The flow and heat transfer of air-cooled heat exchangers play important roles in the performance of indirect dry cooling systems in power plants,so it is of benefit to the design and operation of a typical indirect dr...The flow and heat transfer of air-cooled heat exchangers play important roles in the performance of indirect dry cooling systems in power plants,so it is of benefit to the design and operation of a typical indirect dry cooling system to optimize the thermo-flow characteristics of air-cooled heat exchangers.The entransy dissipation method is applied to the performance optimization of air-cooled heat exchangers in this paper.Two irreversible heat transfer processes in air-cooled heat exchangers,the heat transfer between circulating water and cooling air and the mixing of circulating water,are taken into account and analyzed by means of the entransy dissipation method.The total entransy dissipation rate,which connects the geometrical parameters of air-cooled heat exchanger sectors and the heat capacity rates of the fluids to the heat flow rate in every sector,is obtained.Based on the mathematical relation and the conditional extremum method,an optimization equation group is derived,by which the air-cooled heat exchanger with known air-side parameters is optimized,showing that the entransy dissipation based optimization approach can contribute to the distribution optimization of circulating water in air-cooled heat exchangers of a typical indirect dry cooling system.展开更多
The applicability of cement grout （or cement-based grout） has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump sys...The applicability of cement grout （or cement-based grout） has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump system, repeated heating-cooling cycles may cause adverse effects on the integrity of cement grout in the ground heat exchanger. To account for the temperature cycling effect, the strength degradation of cement grout due to temperature cycling has been examined by measuring the unconfined compression strength of cured specimens in a humidity-temperature controlling chamber with applying temperature cycles between -5℃ and 50℃. There is a tendency that the unconfined compression strength decreases with an increase in the number of temperature cycles. On the other hand, an equivalent hydraulic conductivity of a pipe-embedded cement grout specimen was evaluated by carrying out a modified flexible wall permeameter test equipped with a water circulating system to control temperature inside the pipe section. The applied operating temperature range was from 5 to 35℃. After three cycles of heating-cooling circulation, the equivalent hydraulic conductivity becomes asymptotic to a constant value, which implies there is no severe detachment of the pipe from the cement grout.展开更多
基金National Natural Science Foundation of China and Shenhua Group Corporation Limited(Grant No.U1261108)The Science and Technology Program of China Huaneng Group(Grant No.HNKJ13-H09)
文摘The flow and heat transfer of air-cooled heat exchangers play important roles in the performance of indirect dry cooling systems in power plants,so it is of benefit to the design and operation of a typical indirect dry cooling system to optimize the thermo-flow characteristics of air-cooled heat exchangers.The entransy dissipation method is applied to the performance optimization of air-cooled heat exchangers in this paper.Two irreversible heat transfer processes in air-cooled heat exchangers,the heat transfer between circulating water and cooling air and the mixing of circulating water,are taken into account and analyzed by means of the entransy dissipation method.The total entransy dissipation rate,which connects the geometrical parameters of air-cooled heat exchanger sectors and the heat capacity rates of the fluids to the heat flow rate in every sector,is obtained.Based on the mathematical relation and the conditional extremum method,an optimization equation group is derived,by which the air-cooled heat exchanger with known air-side parameters is optimized,showing that the entransy dissipation based optimization approach can contribute to the distribution optimization of circulating water in air-cooled heat exchangers of a typical indirect dry cooling system.
基金supported by the Fundamental Research and Development Program of the Center of New and Renewable Energy of the Ministry of Knowledge and Economy (Grant No. 2008-N-GE08-R-01)the National Research Foundation of Korea Grant funded by the Korean Government (Grant No. 2010-0011159)
文摘The applicability of cement grout （or cement-based grout） has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump system, repeated heating-cooling cycles may cause adverse effects on the integrity of cement grout in the ground heat exchanger. To account for the temperature cycling effect, the strength degradation of cement grout due to temperature cycling has been examined by measuring the unconfined compression strength of cured specimens in a humidity-temperature controlling chamber with applying temperature cycles between -5℃ and 50℃. There is a tendency that the unconfined compression strength decreases with an increase in the number of temperature cycles. On the other hand, an equivalent hydraulic conductivity of a pipe-embedded cement grout specimen was evaluated by carrying out a modified flexible wall permeameter test equipped with a water circulating system to control temperature inside the pipe section. The applied operating temperature range was from 5 to 35℃. After three cycles of heating-cooling circulation, the equivalent hydraulic conductivity becomes asymptotic to a constant value, which implies there is no severe detachment of the pipe from the cement grout.
