Explanation Write the expression for the mass balance for the mixing chamber which acts as a system. m ˙ in − m ˙ out = Δ m ˙ system (I) Here, mass flow rate of the fluid entering the system is m ˙ in , mass flow rate of the fluid leaving the system is m ˙ out and change in mass flow rate of the system is Δ m ˙ system . For steady state, the change in mass flow rate of the system is zero. Δ m ˙ system = 0 Substitute 0 for Δ m ˙ system in Equation (I). m ˙ in − m ˙ out = 0 m ˙ in = m ˙ out m ˙ 1 + m ˙ 2 = m ˙ 3 Here, mass flow rate of the cold water stream is m ˙ 1 , mass flow rate of the hot water stream is m ˙ 2 and mass flow rate of the mixture is m ˙ 3 . Write the formula to calculate mass flow rate of the water at the shower head ( m ˙ ) . m ˙ = ρ V ˙ (II) Here, density of the water is ρ and volumetric flow rate of the water is V ˙ . For the closed system, write the simplified rate form of the entropy balance on the extended system which includes water and its immediate surroundings. S ˙ in − S ˙ out + S ˙ gen = Δ S ˙ system (III) Here, rate of entropy generation is S ˙ gen , rate of change of entropy of the system is Δ S ˙ system , rate of entropy at inlet condition is S ˙ in and rate of entropy at outlet condition is S ˙ out . For steady state, the rate of change of entropy of the system is zero. Δ S ˙ system = 0 Substitute 0 for Δ S ˙ system in Equation (III). S ˙ in − S ˙ out + S ˙ gen = 0 m ˙ 1 s 1 + m ˙ 2 s 2 − m ˙ 3 s 3 + S ˙ gen = 0 S ˙ gen = m ˙ 3 s 3 − m ˙ 1 s 1 − m ˙ 2 s 2 = m ˙ 3 s 3 − ( m ˙ 1 + m ˙ 2 ) s 1 [ ∵ s 1 = s 2 ] = m ˙ 3 s 3 − m ˙ 3 s 1 = m ˙ 3 ( s 3 − s 1 ) = m ˙ 3 c p ln T 3 T 1 (IV) Here, entropies of the water at states 1, 2 and 3 are s 1 , s 2 and s 2 respectively, specific heat capacity of water is c p and temperature of the water at state 1 and 3 are T 1 and T 3 respectively. Write the formula to calculate entropy generation ( S gen ) . S gen = S ˙ gen ( Δ t ) n p n d (V) Here, time taken by each person to take shower is Δ t , number of person is n p and number of days is n d

8th Edition

ISBN: 8220102809444

Author: CENGEL

Publisher: YUZU

See similar textbooks

Videos

Question

Chapter 8.8, Problem 79P

To determine

The amount of exergy destroyed by the family per year.

Expert Solution & Answer

Want to see the full answer?

Check out a sample textbook solution

See solution

Chapter 8.8, Problem 78P

Chapter 8.8, Problem 80P

Students have asked these similar questions

Refrigerant-22 absorbs heat from a cooled space at 50°F as it flows through an evaporator of a refrigeration system. R-22 enters the evaporator at 10°F at a rate of 0.08 lbm/s with a quality of 0.3 and leaves as a saturated vapor at the same pressure. Determine the rate of exergy destruction in the evaporato.

3) The cold water system in a house is equipped with a pump. 12 kg of water at 5000kPa and 2°C will enter the pump until the pressure rises 3 times and the temperature is 12°C with 3kJ of heat loss. Hot water will be heated in a heat exchanger before entering the mixing chamber. The heat exchanger uses air at 150°C to heat 3kg of 5°C of 5MPA water until 120°C. The temperature of the air will be dropped 10 times than before. Later, the cold water will enter the mixing chamber to be mixed with hot water until the pressure of the water becomes 10MPA. Evaluate : a) work of the pump b) isentropic efficiency of the pump c) mass of the air used to heat the water d) heat add in the hot water e) temperature of the water at the exit of the mixing chamber in °C.

In a refrigerant-cooling system, 1.5 kg/s of refrigerant 134a flows at steady state through a coil having an inside diameter of 0.05 m. The refrigerant enters the tube as superheated vapor at 700 kPa and 70°C and leaves at 32°C and 690 kPa. You want to heat the water from of 25°C to 35°C by placing the coil inside a box and having the water enter and leave the box at a constant mass flow rate. Please answer the following: Please answer the following. a. Create a schematic that accurately describes the situation given in the problem. Include your chosen boundary and the energy interactions present across the boundary. You will select from which side the cold water enters the box; that is, closer to the inlet of the refrigerant at 70°C or closer to the exit of the refrigerant at 32°C. b. Represent the process for the refrigerant on a T-v diagram. Show the isobars corresponding to each state with their value. Include values on the axes using customary units. c. For this part you are going…

Chapter 8 Solutions

EBK THERMODYNAMICS: AN ENGINEERING APPR

Ch. 8.8 - What final state will maximize the work output of...Ch. 8.8 - Is the exergy of a system different in different...Ch. 8.8 - How does useful work differ from actual work? For...Ch. 8.8 - Prob. 4P Ch. 8.8 - Consider two geothermal wells whose energy...Ch. 8.8 - Consider two systems that are at the same pressure...Ch. 8.8 - Prob. 7P Ch. 8.8 - Does a power plant that has a higher thermal...Ch. 8.8 - Prob. 9P Ch. 8.8 - 8–10C Can a process for which the reversible work...

Knowledge Booster

Learn more about

Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, mechanical-engineering and related others by exploring similar questions and additional content below.

The amount of exergy destroyed by the family per year.

Solution Summary: The author calculates the amount of exergy destroyed by the family per year. The mass balance for the mixing chamber acts as a system.

Videos

The amount of exergy destroyed by the family per year.

Want to see the full answer?

Chapter 8 Solutions