Nobuhiro Himeno

Latent heat thermal energy storage of a binary mixture—flow and heat transfer characteristics in a horizontal cylinder

Abstract The characteristics of melting and solidification of a binary mixture of p-C6H4Cl2 and p-C6H4Br2 were experimentally investigated in a horizontal cylindrical capsule. Since segregation occurs in the solidification and density stratification occurs in the melting, non-uniform concentration profiles were formed in both solid and liquid phases. These non-uniform density profiles generated several horizontal cells by free convection in the melting process, while only a few large vortices were generated for pure p-C6H4Cl2. As a result of this difference of free convective motion, heat transfer performance of a binary mixture becomes smaller compared with that of pure material.

Onset of Multilayer Convection in a Partially Heated Circular Cavity

In this article, the time-dependent double-diffusive natural convection is investigated inside a circular cavity containing stably stratified brine solution. The container is heated partially through its sidewalls by a constant heat flux rate. By using Galerkin finite element method, numerical solutions to the Navier-Stokes equations under the Boussinesq flow assumptions have been systematically organized and developed. The evolutions of the stream function, temperature and concentration fields are presented in each evaluated case. Steep and sharp concentration variation in the interfaces together with wavy distribution of temperature within the layers is observed. At first a length scale, which is the vertical displacement of a heated element of the fluid, in a stably stratified solution under Neumann boundary condition is defined. Then a special form of Rayleigh number based on the length scale is obtained and named as universal Rayleigh number. A categorization based on single, two and multilayer formation is established. Temperature distribution along the cavity in the different cases shows a correlation between heat transfer coefficient and the rate of formation and degradation of the layers.

Effects of vibrational relaxation of multi-atomic molecules on stagnation heat transfer

Abstract The flow and temperature fields of multi-atomic gas near the stagnation of a cylinder are theoretically studied, taking molecular vibrational relaxation into account, and putting importance on heat transfer performances. Based on the continuum equations, the velocity and temperature jumps of translational, rotational and vibrational degrees are considered as the boundary conditions and effects of the vibrational relaxation for subsonic flow are discussed. The total heat transferred to the surface is the sum of heats due to the translational-rotational temperature and the vibrational temperature. The ratio of the heats depends much on the ratio of the flow characteristic time to the relaxation time of molecule, and consequently the total heat is much influenced by this ratio of the characteristic times. The effect of the flow-relaxation time on heat transfer is more remarkable in the vibrational nonequilibrium than in the thermal equilibrium main flow. Even in a continuum flow of Knudsen number of about 10 −4 , the effect of vibrational relaxation on stagnation heat transfer is still appreciable.

Condensation of a Binary Mixture of Vapors in a Vertical Tube

Condensation heat transfer of a nonazeotropic binary R113-R114 vapor mixture in a vertical tube is investigated experimentally and theoretically, for cases of both constant and varying wall temperature along a flow direction. Experimental results show that a minimum temperature difference is required for complete condensation at an outlet of the condenser tube. This temperature difference and the heat transfer coefficients can be accurately predicted by a theory which assumes a well-mixed condition in the condensate, that is, a uniform concentration profile in the condensed liquid. When the fin height is 0.2 mm, augmentation of heat transfer by an inner finned surface occurrs in the liquid film but not in a vapor phase. For both cases of the constant and varying wall temperature, the heat transfer coefficients correlate well when an averaged temperature difference between the wall and the bulk flow is used as a characteristic temperature difference.

Theoretical Analysis for the Condensation Heat Transfer of a Binary Vapor Mixture under the Thermal Equilibrium Condition.

The condensation heat transfer of ethanol-water binary vapor mixture is theoretically examined with regard to the assumption of thermal equilibrium in the vapor boundary layer. If the vapor in the boundary layer is subcooled, liquid droplets appear. Under this condition, the effects of the temperature difference between the wall and ambient, and the ambient ethanol mole fraction, on the heat transfer process are investigated. The results show that the heat transfer coefficient under equilibrium conditions decreases from that obtained without droplet formation (nonequilibrium) according to the total amount of the generated liquid droplets.

Heat Transfer Enhancement by Bubble Formation near the Heating Surface.

Convective boiling heat transfer of an immiscible binary liquid mixture has been investigated by using water as the main fluid. R113 and R11 were atomized into the water as volatile materials. When boiling of the volatile material occurs, the heat transfer is enhanced by bubble formation near the heating surface. The heat-transfer enhancement occurs by the addition of a small amount of volatile material, and is insensitive to further increases in its concentration. The enhancement is remarkable in the case of low Reynolds numbers. The heat-transfer enhancement was also observed under the condition that gas bubbles were generated on the heating surface by electrolysis, and it was clarified that the enhancement is caused by the agitation effect of bubbles near the wall

Two dimensional analysis of noncondensable gas effects on heat pipe performance.

ヒートパイプ内の凝縮熱伝達に及ぼす不凝縮気体の影響について、凝縮部端面が断熱、令却壁面一定として軸対称二次元流れを仮定して理論解析を行った。その結果、凝縮部端部には不凝縮気体の顕著な二次元的濃度分布が形成されることを示した。また不凝縮気体建入量と有効伝熱面長さの減少量との関係を定量的に明らかにし、濃度分布の二次元的効果およびヒートパイプの作動条件の変化が熱伝達に及ぼす影響を解明した。

Study on the heat transfer aspect of a thermoelectric power generation system operating under small and medium temperature difference conditions.

A thermoelectric power generation system using thermal energy of little temperature difference has many advantages, such as high reliability, greater safety and maintenance-free operation. as heat transfer augmentation is required to increase the electric power output, a smooth arc-shaped turbulence promoter on the inside surface of the pipe has been proposed from a standpoint of fouling removal by sponge balls. Two types of thermoelectric power generators using cold and warm water pipes with arc-shaped cascade promoters were made. Performances of heat transfer and electric power generation were measured. The optimum condition for power generation is made clear in consideration of pumping power loss. It is concluded that the power generation performance for a pipe with arc-shaped turbulence promoters is better than that for a smooth pipe, in spite of its larger pressure loss.