429. Maximum heat dissipation occurs from a steel wire (k = 0.5 W/m. k) of 15 mm diameter exposed to air (h = 20W/m² .k), when the insulation thickness is __________ mm. September 6, 2025 by Admin A. 15 B. 25 C. 10 D. 30 ✅ The correct answer is option B.