| With the widespread application of cryogenic fluids in the aerospace,medical and superconducting fields,cryogenic fluid management technology is becoming increasingly important.In the field of aerospace,the low boiling point,low surface tension,and other physical properties of the cryogenic propellant and the harsh space environment have led to many challenges in cryogenic fluid management technology,urging researchers to carry out many experimental and theoretical studies of cryogenic propellant management technology,which is an overall technology involving liquid acquisition and evaporation control of cryogenic propellant.In the technology of cryogenic propellant liquid acquisition and evaporation control,porous materials have attracted wide attention in the fields of surface materials and heat and mass transportation due to their excellent properties such as high mechanical strength,high permeability,and heat insulation,and how to accurately characterize the capillary performance and thermal insulation performance of porous materials and obtain the influential mechanism of relevant conditions on its performance is one of the key problems in the application of porous materials in cryogenic propellant management technology.In view of this,in this study,the superhydrophilic copper foam was used as the sample,the effects of surface structure,type of working medium and evaporation on capillary performance of porous materials were systematically studied,and a method for accurately characterizing the capillary performance parameters of porous materials for volatile working fluids was proposed.Then,the characterization method was applied to the study of capillary performance of porous materials in the cryogenic propellant liquid acquisition device,and their comprehensive capillary performance was systematically evaluated.At the same time,the experimental and theoretical study was conducted on the insulation performance of the porous material applied in the cryogenic propellant evaporation control technology under atmospheric pressure,and the mechanism of the influence of environmental humidity on its insulation performance was deeply analyzed.The main research work is as follows:(1)Preparation and structural characterization of superhydrophilic copper foamBased on 60,80 and 100 mesh copper foam,chemical oxidation method was used to prepare superhydrophilic copper foam.Through experimental measurement and theoretical analysis,such as microscopic observation and pedestal drop method,the key physical parameters(surface micromorphology,wettability,and porosity)of superhydrophilic copper foam and conventional copper foam were systematically characterized,and the effects of surface treatment and micro-geometric structure on the structural characteristics were studied.(2)Study on the capillary performance of volatile working fluid on superhydrophilic copper foamBased on the infrared thermography test method,the capillary rise process of different working fluids(ethanol and water)on superhydrophilic copper foam and conventional copper foam was experimentally studied.Combined with different theoretical models of capillary rise,the capillary performance factor(ratio of permeability to effective capillary radius)and other capillary performance parameters were obtained through data processing.By comparing the capillary performance factors of different working fluids on the same mesh superhydrophilic copper foam,it was found that the evaporation of volatile working fluids has a certain effect on the characterization of capillary performance parameters,which cannot be ignored.On the basis of such results,a method for accurately obtaining capillary performance parameters for volatile working fluids was proposed,and this method was used to systematically study and analyze the effect of surface structure and working fluid types on capillary performance of superhydrophilic copper foam,it was found that there is a big difference in capillary performance between superhydrophilic copper foam and conventional copper foam,when the mesh numbers are 60 and 80 mesh,compared to conventional copper foam,superhydrophilic copper foam shows better capillary performance,and compared with the liquid-absorbent core structure commonly used in two-phase heat transfer devices such as heat pipes,superhydrophilic copper foam has better integrated capillary performance and greater application potential in the field of thermal mass transport.(3)Study on the capillary performance of porous materials in the screen channel liquid acquisition deviceScreen channel liquid acquisition device is the key cryogenic propellant liquid acquisition technology for future deep space exploration missions.The porous material Dutch Twill Weave(DTW)is the core component of the screen channel liquid acquisition device.Therefore,DTW200 × 1400,325 × 2300 and 400 × 2800 were slected as the test samples,and their capillary performance were systematically studied.The key physical parameters(surface microstructure,wettability and porosity)of DTW were systematically characterized and analyzed through experimental measurements and theoretical calculation methods such as microscopic observation,sessile drop method and drainage method,the porosity parameters obtained through different testing methods have good consistency,and the deviation from the existing research results does not exceed 15%,which fully verifies the accuracy of the obtained porosity parameters,and on the basis of this result,the influence of micro-geometry on the structural characteristics of DTW was studied.The capillary processes of three kinds of DTWs in the direction of warp wires were experimentally studied with ethanol and acetone as working fluids,and the capillary performance of three kinds of DTWs in the direction of warp wires was comprehensively evaluated by the method of volatile working medium to characterize the capillary performance parameters of porous materials.By comparative analysis of capillary performance parameters obtained by different working fluids under different evaporation intensities,and comparing them with existing research results,the accuracy of the obtained DTW capillary performance parameters was confirmed,furthermore,the rationality of the method for obtaining the capillary performance parameters was further proved.At the same time,the influence of surface structure,working medium type and evaporation intensity on the capillary performance of DTW was analyzed and compared,it was found that: under the test conditions of different working media and different experimental environments,the greater the number of warp and shute wires per inch/square inch among DTW200×1400,325×2300 and 400×2800,the smaller the permeability,equivalent capillary diameter and comprehensive capillary performance(the ratio of permeability to pore diameter)of DTW,and DTW200×1400 has the best overall capillary performance.Meanwhile,for volatile working fluids,evaporation can reduce its capillary rise speed and equilibrium height on DTW.Therefore,it is necessary to take measures to reduce the evaporation of cryogenic propellant for the screen channel liquid acquisition device to ensure the normal working performance of the device,which provides an important theoretical basis for the design and selection of the screen channel liquid acquisition device.(4)Study on the thermal insulation performance of atmospheric composite multilayer thermal insulation materialsIn order to make composite multilayer thermal insulation materials better applied to cryogenic propellant evaporation control technology,experimental and theoretical researches on the thermal insulation performance of composite multilayer thermal insulation materials under different atmospheric humidity at atmospheric pressure were carried out,and the influential mechanism of the ambient humidity on the thermal insulation performance of the composite multilayer thermal insulation materials was analyzed.Under normal atmospheric environment,the influence of environmental humidity on the thermal insulation performance of composite multilayer insulation materials cannot be ignored.When the ambient humidity increases from 43% to 83%,the apparent thermal conductivity of composite multilayer insulation materials increases by 13.07%,which implies the thermal performance is significantly reduced.Moreover,due to the differences in the installation sequence and internal structure of the multilayer thermal insulation materials and polyurethane foam,the increase of atmospheric humidity has a more significant effect on the thermal insulation performance of the multilayer thermal insulation materials,which is the main reason for the deterioration of the thermal insulation performance of the composite multilayer thermal insulation materials.The atmospheric pressure layer-by-layer heat transfer model based on parallel thermal resistance of dry air and condensed water / ice is in good agreement with the experimental results,which improves existing heat transfer model of atmospheric multilayer insulation materials,and this model was further used to analyze the mechanism of the effect of humidity on the thermal insulation performance of multilayer thermal insulation materials. |
