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Q15. An LNG carrier has two spherical tanks each of diameter 45 m. They contain liquefied gas at a temperature of 163°C. The tanks are insulated with a 300 mm thickness of material of thermal conductivity 0.04 W/m K. The outside surface heat transfer coefficient is 8 W/m² K, and the temperature of the surrounding air is 35°C. The thermal resistances of the inside surface film and of the tank wall may be disregarded. The latent heat of evaporation of the gas is 515 kJ/kg. The density of the liquid is 460 kg/m³.

(a) Calculate the total heat transfer rate to the tanks.

(b) Estimate the percentage of the cargo which boils off each day.