A 4.5-KW, 100V, and single phase resistance oven is to have ni-chrome wire heating elements. If the wire temperature is to be 500℃ and that of charge 250℃, calculate the diameter and length of the wire. Resistivity of the ni-chrome alloy is 42.5µΩ-m. Assume the radiating efficiency and the emissivity of the element 0.1 and 0.9, respectively.