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A local brand of water heater has offered a counterflow concentric tube heat exchanger, consisting of thin walled copper drains with a diameter D; = 50 mm. Waste water from the shower enters the heat exchanger at Th = 38 °C while fresh water enters the room at Tei= 10 °C. The waste water flows down the vertical drain wall in a thin, falling film and providing h, = 10 kW/m². K. i. If the annular gap is d = 10 mm, the heat exchanger length is L = 1 m, and the water flow rate is m = 10 kg/min, determine the heat transfer rate and outlet temperature of the warmed fresh water. If a helical spring is installed in an annular gap so the fresh water is forced to flow a spiral path ji. from the inlet to the fresh water outlet, resulting in he = 9050 W/m²-K, determine the heat transfer rate and outlet temperature of the fresh water. iii. Based on the result from Q5(b), calculate the daily saving if 15,000 guests each take 10 minutes shower per day and cost of water heating is RM0.07/kW.h.

A local brand of water heater has offered a counterflow concentric tube heat exchanger, consisting of thin walled copper drains with a diameter D; = 50 mm. Waste water from the shower enters the heat exchanger at Th = 38 °C while fresh water enters the room at Tei= 10 °C. The waste water flows down the vertical drain wall in a thin, falling film and providing h, = 10 kW/m². K. i. If the annular gap is d = 10 mm, the heat exchanger length is L = 1 m, and the water flow rate is m = 10 kg/min, determine the heat transfer rate and outlet temperature of the warmed fresh water. If a helical spring is installed in an annular gap so the fresh water is forced to flow a spiral path ji. from the inlet to the fresh water outlet, resulting in he = 9050 W/m²-K, determine the heat transfer rate and outlet temperature of the fresh water. iii. Based on the result from Q5(b), calculate the daily saving if 15,000 guests each take 10 minutes shower per day and cost of water heating is RM0.07/kW.h.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
Publisher:Kreith, Frank; Manglik, Raj M.
Chapter10: Heat Exchangers
Section: Chapter Questions
Problem 10.46P
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QUESTION 7 A local brand of water heater has offered a counterflow concentric tube heat exchanger, consisting of thin walled copper drains with a diameter D; = 50 mm. Waste water from the shower enters the heat exchanger at Thi= 38 °C while fresh water enters the room at Te,j= 10 °C. The waste water flows down the vertical drain wall in a thin, falling film and providing h, = 10 kW/m²·K. i. If the annular gap is d = 10 mm, the heat exchanger length is L = 1 m, and the water flow rate is m = 10 kg/min, determine the heat transfer rate and outlet temperature of the warmed fresh water. ii. If a helical spring is installed in an annular gap so the fresh water is forced to flow a spiral path from the inlet to the fresh water outlet, resulting in he = 9050 W/m²-K, determine the heat transfer rate and outlet temperature of the fresh water. iii. Based on the result from Q5(b), calculate the daily saving if 15,000 guests each take 10 minutes shower per day and cost of water heating is RM0.07/kW-h.
Transcribed Image Text:QUESTION 7 A local brand of water heater has offered a counterflow concentric tube heat exchanger, consisting of thin walled copper drains with a diameter D; = 50 mm. Waste water from the shower enters the heat exchanger at Thi= 38 °C while fresh water enters the room at Te,j= 10 °C. The waste water flows down the vertical drain wall in a thin, falling film and providing h, = 10 kW/m²·K. i. If the annular gap is d = 10 mm, the heat exchanger length is L = 1 m, and the water flow rate is m = 10 kg/min, determine the heat transfer rate and outlet temperature of the warmed fresh water. ii. If a helical spring is installed in an annular gap so the fresh water is forced to flow a spiral path from the inlet to the fresh water outlet, resulting in he = 9050 W/m²-K, determine the heat transfer rate and outlet temperature of the fresh water. iii. Based on the result from Q5(b), calculate the daily saving if 15,000 guests each take 10 minutes shower per day and cost of water heating is RM0.07/kW-h.
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