A new simple low-shear capillary viscometer for blood 1

A simple and inexpensive low-shear capillary viscometer has been developed. It comprises a coiled plastic capillary 1 mm in dia. and 4–8 m long. A pressure difference is imposed on the capillary by means of a rubber air inflation bulb and is read on an ordinary manometer. The flow rate is measured by timing the blood meniscus between two divisions in a graduated tube. Use of a very long capillary allows one to attain very small shear rates while employing large pressure differences, thus ensuring that surface tension effects are negligible. The range of relative velocity ( U ¯ = 4 Q ˙ / π D 3 , tube diameters/sec) is from 0.1 to 50 sec⁻¹. The instrument requires a sample volume of less than 10 ml and its extreme simplicity, both in construction and operation, is emphasised. Theoretical analysis indicates that errors due to using a coiled capillary and operating under unsteady-state conditions are completely negligible.