Towards thermal design optimization of tubular digesters in cold climates: A heat transfer model

► Low-cost tubular digester are developed for cold climate. ► Thermal performance was analyzed by exhaustive temperature monitoring. ► A one-dimensional, time-dependent heat transfer model was developed. ► Solar gains, influent/effluent flows, ground temperature impact are considered. ► The model agrees with experimental within ±0.47 °C for slurry temperature.