A computational model for a rocket mass heater

A simple one dimensional pseudo-steady computational model of a rocket mass heater is presented. A rocket mass heater is a space heating device that utilizes an insulated “J-tube” to promote complete combustion of burning wood, a steel barrel to act as a heat radiator, and a thermal mass usually shaped into a bench that stores heat from the exhaust before the combustion gases are released to the atmosphere. The gas model is based on fundamental relationships for steady compressible flow through one-dimensional geometry and is coupled to an unsteady finite difference model for two dimensional heat conduction in the thermal mass, which is modeled as a hollow cylinder. The model accounts for detailed heat transfer effects and fluid frictional losses, and is able to predict efficiency, flow rate, and spatial variations in temperature and pressure as functions of key parameters such as burn rate, thermal mass volume and length, duct routing details, and chimney height. Key results demonstrate how insufficient chimney height and narrow barrel clearances can threaten heater performance, how a system damper and increasing duct length can improve heater efficiency, and that axial temperature variation in the mass is small compared to radial gradients.