Modeling and performance of a two-stage collector/regenerator for solar liquid desiccant air conditioning system
A two-stage collector/regenerator (C/R) for the solar liquid desiccant air conditioning system is presented, which adopts a fin-forming absorber plate and where the liquid desiccant flowing process is divided by an isolation board into two stages: regenerating stage I and regenerating stage II. Then a heat and mass transfer mathematical model is established to predict the performance of the two-stage C/R by using calcium chloride as the desiccant. The main results are as follows: (i) The fin-forming absorber plate can increase heat and mass transfer areas and promote turbulence, so that it significantly enhances heat and mass transfer between solution stream and air stream; (ii) Compared with the traditional C/R, a 10 to 25 percent increase in the water evaporation rate for the two-stage C/R can be achieved under the same operating condition.
Augmentation of the performance of solar regenerator of open absorption cooling system
In open cycle liquid desiccant air conditioning, the solar collector regenerator is one of the effective ways of regenerating liquid solution. In this work, the regeneration of liquid solution using cross flow of air stream with flowing film of desiccant on the surface of a solar collector/regenerator has been investigated. To evaluate the effect of cross flow of air stream on the performance of the unit, two identical units are constructed and tested in the same conditions of operation. One of the two units was augmented with air blower. The absorber plate is a black cloth layer. The forced air stream, which flows across the absorber removes the moisture from the liquid solution. The regeneration in the other collector/regenerator unit is free. The results show enhancement of regeneration efficiency for the forced cross flow compared with the free regeneration. The effect of concentration and flow rate on the performance is discussed. Two relations for regeneration efficiency as a function of concentration for the two units are introduced.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.