Investigation in critical radius of thermal insulation for vertical pipes

Thermal insulation of pipelines finds application across various industries, including agricultural technologies. The energy efficiency hinges on minimizing heat losses. The task is primarily achieved through effective heat insulation. Decentralized ventilation systems prove to be efficient in rural low-rise constructions. Among these, regenerative ventilators like Blauberg Vento/Vents TwinFresh stand out. There exists a goal to enhance their operational efficiency, which involves ongoing investigation into heat recovery processes within their thin ducts. Improving the insulation of the experimental setup leads to a reduction in experimental uncertainty. Also, a new gas exchange camera for CO₂ exchange in plants requires very low uncertainty of airflow measurements requiring very high precision of air density measurement. However, heat losses can influence the air temperature deviation in a flow meter. However, within the realm of heat transfer literature, the concept of the critical insulation radius is stated. Increasing the insulation radius beyond a certain point might diminish its efficacy due to outer surface development. Theoretical assumptions posit a constant heat transfer coefficient for the outer surface. Previously, we analysed the critical radius of horizontal cylinder pipes. This study deals with laminar convective flow around the outer vertical cylindrical insulation surface. Employing a formula considering the Grashof number, the average heat transfer coefficient is analysed. The results indicate that increasing insulation thickness reduces the surface temperature and the heat transfer coefficient such as for vertical pipes. An analysis of the thermal resistance function concerning the ratio of outer to inner diameters, and its derivative, was conducted. The asymptotic increase in the thermal resistance was found. This fully disproves the critical radius concept opening new perspectives on energy efficiency and thermotechnical research precision.