Chapter 11: Problem 98
A thermoelectric cooler has a COP of 0.15 and removes heat from a refrigerated space at a rate of \(180 \mathrm{W}\) Determine the required power input to the thermoelectric cooler, in \(\mathrm{W}\).
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An ideal gas refrigeration cycle using air as the working fluid operates between the pressure limits of 80 and \(280 \mathrm{kPa} .\) Air is cooled to \(35^{\circ} \mathrm{C}\) before entering the turbine. The lowest temperature of this cycle is \((a)-58^{\circ} \mathrm{C}\) \((b)-26^{\circ} \mathrm{C}\) \((c) 5^{\circ} \mathrm{C}\) \((d) 11^{\circ} \mathrm{C}\) \((e) 24^{\circ} \mathrm{C}\)
How does a thermocouple work as a temperature measurement device?
The COP of vapor-compression refrigeration cycles improves when the refrigerant is subcooled before it enters the throttling valve. Can the refrigerant be subcooled indefinitely to maximize this effect, or is there a lower limit? Explain
A copper and a constantan wire are formed into a closed circuit by connecting the ends. Now one junction is heated by a burning candle while the other is maintained at room temperature. Do you expect any electric current to flow through this circuit?
Thermoelectric coolers that plug into the cigarette lighter of a car are commonly available. One such cooler is claimed to cool a \(12-0 z(0.771-1 b m)\) drink from 78 to \(38^{\circ} \mathrm{F}\) or to heat a cup of coffee from 75 to \(130^{\circ} \mathrm{F}\) in about \(15 \mathrm{min}\) in a well-insulated cup holder. Assuming an average COP of 0.2 in the cooling mode, determine ( \(a\) ) the average rate of heat removal from the drink, \((b)\) the average rate of heat supply to the coffee, and ( \(c\) ) the electric power drawn from the battery of the car, all in \(\mathrm{W}\).
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