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Energy analysis of a 1-ton generator-absorber-exchange absorption-compression (GAXAC) cooler.

Article Excerpt
INTRODUCTION

Vapor absorption refrigeration technology powered by low-temperature energy sources such as waste heat or solar energy potentially offer a positive impact on the environment. A generator-absorber-exchange (GAX) absorption cycle originates from combining two branches of a double-effect vapor absorption cycle (Herold et al. 1995). In this cycle, internal heat recovered from the absorber is supplied to the generator by maintaining a wide concentration field.

Several GAX absorption cycle configurations have been reported in the literature. Many researchers employed absorption simulation (ABSIM) software to conduct the simulation of a GAX absorption cycle (Priedeman and Christensen 1997; Garimella et al. 1996; Grossman et al. 1995). Staicovici (1995) analyzed a three-stage polybranched regenerative GAX cycle. Velazquez and Best (2002) discussed a methodology for energy analysis of an air-cooled GAX cycle. Kang et al. (1996) discussed the effects of heat transfer coefficient and temperature difference in deciding the size of a rectifier in a GAX cycle. Kang and Kashiwagi (2000) studied the effects of UA (the heat conductance of a heat exchanger) ratio and coolant split ratio on coefficient of performance (COP) in the panel heating GAX and panel heating single-effect cycles. Sabir et al. (2004) compared the performance and design complexity of a GAX-resorption cycle with a simple absorption and resorption cycle and a simple GAX cycle. Hanna et al. (1995) analyzed the GAX cycle by pinch-point technique, and Scharfe et al. (1986) discussed the merits and limits of the GAX cycle. Kang et al. (1999) suggested that by adopting the waste heat recovery generator-absorber-exchange (WGAX) cycle, corrosion problems could be solved.

The GAX absorption cycle can also be combined with a vapor-compression process (GAX absorption-compression cycle) to obtain a higher COP. Figure 1 shows the principle of operation of the single-stage (dashed lines excluding the compressor represent the low-pressure side), GAX (solid lines), and GAX absorption-compression cycles (dashed lines including the compressor represent the low-pressure side). The GAX cycle's basic components are similar to the single-stage absorption cycle. The concentration in absorber and desorber are maintained in such a way that there is the possibility of temperature overlap between them. This possible overlap area is shown in Figure 1 between the two-dot-and-dash lines. This "overlapped" heat is internally transferred from the absorber to the generator, leading to a higher COP. Thus it is seen that conventional GAX cycle COP is higher than the single-stage absorption system COP at same thermal conditions. It is also seen from Figure 1 that increasing the absorber pressure increases the overlapped heat and COP. This increase of absorber pressure can be achieved by introducing a compressor between the absorber and evaporator; this cycle is called a GAX absorption-compression (GAXAC) cycle.

[FIGURE 1 OMITTED]

Kang et al. (2004) developed hybrid GAX cycles for achieving very low evaporator temperature, corrosion minimization, a rise in hot water temperature, and a higher COP. Rameshkumar and Udayakumar (2007) claimed that the GAX absorption-compression cycle has an average of 30% higher COP values than the GAX conventional cycle.

In India, 1TR is the normal cooling requirement for the majority of middle-income households, which constitutes close to 35% of the population of 1 billion. The middle-income group has gradually gained disposable income, and it is expected that the demand for 1TR cooling systems will exponentially increase. This in turn directs excessive electrical energy demand in this country. If an alternate cooling system is made available with desirable performance, the needs of the society could be easily met. Energy analysis of such a cooling system is the first step in this direction. Also, to date, energy analysis based on external and internal circuit balance for each component of a GAX absorption-compression system has not been reported in the literature. Hence, in this study, energy analysis of a GAXAC system for the capacity of 3.54 kW with fuel oil as a heat source is evaluated. For comparison purposes, energy analysis of a GAX conventional system for the same capacity is...

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