Numerical analysis of the sludge drying behaviors with bottom periodic heating

The drying of sludge can reduce its mass and the volume and consequently the cost of storage, handling and transport. In this paper, a one-dimensional model is established for the sludge drying process and hot water from the solar energy is applied as a discontinuous heat source (periodic heating). Based on the simplified physical model, the thermal behavior of the sludge drying process is investigated by numerical method. The effects of the sludge depth, mixing time and heat transfer coefficient are analyzed. The simulation results show that the most important effecting factor is the mixing time. One hour mixing cycle can increase heat transfer rate to 430%, 130% than that of without mixing and two hours mixing cycle, respectively. On the other side, both the sludge thickness and the heat transfer coefficient have some effects. For the cases studied the 40cm thick sludge with 1 hour mixing time is an optimal option.