The heat transfer between an airway and the air flowing though it is an unsteady problem. The governing equation of unsteady heat transfer was solved using the method of separation of variables. The solution is an inf...The heat transfer between an airway and the air flowing though it is an unsteady problem. The governing equation of unsteady heat transfer was solved using the method of separation of variables. The solution is an infinite series including Bessel functions. The theoretical solution was analyzed by solving for the positive roots of the transcendental equation by iteration. The dimensionless surface temperature of the sur- rounding rock is only affected by the Bi number but not by the thermo-physical coefficients of the rock. The dimensionless coefficient of heat transfer, k, decreases with the Fo number similarly to the influence of the Bi number on k. A formula for determining the fully developed stage (FDS) suitable for unsteady heat transfer in the airway is proposed. The FDS from theoretical analysis occurs with Fo from 1.6 to 2. The ratio of excess temperature in the surrounding rock is independent of the initial conditions and only dependent on the Bi number and the relative position in the airway, at the FDS. The calculation error is large when using just the first term from the complete series when Fo is from 2 to 12. Five terms give a solution approximately equal to that found using the complete series. The first term could replace the complete series only when Fo is greater than 12. The FDS plays an important role in predication of the temperature field of the surrounding rock and in simplified calculations.展开更多
With the advantages of low cost,excellent ability of heat and mass transfer and easy accessibility to the supercritical point,supercritical CO_(2) has been applied in many engineering devices recently.Because of the s...With the advantages of low cost,excellent ability of heat and mass transfer and easy accessibility to the supercritical point,supercritical CO_(2) has been applied in many engineering devices recently.Because of the sharply-varying thermophysical properties near the supercritical point,heat transfer and flow behavior of supercritical CO_(2) in tubes become complex and have received a lot of research attention.The main purpose of this paper is to summarize the findings of the published works related to flow phenomena and heat transfer characteristics of supercritical CO_(2).Firstly,influence parameters related to boundary conditions of supercritical CO_(2) flowing in a smooth tube are introduced.Secondly,commonly-used turbulence and mathematic models dealing with internal flows of supercritical CO_(2) are summarized.Then,research works on geometric effects of design parameters,shapes and configurations are introduced.The practical applications of supercritical CO_(2) in recent years are presented.Finally,developments and future challenges of supercritical CO_(2) in tubes are analyzed and summarized.This paper provides basic knowledge of heat transfer and fluid flow mechanisms and related practical applications of supercritical CO,in tubes.展开更多
Simultaneous development of the laminar flow and heat transfer in helicalsquare ducts was numerically studied. The governing equations were written in an orthogonal helicalcoordinate system and fully parabolized in th...Simultaneous development of the laminar flow and heat transfer in helicalsquare ducts was numerically studied. The governing equations were written in an orthogonal helicalcoordinate system and fully parabolized in the axial direction. Results were found out over a widerange of the governing parameters. Two axial velocity entries were taken into account. Thedevelopment of secondary flow, axial velocity and temperature distribution for the large Dean numberwere examined in detail and the effects of different governing parameters on the friction factorand- the Nusselt number were annlyzee. Many new and interesting conclusions were reached. Thepresent results reveal the nature of fluid flow and heat transfer in the developing region ofhelical square ducts.展开更多
An experimental study is conducted to investigate the heat transfer augmentation in developing turbulent flow through a ribbed square duct. The duct is made of 16ram thick bakelite sheet. The bottom surface of the rib...An experimental study is conducted to investigate the heat transfer augmentation in developing turbulent flow through a ribbed square duct. The duct is made of 16ram thick bakelite sheet. The bottom surface of the ribbed wall having rib pitch to height ratio of 10 is heated by passing a c current to the heater placed under it. The uniform heating is controlled using a digital temperature controller and a variac. The results of ribbed duct are compared with the results of a smooth duct under the same experimental conditions. It is observed that the heat transfer augmentation in ribbed duct is better than that of the smooth duct. At Re=5.0× 10^4 , the mean temperature of air flowing through the ribbed duct increases by 2.45 percent over the smooth duct, whereas in the fibbed duct Nusselt number increases by 15.14 percent than that of the smooth duct with a 6 percent increase in pressure drop.展开更多
