Journal of Engineering Thermophysics最新文献

In this study, the boundary layer flow and mixed convection heat transfer of a Casson fluid over a curved stretching surface coiled in a circle of radius (R) have been considered. The effects of thermal radiation are also incorporated by using non-linearized Rosseland approximation. A curvilinear coordinate system is used to develop the mathematical model for the considered flow and heat transfer problem. Similarity solutions of the modeled partial differential equations are computed using shooting method. Influence of different involved parameters on the quantities of interest including fluid velocity, temperature, skin friction coefficient and rate of heat transfer along the surface is discussed through graphs and tables.

The present study investigates the effects of droplet impact height, tilt angle, and surface temperature on the impact and freezing process of water droplet on a cold surface by using a Motionpro high-speed camera and a DSA-30 droplet surface analyzer. The temperature of the plate was changed from an ambient temperature of 24.0°C to (-10.0^{circ})C, while three impact heights ((H) = 100, 150 and 200 mm) were set. The data indicated that increasing impact height led to increase in the maximum spreading diameter and maximum endpoint displacement, but its effect on droplet spreading time was not significant. With decreasing the surface temperature, the rate of change in the droplet diameter was smoother and the droplet freezing time reduced. Moreover, at low Weber number ((We < 200)), the impact height has less effect on the freezing time of the droplet. Besides, compared with the horizontal plate, the droplet freezing time on plate tilted at 30° was higher for the same impact height.

The authors experimentally studied the behavior of evaporation, convection in the liquid, and temperature of the free surface of a pendant droplet of aqueous solution of PEGDA/Irgacure 2959 before and after the onset of polymerization under UV radiation. Data on the temperature of the free surface of droplet were obtained for a wide range of the initial concentration of the polymer base (C_{0}). For (C_{0}= 35)% and less, no polymerization area was observed (according to thermal images). The temperature gradients observed over the droplet surface were very low (less than 0.3°C). At (C_{0}= 65)% and (C_{0}= 90)%, the average temperature (T_{rm S}) on the free surface of droplet changed during polymerization by 2.8C° and 3.7°C, respectively. After polymerization, (T_{rm S}) for the hydrogel became higher than (T_{rm S }) of droplet of pure water. The average velocity of motion of polyamide particles (U_{C}) for water was 2.2–2.4 times higher than that for the PEGDA solution with the initial concentration (C_{0} = 65)%, which is associated with the higher viscosity of the solution. At the onset of polymerization, the velocity (U_{C})dropped to 0 mm/s in a very short time. With increase in the concentration (C_{0}) in the pre-polymer, the time of polymerization reaction start decreased significantly, which shortened the time in which the particles stopped completely. Different limiting factors govern evaporation of a water droplet and a hydrogel droplet. The evaporation rate of droplet of hydrogel decreased with time due to the porous structure of the hydrogel.

Since the initial suggestion that electrically propelled vehicles could be used on the grid-side, numerous significant investigations have been conducted to showcase the capabilities of these technologies, which have proven to be highly advantageous. Nevertheless, there are still many uncertainties surrounding the integration of electric vehicles into the power grid, which is why it has been likened to a black box. These uncertainties include the number of electric vehicles that will be connected to the grid at any given time, the amount of energy that will be stored in their batteries during both the daytime and overnight, and the impact that their charging profiles will have on the overall load placed on the power system. In addition, there are several unanswered questions that need to be addressed. This article presents a novel model that effectively addresses these uncertainties. It is based on a non-stationary Markov chain, and it was introduced in this paper. The findings of the model provide fascinating insights into the number of electric vehicles connected to the grid and the amount of energy saved over the course of a day, as demonstrated by a case study. In addition, this article analyzes and evaluates the ability of the model to accurately represent the load modeling of electric vehicle charging.

PURPOSE. The cathode in a solid oxide fuel cell is responsible for reduction of oxygen molecules to oxygen ions, which then migrate through the electrolyte to the anode. The thermophysical properties of the cathode material play a crucial role for the performance and efficiency of the fuel cell. So, creation of the cathodes of solid oxide fuel cells (SOFCs) requires taking into account the thermal and chemical stability, as well as analysis of the main characteristics of the cathodes, such as the electrocatalyst activity, electrical conductivity, and mechanical strength. This article presents a review of scientific literature on the qualitative characteristics of SOFC cathodes made of various alloys, as well as their operation parameters. In the review, results of functioning of such cathodes are compared in view of possible improvement of their performance parameters in dependence on the composition of the materials used. The composition and microstructure of cathode materials have a great influence on the characteristics of SOFCs. A rational composition of materials is ensured by controlled oxygen non-stoichiometry, and some aspects of defects can improve the ionic and electronic conductivity, as well as catalytic properties for the oxygen reduction in the cathode.

