A manufacturer of ice cream freezers claims that its product has a coefficient of performance of 1.3 while freezing ice cream at 250 K when the surrounding environment is at 300 K. Is this claim valid?
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A manufacturer of ice cream freezers claims that its product has a coefficient of performance of 1.3 while freezing ice cream at 250 K when the surrounding environment is at 300 K. Is this claim valid?
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- Why do the heat engine manufacturers seek for new materials, coatings that can withstand even higher temperatures than the available ones do? Please explain from the 2nd law of thermodynamics point of view.An inventor claims to have developed a resistance heater that supplies 1.2 kWh of energy to a room for each kWh of electricity it consumes. Is this a reasonable claim, or has the inventor developed a perpetual-motion machine? Explain.A Carnot refrigerator is operating between cold reservoir of Temperature 35 degrees C and hot reservoirs of temperatures 209 degrees C. Calculate its coefficient of performance rounding your answer to two decimal points.
- A classroom that normally contains 40 people is to be air-conditioned with window air-conditioning units of 5-kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360kJ/h. There are 10 light bulbs in the room, each with a rating of 100W. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000kJ/h. If the room air is to be maintained at a constant temperature of 21°C, determine the number of window air-conditioning units required.A solar water heating plant is using a flat-plate solar collector with an area A of 28 m2. The collector is operating as follows:• Cold water temperature at the collector inlet Tin = 33°C• Hot water temperature at the collector outlet Tout = 57°C• Effective optical efficiency of the collector ηopt = 0.8• Effective overall heat loss coefficient of the collector Uc,e = 3.9 W/m2K• Ambient air temperature Ta = 27°C• Solar radiation flux incident on the tilted collector surface Ic = 830 W/m2• Isobaric specific heat of the water cp = 4187 J/(kg K) Calculate (i) the useful heat output rate of the collector, and (ii) the water mass flow rate in the collector.In the context of a Spark Ignition (SI) engine, consider a moment during combustion when there is a heat flux through the wall of the combustion chamber at a specific location, measured at 219 kW/m2. The gas temperature within the cylinder at this time is 2300 K, and the convection heat transfer coefficient within the cylinder is 120 W/m2⋅K. The coolant temperature is 80 °C. The thickness of the cylinder wall is 10mm with a thermal conductivity of 200 W/m⋅K. (a) Determine the temperature of the inner surface of the cylinder wall. (b) Find the temperature on the side of the cylinder wall facing the coolant. (c) Calculate the heat transfer coefficient on the coolant side of the cylinder wall