Development Of Activated Carbon Based Composite Adsorbent For Adsorption Refrigeration Powered By Ship’s Waste Heat

In adsorption refrigeration system,the performance of the adsorbent directly influences the cooling efficiency of the refrigeration system.Due to the shortcomings of poor thermal conductivity,long cycle time and large size of adsorption bed,the development of a composite adsorbent with activated carbon as the matrix was developed.In order to improve the heat and mass transfer performance of the adsorbent,two methods were employed to develop the composite adsorbent,the first method is to introduce the expanded graphite to enhance the thermal conductivity of activated carbon(here,the composite is denoted as type I adsorbent);the second method is to add aluminum powder and foaming agent for enhancing its the heat and mass transfer performance,and then formed by silica sol(here,the composite is denoted as type II adsorbent).The researches included are as follows:1)Probing into the influence of process parameters on thermal conductivity of the composite adsorbent.In type I adsorbent,the effects of the heating temperature and duration,the mixing weight ratio of activated carbon to expanded graphite on the thermal conductivity of the composites were investigated.It shows that,where the sample was prepared by mixing the activated carbon with expanded graphite at the same weight ratio and heating at temperature about 700 ℃ for about 40 second,the maximum thermal conductivity of the composite adsorbent can reach 0.591W/(m?K),which is 9.85 times of granular activated carbon.In type II adsorbent,the effects of the mesh of aluminum powders,the mixing ratio of activated carbon to the aluminum powder,foaming agent and binder on the thermal conductivity of the composites were investigated.It is found that,when the mixing weight ratio of activated carbon and aluminum powder,foaming agent and binder was 12:12:3:4,the maximum thermal conductivity of the composite adsorbent is 1.101W/(m?K),which is 18.4 times of granular activated carbon.2)Probing into the effect of the additive amount on the desorption performance of composite adsorbents.In type I adsorbent,the effects of the mixing ratio of activated carbon with expanded graphite on the desorption performance of composite adsorbents were investigated.It reveals that the best performance of the composite adsorbent was prepared by mixing the activated carbon and the expanded graphite by the weight ratio of 2:1,the maximum desorptionrate of the composite adsorbent and the total desorption amount of ammonia within the initial duration of 300 s time 9 and 2.11 times of that of the granular activated carbon.In type II adsorbent,the effects of the mixing ratio of activated carbon with aluminum powder,foaming agent and binder on the desorption performance of composite adsorbents were investigated.Experimental result shows that the best performance of the composite adsorbent prepared by the mixing activated carbon,aluminum powder,foaming agent and binder by the weight ratio3:3:1:1.It is found that the maximum desorption rate of the composite adsorbent and the total desorption amount of ammonia initial duration of 300 s were respectively 17.5 and 2.73 times of those of the granular activated carbon.By comparing the effective desorption capacity of the unit volume of the adsorbent,it can be found that the effective desorption amount of unit volume of I and II type composite adsorbent is 1.85 times and 4.1 times of granular activated carbon,the adsorption bed volume can be reduced to about 46% and 75% by using type I and type II composite adsorbent.3)Analysis of the adsorption equilibrium of ammonia on the activated carbon,type I and type II adsorbent.The adsorption equilibrium data of ammonia was measured on activated carbon,I1,I3,II6 and II8 samples of composite adsorbent,the data were then used to determine the value of the parameters of D-A equation through nonlinear fit.It seems that the mean relative error of the results predicted by D-A equation is less than 5% when the system pressure is about1-1.06 MPa,the adsorption amount of ammonia on the composite adsorbent increased in the mxing ratio of the activated carbon.The Clausius-Clapeyron equation was used to calculate the isosteric heat of ammonia adsorption at temperature 293.15-313.15 K.It shows that the isosteric heat of ammonia adsorption on the activated carbon,I1,I3,II6 and II8 as prepared samples of composite adsorbents is respectively in the range of 13.76-26.06 k J/mol,13.27-26.05 k J/mol,13.37-25.38 k J/mol,11.62-15.52 k J/mol and 11.35-14.71 k J/mol.It may be assumed that the influence of the expanded graphite on the pore structure of the activated carbon is weaker than that of the silica sol.The isosteric heat of ammonia adsorption on the composite adsorbent decreased in the adsorption amount.