Dryer Flowrate Diagnostic Tool

Overview

A low-cost, precise diagnostic tool which estimates rate of air flow through a clothes dryer, used for validation and diagnostic troubleshooting. Digital readout can display flow rate in CFM, m3/min, m3/hr, or L/min. Onboard indicator LEDs also provide status readouts, changing color in the event of a partial or full blockage.

Key Specifications

• COTS barometer IC with external tubing to determine pressure differential
• Wireless communication for data visualization on external devices (and software updates)
• Digital readout and RGB LED to display flowrate and status
• Onboard sensors e.g. temperature and humidity to allow estimation of ambient conditions

Theory

Assuming incompressible, low speed flow, average velocity v can be approximated by the relation

\[ v = \left( \frac{2\Delta P}{\rho} \right)^{1/2} \]

where ΔP represents the difference in pressure, and ρ the fluid density. From this, volumetric flow rate Q can be obtained by the simple relation \[ Q = A \cdot v. \]

where A represents the cross-sectional area of the duct.

No system is ideal, and real-world systems are constrained by ducting bends, backpressure, debris buildup, and the fact that real-world flow is partially turbulent and non-uniform. To account for this, a scaling factor (k) and an offset (b) were introduced to the software, in the form \[ Q_{\text{final}} = k \cdot Q_{\text{raw}} + b. \]

The values for these constants were obtained empirically against known flow characteristics, and provisions were included from a software standpoint for non-standard duct sizes. This prototype successfully managed to perform flowrate calculations at the same or better accuracy than commercially available specialty devices for a fraction of the cost, with increased functionality and usability.