CONCEPT OF POROUS WIRE ANEMOMETER

The paper presents a new scheme of the anemometer [1] sensing element for the gas mean and fluctuation velocity measurement. The sensing ele ment is a porous tube with gas suction through porous tube wall. The o utside surface of the porous tube is at the gas temperature. The analy sis, based on the heat balance at steady and unsteady state is perform ed in order to define the sensitivity and time constant of the porous sensing element. Two cases are considered, namely, the constant curren t and constant temperature anemometer. Comparison is made with the sol id wire anemometer and shown that the proposed porous sensing element can have sensitivity four time higher than the standard hot wire anemo meter with the same geometrical dimensions. With the respective select ion of the physical properties of the sensing element, it could be pos sible to obtain higher frequency range of the measurement. Particular attention is devoted to the low gas velocity measurement. It is recogn ised [2] that the minimum gas velocity to be measured with the solid h ot wire anemometer is determined by the local heat transfer coefficien t. For the low gas velocity,it was proved that the minimum is around . 20 cm/sec [3]. The proposed concept of the sensing element can be used for the very low velocity measurement due to the higher sensitivity o btained by the porous sensing element. Copyright (C) 1997 Elsevier Sci ence Ltd.