The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel r...The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel range from 1 400 to 8 000.The ratios of rib height to hydraulic diameter (e/D) are 0.2and 0.33,respectively.The ratio of rib spacing to height (P/e) ranges from 5to 15.The rib orientations in the opposite surfaces are symmetrical and staggered arrangements.The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number,though at the cost of higher pressure losses.When the rib spacing to height ratio is 10,it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5,10 and 15.The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs,but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.展开更多
Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch an...Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.展开更多
A numerical investigation has been carried out to examine turbulent flow and heat transfer characteristics in a three-dimensional ribbed square channels. Fluent 6.3 CFD code has been used. The governing equations are ...A numerical investigation has been carried out to examine turbulent flow and heat transfer characteristics in a three-dimensional ribbed square channels. Fluent 6.3 CFD code has been used. The governing equations are discretized by the second order upwind differencing scheme, decoupling with the SIMPLE (semi-implicit method for pressure linked equations) algorithm and are solved using a finite volume approach. The fluid flow and heat transfer characteristics are presented for the Reynolds numbers based on the channel hydraulic diameter ranging from 104 to 4 ′ 104. The effects of rib shape and orientation on heat transfer and pressure drop in the channel are investigated for six different rib configurations. Rib arrays of 45° inclined and 45° V-shaped are mounted in inline and staggered arrangements on the lower and upper walls of the channel. In addition, the performance of these ribs is also compared with the 90° transverse ribs.展开更多
The 1 dimensional localization of elastic waves in disordered periodic multi span rib stiffened plates is investigated. The transfer matrix method is employed to obtain the transfer matrix of the system, and the metho...The 1 dimensional localization of elastic waves in disordered periodic multi span rib stiffened plates is investigated. The transfer matrix method is employed to obtain the transfer matrix of the system, and the method for calculating the Lyapunov exponents in continuous dynamic systems presented by Wolf is used to determine the localization factor. As examples, the numerical results of the localization factors are given for a disordered rib stiffened plate. The effects of the degree of disorder of span...展开更多
The National Institute for Occupational Safety and Health(NIOSH)conducted a comprehensive monitoring program in a room-and-pillar mine located in Southern Virginia.The deformation and the stress change in an instrumen...The National Institute for Occupational Safety and Health(NIOSH)conducted a comprehensive monitoring program in a room-and-pillar mine located in Southern Virginia.The deformation and the stress change in an instrumented pillar were monitored during the progress of pillar retreat mining at two sites of different geological conditions and depths of cover.The main objectives of the monitoring program were to better understand the stress transfer and load shedding on coal pillars and to quantify the rib deformation due to pillar retreat mining;and to examine the effect of rib geology and overburden depth on coal rib performance.The instrumentation at both sites included pull-out tests to measure the anchorage capacity of rib bolts,load cells mounted on rib bolts to monitor the induced loads in the bolts,borehole pressure cells(BPCs)installed at various depths in the study pillar to measure the change in vertical pressure within the pillar,and roof and rib extensometers installed to quantify the vertical displacement of the roof and the horizontal displacement of the rib that would occur during the retreat mining process.The outcome from the monitoring program provides insight into coal pillar rib support optimization at various depths and geological conditions.Also,this study contributes to the NIOSH rib support database in U.S coal mines and provides essential data for rib support design.展开更多
Several industrial applications such as electronic devices,heat exchangers,gas turbine blades,etc.need cooling processes.The internal cooling technique is proper for some applications.In the present work,computational...Several industrial applications such as electronic devices,heat exchangers,gas turbine blades,etc.need cooling processes.The internal cooling technique is proper for some applications.In the present work,computational simulations were made using ANSYS CFX to predict the improvements of internal heat transfer in the rectangular ribbed channel using different coolants.Several coolants such as air,steam,air/mist and steam/mist were investigated.The shear stress transport model(SST)is selected by comparing the standard k-ωand Omega Reynolds Stress(ωRS)turbulence models with experimental results.The results indicate that the heat transfer coefficients are enhanced in the ribbed channel while injecting small amounts of mist.The heat transfer coefficients of air/mist,steam and steam/mist increase by 12.5%,49.5%and 107%over that of air,respectively.Furthermore,in comparison to air,the air/mist heat transfer coefficient enhances by about 1.05 to 1.14 times when the mist mass fraction increases from 2%to 8%,respectively.The steam/mist heat transfer coefficient increases by about 1.12 to 1.27 times higher than that of steam over the considered range of mist mass fraction.展开更多
基金supported by the National Natural Science Foundation of China(No.51276088)
文摘The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel range from 1 400 to 8 000.The ratios of rib height to hydraulic diameter (e/D) are 0.2and 0.33,respectively.The ratio of rib spacing to height (P/e) ranges from 5to 15.The rib orientations in the opposite surfaces are symmetrical and staggered arrangements.The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number,though at the cost of higher pressure losses.When the rib spacing to height ratio is 10,it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5,10 and 15.The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs,but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.
