Several embodiments include a method of computing void fraction in a two-phase mixture in a pipe. A driver and a transmitter antenna can transmit a radio frequency (RF) signal through the pipe. The pipe can convey the two-phase mixture extracted from a geothermal well. The RF signal can pass through the two-phase mixture. A receiver antenna in the pipe can receive the RF signal. A receiver circuit can measure signal strength attenuations of the RF signal at the receiver antenna over a time window. A computation engine can compute an average of the signal strength attenuations over the time window. The computation engine or another computing device can then compute, in real-time, a change in a void fraction of the two-phase mixture based on the average of the signal strength attenuations.