EXPERIMENTAL RESEARCH AND DESIGN ON HEAT TRANSFER OF EVAPORATOR USED IN THE LARGE QUICK FREEZE PLANT

The evaporator is the main part of a quick-freeze equipment. There are many factors influencing the heat transfer coefficient of an evaporator. The most important factors among them are the fin shape, tube diameter, distance of fin space, frost, and velocity of air flow etc. They mainly influence the thermal efficiency of an evaporator, and therefore its thermal efficiency has direct relationship with the whole efficiency of the quick freeze plant. Evaporators with different structural types have different heat transfer efficiency, in order to obtain high efficiency structure of evaporator, 8 evaporator models with different fin shape, tube diameter and tube arrangement are analyzed and compared. The calculation results show that the integral waved fins, equilateral-triangle arranged small diameter tubes and varying fin-spacing has the highest heat transfer coefficient. The experimental result also shows that the evaporator with this type of structure has better thermal efficiency. The experimental result is in good agreement with the calculation result, it can instruct engineering design for usual designer. A real quick-freeze equipment is designed and put into production. The result shows that, compared with traditional domestic quick-freeze equipments, this equipment decreases by 40% in size and by 20% in energy consumption.

Coefficient of restitution for particles impacting on wet surfaces： An improved experimental approach

The coefficient of restitution is widely used to characterize the energy dissipation rate in numerical simulations involving particle collisions. The challenge in measuring the coefficient of restitution is the strong scatter seen in experimental data that results from varying particle properties, i.e. shape and surface roughness, and from imperfections in the experimental technique. To minimize this scattering, a novel experimental setup was developed based on two synchronized high-speed cameras capturing the collision behaviour of a particle in three dimensions. To measure the wet restitution coefficient, which describes particle impact in the presence of a liquid layer in the contact region, additional accuracy can be achieved by measuring the liquid layer thickness by a high-precision optical confocal sensor. The coefficient of restitution was measured for glass particles with two different diameters, at different relative velocities and liquid layer thicknesses, with a focus on small collision velocities and thin liquid layers, using both the improved （three dimensional） and the conventional （two dimensional） approaches to quantify the improvement of the new method＇s accuracy.

Experimental evaluation of rate coefficients for Rb (5D_J)+H_2→RbH+H reaction

The Rb（5Dj）＋H2→RbH＋H photochemical reaction has been studied. Rb vapor mixed with H2 is irradiated in a glass cell with 778-nm pulses which populate one of the 52D states by two-photon absorption. Measurements for the relative intensities of the atomic fluorescence and the absorption of the RbH product near the axis of the cell yield the rate coefficients for the Rb（5D3/2）＋H2 and Rb（5D5/2）＋H2 reactions, which are （3.6±1.3） ×10^-11 and （1.7±0.6）×10^-11 cm^3/s, respectively. The relative reactivity with H2 for Rb（5D3/2） is higher than that for Rb（5D5/2）.

EXPERIMENTAL ANALYSIS OF THE TURBULENT TRANSFER COEFFICIENT FOR SENSIBLE HEAT IN THE SURFACE LAYER OVER THE QINGHAI-XIZANG PLATEAU

This study deals with the turbulent structure in the surface layer over the Qinghai-Xizang Plateau.Using gradient transfer and heat balance methods we have determined the nondimensional coefficient 1/(?)_m(?)h in the expression of turbulent transfer coefficient for sensible heat (K_h).It is found that the results are in good agreement with the 1/(?)_m(?)_h obtained by Pruitt,et al.The K_h at a height of 1m under cloudy and cloudless conditions is calculated.Finally,the ratio of K_h to momentum turbulent coefficient over the plateau is compared with those over plains.