I Flow rate calculation of coating application

Thread starter bertcoen
Start date Sep 6, 2022
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Application Calculation Cfd Coating Flow Flow rate Rate

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The discussion focuses on calculating the flow rate for a coating application using a pressure tank and dispensing valve. The user is exploring the Hagen-Poiseuille equation for pressure drop calculations in a flexible hose but questions its applicability due to the variable opening of the dispensing valve. There is a consensus that the flow rate is likely influenced by pressure and viscosity, with suggestions to consider the energy equation and Bernoulli's principles for a more accurate analysis. The user reports fluctuations in flow rate despite stable pressure readings, leading to inquiries about potential viscosity changes and other external factors affecting the coating's behavior. Understanding the theoretical relationships between flow rate, pressure, and viscosity is crucial for optimizing the coating application process.

Sep 8, 2022

Tom.G

Science Advisor

Gold Member

bertcoen said:

curing mechanism of the coating is a humidity reactive system.

Two possible ways I see this could cause your variations:

1) The spray nozzle is not being cleaned at end-of-shift and the residual compound is curing in it during the night.
2) Air used to pressureize the tank is moist causing partial curing. Air right out of a compressor is notoriously wet.

#1 has an obvious solution.
#2 As a test, get a tank of Dry Nitrogen with appropriate pressure regulator. Purge the reservoir,hose, nozzle, etc. and try that for a few days/weeks.

If #2 solves the problem, consider a dryer for the air line (expensive), perhaps a dessicant canister (periodic maintenance required) in the air line, or continue with the Dry Nitrogen tank.

Cheers,
Tom

p.s. As a last resort, farm out the coating process to someone else with a well-written/comprehensive quality requirement.

The downside (beyond cost) is the incoming quality-control inspections needed.