Master's Thesis Paul Seiwert

Analysis of a non-adiabatic spray nozzle airwasher for supply air dehumidification in air handling units

The presented thesis involves experimental research of a counter flow air-washer for the dehumidification
and cooling of supply air. A test rig is erected in order to reproduce the employment
of an air-washer in an HVAC-unit. The properties of the air and water at the entrance and exit are
determined along with the overall performance of the air-washer.
The focus of this experimental research is to determine the effects of drop diameter, air velocity,
water inlet temperature and volume flow on several self defined coefficients and ratios. These
encompass the change of the humidity ratio x, the ratio of latent to sensible heat load ,
the ratio of total heat load to operational energy from the pump and fan and the efficiency of
dehumidification E. The efficiency of dehumdification is defined as the ratio of real to potential
dehumidification, determined by the water inlet temperature.
An experimental design is created methods of design of experiment (DOE). The experimental
design is based on 2 stages. The selection of nozzles is based on calculations of drop trajectories.
Results show that the reduction of drop diameter and water inlet temperature has a significant
effect on virtually all coefficients and ratios and is beneficial for the use of air-washers in HVAC
units. Air speed on the other hand only has a minor influence. An error margin evluation is performed
based on the calculation of error propagation.
The influence of the spray on pressure loss is based on measurements alongside the air-washer.
The measured values show that pressure loss is much lower with the spray than with the drop
separator.
In addition, a simplified estimation of the air-washer’s efficiency compared to an indirect heat
exchanger is made. The comparison is done by calculating the proportions of transferred heat
to operational energy from the pump and fan over the course of a year. It is revealed that the
air-washer, in the test rig with the current configuration, does not have any beneficial effect over
an indirect heat exchanger. The estimation shows that the reduction of pressure loss in the airwasher
improves the efficiency compared to indirect heat exchangers.The presented thesis involves experimental research of a counter flow air-washer for the dehumidification
and cooling of supply air. A test rig is erected in order to reproduce the employment
of an air-washer in an HVAC-unit. The properties of the air and water at the entrance and exit are
determined along with the overall performance of the air-washer.
The focus of this experimental research is to determine the effects of drop diameter, air velocity,
water inlet temperature and volume flow on several self defined coefficients and ratios. These
encompass the change of the humidity ratio x, the ratio of latent to sensible heat load ,
the ratio of total heat load to operational energy from the pump and fan and the efficiency of
dehumidification E. The efficiency of dehumdification is defined as the ratio of real to potential
dehumidification, determined by the water inlet temperature.
An experimental design is created methods of design of experiment (DOE). The experimental
design is based on 2 stages. The selection of nozzles is based on calculations of drop trajectories.
Results show that the reduction of drop diameter and water inlet temperature has a significant
effect on virtually all coefficients and ratios and is beneficial for the use of air-washers in HVAC
units. Air speed on the other hand only has a minor influence. An error margin evluation is performed
based on the calculation of error propagation.
The influence of the spray on pressure loss is based on measurements alongside the air-washer.
The measured values show that pressure loss is much lower with the spray than with the drop
separator.
In addition, a simplified estimation of the air-washer’s efficiency compared to an indirect heat
exchanger is made. The comparison is done by calculating the proportions of transferred heat
to operational energy from the pump and fan over the course of a year. It is revealed that the
air-washer, in the test rig with the current configuration, does not have any beneficial effect over
an indirect heat exchanger. The estimation shows that the reduction of pressure loss in the airwasher
improves the efficiency compared to indirect heat exchangers.