ABSTRACT
This study aims to investigate the magnetohydrodynamic flow induced by a moving surface in a nanofluid and the occurrence of suction and solar radiation effects using the Buongiorno model. The numerical findings are obtained using MATLAB software. The effects of various governing parameters on the rates of heat and mass transfer along with the nanoparticles concentration and temperature profiles are elucidated graphically. Non-unique solutions are discovered for a specific variation of the shrinking strength. The temporal stability analysis shows that only one of them is stable as time passes. Furthermore, raising the Brownian motion parameter reduces both the local Sherwood number and the local Nusselt number for both solutions. It is also observed that increasing the thermophoresis parameter reduces the rate of heat transfer, whereas the opposite trend is observed for the rate of mass transfer.
ABSTRACT
Thermophoresis represents one of the most common methods of directing micromachines. Enhancement of heat transfer rates are of economic interest for micromachine operation. This study aims to examine the heat transfer enhancement within the shell and tube latent heat thermal storage system (LHTSS) using PCMs (Phase Change Materials). The enthalpy-porosity approach is applied to formulate the melting situation and various shapes of inner heated fins are considered. The solution methodology is based on the Galerkin finite element analyses and wide ranges of the nanoparticle volume fraction are assumed, i.e., (0% ≤ φ ≤ 6%). The system entropy and the optimization of irreversibility are analyzed using the second law of the thermodynamics. The key outcomes revealed that the flow features, hexagonal entropy, and melting rate might be adjusted by varying the number of heated fins. Additionally, in case 4 where eight heated fins are considered, the highest results for the average liquid percentage are obtained.
ABSTRACT
An unsteady convection-radiation interaction flow of power-law non-Newtonian nanofluids using the time-fractional derivative is examined. The flow domain is an enclosure that has a free surface located at the top boundaries. Also, the geometry is filled by aluminum foam as a porous medium and the overall thermal conductivity as well as the heat capacity are approximated using a linear combination of the properties of the fluid and porous phases. Additionally, the dynamic viscosity and thermal conductivity of the mixture are expressed as a function of velocity gradients with a fractional power. Marangoni influences are imposed to the top free surface while the bottom boundaries are partially heated. Steps of the solution methodology are consisting of approximation of the time fractional derivatives using the conformable definition, using the finite differences method to discretize the governing system and implementation the resulting algebraic system. The main outcomes reveled that as the fractional order approaches to one, the maximum values of the stream function, the bulk-averaged temperature and cup-mixing temperature are reduces, regardless values of the time.
ABSTRACT
Using phase change materials (PCMs) in energy storage systems provides various advantages such as energy storage at a nearly constant temperature and higher energy density. In this study, we aimed to conduct a numerical simulation for augmenting a PCM's melting performance within multiple tubes, including branched fins. The suspension contained Al2O3/n-octadecane paraffin, and four cases were considered based on a number of heated fins. A numerical algorithm based on the finite element method (FEM) was applied to solve the dimensionless governing system. The average liquid fraction was computed over the considered flow area. The key parameters are the time parameter (100 ≤t≤600 s) and the nanoparticles' volume fraction (0%≤φ≤8%). The major outcomes revealed that the flow structures, the irreversibility of the system, and the melting process can be controlled by increasing/decreasing number of the heated fins. Additionally, case four, in which eight heated fins were considered, produced the largest average liquid fraction values.
ABSTRACT
OBJECTIVE: To evaluate the effect of adjunctive use of vaginal progesterone after McDonald cerclage on the rate of second-trimester abortion in singleton pregnancy. METHODS: A randomized controlled trial at Woman's Health Hospital, Assiut University, Egypt, between April 2017 and March 2019 enrolled women eligible for McDonald cerclage. After cerclage, participants were randomly assigned to receive progesterone (400 mg pessary) once daily until 37 weeks or no progesterone. The primary outcome was rate of abortion before 28 weeks. Secondary outcomes included gestational age at delivery, preterm delivery, mean birthweight, Apgar score, and admission to the neonatal intensive care unit (NICU). RESULTS: The rate of spontaneous abortion was higher in the no-progesterone group (P=0.016). Mean gestational age and mean birthweight was higher in the progesterone group (P<0.001 and P=0.002, respectively). The frequency of preterm neonates, neonates with Apgar score less than 7, and admission to NICU was higher in the progesterone group than in the no-progesterone group (P=0.005, P=0.008, and P=0.044, respectively). CONCLUSION: Adjunctive use of vaginal progesterone after McDonald cerclage was found to decrease the frequency of second-trimester abortion and to improve perinatal outcomes in singleton pregnancy. Clinicaltrials.gov: NCT02846909.
