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A fluid system installed on a vehicle and a method for assessing a property of a fluid flowing in the fluid system. The fluid system and method entail flowing at least a portion of the fluid through a passage within a freestanding portion of a micromachined tube supported above a substrate so as to

A fluid system installed on a vehicle and a method for assessing a property of a fluid flowing in the fluid system. The fluid system and method entail flowing at least a portion of the fluid through a passage within a freestanding portion of a micromachined tube supported above a substrate so as to define a gap therebetween, vibrating the freestanding portion of the micromachined tube at a resonant frequency thereof, sensing the movement of the freestanding portion of the micromachined tube so as to measure at least one of the vibration frequency and deflection of the freestanding portion relative to the substrate and produce therefrom at least one output corresponding to at least one of the mass flow rate, specific gravity, and density of the portion of the fluid flowing through the passage, and then using the output to compute the property of the fluid.

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The invention claimed is: 1. A method of assessing a property of a fluid flowing in a fluid system installed on a vehicle, the method comprising the steps of: flowing at least a portion of the fluid through a passage within a freestanding portion of a micromachined tube supported above a substrate

The invention claimed is: 1. A method of assessing a property of a fluid flowing in a fluid system installed on a vehicle, the method comprising the steps of: flowing at least a portion of the fluid through a passage within a freestanding portion of a micromachined tube supported above a substrate so as to define a gap therebetween; vibrating the freestanding portion of the micromachined tube at a resonant frequency thereof; sensing the movement of the freestanding portion of the micromachined tube so as to measure at least one of the vibration frequency and deflection of the freestanding portion relative to the substrate and produce therefrom at least one output corresponding to at least one of the mass flow rate, specific gravity, and density of the portion of the fluid flowing through the passage; using the output to compute the property of the fluid; and then modifying at least one of the fluid system and the vehicle based on the computed property of the fluid. 2. The method according to claim 1, wherein the output corresponds to the density of the fluid, and the output is used to compute relative concentrations of at least two constituents of the fluid. 3. The method according to claim 2, wherein the fluid system is a fuel system of the vehicle and the fluid is a fuel mixture comprising the at least two constituents. 4. The method according to claim 3, wherein the fuel system is a fuel cell system of the vehicle, the fluid mixture is a fuel cell solution, and the computed property of the fluid is used to modify the performance of the fuel cell system. 5. The method according to claim 4, wherein the at least two constituents comprise water and a fuel chosen from the group consisting of methanol, ethanol, ethylene glycol, isopropyl alcohol, formic acid, sulfuric acid, gasoline, and organic liquids. 6. The method according to claim 3, wherein the fuel system delivers the fuel mixture to an engine of the vehicle, the at least two constituents comprise gasoline and a fuel chosen from the group consisting of methanol and ethanol, and the computed property of the fluid is used to modify the performance of the engine. 7. The method according to claim 1, wherein the fluid is a liquid, the output corresponds to the density of the liquid, and the output is used to determine the presence of gas bubbles in the liquid. 8. The method according to claim 1, wherein the output corresponds to the density of the fluid, and the output is used to determine the presence of solid particles in the fluid. 9. The method according to claim 1, wherein the fluid system is an engine air intake system of the vehicle, the fluid is an air mixture comprising at least two constituents, and the output is used to compute at least one of the volumetric flow rate and mass flow rate of the air mixture and the relative concentrations of the constituents of the air mixture. 10. The method according to claim 1, wherein the fluid system is an engine oil system of the vehicle, the fluid is a lubricating oil comprising at least two constituents, and the output is used to compute at least one of the volumetric flow rate and mass flow rate of the lubricating oil and the relative concentrations of the constituents of the lubricating oil. 11. The method according to claim 1, wherein the fluid system is a transmission system of the vehicle, the fluid is a transmission fluid comprising at least two constituents, and the output is used to compute at least one of the volumetric flow rate and mass flow rate of the transmission fluid and the relative concentrations of the constituents of the transmission fluid. 12. The method according to claim 1, wherein the fluid system is a braking system of the vehicle, the fluid is a braking fluid comprising at least two constituents, and the output is used to compute at least one of the volumetric flow rate and mass flow rate of the braking fluid and the relative concentrations of the constituents of the braking fluid. 13. The method according to claim 1, wherein the fluid system is a cooling system of the vehicle, the fluid is a coolant fluid comprising at least two constituents, and the output is used to compute at least one of the volumetric flow rate and mass flow rate of the coolant fluid and the relative concentrations of the constituents of the coolant fluid. 14. The method according to claim 1, wherein the fluid system is an exhaust system of the vehicle, the fluid is an exhaust gas comprising at least two constituents, and the output is used to compute at least one of the volumetric flow rate and mass flow rate of the exhaust gas and the relative concentrations of the constituents of the exhaust gas. 15. The method according to claim 1, wherein the fluid system is a window washing system of the vehicle, the fluid is a window washing fluid comprising at least two constituents, and the output is used to compute at least one of the volumetric flow rate and mass flow rate of the window washing fluid and the relative concentrations of the constituents of the window washing fluid. 