تجزیه و تحلیل عملکرد ترانسفورماتور حرارتی آبشاری غیرقابل برگشت

By employing an irreversible thermodynamic approach the optimum performance of an cascaded absorption heat-transformer system is investigated. To get closer to real machines, the effects of thermal resistances and internal irreversibilities on the performance of the cascaded cycle is considered. An improved equation for the coefficient of performance (COP) of the system under consideration was obtained. The analyses show that the cascaded cycle has a significant increase in the systems gross temperature lift (GTL) over the single stage heat-transformer

Due to environmental pollution and continually rising conventional fuel prices, various novel apparati for saving energy are being experimentally investigated and produced. Single-stage absorption heat-transformers (SSAHTs) [1], [2], [3], [4], [5] and [6] are some of the most promising devices for upgrading industrial waste heat and heat from geothermal and solar sources to higher temperature levels. There are currently 15 SSAHTs operating in industrial plants worldwide [7], [8] and [9]. SSAHTs are relatively simple, reliable and require little maintenance. However SSAHTs exhibit low coefficients of performance (COPs) and they have limited gross temperature lifts (GTLs) at values of about 50 °C [5]. Since SSAHTs exhibit continuous and stable operation under the part load conditions from 0 to 100%, a combination of them with each other is an efficient way to overcome the above drawbacks. From the literature survey, it appears that none of the previous investigations concerned cascaded absorption heat transformers (CAHTs) including internal and external irreversibilities. In the present study, the optimum performance of an irreversible CAHT is investigated. For this purpose, we define a cyclic model which includes two major irreversibilities, and use it for optimization of performance. A detailed analysis of the system performance is described.

In this study, attention is paid to a theoretical evaluation of the optimum performance of an irreversible cascaded absorption heat-transformer system. To get closer to real machines, the effects of thermal resistances in the heat exchangers and internal dissipations of the working fluids on the performance of the system under consideration are considered. It can be seen clearly, from the numerical example section that the irreversible overall COP was found to be far lower than the fully reversible COP. Therefore, the resulting COP obtained by the present analysis, Eq. (48), is more realistic and can be used as a standard of comparison. It is from Eq. (48) that the conditions γ=R1 and ζ=R3 yields ε=0. Therefore, for a CAHT, we conclude that the practical range for R1 and R3 should be γ<R1<1 and ζ<R3<1 respectively. Also the numerical results yield that the CAHT cycle gives an increase of about 15% in the GTL and 9% in the COP compared with that of an SSAHT [5] under the same operating parameters.