Browsing by Author "Fu, WS"

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A concise method for determining a valve how coefficient of a valve under compressible gas flow
(1998-12-01)
Fu, WS
;
Ger, JS
;
機械工程學系
;
Department of Mechanical Engineering
This work presents a novel method of determining a valve flow coefficient for a valve and transient mass flow rate of compressible gas discharged from a reservoir. The proposed method consists of a set of equations to express the physical phenomena and measurement equipment to measure the indispensable data used in the above equations. Regardless of the kind of valve, the Valve flow coefficient can be obtained efficiently and feasibly. The results of this study indicate not only that the valve flow characteristics of the diaphragm valve significantly differ from those of the ball valve, but also that the C-v flow equation conventionally used is no longer valid for the diaphragm valve. The valve flow coefficient of the ball valve determined by the proposed method is about 48 and the representative one proposed by the ANSI/ISA is about 56. In addition, the mass flow rate of gas flow through a valve under transient process can be estimated without using a flow meter. Moreover, the cumulated masses discharged predicted by the method proposed herein are consistent well with those of the experimental results. The deviations are smaller than 6%. (C) 1999 Elsevier Science Inc. All rights reserved.
A concise method for determining a valve how coefficient of a valve under compressible gas flow
(1998-12-01)
Fu, WS
;
Ger, JS
;
機械工程學系
;
Department of Mechanical Engineering
This work presents a novel method of determining a valve flow coefficient for a valve and transient mass flow rate of compressible gas discharged from a reservoir. The proposed method consists of a set of equations to express the physical phenomena and measurement equipment to measure the indispensable data used in the above equations. Regardless of the kind of valve, the Valve flow coefficient can be obtained efficiently and feasibly. The results of this study indicate not only that the valve flow characteristics of the diaphragm valve significantly differ from those of the ball valve, but also that the C-v flow equation conventionally used is no longer valid for the diaphragm valve. The valve flow coefficient of the ball valve determined by the proposed method is about 48 and the representative one proposed by the ANSI/ISA is about 56. In addition, the mass flow rate of gas flow through a valve under transient process can be estimated without using a flow meter. Moreover, the cumulated masses discharged predicted by the method proposed herein are consistent well with those of the experimental results. The deviations are smaller than 6%. (C) 1999 Elsevier Science Inc. All rights reserved.
A new model for heat transfer of fins swinging back and forth in a flow
(2001-05-01)
Fu, WS
;
Yang, SJ
;
機械工程學系
;
Department of Mechanical Engineering
In this paper, a new concept of an electronic device cooling method is proposed. In this method, extremely thin fins are used for swinging back and forth in a flowing fluid. The boundary layers attaching on the fins are then contracted and disturbed, and the heat transfer rate of the fins can be enhanced remarkably. The dynamic behavior between the fins and fluid is classified into a class of the moving boundary problems. A Galerkin finite element formulation with an arbitrary Lagrangian-Eulerian kinematic description method is adopted to solve this problem. The parameters of velocities of the fluid and the swinging speed of the fins are employed to investigate the variations of the flow and thermal fields. The results show that the velocity and thermal boundary layers may be contracted and disturbed, which results in a significant heat transfer enhancement, being attained. (C) 2001 Elsevier Science Ltd. All rights reserved.
A numerical investigation of effects of a moving operator on airflow patterns in a cleanroom
(2002-07-01)
Yang, SJ
;
Fu, WS
;
機械工程學系
;
Department of Mechanical Engineering
The variations of the airflow induced by a moving operator in a cleanroom installed with a curtain were studied numerically. This situation is cataloged to a class of the moving boundary problems. An arbitrary Lagrangian-Eulerian kinematic description method is utilized to describe the flow field and a penalty finite element formulation with moving meshes is adopted to solve this problem. The effects of the moving operator and curtain on the airflow patterns under different distances from the workbench to the curtain with the moving speed of the operator equal to 2.0 and Reynolds number Re = 500 are taken into account. The results show that recirculation zones are formed around the operator and workbench due to the movement of the operator. The recirculation zones are not favorable to the cleanroom because they may induce a local turbulent flow and entrain and trap contaminants. These phenomena are remarkably different from those of the moving operator assumed as stationary in the cleanroom. Based on the length of the curtain, it is useful for protecting the operator from the hazardous gases. (C) 2002 Elsevier Science Ltd. All rights reserved.
