Deutsche Version  ACT
Thermal Storage
BMBF
Absorption-storage system 12.4.2017

The air handling unit, errected in 2013, consists (among others) of heating- and cooling units and a steam generator.
© FG Solar- und Anlagentechnik, Uni Kassel

Drying with open sorption processes

A junior research group investigated heat and material transfer to an aqueous solution of lithium chloride. Such salt solutions can be used for air conditioning in buildings or waste heat. At the same time it serves as an energy storage. In addition to the salt solutions young researchers testing and synthesizing new sorbents. Also system simulations for building heating and air conditioning are planned in addition to drying applications.

Project status Near completion
Type of storage Adsorption/Absorption; lithium chlorid (others to be identified)
Research objective Heat and mass exchangers between liquid sorbent and air
Storage/Charging Indirect
Storage capacity arbitrary
Storage time long (saisonal)
Charging temperature 60 °C
Discharge temperature 50 °C
Temperatur type low
Project duration October 2012 until September 2017

The research group "OpenSorp" deals with open liquid desiccant systems, to dry air that flows along a liquid desiccant solution. The water vapor absorbed by the solution is regenerated with heat, preferably from renewable energies or waste heat. The liquid desiccant can be stored as concentrated or deluted solution for a long time duration. In the framework of the research project, heat and mass transfer will be investigated initially with an aqueous LiCl-solution, the absorber and regenerator will be further developed, modelled and combined to carry out system investigations. Moreover, new liquid sorption materials will be sythesized and tested. Experimental investigtions of an absorber-regenerator unit will be carried out in a test rig for hay bales. It will to be set into operation in 2014. Numerical investigations are also planned to identify the potential for sorption stores in air conditioning (heating and cooling) applications.

  • Absorber component: The liquid desiccant solution flows in vertical direction along streched textiles; air flows in cross-flow to the solution (from the front to the back). © FG Solar- und Anlagentechnik, Uni Kassel
  • Laboratory test rig for component measurements (absorber, regenerator) © FG Solar- und Anlagentechnik, Uni Kassel
  • Absorber component made of flat plates. Textiles are attached to the plates © FG Solar- und Anlagentechnik, Uni Kassel
  • A shell-and-tube heat and mass exchanger serves as regenerator. The copper pipes are coated, surrounded by textile hoses © FG Solar- und Anlagentechnik, Uni Kassel
  • The air handling unit, errected in 2013, consists (among others) of heating- and cooling units and a steam generator. © FG Solar- und Anlagentechnik, Uni Kassel
  • Mobile absorber-regenerator unit for drying of a hay bale. The plant is installed in an oversea container (shown in the background). © FG Solar- und Anlagentechnik, Uni Kassel
  • Mobile absorber-regenerator unit © FG Solar- und Anlagentechnik, Uni Kassel
  • Mobile absorber-regenerator unit © FG Solar- und Anlagentechnik, Uni
  • The calorimeter to determine the enthalpy of delution (for titration operation) and the entire heat release due to the solution of water vapor in the electrolyte (for perfusion operation). © FG Chemische Hybridmaterialien, Uni Kassel
  • With this experimental set-up the vapor pressure is measured for different concentrations and temperatures. The temperature is set precisely by the electrolyte thermostat. © FG Chemische Hybridmaterialien, Uni Kassel
  • It is possible to produce liquid desiccants with an ion exchanger column. © FG Chemische Hybridmaterialien, Uni Kassel
  • The viskosity is crucial for the wetting of the absorber. It is convenient to measure the viscosity of new liquid desiccant solutions with a rotation viscosimeter. © FG Chemische Hybridmaterialien, Uni Kassel
  • Scheme of an absorber-regenerator unit for drying agricultural or industrial products. Ambient air is being dried in the absorber and then directed to drying goods (right side). The deluted solutions is regenerated with ambient air, while heat is supplied. © FG Solar- und Anlagentechnik, Uni Kassel
  • Scheme of the absorption process: Water vapor of the air is absorbed by a thin LiCl-solution film that streams along vertical plates. © FG Solar- und Anlagentechnik, Uni Kassel
  • Scheme of an absorber made of twin-wall plates. Top: Distribution system of the liquid desiccant solution. Heat can be removed during the absorption process by water that flows through the twin-wall plates. © FG Solar- und Anlagentechnik, Uni Kassel
  • Two dimensional temperature distribution on the liquid-to-air interface between the desiccant solution and the air, calculated with a finite-difference model. © FG Solar- und Anlagentechnik, Uni Kassel
  • In- and outlet temperatures and relative humidity of the air over the time. Results of measurements carried out with a small absorber unit (exchange area: 4 m²). © FG Solar- und Anlagentechnik, Uni Kassel
  • Water vapor of various liquid desiccant solutions measured in a temperature range between 20°C and 30 °C. © FG Chemische Hybridmaterialien, Uni Kassel
  • Measured results of the enthalpy of delution over the mass fraction of the electrolyte in the solution. © FG Chemische Hybridmaterialien, Uni Kassel

