A 3-m spherical tank storing cold fluid has a uniform surface temperature of T₁ = 5°C. The lower temperature of the tank surface is causing condensation of moisture in the air at 13°C and a dew point at 10°C. If the outer surface temperature of the tank drops below the dew point, condensation can occur on the surface. The tank is situated in the vicinity of high voltage devices, and water from the condensation on the tank surface can cause electrical hazards. In an attempt to remedy the situation, the tank is enclosed with a concentric outer cover that provides an evacuated gap in the enclosure. On the outer surface, the natural convection heat transfer coefficient is 3 W/m² ∙ K and radiation exchange with the surrounding is negligible. If the emissivity of the tank and the concentric outer cover is the same at 0.6, determine the necessary gap of the vacuumed enclosure so that the outer cover surface temperature is not below the dew point of 10°C.