16. The method according to claim 1, further comprising the step of sensing the temperature of the portion of the fluid flowing through the passage. 17. The method according to claim 1, further comprising the step of sensing the pressure of the portion of the fluid flowing through the passage. 18. A method according to claim 1, further comprising the step of flowing a second portion of the fluid through a bypass passage in fluidic parallel to the passage within the freestanding portion, wherein the second portion has a greater volumetric flow rate than the portion of the fluid flowing through the passage within the freestanding portion. 19. The method according to claim 1, wherein the vehicle is chosen from the group consisting of land-based, aerospace, and aquatic-based vehicles. 20. A fluid system installed on a vehicle, the fluid system comprising: means for flowing at least a portion of the fluid through a passage within a freestanding portion of a micromachined tube supported above a substrate so as to define a gap therebetween; means for vibrating the freestanding portion of the micromachined tube at a resonant frequency thereof; means for sensing the movement of the freestanding portion of the micromachined tube so as to measure at least one of the vibration frequency and deflection of the freestanding portion relative to the substrate and produce therefrom at least one output corresponding to at least one of the mass flow rate, specific gravity, and density of the portion of the fluid flowing through the passage; means for using the output to compute the property of the fluid; and means for modifying at least one of the fluid system and the vehicle based on the computed property of the fluid. 21. The fluid system according to claim 20, wherein the output corresponds to the density of the fluid, and the using means computes relative concentrations of at least two constituents of the fluid. 22. The fluid system according to claim 21, wherein the fluid system is a fuel system of the vehicle and the fluid is a fuel mixture comprising the at least two constituents. 23. The fluid system according to claim 22, wherein the fuel system is a fuel cell system of the vehicle and the fluid mixture is a fuel cell solution, and the fuel system further comprises means for modifying the performance of the fuel cell system using the computed property of the fluid. 24. The fluid system according to claim 23, wherein the at least two constituents comprise water and a fuel chosen from the group consisting of methanol, ethanol, ethylene glycol, isopropyl alcohol, formic acid, sulfuric acid, gasoline, and organic liquids. 25. The fluid system according to claim 22, wherein the fuel system delivers the fuel mixture to an engine of the vehicle, the at least two constituents comprise gasoline and a fuel chosen from the group consisting of methanol and ethanol, and the fuel system further comprises means for modifying the performance of the engine using the computed property of the fluid. 26. The fluid system according to claim 20 wherein the fluid is a liquid, the output corresponds to the density of the liquid, and the using means determines the presence of gas bubbles in the liquid. 27. The fluid system according to claim 20, wherein the output corresponds to the density of the fluid, and the using means determines the presence of solid particles in the fluid. 28. The fluid system according to claim 20, wherein the fluid system is an engine air intake system of the vehicle, the fluid is an air mixture comprising at least two constituents, and the using means computes at least one of the volumetric flow rate and mass flow rate of the air mixture and the relative concentrations of the constituents of the air mixture. 29. The fluid system according to claim 20, wherein the fluid system is an engine oil system of the vehicle, the fluid is a lubricating oil comprising at least two constituents, and the using means computes at least one of the volumetric flow rate and mass flow rate of the lubricating oil and the relative concentrations of the constituents of the lubricating oil. 30. The fluid system according to claim 20, wherein the fluid system is a transmission system of the vehicle, the fluid is a transmission fluid comprising at least two constituents, and the using means computes at least one of the volumetric flow rate and mass flow rate of the transmission fluid and the relative concentrations of the constituents of the transmission fluid. 31. The fluid system according to claim 20, wherein the fluid system is a braking system of the vehicle, the fluid is a braking fluid comprising at least two constituents, and the using means computes at least one of the volumetric flow rate and mass flow rate of the braking fluid and the relative concentrations of the constituents of the braking fluid. 32. The fluid system according to claim 20, wherein the fluid system is a cooling system of the vehicle, the fluid is a coolant fluid comprising at least two constituents, and the using means computes at least one of the volumetric flow rate and mass flow rate of the coolant fluid and the relative concentrations of the constituents of the coolant fluid. 33. The fluid system according to claim 20, wherein the fluid system is an exhaust system of the vehicle, the fluid is an exhaust gas comprising at least two constituents, and the using means computes at least one of the volumetric flow rate and mass flow rate of the exhaust gas and the relative concentrations of the constituents of the exhaust gas. 34. The fluid system according to claim 20, wherein the fluid system is a window washing system of the vehicle, the fluid is a window washing fluid comprising at least two constituents, and the using means computes at least one of the volumetric flow rate and mass flow rate of the window washing fluid and the relative concentrations of the constituents of the window washing fluid. 35. The fluid system according to claim 20, further comprising means for sensing the temperature of the portion of the fluid flowing through the passage. 36. The fluid system according to claim 20, further comprising means for sensing the pressure of the portion of the fluid flowing through the passage. 37. A fluid system according to claim 20, further comprising means for flowing a second portion of the fluid through a bypass passage in fluidic parallel to the passage within the freestanding portion, wherein the second portion has a greater volumetric flow rate than the portion of the fluid flowing through the passage within the freestanding portion. 38. The fluid system according to claim 20, wherein the vehicle is chosen from the group consisting of land-based, aerospace, and aquatic-based vehicles.