In the framework of the research project, numerical and experimental investigations of sorption processes are carried out. Moreover, new suitable liquid sorption materials (liquid desiccants) will be identified. Measurements will be carried out at the interphase between the liquid desiccant and the air, and in the fluids at the inlet and outlets of the components. Therewith, the investigations reach from relatively small scales with calculations of steady state conditions of the heat and mass transfer up to one year simulations of a complete system with one-hour timesteps on the basis of characteristic curves. The project is devided into five work packages.

Five steps to the goal

Work package 1:
A test environment was designed and installed in 2013 for laboratory experiments, in order to supply the absorber and regenerator with well defined temperatures, flow rates and humidities of the inlet air. In 2014, the installation of a heating and cooling system to supply water with defined temperature profiles and flow rates will be completed.

Work package 2: Test rigs and experiments with components
In 2013 an experimental set-up was errected for thermographic tracing of the heat release at the sorbens-air interface in the laboratory. First measurements were carried out. In order to measure the carry-over of small liquid droplets of the desiccant solution into the air, an experimental method needs to be identified. In first tests, corrosion could not be detected on sample pads. The investigations will be carried on. Moreover experimental models of the absorber and regenerator component were designed and built during the first year of the project. New corrosion protecting coatings were investigated. One of the components was integrated into an existing mobile sorption system test rig. A two-chamber sorption store will prospectively be errected by 2015.

Work package 3: Experimental investigations of systems
Experimental investigations of systems: Newly developed components of the absorber and regenerator for different applications will be combined to a system in the laboratory. First investigations were carried out on the integration of the sorption system into a conventional air conditioning unit. Moreover, a regenerator component was integrated into a mobile test rig. The test rig will be brought into operation in 2014.

Work package 4: Numerical Simulations
For numerical simulations, finite-difference-models as well as efficiency models are enhanced and applied. On the basis of a potential analysis of the energy demand for drying, heating and cooling, system concepts for a sorption system in buildings are examinated using TRNSYS simulations. The investigations are ongoing.

Work package 5:
For the development and investigations of new liquid sorption materials, a precise calorimeter is used. The chemical department at Kassel University carries out titration and perfusion measurements. The reduction of the vapor pressure with temperature and concentration can be measured in a separate test rig. New electrolytes will be synthesized and purified.

Supported by: The Federal Government on the basis of a decision by the German Bundestag

Dates

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Addresses

Coordinator
  • Dr. Ulrike Jordan
    Universität Kassel - Institut für Thermische Energietechnik; Experimentelle und numerische Untersuchungen von Sorptionssystemen - Fachgebiet Solar- und Anlagentechnik
Other Addresses

Infobox

Research funding

The information system EnArgus provides information on research funding, including on this project (German only).