DESIGN OF A NEW MASS-FLOW SENSOR USING TH E PELTIER EFFECT

The present paper deals with design and realization of a new mass flow sensor using the Peltier effect. The sensor, shaped as a bimetallic p rinted circuit includes three continuous parallel strips coated with a great deal of metal plated spots. In such a device, the central track performs as a classical thermoelectrical circuitry whose both plated and uncoated parts provide the thermopile junctions. The two outer str ips are subjected to electrical currents so as to generate numerous sm all thermal gradients owing to the Peltier effect. Then, the resulting differences in temperature induce a Seebeck e.m.f. on to the close in ner strip acting as a receiver. The thermal coupling between transmitt ers and receiver tracks depends on any variation of the surrounding en vironment heat transfert coefficient. Therefore, such a device allows us to detect any shift in physical properties related to the apparent thermal conductivity. In the special case of a steady state fluid, the induced e.m.f. in the receiving track hinges on the thermal conductiv ity. When the fluid is in relative motion along the sensor, the veloci ty can be read out as a function of voltage. As an application, the th ermoelectric circuit is placed in a tube conducting a fluid flow, in o rder to design a new mass flowmeter. Experimental results show that wh en subjected to a steady mass flow rate the e.m.f. remains still, even though the pressure is allowed to vary through the pipe. Actually, th e supplied information depends only on the mass flow rate. The main ad vantage of this measurement method, when compared with classical hot w ire devices, is that any change in the surrounding environment average temperature does not induce any significant shift on the output volta ge. On the other hand, when operated in a wide temperature range, easy compensating techniques can be used to provide accurate and reliable performance over large temperature variations.