Subject: Mechanical engineering coursework
Details: it require metlab, excel, graph , calculation for the answer. it include metlan and excel in the work.
Advanced Heat transfer: Coursework
This coursework is a test of your ability to use some of the techniques outlined in the lecture as well as an opportunity for you to start your revision early. It is also meant to assess your ability to use your general knowledge as well as fact finding skills. The majority of the information is given in the three pdf documents provided, but you are expected to look elsewhere for information needed for the work and to be able to reference correctly where you get the information. There are some marks in each question for clarity and conciseness of presentation. Answer each question as a separate question clearly labelled with short paragraph conclusion summarising result. Too much detail or not enough detail will lose you marks. Equations and images should be smart and completed electronically. Submission will be on moodle as a pdf document only.
Assessment objectives:
By the end of this coursework you should:
- Be able to choose, justify your choice and use empirical correlations for determination of heat transfer coefficient
- Be able to use Heisler charts for 3D problems
- Understand View factor algebra and be able to use it.
- Understand how to set up a iterative transient problem
- Be able to comment on a model and use to provide solution of a problem.
- Be able to clearly and concisely provide coherent information that can easily be comprehended by the reader.
- Be able to understand and interpret solutions with minimal help from authority.Relevant files on Moodle:
- This document
- Coursework solutions from 2014-15
- Matlab model (2015b)
- Empirical correlations document.
- Heisler charts
Words: 2000 wordsWhy do so many roasting recipes say to let the meat stand at room temperature for up to an hour before cooking?
To take the chill off the meat's surface so it browns better. Meat is typically refrigerated at about 2.4C, but browning doesn't begin to occur until about 131C. Letting meat sit out of the refrigerator gradually raises the meat's surface temperature, so when it hits the hot oven, it quickly reaches browning temperature and then develops a thick crust. (Cold meat won't brown as quickly or as easily.) Small roasts (less than 3 pounds) will lose their surface chill in less than 30 minutes, while large roasts can rest at room temperature for up to an hour. (This isn't a food safety issue as long as the meat doesn't stay out for more than two hours.)
The meat at the centre needs to be cooked at 51C for 3 minutes to kill the bacteria.
A medallion of lean beef steak with dimension shown in figure 1 is taken from a refrigerator which has an internal temperature of 2.4 C and left standing in a room with temperature 20C. Follow the guidance below to determine what the centre temperature will be after 2 minutes?
(a) Using the correlations sheet on moodle, calculate the maximum heat transfer coefficient of the air with the top surface of the medallion.
(b) Using a combination of the infinite plate and infinite cylinder solution (page 57 in notes), calculate the centre temperature after 2 minutes. (Note the different lengths scales needed)
The medallion steak is then placed in an oven. The walls and air in the oven are at 180ºC. The dimensions of the oven is given in figure 2.
(c) Assume that the medallion steak is at a constant temperature over its surface (call surface 1). Also assuming that the oven is at a constant temperature (call surface 2). Calculate or state all four view factors between the two surfaces.
(d) Using the definition of the Fourier number, approximately how long will it take in seconds for the medallion to feel the heat at the centre?
(e) If the heat transfer coefficient between the air and the medallion is 50 W/m2k, what will be the maximum thickness of slices that you can use to accurately simulate the temperature distribution? How many layers should you split the problem into?
(f) In the appendix to this file, the equation for the surface node is calculated (equation A:1). In a similar manner, explaining each reasonable step in sufficient detail, derive the equation for the centre node of the medallion.
(g) With reference to equation (A:1), define the minimum time step allowable to solve this transient problem.
(h) Sketch and clearly label the resistance network showing the convective heat entering the base and top of the medallion and the resistance and capacitance of all the layers you have chosen. Ignore radiation exchange with the oven wall.
(i) The problem is set-up in Matlab Simscape in the downloadable file. This includes radiation exchange between the wall of the oven and the medallion as well as convection between the air and wall. The model only considers heat flow from one direction. Why is it possible to put an insulation block in this model?
(j) Take a moment to check that you understand the input parameters to the model. Then design a set of numerical experiments to estimate the temperature that the oven should be set to and the time that the medallion needs to be in the oven, so that the surface of the medallion is just browned after the centre has been sterilised of germs by cooking for 3 minutes at a temperature above 51C. (This is for a rare steak).
a. Explain and table your choice of oven temperatures to test.
b. Show a graph comparing the centre temperature only against time for different temperatures. Annotate to identify important features and explain the meaning of graph.
c. Show a graph comparing the surface temperature only against time for different oven temperatures. Annotate to identify important features and explain the meaning of graph.
d. Write a short summary paragraph highlighting advice you would give to the novice chef who wishes to cook the perfect rare steak. Consider the effect of leanness of the meat on the result.