Volume 48, Issue 1

Continuous effort is made on Gifford-McMahon cryocoolers (GMC) to amplify its refrigeration power, so they can be used to cool the cryopumps, high Tc magnets and development of efficient small-scale hydrogen liquefiers, etc. The fluidic-driven GMC is considered to be more reliable and prominent candidate than the mechanically-driven GMC due to its structural simplicity and reliability. Nonetheless, cooling mechanism of the fluidic-driven GMC is complicated, as the displacer motion inside the displacer cylinder is simultaneously controlled by the pressure difference between drive chamber and compression/expansion chamber. Different paths of displacer can be traced inside the displacer cylinder for different drive-chamber discharging process, hence, pressure–volume power of compression and expansion chambers, and refrigeration power changes. A theoretical study is conducted in present paper to visualize the influence of drive-chamber discharging process on the thermodynamic characteristics of fluidic-driven GMC for the first time. Thermodynamic cycles are drawn at the expansion chamber of the fluidic-driven GMC for different values of drive-chamber discharging process for two types of valve timing arrangements. Energy and work loss behaviors in different components of the GMC are also analysed. Adequate experimental investigations have also been carried out on a fluidic-driven displacer type GMC to verify the simulation results.

The internal heat source and reaction effects on the onset of thermosolutal convection in a local thermal non-equilibrium porous medium are examined, where the temperature of the fluid and the solid skeleton may differ. The linear instability and nonlinear stability theories of Darcy–Brinkman type with fixed boundary condition are carried out where the layer is heated and salted from below. The D 2 {D^{2}} Chebyshev tau technique is used to calculate the associated system of equations subject to the boundary conditions for both theories. Three different types of internal heat source function are considered, the first type increases across the layer, while the second decreases, and the third type heats and cools in a nonuniform way. The effect of different parameters on the Rayleigh number is depicted graphically. Moreover, the results detect that utilizing the internal heat source, reaction, and non-equilibrium have pronounced effects in determining the convection stability and instability thresholds.

Chemical engine is an abstract model of some devices, such as solid state, photochemical, and electrochemical devices, photovoltaic cell, and mass exchangers. Finite chemical-potential source is one of its features. Finite time thermodynamics provides effective theoretical tool for determining performance limits for given thermal systems, and determining optimal process paths of thermal systems for given performance objectives. Endoreversible model is its basic model. A model of endoreversible non-isothermal chemical engines operating between a finite chemical-potential source and an infinite chemical-potential sink with mass resistance and heat resistance is established. Mass transfer processes between chemical potential reservoir and working fluid of the model are assumed to obey Onsager equations in linear irreversible thermodynamics. With a fixed cycle period, optimal cycle configuration for the maximum work output of the model is derived by applying optimal control theory. The results obtained include optimal performance and optimal path results in many previous literatures, and can provide some theoretical guidelines for optimal designs of practical chemical plants.

Densities and isothermal compressibilities of several nanofluids were modelled using a perturbed hard-chain equation of state (EoS) by an attractive term from Yukawa tail in 273–363 K range and pressure up to 45 MPa. The nanofluids of interest comprise TiO 2 -Anatase (-A), TiO 2 -Rutile (-R), SnO2, Co 3 O 4 , CuO, ZnO, and Al 2 O 3 as nanoparticles dispersed in ethylene glycol, water, poly ethylene glycol, ethylene glycol + water, and poly ethylene glycol + water as base fluids. The EoS was capable of estimating 1397 density data of 9 nanofluids with the overall average absolute deviations (AAD) of 0.90%. The coefficients of isothermal compressibility of 6 selected nanofluids were also predicted using the EoS with the AAD of 5.74% for 1095 data points examined. The PHDC EoS was not capable of estimating the excess volumes of 3 selected EG-, PEG-, and water-based nanofluids accurately as the relative deviations from the literature data were greater than 34%, even though the trend of results against the nanoparticle concentration was in accord with the literature. To further investigate the density prediction, we have trained a neural network with a single hidden layer and 17 neurons which was able to predict the densities of nanofluids accurately.

We present a novel theoretical model to investigate the pressure-driven flow of a non-Newtonian Oldroyd-B nanofluid in an expanding channel. The momentum and temperature field equations are developed on the bases of momentum conservation law and Fourier’s principle of heat transfer in conjunction with Buongiorno’s model of nanofluids. Numerical investigations on a viscoelastic Oldroyd-B fluid flowing in horizontal, converging, and diverging channel have been carried out to collect point-by-point stress data i.e., the shear stresses and flow field). The constitutive model of a viscoelastic fluid adopting the Oldroyd-B model is considered to characterize the rheological behavior of the fluid. The flow equations are changed to a non-linear system and solved numerically using the Runge–Kutta Butcher method via MATLAB code. Numerous emerging flow parameters are probed for their effects on flow and heat transfer characteristics using extensive numerical computing. In converging flow, increasing the Reynolds number and channel angle leads to an increase in velocity distribution, indicating that backflow is eliminated. However, the velocity decreases as the retardation parameter increases significantly. Furthermore, the Oldroyd-B nano liquid literature is elevated by the Brownian motion and thermophoresis parameter, while for the concentration of the nanoparticles the behavior is contrary. The velocity field of an Oldroyd-B fluid is compared with the velocity fields for viscous fluids, which are then traced out as limiting instances. In comparison, the results for polymer solutions obtained in this analysis are compared with a Newtonian fluid.

In “soft–soft nanocomposites” based on film formation of latexes with structured particles, the combination of particle structure and interparticle crosslinking leads to materials that behave as nonlinear viscoelastic fluids at small strains and as highly elastic networks at larger strains. Similarly, in studies of flow-induced crystallization in polymers, a two-phase model is often invoked in which a soft viscoelastic component is coupled with a rigid semi-crystalline phase providing stiffness. In the present work, we use the framework of non-equilibrium thermodynamics (NET) to develop stress-strain relationships for such two-phase systems characterized by a viscoelastic and an elastic component by making use of two conformation tensors: the first describes the microstructure of the viscoelastic phase while the second is related to the elastic Finger strain tensor quantifying the deformation of the elastic phase due to strain and is responsible for strain-hardening. The final transport equations are formulated in the context of the generalized bracket formalism of NET and can describe the rheological behavior and mechanical response of a large variety of soft materials ranging from rubbers to artificial tissues.

For the given initial finite high-temperature heat reservoir temperature, continuous Hamilton–Jacobi–Bellman equations are established to obtain optimal finite high-temperature heat reservoir temperature for minimum power consumption of multistage Carnot heat pumping system with generalized convective heat transfer law [ q ∝ (Δ T ) m ]. Analytical expression of optimal heat reservoir temperature with Newtonian heat transfer law ( m = 1) is obtained based on generalized optimization results for minimum power consumption. For other heat transfer laws ( m ≠ 1), numerical solutions for minimum power consumption are provided. Optimization results for multistage Carnot heat pumps are compared with maximum power output solutions of multistage irreversible Carnot heat engines.