Number of experimental and theoretical studies have been dedicated to the question about additive effect on the absorption cycle performance or on the absorber
performance in particular. Experimental research was
carried out, generally, with absorbers utilising vertical
tubes or a bundle of horizontal tubes. Falling film heat
transfer coefficient or absorption rate were used as
parameters in order to establish the enhancement caused
by the additive. 2-Ethyl-1-hexanol and 1-octanol are
generally used in the experiments.
In the present study we have chosen 2-methyl-1-pentanol.
The choice of this additive was based on the stability
analysis fulfilled by Gustafsson [18, 21]. The
objective of this study was to establish experimentally
2MP effect on the absorption chiller performance. A
mini absorption chiller utilising lamella surfaces was
used in the experiments. Cooling effect in the evaporator
was measured experimentally and used as a parameter
in order to estimate the enhancement ratio.
Two experimental series have been carried out. In one
experimental series the additive was injected into the
LiBr solution. The enhancement ratio up to 20% was
observed at the optimum additive concentration. In the
second experimental series the additive was injected into
the refrigerant. The amount of additive for this case was
taken according to 1 mg of 2MP per 1 kg of LiBr solution
charged to the facility. The enhancement ratio
became 32%, which is substantially better. Different
additive concentrations have been tested in both series.
LiBr solution samples as well as refrigerant samples
have been examined during the experiments. Examination
revealed that 2MP performed maximum enhancement
at the concentration over the solubility limit when it
was injected into LiBr solution. LiBr solution samples
also contained additive when it was injected into evaporator.
This can be explained by the fact that the additive
as a volatile component transported to the vapour
phase and then absorbed in the absorber. The additive
content in the LiBr solution samples was smaller than
the solubility limit when 2MP was injected into evaporator.
Rough estimation of the vapour composition in
the absorber/evaporator unit revealed a value of 0.05–
0.1 wt.%. The presence of additive in the vapour phase
in very small amounts promotes heat and mass transfer in
the absorber more efficiently compared to the additivein-
solution case. Experimental results and observations
seem to support theories advanced by Herold [10] and
Setterwall [19]. This new additive was subsequently used
to increase the capacity of the commercial absorption
chiller. The capacity has been increased by a factor of
30–35% that is in a very good agreement with the
experimental data