Influence of co-firing rate on SO 2 emission from co-firing municipal solid waste(MSW) and bituminous containing high amount of sulfur(1.79%) was studied in a 0.15 MWt circulating fluidized bed(CFB). The temperature ...Influence of co-firing rate on SO 2 emission from co-firing municipal solid waste(MSW) and bituminous containing high amount of sulfur(1.79%) was studied in a 0.15 MWt circulating fluidized bed(CFB). The temperature selected is 1123 K, typical for MSW incineration using CFB. The particle concentration in the dilution zone of the furnace, the alkali metal concentration and sulfate concentration in the recirculating ash and fly ash, and flue gas composition were determined. The results showed that the addition of MSW leads to a significant decrease in SO 2 emission. Concentration of SO 2 in flue gas decreased to 0 with the co-firing rate greater than 51%. This reduction in SO 2 emission is attributed both to the high particle concentration in the dilution zone of the furnace, the high content of alkali metals in the bed material, and to the comparatively high concentration of HCl in flue gas during co-firing of MSW and bituminous.展开更多
A numerical analysis of the laser drying process by employing a generalized,Maxwell-Cattaneo equation to treat both heat and mass transfer was presented. Calculations wereperformed to illustrate the non-classical tran...A numerical analysis of the laser drying process by employing a generalized,Maxwell-Cattaneo equation to treat both heat and mass transfer was presented. Calculations wereperformed to illustrate the non-classical transport of heat and moisture. The effect of the heatflux density and the initial moisture content on water removal was also investigated. The resultsindicate that the non-equilibrium mass diffusion plays an important role during the very earlystages of moisture removal, especially at the surface of the medium. Away from the surface, thenon-Fickian model shows a delay in the reduction of the moisture content. The calculation resultsalso show that the initial moisture content of the medium has a considerable effect on waterremoval.展开更多
An experimental study of bioheat transfer characteristics induced bypulsed-laser irradiation was presented. The heat transfer characteristics of bio-materials, and theinfluences of pulse duration, power density, speci...An experimental study of bioheat transfer characteristics induced bypulsed-laser irradiation was presented. The heat transfer characteristics of bio-materials, and theinfluences of pulse duration, power density, species of bio-materials, thickness and initialmoisture content of bio-materials on heat transfer were studied in details. The experimental resultsindicate that the penetration and absorption of laser in bio-materials are considerable, the heattransfer inside the bio-materials should include the effects of volumetric absorption, pulseduration, power density, bio-materials thickness, and material species have a significant influenceon the temperature variation.展开更多
The mechanism of heat transfer in a crossflow moving packed bed heat transfer exchanger is analyzed and a two dimensional heat transfer mathematical model has been developed based on the two fluid model (TFM)approach,...The mechanism of heat transfer in a crossflow moving packed bed heat transfer exchanger is analyzed and a two dimensional heat transfer mathematical model has been developed based on the two fluid model (TFM)approach, in which both phases are considered to be continuous and fully interpenetrating.This model is solved by means of numerical method and the results are approximately in agreement with the experimental ones.展开更多
An experimental study was performed to evaluate the suitability of using an electrical capacitance tomography (ECT) system to visualize the flow patterns, and to measure the film thickness of the annular flow in a two...An experimental study was performed to evaluate the suitability of using an electrical capacitance tomography (ECT) system to visualize the flow patterns, and to measure the film thickness of the annular flow in a two-phase closed thermosyphon (TPCT). The performance of the ECT system was examined over a range of flow conditions.The experimental data were compared with the visual observations and existing correlations. Results indicated that the ECT system, with the linear back projection (LBP) algorithm, could be used to give an on-line qualitative image of the flow patterns. The Landweber iteration algorithm with optimal step length was implemented off-line to reconstruct high-resolution images. Then, the images were analyzed to obtain the film thickness of the annular flow. The experimental data compared well with the Nusselt's equation in low vapor velocity range, but showed an increasing deficiency with the increase of vapor velocity.展开更多
A two dimensional cold CFB test rig has been established, investigation on horizontal mixing of particles in dense bed has been carried out on this test rig. Mixing model has been used in data reduction,the horizontal...A two dimensional cold CFB test rig has been established, investigation on horizontal mixing of particles in dense bed has been carried out on this test rig. Mixing model has been used in data reduction,the horizontal miring coefficients of particles in different experimental conditions and in different structures of dense bed have been obtained and compared. By using dimensional analysis, non-dimensionalexpression of experimental condition and mixing coefficient have been obtained.展开更多
