School of Engineering UCLan Coursework Assessment Brief 2020-2021

Module Title: Fluid Dynamics of Fire

Module Code: FV2001 Level 5

FV2001 – Design Assignment This assessment is worth 40% of the overall module mark

THE BRIEF/INSTRUCTIONS

Please answer ALL questions, showing workings out where appropriate, and appropriate referencing.

It is your responsibility to ensure that you are using the correct, most up to date version of any guidance documents. The word count for this assignment is approximately 2000 words. This assignment is designed to help you assimilate the fundamental principles underlying fluid flow in order to be able to apply them these to fires and explosions.

Mark allocation for each question is given at the end of each question.

Learning outcomes

This assessment has been designed to test the learning outcomes, as described in the module descriptor, specifically:

1. Describe fundamental principles developing in fluid dynamics, heat and mass transfer

4. Examine the main characteristics of jet and buoyant flames, fire plumes and flows encountered in fire environments.

PREPARATION FOR THE ASSESSMENT

• Information for this assignment will be provided on Blackboard and discussed in the weekly laboratory classes.

• Click LINK to go to the reading list for this module.

RELEASE DATES AND HAND IN DEADLINE

Assessment Release date: 6 November 2020

Assessment Deadline Date and time: The deadline is 16.00 (4pm) on 26th March 2021

Please note that this is the final time you can submit – not the time to submit!

Your feedback/feed forward and mark for this assessment will be provided on 19th April 2021

SUBMISSION DETAILS

Presentation Instructions – It is your responsibility to ensure that your work is neatly and accurately presented.

The work must be:

• Word-processed

• 1.5 or double line spaced, Arial 12-point font, Justified

• Page numbered, Margins left and right 3cm

Marks may be deducted for failure to follow these instructions. Please look at the Student Guide to Assessment for more information.

Referencing

All academic writing must be referenced. If you use other people’s ideas without referencing them, you are plagiarising their work.

Either:

Use the Harvard system of referencing within your text. This will take the form: surname, year of publication, page number, and is enclosed within brackets, for example (Bradley 1998, 277). At the end of your work you should provide an alphabetical list of all the works you cite.

Or:

Use the Numeric System of referencing within your text. At every point in the text where a reference is made, insert a number (in brackets or superscript) and then list the references numerically at the end of your work,

Plagiarism

The use of work produced for another purpose by you, working alone or with others, must be acknowledged. Copying from the works of another person (including Internet sources) constitutes plagiarism, which is an offence within the University’s regulations. Brief quotations from the published or unpublished works of another person, suitably attributed, are acceptable. You must always use your own words except when using properly referenced quotations.

You are advised when taking notes from books or other sources to make notes in your own words, in a selective and critical way.

Submission

Your work must be submitted electronically and anonymously via Turnitin (a guide to submitting work via Turnitin can be found on Blackboard).

Assessment Deadline Date and time: The deadline is 16.00 (4pm) on 26th March 2021

Please note that this is the final time you can submit – not the time to submit!

Your feedback/feed forward and mark for this assessment will be provided on 19th April 2021

HELP AND SUPPORT

If you have any questions arising from this assessment brief you can:

• Post a question on the Teams area for this module.

• Message the module tutor on Teams or

• Email the module tutor.

Information and guidance will be given in lectures and in the tutorials during semester 1.

• For support with using library resources, please contact Bob Frost or SubjectLibrarians@uclan.ac.uk. You will find links to lots of useful resources in the My Library tab on Blackboard.

• If you have not yet made the university aware of any disability, specific learning difficulty, long-term health or mental health condition, please complete a Disclosure Form. The Inclusive Support team will then contact to discuss reasonable adjustments and support relating to any disability. For more information, visit the Inclusive Support site.

• To access mental health and wellbeing support, please complete our online referral form. Alternatively, you can email wellbeing@uclan.ac.uk, call 01772 893020 or visit our UCLan Wellbeing Service pages for more information.

