Monolithic flow sensor for measuring millilitre per minute liquid flow

Micro-liquid flow sensor

“…Recently there 1s a growmg interest m the research on micro-liquid handhng systems [l] One of the basic components m hqmd handling systems 1s the mlcrohqmd flow sensor Liquid flow sensors described m the literature make use of the 'time-of-flight' flow-sensing technique [ 2,3] Other nucromachmed flow sensors which are reahsed m or close to the flow channel are designed for sensing gas flow [4-61 They make use of a heater the temperature of wtuch 1s a function of the heat carried away by the medmm Other flmd-sensmg techniques are described m ref 7 The dlsslpatlon m the heater causes a temperature dlstrlbutlon m the flow channel, which 1s modulated by the medium Flow sensors, which make use of more than one temperature sensor to get a signal, that IS related to the flow, are deslgned to sense the flow of gaseous media [S, 8,9] For an optnnal design one can make use of a numerical approach [lo] For a good understandmg and for obtammg design rules it 1s advantageous to derive an analytical model Figure 1 illustrates the pnnciple of the flow sensor Three resistors are located m the middle of the flow channel Heat is dissipated m the rmddle resistor called the heater (H) The resultmg temperature dlstrlbutlon 1s sensed with two temperature sensitive resistors T, and T, symmetncally located near the heater One reslstor 1s located upstream relative to the heater and one resistor is located downstream The heater as well as the sensing resistors are located on supporting beams which cross the flow channel in the x-y plane (see Figs 7 and 8) 0924-4247/93/$6 00 Rg I The flow IS measured by Its mfluence on the temperature dlstnbutlon m the sensor resulting from heat generation m the heater H T, (upstream) and T, (downstream) are temperature sensors At zero flow rate, no convection exists m the flow channel, and the heat generated by the heater will be transferred only by the axial and tangential diffusion through the fluid and by the conduction through the heater and sensor support to the flow channel walls A simple model for the conduction m the z-y plane perpendicular to the flow channel axis is based on lumped elements for the thermal conductlvlty present (see Fig 2) The heat is homogeneously dlsslpated along the resistor m the y dlrectlon The conduction m the beam 1s modelled wth Gb and that m the flmd with Gr If we model the channel cross section \lirlth n lumped elements (m the beam), the &fferent lumped element values are gven m the followmg equations…”

Miniature Liquid Flow Sensor and Feedback Control of Electroosmotic and Pneumatic Flows for a Micro Gas Analysis System

“…Thermal sensors made using silicon chip technologies for continuous measurement have been previously reported. [9][10][11] However, their measurable ranges are milliliters per minute and therefore are not suitable for micro chemical analysis devices. Also, further the heating sensor may induce the generation of bubbles, which would seriously interfere with the analytical signals.…”

Optimization of a thermal flow sensor for acoustic particle velocity measurements

“…The amplitude of the particle velocity (the instantaneous flow) of the acoustic wave depends on fluid parameters such as the density and is thus temperature dependent, so that it cannot be considered to be constant along the channel. For a harmonically varying wave in the channel with a velocity corresponding to an acoustic pressure at room temperature , one can write in good approximation (12) with the acoustic impedance at room temperature ( at ). For the latter relation between velocity and pressure, the "free field" condition was assumed to be fulfilled.…”

“…The Microflown is also used as an add-on microphone for professional recording purposes [10]. The advantage of the sensor, contrary to pressure gradient microphones, is its comparatively high sensitivity to low-frequency sound waves; it can thus be used as well for the measurement of dc flows [11], and can be applied as a mass flow sensor [12]- [14].…”