Concept explainers
The exergy lost in the cooling tower.

Answer to Problem 113P
The exergy lost in the cooling tower is
Explanation of Solution
As the process is a steady flow and thus the mass flow rate of dry air remains constant during the entire process.
Here, the mass flow rate of air at inlet is
Express the water mass balance:
Here, mass flow rate of water at inlet and exit is
Express the energy balance.
Here, the rate of total energy entering the system is
Determine the mass flow rate of steam at state 3 per unit mass of dry air.
Determine the mass flow rate of steam at state 4 per unit mass of dry air.
Determine the change in entropy of water steam.
Determine the change in entropy of water vapour in the air stream.
Determine the partial pressure of water vapour at state 1 for air steam.
Determine the partial pressure of dry air at state 1 for air steam.
Here, the pressure at the state 1 is
Determine the partial pressure of water vapour at state 2 for air steam.
Determine the partial pressure of dry air at state 2 for air steam.
Here, the pressure at the state 1 is
Determine the entropy change of dry air.
Here, the temperature at the state 1 is
Determine the entropy generation in the cooling tower is the total entropy change.
Determine the exergy destruction per unit mass of dry air.
Conclusion:
Refer Figure A-31, “psychometric chart at
Refer Figure A-31, “psychometric chart at
Refer Table A-4, “saturated water-temperature table”, and write the enthalpy and entropy at state 3 at temperature of
Here, enthalpy of saturation liquid is
Refer Table A-4, “saturated water-temperature table”, and write the enthalpy at state 4 at temperature of
Here, enthalpy of saturation liquid at temperature of
Write the formula of interpolation method of two variables.
Here, the variables denote by x and y is temperature and specific enthalpy at state 4 respectively.
Show the specific enthalpy at state 4 corresponding to temperature as in Table (1).
Temperature |
Specific enthalpy at state 4 |
20 | 83.915 |
22 | |
25 | 104.83 |
Substitute
Substitute
Repeat the Equation (XIV), obtain the value of entropy for water streams at
Substitute
Substitute
Substitute
Substitute
Refer Table A-4, “saturated water-temperature table”, and write the entropy at state 1 at temperature of
Repeat the Equation (XIV), obtain the value of entropy for water vapour at
Substitute
Substitute
Substitute 1 atm for
Substitute
Substitute 1 atm for
Substitute
Substitute
Substitute
Thus, the exergy lost in the cooling tower is
Want to see more full solutions like this?
Chapter 14 Solutions
THERMODYNAMICS-SI ED. EBOOK >I<
- Liquid pentane is flowing in the shell of a shell and tube heat exchanger at a rate of 350,000lbm/hr and an average temperature of 20°F. The shell has a diameter of 27 in and a length of 16ft. The tubes in the heat exchanger are ¾-in 15 BWG tubes on a 1-in triangular pitch. The purposeof this problem is to investigate how the number of baffles impacts the heat transfer and thepressure drop on the shell side of the heat exchanger. Calculate the shell-side convective heattransfer coefficient and pressure drop for the case where the heat exchanger has 10 baffles. Repeatthe calculation for 20 baffles. Then determine thea. Ratio of the shell-side convective heat transfer coefficient for the 20-baffle heat exchangerto the 10-baffle heat exchangerb. Ratio of the shell-side pressure drop for the 20-baffle heat exchanger to the 10-baffle heatexchangerc. If the optimum baffle spacing is somewhere between 0.4Ds and 0.6Ds, how many baffleswould you recommend for this heat exchanger? What are the…arrow_forwardThe evaporator of a vapor compression refrigeration cycle utilizing R-123 as the refrigerant isbeing used to chill water. The evaporator is a shell and tube heat exchanger with the water flowingthrough the tubes. The water enters the heat exchanger at a temperature of 54°F. The approachtemperature difference of the evaporator is 3°R. The evaporating pressure of the refrigeration cycleis 4.8 psia and the condensing pressure is 75 psia. The refrigerant is flowing through the cycle witha flow rate of 18,000 lbm/hr. The R-123 leaves the evaporator as a saturated vapor and leaves thecondenser as a saturated liquid. Determine the following:a. The outlet temperature of the chilled waterb. The volumetric flow rate of the chilled water (gpm)c. The UA product of the evaporator (Btu/h-°F)d. The heat transfer rate between the refrigerant and the water (tons)arrow_forwardThe blade support of a hacksaw is subject to compression when a blade is installed and tightened. What is the state of stress (total combined stress) at A in MPa if the compression in the support is 1,524 N. Note: pay close attention to what is compression and what is tension and use a negative sign for the former. 100 mm 8 mm 3 mm 75 mm A 8 mm 3 mm B 50 mmarrow_forward
- An open channel of square cross section had a flowrate of 17.2 ft³/s when first used. After extended use, the channel became 0.6-filled with silt. Determine the flowrate for this silted condition. Assume the Manning coefficient is the same for all the surfaces. Qs= ! ft³/sarrow_forward(Manning equation) The triangular flume shown in the figure below is built to carry its design flowrate, Qo, at a depth of 0.991 m as is indicated. If the flume is to be able to carry up to twice its design flowrate, Q = 2Qo, determine the freeboard, I, needed. ✓ -90°- 0.991 m i marrow_forwardWater flows in a 2-ft-wide rectangular channel at a rate of 10 ft³/s. If the water depth downstream of a hydraulic jump is 2.5 ft, determine (a) the water depth upstream of the jump, (b) the upstream and (c) downstream Froude numbers, and (d) the head loss across the jump. (a) y₁ = i (b) Fr₁ = i (c) Fr₂ = i (d) h₁ = ft ftarrow_forward
- A hydraulic jump at the base of a spillway of a dam is such that the depths upstream and downstream of the jump are 0.8 and 3.2 m, respectively (see the Video). If the spillway is 12 m wide, what is the flowrate over the spillway? Q= i m³/sarrow_forward(Manning equation) Water flows in a rectangular channel of width b at a depth of b/2. Determine the diameter of a circular channel (in terms of b) that carries the same flowrate when it is half-full. Both channels have the same Manning coefficient, n, and slope. barrow_forward(Manning equation) A weedy irrigation canal of trapezoidal cross section is to carry 20 m³/s when built on a slope of 0.60 m/km. If the sides are at a 45° angle and the bottom is 8 m wide, determine the width of the waterline at the free surface. i marrow_forward
- Elements Of ElectromagneticsMechanical EngineeringISBN:9780190698614Author:Sadiku, Matthew N. O.Publisher:Oxford University PressMechanics of Materials (10th Edition)Mechanical EngineeringISBN:9780134319650Author:Russell C. HibbelerPublisher:PEARSONThermodynamics: An Engineering ApproachMechanical EngineeringISBN:9781259822674Author:Yunus A. Cengel Dr., Michael A. BolesPublisher:McGraw-Hill Education
- Control Systems EngineeringMechanical EngineeringISBN:9781118170519Author:Norman S. NisePublisher:WILEYMechanics of Materials (MindTap Course List)Mechanical EngineeringISBN:9781337093347Author:Barry J. Goodno, James M. GerePublisher:Cengage LearningEngineering Mechanics: StaticsMechanical EngineeringISBN:9781118807330Author:James L. Meriam, L. G. Kraige, J. N. BoltonPublisher:WILEY





