Discharge Coefficient

The research objectives of this study are to develop and validate a detailed simulation model of a test cell which was used to measure heat balances for comfort evaluation. 

Accuracy in estimation of airflow through windows is the key parameter for modelling and designing of naturally ventilated buildings. The flow through windows is usually described by the orifice flow plate equation. This equation involves the discharge coefficient. In practice, often a constant value of discharge coefficient is used. The constant value of discharge coefficient leads to deceptive airflow estimation in the cases of centre-pivot roof windows. The object of this paper is to study and evaluate the discharge coefficient of the centre pivot roof window.

The objective of this paper is to present a new method for estimating effective flow areas not only in the external wall of a house but also in the internal walls between rooms using only one type of tracer gas. The discharge coefficient of each wall and the pressure in each room—which are unknown variables—are determined using nonlinear simultaneous equations, which consist of balance equations for the air mass and tracer-gas concentration in the rooms. To verify the validity of this method, we performed a numerical experiment.

This paper reviews the application of CFD for designing and parametric studies of wind-induced natural ventilation. The approaches employed in such applications of CFD are whole-domain and domain-decoupled CFD modelling. The domain-decoupled technique separately analyses the external airflow fields outside and internal flows inside a building. In the whole-domain approach, the outdoor and indoor airflow is modelled simultaneously and within the same computational domain.

The prediction of indoor airflow is indispensable in evaluating the thermal sensation of occupants in a cross-ventilated space because enhanced heat loss due to the elevated convective heat transfer in the occupied zone is an essential part of improving thermal comfort. A domain decomposition technique was developed to separate CFD for internal cross-ventilation flow from external flow outside buildings, and to predict indoor airflow with reasonable computational effort and sufficient accuracy.

Variation of discharge coefficients with wind direction and opening position is one of the main factorsdebasing accuracy of cross-ventilation flow rate prediction. The local dynamic similarity model wasdeveloped to solve this problem, and previous studies had validated it for inflow openings. In thepresent study, two experiments were carried out to investigate its validity for outflow openings.

In natural ventilation systems fresh air is often provided through opening of windows. However, the knowledge of the performance of windows is rather limited. Computation of natural ventilation air flow through windows is most commonly made using discharge coefficients, that are regarded as being constant. The reported results show that the discharge coefficient for a window opening cannot be regarded as a constant and that it varies considerably with the size of the opening area, the window type and the temperature difference.