Improvements of evaporation drag model

A special visible experiment facility has been designed and built, and an observable experiment is performed by pouring one or several high-temperature particles into a water pool in the facility. The experiment result has verified Yang‘s evaporation drag model, which holds that the non-symmetric profile of the local evaporation rate and the local density of vapor would bring about a resultant torce on the hot particle so as to resist its motion. However, in Yang‘s evaporation drag model, radiation heat transfer is taken as the only way to transfer heat from hot particle to the vapor-liquid interface, and all of the radiation energy is deposited on the vapor-liquid interface and contributed to the vaporization rate and mass balance of the vapor film. In improved model heat conduction and heat convection are taken into account. This paper presents calculations of the improved model, putting emphasis on the effect of hot particle‘s temperature on the radiation absorption behavior of water.     

蒸汽爆炸粗混合阶段冷液中高温球传热阻力耦合特性的实验研究

采用蒸发电力模型,设计了高温颗粒同水相互作用的实验装置,进行了一系列单个,多个粒子在不同温度,不同入水初速度和不同冷液过冷度情况下的系列阻力实验,初步实验分析表明,高温颗粒在刚刚穿过冷液表面的下沉速度明显低于冷态颗粒的速度,实验值与蒸发曳力模型计算值符合较好.     

膜态沸腾条件下高温颗粒周围流体热动力特性的实验研究

利用已有的实验和理论基础 ,对高温球体与冷液在膜态沸腾条件下的多相混合结构进行详细的小规模实验研究 ,分析了单个高温颗粒在水中阻力受力的情况。发现高温小球在冷却剂中的速度比冷球的低 ,且随球温的升高而减小。目的是利用小规模实验研究单个高温颗粒的传热和阻力特性 ,可以分割各种在膜态高速沸腾条件下干扰换热与运动的影响因素 ,从而从本质上了解该结构条件下的热动力特性。     

冷液中运动高温球传热阻力耦合特性实验研究

高温颗粒与冷液接触会引发剧烈的沸腾蒸发瞬变现象，涉及到工程安全，是一高速瞬变多相传热问题。本实验室设计建立了高温颗粒下落冷液沸腾可视化实验装置，初次实验将1个或有限几个高温球形颗粒坠入水中，利用高速摄像机记录其在冷液中的运动速度，证实了确实存在由周围冷液快速蒸发引起的作用在运动中高温颗粒上的特殊阻力，验证了高温颗粒的蒸发曳力模型。     

Experimental research on heat transfer to liquid sodium and its incipient boiling wall superheat in an annulus

Liquid sodium is mainly used as a cooling fluid in the liquid metal fast breeder reactor （LMFBR）, whose heat transfer, whether convective heat transfer or boiling heat transfer, is different from that of water. So it is important for both normal and accidental operations of LMFBR to perform experimental research on heat transfer to liquid sodium and its boiling heat transfer. This study deals with heat transfer with high temperature （300-700℃） and low Pe number （20-70） and heat transfer with low temperature （250-270℃） and high Pe number （125-860）, and its incipient boiling wall superheat in an annulus. Research on heat transfer involves theoretical research and experiments on heat transfer to liquid sodium. It also focuses on the theoretical analysis and experimental research on its incipient boiling wall superheat at positive pressure in an annulus. Semiempirical correlations were obtained and they were well coincident with the experimental data.     

Non-linear dynamics of a two phase flow system in an evaporator: The effects of (i) a time varying pressure drop (ii) an axially varying heat flux

In this paper we study the phenomena of density wave oscillations (DWO) in a vertical heated channel. The homogeneous equilibrium model is used to simulate the flow in the two-phase region. The equations are solved numerically using a ‘shooting-method' technique. This in its turn employs an implicit backward finite difference scheme. The scheme can incorporate the movement of the interface. It is very elegant and does not involve storage of variables in large N×N matrices. This scheme is sufficiently general and can be used to simulate the dynamic behaviour when: (i) the heat flux imposed at the surface is non-constant, i.e. exhibits an axial variation; and (ii) the imposed pressure drop is varied periodically at a fixed frequency. A possible explanation for the conflicting reports of the effect of a periodic variation in heat flux is provided using a linear stability analysis and the D-partition method. The interaction of the natural frequency of the DWO and the fixed forcing frequency of the imposed pressure drop gives rise to various phenomena viz relaxation oscillations, sub-harmonic oscillations, quasi-periodic and chaotic solutions. To aid the experimentalist describe this infinite-dimensional system on the basis of his experimental results we discuss the characterisation using only the velocity time series data. This is done employing the method of delay coordinate embedding. The phase portraits, stroboscopic map and correlation dimension of the actual attractor are compared with that of the reconstructed attractor from the velocity time series.