Coupled thermoeconomic assessment of cold-water pipe heat gain in ocean thermal energy conversion systems

Heat gain in the cold-water pipe (CWP) reduces the temperature span available to an ocean thermal energy conversion (OTEC) cycle. This study couples a transient finite-volume heat-transfer model to a quotation-based CWP cost indicator. Numerical convergence, boundary conditions and operating parameters were examined through independent solutions and sensitivity tests. For the 800 m, 2.0 m reference pipe with the low-conductivity annulus used in the calculation, the converged 24 h outlet temperature is 5.879 °C at a volumetric flow of 0.05 m 3 /s. The annulus limits the difference between the three pipe materials. HDPE retains the lowest cost indicator under the stated material-price scenarios. A separate, consistently coupled assessment at 8500–10000 kg/s uses constant DR = 26 and includes CWP pumping power. At 9500 kg/s, the 2.25 m candidate satisfies the selected 3 m/s velocity limit and gives a CWP cost indicator of about 16.1 USD/MWh; the 2.0 m candidate exceeds that limit. These results quantify the trade-off between intake heat gain, pumping demand and CWP cost for the prescribed temperature profile and tested design range.