Fabricação de um dessalinizador térmico com parâmetros operacionais controláveis

Abstract

Solar thermal desalination systems operate with a variable heat source, such as solar radiation, which makes it difficult to identify the influence of process variables and constructive geometric parameters in their performance. In operation, brackish or salt water is heated in a storage tank, where it evaporates and condenses on the lower walls of a metal tray (first stage) installed above this tank. The steam flows upwards to transfers its heat to the salt water in the above stage, where it condenses and flows to be collected outside the tank. The present work presents the development of a new prototype of the thermal desalination system with a controllable heat source, which allows transient and steady state operations. In the prototype, brackish or salty water is heated up by electrical resistance with controllable voltage source, allowing variations of the desirable heating power. Besides the electrical control, the electrical resistance can be easily changed to allow heating in other power levels. The side and bottom walls are insulated with polyurethane coated with aluminum, to minimize heat losses to the environment. PT-100 temperatures sensors were installed in different positions in the storage tank and stages. They were specially made to adjust to the system dimensions. The mass of water in the tank was measured by a precision balance. With the experimental data, temperature charts were plotted for the steady state and transient operation during heating and cooling periods. The data were used in the calculation of performance parameters. Water mass measurements were used to experimentally determine the evaporation rate from the storage tank.