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Introduction – Fluids Laboratory Data Wrangling.

It is still necessary for scientists and practicing engineers to spend time analysing data from physical experiments, tests and their results to find correlations, test theories or calibrate equipment. The concept behind this report is designed to give you practice in the skills required to analyse original experimental work, where a definitive answer is not yet known and may not even exist. In this lab, you are asked to analyse data from a practical investigation involving air flow forced forwards, then backwards, through a ‘one-way’ Tesla Valve. This is an example of practical fluid mechanics, which is a core skill item for architectural engineers. The objective of this lab is to look for any relationship between any operating characteristic such as loss factor k, static air pressure, kinetic air pressure, flow rate or diodicity caused by the Tesla Valve, then to describe the attempts that you made to describe any relationship that you found. The best way to do this is with equations of line-fits after analysing graphs.

You may perform any mathematical function that you want on the data to look for relationships: for instance, log plots, y=ax2+bx + c, etc.. You will definitely have to produce graphs.

You will note from the marks allocation breakdown below that finding a relationship is not important: it’s what you did to try to find one that will determine your marks.

Tip: it’s okay (in fact it’s essential) that you say what didn’t work for you, as well as what did work. You can’t loose marks – only gain them.

Tip: don’t waste time looking at other students or groups. There are a multitude of things that might be correlations. I don’t know what will work either – this is real, original, science. Just describe accurately what you did to analyse your data.

Background

The device you are analysing is known as a Tesla Valve, invented by the famous Nikola Tesla, 100 years ago. It has found various uses in the past, none of which were widespread. We are researching this because it may be very useful in the very high-rise buildings that are planned for the mid-to-long term urban developments, which have particular problems venting their wastewater drainage-waste-vent (DWV) systems. The particular aspect of the Tesla Valve that is applicable here is that the valve’s resistance to air flow is low in one direction, and much higher in the reverse direction. A simple one-way (or check) valve will achieve this, but stopping (or even reducing) the airflow quickly is very undesireable as that leads to sudden air pressure spikes. The Tesla Valve impedes the airflow progressively and with no moving parts.

In the past, the Tesla Valve has been successfully used for very high air pressures and flow rates found in the oil and gas industries. The data gathered here for this lab though is targetted at the much smaller air pressures and flow rates that are found in DWV systems and especially in very tall buildings. Presious D10LP groups have analysed similar data, but never at such high air pressures. As usual, this is a double-blind experiment: I haven’t analysed this yet either and don’t know what (or even if) any links exist. You will find endless information resources on Tesla Valves on the ‘web, but you don’t need anything more than this Brief and the associated data to fully complete this part of D10LP.

Tutorials and help

All of the data gathering has been done for you. This is because gathering data nowadays is a trivial matter – it’s analysing it that counts. The timetabled slot in EC.G12 for Part 1 is for tutorials only, to help you analyse the data and help you get going. Tutorials are optional. You can also arrange directly with me via Teams if you prefer – individually or in groups. You can e-mail me anytime and as many times as you want if you are stuck or have questions. This includes situations where you want to do something but don’t know how, for example complex Excel functions. Don’t wait for the timetables slots!

Procedure.

Data has been gathered for you with the equipment shown in the pictures at the end of this Brief. If you were performing the data collection yourself it would have taken exactly 3 minutes: it’s the analysis of the data that is important, not gathering it. The data is in a separate spreadsheet with two tabs – one each for the forward and reverse orientations of the valve. The data in each tab was gathered by two air pressure transducers which recorded a changing voltage according to the air pressures. This voltage is then to be converted into air pressures (mm H2O) by a calibration factor. By using two transducers, in two different locations, the static air pressure (PS) and kinetic air pressure (PK) are recorded. Static pressure (PS) is taken with a small tube flush with the pipe wall. Kinetic pressure (PK) is taken with a tube (Pitot-Static tube) in the middle of the airflow. The static and kinetic pressures allow all of the required information to be determined – some useful equations for doing this are given below.

Tip: when including the equations in an Excel spreadsheet, break the calculations down into single steps in each column – easier to trace your steps and fix mistakes that way, and much easier for me to help you if needed.

You can neglect errors, because the resolution of the recording devices is several orders of magnitude smaller that the signals being measured, but there will be a lot of noise in the data. The source of the noise is turbulence caused by the air pump, friction and the Tesla valve itself, and is not part of the experiment so it should be ignored. You should come up with your own way of getting round the noise, such as various smoothing facilities offered in Excel.

Tip: be careful – smoothing too much may hide any changes that you are looking for.

The data was gathered by starting with ambient air pressure applied to the Tesla Valve for a few seconds, then the air pressure was increased and left to stabilise, then stepped up again, and repeated to give one complete test (this spreadsheet is labelled “right way”). The Tesla Valve direction was then reversed and the whole procedure repeated in a second test  (this spreadsheet is labelled “wrong way”). So, your raw data for each test will appear to have relatively stable regions with sections of change between them. The power of the air pump at each step was identical between the two tests, so any differences you see will be due to the Tesla Valve direction. The time durations for each of the stable regions were under experimenter control, so you should ignore time: it was only needed to separate the pressure regions which were the real focus of the tests.

Tip: use the first stable region (zero static and kinetic air pressures) to establish a baseline zero for the tests.

Marks Allocation (with page length suggested guidance):

LO1: presentation throughout (consistent units, axes titles, sig.figs. etc)

LO2: analysis techniques used to find any relationship

LO3: describing the relationship or showing that none exists

AHEP4 (Engineering Council) Skills

This is the overlap between the work that you have to do and the AHEP4 Skills that you will need for C.Eng. Chartership after graduation. You don’t need to report on these for D10LP, but if you come back for 5th yr (M.Eng.) you will need to know this.

M1. Apply a comprehensive knowledge of mathematics, statistics, natural science and engineering principles to the solution of complex problems. Much of the knowledge will be at the forefront of the particular subject of study and informed by a critical awareness of new developments and the wider context of engineering

M2. Formulate and analyse complex problems to reach substantiated conclusions. This will involve evaluating available data using first principles of mathematics, statistics, natural science and engineering principles, and using engineering judgment to work with information that may be uncertain or incomplete, discussing the limitations of the techniques employed

M3. Select and apply appropriate computational and analytical techniques to model complex problems, discussing the limitations of the techniques employed

M7. Evaluate the environmental and societal impact of solutions to complex problems (to include the entire life-cycle of a product or process) and minimise adverse impacts

M9. Use a risk management process to identify, evaluate and mitigate risks (the effects of uncertainty) associated with a particular project or activity

M12. Use practical laboratory and workshop skills to investigate complex problems M16. Function effectively as an individual, and as a member or leader of a team. Evaluate effectiveness of own and team performance

M17. Communicate effectively on complex engineering matters with technical and non-technical audiences, evaluating the effectiveness of the methods used

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