Application of Response Surface Methodology to Optimize the Preparation of Rubber Foam Composite as Sound-Absorbing Material Using Scrap Rubber Powder

In this paper, scrap rubber powder(SRP), azodicarbonamide(ADC) as foaming agent and double-component epoxy resins(ER) as binder were used to prepare porous sound-absorbing material of rubber foam composite(RFC) by hot-pressing process. Response surface methodology(RSM) was employed to evaluate three process variables, i e, specimen thickness(A), ADC dosage(B) and foaming temperature(C), and to establish two polynomial function model equation between sound absorption coefficient(α) and three process factors(A, B, C) at middle and low frequency 250 Hz, 500 Hz, 800 Hz, 1 000 Hz to determine the optimal preparation condition of RFC. The statistical analysis of results demonstrated that specimen thickness(A) exerted significant impact on sound absorption properties of RFC. And the optimum prepared condition of RFC was 10 mm specimen thickness, 3.00 g ADC dosage, and approximately 196 ℃ foaming temperature. Under optimal condition, sound absorption coefficient of RFC could reach 5.68%(250 Hz), 7.67%(500 Hz), 20.73%(800 Hz), 18.71%(1 000 Hz), coinciding with the predicted values 5.70%(250 Hz), 7.69%(500 Hz), 20.77%(800 Hz), 18.74%(1 000 Hz) from the predicted polynomial function model, which exhibited that RSM could be used to optimize the preparation process of sound-absorbing materials.

Tree-ring response of Larix chinensis on regional climate and sea-surface temperature variations in alpine timberline in the Qinling Mountains

Tree-ring width chronologies of Larix chinensis were developed from the northern and southern slopes of the Qinling Mountains in Shaanxi Province,and climatic factors affecting the tree-ring widths of L.chinensis were examined.Correlation analysis showed that similar correlations between tree-ring width chronologies and climatic factors demonstrated that radial growth responded to climate change on both slopes.The radial growth of L.chinensis was mainly limited by temperature,especially the growing season.In contrast,both chronologies were negatively correlated with precipitation in May of the previous year and April of the current year.Spatial climate-correlation analyses with gridded land-surface climate data revealed that our tree-ring width chronologies contained a strong regional temperature signal over much of northcentral and eastern China.Spatial correlation with seasurface temperature fields highlights the influence of the Pacific Ocean,Indian Ocean,and North Atlantic Ocean.Wavelet coherence analysis indicated the existence of some decadal and interannual cycles in the two tree-ring width chronologies.This may suggest the influences of El Nin˜o-Southern Oscillation and solar activity on tree growth in the Qinling Mountains.These findings will help us understand the growth response of L.chinensis to climate change in the Qinling region,and they provide critical information for future climate reconstructions based on this species in semi-humid regions.

Exergy analysis of operation process of district heating systems

The nature of the exergy consumption of district heating(DH) systems can not be explained clearly using the first law of thermodynamics.Exergy analysis method was used.A case study based on a DH system in Inner Mongolia,China,was carried out.The impact of operating parameters and design parameters on the energy quality of circulating water and exergy losses of DH systems during heat distribution was revealed.Results show that the energy quality of circulating water and exergy losses of DH systems during heat distribution could be reduced by decreasing the indoor temperature or increasing radiator areas.Compared with other factors,the outdoor temperature and indoor temperature have a greater impact on the energy quality of circulating water,exergy losses of circulating water,and total exergy losses during heat distribution.When the outdoor temperature varied by 10.00%,the average variation rates of such parameters were 85.12%,90.02%,and 64.60%,respectively.When the outdoor temperature was 273.00 K and indoor temperature varied by 50.00%,the average variation rates of such parameters were 83.88%,99.34% and 32.87%,respectively.It can be observed that the energy quality and exergy losses of DH systems can be reduced in the operation process.

Optimizing environmental insulation thickness of buildings with CHP-based district heating system based on amount of energy and energy grade

The increase of insulation thickness(IT)results in the decrease of the heat demand and heat medium temperature.A mathematical model on the optimum environmental insulation thickness(OEIT)for minimizing the annual total environmental impact was established based on the amount of energy and energy grade reduction.Besides,a case study was conducted based on a residential community with a combined heat and power(CHP)-based district heating system(DHS)in Tianjin,China.Moreover,the effect of IT on heat demand,heat medium temperature,exhaust heat,extracted heat,coal consumption,carbon dioxide(CO_(2))emissions and sulfur dioxide(SO_(2))emissions as well as the effect of three types of insulation materials(i.e.,expanded polystyrene,rock wool and glass wool)on the OEIT and minimum annual total environmental impact were studied.The results reveal that the optimization model can be used to determine the OEIT.When the OEIT of expanded polystyrene,rock wool and glass wool is used,the annual total environmental impact can be reduced by 84.563%,83.211%,and 86.104%,respectively.It can be found that glass wool is more beneficial to the environment compared with expanded polystyrene and rock wool.