Question 11. Dielectric heating apparatus consists of

Question 12. A slab of insulating material of thickness 6 cm and thermal conductivity 1.4kJ/m hr deg is placed between and is in contact with two parallel electrodes, and is then subjected to high frequency dielectric heating at a uniform rate of 140,000kJ/m³ hr. At steady state coefficients of combined radiation and convection are 42 and 48 kJ/m² hr deg. If atmospheric temperature is 25 degree Celsius, find surface temperatures?

Question 13. A 25 mm diameter egg roll (k = 1 W/m degree) is roasted with the help of microwave heating. For good quality roasting, it is desired that temperature at the center of roll is maintained at 100 degree Celsius when the surrounding temperature is 25 degree Celsius. What should be the heating capacity in W/m³ of the microwave if the heat transfer coefficient on the surface of egg roll is 20 W/m² degree?

Question 14. A concrete column used in bridge construction is cylindrical in shape with a diameter of 1 meter. The column is completely poured in a short interval of time and the hydration of concrete results in the equivalent of a uniform source strength of 0.7 W/kg. Determine the temperature at the center of the cylinder at a time when the outside surface temperature is 75 degree Celsius. The column is sufficiently long so that temperature variation along its length may be neglected. For concrete
Average thermal conductivity = 0.95 W/m K
Average density = 2300 kg/m³

Question 15. The constants of integration are to be determined from the relevant boundary conditions which are
(i) t = t w at r = R
(ii) q g (π L R²) = -k (2 π R L) (d t/d r)
(iii) Increasing temperature gradient
Choose the correct option?

Question 16. Generally heat generated depends on some parameters. It is directly proportional to

Question 17. Unit of specific resistance is

Question 18. Consider a 1.2 m thick slab of poured concrete (k = 1.148 W/m degree) with both of side surfaces maintained at a temperature of 20 degree Celsius. During its curing, chemical energy is released at the rate of 80 W/m³. Workout the maximum temperature of concrete

Question 19. The insulating material used in dielectric heating is

Question 20. What maximum thickness of concrete can be poured without causing the temperature gradient to exceed 98.5 degree Celsius per meter anywhere in the slab? Consider a 1.2 m thick slab of poured concrete (k = 1.148 W/m degree) with both of side surfaces maintained at a temperature of 20 degree Celsius. During its curing, chemical energy is released at the rate of 80 W/m³. Workout the maximum temperature of concrete