基金provided by the Postdoctoral Science Foundation of China (No. 2011M500974)Fundamental Research Funds for Central Universities (No. 2011QNA16)+1 种基金Postdoctoral Foundation of state key laboratory for GDUE (No. PD1101)Natural Science Foundation for Young Scholars of SMCE, CUMT(No. lj2010qnjj004)
文摘The heat transfer between an airway and the air flowing though it is an unsteady problem. The governing equation of unsteady heat transfer was solved using the method of separation of variables. The solution is an infinite series including Bessel functions. The theoretical solution was analyzed by solving for the positive roots of the transcendental equation by iteration. The dimensionless surface temperature of the sur- rounding rock is only affected by the Bi number but not by the thermo-physical coefficients of the rock. The dimensionless coefficient of heat transfer, k, decreases with the Fo number similarly to the influence of the Bi number on k. A formula for determining the fully developed stage (FDS) suitable for unsteady heat transfer in the airway is proposed. The FDS from theoretical analysis occurs with Fo from 1.6 to 2. The ratio of excess temperature in the surrounding rock is independent of the initial conditions and only dependent on the Bi number and the relative position in the airway, at the FDS. The calculation error is large when using just the first term from the complete series when Fo is from 2 to 12. Five terms give a solution approximately equal to that found using the complete series. The first term could replace the complete series only when Fo is greater than 12. The FDS plays an important role in predication of the temperature field of the surrounding rock and in simplified calculations.
基金supported by Key Laboratory Continuously Supporting Project(Grant No.WDZC6142703202216)the Natural Science Foundation of Hunan Province(Grant No.2023JJ40733).
文摘With the advantages of low cost,excellent ability of heat and mass transfer and easy accessibility to the supercritical point,supercritical CO_(2) has been applied in many engineering devices recently.Because of the sharply-varying thermophysical properties near the supercritical point,heat transfer and flow behavior of supercritical CO_(2) in tubes become complex and have received a lot of research attention.The main purpose of this paper is to summarize the findings of the published works related to flow phenomena and heat transfer characteristics of supercritical CO_(2).Firstly,influence parameters related to boundary conditions of supercritical CO_(2) flowing in a smooth tube are introduced.Secondly,commonly-used turbulence and mathematic models dealing with internal flows of supercritical CO_(2) are summarized.Then,research works on geometric effects of design parameters,shapes and configurations are introduced.The practical applications of supercritical CO_(2) in recent years are presented.Finally,developments and future challenges of supercritical CO_(2) in tubes are analyzed and summarized.This paper provides basic knowledge of heat transfer and fluid flow mechanisms and related practical applications of supercritical CO,in tubes.
文摘Simultaneous development of the laminar flow and heat transfer in helicalsquare ducts was numerically studied. The governing equations were written in an orthogonal helicalcoordinate system and fully parabolized in the axial direction. Results were found out over a widerange of the governing parameters. Two axial velocity entries were taken into account. Thedevelopment of secondary flow, axial velocity and temperature distribution for the large Dean numberwere examined in detail and the effects of different governing parameters on the friction factorand- the Nusselt number were annlyzee. Many new and interesting conclusions were reached. Thepresent results reveal the nature of fluid flow and heat transfer in the developing region ofhelical square ducts.
文摘An experimental study is conducted to investigate the heat transfer augmentation in developing turbulent flow through a ribbed square duct. The duct is made of 16ram thick bakelite sheet. The bottom surface of the ribbed wall having rib pitch to height ratio of 10 is heated by passing a c current to the heater placed under it. The uniform heating is controlled using a digital temperature controller and a variac. The results of ribbed duct are compared with the results of a smooth duct under the same experimental conditions. It is observed that the heat transfer augmentation in ribbed duct is better than that of the smooth duct. At Re=5.0× 10^4 , the mean temperature of air flowing through the ribbed duct increases by 2.45 percent over the smooth duct, whereas in the fibbed duct Nusselt number increases by 15.14 percent than that of the smooth duct with a 6 percent increase in pressure drop.
