The feasibility of an exothermic fused chemical reaction (FCR) system to control the temperature profile inside a tubular reactor is demonstrated in a 300-m laboratory-scale flow loop. The exothermic FCR system consists of a reactive slug containing the two reactants, ammonium chloride and sodium nitrite, and the citric acid catalyst contained in polymer-coated capsules. The citric acid catalyst is designed to only release to the reactive slug when the slug reaches the destination region. Once the acid catalyst is released, it catalyzes an exothermic reaction, generating a substantial amount of heat in situ. The location or time of the heat release is controlled by the thickness of the polymeric coating, while the maximum temperature and the rate of heat release are determined by the in situ concentrations of the reactant and acid catalyst. The in situ concentrations of the reactants were found to be controlled by the fluid Peclet number and the ratio between the reactive slug length and the flow length. Meanwhile, the in situ concentration of the acid catalyst depends on the flow of the capsules and the controlled release of the acid catalyst from the capsules. The turbulent dispersion of the capsules depended on the capsule Stokes number, while the flow of the capsule relative to the reactive slug was correlated to the capsule Reynolds number and the capsule Froude number. Good agreement between experimental and simulation temperature profiles was achieved. Simulations can then be used to determine all required system parameters for a desired temperature profile inside the tubular reactor.