Abstract
The present paper aimed at exploring absorption heat transformer (AHT) to upgrade ultralow grade waste heat in the temperature range of 40–60 °C. The performance of AHTs with different configurations, including single stage, double stage and double effect, were numerically analysed and compared in terms of temperature lift, coefficient of performance (COP) and exergy coefficient of performance (COPe). The most influential and crucial factor for the studied AHTs is the recirculation flow ratio (FR), the increase of which results in an increasing temperature lift but gradually declining COP. The COPe can achieve its maximum value with a certain FR, and such a state can be considered as the optimal working condition. Within the studied waste heat temperature range, the optimal FR in single stage AHT is in the range of 10–12, at which the system can deliver 17.1~34.7 °C temperature lift with COP at 0.471~0.475. The best configuration amid the studied four different double stage AHTs has a temperature lifting capacity of 31.8~68.6 °C with a COP around 0.30. The double effect AHT compromises its temperature lifting capacity for the highest COP among all the AHTs studied, which can reach about 0.65 though necessitates relatively higher waste heat temperature and higher strong solution concentration to drive the cycle; the double effect AHT is not recommended for the upgrading of ultralow grade waste heat.
Highlights
Energy demand in industry sectors accounts for around 17% of the total energy consumption in the UK [1], and the worse thing is that the average industrial thermal waste via radiation, exhausted gas or air, cooling fluids and so on is about one sixth of this total energy demand [2]
The experiment was conducted under the conditions of Tg = 76.5~78.5 °C, Te = 53.0~59.8 °C and Tc = 35.8~37.5 °C; COPint was defined as the internal coefficient of performance (COP), of which the heat was calculated based on the enthalpy change of the solution and refrigerant, while the external COP, COPext, was calculated based on the heat released or absorbed by the external heat transfer fluids
The performance comparison of stage AHT (SAHT), the best Double stage AHT (DAHT), i.e. DAHT4, and Double effect absorption heat transformer (DeAHT) is presented in Fig. 17(a) to (c) in terms of the temperature lift, COP and coefficient of performance (COPe), respectively, while Table 2 lists the optimal working performances of these absorption heat transformer (AHT) based on the maximum COPe values
Summary
Energy demand in industry sectors accounts for around 17% of the total energy consumption in the UK [1], and the worse thing is that the average industrial thermal waste via radiation, exhausted gas or air, cooling fluids and so on is about one sixth of this total energy demand [2]. Three more configurations other than the conventional configuration (named as SAHT-1 in present paper) were introduced and evaluated, including SAHT-2 in which the water carrying waste heat transferred the heat to the evaporator prior to the generator; SAHT-3 in which it had an additional absorber heat exchanger on the basis of SAHT-2; and SAHT-4 in which it was based on SAHT-3 and mounted with another refrigerant heat exchanger at the inlet of evaporator These three new configurations reduced the crystallisation risk of using LiBr–H2O as working solution. Zhao et al [33] investigated the DeAHT system using TFE–E181 and LiBr–H2O as working solutions, and the analytical results showed a 30 °C temperature lift could be achieved with waste heat temperature at 70 °C; the corresponding COP value was as high as 0.58 and 0.64, respectively for the studied two working solutions. This work carried out analytical study on six different AHTs using LiBr–H2O with primary interest in heat transformation of the ultralow grade heat from 40 to 60 °C
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
