Symmetric Heat Transfer Research Articles

Analysis on heat transfer performance sub-channels of sodium-cooled fast reactor fuel assemblies based on entransy

In this paper, the symmetric heat transfer performance of sodium-cooled fast reactor fuel assemblies was analyzed and studied. The model is analytically optimized based on sub-channel calculations. The deviations of the numerical simulation results from the pre-existing experimental data in the literature are within 10 %, with an average deviation of 2.5 %, which tested the reliability of the model. The calculated results demonstrated that the distribution of the axial power, temperature, and coolant of the reactor core is approximately symmetric M-shape. The reactor core coolant has a monotonic increase in axial distribution with the cladding temperature and the temperature peaks all appear at the reactor core outlet. The individual fuel assemblies' internal temperature is relatively sensitive to the axial power distribution, and there are troughs around the imports and exports. The simulated results showed that the center temperature of the hottest rod reactor core block reached 965.65 K. This pa- per provides a better guide to understanding the overall heat transfer effect by optimizing the heat transfer model.

Symmetric Heat Transfer Pattern of Fuel Assembly Subchannels in a Sodium-Cooled Fast Reactor

The method outlined in this paper is convenient and effective for studying the thermal performance of fuel assemblies cooled with sodium fast reactors using the subchannel procedure. To initially study an optimization model for a symmetric single fuel assembly heat transfer pattern analysis in a fast sodium-cooled reactor based on subchannel calculations, this paper innovatively proposes a subchannel heat transfer analysis method with the entransy dissipation theory, which can solve the limitations and inaccuracies of the traditional entropy method such as poor applicability for heat transfer processes without functional conversion and the paradox of entropy production of heat exchangers. The symmetric distributions of the thermal-hydraulic parameters such as coolant flow rate, coolant temperature, cladding temperature, and fuel pellet temperature were calculated, and the entransy dissipation calculation method corresponding to the fuel assembly subchannels was derived based on the entransy theory. The effect of subchannel differences on the thermal-hydraulic parameters and the symmetric distribution pattern of entransy dissipation during the cooling process of the fuel assembly was analyzed and compared from the symmetrical arrangement of subchannels in the axial and radial directions.

A simple model of heating and evaporation of droplets on a superhydrophobic surface

A new model for heating and evaporation of a droplet on a superhydrophobic surface is proposed. The model uses the analytical solution to the spherically symmetric heat transfer equation with the source term which is implemented in the numerical code and used at each time step of the calculations. It is assumed that heat supplied by conduction and radiation from the substrate to the droplet is instantaneously and homogeneously distributed throughout the whole droplet volume. Both these assumptions are acceptable only in the case when these heats are much smaller than heat supplied to the droplet from ambient gas by convection. It is shown that in some cases heat supplied to the droplet by conduction is comparable or greater than that supplied to the droplet by convection. This happens predominantly at the final stages of droplet evaporation and in this case the model cannot be used. Another assumption on which the model is based is that the effects of the ambient gas temperature gradient on convection droplet heating can be ignored and that this heating can be considered assuming that the temperature of the ambient gas around the droplet is homogeneous. The model is validated using in-house experimental data and experimental data available from the literature. Good agreement between modelling and experimental results is demonstrated when the assumptions on which the model is based are satisfied.

Experimental study on temperature drop during roller quenching process of large-section ultra-heavy steel plate.

Large-section ultra-heavy steel plates feature low cooling rate of central part during quenching process, as well as great differences in texture and performance along thickness direction. Wet jet impingement quenching test apparatus and multi-channel temperature recorder were developed to explore the temperature drop characteristics and its influential factors of ultra-heavy steel plate. The temperature drop curves of plates with different thickness (160, 220, and 300 mm) and weight (23-43 tons) were recorded during the quenching process, accompanied with the exploration on distribution rules of temperature gradient, heat flux density and cooling rate along thickness direction under different water volumes (9000-9400 m3/h) and pressures (0.4-0.8 MPa), upon which the three-dimensional inverse heat conduction model, surface heat transfer coefficient model and thermophysical parameter model were established using finite element and optimization methods. The overall results indicate the symmetric heat transfer between the upper and lower plate surfaces can be realized, when the water flow ratios of the upper and lower surfaces were 1:1.25 and 1:1.4 under pressures of 0.8 MPa and 0.4 MPa, respectively. The "temperature return" phenomenon was accompanied with changing heat flux density of wall surface of 220 mm- and 300 mm-thick plates. The lowest cooling rate along thickness direction appeared at 1/4 thickness position for the 160 mm- and 220 mm- thick plates during quenching, which was attributable to the synergy between heat flux density and temperature gradient. This work may pave a way for improving the cooling rate and quenching uniformity of ultra-heavy steel plates along thickness direction.

