Minichannel heat exchangers for compression resorption heat pumps

Absorption and desorption of ammonia-water solution is under study in order to optimize the design of the heat exchangers contained in the compression-resorption heat pumps.

The heat exchangers that are incorporated in the experimental setup consist of two vertical mini-channels where the desorption process of ammonia-water solution takes place inside the inner channel, while the absorption process occurs in the outer channel.

The test section consists of twelve heat exchangers with stainless steel tubes and inner diameters of 2.0, 1.1 and 0.5 mm and lengths of 0.2, 0.4, 0.6 and 0.8 m and one 6 mm tube heat exchanger. The inlet temperature and pressure conditions of the absorption and desorption streams are controlled with a utility section.

The utility section is separated into two identical sides: one loop for the absorption stream and one loop for the desorption stream. Each side consists of a plate heat exchanger, a pump, an expansion vessel and two coil heat exchangers. Two thermostatic baths are used to adjust the inlet temperatures of the absorption and desorption streams. The streams are totally absorbed in the plate heat exchangers from which they are leaving in a subcooled liquid state. The piston pumps provide circulation and pressurize the stream. The two coil heat exchangers are used for heating the desorption streams to saturated liquid or to saturated vapor for the absorption stream.

Two differential pressure transducers are used to measure the pressure drop between the inlet and outlet of the channel for the two sorption streams. The temperature of the fluids is measured by high accuracy temperature sensors. The mass flux and density are measured by a Coriolis flow meter.

Rock wool insulation is wrapped around the test section in order to reduce heat losses to the ambient and all lines are insulated with heat resistant foam.

The set-up allows for the determination of the heat transfer coefficients and pressure drops of ammonia-water during desorption and absorption inside small diameter tubes.

Related projects

This is part of ISPT (= Institute of Sustainable Process Technology) project Heat Pumps in Bulk Separation Processes, realized with support and direct involvement of industrial ISPT partners Akzo Nobel, Bronswerk Heat Transfer, DSM, Huntsman, Jacobs and LyondellBasell.