A numerical study of effects of the swinging amplitude of fins on heat transfer characteristics in a flow
(2001-11-01)
Fu, WS
;
Yang, SJ
;
機械工程學系
;
Department of Mechanical Engineering
A new method for enhancing heat transfer of a finned heat sink is proposed in this study. In this method, extremely thin fins are installed in the finned heat sink, and these fins may swing back and forth in a flow because of the fluid flowing pass them. As a result, the velocity and thermal boundary layers attached on the fins are then contracted and disturbed, and the heat transfer rate of the fins can be enhanced. The variations between the fluid and fins are dynamic and belong to a kind of the moving boundary problems. The arbitrary Lagrangian-Eulerian (ALE) kinematic description method is available and adopted to describe the flow and thermal fields, and the governing equations are solved using the Galerkin finite element method with moving meshes. The effects of variations in the Reynolds number, swinging speed and amplitude of the fins on the heat transfer of the fins are investigated. The results show that the velocity and thermal boundary layers may be contracted and disturbed as the fins swing with a large speed, and the heat transfer rates are remarkably affected by the swinging speed and amplitude of the fins.
A numerical study of heat transfer of a porous block with the random porosity model in a channel flow
(2002-08-01)
Fu, WS
;
Chen, SF
;
機械工程學系
;
Department of Mechanical Engineering
In this paper, heat transfer of a hot plate with a porous block in a channel flow is numerically investigated. A porous block is simulated as a fin type heat sink. The random/artificial porosity models are used to generate the distribution of porosity. In fact, the distribution of porosity in porous medium is irregular, thus the random porosity model is more realistic than the constant or variable porosity model to describe the phenomena happening in porous medium. Therefore, the distribution of porosity of porous block obeys the random porosity model, and the factors of mean porosity and standard deviation are taken into consideration. The variations of the porosity and the velocity in porous block are no longer smooth. For obtaining more heat transfer rate, the artificial porosity model is proposed. The heat transfer rates of the several cases derived by the artificial porosity model are better than those of the random porosity model. The thermal performance of porous block is larger than that of solid block as the mean porosity is larger than 0.5.
A numerical study of the effects of a moving operator on particles in a cleanroom with a curtain
(2002-02-01)
Fu, WS
;
Chen, SF
;
Yang, SJ
;
機械工程學系
;
Department of Mechanical Engineering
The motion of airflow and particles induced by a moving operator in a cleanroom installed with a solid worktable and a vertical isolating curtain were studied numerically. This situation is classified as a kind of moving boundary problem, and a Galerkin finite element formulation with an arbitrary Lagrangian-Eulerian kinematic description method is adopted to analyze this problem. Two different moving speeds of the operator under Reynolds number Re = 500 and Schmidt number Sc = 1.0 are taken into consideration. The results show that recirculation zones, which are disadvantageous to remove the particles, are observed around the operator and near the worktable. The behavior of the operator usually prevents the particles from being removed, and the higher moving speed of the operator demonstrates that the removal of particles becomes more difficult. These phenomena are quite different from those that regard the moving operator as stationary in the cleanroom.
A two-reservoir model to simulate the air discharged from a pulse-jet cleaning system
(1999-08-01)
Fu, WS
;
Ger, JS
;
機械工程學系
;
Department of Mechanical Engineering
This work presents a novel two-reservoir model to simulate, for a pulse-jet cleaning system, the air discharged from an air reservoir via a diaphragm valve to a blowpipe and ultimately into the atmosphere. The air reservoir and blowpipe are referred to reservoir 1 and reservoir 2, respectively. The proposed model consists of (1) a set of governing equations that are solved by a finite difference and (2) an iterative calculation method to describe the physical phenomena. The feasibility of the proposed model is also evaluated via experiments performed herein. Comparing the mass flow rates predicted by the proposed model with those of the benchmark solutions reveals that the model predictions are about 10% overestimated. In addition, the proposed model is more accurately simulated by considering the friction effects induced by the exit of the air reservoir and the nozzles on the blowpipe. The former increases the Mach number of the air and equals that of a frictional pipe of 4fLe/D-h. The latter decreases the mass flow rate discharged from the nozzles. A discharge coefficient Cd-n is introduced to represent the ratio of the mass flow rate discharged from a real nozzle and an ideal one. Moreover, experimental methods are developed to determine the values of 4fLe/D-h and Cd-n. When the parameters of 4fLe/D-h and Cd-n were included in the model, the accuracy of the model predictions was significantly improved. The deviations between the mass flow rates of the model predictions and the bench mark solutions were markedly reduced to 3%.
An investigation of a block moving back and forth on a heat plate under a slot jet
(2001-07-01)
Fu, WS
;
Wang, KN
;
Ke, WW
;
機械工程學系
;
Department of Mechanical Engineering
An investigation of heat transfer rate of a heat plate under a slot jet was studied numerically. For enhancing the heat transfer rate of the heat plate, a block moves back and forth on the heat plate. Then the thermal boundary layer on the heat plate is destroyed by the moving block and a new thermal boundary layer reforms immediately as the block passes through. Consequently, the remarkable heat transfer enhancement of the heat plate is attained. This subject belongs to a kind of moving boundary problems, the modified arbitrary Lagrangian Eulerian (ALE) method is suitable for solving this subject. The results show that the maximum increment of heat transfer rate is about 200% in the largest velocity case. (C) 2001 Elsevier Science Ltd. All rights reserved.
