Application of NiTi shape memory alloy in ocean thermal energy conversion

Ocean Thermal Energy Harvester (OTEH) conceptual design is proposed using NiTi Shape Memory Alloys (SMA) spring. Thermo-mechanical energy conversion is produced by the shape memory effect. A constitutive model for the SMA wire is formulated using conservation law of energy and momentum, and a modified Landau phenomenological model. The proposed models are further extended to SMA spring and applied on the OTEH engine. A prototype OTEH at a lab-scale is designed and constructed. Experimental tests are performed, and found that the angular rotation speed is affected by the temperature difference of hot and cool waters. The output power is affected by both thermal and external torque loadings. The engine’s performance is evaluated with the output power showing a non-monotonic trend. Maximum output power values are 4.3 watts at 48 rpm, 4.75 watts at 70 rpm, and 5.4 watts at 85 rpm for the temperature difference of 60 °C, 80 °C, and 90 °C, respectively. Engine efficiency indicates a non-linear relationship with angular speed and increases with temperature difference. Comparison between the experimental data and simulated ones shows a good fitting. It is verified that the OTEH using SMA spring is feasible, and this research could be a reference for OTE harvesting.

The research aimed at modeling and application of SMA in the field of renewable (ocean thermal energy conversion).

As with the current global energy mission of tilting toward using renewable energy, scientists and government’s attention all over the world are attracted. It can be seen here in this research, that the shape memory alloy material (Nitinol) is being applied to convert OTE into a useful energy source. Although the idea has been on for a long time, the commercialization of this system has yet not been achieved. The major uncertainty in the research is temperature difference and its stability for a long time. But in tropical regions close to equator, high temperature is obtainable. In this research, a certain significant engine output is achieved. But still more effort is needed.