Computational Fluid Dynamics (CFD) was developed to model many flow types and in addition, can be used to solve heat transfer problems. A tube-in-tube exchanger, with hot water (single phase) flowing in the inner tube and cold water in the annulus was investigated. The heat exchanger was numerically modelled in threedimensions in CFD. The heat transfer coefficients and the friction factors were determined with CFD and compared to established correlations. The results showed reasonable agreement with empirical correlations, while the trends were similar. When compared with experimental data the CFD model’s results showed good agreement. The second part of the study investigated the CFD’s ability to model a prototype configuration of a tube-in-tube exchanger. This ability will greatly reduce cost and time when developing a new heat exchanger. The numerical data was compared with analytical predictions and experimental results. Recommendations were made on CFD’s value as a tool to characterise an exchanger. NOMENCLATURE a annular diameter ratio A area C circumference cp specific heat d1 diameter of outer wall of inner tube d2 diameter of inner wall of outer tube di inner diameter of inner tube dh hydraulic diameter f friction factor h convective heat transfer coefficient k thermal conductivity k turbulent kinetic energy L length of heat exchanger m& mass flow rate n number of times fractal is applied Nu Nusselt number ∆p pressure drop Pr Prandtl number q heat transfer q0 benchmark heat transfer Re Reynolds number ∆TLMTD log-mean temperature difference T temperature T∞ free stream temperature U overall heat transfer coefficient v flow velocity xo original square length α variable ε dissipation rate γ corrective function μ viscosity ρ density