Three types of nozzles: a low-pressure multistage nozzle, an effervescent nozzle and a newly developed internal- mixing air-blast nozzle, for atomization of Coal-Water Slurry (CWS) were investigated. Influence of CWS ...Three types of nozzles: a low-pressure multistage nozzle, an effervescent nozzle and a newly developed internal- mixing air-blast nozzle, for atomization of Coal-Water Slurry (CWS) were investigated. Influence of CWS properties including surface tension and apparent viscosity on atomization was studied. Comparisons among the nozzles were carried out in terms of spray droplet mean diameter and fuel output. Versatility of each nozzle was investigated and atomization mechanism of each nozzle was analyzed as well. The results showed that the newly developed internal- mixing air-blast nozzle has high fuel output and small mean droplet size in the spray, but the multistage nozzle has high versatility for handling of low quality CWS.展开更多
Electrical capacitance tomography(ECT) was applied in measuring solids distribution in square circulating fluidized beds. The fluidization conditions varied from bubbling fluidized bed to circulating fluidized bed. In...Electrical capacitance tomography(ECT) was applied in measuring solids distribution in square circulating fluidized beds. The fluidization conditions varied from bubbling fluidized bed to circulating fluidized bed. In the whole range of fluidization conditions, ECT was able to instantaneously provide the solids concentration and voids distributions in the fluidized beds. According to the acquired data from ECT and reconstructed image, different fluidization regimes can also be identified.展开更多
Capillary Pumped Loop (CPL) is a tWo Phase closed system. The tWo main components of CPL, both evaporatorand reservoir are generally believed to play significant roles in its unsteady operation. In thes paper, experim...Capillary Pumped Loop (CPL) is a tWo Phase closed system. The tWo main components of CPL, both evaporatorand reservoir are generally believed to play significant roles in its unsteady operation. In thes paper, experimentaland theoretical investigations are carried out on the influences of unsteady chararterishcs of both of them. Theprevious analyhcal results show that there is a pressure oscillation source in the evaporator and the internaloscillation frequency can be obtained. The reservoir also has an unsteady characterishcs, when the reservoir line hasa smaller damping value, there will be a self-oscillation of Pressure in the reservoir, and its analyhcal frequenciesare normally one or two quantihes bigger than the inherent frequencies of the evaporator. In order to keep CPLoperate steadily, on one hand, the structure of evaporator must be increased to make the conhnuous generated vaporflow out the wick easily, on the other hand, the return liquid ought to be subcooled enough to the reservoirtemperature set value.展开更多
This paper presents our recent experimental investigation on the feasibility of monitoring the froth molding, a special case of solidification process, of polyurethane by using electrical capacitance tomography. The m...This paper presents our recent experimental investigation on the feasibility of monitoring the froth molding, a special case of solidification process, of polyurethane by using electrical capacitance tomography. The major challenge is the extremely low solid density of the solidified material during the process due to the very large expansion ratio. Suitable calibration method is sought and adequate image reconstruction algorithm is applied for such a task. Different expansion modes have been observed during experiment and corresponding images reconstructed. This visualization technique clearly revealed the expansion process by a time series of images of the solid density. The test results proved the capability of electrical capacitance tomography in monitoring the expansion of polyurethane. Future ways for improvement are also suggested.展开更多
This paper presents the results of experiments and numerical simulation of the turbulent swirling flow and heat transfer in a duct.The calculated results are in good agreement with data obtained by measurements.It is ...This paper presents the results of experiments and numerical simulation of the turbulent swirling flow and heat transfer in a duct.The calculated results are in good agreement with data obtained by measurements.It is found that the swirling flow promotes heat transfer to the wall of the duct;the swirl numbers are dependent upon the vane exit angles of the swirler,distance from the swirler and the duct Reynolds number.But the decay of swirling flow in streamwise direction is related to local Reynolds numbers and is independent of the swirler exit angle.The swirl flow characteristics presented in this paper may be used for engineering purposes.展开更多
