Consolidated Composite Reactive Bed for Refrigeration Sorption System.pdf

1、The presented work focused in the design and test of a consolidated composite reactive bed with enhanced heat and mass transfer to be used in refrigeration chemisorption systems for ice production.Ammonia was the refri

2、gerant chosen and the bed was made from expanded graphite powder impregnated by CaCl2.Several heating temperatures and times were tested to assess the most suitable condition to perform the expansion of the graphite.On

3、ce the expanded graphite was impregnated with calcium chloride,it was compressed to produce blocks with enhanced heat transfer properties. The system was instrumented with temperature sensors,a difierential pressur

4、e sensor and an absolute pressure sensor.The amount of ammonia that reacted with the salt was assessed by measuring the variation of the refrigerant level inside the evaporator/condenser with a magnetostricitive level

5、 sensor.The temperature profiles and pressure drop within the bed were analysed to identify which was the limiting factor in the conversion rate.Four difierent kinds of blocks were studied in which the density of the b

6、lock and the proportion of expanded graphite varied.The specific cooling power(SCP)and the coefficient of performance(COP)obtained with the consolidated reactive compound were calculated under difierent operation condi

7、tions.Furthermore,a mathematical model was developed to describe the kinetics,the heat transfer and the mass transfer in the bed.The kinetics,heat transfer and mass transfer coefficients.related to the consolidated com

8、pound were identified by minimizing the sum of the squared deviations between the experimental and the simulated temperatures,pressures and global conversion.The mathematical model with the identified toefficients was u

9、sed in several other simulations,which allowed a better understanding of the factors that influence the performance of the reactive block. Besides the study of the consolidated compound，an experimental set-up was pl

10、anned and proposed to assess the heat transfer coefficient of a split heat pipe,when applied to cool an adsorbent bed，and a simulation was performed to estimated which specific cooling power and COP could be expected

11、if a split heat pipe adsorption machine employs the studied the studied consolidated compound. The expanded graphite showed to be a suitable matedal to avoid the agglomeration phenomenon in the salt.The compound had a

12、 stable absorption capacity since the first cycles where the amount of refrigerant absorbed in any operation condition was more than 97％ of the maximum value that could be obtained when CaCl2.2 NH3 is converted into CaC

13、l2.8 NH3.The formulation with 50％ of expanded graphite and compressed to an expanded graphite density in the block of 0.30 g cm-3 produced SCP higher than 1000 W kg-1 under difierent evaporation and heat sink temperatur

14、es normally employed for ice production.The COP was calculated to be close to 0.35 when the consumed mass of refrigerant in the reaction was 0.80kg kg-1.It was observed a great change in the SCP with the synthesis time a

15、nd with the degree of reaction.Furthermore，the time that maximise the SCP or COP depends on the operation conditions.and bOth figures cannot be maximised simultaneously.The COP obtained when the SCP is maximised under fa

16、vourable reaction conditions is not so lower than the maximum COP，while when the SCP iS maximised under non-favourable reaction conditions，the reduction of the COP can be as high as 50％. The synthesis time，the SCP a

17、nd the COP of the consolidated compound with 50％ of expanded graphite were simulated for bed dimension and working conditions different from the experimentally studied.The results showed that the SCP obtained at better

18、reaction conditions(constraint pressure and temperature of 2.91 bar and 20℃.respectively)can be about two to more than three times the value obtained at worse conditions(constraint pressure and temperature of 1.90 bar

19、 and 30℃，respectively)，depending on the bed dimension and position of the heat sink. The simulation results also showed that if the split heat pipe adsorption machine developed by the research group in sorption system

20、 of Shanghai Jiao Tong University employs the consolidated compound made with 50％ of expanded graphite presented in this report，the cooling power of the machine could be 18 to 32％ higher than the cooling power obtaine