A helical coil-tube heat exchanger is widely used in industrial applications due to its compactness. The performance of compact heat exchangers has been recognized in various industries for the last 60 years or more due to several advantages. However, flow rate and heat transfer correlation related to helical coil-tube heat exchanger are very sophisticated. A computational fluid dynamics (CFD) methodology using ANSYS FLUENT 15.0 is used here to investigate effects of tube diameter and mass flow rate on the heat transfer and pressure drop characteristics in a helical coil heat exchanger. Simulation has been done by varying the mass flow rate from 180 Lph to 420 Lph on different configuration of helical coiled tube. The result shows that the temperature drop, and pressure drop are affected by geometry of helical coil heat exchanger.