Page 152 - Analysis and Design of Energy Geostructures

124 Analysis and Design of Energy Geostructures

jj. In general, can you neglect the different values of thermal diffusivity of the dif-
ferent materials involved with energy geostructures? Why?
kk. It has been observed that the potential variable characterising heat transfer is the
temperature. What is the potential variable characterising mass transfer?
ll. Can you mathematically define the total head, expressing the physical meaning
of each constituting term?
mm. In which conditions can the total head be reduced to the piezometric head?
nn. Define mathematically the Reynolds number.
oo. What does the Reynolds number physically represent?
_
3
pp. A fluid flows turbulently in z-direction, at a rate of V 5 3.5 m /s, through a
2
cylindrical pipe. The pipe has a cross-sectional area of 0.5 m and the fluid has
2
a viscosity of 1.2 N/(s m ) and a Reynolds number of 6283. What is the density
3
of the fluid (expressed in kg/m )? Assume the fluid is incompressible and the
flow is at the steady state.
qq. Write Darcy’s law and discuss its validity depending on the flow regime.
rr. Which is the fundamental parameter that allows understanding if convection
plays a major role in heat transfer in soils? To which law is this parameter
related?
ss. What are the units of the hydraulic conductivity? How this variable is related
to the intrinsic permeability?
tt. What is the threshold value (or range of values) of groundwater flow velocity
that may be accounted for considering or neglecting convection in practical
analyses and designs of energy geostructures?
uu. Write the mathematical expression of the mass conservation equation and dis-
cuss its terms.
vv. Is it reasonable to foresee thermal energy storage through energy geostructures
for a site that is characterised by significant groundwater flow? Why?
ww. Consider an energy pile located below a very large raft of a building and oper-
ating as a geothermal heat exchanger. Assume that a very thick thermal insula-
tion layer is placed at the uppermost surface of the slab, so that no influence of
the ambient conditions is experienced in the subsurface. Consider that the soil
is saturated and that no groundwater flow occurs. Which is/are the main
mode/s of heat transfer occurring in the soil?