Total heat transfer coefficient K of the heat exchanger

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Dear seniors: I have a question: I am calculating the heat transfer area of a shell-and-tube heat exchanger, and it’s very difficult to determine the overall heat transfer coefficient K. Could some expert please offer some guidance? Its process parameters are as follows: The liquid to be heated is an aqueous solution of Zn2+, NH3+, Cl-, and HCO3-. Concentrations of the components in this solution are: Zn at 80 g/l, NH4+ at 100 g/l, NH3 at 50 g/l, Cl- at 300 g/l, and HCO3- at 70 g/l. The inlet temperature of the liquid to be heated is 50 degrees Celsius, while the outlet temperature is 70 degrees Celsius. The flow rate is 1103/h. The density is 1.15 t/m3, and the viscosity is 1.2. The heating medium is saturated steam, with a saturation pressure of 0.5–0.7 MPa. The design pressure is determined in accordance with the regulations for pressure vessel design. The specifications for the heat exchange tubes are such that they meet or exceed standards of grade 20. The material used for the flow-through elements is titanium or titanium alloy; the diameter of these elements is determined based on design requirements. The setup is vertical/horizontal: horizontal. The flow-through elements are made of titanium, while the shell side is made of 316L material, and the bolts are also made of 316L