Abstract
Heat pump drying systems require a method to change the inflow air temperature of the drying chamber. Pulse-widthmodulation (PWM) technique with duty cycle provides a measure of controlling the voltage supplied to the electric motors. Therefore, we conducted this research to PWM control a heat pump dryer to change the air circuit parameters. In the Parallel-Flow condensers, inlet and outlet temperatures, and relative humidity, data were collected, and the average temperature values were recorded. The duty cycle was changed by developing a program using the Python programming language. An Excel-based psychrometric calculator was developed to analyze the collected data. The average condenser outlet temperatures were 56.6±0.1℃, 54.9±0.1℃, and 52.6±0.1℃, and the average condenser inlet temperatures were 43.2±0.0℃, 42.8±0.1℃, and 41.2±0.1℃ for 60%, 80%, and 100% duty cycles, respectively. The power consumption rate of the condenser reduced with an increasing duty cycle. The results concluded that the PWM control system is a viable method to control the inflow air temperature to the drying chamber.
Highlights
Pulse-width-modulation (PWM) controls specific analog quantities by the varying pulse width of a fixed frequency rectangular waveform (Toulson and Wilmshurst, 2012)
We developed the data acquisition system using six DHT22 sensors connected to the Raspberry Pi 3 control system
The voltage supplied to the condenser fans was controlled through PWM to obtain different duty cycles
Summary
Pulse-width-modulation (PWM) controls specific analog quantities by the varying pulse width of a fixed frequency rectangular waveform (Toulson and Wilmshurst, 2012). The PWM generates variable-width pulses to represent the amplitude of an analog input signal. The digital nature (fully ON or OFF) of the PWM circuit is less costly to fabricate than an analog circuit that does not drift over time (Christ and Wernli Sr, 2013). The PWM is used in many applications, ranging from communications to power control and conversion, such as controlling the speed of electric motors, the brightness of lights, ultrasonic cleaning applications, etc. The duty cycle of PWM refers to the process "ON" time/Period
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