Experimental and Computational Model Comparisons of Thermal Profiles Within a Column Photobioreactor

Abstract

In a bubble column-based photobioreactor, sparger design and placement govern the bubble size distribution and gas hold-up. These factors in turn influence flow pattern, effective interfacial area, rates of mass and heat transfer, and mixing. Previous computational studies of the hydrodynamic and heat transfer effects within a column photobioreactor for one sparger row have found that bubble Nusselt number and heat transfer coefficient with respect to superficial velocity do not follow any particular pattern. This study evaluates the temperature distribution and heat transfer within a photobioreactor in an effort to explain the earlier study results. Experimental and computational studies will focus on the bubble flow pattern and heat transfer within a rectangular column photobioreactor (33.65 cm long × 30.48 cm wide × 33.97 cm tall) with a single row sparger located either lengthwise or widthwise at the center of the base (27.94 cm long × 1.27 cm wide). Temperature distribution and heat transfer for both sparger positions will be compared. Carbon dioxide, water, light photons, algal cells, and nutrients need to come together continuously for successful algal production, hence mixing of the nutrients, algal cells, and carbon dioxide is essential. Instead of a light source, a heat source is used in the system. Constant electric energy is supplied to the heating pad, which converts the electric energy to thermal energy. Thermocouples are placed inside the PBR to record temperature at 36 different spatial positions. The experimental results are compared with previously developed CFD simulations. The sparger not only effects the aeration inside the PBR, but also creates mixing in the PBR. Proper design and placement of the sparger ensures proper mixing in the PBR. The present study shows the effects bubble movement and flow pattern have on the temperature distribution and how well the simulation predicts the temperature distribution inside a PBR. The present research is a continuum of previous work aimed at pursuing the optimum design of a column PBR which is commercially viable and effective at producing algal biofuels and bioproducts.