The particle collision behavior is investigated to analyze the heat transfer enhancement mechanism in a down-flow circulating fluidized bed evaporator. Water and Polyformaldehyde particles are selected as working media. Collision acceleration signals at varied amount of added particles (0-2%), circulation flow rate (2.15-5.16 m(3)/h) and heat flux (8-16 kW/m(2)) are analyzed with kurtosis and power spectral density. Results show that the frequency range of particle collision is 6000-16,000 Hz. Particles provide main energy contribution in multiphase flow collisions. The generation of vapor phase obviously strengthens the collisions of other phases. With increased amount of added particles, the signal power increases, but the heat transfer enhancing factor initially increases and then decreases. Both the heat transfer enhancing factor and signal power increase with increased circulation flow rate. With increased heat flux, the signal power increases but the heat transfer enhancing factor decreases. (C) 2020 Elsevier B.V. All rights reserved.