Effects of temperature and fluid velocity on beer pasteurization in open and closed loop heating systems: numerical modeling and simulation

Abstract A two-dimensional symmetric heat transfer model and a fluid rotation model were established to study beer pasteurization process through the COMSOL Multiphysics software. Two heating modes, including closed-loop heating (CLH) and open-loop heating (OLH), were considered. There was a significant natural convection phenomenon in both heating systems. However, the natural convection became weaker with a gradual increase in the heating temperature of the beer. The maximum fluid velocity (FV) in CLH and OLH modes was 69.34 and 43.74 mm/s, respectively. After heating at 333.13 K for 20 min, the minimum and maximum pasteurization unit (PU) values in CLH were 55 and 59, respectively, while the corresponding values for OLH were 30 and 55, respectively. The pasteurization effect under the CLH mode was better than the OLH one. The heat transfer was also affected by fluid flow (laminar and turbulence) patterns. The PU value was nonlinearly related to the FV. The optimal FV can be obtained at ∼50 mm/s.

Performance analysis and structural optimization of multi-tube type heat integrated distillation column (HIDiC)

Abstract In this research, a multi-tube type heat integrated distillation column was developed and investigated by process simulation. By proper simplification and assumption, the process simulation model of multi-tube type HIDiC was developed in Aspen Plus. Tested by two different binary mixtures, benzene & toluene as well as p-xylene & o-xylene, a detail performance analysis was implemented based on the results of the process simulation. Besides the traditional evaluating parameters such as compression ratio, temperature profile and energy saving, the available energy efficiency and duty drop ratio were first proposed to give a more complete analysis. A systematic economic evaluation was applied to assist the structural optimization process. Moreover, the concept of a symmetric heat transfer HIDiC was proposed to improve operational flexibility and given an advanced research.

Fundamental solutions of the thermoelastic equations for transversely isotropic plates

The problem of thermoelasticity for transversely isotropic plates acted upon by concentrated heat sources is solved. The {1, 2}-order equations of thermoelasticity that incorporate the transverse shear and normal stresses are used. A bending heat source with symmetric heat transfer is considered. The dependence of thermal stress components on the thermal and thermomechanical parameters of transversely isotropic plates is studied

A fundamental solution of the equations of thermoelastic bending of orthotropic plates

We construct a fundamental solution of the equations of thermoelastic bending of orthotropic plates under symmetric heat transfer and a linear heart distribution over the thickness. On the lateral surfaces convective heat transfer with a surrounding medium occurs in accordance with Newton's law. The effect of the orthotropy parameters and heat transfer on the magnitude of the bending moment and torque is studied numerically. Two figures. Bibliography: 4 titles.

Vapour bubble collapse: The influence of the initial radius and of subcooling

Experimental results for rising bubbles with initial radii ranging from 0.06 to 1 cm collapsing in water during a short pressure rise are presented. Data are analysed in two ways: -firstly investigating the influence of the initial radius and of subcooling on the bubble wall velocity; -secondly experimental data relating to bubble radius decrease are compared in dimensionless form, with a spherically symmetric heat transfer theory. A strong influence of the initial radius and of subcooling contradictory to the theory is still shown.

Heat transfer in LMFBR fuel elements Part I: Effects of fuel pellet displacement

Random displacement of mixed oxide fuel pellet axes from the central axis of their overall liquid metal fast breeder reactor fuel element occurs when the pellcts are randomly loaded within the fuel element cladding sheath. Assuming azimuthally symmetric heat transfer from the outer cladding surface to the bulk coolant, the influence of this random displacement upon the temperature distribution throughout the fuel element is examined when the granular or porous detailed fuel structure and cracks in the fuel (discussed in Part II) are ignored. It is shown that for a typical example, in which the maximum displacement is only 0.0075 cm and the fuel pellet radius is 0.2465 cm, the variance of the maximum fuel temperature is in the vicinity of 115° C, so that this random displacement effect can be quite important especially for those fuel pellets with an expected maximum temperature near the melting point of the fuel.