Introduction
“The laws of thermodynamics:
- You cannot win, you can only break even
- You can only break even at absolute zero
- You cannot reach absolute zero (Anonymous)”
This rather silly quotation may seem a bit off putting at first, but whilst it is technically correct, don’t be too down heartened by it – after all, if it was meant to be taken seriously, whoever came up with it would have their name attached.
This unit looks at the study and behaviour of gases and vapours, and it would be beneficial if you had some understanding of basic thermodynamics before beginning it. It is worth 1 SQA credit at level 7 and should nominally take around 40 hours of study, though this is a very variable figure and really should only be used as a very rough guide. Further information is available from the SQA approved descriptor which is also provided.
If you need any further help or information, please do not hesitate to get in touch with your tutor.
Content of the unit
The unit is intended to provide you with the opportunity to develop knowledge, skills and understanding relating to a range thermofluids principles such as would be expected if you were seeking to use an HNC as an exit award, or if you wished to go on to further study.
The unit is divided into 3 learning outcomes, with each outcome containing a variety of subtopics that all fall into a logical grouping. The learning outcomes describe what you will be able to do when you successfully complete the unit. Namely:
- Evaluate properties, changes, and energy transfers of state for perfect gases.
- Evaluate properties, changes, and energy transfers of state for vapours.
- Apply energy, continuity, and momentum principles to steady flow processes.
Don’t worry if you don’t understand what these mean at the moment, all will become clear as you work through the unit.
Learning outcome 1
Evaluate properties, changes, and energy transfers of state for perfect gases
The first outcome is intended to last around 20 hours and looks at solving problems for a variety of different perfect gases and thermodynamic processes. Over the course of this learning outcome we will look at (SQA, 2007):
- The ideal gas laws
- Combined gas law
- Universal gas constant
- Use of process diagrams
- Specific heat capacities of gases
- Internal energy and enthalpy
- Tables of properties
- Relationship between temperature scales
- Relationship between different types of pressure
- Relationship between heat and work
- Conservation of energy
- Open and closed thermodynamic systems
- Thermodynamic processes:
- Flow and non-flow processes
- Constant volume, constant pressure, isothermal, polytropic and adiabatic processes
- Energy transfers
Learning outcome 2
Evaluate properties, changes, and energy transfers of state for vapours
Outcome 2 is similar to outcome 1, except that rather than looking at gaes we will look at vapours. This outcome is expecyed to last around 10 hours. In this learning outcome we will look at (SQA, ibid):
- Use of process diagrams
- Specific heat capacities of vapours
- Internal energy and enthalpy
- Tables of properties
- Mass and volumetric flow rates
- The steady flow energy equation
- Energy transfer principles for:
- Boilers
- Superheaters
- Condensers
- Turbines
- Basic steam terminology:
- Dry steam
- Wet steam
- Superheated steam
- Specific volume
- Internal energy
- Dryness fraction
- Degree of superheat
Learning Outcome 3
Apply energy, continuity, and momentum principles to steady flow processes.
This final outcome looks at flow and will involve solving problems for flow though pipes of varying sections, inclinations and bends using Bernoulli’s equation and vector analysis. This outcome is expected to last around 10 hours. Over the course of the outcome we will look at (SQA, ibid):
- Bernoulli equation
- Flow through pipes and vanes
Assessment of the unit
You will be assessed on the unit by using a closed book unseen examination paper – just like a school exam. The total amount of time spent in examining the unit should not be more than 2 hours, unless special arrangements are in place which would need to be agreed in advance. You will probably be examined by a single exam at the end of the unit, lasting the full two hours, and covering all 3 of the learning outcomes. This will be done on a sampling basis – that is you will not necessarily be examined on every topic, but will need to know every topic as you will not know which ones you are being examined on in advance. The exam will be a mix of short answer, restricted response and structured questions. Your tutor will explain how you will be examined. No matter how you are examined the total time should not be more than 2 hours.
The assessment is on a pass/fail basis with a threshold score set for the examination – again your tutor will let you know what score this is. If you are not successful at the first attempt you will be given another go. Remember when completing your exam to show your working – it’s usually worth more marks than the final answer. You will be given a formula sheet in the examination but will need to provide your own calculator.
How to use these materials
These materials are designed to guide you through the unit and ensure that you are properly prepared for your assessment. This is done by a series of written notes, videos explaining some of the key concepts, and plenty of practice materials. In addition practice questions are provided – it is recommended you try these in the run up to your examination, and preferably attempt them under exam conditions before going back and checking your answers. The practice questions are written in a way to give you an idea of what to expect in the actual exam.
Precisely how you work through the materials is a matter of personal choice, but a suggested method could be to watch the video, read the notes and then attempt the practice questions. If you find when trying the practice questions that you are struggling, refer back to the videos and the notes until it makes sense. There are plenty of practice questions, be sure to make use of them. You do not have to work through the materials in the order they are provided but it is strongly recommended as they build on each other.
Finally remember – if in doubt, ask!
References
Anonymous quote taken from Todayinsci available from https://todayinsci.com/QuotationsCategories/T_Cat/Thermodynamics-Quotations.htm (Accessed 4th August 2021)
SQA, 2007. Thermofluids. Dalkeith: Scottish Qualifications Authority.