Thermodynamic analysis of novel heat pump cycles for drying process with large temperature lift

Abstract

Summary Heat pump–assisted drying has been recognized a prospective technology to meet the requirement of energy saving. However, large temperature lift will be resulted by the single‐stage heat pump cycle during the high‐temperature drying, especially operating with low ambient temperature for open‐loop drying, which leads to insufficient heat output, high compression ratio, and low coefficient of performance (COP). Two heat pump cycles, namely, multitemperature cascade cycle and combined single‐stage cycle, are proposed to address the above problems in the drying process with large temperature lift in this paper. The effects of varying operation parameters on the heat pump cycles are analyzed to optimize the cycle performance. Afterwards, the above two cycles as well as a conventional cascade cycle, a two‐stage compression cycle, and a single‐stage compression cycle are compared with each other in terms of cycle performance and drying performance under specified drying conditions. It is indicated by the results that the COPs of the multitemperature cascade cycle and combined single‐stage cycle are about 95% and 88% higher than that of the single‐stage compression cycle, respectively. As for the two cascade cycles (ie, conventional cascade cycle and multitemperature cascade cycle), 49% more water evaporation with the same power input can be resulted by the added condenser and evaporator. Among the five analyzed cycles, the multitemperature cascade cycle is the most promising to be used in the retrofitting of the drying equipment with large temperature lift.

Thermal performance of a solar‐assisted heat pump drying system with thermal energy storage tank and heat recovery unit

“…The SAHP drying system is preferred for chili peppers because the rates of heat and mass transfer are high and it is capable of working throughout nighttime and daytime . A couple of heat pump cycles, multitemperature cascade cycle and combined single‐stage cycle, has been recommended to tackle the aforementioned shortcomings in drying process with large temperature lift . The impact of various operation variables on heat pump cycles has been studied to develop an optimal cycle performance.…”

“…Regarding the bi‐cascade cycles (ie, traditional cascade cycle and multitemperature cascade cycle), 49% more water evaporation with identical power may be produced through adding condenser and evaporator. Among the five cycles being examined, the multitemperature cascade cycle was found to be the optimal for retrofitting the drying equipment with large temperature lift …”

“…12 A couple of heat pump cycles, multitemperature cascade cycle and combined single-stage cycle, has been recommended to tackle the aforementioned shortcomings in drying process with large temperature lift. 35 The impact of various operation variables on heat pump cycles has been studied to develop an optimal cycle performance. Then, the aforementioned cycles in addition to a traditional cascade cycle, a bi-stage compression cycle, and a mono-stage compression cycle have been contrasted against each other to highlight cycle performance and drying performance in specific drying settings.…”

“…Among the five cycles being examined, the multitemperature cascade cycle was found to be the optimal for retrofitting the drying equipment with large temperature lift. 35 Searching the literature about the solar assisted heat pump (SAHP) drying system reveals that there are no previous studies related SAHP drying system with thermal energy storage (TES) tank and HRU for long-term operation period. The SAHP drying system can be used in different industrial applications with the TES tank and HRU during all seasons.…”

Thermodynamic and thermoeconomic analyses of an ejector/booster enhanced heat pump system with zeotropic mixture

“…The productivity of the suggested plant was compared, where the results indicated that by raising the CO 2 discharging pressure the system could operate more effectively, as the COP and exergy efficiencies were enhanced by 54.7% and 17.5%, respectively. In another research, two innovative heat pump systems were designed and analyzed for drying purposes by Peng et al 19 The heat pumps were, in fact, poly‐temperature cascade and integrated single‐stage heat pumps. The authors also optimized their systems by examining and comparing the impacts of varying operation parameters.…”