainly on the window which has a relatively narrow cavity.
To reveal the airflow and thermal properties of the window which has a relatively wide cavity, we conducted Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD) analysis. The analyses were made with the window with internal blinds of which cavity was 130mm width and in a total of 24 cases (3 slat angle of Venetian blinds and 8 patterns of temperature condition). The experimental apparatus consists of a glass pane, a Venetian blinds and an aluminum panel. The glass and blinds were heated by energization to simulate absorption of solar radiation and the aluminum panel was heated or cooled by a chilling unit. CFD modelling was made to reproduce the experimental setup. Results are given in the form of airflow velocity, airflow rate, and convective heat transfer. Comparison of PIV and CFD results shows the following:
1) The airflow vector map from CFD results were in almost good agreement with PIV. The CFD model described here could be used for predicting the airflow properties of the window with relatively wide cavity. In CFD, the airflow snaking through the blinds slats was observed.
2) The larger the temperature difference between the glass or the blinds and the cavity, the larger the airflow velocity, airflow rate, and convective heat transfer. For the maximum vertical airflow velocity of the cavity, CFD results were slightly larger than those of experiment. However, the thickness of velocity boundary layer in experiment is larger than CFD, which indicates that diffusivity is higher in the experiments. Consequently, the airflow rate in CFD was slightly smaller than those in experiment.
3) Blinds slat angle does not significantly affect the velocity, airflow rate and convective heat transfer both in experiment and CFD.
