| Solar interface evaporation is a low energy consumption and zero emission fresh water separation technology,which is widely used in seawater desalination,sewage treatment and other fields.The key to improve the performance of solar interface evaporator is to improve its material transfer capacity.Because of its abundant pores and good hydrophilicity,wood has a structural basis to ensure the efficient transmission of liquid,and has great application potential in solar energy interfacial evaporators.However,the untreated wood has low liquid permeability,which is difficult to meet the requirements of solar interface evaporator for liquid transmission capacity.Previous studies found that ultra-high-pressure(HP)treatment can effectively improve the liquid permeability of wood,but its lifting effect,treatment process and the performance of treated wood used for solar interface evaporator have not been studied.Therefore,this study clarified the significant effect of HP reatment on wood liquid permeability,explored the characterization method of HP treatment to improve wood liquid permeability,and then optimized and analyzed the process parameters of HP treatment to improve wood liquid permeability.The mechanism by which HP treatment increases the liquid permeability of wood was elucidated.On this basis,a wood-solar interfacial evaporator based on HP treated wood with high permeability was prepared,and its steam generation-related properties were studied.The main research contents and results of this study are as follows:(1)HP treatment can significantly improve the liquid permeability of wood.The penetration characteristics of wood treated with HP,such as penetration effect,penetration strength and penetration quality,were evaluated by dyeing and tracing method,and the penetration uniformity of wood after HP treatment was analyzed.The results showed that in terms of penetration effect,penetration color intensity and penetration quality,compared with the 90℃ heat treatment group,the penetration effect of the outer surface and inner section of poplar treated with 120 MPa HP was significantly improved,and the color intensity value of the outer surface is increased by 179.93%,the color intensity value of the inner section is increased by 949.80%,the dyeing uptake of colored solutes is increased by 155.19%,and the penetration efficiency was also significantly improved.In terms of penetration uniformity,after HP treatment,the average color difference of the cross-section,chord-section,radial-section of outer surface and the cross-section,chordsection,and radial-section of inner section of poplar is between 0.94 and 1.94,and the fractal dimension of color was between 2.25 and 2.58,indicating good penetration uniformity;there was no significant difference in the color intensity of the cross-section,chord-section,and radialsection of inner section and the color intensity in the three depths of 5,10,and 15 mm of poplar,indicating that there was good penetration uniformity between inner section in different directions and between inner section at different depths.The color index was used to quantitatively characterize the liquid permeability of wood after HP treatment.Through the correlation analysis,it was found that the liquid permeability of poplar has a significant correlation with the L*value of the outer surface,the L*value of the inner section and the a*value of the inner section of the poplar.The established regression model had a great goodness of fit.These three indicators can be used to quantitatively characterize the liquid permeability of the HP treated poplar.(2)The optimization analysis was carried out on the process parameters of HP to improve the permeability of wood liquid.The a*value of the inner section of the wood was selected to represent the liquid permeability of the wood after the HP treatment.Through the single factor test,the change of the liquid permeability of the wood treated with different HP process parameters was studied.Through multi-factor optimization experiments and model analysis,the influence model of process parameters on wood liquid permeability was studied,and the optimal process parameters were determined.The results showed that the volume ratio of poplar to colored water solution,the volume of poplar,and the moisture content of poplar has no significant effect on the liquid permeability of poplar,while the pressure,pressure-holding time and concentration of colored solute has significant effects on the liquid permeability of poplar.The optimal process range obtained by the single factor test is that the pressure is 80-160 MPa,the pressure-holding time is 30-90 s,and the concentration of the colored aqueous solution is 0.15%～0.25%.The established response function(inner cross section a*of poplar)was affected by three factors(pressure,holding time,colored solute concentration),which is a composite effect model of primary,interactive and secondary effects,can effectively predict the effects of the three factors on the liquid permeability of poplar(R2=0.9765).The optimal process combination of HP to improve the liquid permeability of poplar was that the pressure is 110 MPa,the pressure-holding time is 65 s,and the concentration of the colored aqueous solution is 0.22%.Experiments were carried out to verify the optimal process,and the relative error with the predicted value was 1.42%.There was also a significant interaction between the three factors of pressure,pressure-holding time and colored solute concentration.(3)It was revealed that the mechanism of HP treatment to increase the liquid permeability of wood is due to its amplification effect on the pore structure of wood.Selected poplar and fir respectively to study the chemical composition,pore distribution and microscopic morphology of the heartwood and sapwood of the two woods before and after HP treatment,studed the changes of wood pit membrane after HP treatment,and explored the influence of the key factors ofwood liquid permeability,and then revealed the mechanism of HP treatment to improve the permeability of wood liquid.The results showed that no chemical changes occurred in poplar and fir during HP treatment.Further research found that the HP treatment caused the fracture and damage of the pit membrane of poplar heartwood and sapwood,which increased the pore size of the pit membrane,opened the original closed pits of poplar heartwood and sapwood,and increased the number of pores.The HP treatment caused the openings on the fir heartwood pit membrane to be torn and destroyed,thereby expanding the pore size of the fir heartwood pit membrane.Therefore,the HP treatment maked the occluded pit membrane in the wood reset to a non-occluded pit,or the pit membrane is broken or damaged,and the material transport channel between the ducts or tracheids was enlarged and unblocked,thereby improving the liquid permeability of the wood.(4)The performance of highly permeable wood for solar interfacial evaporator was studied.Based on the amplification effect of HP treatment on the pore structure of wood,a wood-solar interface evaporator was prepared by surface carbonization,and the material transport and energy management performance,evaporation performance(evaporation rate and evaporation efficiency),cyclic stability and structural durability during actual seawater desalination and long-term cyclic use were studied.It was found that in terms of material transport and energy management performance,compared with untreated wood,the liquid infiltration height of HP-carbonized wood was increased by 37.84%,the light absorption capacity was significantly improved,and its thermal conductivity was reduced by 22.45%.HP-carbonized wood had good material transport ability,and can generate heat through photothermal conversion,and localized the heat of the top photothermal conversion layer at the evaporation interface.In terms of evaporation performance,the evaporation rate of the wood-solar interfacial evaporator with HP-carbonized wood as the main body is 1.48 kg·m-2·h-1,and the evaporation efficiency can reach 80.77%under the irradiation of 1 intensity of sunlight.Under the same conditions,the evaporation efficiency is 17.11%higher than that of carbonized wood,and 13.52%higher than that of heat-treatedcarbonized wood.Compared with the biomass material(carbonized bimodal porous wood)reported by similar studies,the evaporation rate and evaporation efficiency were improved by 85.0%and 41.7%,respectively.In addition,the evaporator also has good seawater desalination performance,anti-salt deposition performance and cycle stability performance. |
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