Universal temperature model for large-scale outdoor horizontal tubular microalgae photobioreactor plants

While the broth temperature is crucial for the design, optimal operation and yield assessment of the microalgae photobioreactors (PBRs), no universal temperature model is available for large-scale outdoor fence-type horizontal tubular PBR plants. A temperature model is created as a function of both the static (location, orientation, and reactor geometry) and dynamic (light irradiance, air temperature, wind velocity, and operation) parameters. The mutual shading among the tubes has a significant effect on the broth temperature and is carefully considered. The model is applicable to both single-row and double-row coiled types of PBRs. The broth temperature in a plant consisting of 10 double-row coiled PBRs, each with 2600 L of gas-free cultivation broth, was subsequently predicted using the model. Based on an analysis of the suitability of various climate zones for algae production, subtropical and temperate monsoon climates are identified as favorable regions. Finally, the relative magnitudes of the various heat transfer rates causing the change in broth temperature are compared. The primary factors affecting the broth temperature are solar radiation, air convection and net longwave radiation, and the direct solar radiation captured by the tubular part of the plant is the most substantial contributor.