Fluid Dynamic Design of Heat Exchanger Safety Devices

Abstract

Safety devices usually mounted on heat exchangers (specifically boilers), for protection against excessively high pressures, consist of three basic types: full stroke (popping) or proportionally opening pressure relief valves, combination units consisting of a pressure relief valve with pre-installed rupture disc and rupture discs sometimes including a vacuum support. The fluid dynamic design of these safety devices requires the pressure drop — mass flow rate relationship, which generally is not available for two-phase flow conditions. Based on recent experimental and theoretical research the predictive accuracy of available correlations and of a preliminary mechanistic sequential model will be presented as a status report on the state of the fluid dynamic pressure relief valve design. The presented calculation method for combination devices uses an engineering design approach based on the discharge coefficient of the safety relief valve. For the assessment of the two-phase pressure drop in bur-sted rupture discs a practical solution based on orifice meter design is proposed.