MEC551Problem Based Learning/ Complex Engineering Problem

Assignment Description

Commence Date: 21st November 2015 Due Date: 20 December 2015

Course OutcomesThis assignment is established to achieve these Course Outcomes:

CO1 Describe the principles of heat transfer mechanisms, combustion, refrigeration and air conditioning systems in its fundamental aspect with relation to existing energy systems [PO1, LO1, SS1]{C2}.

CO2 Apply relationship between theoretical and practical aspects of heat transfer application [PO1, LO1, SS1]{C3}.

CO3 Analyse principles of energy mechanisms to solve a wide range of thermal engineering problems [PO2, LO3, SS1]{C4}.

CO4 Develop solutions for mathematical models and propose appropriate results for thermal engineering applications [PO3, LO3, SS1]{C5}.

CO5 Explain the importance of efficient energy utilization in engineering practices and its impact on the environment as part of the need for sustainable development. [PO7, LO6, SS4]{A3}.

Objective

The objective of this assignment is for students to conduct preliminary design calculations of an air conditioning system combining all the relevant topics in thermal engineering.

Problem Statement

A simple ideal vapor-compression heat-pump system is shown in Figure 1 to provide a heating effect for a building. The heat from evaporator of the refrigeration system is dissipated to the outdoor air flowing at 20,000 cfm from 0°C to condition it to 40°C and the relative humidity is 40%, respectively. An unmixed cross flow heat exchanger is used to increase the temperature to 18°C. The heat exchanger is made of tubes through which flows hot fluid from the compressor of the refrigeration system. Then, the air is humidified by the injection of hot steam in the humidifying section.

A. Air-conditioning processThe conditioned air flows in a 0.5 m x 0.5 m square cross section conduit before being discharged to the room through a vent.

1. Provide a sketch of the air-conditioning processes with the ambient pressure of 100 kPa. (CO1)

2. Solve the required heat extraction rate at the heating section when the ambient air enters at 0°C and 95% of relative humidity and leave the system at 18°C. (CO2)

3. Analyze the rate of water vapor if the room temperature is in the range between 20 °C and 25°C (increment of 1 °C ) and the relative humidity is between 40% to 75%. Plot the graph. (CO3)

4. A mixing chamber is introduced in the system. Some of the indoor air temperature is recycled and mix with the outdoor air to save energy. If the required temperature entering the condenser is set at 20 °C, sketch the schematic diagram; then evaluate the amount of recycle indoor air required (in %) and the heating rate of the condenser (in kW) for the exit temperature ranges from 21 °C to 25 °C (CO4)

Tips: a. There is no change in specific humidity of air for a sensible heating process.

1

COMBUSTION CHAMBERDiesel - C12H26 Air : ath (O2 +3.76N2)at 273K

Water in for Humidifier

HEAT EXCHANGEREVAPORATOR

1

2

HUMIDIFIYING

3

UNMIXED CROSS FLOW HEAT EXCHANGER

AD

T2 = 15°C 2 = ?

T3 = 20 - 24°C 3 = 40% - 75%

EXPANSION VALVE

HEAT EXCHANGEREVAPORATOR

T1 = 0C 1 = 95%P = 100 kPa 20,000 cfm

B

C

HEAT REJECTED TO HEAT COLD AIR,

Compressor Power Input,

HUMIDIFIYINGSECTION

COMPRESSOR

b. The water vapor enters as saturated vapor in the humidifying section at 100 °C.

Figure 1. Air-conditioning System LayoutB. Refrigeration cycle

If the refrigerant exits the evaporator as saturated vapor,1. Select 2 working refrigerants for the system and explain the reasons of selection based on

safety and thermal properties. (CO1)2. Choose operating conditions for the heat pump system such as the evaporator and

condenser pressure if the surrounding temperature is 0°C and solve the required refrigerant mass flow rate to obtain the desired heating effect cycle. (CO3)

3. Propose an innovative system that can improve the current COP i.e multistages or cascade refrigeration cycle. Prove your suggestion using analytical analysis. (CO4)

4. Compare the estimated cost for running the system (single cycle and multistage or cascade) for a 12 hour operation (based only on the compressor work input) under steady conditions. Assume any country in northen hemisphere region with daylight electrical tariff. (CO5)

Tips: a. Refer to any coolant manufacturer website, such as CoolPack, for the list of potential

coolants and its propertiesb. The compressor efficiency is 75%.