The intention behind this research work is to analyze the flow, heat transfer and entropy generation in a vertical channel filled with a nanofluid. The vertical microchannel is made of two parallel porous and slippy plates. The hot fluid is injected from the left side and succeeded from the right side. Fluid flow within the channel is induced due to an applied favorable/adverse pressure gradient (due to Couette–Poiseuille flow), right plate movement, buoyancy force due to the temperature difference of the channel plates in the presence of heat generation/absorption inside the channel and subjected to a constant applied transverse magnetic field. The resulting governing equations are solved numerically by the shooting method. The conventional fluids are chosen as water, and ethylene glycol-water mixture. The nanoparticles are selected as Al₂O₃ and CuO. Nanofluids modeling, which takes care of base fluid temperature, Brownian motion, diameter and concentration of nano particles, and base fluid physical properties are considered here. Roles of pressure gradient P (at the inlet), temperature of base fluids, heat generation/absorption, the density of the nanoparticle volume fraction on flow and heat transfer characteristics (velocity and temperature distribution, Nusselt number (Nu) distribution, entropy generation and Bejan Number) are investigated here. How the sequence of appearance of curves of flow and heat transfer characteristics (due to variation of aforesaid parameters) are disturbed by the presence of injection/suction, radiation and convective boundary condition is discussed here. A critical analysis is conducted on the individual contribution of irreversibilities due to heat flow, fluid friction and Joule heating to the total entropy generation. At last, we try to find an optimum condition at which local and global entropy generation are minimally generated in the channel.

An experimental investigation of the heat capacity of corrosion-resistant refractory nickel base alloy ChS88U-VI used as a material of the turbine blades for marine engines, blades of converted aircraft gas turbine engines and industrial gas turbine was carried out for the first time. The heat capacity of the alloy has been measured by the method of differential scanning calorimetry in the temperature range 300–1270 K of the solid state, including the phase transition region. The estimated error of the data obtained was 2–4%. The comparison with the promising nickel based superalloys Inconel 617 and Inconel 718 was made. Approximation equations and a table of recommended values of ChS88U-VI alloy heat capacity were developed for use in various engineering and scientific tasks.

The article addresses the thermodynamic issues of supercritical CO₂ power cycles at combustion of methane with oxygen. By the example of cycle with single-stage pump pressure rise with condensation of the working fluid, we consider the issue of ensuring the temperature of the working fluid supplied to the combustion chamber and the value of the theoretical specific heat flux into the regenerative system of cycle for a wide range of initial parameters at the turbine inlet. It has been shown that, depending on the pressure, the heat flux into the regenerative system is 700–1000 kJ/kgCO₂ when an initial temperature of 1000°C is provided, and its fraction in the total heat transfer to the working fluid is 0.5–0.6 in the zone of operational initial parameters. It has been determined that for the cycle efficiency to be high, the temperature of the working fluid supplied to the combustion chamber in the regenerative heat exchanger should be at least (sim 2/3) of the temperature at its outlet.

The results of an experimental study of thermal expansion of the polycrystalline nickel NP2 brand in the temperature range 293.15–1400 K are presented. An anomaly of the linear thermal expansion coefficient in the temperature region of 500–700 K are observed. The effect of the purity of the metal on the temperature of the phase transition of the second kind is confirmed. The temperature dependences of volumetric properties of nickel NP2 brand are determined.

The paper presents 3D numerical modeling of spreading dynamics of R21 (mol. fraction: 0.9) and R114 refrigerant mixture film. We considered an outer flow along a round vertical cylinder at Reynolds number 104 and contact angles of 10°, 30°, 50°, 70°, and 90°. The simulation was performed in OpenFOAM software on the basis of the volume of fluid (VOF) method. Simulated results show an occurrence of the liquid jets flowing from the upper continuous falling film in the range of contact angles 30°–90°, while the liquid flow at contact angle of 10° keeps the only continuous film till the bottom boundary of the cylinder. We defined two scenarios for wetting of the cylinder sidewall at different contact angles: liquid near the contact line moves down and towards to the cylinder surface at (theta = 10^circ), 30°, and 50°, while only vertical velocity differs from zero at (theta = 70^circ) and 90°, excluding jets at (theta = 70^circ). The increase of the contact angle leads to complication of the structure of the refrigerant mixture falling films, arising of jets and redistribution of flow rate between them.