The outer surface of a transistor is cooled convectively by a fan-induced flow of air at a temperature of 25 °C and a pressure of 1 atm. The transistor's outer surface area is 5x 10 *m. At steady state, the electrical power to the transistor is 3 W. Negligible heat transfer occurs through the base of the transistor The convective heat

A pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 1500 kg / hour. The steam pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe that needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam only decreases slightly to 95%. The temperature of the outer surface of the insulation is assumed to be 25 ° C. The conductive of the pipe material and the situation of no pressure drop in the pipe.        A. Determine the enthalpy of incoming vapor = Answer     kJ / kg.        b. Determine the enthalpy of steam that comes out = Answer     kJ / kg.        c. Determine the change / loss of steam heat along the flow = Answer     watt.        d. Determine the minimum required insulation thickness = Answer     cm.

In a certain experiment, cylindrical samples of diameter 4 cm and length 7 cm are used, as shown in Figure 5 below. The two thermocouples in each sample are placed 3 cm apart. After initial transients, the electric heater is observed to draw 0.6 A at 110 V, and both differential thermometers read a temperature difference of 8°C. Determine the thermal conductivity of the sample. Cooling fluid Thermo couple Sample L = 3 cml }AT; 7 cm 4 сm a a Resistance heater L= 3 cm[ }AT, Sample Insulation -Cooling fluid Figure 5

As the temperature increases, the thermal conductivity of a gas... (A) increases (B) decreases (C) remains constant (D) increases up to a certain temperature and then decrease