An investigation of a block moving back and forth on a heat plate under a slot jet. Part II (the effects of block moving distance and vacant distance)
(2001-12-01)
Fu, WS
;
Wang, KN
;
機械工程學系
;
Department of Mechanical Engineering
A continuous investigation of a block moving back and forth on a heat plate under a slot jet was studied numerically. This study investigates the effects of block moving distance and vacant distance between the block and heat plate on the heat transfer of heat plate. This subject belongs to a kind of moving boundary problems, and the modified Arbitrary Lagrangian Eulerian (ALE) method is suitable for solving this subject. The results show that the increment of the heat transfer rate of heat plate is not direct proportion to the block moving distance, and the smaller vacant distance is expected for obtaining the larger heat transfer rate of heat plate. (C) 2001 Elsevier Science Ltd. All rights reserved.
Appropriate sizes of porous and solid blocks for heat transfer under an impinging jet
(1997-03-01)
Fu, WS
;
Huang, HC
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
A study of appropriate sizes of both porous and solid blocks mounted on a heated region impinged by a laminar slot jet was investigated numerically. A numerical method of SIMPLEC is adopted to solve governing equations, and a one-equation thermal model with Van Driest's wall function is considered for solving the energy equation of the porous block. The results indicated that enhancement of heat transfer is obtained for both shorter porous and solid block cases and decreasement of heat transfer occurs for longer block cases. Compared with the without block case, there exists an appropriate length of the porous block to gain the maximum thermal enhancement efficiency. As for the solid block case, as the length becomes shorter, the thermal enhancement efficiency becomes better.
Effect of moving distance of a moving block on heat transfer in a channel flow
(2001-04-01)
Fu, WS
;
Chen, SF
;
Wang, KN
;
機械工程學系
;
Department of Mechanical Engineering
A numerical investigation of heat transfer rate of an insulated block moving on a heated surface in a channel was studied. The study mainly investigated the effect of block moving distance on the heat transfer rate of heated surface. This subject belongs to a kind of moving boundary problems, and the modified Arbitrary Lagrangian Eulerian method is suitable for solving this subject. The results show that the block moving distance affects the flow and thermal fields remarkably. The heat transfer rate of heated surface increases proportionally to the increment of the block moving distance, when the block moving distance is larger than a critical value. (C) 2001 Elsevier Science Ltd.
Effects of a random porosity model on double diffusive natural convection in a porous medium enclosure
(2000-01-01)
Fu, WS
;
Ke, WW
;
機械工程學系
;
Department of Mechanical Engineering
A double diffusive natural convection in a rectangular enclosure filled with porous medium is investigated numerically. The distribution of porosity is based upon the random porosity model The Darcy-Brinkman-Forchheimer model is used and the factors of heat flux, mean porosity and standard deviation are taken into consideration. The SIMPLEC method with iterative processes is adopted to solve the governing equations. The effects of the random porosity model on the distributions of local Nusselt number are remarkable and the variations of the local Nusselt number become disordered. The contribution of latent heat transfer to the total heat transfer of the high Rayleigh number is larger than that of the low Rayleigh number and the variations of the latent heat transfer are not in order. (C) 2000 Elsevier Science Ltd.
Effects of a random porosity model on heat transfer performance of porous media
(1999-01-01)
Fu, WS
;
Huang, HC
;
機械工程學系
;
Department of Mechanical Engineering
Due to the non-uniform distribution and fractural structure of the beads inside a porous medium, the porosity distributed in the porous medium is random for most realistic situations. Therefore, the effects of the porosity distributed casually inside a porous block mounted on a heated region with a laminar slot impinging jet on flow and thermal fields are investigated numerically. A numerical method of SIMPLEC is adopted to solve governing equations, as for the energy equation, a one-equation thermal model with Van Driest's wall function is adopted. AU the non-Darcian effects including the solid boundary and inertial effects are considered and three different porosity models of constant, variable and random are examined. The results indicate that the relationship between the local Nusselt number Nu(x) and the near wall local porosity epsilon(x) is a negative correlation. Consequently, in order to enhance the thermal performance of the porous medium, the porosity near the solid plate should be smaller to make the conductive heat transfer to be dominant. (C) 1998 Elsevier Science Ltd. All rights reserved.
