Consider the following statements:
1. Under certain conditions, an increase in thickness of insulation may increases the heat loss from a heated pipe. (IES-96)
2. The heat loss from an insulated pipe reaches a maximum when the outside radius of insulation is equal to the ratio of thermal conductivity to the surface coefficient.
3. Small diameter tubes are invariably insulated
4. Economic insulation is based on minimum heat loss from pipe.
Which of these statements are correct?
(a)1 and 3 (b) 1 and 2
(c) 2 and 4 (d) 3 and 4