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4. The following heat exchanger uses 10 kg/s of hot air to heat and boil liquid water into saturated steam at 500 kPa. (a) Find the steam flow (kg/s) (b) Determine whether the process is allowed by the second law (Answer: It is not!) (c) On the surface, the process looks OK as Tair>Twater at both the inlet and outlet. You should be able to see the problem if you sketch the air and the water temperature profiles as you move left to right through the exchanger. (Hints: The air will be essentially a straight line, while the water will not. For the water, think about what happens when it is changing phase.) This is called a pinch point violation, and it is a very important design consideration in advanced combined cycle systems and in nuclear power plants. Air 100 kPa 160°C 10 kg/s Saturated Vapor 500 kPa Air: 160°C Steam: 151.8°C Q Air 100 kPa 30°C Liquid Water 500 kPa, 20°C

4. The following heat exchanger uses 10 kg/s of hot air to heat and boil liquid water into saturated steam at 500 kPa. (a) Find the steam flow (kg/s) (b) Determine whether the process is allowed by the second law (Answer: It is not!) (c) On the surface, the process looks OK as Tair>Twater at both the inlet and outlet. You should be able to see the problem if you sketch the air and the water temperature profiles as you move left to right through the exchanger. (Hints: The air will be essentially a straight line, while the water will not. For the water, think about what happens when it is changing phase.) This is called a pinch point violation, and it is a very important design consideration in advanced combined cycle systems and in nuclear power plants. Air 100 kPa 160°C 10 kg/s Saturated Vapor 500 kPa Air: 160°C Steam: 151.8°C Q Air 100 kPa 30°C Liquid Water 500 kPa, 20°C

Elements Of Electromagnetics
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
Problem 1.1MA
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4. The following heat exchanger uses 10 kg/s of hot air to heat and boil liquid water into saturated steam at 500 kPa. (a) Find the steam flow (kg/s) (b) Determine whether the process is allowed by the second law (Answer: It is not!) (c) On the surface, the process looks OK as Tair>Twater at both the inlet and outlet. You should be able to see the problem if you sketch the air and the water temperature profiles as you move left to right through the exchanger. (Hints: The air will be essentially a straight line, while the water will not. For the water, think about what happens when it is changing phase.) This is called a pinch point violation, and it is a very important design consideration in advanced combined cycle systems and in nuclear power plants. Air 100 kPa 160°C 10 kg/s Saturated Vapor 500 kPa Air: 160°C Steam: 151.8°C Q Air 100 kPa 30°C Liquid Water 500 kPa, 20°C Air: 30°C Water: 20°C
Transcribed Image Text:4. The following heat exchanger uses 10 kg/s of hot air to heat and boil liquid water into saturated steam at 500 kPa. (a) Find the steam flow (kg/s) (b) Determine whether the process is allowed by the second law (Answer: It is not!) (c) On the surface, the process looks OK as Tair>Twater at both the inlet and outlet. You should be able to see the problem if you sketch the air and the water temperature profiles as you move left to right through the exchanger. (Hints: The air will be essentially a straight line, while the water will not. For the water, think about what happens when it is changing phase.) This is called a pinch point violation, and it is a very important design consideration in advanced combined cycle systems and in nuclear power plants. Air 100 kPa 160°C 10 kg/s Saturated Vapor 500 kPa Air: 160°C Steam: 151.8°C Q Air 100 kPa 30°C Liquid Water 500 kPa, 20°C Air: 30°C Water: 20°C
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