Effects of a vibrational heat surface on natural convection in a vertical channel flow
(2006-04-01)
Fu, WS
;
Huang, CP
;
機械工程學系
;
Department of Mechanical Engineering
A numerical simulation is performed to study effects of a vibrational heat surface on natural convection in a vertical channel flow. This subject is a kind of moving boundary problems, and the finite element method and arbitrary Lagrangian-Eulerian kinematics description method is then utilized. The main parameters of Rayleigh number, amplitude and frequency are taken into consideration, and the mechanisms are examined in detail. The results show that for the same Rayleigh number, natural convection of a vibration heat plate with a certain combination of frequency and amplitude is possibly smaller than that of a stationary state. According to the results, the critical frequency could be derived and expressed in terms of Rayleigh number and amplitude. (c) 2005 Elsevier Ltd. All rights reserved.
Effects of eccentricity of cylinder and blockage ratio on heat transfer by an oscillating cylinder in a channel flow
(2003-04-01)
Fu, WS
;
Tong, BH
;
機械工程學系
;
Department of Mechanical Engineering
A numerical simulation is performed to study the influence on heat transfer rate of heated walls in a channel with an oscillating cylinder. An arbitrary Lagrangian-Eulerian kinematic description method is adopted to describe the flow and thermal fields. A penalty consistent finite element formulation is applied to solve the governing equations. The effects of the eccentricity of cylinder ratio and blockage on the heat transfer characteristics of the heated wall are examined. The results show that the position and the diameter of the cylinder in the cylinder have great effects on the flow and thermal fields in the channel flow. (C) 2003 Elsevier Science Ltd.
Evaporation of water film in an enclosure filled with a porous medium
(1999-05-01)
Fu, WS
;
Ke, WW
;
機械工程學系
;
Department of Mechanical Engineering
A double diffusive natural convection in an enclosure filled with a porous medium is investigated numerically. To enhance the heat transfer rate of a heat wall, the heat wall is wetted with a thin water film, then sensible and latent heat transfer occur simultaneously. The Darcy-Brinkman-Forchheimer model is used and the factors of heat flux, porosity and diameter of bead are taken into consideration. The SIMPLEC method with iterative processes is adopted to solve the governing equations. The results show that the effect of evaporation on the heat transfer rate is apparent, and the latent heat transfer plays an important role in the high Darcy-Rayleigh number situations. The averaged Nusselt number <(Nu)over bar> is approximately 2.5 when Ra*<4. In the range of 4
Heat transfer induced by a body moving in opposition to a flowing fluid
(2001-01-01)
Fu, WS
;
Yang, SJ
;
機械工程學系
;
Department of Mechanical Engineering
The heat transfer problem of a body moving in opposition to a flowing fluid in a channel is investigated numerically. This problem belongs to a class of the moving boundary problems and an arbitrary Lagrangian-Eulerian method with a Galerkin finite element method is adopted to analyze this problem. Several different moving Velocities of the body and Reynolds numbers are taken into consideration. The results show that the fluid simultaneously replenishes the vacant space induced by the movement of the body and new recirculation zones are formed around the body. These phenomena are quite different from those of the body fixed in the flowing fluid. Heat transfer rates of the body are enhanced remarkably as the body moving in opposition to the flowing fluid. In the computing range, the mean global Nusselt number Nu can be estimated by an equation of 0.664(Re V-b)(1/2) - 1.34. (C) 2000 Elsevier Science Ltd. All rights reserved.
Heat transfer of porous medium with random porosity model in a laminar channel flow
(2001-07-01)
Fu, WS
;
Wang, KN
;
Ke, WW
;
機械工程學系
;
Department of Mechanical Engineering
In this paper, force convection heat transfer of a porous medium in a laminar channel flow is numerically investigated. The porous medium with random porosities is used to enhance heat transfer and the random porosities are derived by the Kinderman-Ramage procedure. The results show that when the mean porosity is larger than 0.5, the average Nusselt numbers are enhanced and better than the solid block case. Therefore, a porous medium with larger porosity and the proper bead diameter could provide more heat dissipation. For the random porosity distribution, the profiles of velocities are disordered and the channeling effect is not apparent near the plate region.
Laminar forced convection in a channel with a moving block
(2001-07-01)
Fu, WS
;
Ke, WW
;
Wang, KN
;
機械工程學系
;
Department of Mechanical Engineering
Heat transfer rate in a channel with an insulated moving block on a heated surface was studied numerically. For enhancing the heat transfer rate of the heated surface, the block moves back and forth on the heated surface. Then the thermal boundary layer attached to the heated surface is destroyed by the moving block and a new thermal boundary layer reforms immediately as the block passes through. Consequently, a remarkable heat transfer enhancement of the heated surface is attained. This subject belongs to a kind of moving boundary problems, and the modified Arbitrary Lagrangian Eulerian method is suitable for solving this subject. The results show that the maximum increment of heat transfer rate is about 98% in the study. (C) 2001 Elsevier Science Ltd. All rights reserved.