Analysis on Membrane Heat Exchanger Applied to Absorption Chiller

Abstract

A novel membrane heat exchanger was proposed and analyzed. It was expected that the novel heat exchanger could be applied to the lithium bromide absorption chiller. Polyvinylidene fluoride hollow fiber module was adopted as the solution heat exchanger. The hot feed solution from the generator flowed into the lumen side of the membranes while the cold feed solution from the absorber flowed away from the shell side. Heat transfer and mass transfer occurred simultaneously in the membrane module, and only water vapor could diffuse across the membrane pore due to the water vapor pressure difference between the inside and outside of the membrane. Mathematical equations of the heat and mass transfer processes in the membrane heat exchanger were built, and the parallel flow process and the counter flow process were compared by numerical simulation. The simulation results show that the counter flow process was the better flow mode because the mean temperature difference was larger and the mass transfer was more steadily from the lumen side to the shell side. The heat caused by water vapor mass transfer may account for one-third of the total heat transfer. As a result, the membrane heat exchanger not only reinforced the heat recovery but also enlarged the deflation range and reduced the circulation rate and the heat loads of the generator and absorber. Eventually, the coefficient of performance of the heat exchanger was increased.

Role of Membrane Technology in Absorption Heat Pumps: A Comprehensive Review

“…These membrane characteristics helped to achieve the higher COP. Wang et al [ 130 ] reported a mathematical model to solve the heat and mass transfer processes in a 10 kW of cooling capacity-membrane heat exchanger operated with the LiBr-water mixture. A hollow membrane module, with an outer diameter of 50 mm, 800 mm length, an effective 1.2 m 2 of membrane area, and a bundle with 600 individual hollow fiber membranes, was simulated.…”

A review of membrane contactors applied in absorption refrigeration systems

“…Wang et al [6,54] used the concept of vacuum distillation to separate the refrigerant from feed solution and investigated the use of the hollow fiber module as a desorber in the absorption refrigeration system. Wang et al [55,56] and Wang et al [57] investigated and proposed the hollow fiber module as an alternative to the solution heat exchanger of the H 2 O/LiBr absorption refrigeration system. Hollow fiber membrane modules used in the absorption refrigeration systems can be classified into two types; an ordinary hollow fiber membrane module which is usually utilized as a desorber and a hybrid hollow fiber membrane module which is utilized as an absorber.…”

“…Shell and tube configurations are usually adopted for the solution heat exchanger in conventional absorption refrigeration systems. Wang et al [55,56] and Wang et al [57] proposed and analysed a hollow fiber membrane heat exchanger for water/LiBr absorption refrigeration systems. The shell side of the module contains hundreds of membrane tubes through which the hot feed solution from the desorber flows, while the cold feed solution from the absorber is passed to the desorber through the shell side.…”

“…The shell side of the module contains hundreds of membrane tubes through which the hot feed solution from the desorber flows, while the cold feed solution from the absorber is passed to the desorber through the shell side. Wang et al [57] reported that the use of hollow fiber membrane modules instead of conventional solution heat exchanger could not only enhance heat transfer as a result of the large heat transfer interfacial area provided by the small membrane tubes but that the mass transfer of the refrigerant vapour could also contribute about one third of the total heat duty. The water vapour mass transfer in the membrane based solution heat exchanger also simultaneously increases the concentration of refrigerant in the solution rich in refrigerant and further decreases the concentration of refrigerant in the solution weak in refrigerant, which helps to minimize the solution circulation ratio.…”