Thermal mass flowmetering

Abstract

Metering and related control of fluid flow are achieved both accurately and at high response speed by way of a unique sequencing of thermal exchanges with the fluid under closely-regulated and inter-dependent thermal conditions. The flowing fluid is first conditioned by being raised to a temperature above its highest anticipated ambient, preferably by way of a temperature-sensitive electrical heater resistance which is part of an exceptional self-balancing bridge and control-loop network, and the conditioned fluid is then similarly increased to yet higher temperature, with measurements related to energy involved in producing the second temperature increase being used to characterize the flow. When the fluid is at the same time further conditioned immediately downstream by another similar heating arrangement which allows the fluid to cool to between temperatures developed by the earlier sequencing, the measurements are rendered more stable and can advantageously be made more linearly proportional to mass flow rate. Additional isolation from ambient temperature disturbances is promoted by controlling the environment within which the sequencing of thermal exchanges takes place, preferably by way of a heated enclosure in which electrical regulation of temperature is also swift and exact.