Shell and helically coiled tube heat exchangers (SHCTHEXs) are a special type of shell-and-tube heat exchangers and they are widely used in industry in many processes. The tubes inside the shell are curved to form a helical coil which has a positive impact on heat transfer. The main purpose of this study is to investigate thermal performance enhancement potential of using a new type of hybrid nanofluid in SHCTHEXs. In this study, two types of SHCTHEXs - one vertically oriented and the other horizontally oriented - have been designed with the same geometrical dimensions. These designs have been simulated with two types of fluid on the shell side: water and Al2O3-TiO2/water hybrid-type nanofluid at various shell-side flow rates in order to reveal the heat transfer improvement potential of using this hybrid nanofluid in SHCTHEXs. The simulations indicated that utilizing Al2O3-TiO2/water hybrid-type nanofluid on the shell side resulted in 7.7% increase in the average heat transfer rate for vertically oriented SHCTHEX and 9% increase for the horizontally oriented SHCTHEX. Calculated heat transfer rate values ranged between 3337 and 5136 W. Among the simulated designs the best performing combination has been horizontally oriented SHCTHEX with Al2O3-TiO2/water hybrid-type nanofluid on the shell side. This combination provided 2.5 degrees C better cooling at the hot fluid outlet compared to poorest performing combination: vertically oriented SHCTHEX with water (both streams at 3 lpm). Using nanofluid increased the overall heat transfer coefficient parameter in horizontally and vertically oriented heat exchangers as 17.2% and 13.7%, respectively. The achieved outcomes of this work indicate that utilizing an Al2O3-TiO2/water hybrid nanofluid provides a notable amount of increase in heat transfer rate. In addition, overall results of the study showed that horizontally oriented SHCTHEX had better performance in comparison with vertically oriented one.