Study On Additives Used To Increase The Solubility Of The Circuit Board Precipitate In Refrigerant

With the rapid development of big data and large-scale scientific computing,immersion liquid cooling technology has become the main technology of current server cooling.Since sugon delivered the"first commercial immersed liquid-cooled server"in 2017,it has become a leader in domestic liquid-cooled server technology.This precipitate reduces the heat dissipation effect of the liquid-cooled server and needs to be cleaned regularly,thus affecting the long-term stable operation of the server.For this reason,this paper intends to carry out research on additives that increase the solubility of this precipitate in refrigerant,so as to solve the problem that the precipitate reduce the heat dissipation effect of the server.Firstly,the composition analysis of the circuit board precipitate was carried out by GC-MS techniques.The results showed that the circuit board precipitate is mainly 4,4’-bis（α,α-dimethylbenzyl）diphenylamine,which was derived from precipitation of antioxidants in circuit boards.Based on the potential solubility of 4,4’-bis（α,α-dimethylbenzyl）diphenylamine,26 additives were preliminarily screened.By studying the mutual solubility of additives and refrigerant,the solubility of additives to this precipitate,and the solubility of additives to CPU frame,two additives,ethyl acetate and methylcyclohexane,were finally screened.Then,the solubility of this precipitate in ethyl acetate,methylcyclohexane,refrigerant,ethyl acetate（methylcyclohexane）+refrigerant mixed solvent was studied by HPLC.The research results show that this precipitate is insoluble in the refrigerant,and the solubility in the additives and the additives+refrigerant mixed solvent increases with the increase of temperature and the addition of the additives,and the solubility in the ethyl acetate system is higher than that in the methylcyclohexane system.After that,the solubility data were correlated with the solid-liquid equilibrium model.For pure solvent systems,the three empirical equations（Van’t Hoff equation,Apelblat equation,λh equation）and the two activity coefficient equations（NRTL equation,Wilson equation）were used to correlate the solubility data,it is found that all equations can fit the experimental values well,in which two activity coefficient equations with ARD less than 0.5%give the best regression effect.For the mixed solvent system,the JA-Apelblat empirical equation was added on the basis of the above-mentioned5 equations,a total of 6 models were used to correlate the solubility data,and the results showed that 4 empirical equations with ARD less than 2%can fit the experimental values well,but the fitting effect of the two activity coefficient equations is poor and their ARD are more than 6%.In addition,the thermodynamic parameters in the dissolution process were calculated based on the modified Van’t Hoff model,and it was found thatΔ^°₇),Δ^°₇)andΔ^°₇)were all greater than 0,which proved that all processes are endothermic,entropy increasing,and non-spontaneous.Finally,this paper carried out a small industrial test research.The combustion and explosion characteristics of the additive+refrigerant mixture were measured,and the results show that the ethyl acetate（methylcyclohexane）+refrigerant mixture does not burn and does not explode under the environment of heat,full filling and good ventilation.Further,the compatibility of the mixed solution to the circuit board was studied.It was found that after the components of the circuit board were immersed in the mixed solution for three months,the weight of the components,the appearance of the components and the composition of the mixed solution did not change.The results show that the ethyl acetate（methylcyclohexane）+refrigerant mixture has good compatibility with the circuit board.In this paper,a real machine platform was also built to test the solubility of ethyl acetate（methylcyclohexane）+refrigerant mixture to the circuit board precipitate in real machine environment.Adding 4.34%ethyl acetate（4.81%methylcyclohexane）to the real machine containing 25 kg of refrigerant,and after running for three months,it is found that all the precipitates on the circuit board are dissolved.The additives developed in this research have the advantages of low cost,good compatibility and well combustion and explosion characteristics.Combined with the original refrigerant,it can effectively dissolve the circuit board precipitate,solve the problem that the circuit board precipitate reduces the heat dissipation effect,and make the liquid-cooled server long-term and stable operation.