MECH3201 - Midterm practice problems

pdf

School

Western University *

*We aren’t endorsed by this school

Course

2273

Subject

Mechanical Engineering

Date

Oct 30, 2023

Type

pdf

Pages

3

Uploaded by ChiefLapwing3739

Report
Midterm review | MECH 3201 Engineering Thermodynamics Solutions are provided to every problem listed in this document. They are located in a separate PDF and contain worked solutions for each problem, please be sure to check the additional files uploaded alongside this one. Chapter 1 Review of thermo 1 and Chapter 2 Exergy questions: Question 1: A heat engine receives heat from a heat source at 1227 C at a rate of 700 kJ/s, and it rejects the waste heat to a medium at 47 C. The measured power output of the heat engine is 320 kW, and the environment temperature is 25 C. Determine (a) the reversible power, (b) the rate of irreversibility, and (c) the second-law efficiency of this heat engine. Question 2: A piston-cylinder device initially contains 1.4 kg of refrigerant-134a at 100 kPa and 20 C. Heat is now transferred to the refrigerant from a source at 150 C, and the piston, which is resting on a set of stops, starts moving when the pressure inside reaches 120 kPa. Heat transfer continues until the temperature reaches 80 C. Assuming the surroundings to be at 25 C and 100 kPa, determine (a) the work done, (b) the heat transfer, (c) the exergy destroyed, and (d) the second-law efficiency of this process. Chapter 3 Refrigeration cycles Question 1: Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.2 MPa and 200 kPa with refrigeration-134a as the working fluid. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counterflow heat exchanger where the pressure in the upper and lower cycles are 0.4 MPa and 0.5 MPa, respectively. In both cycles, the refrigerant is a saturated liquid at the condenser exit and a saturated vapor at the compressor inlet, and the isentropic efficiency of the compressor is 90%. Assume steady operating conditions exist and kinetic and potential energy changes are negligible. If the mass flow rate of the refrigerant through the lower cycle is 0.15 kg/s, determine (a) enthalpies of states 2 and 6, (b) the mass flow rate of the refrigerant through the upper cycle, (c) the rate of heat removal from the refrigerated space, (d) the COP of this refrigerator, and (e) the second law efficiency of this refrigerator.
Midterm review | MECH 3201 Engineering Thermodynamics Chapter 4 Thermodynamic property relations Question 1: Determine the change in enthalpy of helium, in kJ/kg, as it undergoes a change of state from 150 kPa and 20 C to 750 kPa and 380 C using the equation of state 𝑃(𝑣 − 𝑎) = 𝑅𝑇 where 𝑎 = 0.01 𝑚 3 /𝑘𝑔 , and compare the result to the value obtained by using the ideal gas equation of state. Chapter 5 Compressible flows Question 1: Is it possible to accelerate a gas to a supersonic velocity in a converging nozzle? Explain. Answer 1: No, it is not possible. In order to achieve supersonic velocity, you will need a converging-diverging nozzles. Converging nozzles can only achieve a sonic velocity. Question 2: Is it possible to accelerate a fluid to supersonic velocities with a velocity other than the sonic velocity at the throat? Explain. Answer 2: No, if the flow in the throat is subsonic. If the velocity at the throat is subsonic, the diverging section would act like a diffuser and decelerate the flow. Yes, if the flow in the throat is already supersonic, the diverging section would accelerate the flow to even higher Mach number. Question 3: How does the parameter Ma* differ from the Mach number, Ma? Answer 3: Ma* is the local velocity non-dimensionalized with respect to the sonic speed at the throat, whereas Ma is the local velocity non-dimensionalized with respect to the local sonic speed. The two are identical at the throat when the flow is choked. Question 4 : How does the normal shock affect (a) the fluid velocity, (b) the static temperature, (c) the stagnation temperature, (d) the static pressure, and (e) the stagnation pressure? Answer 4: (a) velocity decreases, (b) static temperature increases, (c) stagnation temperature remains the same, (d) static pressure increases, and (e) stagnation pressure decreases. In addition, the Mach number goes from supersonic (Ma > 1) to subsonic (Ma < 1). Question 5: How do oblique shocks occur? How do oblique shocks differ from normal shocks?
Midterm review | MECH 3201 Engineering Thermodynamics Answer 5 : Oblique shocks occur when a gas flowing at supersonic speeds strikes a flat or inclined surface. Normal shock waves are perpendicular to flow whereas inclined shock waves, as the name implies, are typically inclined relative to the flow direction. Also, normal shocks form a straight line whereas oblique shocks can be straight or curved, depending on the surface geometry. In addition, while a normal shock must go from supersonic (Ma > 1) to subsonic (Ma < 1), the Mach number downstream of an oblique shock can be either supersonic or subsonic. Question 6: Can the Mach number of a fluid be greater than 1 after a normal shock wave? Explain. Answer 6 : No, the second law of thermodynamics requires the flow after the shock to be subsonic. A normal shock wave always goes from supersonic to subsonic in the flow direction.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help

Browse Popular Homework Q&A

Q: What is the net force, in Newtons, on an object that experiences the following horizontal forces?…
Q: Consider the indefinite integral n(z)* dz: This can be transformed into a basic integral by letting…
Q: An unknown compound contains only carbon, hydrogen, and oxygen ( CxHyOz ). Combustion of 7.50  g  of…
Q: he cervical vertebrae are elative to the lumbar vertebrae. he humerus is he sternum. he spinal cord…
Q: What is the output of the following code? fruit_counts = {"apple": 5, "orange": 3, "banana": 6}…
Q: = A block of mass m₁ = 3.59 kg on a frictionless plane inclined at an angle 25 degrees (as in the…
Q: Evaluate f 1 x-2x³/4-8√√T da by substitution of a = u and then partial fractions.
Q: Initial values are:      PX = $9500     PY = $10000   I = $15000      A = $170000   W = 160 This…
Q: You want to be able to withdraw $50,000 each year for 20 years. Your account earns 5% interest
Q: When laser light is passed through two narrow slits separated by 153 µm, an interference pattern is…
Q: Match the function with its power. f(x) = 3x² - 4+5x¹ f(x) = 3x √x + 5 f(x) = 6-x² :: Power: 1/2 ::…
Q: (a) Formulate a linear programming model for maximizing total profit contribution. (Let  Pi =  units…
Q: Determine whether the given matrix is in row echelon form. If it is, state whether it is also in…
Q: A 3,472 mile flight headed west experienced a tailwind and made the trip in 7 hrs. The same return…
Q: Consider the following vectors. v = 2, u, u2 Give the corresponding linear combination. (If an…
Q: Procedure Name: Update_Emp_Job Purpose: To update an employee to a new job Input Parameters: 1)…
Q: Cause of well-being can be attritbuted to: O Personality O Temperment Resilience All of the above
Q: A factory manufactures three products (doohickies, gizmos, and widgets) and ships them to two…
Q: Write B as a linear combination of the other matrices, if possible. (If not, enter DNE in all…
Q: 12. In the phylogeny below, circle the following: (Label "A") The least inclusive clade that…
Q: 6. Standard addition was performed to determine the iron contained in Shiraz red wine from south…
Q: What is the average number of boats that will be waiting for service?   (c) What is the average time…