The optimal design of a water heater system is critical for achieving enhanced heat transfer and reduced energy consumption. In this study, a comprehensive review of various design aspects will be presented to identify the most efficient ways of increasing the heat transfer in a water heater system, focusing on the field of solar water heaters.

A major factor that affects the efficiency of a solar water heater system is the type of collector used. For instance, flat plate collectors are widely used due to their simple design and easy installation, whereas evacuated tube collectors are preferred for their higher temperature range and improved efficiency. An evacuated tube collector is typically comprised of an inner tube, an outer tube, and a vacuum in between to minimize radiation losses.

In addition to the collector type, surface roughness is another key design factor for increased heat transfer. By analyzing the effects of surface roughness on the heat transfer enhancement, it has been observed that an increased surface roughness leads to improved fluid flow and heat transfer. Furthermore, detailed studies were conducted to understand how hydrophilic surfaces can increase water wettability and enhance heat transfer.

The installation of an extended surface heat exchanger to the heat transfer enhancement design obtained through the above two modifications significantly increased the overall thermal efficiency of the system. The implementation of both numerical and experimental studies was presented to verify the results. Thus, the obtained results suggested that employment of surface roughness and hydrophilic coating for both the inner tubes is the new trend in the field of water heaters and plays a prime role for efficient performance and better heat transfer.

It is the collective and continued study in this area by the energy experts and researchers will eventually pave the path towards higher increase in overall system efficiency and can be used for eco-friendly practices and cost savings.