Journal of Engineering Thermophysics最新文献

The purpose of this paper is to investigate the energy potential due to salinity gradient of the two selected river estuaries, i.e., Sebou-estuary (Morocco) and Muthupet-estuary (India) for first time using Reverse Electro-Dialysis (RED) process to estimate the available energy, based on thermodynamic equations. The results showed that the energy potential for both estuaries varies from 12.25 MW to 430.44 MW for a river discharge ranges from 21.93 m³s(^{-1}) to 85.67 m³s(^{-1}) in River-Estuarine system (i.e., Sebou estuary); and from 0 MW to 175. 15 MW for a river discharge ranges from 0 m³s(^{-1}) to 47.63 m³s(^{-1}) in Mouth-Lagoon system (i.e., Muthupet-estuary). In addition, the energy potential at Mouth-Estuarine system (i.e., Sebou-estuary) and Mouth-Lagoon system (i.e., Muthupet estuary) for both estuaries is negligible (<8) MW.

The motion of ferromagnetic liquid entering the distilled water stream in the channels of the tesla micromixer M-4 configuration with a characteristic size of 400 (mu)m was investigated in this paper. The interface between two liquids in a magnetic field and without it was considered. The source of the magnetic field was located on different sides relative to the feeding ferromagnetic liquid. It has been shown that when an object is located in a magnetic field, the solubility of the ferrofluid in the base liquid increases. A significant part of the ferroparticles of colloidal liquid in small channels is attracted to the source of the magnetic field (up to 80%), which allows reasonably assuming that the use of ferroparticles for the transportation of medicines is promising.

The study of flow boiling heat transfer inside larger diameter tubes, which are used in water tube boilers, is sparse in the literature. Accordingly, the present study explore numerically saturated flow boiling phenomenon of water in a horizontal plain stainless steel tube at atmospheric condition. The effect of mass flux (254.67 kg/m²s–600.00 kg/m²s), heat flux (16.97–135.00 kW/m²), surface roughness (0.15 mm–0.5 mm), inclination angle (0°–60°) and the tube diameter (5 mm–50 mm) on the flow boiling heat transfer coefficient (HTC) and overall vapor volume fraction (VVF) is investigated. A 2D k-(varepsilon) turbulence model of ANSYS-FLUENT platform is used along with the Volume of Fluid (VOF) model to track the interface between the water and vapor. The numerical findings indicate that HTC rises with a rise in mass flux and declines with a rise in heat flux. Furthermore, it is revealed that when heat flux rises, the VVF in the domain increases, corroborating the observation of a drop in HTC. The observed phenomenon is quite true for conventional tubes used in industries. An improvement in flow boiling HTC is also observed for tubes with higher surface roughness. The influence of inclination angle has substantial effect on the HTC, and the HTC rises with rise in inclination angle except for larger mass flux. The HTC of smaller tube diameter is larger compared to larger tube diameter tube, and after certain range of tube diameter (20 mm) the change in HTC is insignificant.

The paper presents the results of a study of heat transfer in a falling film of freon R21 on a single-row bundle of horizontal tubes made of aluminum alloys with outer diameters of 10 mm and modified oxide porous coatings. The oxide coatings were deposited by micro-arc oxidation (MAO) in phosphate, acid, and silicate-alkaline electrolytes. The surface modification of the MAO coatings consisted in the deposition of copper particles in a solution of copper sulphate. The heat transfer coefficients for the modified MAO coatings were compared with the results for the surface of tubes with base MAO coatings in electrolytes of similar compositions, as well as for a smooth metal tube without coating for Reynolds numbers of the falling film varying from 600 to 1500. Additional surface treatment of the porous ceramic coatings by the deposition of copper particles has led to a significant decrease in the heat transfer coefficients in the falling film compared with the base MAO coatings. The highest enhancement of the heat transfer relative to the case of the smooth tube (of up to 80%) was obtained on the modified MAO coating deposited in the phosphate electrolyte.

This article presents the results of experimental studies of the efficiency of heat transfer under conditions of intense fields of mass forces on a flat rectangular ((16 times 24) mm²) heat-transfer surface (HS) modified by additive manufacturing. A porous sinusoidal-form coating consisting of spherical bronze granules of average diameter of 35 (mu)m was 3D printed on the brass base of the heat-transfer unit. The thickness of the coating was 150 (mu)m in the deepenings and 300 (mu)m on the ridges. Comparative experimental studies were carried out on an unmodified HS and modified HS in liquid nitrogen under conditions of centrifugal accelerations of up to 4090 g. The heat transfer was studied in the range of heat flux densities of (4 cdot 10^{4}{-}8.9cdot 10^{5}) W/m². It has been shown that in the range of heat flux densities of (80,000<q< 320,000) W/m², increase in the intensity of the mass force fields leads to growth in the heat transfer coefficient up to 4 times at transition from the developed boiling regime to the single-phase convection regime. In the region of developed boiling, for the heat flux density range corresponding to a given overload, the heat transfer coefficient normalized to the value of the heat transfer coefficient calculated as per the Borishansky relation for these conditions decreases with increasing centrifugal overload. The dependence of the relative heat transfer coefficient on the overload is close to the ratio (alpha_{rm s}/alpha_{rm sB} sim eta^{-1/6}).

