Apparatus for measuring the flow rate and/or viscous characteristics of fluids

Apparatus for measuring the flow rate and/or the viscous characteristics of a fluid, comprising:

• a. a casing having a plurality of substantially identical fluid passages, a fluid inlet cavity for connection to a source of pressurized fluid and forming a substantially unobstructed flow path for fluid to the whole area of the inlet end of each fluid passage, normal to the direction for flow of fluid in the fluid passage, and a fluid outlet cavity for the escape of fluid from the casing and forming a substantially unobstructed flow path for each fluid passage,
• b. fluid pressure detecting means in the casing for detecting a fluid pressure differential between spaced positions in at least one of the fluid passages in the direction for flow of fluid therein, and
• c. fluid pressure indicating means, connected to the fluid pressure detecting means, from which the fluid pressure differential in at least the said one of the fluid passages can be deduced, and wherein,
• d. the ratio of the mean breadth to the mean width of each fluid passage area, normal to the direction for flow of fluid therein, is at least ten to one for at least the portion of the fluid passages which extends between the said spaced positions,
• e. the area of each fluid passage, normal to the direction for flow of fluid in the fluid passage, and for at least the same portion of each fluid passage as that which extends between the said positions, continuously reduces in size in the direction for flow of the fluid such that laminar flow will be maintained of the fluid flowing in each fluid passage, and each fluid passage is such that when using substantially pure water at 70.degree.F as a standard, and
• i. the static pressure differential a at said spaced locations is dependant upon the mass flow rate G of the substantially pure water through the fluid passage and satisifies the relationship in consistent units:
• .DELTA.p = K.sub.1 (G).sup.2 + K.sub.2 (G),
• and
• ii. the total pressure differential at said spaced locations is linearily dependant upon the mass flow rate G of the substantially pure water in the fluid passage, and
• the above pressure differential relationships for static and total pressure differential (.DELTA.p and .DELTA.P respectively) are over a range of flow rates for the substantially pure water for which the difference between the maximum Reynolds numbers in the fluid passage between the said spaced positions therein is within the range 0 and 8000, where the Reynolds number R.sub.e is defined, in consistent units, by:
• R.sub.e = h.rho.U/.mu.,
• where
• h = the mean width of the fluid passage at the position between the said spaced positions for which the Reynolds number is a maximum,
• .rho. = the fluid density of the substantially pure water,
• U = the mean velocity of the substantially pure water at the position between the said spaced positions for which the Reynolds number is a maximum,
• .mu. = the absolute viscosity of the substantially pure water,
• and where in the case of static pressure differential the ratio
• K.sub.1 /k.sub.2 is greater than 0.01, and K.sub.1 and K.sub.2 are constants for given substantially identical fluid passage geometries and are determined from the relationships:
• ##EQU11## and ##EQU12## where .DELTA.p.sub.1 = static pressure differential between the said spaced positions when the maximum Reynolds number in the fluid passage between the said spaced positions is 8000,
• G.sub.1 = the fluid mass flow rate of the substantially pure water through the fluid passage when the maximum Reynolds number in the fluid passage between the said spaced positions is 8000,
• .DELTA.p.sub.2 = static pressure differential between the said spaced positions when the maximum Reynolds number in the fluid passage between the said spaced positions is 3500,
• G.sub.2 = the fluid mass flow rate of the substantially pure water through the fluid passage when the maximum Reynolds number in the fluid passage between the said spaced positions is 3500, so that
• f. the characteristic to be measured is related to the pressure differential, indicated by the fluid pressure differential indicating means, and is deducible therefrom in a consistent manner for different fluids.