Transitional heat transfer

Transitional heat transfer

One of the grand challenges is to provide energy for the developing communities of the world
with a population that will increase from 7 to 9 billion by 2050. However, the present methods
to generate electricity with fossil fuels and nuclear power stations are not sustainable as it is
not environmentally friendly. An alternative environmentally friendly method is to make use of
renewable energy.

The sun is probably the most important source of renewable energy available
today. Traditionally, the sun has provided energy for practically all living creatures on earth,
through the process of photosynthesis, in which plants absorb solar radiation and convert it
into stored energy for growth and development. Scientists and engineers today seek to utilize
solar radiation directly by converting it into useful heat or electricity.

Two main types of solar energy systems are in use today: photovoltaics, and thermal systems.
The University of Pretoria and Stellenbosch University formed a solar hub that is being funded
by the DST and the NRF to conduct research on thermal systems. The focus of the University of
Pretoria is to conduct research on heat exchangers of concentrated solar power (CSP) systems.

One of the most basic types of heat exchangers that are being used in CSP systems is a
parabolic trough that consists of a linear parabolic reflector that concentrates light onto a

receiver positioned along the focal line of the reflector. The receiver is a tube positioned
directly above the middle of the parabolic mirror and filled with a working fluid. The reflector
follows the sun during the daylight hours by tracking along a single axis. A working fluid is
heated to 150–350 °C as it flows through the receiver and is then used as a heat source for a
power generation system.


Fluids that are being used in the receiver are water, water mixed with other fluids, molten salt,
oils, etc. To augment the heat transfer from the sun to the fluids,...

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