Thermoelectric Flow Sensors

Thermocapacitive Flow Sensor Thermoelectric Flow Sensors... 

Thermoelectric flow sensors indirectly measure the velocity of gases and liquids close to the wall and the volume flow rate in a microchannel. Electrical heating, thermoelectric temperature sensing, appropriate cahbration, and sensor control are essential for fast, reliable, and sensitive measurement. 

The flow sensor consists mainly of the heating element and temperature sensors, which measure the temperature of the heater or of the fluid before and after the heater. The streaming fluid is mainly heated by resistance heaters. The temperature can be measured either by electrical resistance sensors or by thermocouples. This essay concentrates on the latter method for thermoelectric flow sensors. 

Thermoelectric temperature measurement has been established for more than a century, and the sensing devices, including thermocouples, have been miniaturized from the start. Van Herwaarden and Sarro [1] presented thermoelectric flow sensors, which were then adopted in the textbook by Middelhoek and Audet [2]. The basic measuring principle was not changed but was modified and improved by the choice of different materials, geometry, and device design. 

Thermoelectric Flow Sensors, Fig. 1 Setup of a thermoelectric flow sensor in a channel consisting of a heater and two tcanpcaatnre sensors upstream and downstream of the healer, method A top crmductive heat transfer with symmetric tcanperatnre profile bottom ctmvective heat transfer with highCT tcanperatnre at scarsm 2... 

Thermoelectric Flow Sensors, Fig. 2 Thermoelectric flow sensor consisting of an electrical heater on a thin membrane with parallel meandering thermoelectric sensors, two thermopiles with 15 thermoelements [4]... 

Thermoelectric Flow Sensors, Fig. 3 Two-axis flow measurement from convective cooling of the sensor device with connected temperature sensors and direct heating of the membrane, acc. to van Oudheusden [7]... 

A summary of the common standardized thermocouples is given in Table 1. Besides the thermoelectric properties of the Seebeck coefficient, the thermal and electrical conductivities are important for the sensitivity and time response of the thermoelectric flow sensor. 

Thermoelectric Flow Sensors, Table 1 Choice of commercially available thermocouples for temperature measurement aC 584-1)... 

Thermoelectric Flow Sensors, Table 7 Overview of existing thermoelectric flow sensor devices [16]... 

The electrical insulation of the heater and the sensors is not critical when designing gas flow sensors, but has to be considered for liquid flows. In many cases, insulating layers, such as metals oxide or polymer Aims, are deposited on the surface of the electrical conducting layers. Many thermoelectric flow sensor devices have... 

Buchner R, Froehner K, Sosna C, Benecke W, Lang W (2008) Toward flexible thermoelectric flow sensors a new technological approach. J MEMS 17 1114-1119... 

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