This paper presents an experimental study of the three-dimensional turbulent flow fields in a lowspeed annular cascade of high turning angle turbine blades. Detailed measurements were performed on the blade surfaces a...This paper presents an experimental study of the three-dimensional turbulent flow fields in a lowspeed annular cascade of high turning angle turbine blades. Detailed measurements were performed on the blade surfaces and mid-streamsurface in the passage and at three axial planes downstream of the cascade by using wall static pressure taps, a five-hole probe and a hot-wire anemometer. The test data include static pressure distribution on blade surfaces, total pressure loss coefficient, mean flow velocity components, radial flow angle, turbulence intensity and Reynolds shear stress. Analyses of the three-dimensional cascade flow characteristics were made on the onset location of high loss vortices, the variation of pressure gradient inside the cascade passage and the properties of endwall boundary layers,total pressure loss distributions, secondary vortex turbulent dissipation and wake decay downstream of the cascade. These experimental results are valuable for revealing the details of the complex vortex flow structure in modern highly loaded axial turbomachines and validating the three-dimensional flow numerical computation codes.展开更多
Dual-phase lag (DPL) model is used to describe the non-Fourier heat conduction in a finite medium where the boundary at x=0 is heated by a rectangular pulsed energy source and the other boundary is tightly contactal w...Dual-phase lag (DPL) model is used to describe the non-Fourier heat conduction in a finite medium where the boundary at x=0 is heated by a rectangular pulsed energy source and the other boundary is tightly contactal with another medium and satisfies the continuous boundary condition. Numerical solution of thes kind of non-Fourier heat conduction is presented in this paper. The results are compared with those predicted by the hyperbolic heat conduction (HHC) equation.展开更多
When condensation occurs in supersonic flow fields, the flow is affected by the latent heat released, and if the heat released exceeds a certain quantity, a condensation shock wave will occur There are many papers for...When condensation occurs in supersonic flow fields, the flow is affected by the latent heat released, and if the heat released exceeds a certain quantity, a condensation shock wave will occur There are many papers for the passive control of shock-boundary layer interaction using the porous wall with a plenum underneath on the application of the technique to transonic airfoil flows. In the present study, this passive technique is applied to the control of a steady condensation shock wave generated in a supersonic nozzle. In order to clarify the effect of the passive shockboundary layer control on condensation shock, Navier-Stokes equations were solved numerically using a 3rd-order MUSCL type TVD finite-difference scheme with a second-order fractional-step for time integration. As a result, the simulated flow fields were compared with experimental data in good agreement and the aspect of the flow field has been clarified.展开更多
When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing f...When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.展开更多
In this paper, theoretical analysis on evaporating heat transfer in capillary with equilateral triangular cross section is presented and numerical calculations based on glass-water system are carried out. Considering ...In this paper, theoretical analysis on evaporating heat transfer in capillary with equilateral triangular cross section is presented and numerical calculations based on glass-water system are carried out. Considering evaporation mechanism in capillary with polygonal section, one-dimensional model is used to describe the three-dimensional case. The evaporating meniscus in the capillary along axis can be divided into six regions. The following conclusions are obtained: (1) The local heat transfer coefficients and heat fluxes in capillary increase quickly in the first and second regions, and slowly in the third region. The maximum value appears at interline between the third and fourth regions, then gradually decreases in the last three regions. (2) The average heat transfer coefficients decrease when the sizes of the capillary section increase, and become larger under higher wall temperature.展开更多
Two-dimensional turbulent mixed convection-surface radiation interaction phenomenon in a back-wall-heated open square cavity is numerically investigated. The flow medium is air, and the turbulence model used is the Lo...Two-dimensional turbulent mixed convection-surface radiation interaction phenomenon in a back-wall-heated open square cavity is numerically investigated. The flow medium is air, and the turbulence model used is the Low-Reynolds-Number κ-ε Scheme. Calculations have been performed for Grashof numbers Gr up to 10^(10). And the Richardson number Ri covers a range of 4×10^(-3)-45. It is shown that within a rather extensive range of Ri, the effects of radiation on the heat transfer and fluid flow in the cavity are significant, should not be neglected and become stronger with the increase of Ri and Gr.展开更多
