Heat Transfer
Objectives
Know the three modes of heat transfer -- conduction, convection and radiation -- the corresponding laws and models.
Acquire skills to formulate and solve common problems concerning heat transfer in various engineer situations such as insulation and heat exchange, resorting to computacional methods when found necessary.
Learn to manage the limited time available at all moments of evaluation. Exercise autonomous study. Know how to apply what has been learnt to new situations and in which various parts of the study matter may be present, particularly in the assessment elements. Use computational tools as means to assist in the understanding of the study matter.
General characterization
Code
10505
Credits
6.0
Responsible teacher
Daniel Cardoso Vaz, Luís Miguel Chagas da Costa Gil
Hours
Weekly - 4
Total - 66
Teaching language
Português
Prerequisites
It is assumed knowledge of matters dealt with in: «Física II», «Análises Matemáticas», «Álgebra Linear», «Mecânica dos Fluidos» and «Termodinâmica Aplicada» (energy balances, specific heat, heat exchanger efficiency, ...).
The written and laboratory work evaluations have implicit that the student is able to express his/hers train of thought intelligibly, either in portuguese or english, know how to use spreadsheet or another computational aid, and to apply the tools that were used in the course.
Bibliography
One of the following textbooks:
1. Carvalho, J. L. (2017), "Transferência de Calor e Eficiência Energética", NOVA Editorial - FCT/UNL.
2. Incropera e DeWitt (2011), "Fundamentals of Heat and Mass Transfer", John Wiley & Sons.
3. Holman, J. P. (2010), "Heat Transfer", McGraw-Hill.
4. Çengel, Yunus A. (2006), "Heat and Mass Transfer: A Practical Approach", McGraw‑Hill.
5. Bejan, Adrian (2013), "Heat Transfer", John Wiley & Sons.
6. Figueiredo, Rui (2015), "Transmissão de Calor - Fundamentos e Aplicações", Ed. Lidel.
Teaching method
There are theorectical (1.5 h/week) and problem-solving (2.5 h/week) classes, as well as a laboratory session. In the theorectical classes the study matter is presented while giving space for students'''' questions. There is yet an experimental demonstration (on natural convection). In the problem-solving sessions, the approach is centrered in the application of concepts, by proposing exercises and seeking the active participation of the students in solving them; there are computacional laboratory demonstrations (extended surfaces and flow over flat plate).
With the reduction of contact hours there are parts of the programme that involve more autonomous study and that are consolidated by means of two works (finite diference method and heat exchangers), contributing to the final grade, and using computational means.
Evaluation method
Continuous assessment consists of a "theoretical-practical" type component and another of "laboratory or project" type. The first consists of three tests, T1, T2 and T3, counting 32,5%, 27,5% and 20% respectively for the final grade (NF). The second, weighing 20% in the final grade, consists of two practical problems to be made individually (P1 and P2, weighing 10% each) to be solved outside the classes and using computational aids. The frequency is obtained with the submission of both problems with an arithmetic mean >= 7,5 val.
Work P1 is to be done just after the finite difference matter and work P2 just after the heat exchanger matter. The deadlines will be set after the semester''s tests dates are fixed by the Scientific Commitee.
In the exam route, its weight in the final grade is the same as that of the three tests, i.e. 80%. The parcels enter these expressions rounded to the tenth.
For the tests and/or exams, students should bring their set of tables and graphs that are found at the end of the Proposed Exercises booklet, without annotations, and these shall be the only element of consultation. Thus, only simple scientific calculators can be used, although others may be admitted as long they are in exam mode. Transgressions are dealt with according to the «Regulamento de Avaliação de Conhecimentos».
Final grades greater than or equal to 17 val. may be subject to defense of grade, by oral exam.
Subject matter
1- Heat transfer modes: Fourier, Newton and Stefan-Boltzmann laws. Heat diffusion equation. Thermal diffusivity. Isotherms and heat flux. Electrical analogy.
2 - Steady-state conduction: mathematical and numerical methods (finite differences). Extended surfaces (fins).
3- Dynamic conduction: Biot and Fourier numbers. The Heisler charts. Periodic regime.
4- Forced convection: brief revision of fluid dynamics concepts. Differential quation of energy conservation in the thermal boundary layer. Prandtl and Nusselt numbers. Empirical correlations.
5- Heat exchangers: Logarithmic Mean Temperature Difference (LMTD); configurations; thermal design; LMTD and efectiveness-NTU methods.
6- Natural convection: Grashof number. Empirical correlations.
7- Radiation: properties. The black and grey bodies. Kirchhoff and Wien laws. Monochromatic and total emissivities. Shape factors.