The subject aims to present and discuss some advanced topics in the field of engineering thermodynamics and heat transfer. Both theoretical and applied aspects are considered. In particular, modeling and numerical methods are presented and applied to relevant systems in engineering thermodynamics. This course is designed to broaden the student’s background required for the analysis and design of real systems and devices involving fluid flow and heat transfer phenomena.

The student is expected to know physical, technical and design aspects of some typical energy systems. Additionally the course provides to the student the basic knowledge to deal with design aspects of fluid distribution networks and steam generators. Another objective is to convey to the student the ability to understand the complex phenomena related to radiative heat transfer.
Furthermore the student is expected to know the numerical techniques necessary to model fluid distribution network. Similarly the student is also expected to learn the ability to implement numerical models that describe radiative heat transfer in engineering systems, and to become familiar with the theory and the numerical models commonly used to calculate the energy demand of a building and the energy provided by the heating system and equipment.

The prerequisites for this subject are the subjects on thermodynamics and heat transfer, chemistry, and advanced engineering thermodynamics.
Contents

Generality:
The subject is structured on theoretical lessons and practical applications. In particular, a district heating system (users + pipe network + thermal plant) is considered as the application of the numerical methods that are introduced.
The first part of the subject is focused on fluid distribution networks. On the basis of conservation equations introduced in previous courses fluid distribution networks are theoretically characterized. Computational techniques are introduced to numerically solve the fluid dynamic and thermal problems typical of a fluid distribution network. Then the student is required to apply the methods illustrated during the lectures to a district heating network.
Afterwards, the topics related to the energy demand calculation of a building and its equipment are provided and some relevant energy savings measures are discussed. The theory outlined in this section is at the basis of the numerical methods commonly used to calculate the primary energy demand of a building.
In the last part of the subject , convection and radiation heat transfer are considered. Radiation exchange between gray bodies and radiative behavior of participating media, such as gases, are presented. The zonal model is presented as numerical technique to solve radiative heat transfer problems involved in engineering systems. An application of the zonal model to a steam generator is proposed. In such analysis both convective and radiative heat transfer are numerically modeled in order to compute the temperature field in the system and the radiative heat transfer rate.

Topics:
Introduction to the subject.
Introduction to numerical techniques and its relevance in the field of the field of engineering thermodynamics.
Radiative exchange between gray surfaces. Net radiative heat flux. Introduction to radiative heat transfer: geometrical definitions, emitted radiation, incident radiation, interaction between radiation and matter. Black and gray body concepts. Radiative heat transfer between black surfaces.
Introduction to zonal model and radiative heat transfer in a cavity of grey surfaces. Total interchange areas and adiabatic surfaces. Radiative heat transfer in the presence of a participating media. Gas-surface and surface-surface radiative exchange. Real gas model and direct flux surfaces. Energy balances.
Recall of the continuum mechanics. Continuity, momentum and energy equations. Initial and boundary conditions. One dimensional form of the equations. Introduction to networks. Numerical models for the analysis of fluid distribution networks. Constrains, objectives, type of problem and methodologies involved in the analysis of typical real networks. Graph theory and mono-dimensional models of complex systems. Topological model, branch and node concept. Definition of graph, tree, co-tree, cut-set and loop. Incidence matrix an major topological correlations. Physical models and conservation equations. The steady-state fluid dynamic problem for a fluid distribution network. SIMPLE algorithm for the solution of the fluid-dynamic problem. Upwind method for the solution of the thermal problem.

During an application to a district heating system is proposed to the students. The application is composed of various parts, each corresponding to the application of a numerical method to a portion of the system.
The first part concerns the evaluation of the energy demand for space heating of buildings connected to a district heating network and the corresponding heat load for the plant. Calculation of the plant efficiencies is also performed.
Second part consists in the detailed design of a waste-to-energy cogeneration system which supplies heat to the network.. A numerical model is developed to study the combustion process and the heat transfer phenomenon taking place in the system. Specifically the zonal model is used to model radiative heat transfer in the combustion chamber considering the interaction between radiation and combustion products. The results are then compared with those obtained applying a continuum model implemented through a commercial software. Then the analysis of the heat recovery steam generator is performed. Possible advantages in integrating a thermal storage unit are also examined
Last part of the practice consists in the design of a district heating network. The problem consists in the choice of pipe diameters and the evaluation of mass flow rates and pressure drops along the network. Two configurations of the network are examined.

A textbook covering the program of the course is available.
Notes of the lectures available online on the "Portale della Didattica".

Text books:
A. Sciacovelli, V. Verda, R. Borchiellini. Numerical Design of Thermal Systems, Clut, 2015
A. Bejan, "Advanced Engineering Thermodynamic" John Wiley & Sons 1997.
F.P. Incropera, D.P. DeWitt, Fundamentals of Heat and Mass Transfer, John Wiley & Sons, 2002.
H.C. Hottel, A. F. Sarofim. "Radiative Transfer" McGraw – Hill, Inc. 1967.
M. F. Modest, "Radiative heat transfer" Academic Press 2003.
R. Siegel, J.R. Howell, "Thermal radiation heat transfer". CRC Press, 1992.

The exam is in the written form and it is based on the theoretical aspects and the proposed application. An optional oral integration is possible. A written report is requested for the proposed applications.