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Moisture Condensers
Published in Vasile Minea, Industrial Heat Pump-Assisted Wood Drying, 2018
Among pure fluorinated fluid used as refrigerants in high-temperature heat pumps, there is HFC-245fa (1,1,1,3,3-pentafluoropropane). It is a hydrofluorocarbon (Table 13.1) that has a relatively high GWP value (950) (i.e., 950 times the global warming effect of CO2), no ozone depletion potential, is nearly nontoxic, nonreactive, nonflammable, non-mutagenic, noncorrosive toward all commonly used metals including carbon steel, stainless steel, copper, and brass (but there is a concern with the use of aluminum due to the reactive nature of this metal), and, practically, nonbiodegradable with a lifetime of 7.2 years when it eventually does escape into the atmosphere. R-245fa has a high degree of thermal and hydrolytic stability, at temperatures ranging from 75°C to 200°C, and exhibits acceptable miscibility in a wide range of polyols.
Experiments and Correlations for Single-Phase Convective Heat Transfer in Brazed Plate Heat Exchangers
Published in Heat Transfer Engineering, 2023
Angela Mutumba, Francesco Coletti, Alex Reip, Mohamed M. Mahmoud, Tassos G. Karayiannis
A literature survey shows that there has been a lot of experimental work on Plate Heat Exchangers (PHEs) focused on refrigerant applications. Common working fluids included the use of both pure fluids and mixtures. However, the use of such substances was found to affect the ozone layer and contributed to greenhouse effects. Consequently, international environmental regulations promoted the development of alternative and suitable refrigerants such as Hydrofluoroolefins (HFOs) with both low Global Warming Potential (GWP) and Ozone Depletion Potential (ODP). However, their performance in energy conversion systems such as the Organic Rankine Cycles (ORCs) is yet to be determined. ORCs are particularly well-suited to converting low- to medium-grade heat (below 100 °C to 300-400 °C) to power. Recently, HFOs like R1233zd(e) and R1336mzz(z) have shown to be a promising replacement for R245fa; commonly used in ORCs. For example, Moles et al. [2] evaluated the performance of R1233zd(e) and R1336mzz(z) as potential substitutes for R245fa in an ORC for waste heat recovery. Throughout the range of operating conditions and configurations examined, the alternative refrigerants consumed lower pumping power and could therefore achieve higher values of net cycle efficiency. This study showed that R1233zd(e) required 10.3%−17.3% less pumping power and produced up to 10.6% higher net cycle efficiencies than R245fa, over the range of cycle conditions examined. The possibility of replacing R245fa with R1233zd(e) is also supported by the similar thermo-physical properties as shown in Table 1. The values reported in Table 1 are based on Engineering Equation Solver (EES) software and reference [3].
A modeling of electricity generation by using geothermal assisted organic Rankine cycle with internal heat recovery
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
A. S. Canbolat, A. H. Bademlioglu, O. Kaynakli
One of the important factors determining the thermodynamic performance of the organic Rankine cycle is the evaporator pressure. In this study, energy and exergy analyses of the cycle based on the change of the evaporator pressure were carried out for different refrigerants. The results obtained are as following:Generally, under constant operating conditions, the thermal efficiency of the cycle increases as the evaporator pressure increases. Depending on operating conditions and evaporator pressure, a maximum 4.86% improvement in the thermal efficiency of the cycle has been achieved.Similarly, as the evaporator pressure increases the total exergy destruction in the system decreases, resulting in an increase in the exergy efficiency of the system. Considering the evaporator pressure within the scope of this study, a maximum 19.78% improvement in the efficiency of the cycle has occurred.It has been determined that R245fa is the preferable fluid among the refrigerants used due to high thermal and exergy efficiency of the cycle, while R227ea obtained lower thermal and exergy performance than other refrigerants.Considering the evaporator pressure within the scope of this study, the turbine work produced has increased by a maximum of 84.2% and similarly, the amount of heat supplied to the evaporator from the geothermal source increases by a maximum of 7.3%.It has been calculated that the exergy efficiency of the turbine is a maximum of 86.22%, while the exergy efficiency of the evaporator is a maximum of 76.6% depending on the evaporator pressure, and the refrigerant used.Depending on the refrigerant flow rate used and the evaporator pressure, the amount of heat rejected from the condenser increases by a maximum of 2.1%, while the exergy efficiency of the condenser decreases by a maximum of 2.2%.By increasing the evaporator pressure from 1000 to 2000 kPa, the amount of heat transferred in the heat exchanger increases by 52.1%, while the exergy efficiency of the heat exchanger decreases by a maximum of 2.5%.It has been found that the pump work required is a maximum of 3.83 kW depending on the refrigerants used and evaporator pressures, but the exergy efficiency of the pump decreases by a maximum of 0.23%.