Ahollow aluminum sphere, with an electrical heater in the center, is used in tests to determine the thermal conductivity of insulating materials. the inner and outer radii of the sphere are 0.18 and 0.21 m, respectively, and testing is done under steady-state conditions with the inner surface of the aluminum maintained at 250°c. in a particular test, a spherical shell of insulation is cast on the outer surface of the sphere to a thickness of 0.15 m. the system is in a room for which the air temperature is 20°c and the convection coefficient at the outer surface of the insulation is 30 w/m2 ⋅ k. if 80 w are dissipated by the heater under steady-state conditions, what is the thermal conductivity of the insulation?

Amass of m 1.5 kg of steam is contained in a closed rigid container. initially the pressure and temperature of the steam are: p 1.5 mpa and t 240°c (superheated state), respectively. then the temperature drops to t2= 100°c as the result of heat transfer to the surroundings. determine: a) quality of the steam at the end of the process, b) heat transfer with the surroundings. for: p1.5 mpa and t 240°c: enthalpy of superheated vapour is 2900 kj/kg, specific volume of superheated vapour is 0. 1483 m/kg, while for t 100°c: enthalpy of saturated liquid water is 419kj/kg, specific volume of saturated liquid water is 0.001043m/kg, enthalpy of saturated vapour is 2676 kj/kg, specific volume of saturated vapour is 1.672 m/kg and pressure is 0.1 mpa.

The y form of iron is known as: a) ferrite b) cementite c) perlite d) austenite

Manometers are good examples of measuring instruments, nowadays they are not as common as before. a)-capacitive probe gauges b)-gravitational gauges deformation ) gauges d)-digital gauges