a reaction vessel for conducting low temperature reactions is disclosed , the reaction vessel comprising : a circulation chamber with an entry port for the supply of a cooling medium at a temperature below ambient to said circulation chamber and an exhaust port ; and a reaction chamber and a centrifugal fan arranged concentrically - inside the circulation chamber so that gas in said circulation chamber is forced radially outwards by the operation of said fan , wherein the movement of the gas past the reaction chamber maintains the temperature of reactants inside the reaction chamber at a temperature below ambient . a chiller for providing a gas supply at a temperature below ambient is also disclosed which may be used with the above reaction vessel .