Steam in a heating system flows through tubes whose outer diameter is 5 cm and whose walls are maintained at a temperature of 19
8.06°C. Circular copper alloy fins (k =285 W/m · °C) of outer diameter 6 cm and constant thickness 1 mm are attached to the tube. The space between the fins is 3 mm, and thus there are 250 fins per meter length of the tube. Heat is transferred to the surrounding water at T= 43.06°C, with a heat transfer coefficient of 5300 W/m2 · °C. Determine the increase in heat transfer from the tube per meter of its length as a result of adding fins and fin effectiveness
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Answer:
The maximum power dissipation of the zener diode 112mV.
Explanation:
The minimum zener current should be:
5 * Iza= 5 * 1= 5 mA.
Since the load current can be at maximum 15 mA, we should select R so that, IL= 15 mA.
A zener current of 5 mA is available, Thus the current should be 20 mA, which leads to,
R = = 470 Ω.
Maximum power dissipated in the diode occours when, IL=0 is
Pmax = 20 * * 5.6 = 112mV.