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In this study, a three-dimensional model of a concrete pump truck conveying pipe was established, and a computational fluid dynamics-discrete element method (CFD-DEM) coupling model was used to simulate the pumping process of fresh concrete in different pipes. The influences of the structural parameters and inclination angles of the taper pipe, bend pipe, and their combination on the pressure loss were numerically investigated. Taking the minimum pumping pressure loss as the optimization goal, an objective function was established for the pressure loss of the pump truck conveying pipe. Using the spatial position of the pump truck conveying pipe as the constraint, an optimization method was proposed for the pump truck conveying pipe, based on combining the CFD-DEM coupling model and a single objective optimization algorithm. A comparison between the optimized and initial models shows that the pressure loss of the optimized model of the pump truck conveying pipe is reduced by 5.45%; the average velocity of the coarse aggregate at the exit of the pipe is also reduced.

This paper has studied the influence of ambient pressure and oxygen content on spontaneous ignition of wood by conducting contrastive experiments with wood slab exposed to high temperature radiation at two different altitudes. The measurement of mass loss, time to ignition, and surface temperature of wood are carried out. Results show that mass loss rate of wood at high altitudes (3650 m) is higher than the one at low altitudes (50 m), while ignition delay time of the sample at high altitude is shorter. The surface temperatures at the time of ignition in the two different places are both close to each other, which indicates that the pressure did not affects the ignition temperature. The theoretical analysis on the phenomenon of different ignition behavior of wood in these two altitude environments has been presented.

This paper describes an investigation of the charring of wood exposed to a time-increasing heat flux and constant heat fluxes by using a modified partial differential equation (PDE) model, whose calculated result is validated by experimental result under time-increasing heat fluxes. It is assumed that the base of the char layer can be defined by the temperature of 300 °C. The results have shown that the rate of increase of heat flux and the density of woods significantly affect the charring rate and the charring rate of woods under time-increasing heat fluxes is smaller than that exposed to a constant heat flux. Linear regression conducted on the predictions of charring depth with time as the dependent time-increasing was suitable for time-increasing heat fluxes, while power regression was more suitable for constant heat flux. A successful experiential expression, which describing the relationship among char rate of woods and the increasing rate of heat fluxes and density of wood, has been suggested under time-increasing heat fluxes.

A considerable amount of research has been conducted on the pyrolysis, ignition of wood under constant heat flux. However, the heat flux accepted by materials during the fire is increasing with time. This paper describes the theoretical and experimental investigation on pyrolysis and spontaneous ignition of wood exposed to heat fluxes linearly increasing with time. A one-dimensional model that describes the pyrolysis of wood subject to a linearly increasing heat flux is presented. Experiments are conducted for different wood species subjected to several increasing rates of heat fluxes. Some special characteristics of wood pyrolysis and spontaneous ignition have been proposed based on those investigations.

The ignitability of solid combustibles by a radiation source has been investigated experimentally as a function of distance between the solid and the source, for heating with a uniform incident heat flux. Unlike piloted ignition, the critical incident heat flux for autoignition increases with the increase of radiant distance, which is a result that has not been reported before. It is found that the generation rate of combustible pyrolysis volatiles is a necessary but not sufficient condition for autoignition. By two dimensionless parameters, it is clearly indicated that the occurrence of autoignition needs both sufficient gas-phase temperature and sufficient concentration of combustible pyrolysis volatiles simultaneously, especially for the larger radiant heating distance condition which is also closer to realistic fire conditions.