The boiling behavior of the liquid nitrogen (LN2) under the transient high heat flux urgently needs to be researched systematically. In this paper, the high power short pulse duration laser was used to heat the satura...The boiling behavior of the liquid nitrogen (LN2) under the transient high heat flux urgently needs to be researched systematically. In this paper, the high power short pulse duration laser was used to heat the saturated LN2 rapidly, and the high-speed photography aided by the spark light system was employed to take series of photos which displayed the process of LN2's boiling behavior under such conditions. Also, a special temperature measuring system was applied to record the temperature variation of the heating surface. The experiments indicated that an explosive boiling happened within LN2 by the laser heating, and a conventional boiling followed up after the newly-defined changeover time. By analyzing the temperature variation of the heating surface, it is found that the latent heat released by the crack of the bubbles in the bubble cluster induced by the explosive boiling is an important factor that greatly influences the boiling heat transfer mechanism.展开更多
Experimental investigations of boiling heat transfer from porous suffaces at atmospheric pressure were performed. The porous surfaces are plain tubes covered with metal screens, V-shaped groove tubes covered with sc...Experimental investigations of boiling heat transfer from porous suffaces at atmospheric pressure were performed. The porous surfaces are plain tubes covered with metal screens, V-shaped groove tubes covered with screens, plain tubes sintered with screens, and V-shaped groove tubes sintered with screens.The experimental results show that siatering metal screens around spiral V-shaped groove tubes can greatly improve the boiling heat transfer. The boiling hysteresis was observed in the experiment. This paper discusses the mechanism of the boiling heat transfer horn those kinds of porous surfaces stated above.展开更多
文摘Influence of co-firing rate on SO 2 emission from co-firing municipal solid waste(MSW) and bituminous containing high amount of sulfur(1.79%) was studied in a 0.15 MWt circulating fluidized bed(CFB). The temperature selected is 1123 K, typical for MSW incineration using CFB. The particle concentration in the dilution zone of the furnace, the alkali metal concentration and sulfate concentration in the recirculating ash and fly ash, and flue gas composition were determined. The results showed that the addition of MSW leads to a significant decrease in SO 2 emission. Concentration of SO 2 in flue gas decreased to 0 with the co-firing rate greater than 51%. This reduction in SO 2 emission is attributed both to the high particle concentration in the dilution zone of the furnace, the high content of alkali metals in the bed material, and to the comparatively high concentration of HCl in flue gas during co-firing of MSW and bituminous.
基金This work was financially supported by the State Key Fundamental Research Plan of China (N0.G2000026306)the National Natural Science Foundation of China (50376063).
文摘A numerical analysis of the laser drying process by employing a generalized,Maxwell-Cattaneo equation to treat both heat and mass transfer was presented. Calculations wereperformed to illustrate the non-classical transport of heat and moisture. The effect of the heatflux density and the initial moisture content on water removal was also investigated. The resultsindicate that the non-equilibrium mass diffusion plays an important role during the very earlystages of moisture removal, especially at the surface of the medium. Away from the surface, thenon-Fickian model shows a delay in the reduction of the moisture content. The calculation resultsalso show that the initial moisture content of the medium has a considerable effect on waterremoval.
基金This research was financially supported by the Chinese National Key Foundation Research Subject (No.G2000026305), National Natural Science Foundation of China (No.50276060), and the director foundation of Institute of Engineering Thermophysics, Chinese A
文摘An experimental study of bioheat transfer characteristics induced bypulsed-laser irradiation was presented. The heat transfer characteristics of bio-materials, and theinfluences of pulse duration, power density, species of bio-materials, thickness and initialmoisture content of bio-materials on heat transfer were studied in details. The experimental resultsindicate that the penetration and absorption of laser in bio-materials are considerable, the heattransfer inside the bio-materials should include the effects of volumetric absorption, pulseduration, power density, bio-materials thickness, and material species have a significant influenceon the temperature variation.
文摘The mechanism of heat transfer in a crossflow moving packed bed heat transfer exchanger is analyzed and a two dimensional heat transfer mathematical model has been developed based on the two fluid model (TFM)approach, in which both phases are considered to be continuous and fully interpenetrating.This model is solved by means of numerical method and the results are approximately in agreement with the experimental ones.
