Purpose The purpose of this paper is to investigate the enhancement of the performance of bubble absorber using hybrid nanofluid as a cooled NH3/H2O absorption system to reduce their size and to find the best fitting model. A numerical model for ammonia-water bubble absorber was developed to show the influence of operating conditions and design parameters on the absorber performance. Design/methodology/approach A finite difference numerical method is used to solve the numerical model. The model is subjected to the inlet conditions of liquid, vapor and coolant flow regimes. The absorber modeling was divided into small elements along the absorber length. Findings The model proposed is validated with previously published works. Then agreement between the both is considered as good. Research limitations/implications Numerical results/The use of hybrid nanofluids. Originality/value The results showed that the hybrid nanofluid is the best cooling medium. Very high heat transfer rates are obtained because of the high thermal conductivity and specific heat of hybrid nanofluid, and consequently, the absorber size decreases. It was also found that the absorber thermal load and the mass absorption flux increase with increasing of solid volume fraction. Also, the existence of an optimal absorber length was revealed, required for complete absorption when using hybrid nanofluid as a cooling medium. It is recommended that using hybrid nanofluid to remove the heat from the absorber is the best candidate for NH3/H2O absorption performance enhancement.
This paper aims to study the influence of hybrid nanofluid and coolant flow direction on mass and heat transfer improvement for a bubble absorber in order to reduce the absorber length required for complete absorption. Hybrid nanofluid is used as the cooling medium. A finite difference method was used to solve the system of nonlinear differential equations. The absorber length is divided into differential elements of an incremental length dL along the absorber length. A parametric study comparing two different flow configuration (co/countercurrent coolant flow direction) of the bubble absorber was conducted to gage the influence of solid volume fraction (0% ≤ Phi ≤ 2%), direction of coolant flow, type of working fluid on heat, and mass transfer enhancement. The results show that the absorption process depends on the direction of coolant flow and the type of working medium. The absorption rate with coolant in countercurrent flow direction is higher than that cocurrent flow direction. In addition, results reveal that the heat and mass transfer, the mass absorption flux, the absorber thermal load, Stanton, and Reynolds number in binary hybrid nanofluids are enhanced more than that the binary nanofluid and NH3/H2O solution, which increase the absorption rate and consequently decrease the absorber length. The type of working medium and the solid volume fraction are the key parameters. Also results reveal that an optimal absorber length is found when using binary hybrid nanofluid as a working medium.
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