Diffusion and sound absorption properties of the quadratic residue diffuser structure with perforated panel

Acoustic structure study always is the academic research interest. Diffusion ab？sorbing structure（DiflFsorber） has good research value because it has both diflFusion property and sound absorption property. Quadratic residue diffusers（QRD） structure which had good diffusion property was combined with the perforated panel which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-panels which had1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams of different structure were analyzed to derive the diffusion coefficients. Results showed that the composite structure still had good diffusion performance in the frequency range from100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated panel resonance frequency range where there was about 2 dB reduction averagely.The study result can provide the reference for the design and development of diifsorber.

Multi－diffused Reflection Spectroscopy of Rare Earths Doped LaOCl Powder Samples and the Calculation of Quantum Efficiency

The excitation and emission spectra, the relaxation time of principal spectral lines and multi-diffused reflection spectra in LaOCl: Er, LaOCl: Ho powder samples were measured. The diffused absorption spectrum was derived from the multi-diffused reflection spectrum. According to Judd-Ofelt theory,the intensity parameters, radiative transition probabilities and quantum efficiencies of luminescence emission were calculated. Then comparison with erbium and holmium doped floride glass and other matrices were made.

Modelling and Thermodynamic Analysis of a Hot-Cold Conversion Pipe Using R134a-DMF-He as the Working Pair

Based on the concept of a diffusion absorption system,a hot-cold conversion pipe utilizing 1,1,1,2-tetrafluoroethane(R134 a)-dimethylformamide(DMF)-helium(He)as the working pair is presented with the aim of cooling output by recovering the low-grade waste heat.The model of the hot-cold conversion pipe is established,in which a heat pipe is used to transfer the waste heat as the heat input.The equations of the thermodynamic properties of the working pair are established by equation of state method(EOS).The model of the hot-cold conversion pipe is built based on the mass,species and energy balance equations of each component.The direct conversion of heat to cold is achieved by the desorption,absorption,condensation and diffusion evaporation processes of R134 a.The hot-cold conversion pipe is cooled by natural convection,which can be enhanced by chimney effect.The thermodynamic analysis is carried out to analyze the effect of the boundary conditions,i.e.the heat source temperature,the refrigeration temperature,and the environmental temperature,on the system performance.This paper provides a theoretical basis for actual application of the hot-cold conversion pipe in waste heat recovery field.