文摘An experimental study was performed to evaluate the suitability of using an electrical capacitance tomography (ECT) system to visualize the flow patterns, and to measure the film thickness of the annular flow in a two-phase closed thermosyphon (TPCT). The performance of the ECT system was examined over a range of flow conditions.The experimental data were compared with the visual observations and existing correlations. Results indicated that the ECT system, with the linear back projection (LBP) algorithm, could be used to give an on-line qualitative image of the flow patterns. The Landweber iteration algorithm with optimal step length was implemented off-line to reconstruct high-resolution images. Then, the images were analyzed to obtain the film thickness of the annular flow. The experimental data compared well with the Nusselt's equation in low vapor velocity range, but showed an increasing deficiency with the increase of vapor velocity.
文摘A two dimensional cold CFB test rig has been established, investigation on horizontal mixing of particles in dense bed has been carried out on this test rig. Mixing model has been used in data reduction,the horizontal miring coefficients of particles in different experimental conditions and in different structures of dense bed have been obtained and compared. By using dimensional analysis, non-dimensionalexpression of experimental condition and mixing coefficient have been obtained.
文摘Three types of nozzles: a low-pressure multistage nozzle, an effervescent nozzle and a newly developed internal- mixing air-blast nozzle, for atomization of Coal-Water Slurry (CWS) were investigated. Influence of CWS properties including surface tension and apparent viscosity on atomization was studied. Comparisons among the nozzles were carried out in terms of spray droplet mean diameter and fuel output. Versatility of each nozzle was investigated and atomization mechanism of each nozzle was analyzed as well. The results showed that the newly developed internal- mixing air-blast nozzle has high fuel output and small mean droplet size in the spray, but the multistage nozzle has high versatility for handling of low quality CWS.
文摘Electrical capacitance tomography(ECT) was applied in measuring solids distribution in square circulating fluidized beds. The fluidization conditions varied from bubbling fluidized bed to circulating fluidized bed. In the whole range of fluidization conditions, ECT was able to instantaneously provide the solids concentration and voids distributions in the fluidized beds. According to the acquired data from ECT and reconstructed image, different fluidization regimes can also be identified.
文摘Capillary Pumped Loop (CPL) is a tWo Phase closed system. The tWo main components of CPL, both evaporatorand reservoir are generally believed to play significant roles in its unsteady operation. In thes paper, experimentaland theoretical investigations are carried out on the influences of unsteady chararterishcs of both of them. Theprevious analyhcal results show that there is a pressure oscillation source in the evaporator and the internaloscillation frequency can be obtained. The reservoir also has an unsteady characterishcs, when the reservoir line hasa smaller damping value, there will be a self-oscillation of Pressure in the reservoir, and its analyhcal frequenciesare normally one or two quantihes bigger than the inherent frequencies of the evaporator. In order to keep CPLoperate steadily, on one hand, the structure of evaporator must be increased to make the conhnuous generated vaporflow out the wick easily, on the other hand, the return liquid ought to be subcooled enough to the reservoirtemperature set value.
文摘This paper presents our recent experimental investigation on the feasibility of monitoring the froth molding, a special case of solidification process, of polyurethane by using electrical capacitance tomography. The major challenge is the extremely low solid density of the solidified material during the process due to the very large expansion ratio. Suitable calibration method is sought and adequate image reconstruction algorithm is applied for such a task. Different expansion modes have been observed during experiment and corresponding images reconstructed. This visualization technique clearly revealed the expansion process by a time series of images of the solid density. The test results proved the capability of electrical capacitance tomography in monitoring the expansion of polyurethane. Future ways for improvement are also suggested.
文摘This paper presents the results of experiments and numerical simulation of the turbulent swirling flow and heat transfer in a duct.The calculated results are in good agreement with data obtained by measurements.It is found that the swirling flow promotes heat transfer to the wall of the duct;the swirl numbers are dependent upon the vane exit angles of the swirler,distance from the swirler and the duct Reynolds number.But the decay of swirling flow in streamwise direction is related to local Reynolds numbers and is independent of the swirler exit angle.The swirl flow characteristics presented in this paper may be used for engineering purposes.
