Optimization of Acid and Steam Explosion Pretreatment of Cogon Grass for Improved Cellulose Enzymatic Saccharification

Acid-impregnation and its combination with steam explosion were evaluated and optimized using Response Surface Methodology. At 10% solid-liquid ratio, cogon was impregnated with diluted H2SO4 solution (0 to 3%, w/w) at different ranges of temperature (40 to 120 °C) and varied time (0 to 130 min). Impregnated samples were then subjected to enzymatic saccharification using 60 FPU/g Accelerase 1500™. After enzymatic saccharification, the concentration of reducing sugar released was measured using Dinitrosalicylic (DNS) Colorimetric Method. Based on the results, Response Surface Model (RSM) showed that the optimum condition, predicting 7.18% Reducing Sugar Yield (RSY), was impregnation of cogon using 1.9% H2SO4 at 91.8 °C for 56 min. Experimental verification of optimum condition, done in triplicates, showed 6.35 + 0.05% RSY. Acid-impregnated cogon was subjected to steam explosion to improve saccharifiability. Factors varied were temperature (137 to 222 °C) and exposure time (17 to 582 s). Steam-exploded samples were saccharified and RSY was determined. RSM indicated that the best steam explosion condition, predicting 7.91% RSY, was 179 °C and 500 s. Experimental verification of optimum condition showed 8.78 + 0.02% RSY. Using RSY as basis, steam explosion improved saccharifiability of H2SO4-impregnated cogon by 38%, thus, increasing production of reducing sugars for potential bioethanol production.

Field Test Study of the Blast-Resistance Performance of Optimal Composite Anchorage Structure

This paper introduced the comparison test of new optimal composite anchorage structure and single anchorage structure. The measured results show that the particle acceleration of single anchorage structure is 2.22 times higher than that of the optimal composite anchorage structure. The dynamic strain of the former is 5.3~4.5 times higher than that of the latter. The blast-resistance of the optimal composite anchorage structure is 5.10 times higher than that of the single anchorage structure. Under the limit damage condition, the former is 4.13~3.40 higher than that of the latter. The optimal composite anchorage structure has excellent blast-resistance. Optimal weakened zone is between the reinforced support structure and the surround rock. Under the explosion condition, weakened zone is firstly deformed, cracked, crushed or densified, and at the same time, a great deal of blast energy is absorbed. Therefore, the crisis of the reinforced support structure is transferred into the weakened zone.

Homogeneous Nucleation Boiling During Jet Impingement Quench of Hot Surfaces

In the present study, we focused on the rapid liquid heating process and the subsequent boiling explosion that occurs when a liquid jet comes in contact with a very hot surface during jet impingement quenching. Assuming the liquid jet as 1-D semi-infinite solid during its brief contact with the surface, a model has been proposed based on the ideas of 1-D heat conduction and homogeneous nucleation. In this model, a liquid control volume having the size of a critical cluster at the boundary is considered and the corresponding energy balance is obtained by accounting for the two parallel competing processes that takes place inside the liquid control volume, namely, transient external heat deposition and internal heat consumption due to liquid superheat, bubble nucleation and subsequent growth. Results obtained are presented in terms of the liquid temperature escalation within the control volume, the limit of maximum attainable liquid temperature and the time necessary to reach the temperature limit at the boiling explosion. The boiling explosion condition as defined in the present model is also compared with the theoretical boiling explosion condition denoted by the upper bound of evaporative heat flux across the liquid-vapor interface, qmax,max. The time duration of the solid-liquid contact prior to the boiling explosion at different surface temperatures as obtained by the proposed model may be helpful for better understanding the possible surface temperature oscillations due to repetitive solid-liquid contact in the first few microseconds of jet impingement quenching.