Many processes are carried out at high temperatures for the preparation of chemical species that must be recovered near room temperature. However, more or less important losses of the products occur during the cooling period because of undesired side reactions. in order to minimize these phenomena, it is necessary to design a quenching reactor just after the high temperature section. The purpose of the present paper is to propose a model representing the decay of the concentration and of the temperature of the species (produced by a high temperature solar reactor) inside a quenching reactor. The heat and mass balances an numerically solved with very simple assumptions and in the cases of cylindrical and annular reactors. The results are functions of couplings between chemical, heat transfer and flow phenomena. Thanks to the use of non dimensional numbers, the conclusions are valid inside very wide ranges of chemical and experimental conditions. The annular reactor in laminar flow confirms its high efficiency. The mean cooling rates can be much higher than 10(7) K s(-1). The proposed methodology would be also valid for other more complicated practical situations.