Abstract:
Nanofluids are fluids with immersed nanoparticles in it. It demonstrates much higher
convective heat transfer coefficient than conventional working fluids. Single-phase and
mixture-phase models are the two models that are being used for the nanofluid study. In
this study, forced convection heat transfer of nanofluids is done using both single-phase
and mixture-phase models and the results are compared with experimental results. The
nanofluid is then used as the working fluid in a flat plate solar collector to investigate the
performance improvement of the collector. The governing equations of various studies
here are discretised using the finite volume method. The models are assumed axisymmetric
and at steady state. Hybrid differencing scheme is used during discretization. A
code is written using SIMPLER algorithm and then solved using the MATLAB engine.
The mixture-phase model studied here, considers two slip mechanisms between
nanoparticle and base-fluid, namely Brownian diffusion and thermophoresis. Al2O3-water
nanofluid is used for the study of nanofluid and the study shows significant increase in
convective heat transfer coefficient while the mixture-phase model demonstrates slightly
lower values than the single-phase model. The study is done with various nanoparticle
concentrations and Reynolds numbers. With increasing particle concentration and
Reynolds number, the convective heat transfer coefficient increases and as well as the
shear stress. For low concentrations of the nanoparticle, Nusselt number is slightly lower
than the base fluid and as the concentration increases, the Nusselt number also increases
than the base fluid. The study also investigates the effect of particle size but the mixturephase
model didn’t provide any variation with particle size. The Al2O3-water nanofluid is
then used as the working fluid of a flat plate solar collector. The study is done with various
nanoparticle concentration and flow rates and the efficiency increases with increase of
both nanoparticle concentration and flow rates. The efficiency found by Al2O3-water
nanofluid is then compared with CuO-water nanofluid in the flat plate collector and the
CuO-water provides better results. The efficiency increases by 6.6% and 8.6% for Al2O3-
water and CuO-water nanofluid respectively for 0.025 mL/s of flow rate. There is also a
significant efficiency increase of 10.3% found by using internal fins to the riser tube.
