The leakage research on supercritical carbon dioxide fluid in rolling piston expander was investigated experimentally.Using expander instead of throttle valve is an important way to improve the efficiency of carbon di...The leakage research on supercritical carbon dioxide fluid in rolling piston expander was investigated experimentally.Using expander instead of throttle valve is an important way to improve the efficiency of carbon dioxide refrigeration system.However,the supercritical fluid leakage in expander is serious and is the main factor affecting the expander's efficiency.This paper presented and compared four classic leakage models.The analysis indicated that laminar leakage model is suitable in leakage simulation of expander.A leakage test system,including the leakage test part which has two types of leakage specimens with different gaps ranging from 5 to 15 m,was established.The experimental results indicated that lubricant film played an important role.When the leakage clearance of cylindrical specimen was 5 m,the mass flow rate of leakage was about 0.88 g s-1.The data was 3.638 g s-1 with leakage clearance being 10 m and 7.11g s-1 with leakage clearance being 15 m.A modified leakage model was developed,whose average deviation was within 10% compared with the experimental data.At last,this paper simulated the leakage in rolling piston expander presented by Tian et al.(2010).The leakage between rolling piston and cylinder was the most serious part with the value up to 0.04 kg s-1.展开更多
The expansion mechanism inside carbon dioxide expander is analyzed theoretically in this paper.The mechanism analysis of metastable equilibrium indicates that there is a potential barrier during phase change process.T...The expansion mechanism inside carbon dioxide expander is analyzed theoretically in this paper.The mechanism analysis of metastable equilibrium indicates that there is a potential barrier during phase change process.That is to say energy is required to overcome the potential barrier when the new interface is formed from primary phase.The superheat of liquid is the impetus of phase change and has an exponential decrease with the increase of the saturated temperature of fluid.The analysis also indicates that there is a critical radius during the phase change process.The bubble will grow up when its radius is larger than the critical value,otherwise,will disappear.When considering the metastable phase change,calculation of P and V during expansion process indicates that the phase-change will be delayed with the decline of pressure,which is called lag phenomenon.The phase-change delay time decreases with the increase of initial temperature.When the initial temperature is close to the critical temperature,the delay time is close to zero.The phase-change delay brings energy losses,which decrease with the increase of initial temperature and its decrease ratio also has a decrease trend.When the initial pressure is 10 MPa,the energy loss will be 1.06 W with an initial temperature of 10℃ while 0.34 W with that of 20℃.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 50676064)
文摘The leakage research on supercritical carbon dioxide fluid in rolling piston expander was investigated experimentally.Using expander instead of throttle valve is an important way to improve the efficiency of carbon dioxide refrigeration system.However,the supercritical fluid leakage in expander is serious and is the main factor affecting the expander's efficiency.This paper presented and compared four classic leakage models.The analysis indicated that laminar leakage model is suitable in leakage simulation of expander.A leakage test system,including the leakage test part which has two types of leakage specimens with different gaps ranging from 5 to 15 m,was established.The experimental results indicated that lubricant film played an important role.When the leakage clearance of cylindrical specimen was 5 m,the mass flow rate of leakage was about 0.88 g s-1.The data was 3.638 g s-1 with leakage clearance being 10 m and 7.11g s-1 with leakage clearance being 15 m.A modified leakage model was developed,whose average deviation was within 10% compared with the experimental data.At last,this paper simulated the leakage in rolling piston expander presented by Tian et al.(2010).The leakage between rolling piston and cylinder was the most serious part with the value up to 0.04 kg s-1.
基金supported by the National Natural Science Foundation of China (Grant No 50676064)
文摘The expansion mechanism inside carbon dioxide expander is analyzed theoretically in this paper.The mechanism analysis of metastable equilibrium indicates that there is a potential barrier during phase change process.That is to say energy is required to overcome the potential barrier when the new interface is formed from primary phase.The superheat of liquid is the impetus of phase change and has an exponential decrease with the increase of the saturated temperature of fluid.The analysis also indicates that there is a critical radius during the phase change process.The bubble will grow up when its radius is larger than the critical value,otherwise,will disappear.When considering the metastable phase change,calculation of P and V during expansion process indicates that the phase-change will be delayed with the decline of pressure,which is called lag phenomenon.The phase-change delay time decreases with the increase of initial temperature.When the initial temperature is close to the critical temperature,the delay time is close to zero.The phase-change delay brings energy losses,which decrease with the increase of initial temperature and its decrease ratio also has a decrease trend.When the initial pressure is 10 MPa,the energy loss will be 1.06 W with an initial temperature of 10℃ while 0.34 W with that of 20℃.
