Influence of horizontal tube bundle arrangement on flow and heat transfer properties of oily wastewater spray falling film

Recently, spray heat exchangers have become an important technology for recovering heat energy from oily wastewater in sewage source heat pumps (SSHP), which makes it attractive to study the heat transfer charac-teristics and its enhancement. It's indicated in previous studies the arrangement of the tube bundle is the key influential factor for falling film flow and heat transfer. Considering the specific physical properties of oily wastewater, it's necessary to study the role of oily content in bundle arrangement influences. Therefore, in this paper, inline tube bundles and triangle tube bundles are designed, and falling film of oily wastewater over these tubes were numerically investigated. The CFD model was established with VOF method to capture the gas-liquid interface, and the influence of different tube arrangement on the flow pattern and heat transfer effect of the liquid film under the flow parameters and structural parameters are analyzed. It is found that there is a sig-nificant difference in the falling film flow outside the horizontal tube between the triangle and inline tube bundle arrangement. The film flow of the triangle arrangement is more unstable, with liquid bridges between the liquid films, and the velocity inside the liquid film is relatively higher. Obvious variations of local heat transfer coef-ficient (HTC) during theta = 0 degrees -30 degrees were observed in both types of tube bundle arrangements. The average HTC of triangle arrangement is higher than that of the inline arrangement by 8 % to 16.8 % under various operating conditions.

Automated summary

Recently, spray heat exchangers have gained significance in the recovery of heat energy from oily wastewater in sewage source heat pumps. Previous studies have emphasized the importance of tube bundle arrangement in falling film flow and heat transfer. This paper investigates the influence of oily content on bundle arrangement and analyzes the flow pattern and heat transfer effect using a numerical simulation. The results show significant differences in falling film flow and heat transfer coefficient between triangle and inline tube bundle arrangements, with the triangle arrangement showing higher heat transfer performance.