Absorption Refrigeration Systems – The electrochemical ARS
Recently, Newell (2000) has proposed a new electrochemical ARS as shown in Figure 3.52, which consists of four main components. An electrochemical cell is the heat absorber, equivalent to an evaporator in a conventional vapor compression refrigeration system. A fuel cell rejects heat in a manner similar to a condenser in a common vapor compression refrigeration cycle. The third component is a heat exchanger between gas streams and water flow stream. The fourth component is a current pump for elevating the fuel cell’s voltage output to a level sufficient for driving the electrochemical cell. The voltage required is sufficiently low such that the cycle may be one that is conveniently matched for solar photovoltaic cells or other direct current electric energy conversion systems. In fact, the system shown in Figure 3.52 can be used as a thermally driven power cycle by operating the fuel cell at a temperature lower than the electrochemical cell. The voltage supply becomes a load driven by the electric circuit. Lowering component irreversibilities is essential to reach a breakeven operating condition where the fuel cell is generating sufficient power for operation of the electrochemical cell. Newell’s system is based on a water/hydrogen/oxygen fuel cell and electrochemical cell combination. Other combinations are also considered. Each one has its own advantages or disadvantages. The configuration envisioned for the system operates near atmospheric pressure. The components could be operated at nearly uniform pressures with gravitation, surface tension, or low head pumping used for transporting the working fluids within and between components. Water may be moved from the electrochemical cell and fuel cell to external heat exchange surfaces, or the cells could be configured for direct heat exchange with their surroundings.