Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.
Direct solar collectors are designed to absorb solar energy
into a carrier fluid which then transports the heat
away to some storage area. To increase the efficiency
of the solar collectors the design is changed to that of a
direct solar collector and nanoparticles are suspended
in the heat transfer fluid. A two dimensional model
of a static nanofluid in a solar collector is presented in
this paper. Two equations are integral in describing the
problem mathematically; the radiative transfer equation
accounts for the attenuation of solar radiation through
the depth of the collector and the heat equation describes
the distribution of heat in the collector. The source term
that accounts for the volumetric heat release is derived
under the assumption of independent scattering. Taking
advantage of the small aspect ratio the full model is approximated
by the one-dimensional limit. Furthermore,
a decaying exponential function is used to approximate
the source term which allows for an exact analytical
solution to be presented. In power generation applications
high operating temperatures and maximum energy
absorption are favourable. Therefore, the collector efficiency
is measured in terms of the Carnot number and
total solar energy absorption. For a fixed collector height,
varying nanoparticle concentrations and exposure times
are investigated to maximise collector efficiency