2

C12H26 25°Cath (O2 +3.76N2)273KXCO2 +YH2O+ ZN21000°CTo exhaust

C. Combustion chamber for Internal combustion engine

Diesel fuel (C12H26) enters a combustion chamber of the internal combustion engine at 25 °C. The diesel is burned with stoichiometric amount of air that enters the combustion chamber at the 0°C. The combustion products (hot gases) exit at 1000 °C. Solve;1. Solve the mass flow rate of the fuel and air if the rate of the heat transfer is 1.5 MWatt (CO2)The heat release from the ignition of the air-fuel mixture (resulting in sudden increase in heat is wasted in the form of heat transfer to the engine block (and thus the engine block need to be temperature and pressure) are used to do work (by pushing the piston in the power cycle). Some of this useful cooled by flowing water in the block cavities. The remainder of the energy is wasted and exited with the exhaust flow. By using the result in part A, 2. Analyze the amount of recovered energy from the combustion process if the inlet water temperature is 5 °C. Plot a graph for your analysis. (CO3)

Figure 2. Natural gas combustorReport (technical writing)

Your team (1 leader and 3 members) will present approximately 10 pages of technical written report. The report content should be presented as according to the course outcome for each part.

Part Question Course Outcome MarksA 1 CO1 10%

2 CO2 10%3 CO3 10%

B 1 CO1 10%2 CO3 10%3 CO4 10%4 CO5 20%

C 1 CO2 10%2 CO3 10%

The report must be submitted on the last day of the lecture. Please refer to report rubrics in the attachment.

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RUBRIC ASSESSMENTScale 1 2 3 4 5 Total MarksCriteria Poor Acceptable Excellent

[CO1, PO1]The principles and fundamentals are poorly correlated with the problem given.

The principles and fundamentals are moderately describe and are correlated with the problem given.The principles and fundamentals are well describe and are correlated with the problem given

20%

[CO2, PO1]

Make many errors in applications of heat transfer and thermodynamics principles and concepts. Many are not properly applied.

Make some but tolerable errors in applications of heat transfer and thermodynamics principles and concepts.

All relevant heat transfer and thermodynamics principles and concepts are accurately and comprehensively demonstrated and applied20%

[CO3, PO3]

Contain certain erroneous elements in interpretations, discussion, and conclusion of the thermal engineering. Only a very general discussion is made.

Correct interpretation of all results but lack insightfulness. Insightful, supported and comprehensive discussions or conclusions of the thermal engineering. Have some useful recommendations.

Correct and complete interpretation of all results. Draw Insightful, thoughtful, supported and comprehensive discussions or conclusions of the thermal engineering. Use and technically sound recommendations.

30%

[CO4, PO3] Errors in integrating mathematical solutions and problem statement. No solution propose for the given problem

Substantially define the mathematical model and its problem statement Fairly define the solution of given problem statement

The mathematical and problems statement are well correlatedHas given a comprehensive solution for the given problem

10%

[CO5, PO9]

No understanding or appreciation of importance of environment concern No consideration of public interest or environmental impact. None or erroneous evaluation of financial effect.

Sound understanding of environmental aspects. Mostly effective in addressing environmental issues. Sound understanding of public interest or environmental impact. Mostly effective evaluation of engineering selection leads to improve financial results.

Complete understanding of environmental aspects.Effective in addressing environmental issues leading to a better result.Complete understanding of public interest or environmental impact. Effective assessment of engineering selection impact support correlating with the financial improvement and explain results.

20%

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UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN MEKANIKAL 40450 Shah Alam, Selangor Darul Ehsan, Malaysia Tel. : 03-5543 6268 Fax: 03-5543 5160

Report Assessment

Assignment’s Title : ________________________________________________________

Groups’ Name : ________________________________________________________

Leader’s Name : ________________________________________________________

Member’s Name : 1) _______________________________________________________

2) _______________________________________________________

3) _______________________________________________________

Scale 1 2 3 4 5Level Poor Acceptable Excellent

Part Question Course Outcome Maximum Marks Given MarksA 1 CO1 10%

2 CO2 10%3 CO3 10%4 CO4 10%

B 1 CO1 10%2 CO3 10%3 CO4 10%4 CO5 10%

C 1 CO2 10%2 CO3 10%

TOTAL 100%

COURSE OUTCOME ACIEVEMENT SUMMARY

COURSE OUTCOME MAXIMUM MARKS GIVEN MARKSCO1 20%CO2 20%CO3 30%CO4 20%CO5 10%TOTAL 100%

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