文摘This paper presents an experimental study of the three-dimensional turbulent flow fields in a lowspeed annular cascade of high turning angle turbine blades. Detailed measurements were performed on the blade surfaces and mid-streamsurface in the passage and at three axial planes downstream of the cascade by using wall static pressure taps, a five-hole probe and a hot-wire anemometer. The test data include static pressure distribution on blade surfaces, total pressure loss coefficient, mean flow velocity components, radial flow angle, turbulence intensity and Reynolds shear stress. Analyses of the three-dimensional cascade flow characteristics were made on the onset location of high loss vortices, the variation of pressure gradient inside the cascade passage and the properties of endwall boundary layers,total pressure loss distributions, secondary vortex turbulent dissipation and wake decay downstream of the cascade. These experimental results are valuable for revealing the details of the complex vortex flow structure in modern highly loaded axial turbomachines and validating the three-dimensional flow numerical computation codes.
文摘Dual-phase lag (DPL) model is used to describe the non-Fourier heat conduction in a finite medium where the boundary at x=0 is heated by a rectangular pulsed energy source and the other boundary is tightly contactal with another medium and satisfies the continuous boundary condition. Numerical solution of thes kind of non-Fourier heat conduction is presented in this paper. The results are compared with those predicted by the hyperbolic heat conduction (HHC) equation.
文摘When condensation occurs in supersonic flow fields, the flow is affected by the latent heat released, and if the heat released exceeds a certain quantity, a condensation shock wave will occur There are many papers for the passive control of shock-boundary layer interaction using the porous wall with a plenum underneath on the application of the technique to transonic airfoil flows. In the present study, this passive technique is applied to the control of a steady condensation shock wave generated in a supersonic nozzle. In order to clarify the effect of the passive shockboundary layer control on condensation shock, Navier-Stokes equations were solved numerically using a 3rd-order MUSCL type TVD finite-difference scheme with a second-order fractional-step for time integration. As a result, the simulated flow fields were compared with experimental data in good agreement and the aspect of the flow field has been clarified.
文摘When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.
基金National NedScience FOundation of China, No: 59995550--4.
文摘In this paper, theoretical analysis on evaporating heat transfer in capillary with equilateral triangular cross section is presented and numerical calculations based on glass-water system are carried out. Considering evaporation mechanism in capillary with polygonal section, one-dimensional model is used to describe the three-dimensional case. The evaporating meniscus in the capillary along axis can be divided into six regions. The following conclusions are obtained: (1) The local heat transfer coefficients and heat fluxes in capillary increase quickly in the first and second regions, and slowly in the third region. The maximum value appears at interline between the third and fourth regions, then gradually decreases in the last three regions. (2) The average heat transfer coefficients decrease when the sizes of the capillary section increase, and become larger under higher wall temperature.
文摘Two-dimensional turbulent mixed convection-surface radiation interaction phenomenon in a back-wall-heated open square cavity is numerically investigated. The flow medium is air, and the turbulence model used is the Low-Reynolds-Number κ-ε Scheme. Calculations have been performed for Grashof numbers Gr up to 10^(10). And the Richardson number Ri covers a range of 4×10^(-3)-45. It is shown that within a rather extensive range of Ri, the effects of radiation on the heat transfer and fluid flow in the cavity are significant, should not be neglected and become stronger with the increase of Ri and Gr.
文摘The boiling behavior of the liquid nitrogen (LN2) under the transient high heat flux urgently needs to be researched systematically. In this paper, the high power short pulse duration laser was used to heat the saturated LN2 rapidly, and the high-speed photography aided by the spark light system was employed to take series of photos which displayed the process of LN2's boiling behavior under such conditions. Also, a special temperature measuring system was applied to record the temperature variation of the heating surface. The experiments indicated that an explosive boiling happened within LN2 by the laser heating, and a conventional boiling followed up after the newly-defined changeover time. By analyzing the temperature variation of the heating surface, it is found that the latent heat released by the crack of the bubbles in the bubble cluster induced by the explosive boiling is an important factor that greatly influences the boiling heat transfer mechanism.
文摘Experimental investigations of boiling heat transfer from porous suffaces at atmospheric pressure were performed. The porous surfaces are plain tubes covered with metal screens, V-shaped groove tubes covered with screens, plain tubes sintered with screens, and V-shaped groove tubes sintered with screens.The experimental results show that siatering metal screens around spiral V-shaped groove tubes can greatly improve the boiling heat transfer. The boiling hysteresis was observed in the experiment. This paper discusses the mechanism of the boiling heat transfer horn those kinds of porous surfaces stated above.
