Fluid Mechanics and ThermodynamicsWeekly Assessed Tutorial Sheets

Tutor Sheets: WATS 4.

The WATS form a collection of weekly homework type problems in the form of out-of-class tutorial sheets.

Each WATS typically comprises of a couple of main questions of which each has around four/five linked supplementary questions. They were developed as part of an LTSN Engineering Mini-Project, funded at the University of Hertfordshire which aimed to develop a set of 'student unique' tutorial sheets to actively encourage and improve student participation within a first year first ‘fluid mechanics and thermodynamics’ module. Please see the accompanying Mini-Project Report “Improving student success and retention through greater participation and tackling student-unique tutorial sheets” for more information.

The WATS cover core Fluid Mechanics and Thermodynamics topics at first year undergraduate level. 11 tutorial sheets and their worked solutions are provided here for you to utilise in your teaching. The variables within each question can be altered so that each student answers the same question but will need to produce a unique solution.

FURTHER INFORMATION

Please see http://tinyurl.com/2wf2lfh to access the WATS Random Factor Generating Wizard.

There are also explanatory videos on how to use the Wizard and how to implement WATS available at http://www.youtube.com/user/MBRBLU#p/u/7/0wgC4wy1cV0 and http://www.youtube.com/user/MBRBLU#p/u/6/MGpueiPHpqk.

For more information on WATS, its use and impact on students please contact Mark Russell, School of Aerospace, Automotive and Design Engineering at University of Hertfordshire.

© University of Hertfordshire 2009 This work is licensed under a Creative Commons Attribution 2.0 License.

Fluid Mechanics and ThermodynamicsWeekly Assessed Tutorial Sheet 4 (WATS 4)

TUTOR SHEET – Data used in the Worked Solution

Q1. A system executes a cycle which is made up of four processes. The heat and work transfers that take place in the first three processes are:

Process 1 Q1 =1.60 kJ and W1 = -58.60kJProcess 2 Q2 = 70.60kJ and W2 = -11.10kJProcess 3 Q3 = -23.90kJ and W3 = 59.90kJ

If the work transfer during the fourth process i.e. W4, is 78.20 kJ determine the corresponding heat transfer Q4 (kJ) (1 mark)

Q2. Using the Thermodynamic and Transport Properties of Fluids -

i) Find the specific enthalpy (kJ/kg) of saturated water in the liquid phase at 40C (1 mark)1

ii) Find the specific enthalpy (kJ/kg) of saturated water in the vapour phase at 26C (1 mark)

iii) Find the specific enthalpy change (kJ/kg) between saturated water vapour and saturated water liquid when it is at 34C (1 mark)

Q3 0.30kg of water enter a device as a saturated vapour at 0.20 Bar and, after undertaken a process, leaves as a saturated liquid. Calculate

i) the internal energy of the water as it enters the device (kJ), (1 mark)

ii) the internal energy of the water as it leaves the device (kJ) and (1 mark)

iii) the change in internal energy as a consequence of the process (kJ). (1 mark)

iv) Given the conditions noted in Q3 find the saturation temperature of the water (C) (1 mark)

_______________________________________________________________________________________________WATS 4. Mark Russell (2005)Student number51 School of Aerospace, Automotive and Design Engineering

University of Hertfordshire

WATS 4 Worked solution

This sheet is solved using the TUTOR data set.

Q1 … calculate the corresponding heat transfer

This question reminds you that for a cyclic system the sum of work = the sum of heat transfer. i.e.

∮W =∮Qand taking account of the sign conventions.

In our case we use - work done by a system = +vework done on a system = -veheat transferred to a system = +veheat transferred from a system = -ve

Process number Heat (kJ) Work (kJ)1 1.6 -58.62 70.6 -11.13 -23.9 59.94 ?? 78.2

Sum 48.3 68.4

From which the heat transfer that must be occurring to make the work and heat balance = 20.1 kJ

Q2 … reading data from steam tables

From your 'steam tables'. you will find

i) Water at 40C hf = 167.5 kJ/kgii) Water at 26C hg = 2548.4 kJ/kgiii) Water at 34C hg = 2420.4 kJ/kg

_______________________________________________________________________________________________WATS 4. Mark Russell (2005)Student number51 School of Aerospace, Automotive and Design Engineering

University of Hertfordshire

Q3

i) internal energy as fluid enters device.

From the steam tables the specific internal energy under these conditions (0.2 Bar, saturated vapour) can be read as 2468 kJ/kg.

Since the question asks for internal energy and not specific internal energy this value needs to take account of the mass of fluid flowing into the device. i.e. 0.3 kg/s.

Internal energy entering device (Ug) = ug∗m = 2468 * 0.3 = 740.4 kJ/s = 740.4 W

ii) internal energy as fluid leaves device.

Similarly, from the steam tables the specific internal energy under these exit conditions, (0.2 Bar, saturated liquid), can be read as 251 kJ/kg.

Again, the question asks for internal energy and not specific internal energy. Therefore the mass flow rate needs to be considered

Internal energy leaving device (Uf) = u f∗m = 251 * 0.3 = 75.3 kJ/s = 75.3 W

iii) change in internal energy as a consequence of this process

ΔU=U leaving−U entering = 75.3 - 740.4 = -665.1 kJ/s = -665.1 W

iv) using the conditions noted, find the saturation temperature

This again comes from looking in the steam tables. In this instance the saturation temperature, which will be constant for this phase change process, is 60.1C

If you see any errors or can offer any suggestions for improvements then please e-mail me at m.b.russell@herts.ac.uk

_______________________________________________________________________________________________WATS 4. Mark Russell (2005)Student number51 School of Aerospace, Automotive and Design Engineering

University of Hertfordshire

CreditsThis resource was created by the University of Hertfordshire and released as an open educational resource through the Open Engineering Resources project of the HE Academy Engineering Subject Centre. The Open Engineering Resources project was funded by HEFCE and part of the JISC/HE Academy UKOER programme.

© University of Hertfordshire 2009

This work is licensed under a Creative Commons Attribution 2.0 License.

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_______________________________________________________________________________________________WATS 4. Mark Russell (2005)Student number 51 School of Aerospace, Automotive and Design Engineering

University of Hertfordshire