ME 3293 HW 9 KEY

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Feb 20, 2024

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ME 3293 - Thermodynamics I | Page 1 of 6 UTSA ID (abc123): Name: Please neatly print your UTSA abc123, First middle and last name no upper case ABC123 ME 3293 Thermodynamics I Homework Assignment #9: Chapters 8 & 10 Instructions • The work must be in your own handwriting, in dark color(s) (e.g., black or dark gray), on white paper (or a white background, if done on a computer tablet). If graph paper is used, then the background must be white and the gridlines must be light, so as to not distract from the handwriting. • If not using this template, then, in the upper right corner of the first page, write your full name (last name first), your UTSA ID (abc123), and the assignment (e.g., Homework Assignment #9 ), and the date. On each subsequent page write your full name and UTSA ID in the upper right corner. • For each problem, number the problem, write the complete problem statement , show the solution process , and box in the final answer (do not box a plot or a table). If a problem has multiple subparts with the same statement, write the statement only once. • Your submittal must show the problems in the same order as they appear on the homework assignment . • The work must be legible, solution processes well-organized, and the overall appearance professional. • Upload the work due as a single and readable PDF file . You must assign problems to the corresponding page(s) in the PDF file submitted to Gradescope in order to receive credit . - Procedures for scanning your work are provided in the following link (e.g., using the free apps for iOS and Android devices): https://gradescope-static-assets.s3-us-west-2.amazonaws.com/help/submitting_hw_guide.pdf - For more information on how to upload homework assignments to Gradescope and assign problems to pages, see the following video: https://www.youtube.com/watch?v=u-pK4GzpId0 • The submittal time indicated by Gradescope must not be later than the due time. Late homework will not be accepted, and the grade of the assignment will be zero (0) . Grading of homework assignments will be as follows: • 10% or more may be deducted for each of the above submittal requirements not met. A 0% may be given if the submittal is illegible, very poorly organized, or otherwise too burdensome to grade. A 0% will be given in case cheating is detected (e.g., copying solutions from others or from online tutoring centers such as chegg.com, a case of scholastic dishonesty will be filed). • A detailed rubric will be provided in Gradescope to indicate the weight/contribution of each problem to the final homework grade. For a student to earn full credit for a problem, the student must show all of the following: 1. The problem statement. 2. The correct solution process, including units and critical intermediate steps. 3. The correct answer, boxed in (do not box a plot or a table). In addition, consider the following: • A student may receive partial credit for a problem if the solution process is generally correct, but the answer is incorrect due to transcription errors or other minor errors. • In some cases, homework assignments might be graded more leniently than exams, or errors on homework assignments might be overlooked. • The student is responsible for reviewing posted solutions in Blackboard and contacting the Teaching Assistant to ask questions regarding the grading process of the homework assignment or the solution steps required to successfully complete a problem. • Any questions/requests regarding a grading discrepancy should be brought up within 1 week after returning the assignment. • Please keep all your graded homework until you receive your final course grade.

Name: Homework Assignment #9 UTSA ID (abc123): Date: ME 3293 - Thermodynamics I | Page 2 of 6 1. Water is the working fluid in an ideal Rankine cycle. Steam enters the turbine at 1,400 lbf/in 2 and 1,000 °F. The condenser pressure is 2 lbf/in 2 . The net power output of the cycle is 1 x 10 9 Btu/h. Cooling water experiences a temperature increase from 60 °F to 76 °F, with negligible pressure drop, as it passes through the condenser. Determine for the cycle (a) the mass flow rate of steam, in lbm/h, (b) the rate of heat transfer, in Btu/h, to the working fluid passing through the steam generator (boiler), (c) the thermal efficiency, in %, and (d) the mass flow rate of cooling water, in lbm/h.

Name: Homework Assignment #9 UTSA ID (abc123): Date: ME 3293 - Thermodynamics I | Page 3 of 6

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Name: Homework Assignment #9 UTSA ID (abc123): Date: ME 3293 - Thermodynamics I | Page 4 of 6 2. If the turbine and pump isentropic efficiency in problem #1 is 95%, determine: (a) the specific enthalpy at the turbine and pump exit, in Btu/lbm (hint: the state at the turbine and pump inlet do not change), and (b) The thermal efficiency, in %.

Name: Homework Assignment #9 UTSA ID (abc123): Date: ME 3293 - Thermodynamics I | Page 5 of 6 3. A vapor-compression refrigeration cycle operates at steady state with Refrigerant 134a as the working fluid. Saturated vapor enters the compressor at 2 bar, and saturated liquid exits the condenser at 8 bar. The isentropic compressor efficiency is 80%. The mass flow rate of refrigerant is 7 kg/min. Determine (a) the compressor power, in kW, (b) the refrigeration capacity, in tons, and (c) the coefficient of performance.