基金Supported by the National Natural Science Foundation of China(11472093 and21276056)
文摘Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.
文摘A numerical investigation has been carried out to examine turbulent flow and heat transfer characteristics in a three-dimensional ribbed square channels. Fluent 6.3 CFD code has been used. The governing equations are discretized by the second order upwind differencing scheme, decoupling with the SIMPLE (semi-implicit method for pressure linked equations) algorithm and are solved using a finite volume approach. The fluid flow and heat transfer characteristics are presented for the Reynolds numbers based on the channel hydraulic diameter ranging from 104 to 4 ′ 104. The effects of rib shape and orientation on heat transfer and pressure drop in the channel are investigated for six different rib configurations. Rib arrays of 45° inclined and 45° V-shaped are mounted in inline and staggered arrangements on the lower and upper walls of the channel. In addition, the performance of these ribs is also compared with the 90° transverse ribs.
基金National Natural Science F oundation of China (19972 0 18) and Projectsupported by the National Key Basic Research Foun-dation of China (G19980 2 0 3 17)
文摘The 1 dimensional localization of elastic waves in disordered periodic multi span rib stiffened plates is investigated. The transfer matrix method is employed to obtain the transfer matrix of the system, and the method for calculating the Lyapunov exponents in continuous dynamic systems presented by Wolf is used to determine the localization factor. As examples, the numerical results of the localization factors are given for a disordered rib stiffened plate. The effects of the degree of disorder of span...
基金The authors want to thank Todd Minoski for preparing the data collection system and James Addis and Cynthia Hollerich for help with installing the test instruments.
文摘The National Institute for Occupational Safety and Health(NIOSH)conducted a comprehensive monitoring program in a room-and-pillar mine located in Southern Virginia.The deformation and the stress change in an instrumented pillar were monitored during the progress of pillar retreat mining at two sites of different geological conditions and depths of cover.The main objectives of the monitoring program were to better understand the stress transfer and load shedding on coal pillars and to quantify the rib deformation due to pillar retreat mining;and to examine the effect of rib geology and overburden depth on coal rib performance.The instrumentation at both sites included pull-out tests to measure the anchorage capacity of rib bolts,load cells mounted on rib bolts to monitor the induced loads in the bolts,borehole pressure cells(BPCs)installed at various depths in the study pillar to measure the change in vertical pressure within the pillar,and roof and rib extensometers installed to quantify the vertical displacement of the roof and the horizontal displacement of the rib that would occur during the retreat mining process.The outcome from the monitoring program provides insight into coal pillar rib support optimization at various depths and geological conditions.Also,this study contributes to the NIOSH rib support database in U.S coal mines and provides essential data for rib support design.
基金Supported by the China Scholarship Council (CSC) under Grant No.2011BSZF88
文摘Several industrial applications such as electronic devices,heat exchangers,gas turbine blades,etc.need cooling processes.The internal cooling technique is proper for some applications.In the present work,computational simulations were made using ANSYS CFX to predict the improvements of internal heat transfer in the rectangular ribbed channel using different coolants.Several coolants such as air,steam,air/mist and steam/mist were investigated.The shear stress transport model(SST)is selected by comparing the standard k-ωand Omega Reynolds Stress(ωRS)turbulence models with experimental results.The results indicate that the heat transfer coefficients are enhanced in the ribbed channel while injecting small amounts of mist.The heat transfer coefficients of air/mist,steam and steam/mist increase by 12.5%,49.5%and 107%over that of air,respectively.Furthermore,in comparison to air,the air/mist heat transfer coefficient enhances by about 1.05 to 1.14 times when the mist mass fraction increases from 2%to 8%,respectively.The steam/mist heat transfer coefficient increases by about 1.12 to 1.27 times higher than that of steam over the considered range of mist mass fraction.
