**In part two of this article, we will discuss the effect of surface area and other variables on the efficiency of heat exchangers, why and how fins are used, the effect that a pressure drop has on their operation and examining the use of internal versus external heat exchangers in vacuum furnaces.**

In part one we identified the variables most impactful of heat exchanger design and explained the significance of the convection heat transfer coefficient, the thermal conductivity of the tube material, fin material, and the importance of turbulent flow. Reviewing Newton’s law of cooling, Q = hA(T_{a} – T_{b}), another variable playing a critical role is the surface area (A) available for heat transfer. Put simply, the greater the area of heat exchange the more effective the heat exchanger will be. For this reason, one of the most important design goals for heat exchanger engineering is the maximizing of the area available for heat transfer while at the same time minimizing the physical size of the exchanger.