Modeling of the Mutual Placement of Thermoanemometer Sensors on a Flat Surface of an Air Flow

A functional model of a thermoanemometer measuring the air flow velocity on a flat wall surface of the flow has been developed. From the heat balance equation of the sensing elements in the thermoanemometer, a dependence has been derived for determining the heating temperature of the sensing elements. The distribution of the temperature field in the boundary layer was modeled by analogy with the velocity distribution, following a cubic dependence. The distribution of the temperature field on a flat wall surface of the flow from the heating of the sensing elements was obtained analytically by solving the heat conduction equation in the direction of the coordinate of the air flow velocity vector for the boundary conditions of the II as well as II and III kinds. The developed mathematical dependencies enable both the modeling of the distribution of temperature fields in the sensing elements and justifying the distance between them. The reliability of measurements of the air flow velocity on the wall surface of the flow depends on the impossibility of influencing the temperature of one sensing element of the sensor on the temperature of the other. The task of justifying the distance between the sensing elements of the sensor, which are located in the direction of the air flow velocity vector, aims to prevent the interaction of the temperature fields of the elements with each other. The boundary condition is that at the boundary of separation between the temperature fields of the sensing elements, there is a temperature that is 5 to 10% lower than the temperature of the colder sensing element. The ratio of the resistances of the sensing elements is 4/1. The power released by the first sensing element of the sensor, aligned along the air flow velocity vector, is 4 times lower than the heating power of the second sensing element of the sensor. The modeling was carried out at an air flow velocity within 30 and 330 m·s−1. The values of the distances between the sensing elements of the thermal anemometer vary with the supply voltage. The material of the sensing elements is nickel. The contact area of the surface of the sensing elements was 214.337 mm2.