This work consists of a numerical evaluation of the geometry of an arrangement of square heated obstacles under mixed convective turbulent flows. The geometry is evaluated using the Constructal Design method. The geometry has two degrees of freedom: the longitudinal distance ratio between the frontal bluff body and the posterior ones and the ratio of the transversal distance between the posterior bluff bodies. The flow is also evaluated for three Richardson number values. In all simulations, Reynolds and Prandtl numbers are considered equal to (Re_{D}= 22,000) and (Pr= 0.71), respectively. The problem is modeled through the classical turbulence modeling with the SST—(kappa)-(omega) closure model. The main objective of the study is to evaluate how the variation in geometry of the arrangement of bluff bodies and different conditions of mixed convection influences the mean drag coefficient and Nusselt number on the arrangement. The variation of mixed convection conditions led to different effects of longitudinal and transversal pitches over the performance indicators, demonstrating that the mechanism of mixed convection strongly influences the arrangement design. For Ri = 1.0, the solutions for the drag coefficient and Nusselt number curves are smoothed due to the natural convection being in the auxiliary flow direction, which thins the boundary layers. The opposite is noticed for (Ri= -1.0), where the opposing forces between natural and forced convection intensified the free shear flow, increasing the thickness of turbulent boundary layers.

The article elucidates characteristic features of heat transfer during rapid transfer of single-phase solution beyond the liquid-liquid spinodal. It also investigates particularities of the thermal response accompanying decay of unstable state. The objects of the study were aqueous solutions of polypropylene glycols and ethylene glycol monobutyl ether. Controlled pulsed heating of probe was applied, based on the thermal mode of probe temperature stabilization at a given temperature T ^st. The temperature stabilization stage lasted for 20 to 100 ms; the temperature T ^st was increased step by step from the initial value T ⁰ up to 673–773 K. The values of the instantaneous coefficient of heat transfer to pure components and their solutions were calculated from the primary data. At a certain degree of superheating, a temperature-threshold effect of heat transfer enhancement up to 2–3 times was found, which is associated with the decay of unstable state of the solution. The fundamental possibility was revealed for determination of approximation for the lateral and upper spinodal branches, reconstructed on the basis of the characteristic change in the response signals. The concentration of the solution was changed step by step in the zone of compositions lying under the liquid-liquid equilibrium line.

Effective ground thermal properties are the most important parameters in the design of borehole heat exchanger (BHE), which are usually can be obtained by thermal response test (TRT). They’re often vary with depth and influenced by heat injection. This paper presents a method combining TRT and thermal recovery test (TrT) to evaluate the ground thermal properties. The TRT and TrT conducted on a single U-pipe BHE by the TRT rig and two measurement lines each with ten three-wire Pt-100 temperature sensors. Thermal conductivity and borehole thermal resistance at different depths were inferred by the infinite line source model (ILSM) during the TRT while by combining the ILSM with the superposition principle and parameter estimation method during the TrT. Results reveal that, although the heat injection rate varies significantly in the TRT period, the average effective ground thermal conductivity and borehole thermal resistance inferred from the TRT are similar to those inferred from the TrT. However, the results at different depths show great variability and correspond to groundwater and geological information. In addition, TrT results showed that acceptable results (within 5% error) could be obtained for 22 hours in a TrT.

An analysis has been carried out to explore the impact of slip mechanism on MHD flow of Casson nanofluid over a permeable stretching sheet. Besides, we documented the flow aspects which include thermal radiation, variable wall thickness and chemical reaction. We alter the partial differential flow-related conditions into nonlinear ordinary ones employing the similarity transformation approach. Then, using a popular semi-analytical technique known as the Homotopy Analysis Method (HAM), we were able to untangle them. This method yields to power series solutions to nonlinear differential equations. To illustrate the impact of the velocity, temperature and concentration profiles, a parametric research has been done using tables and diagrams. In the limiting sense, the numerical results of our methodology are in great association with the outcomes of previous research. Finally, it is noted that higher values of the velocity slip constraint cause an enhancement in fluid velocity, while escalating values of the thermal slip constraint cause a decline in temperature distribution. Additionally, owing to an escalate in velocity power index, together the temperature and nanoparticle size fraction profiles considerably accelerate.