Summary: In this work, a method is presented for the approximation of dynamic processes. Dynamic inputs of membrane distillation can be approximated by a regression equation as several steady state steps after each other. A regression equation of the flux was developed based on a validated steady state model and a wide range of process parameters. The regression equation of the flux is then used to approximate a dynamic process. To test the approximation on a dynamic process, a new test setup was developed to provide quick changes to the temperatures or flow. It was found that the approximation corresponds well to the test results. While this paper only approximates the flux, the method presented in this paper can also be used to approximate other variables. The presented method is also applied to the concentration of aqueous sucrose solutions with an AGMD module with oleophobic and hydrophobic properties. Three semi batch tests were done. The approximation corresponds well to the test results. A maximum Brix concentration of 56.9 was reached in the tests.