A numerical investigation of the flow and heat transfer characteristics in a shuttle kiln is performed using the CFD software FLUENT with non-conformal grids and the standard κ-εturbulence model. The integral and local heat transfer non-uniformities of stacks are evaluated, and furthermore, the formation mechanism of such non-uniformities is analyzed. The results show much greater heat transfer intensity among the peripheral stacks than that among the internal ones, which contributes to the integral non-uniformity. The longitudinal heat transfer non-uniformity is primarily caused by the layer-like nozzle jets and bottom outlet, which form three layer-style surrounding streams converging to outlet. The periodical arrangement of stacks together with the strong impingement of jets, leads to the peripheral heat transfer non-uniformity. Based on the comprehensive understanding of flow and heat transfer, innovative efforts are made to improve heat transfer performance by adjusting flowrate distribution among nozzles.

Thermochemical gasification of biomass has been identified as a possible system for producing renewable hydrogen. A continuous tubular supercritical water gasification system is under development that can be used for solution or slurry materials gasification without drying. A unique feature of this system is its ability to realize the overall high-pressure continuous reaction by operating the valves. By the use of this system, designed for temperatures up to 923.15K and pressures up to 35MPa, glucose, as a model compound of biomass, was gasified in supercritical water at a series of temperature and pressure during different resident times to form a product gas composed of H2, CO, CH4, CO2, and a small amount of C2H4 and C2H6. Glucose at low concentrations (ca. 0.1M) can be completely gasified in 923.15K, 25MPa, and 3.6min resident time and no char or tar was observed. Consequently, we adopted these conditions as baseline reaction conditions for the following glucose concentration, alkali addition and reactor tube diameter effect studies. The raw biomass feedstock of sawdust with some CMC was also gasified in this system, the gasification efficiency in excess of 95% was reached.

Fractional pressure drops of single-phase water and steam-water two-phase flows were studied in a pressure range of 3.0-3.5 Mpa. Two helical coiled tubes were employed as test sections and their four different helix axial inclinations were examined. It is found that helix axial angles have little influence on the single-phase Frictional pressure drop, while variation of the steam-water two-phase flow frictional pressure drop is enlarged to 70%. For single-phase flow, some previous correlations were quite accurate in predicting the frictional pressure drop for lower Reynolds number conditions, and a modified correlation was obtained from an enlarged Reynolds number range of the present test. For boiling two-phase flow, great deviation was found among the published few empirical equations and their capability of practical utilization is rather poor on account of their complication in structure. A new easily stipulated correlation is deducted from our present data.

Experiments were conducted to investigate the effects of pulsation upon transient heat transfer characteristics for fully-developed turbulent flow in a uniformly heated helical coiled tube. The non-uniform feather of local heat transfer with steady flow was also examined. The secondary flow mechanism and the effect of interaction between the flow oscillation and secondary flow were analyzed on the basis of the experimental data. Some new phenomena were observed and explained. A series of correlations were proposed for the average and local heat transfer coefficients both under steady and oscillatory flow conditions. The results showed that there were considerable variations in local and peripherally timeaverage Nusselt numbers for pulsating flow in a wide range of parameters.

Systematic investigations of pressure drop type oscillations and their thresholds were conducted for steam-water two-phase flow in a uniformly heated, helically coiled tube. Experiments were conducted to obtain the critical conditions for the occurrence of pressure drop type dynamic oscillation in a closed-circulation helically coiled tubing steam generator. The study showed that different locations of the tank which provided a compressible gas volume (called compressible volume for short) corresponded to different oscillation initial boundaries as well as different oscillating amplitudes and time periods. Moving compressible volume from the inlet of the steam generator upstream could dramatically suppress the occurrence of pressure drop oscillation. Also, non-uniform heat flux distribution along the evaporating channel could change oscillating boundaries significantly, especially when higher heat flux was applied to the higher mass quality region. A study of pressure drop oscillation in various steam generator inclinations showed that gravity has little influence upon the oscillating boundaries. Based on the experimental observations, a set of new methods was first proposed to eliminate the occurrence of pressure drop oscillation.