Exhaust hot water(EHW)is widely used for various industrial processes.However,the excess heat carried by EHW is typically ignored and discharged into the environment,resulting in heat loss and heat pollution.An organi...Exhaust hot water(EHW)is widely used for various industrial processes.However,the excess heat carried by EHW is typically ignored and discharged into the environment,resulting in heat loss and heat pollution.An organic Rankine cycle(ORC)is an attractive technology to recycle heat from low-temperature energy carriers.Herein,ORC was used to recycle the heat carried by EHW.To investigate the energy and exergy recovery effects of EHW,a mathematical model was developed and a parametric study was conducted.The energy efficiency and exergy efficiency of the EHW-driven ORC system were modeled with R245fa,R113 and R123 as the working fluids.The results demonstrate that the EHW and evaporation temperatures have significant effects on the energy and exergy efficiencies of the EHW-driven ORC system.Under given EHW conditions,an optimum evaporation temperature exists corresponding to the highest exergy efficiency.To further use the low-temperature EHW,a configuration retrofitted to the ORC by combining with flash evaporation(FE)was conducted.For an EHW at 120℃ and 0.2 MPa,the maximum exergy efficiency of the FE-ORC system is 45.91%at a flash pressure of 0.088 MPa.The FE-ORC performs better in exergy efficiency than the basic FE and basic EHW-driven ORC.展开更多
The group-contribution (GC) methods suffer from a limitation concerning to the prediction of process-related indexes, e.g., thermal efficiency. Recently developed analytical models for thermal efficiency of organic Ra...The group-contribution (GC) methods suffer from a limitation concerning to the prediction of process-related indexes, e.g., thermal efficiency. Recently developed analytical models for thermal efficiency of organic Rankine cycles (ORCs) provide a possibility of overcoming the limitation of the GC methods because these models formulate thermal efficiency as functions of key thermal properties. Using these analytical relations together with GC methods, more than 60 organic fluids are screened for medium-low temperature ORCs. The results indicate that the GC methods can estimate thermal properties with acceptable accuracy (mean relative errors are 4.45%-11.50%);the precision, however, is low because the relative errors can vary from less than 0.1% to 45.0%. By contrast, the GC-based estimation of thermal efficiency has better accuracy and precision. The relative errors in thermal efficiency have an arithmetic mean of about 2.9% and fall within the range of 0-24.0%. These findings suggest that the analytical equations provide not only a direct way of estimating thermal efficiency but an accurate and precise approach to evaluating working fluids and guiding computer-aided molecular design of new fluids for ORCs using GC methods.展开更多
To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles(ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area(UHEA) net p...To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles(ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area(UHEA) net power, embodying the cost/performance ratio of an ORC system, was proposed as a new indicator to judge the suitability of ORC working fluids on a given condition. The heat exchange area was computed by an improved evaporator model without fixing the minimum temperature difference between working fluid and hot fluid, and the flow pattern transition during heat exchange was also taken into account. The maximum UHEA net powers obtained show that dry organic fluids are more suitable for ORCs than wet organic fluids to recover low-temperature heat. The organic fluid 1-butene is recommended if the inlet temperature of hot fluid is 353.15-363.15 K or443.15-453.15 K, heptane is more suitable at 373.15-423.15 K, and R245 ca is a good option at 483.15-503.15 K.展开更多
For efficient utilization of a limited geothermal resource in practical projects,the cycle parameters were comprehensively analyzed by combining with the heat transfer performance of the plate heat exchanger,with a va...For efficient utilization of a limited geothermal resource in practical projects,the cycle parameters were comprehensively analyzed by combining with the heat transfer performance of the plate heat exchanger,with a variation of flowrate of R245 fa.The influence of working fluid flowrate on a 500 W ORC system was investigated.Adjusting the working fluid flowrate to an optimal value results in the most efficient heat transfer and hence the optimal heat transfer parameters of the plate heat exchanger can be determined.Therefore,for the ORC systems,optimal working fluid flowrate should be controlled.Using different temperature hot water as the heat source,it is found that the optimal flowrate increases by 6-10 L/h with 5 ℃ increment of hot water inlet temperature.During experiment,lower degree of superheat of the working fluid at the outlet the plate heat exchanger may lead to unstable power generation.It is considered that the plate heat exchanger has a compact construction which makes its bulk so small that liquid mixture causes the unstable power generation.To avoid this phenomenon,the flow area of plate heat exchanger should be larger than the designed one.Alternatively,installing a small shell and tube heat exchanger between the outlet of plate heat exchanger and the inlet of expander can be another solution.展开更多
