Page 97 - Analysis and Design of Energy Geostructures

CHAPTER 3

Heat and mass transfers in the context

of energy geostructures

3.1 Introduction
Heat and mass transfer phenomena arise because of the gradient of variables and may
be considered independently from each other. Heat transfer characterises the thermal
behaviour of materials and is often associated with the influence of thermal loads. Mass
transfer characterises the hydraulic behaviour of materials and is often associated with
the influence of hydraulic loads. However, heat and mass transfers are coupled phe-
nomena: one phenomenon (i.e. the flow) can be triggered by the gradient of the vari-
able typically associated with the other phenomenon. That is heat transfer can trigger
mass transfer and the opposite is true.
Heat and mass transfer phenomena crucially characterise energy geostructures
through the thermohydraulic response of the materials involved. Understanding the
physical principles governing heat and mass transfers, and accounting in a suitable way
for the coupling between these phenomena in the analysis and design of energy geos-
tructures is crucial.
This chapter presents a theoretical treatment of heat and mass transfers in the con-
text of energy geostructures. The topic is addressed by focusing on the features of heat
and mass transfers that may be considered for the characterisation of the thermohy-
draulic behaviour of materials and the related analysis and design of energy geostruc-
tures. Comments on the coupling between heat and mass transfers are also provided.
To this aim, idealisations and assumptions are presented first: in this context, the
objective is to propose a summary of the conceptual descriptions and hypotheses that

are employed for describing heat and mass transfer phenomena. Second, principles of
heat transfer are described: the purpose of this part is to characterise the physical phe-
nomenon of heat transfer in the context of the analysis and design of energy geostruc-
tures. Third, conduction, convection and radiation are addressed: the purpose of this part is

to discuss salient features of the considered modes of heat transfer. Next, the energy con-
servation equation and the associated initial and boundary conditions are presented: in this
framework, the aim is to propose mathematical expressions that allow the modelling
of any given heat transfer problem together with the use of initial and boundary con-
ditions. The principles of mass transfer are subsequently discussed: the purpose of this sec-
tion is to describe the fundamentals of the considered physical phenomenon.

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Analysis and Design of Energy Geostructures
DOI: https://doi.org/10.1016/B978-0-12-816223-1.00003-5 All rights reserved. 69