Measuring and testing – Volume or rate of flow – Thermal type
Patent
1994-07-26
1996-11-19
Chilcot, Richard
Measuring and testing
Volume or rate of flow
Thermal type
73 3, G01F 168
Patent
active
055764878
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a fluid mass flowmeter.
Fluid mass flowmeters are known for providing an output representative of the mass flow of a target fluid through a conduit. The known flowmeters comprise a transducer for location in the conduit, means for supplying heating power to the transciucer, means for measuring the rate at which power is supplied to the transducer, means for measuring the temperature of the fluid within the conduit, means for measuring the temperature of the transducer, and means for calculating the mass flow from the measured rate of power supply, fluid temperature and transducer temperature. The underlying principle of operation is that, the greater the rate of flow, the greater is the rate of heat loss from the transducer.
The known flowmeters once calibrated provide accurate results. Unfortunately calibration is a major problem and the calibration process represents a large proportion of the cost of flowmeters which are generally delivered to the end user calibrated for a specific target gas. Typically, the end user specifies to the flowmeter supplier the identity of the target gas or mixture of gases, operating parameters such as minimum and maximum flow rates, and the required meter accuracy. The manufacturer calibrates the flowmeter by obtaining a supply of the target gas or mixture of gases and running that supply through a test rig to which the flowmeter is connected. In this way calibration data is obtained directly in a test environment which is a near as possible identical to the intended conditions of use of the flowmeter.
The above calibration procedure is easy to execute if the target gas is air. It is also relatively easy no execute if the target gas is a readily available inert gas which can be purchased at a relatively low price and can be handled using simple procedures. Where the target gas is not readily available, or is for example potentially explosive or poisonous and therefore must be handled with great care, the test procedures become very expensive and inconvenient.
The transducers which are used in the known flowmeters generally have a cylindrical outer wall which is in contact with the target gas. There has been much research into heat loss from cylinders in gas flows and this indicates that there is no simple relationship that is independent of the nature of the target gas. Fortunately, the available literature has been thoroughly surveyed in the document "The Overall Convective Heat Transfer from Smooth Circular cylinders" by V. T. Morgan, PP199-264 Advances in Heat Transfer, Volume 11, 1975, Academic Press Inc. (London) Limited, 24/28 Oval Road, London NW1. This review explores the relationship between Nusselt Number for any given Reynolds Number. The mathematical correlation produced from the reviewed data indicated a variation in Nusselt Number of from 10% to 46% for any given Reynolds Number. The Reynolds Number is a dimensionless number which is significant in modelling any system in which the effect of viscosity is important in controlling the velocity or flow pattern of a fluid. It is equal to the density of the fluid, multiplied by its velocity, multiplied by a characteristic length, and divided by the fluid viscosity. The Nusselt Number is a dimensionless number used in the study of forced convection which gives a measure of the ratio of the total heat transfer to conductive heat transfer and is equal to the heat transfer coefficient multiplied by a characteristic length divided by the thermal conductivity.
The literature reviewed by Morgan indicates that for a specified gas and a specified rate of power supply to the transducer, a unique curve interrelating Nusselt Number and Reynolds Number can be derived. Thus if the rate of power supplied to a transducer is maintained constant, and the relationship between Nusselt Number and Reynolds Number is established using a supply of gas on a test rig, the thus calibrated flow meter could be used to monitor the flow of that same gas in a practical application, the predetermined Nusselt Number
REFERENCES:
patent: 4335605 (1982-06-01), Boyd
patent: 4415279 (1983-11-01), Beuse et al.
patent: 4501145 (1985-02-01), Boegli et al.
patent: 4961348 (1990-10-01), Bonne
patent: 5177696 (1993-01-01), Bonne
patent: 5237523 (1993-08-01), Bonne et al.
Chilcot Richard
Endress & Hauser Limited
Patel Harshad
LandOfFree
Apparatus for calibrating a fluid mass flowmeter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for calibrating a fluid mass flowmeter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for calibrating a fluid mass flowmeter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-542332