The unit operation studied is a falling film evaporator that concentrates an aqueous sugar solution under a vacuum pressure to account for the heat-sensitive product. The evaporator is a heat exchanger with vertical tubes where a falling film flows downwards by gravity. The experiment aims to select the optimal parameters that allow high heat transfer coefficients, small temperature difference and a concentrated liquid product with the highest sugar concentration possible. Throughout the experiments, samples of the solution were collected at equal intervals and then weighted to calculate their densities which depend on concentration. A stand curve can then be obtained using the densities and the sugar concentrations collected to obtain the final sugar concentration. Another stand experiment was conducted to determine the operation time for each test, which was 30 min. After reaching a steady state, multiple temperature profiles can be graphed for each experiment run, which will be used for heat transfer calculations. The parameters that were aimed to be changed throughout the experiments affect the heat transfer process and are the flow rate of recirculation, the vacuum pressure, the initial sugar concentration, the steam pressure and the coldwater flow rate. The recirculation flow rate influences the falling film flow’s nature and viscosity. The vacuum pressure and the steam pressure control the boiling point of the solution, which affects the temperature difference and, therefore, the heat transfer process. The cold-water flow rate controls the steam flow rate supplied to the heat exchanger, affecting heat transfer coefficients. A temperature profile was obtained after each test to help determine the heat transfer coefficients.

Excerpt:

CHG 4116 Falling Vapor Lab Report

ABSTRACT
The unit operation studied is a falling film evaporator that concentrates an aqueous sugar solution under a vacuum pressure to account for the heat-sensitive product. The evaporator is a heat exchanger with vertical tubes where a falling film flows downwards by gravity. The experiment aims to select the optimal parameters that allow high heat transfer coefficients, small temperature difference and a concentrated liquid product with the highest sugar concentration possible.