• If you have any other query or require further support you can contact The *, The Student Information and Support Centre. Speak with us for advice on accessing all the University services as well as the Library services. Whatever your query, our expert staff will be able to help and support you. For more information , how to contact us and our opening hours visit Student Information and Support Centre.
• If you have any valid mitigating circumstances that mean you cannot meet an assessment submission deadline and you wish to request an extension, you will need to apply online prior to the deadline.
Disclaimer: The information provided in this assessment brief is correct at time of publication. In the unlikely event that any changes are deemed necessary, they will be communicated clearly via e-mail and a new version of this assessment brief will be circulated. Version: 1
Please answer ALL 17 questions, showing workings out where appropriate, and appropriate referencing.
Mechanics of fluids: Hydrostatics
1. The three vessels depicted in the Figure 1 bellow contain water in the same height (H) from their base and have the same base surface area (s). The pressure of the water and the total force in the base of each vessel is the same. Nevertheless, the total weight of the water is different for each vessel. Please explain this paradox.
(3 marks)
Figure 1. Three vessels containing hexane.
2. Calculate the pressure at the base of the vessels in Figure 1, assuming h=0.1 m, g = 9.8 m/s2, ρ = 659.4 kg/m3 and atmospheric pressure Po= 1.01 x105 Pa. Resulting value of pressure should be presented in both Pascals (Pa) and atmospheric pressure (atm) units.
(2 marks)
3. Find the force exerted on the right-side wall of a container filled with hexane as shown in the Figure 2. Assume density of the fuel, ρ=659.4 kg/m3, height of the liquid, H=0.1m, the depth of the vessel is d=0.05m and the area of the side walls, S=dxL=0.05×0.07=0.0035m2. Ignore the external atmospheric pressure.
(10 marks)
Figure 2. Force applied in the right-side wall of the container.
4. What is the exact location of application of the force you calculated in Question 3? Take into consideration that at the point of calculations as indicated in Figure 2 the composition of the sum of the all torque exerted on the side wall is zero.
(10 marks)
Mechanics of fluids: Bernoulli’s law
5. What are the restrictions on the use of the Bernoulli’s equation?
(5 marks)
6. Explain the terms in Bernoulli’s equation when the fluid is static.
(5 marks)
7. Use the Bernoulli’s equation to calculate the pressure in a fire hose nozzle. The fire hose, as depicted in Figure 3, has a diameter of 6.4 m and can accommodate a flow of 40 L/s, starting at a gauge pressure of 1.62×106 N/m2. The hose rises to 20 m along a ladder to a nozzle having a diameter of 3 cm. what is the pressure in the nozzle?
(10 marks)
Figure 3. Fire hose.
8. The water pressure inside a hose nozzle can be less than the atmospheric pressure. This is attributed to the Bernoulli effect. Please, explain how the water can actually emerge from the water against the opposing atmospheric pressure.
(5 marks)
Fire plumes
9. Consider a circular 20m2 pool fire. The fuel, hexane, is burning at a regression rate of 7 mm/min (i.e., the fuel surface goes down due to evaporation at a rate of 7mm/min). determine the average flame height of a free plume in the absence of wind for an ambient temperature equal to 15oC, if the pool is circular.
(10 marks)
10. Repeat the calculations considering ambient temperature equal to 35oC.
(2 marks)
11. Repeat the calculations assuming the pool is now rectangular, with one side equal to 20m and one side equal to 1m, for ambient temperature equal to 15oC, and assuming the same regression rate.
(3 marks)
12. Compare the result to the flame height for circular pool and explain the differences.
(5 marks)
13. List and analyse the assumptions and approximations that led to formation of the steady-state axisymmetric buoyant plume.
(5 marks)
14. List the empirical correlations of Heskestad and McCaffrey for the calculation of the centreline plume velocity and temperature difference at the far-field plume region.
(5 marks)
Shock Waves and Detonation
15. Distinguish between deflagration and detonation.
(2 marks)
16. For a steady one-dimensional detonation (Chapman-Jouguet or CJ detonation), define the CJ detonation velocity, vD or also found in the literature as DCJ, for an ideal-gas mixture following a one-dimensional approach, as shown in Figure 4. Assume one-dimensional steady flow, constant area, ideal gas behavior, constant and equal specific heats, negligible body forces and adiabatic conditions. Furthermore, assume that the pressure of the burned gases, P2, is much greater than that of the unburned mixture, P1, i.e. P2>>P1.
(8 marks)
Figure 4. One-dimensional detonation wave in a constant area duct.
17. A combustion wave propagates in a constant area duct. Determine the velocity of a detonation wave propagation assuming an ideal-gas mixture having a constant specific heat, Cp of 1200 J/kg K. The mixture is initially at 2 atm and 500 K. The heat release per unit mass of mixture, q, is 3×106 J/kg and the mixture molecular weight, MW, is 29 kg/k mol. Assume that the pressure of the burned gases, P2, is much greater than that of the unburned mixture, P1, i.e. P2>>P1.
(10 marks)
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