Volume 45, Issue 1

In this work, the effect of temperature-dependent thermal conductivity (k(T)k(T)) and viscosity (μ(T)\mu (T)) variation on entropy generation in circular channels with an approach from macro- to micro-scale is numerically investigated. Thermally as well as hydrodynamically fully developed flow of water through the fixed length channels with constant total heat flow rate and total mass flow rate is considered. The effects of k(T)k(T) variation and μ(T)\mu (T) variation on entropy generation are analyzed individually as well as collectively. It is observed that in the case of Constant Property Solutions (CPS) Sgen,tot{S_{\mathit{gen},\mathit{tot}}} is maximum at the macro-level; however, in the case of combined k(T)k(T) and μ(T)\mu (T) variations it is maximum at the micro-level. The Bejan number (Be\mathit{Be}) and irreversibility distribution ratio ( φ ) are also calculated for asserting the dominance of frictional irreversibility and conduction heat transfer irreversibility. Additionally, the optimum diameter (D∗{D^{\ast }}) corresponding to the optimum number of channels is calculated at minimum total entropy generation. It is observed that D∗{D^{\ast }} is minimum for k(T)k(T) variation followed by CPS, μ(T)\mu (T) variation, and combined k(T)k(T) and μ(T)\mu (T) variations.

One of the recognized differences between normal and cancer cells is in their metabolic profile. Tumor cells tend to produce energy through glycolysis rather than the much more efficient oxidative phosphorylation pathway, which healthy cells generally prefer. This phenomenon is identified as the Warburg effect. Although several functional explanations have been proposed for the Warburg effect, the competitive advantage of it is still subject of debate. Here we present a thermodynamic model to simulate the competition of cancer and normal cells in terms of bioenergetics. Our model shows that the Warburg effect has an advantage because the entropy production rate is increased and metabolic efficiency is decreased for cancer cells. Although inefficiency is generally considered a competitive disadvantage for living organisms, the thermodynamic model shows that it is not always the case. Indeed, when the energy resources are abundant and the system has a limited ability to export entropy, the organism with a higher rate of entropy production will have a higher chance of survival despite its lower metabolic efficiency. This thermodynamic model predicts that as long as there are enough nutrients in circulating blood, there are two thermodynamic strategies to control cancer cell populations, i. e., (i) decreasing the entropy production rate of cancer cells and (ii) increasing normal cells’ entropy production rate.

Non-equilibrium thermodynamics provides a general framework for the description of mass and thermal diffusion, thereby including also cross-thermal and material diffusion effects, which are generally modeled through the Onsager coupling terms within the constitutive equations relating heat and mass flux to the gradients of temperature and chemical potential. These so-called Soret and Dufour coefficients are not uniquely defined, though, as they can be derived by adopting one of the several constitutive relations satisfying the principles of non-equilibrium thermodynamics. Therefore, mass diffusion induced by a temperature gradient and heat conduction induced by a composition gradient can be implicitly, and unexpectedly, predicted even in the absence of coupling terms. This study presents a critical analysis of different formulations of the constitutive relations, with special focus on regular binary mixtures. It is shown that, among the different formulations presented, the one which adopts the chemical potential gradient at constant temperature as the driving force for mass diffusion allows for the implicit thermo-diffusion effect to be strictly absent while the resulting Dufour effect is negligibly small. Such a formulation must be preferred to the other ones since cross-coupling effects are predicted only if explicitly introduced via Onsager coupling coefficients.

A fugacity-based thermodynamic model for hydrate has been used to determine the equilibrium pressures of hydrate formation. This fugacity-based model uses the PRSV equation of state, which is used to represent the gas phases in the hydrate. The parameters of the model are fitted to the experimental data of binary guest hydrates. The present study is aimed at investigating binary mixtures of CH4{\text{CH}_{4}}–H2{\text{H}_{2}}S, C3H8{\text{C}_{3}}{\text{H}_{8}}–N2{\text{N}_{2}}, N2{\text{N}_{2}}–CO2{\text{CO}_{2}}, CH4{\text{CH}_{4}}–i-butane, C3H8{\text{C}_{3}}{\text{H}_{8}}–i-butane, CH4{\text{CH}_{4}}–n-butane, C3H8{\text{C}_{3}}{\text{H}_{8}}–n-butane, i-butane–CO2{\text{CO}_{2}}, and n-butane–CO2{\text{CO}_{2}} hydrates, which have not been modeled before. Unlike previous studies, the Kihara potential parameters were obtained using the second virial coefficient correlation and the data of viscosity for gases. The fugacity-based model provides reasonably good predictions for most of the binary guest hydrates (CH4{\text{CH}_{4}}–C3H8{\text{C}_{3}}{\text{H}_{8}}). However it does not yield good prediction for hydrates of (CO2{\text{CO}_{2}}–C3H8{\text{C}_{3}}{\text{H}_{8}}). The transitions of hydrate structure from sI to sII and from sII to sI have been also predicted by this model for binary guest hydrates. The AAD % calculated using the experimental data of natural gas hydrates is only 10 %, which is much lower than the AAD % calculated for the equilibrium data predicted by the VdP-w model.

Developing an effective model for non-equilibrium states is of great importance for a variety of problems related to chemical synthesis and combustion. Rate-Controlled Constrained-Equilibrium (RCCE), a model order reduction method that originated from the second law of thermodynamics, assumes that the non-equilibrium states of a system can be described by a sequence of constrained-equilibrium states kinetically controlled by a relatively small number of constraints within acceptable accuracy. The full chemical composition at each constrained-equilibrium state is obtained by maximizing (or minimizing) the appropriate thermodynamic quantities, e. g., entropy (or Gibbs functions), subject to the instantaneous values of RCCE constraints. Regardless of the nature of the kinetic constraints, RCCE always guarantees a correct final equilibrium state. This paper reviews the fundamentals of the RCCE method, its constraints, constraint potential formulations, and major constraint selection techniques, as well as the application of the RCCE method to combustion of different fuels using a variety of combustion models. The RCCE method has been proven to be accurate and to reduce computational time in these simulations.

In order to meet the current challenges in the fabrication of nanobiomaterials and enhancement of thermal extrusion systems, current theoretical continuation is targeted at the rheology of couple stress nanofluid by exploiting activation energy, porous media, thermal radiation, gyrotactic micro-organisms, and convective Nield boundary conditions. The heat and mass performances of nanofluid are captured with an evaluation of the famous Buongiorno model, which enables us to determine the attractive features of Brownian motion and thermophoretic diffusion. The couple stress fluid is beneficial to examine multiple kinds of physical problems because this fluid model has the capability to describe the rheology of various complex fluids, e. g., fluids having long-chain molecules as a polymeric suspension, liquid crystals, lubricants, and human and animal blood. Simultaneous behavior of the magnetic field and porosity are studied with thermal radiation effects. The distribution of velocity has been conducted by using second-order velocity slip (Wu’s slip) and activation energy features. For the dimensionless purpose, the similarity variable has been initiated, and the modeled equations are renovated sufficiently. A famous shooting method is used to determine the numerical solutions, and accurate results have been obtained. A variety of critical flow parameters is graphically illustrated with physical significance.