Measurement Method for the Effective Area using an Isothermal Chamber.

The flow characteristics of valves and restrictions are often represented by the effective area. The effective area is often measured using a method defined in the ISO standards. The method is to measure the flow rate and differential pressure between the tested valve. Therefore, the accuracy of the method depends to a great extent on the accuracy of the flow meter.On the other hand, a more simplified method to measure the effective area is defined in the JIS standards. This method discharges air from the chamber through the tested valve, and the effective area is measured indirectly from the pressure response of the air in th chamber. The method calculates the effective area, assuming the adiabatic conditions during discharge. Though, even in-a sudden discharge, the heat is transferred into the chamber. Therefore, this causes a measurement error.In this study, the relation between the temperature change of the air and the measurement error of the JIS method owing to the chamber volume and the length of the pipeline are examined. Then, it became clear that by stuffing the steel wool into the chamber, the transfer area and heat transfer coefficient could be made larger and an isothermal condition could almost be realized. This chamber is called an “Isothermal chamber”. The method to measure the effective area has been proposed using an isothermal chamber. The proposed method can lessen the measurement error as a result of the chamber volume and length of the pipeline compared with the JIS method.