Analytical approach for entropy generation and heat transfer in CNT-nanofluid dynamics through a ciliated porous medium

The transportation of biological and industrial nanofluids by natural propulsion like cilia movement and self-generated contraction-relaxation of flexible walls has significant applications in numerous emerging technologies. Inspired by multi-disciplinary progress and innovation in this direction, a thermo-fluid mechanical model is proposed to study the entropy generation and convective heat transfer of nanofluids fabricated by the dispersion of single-wall carbon nanotubes (SWCNT) nanoparticles in water as the base fluid. The regime studied comprises heat transfer and steady, viscous, incompressible flow, induced by metachronal wave propulsion due to beating cilia, through a cylindrical tube containing a sparse (i.e. high permeability) homogenous porous medium. The flow is of the creeping type and is restricted under the low Reynolds number and long wavelength approximations. Slip effects at the wall are incorporated and the generalized Darcy drag-force model is utilized to mimic porous media effects. Cilia boundary conditions for velocity components are employed to determine analytical solutions to the resulting non-dimensionalized boundary value problem. The influence of pertinent physical parameters on temperature, axial velocity, pressure rise and pressure gradient, entropy generation function, Bejan number and stream-line distributions are computed numerically. A comparative study between SWCNT nanofluids and pure water is also computed. The computations demonstrate that axial flow is accelerated with increasing slip parameter and Darcy number and is greater for SWCNT- nanofluids than for pure water. Furthermore the size of the bolus for SWCNT-nanofluids is larger than that of the pure water. The study is applicable in designing and fabricating nanoscale and microfluidics devices, artificial cilia and biomimetic micro-pump

Effects of friction and temperature-dependent specific-heat of the working fluid on the performance of a Diesel-engine

Using finite-time thermodynamics, the relations between the power output, thermal efficiency and compression ratio have been derived. The effect of the specific heat of the working fluid, being temperature dependent, on the irreversible cycle performance, is significant. The conclusions obtained in this investigation are in full agreement with those of published studies for other cycles and may be used when considering the designs of actual diesel-engines.Finite-time thermodynamics Diesel-cycle Heat resistance Friction Variable specific-heat

Combustion in a spark-ignition engine

This paper describes a simple analysis for the prediction of pressure within a spark ignition engine. This is done by modelling the combustion process using the Wieb function approach, which is an exponential function in the form y=1-e-axm, to calculate the rate of fuel burned. By careful selection of a and m, any spark ignition engine with any combustion chamber shape and any specified dimensions can be assessed by this model. The validity of the model has been tested by comparing the model results with those obtained from running the engine under the same operating conditions. The results obtained from the theoretical model when compared with those from the experimental ones show a good agreement. Also, the effects of the many operating conditions, such as compression ratio, engine speed, and spark timing have been studied.