Abstract
The heat transfer in double pipe heat exchangers is very poor. This complicates its application in absorption cooling systems, however, the implementation of simple passive techniques should help to increase the heat and mass transfer mainly in the absorber. This paper carried out a simulation and its experimental comparison of a NH3-H2O bubble absorption process using a double tube heat exchanger with a helical screw static mixer in both central and annular sides. The experimental results showed that the absorption heat load per area is 31.61% higher with the helical screw mixer than the smooth tube. The theoretical and experimental comparison showed that the absorption heat load difference values were 28.0 and 21.9% for smooth tube and the helical mixer, respectively. These difference values were caused by the calculation of the log mean temperature difference in equilibrium conditions to avoid the overlap of solution temperatures. Therefore, the theoretical and experimental results should be improved when the absorption heat is included in the heat transfer equation or avoiding the operation condition when output is lower than input solution temperature.
Highlights
The employment of absorption systems are a sustainable way to be used in air conditioning applications and reduce the electricity consumption in warm and hot climates
The heat transfer from bulk (hL) was calculated by ∆TML in the sensible heat zone, but hL was calculated by ∆TML,EQ equilibrium conditions in the absorption heat zone, because the results showed that the outlet solution temperature was higher than the inlet temperature input
The following conclusions were drawn from this study: A mathematical model was carried out in order to analyze the behavior of the absorber process with an smooth pipe (SP) and an helical screw static mixer (HM) using empirical correlations in the inside tube
Summary
The employment of absorption systems are a sustainable way to be used in air conditioning applications and reduce the electricity consumption in warm and hot climates. They are still more expensive and bulkier than vapor compression systems due to the low coefficient of performance caused basically by the thermodynamic properties of the working fluids and the low heat transfer rate in the components. The design of the heat exchangers is still complicated in the absorption systems, mainly the absorber component. Presented a review of experimental and theoretical studies related to heat exchangers using passive techniques such as tape inserts or nanoparticles. The study describes the results of the heat transfer enhancement at different Reynolds number, Nusselt number, the concentration of nanofluids, and size of the nanoparticle
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