A plate with a surface area of 1 m² has a surface temperature of 70°C. The plate is in an ambient air with a temperature of 20°C and a heat transfer coefficient of 13.2 W/m2K. In order to increase the heat loss from the plate by 3 times, how many aluminum needle fins with a circular cross-section of 2 cm diameter and 10 cm length with a heat transfer coefficient of 204 W/m·K need to be attached to the surface of the plate? (Only two needle fins are shown on the figure as a representative example.) Assume steady-state conditions and neglect radiation and contact resistance. 

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