An aluminum rod 0.500 m in length and with a cross-sectional area of 2.50 cm^2 is inserted into a thermally insulated vessel containing liquid helium at 4.20 K (B.P. for helium). The rod is initially at 300 K. (𝑐_𝐴𝑙=900 𝐽/𝑘𝑔°𝐶, 𝐿_(𝑣,𝐻𝑒)=2.09×10^4 𝐽/𝑘𝑔)

Question

An aluminum rod 0.500 m in length and with a cross-sectional area of 2.50 cm^2  is inserted into a thermally insulated vessel containing liquid helium at 4.20 K (B.P. for helium). The rod is initially at 300 K. (𝑐_𝐴𝑙=900 𝐽/𝑘𝑔°𝐶, 𝐿_(𝑣,𝐻𝑒)=2.09×10^4 𝐽/𝑘𝑔) 
If one half of the rod is inserted into the helium, how many liters of helium boil off by the time the inserted half cools to 4.20 K? Assume the upper half does not yet cool.