In fact, I am going to explain the process from the point of view of the thermal side estimation . Let us consider the heat exchanger is composed from the immersion coil in a tank type. Usually, the tube side, is considered as a forced convection, laminar or turbulent, depending on the Reynolds number. For the tank side, it is usually considered as a free (Natural) convection process where the Grahshoff and Prandtl numbers control the heat transfer mechanism. Accordingly, both of the heat transfer coefficients are estimated and the overall heat transfer coefficient is defined.

Regards

You have to use just the single flow solutions in the tube or channel that the fluid is flowing and for the other heat exchange fluid which is stationary finding the natural convection coefficient if exists and use it as a boundary condition on the surface of the flowing fluid.

Energy and mass balance could be used to obtain heat flow rate, temperatures, mass flow rate and cross-sectional area. Then you may use empirical formulas for flow in pipes to obtain the heat transfer coefficient and the surface area.

Thanks Ashjaee and Fellah for your inputs

I have got it done using mass and energy balance as said by Fellah

I assume that you are interested to determine the htc on the tube side. The fluid on the shell side is stationary and the higher temperature of which u known. Assuming the surface temperature of the tube as the liquid temperature on the shell side, you can determine the htc on the tube side for the known flow conditions. Compared to htc on the tube side, the htc on the shell side can be neglected as it is small. Further improvements can be made depending on the extent of complexity you intend.