Sound amplification from controlled excitation reactions: Experimental observations in chemically reacting H2/Cl2 mixtures

Abstract

A study of sound propagation in chemically reacting mixtures has led to experimental observation of sound amplification. Photoinitiated Cl2–H2 reactions provided the energy for the amplification observed. Amplification experiments were conducted in two modes which were termed pulsed and cw. For the pulsed experiments, high-intensity UV flash lamps dissociated molecular chlorine at the start of the experiments and the Cl2–H2–Ar reactions quickly went to completion; amplification was observed for about 6 ms. The measured gain was 1.8 at 2 kHz compared to a gain of 4 predicted by theory. The source of this difference has not been resolved completely. In cw experiments, low-intensity UV fluorescent lamps dissociated molecular Cl2 continuously during the experiments, extending the time amplification was observed to about 800 ms. Experiments were conducted for three Cl2–H2–SF6 mixtures and four frequencies, 1.0, 2.5, 4.0, and 6.5 kHz. Computer calculations correctly predicted the frequency dependence of amplification and gave amplification values which were in fair agreement with the observations