基金Projects(51704069,51734004,71403175)supported by the National Natural Science Foundation of ChinaProject(N162504011)supported by the Fundamental Research Funds for the Central Universities,China
文摘Exhaust hot water(EHW)is widely used for various industrial processes.However,the excess heat carried by EHW is typically ignored and discharged into the environment,resulting in heat loss and heat pollution.An organic Rankine cycle(ORC)is an attractive technology to recycle heat from low-temperature energy carriers.Herein,ORC was used to recycle the heat carried by EHW.To investigate the energy and exergy recovery effects of EHW,a mathematical model was developed and a parametric study was conducted.The energy efficiency and exergy efficiency of the EHW-driven ORC system were modeled with R245fa,R113 and R123 as the working fluids.The results demonstrate that the EHW and evaporation temperatures have significant effects on the energy and exergy efficiencies of the EHW-driven ORC system.Under given EHW conditions,an optimum evaporation temperature exists corresponding to the highest exergy efficiency.To further use the low-temperature EHW,a configuration retrofitted to the ORC by combining with flash evaporation(FE)was conducted.For an EHW at 120℃ and 0.2 MPa,the maximum exergy efficiency of the FE-ORC system is 45.91%at a flash pressure of 0.088 MPa.The FE-ORC performs better in exergy efficiency than the basic FE and basic EHW-driven ORC.
基金Project(51778626) supported by the National Natural Science Foundation of China
文摘The group-contribution (GC) methods suffer from a limitation concerning to the prediction of process-related indexes, e.g., thermal efficiency. Recently developed analytical models for thermal efficiency of organic Rankine cycles (ORCs) provide a possibility of overcoming the limitation of the GC methods because these models formulate thermal efficiency as functions of key thermal properties. Using these analytical relations together with GC methods, more than 60 organic fluids are screened for medium-low temperature ORCs. The results indicate that the GC methods can estimate thermal properties with acceptable accuracy (mean relative errors are 4.45%-11.50%);the precision, however, is low because the relative errors can vary from less than 0.1% to 45.0%. By contrast, the GC-based estimation of thermal efficiency has better accuracy and precision. The relative errors in thermal efficiency have an arithmetic mean of about 2.9% and fall within the range of 0-24.0%. These findings suggest that the analytical equations provide not only a direct way of estimating thermal efficiency but an accurate and precise approach to evaluating working fluids and guiding computer-aided molecular design of new fluids for ORCs using GC methods.
基金Projects(U0937604,50876116)supported by the National Natural Science Foundation of ChinaProjects(2010QZZD0107,2014zzts192)supported by the Fundamental Research Funds for the Central Universities of China
文摘To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles(ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area(UHEA) net power, embodying the cost/performance ratio of an ORC system, was proposed as a new indicator to judge the suitability of ORC working fluids on a given condition. The heat exchange area was computed by an improved evaporator model without fixing the minimum temperature difference between working fluid and hot fluid, and the flow pattern transition during heat exchange was also taken into account. The maximum UHEA net powers obtained show that dry organic fluids are more suitable for ORCs than wet organic fluids to recover low-temperature heat. The organic fluid 1-butene is recommended if the inlet temperature of hot fluid is 353.15-363.15 K or443.15-453.15 K, heptane is more suitable at 373.15-423.15 K, and R245 ca is a good option at 483.15-503.15 K.
基金Project (2012AA053001) supported by High-tech Research and Development Program of China
文摘For efficient utilization of a limited geothermal resource in practical projects,the cycle parameters were comprehensively analyzed by combining with the heat transfer performance of the plate heat exchanger,with a variation of flowrate of R245 fa.The influence of working fluid flowrate on a 500 W ORC system was investigated.Adjusting the working fluid flowrate to an optimal value results in the most efficient heat transfer and hence the optimal heat transfer parameters of the plate heat exchanger can be determined.Therefore,for the ORC systems,optimal working fluid flowrate should be controlled.Using different temperature hot water as the heat source,it is found that the optimal flowrate increases by 6-10 L/h with 5 ℃ increment of hot water inlet temperature.During experiment,lower degree of superheat of the working fluid at the outlet the plate heat exchanger may lead to unstable power generation.It is considered that the plate heat exchanger has a compact construction which makes its bulk so small that liquid mixture causes the unstable power generation.To avoid this phenomenon,the flow area of plate heat exchanger should be larger than the designed one.Alternatively,installing a small shell and tube heat exchanger between the outlet of plate heat exchanger and the inlet of expander can be another solution.
