Study On The Permeability And Thermal Conductivity Of Compound Adsorbent

Adsorption refrigeration is a green,environmental benign and energy saving refrigeration technology, has a great potential for the utilization in low-grade energy, such as waste heat, underground heat and solar energy. However, because of the limitation of the traditional adsorption refrigeration technology in circulation and adsorbent bed technology, which lead to low efficiency for refrigeration, comparing with the absorption and the traditional evaporation compressed refrigeration, it is still lacking of competitive power. One of the core technologies in adsorption refrigeration system is the heat and mass transfer technology on adsorbent bed, here focus on the permeability and thermal conductivity of compound adsorbent on the adsorbent bed, be aimed at the relationship between the value of the permeability and thermal conductivity and proportion of mixture and density changes in the compound adsorbent,and then find out the optimized proportion of mixture for the compound adsorbent for the further research on the characteristics of heat and mass transfer. Firstly, the plane heat source method was used to measure the conductivity of the matrix material of adsorbent, i.e. expanded graphite, and then found out the optimized expansion processing of the expanded graphite. Secondly, the testing system of the permeability and thermal conductivity were designed and manufactured based on the anisotropic property of the compact material, then the permeability of the compact expanded graphite, activated carbon/expanded graphite, calcium chloride/expanded graphite were tested by gas of nitrogen, the thermal conductivity was tested by steady heat source method at the same time, the results are the followings:(1) The expanded graphite were expanded at different temperatures and different time are compared under the condition of same densities by Hot Disk thermal analysis instrument, and the results show that the samples expanded at the temperature of 600℃for about 10 minutes has the highest thermal conductivity,which is 0.09498W.m^-1.K^-1. It is improved by 5.5%, 16.4% and 27.9%, respectively, if compared with the optimal value gotten at 500℃, 700℃and 800℃.(2) The optimized sample of expanded graphite was compacted by compressing machine to test its permeability based on the Ergun model and the thermal conductivity tested by steady heat source method, the results show that when the curing density changed from 100 kg.m-3 to 500 kg.m-3, the permeability varied between 10-15-10-12, the thermal conductivity ranged from 1.7 W.m^-1.K^-1 to 3.2 W.m^-1.K^-1.(3) The compact physical adsorbent of AC with EG has the highest thermal conductivity of 2.61W.m^-1.K^-1 when the ratio between EG & AC is 1.5:1. The value of the thermal conductivity drops down with the ratio of EG decreases. The thermal conductivity is 2.08W.m^-1.K^-1 even when EG reaches the minimum ratio of 28.6%, and it is increased by 5.8 times compared with the result of granular AC, and the permeability is 5.16×10-11m2.(4) For compact chemical adsorbents of CaCl2 with EG, results show that permeability and the thermal conductivity vary with the ratio of EG and the density of compact adsorbents. Permeability were between 10-13-10-11m2 when the density of compact sample changed from 400 kg.m-3 to 550kg.m-3, and it kept increasing linear with the decreasing mass ratio of EG. Thermal conductivity was 1.08W.m^-1.K^-1 when the density was 550kg.m-3 and the ratio of EG is the minimum value of 16.7%, which is increased by 5 times compared with granular CaCl2.(5) Although expanded graphite as a matrix in the adsorbents can enhance the value of the thermal conductivity of the compound adsorbent, it is also decrease the permeability at the same time, when compared with the two compound adsorbent, results show that the compact physical adsorbent of AC with EG not only has high value of thermal conductivity, but also has high permeability.