Teacher

prof. Onorio SARO

Credits

6 CFU

Objectives

Objective of this module is providing civil engineering students with the necessary background for the formulation of first (energy) and second law (entropy) balances. The behaviour of perfect gases, pure substances and mixtures of gases with particular reference to wet air are presented. Furthermore, in this module the necessary background for the analysis of conduction, convection and radiation processes is provided. The acquired notions are utilized for simplified modeling of plant components and heat transfer in buildings. The topics covered are the foundation for further studies in the fields of Heating, Air Conditioning and Energy.

Acquired skills

- Energy balances (first law) for control mass and control volume systems,
- Entropy balances (second law) for control mass and control volume systems,
- Energy analysis of thermal and air conditioning plant components,
- Energy analysis of direct and inverse thermodynamic basic cycles,
- Modeling of steady-state and simplified transient heat conduction,
- Modeling of forced and free convection processes,
- Modeling of thermal radiation processes.

Contents

Thermodynamic systems and laws of thermodynamics Scales of temperature. Mass conservation and energy balances for thermodynamic systems. First law of thermodynamics: Formulation for control mass and control volume systems. Thermal efficiency of power cycles and coefficient of performance of refrigeration and heat pump cycles. Internal energy, enthalpy and specific heat capacities. Second law of thermodynamics. Formulation. Reversible and irreversible processes. Carnot cycle. Thermodynamic temperature. Entropy definition. Entropy evaluation for solid and liquid media. Clausius inequality. (9 hours)
Perfectg gases and pure substances State equation of perfect gas, thermodynamic processes of perfect gas: iso-choric, isobaric, isothermal and adiabatic. The p-v-T surface for pure substances, thermodynamic diagrams, compressibility factor. (6 hours)
Energy conversion Basic gas and vapour power cycles. Simple vapour inverse cicles. (6 hours)
Gaseus mixtures Gaseus mixtures with variable composition; psychrometric diagram, air conditioning processes. Notes on air-conditioning cicles (8 hours)
Thermal conduction Steady state and transient conduction equations, thermal conductivity. Monodimensional steady state conduction: the plane wall; the cylindrical wall. The overall heat-transfer coefficient. Unsteady-state conduction: lumped heat-capacity system; periodic unsteady heat conduction in a semi-infinite solid. Periodic thermal transmittance (8 hours)
Thermal convection Classification of convection; boundary layer. Nusselt number. Forced convection: Reynolds number, Prandtl number. Free convection: Grashof and Rayleigh numbers. Empirical relations for forced and free convection heat transfer. Examples of tecnical interest. (8 hours)
Radiation heat transfer Radiation properties. The laws of black-body radiation. The radiation shape factors, radiation heat exchange between black-bodies and between grey-bodies. Radiation networks. (8 hours)
Combined modes of heat transfer Heat exchangers: the Log mean temperature difference. Heat exchanges in buildings. (5 hours)
Guided tours (2 hours)

References

- G. Comini, Fondamenti di Termodinamica Applicata, SGE, Padova, 2000
- G. Comini e G. Cortella, Fondamenti di Trasmissione del Calore, SGE, Padova, 2000
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