Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
18
5
2011
NUMERICAL SIMULATION ON TURBULENT FLUID FLOW AND HEAT TRANSFER ENHANCEMENT OF A TUBE BANK FIN HEAT EXCHANGER WITH MOUNTED VORTEX GENERATORS ON THE FINS
361-374
Wan-Ling
Hu
School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou, 730070, China; Key Laboratory of Railway Vehicle Thermal Engineering (Lanzhou Jiaotong University), Ministry of Education of China, Lanzhou, 730070, China
Yong-Heng
Zhang
Key Laboratory of Railway Vehicle Thermal Engineering (Lanzhou Jiaotong University) Ministry of Education, Lanzhou, 730070 P. R. China;Department of Mechanical Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070 P. R. China
Liang-Bi
Wang
School of Mechanical Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, PR China; Key Laboratory of Railway Vehicle Thermal Engineering of MOE, Lanzhou Jiaotong University, Lanzhou,
Gansu 730070, PR China
Three-dimensional turbulent flow and heat transfer enhancement in the channel formed by staggered tube bank fin heat exchangers with vortex generators (VGs) were studied using a numerical method. Numerical calculations were performed in the range of Reynolds number from 3000 to 20,000. The average Nusselt number and the corresponding friction factor obtained from the numerical study were compared with those obtained from naphthalene sublimation heat/mass analogy experiments in order to validate the numerical method. It was found that the average Nusselt number for the four-row tube bank fin channel mounted with VGs increased by 30.9−47.7% over its counterpart without VGs, and the corresponding friction factor increased by 56.0−66.3%. The local Nusselt number distribution reveals that when VGs are mounted on one fin surface, they can efficiently enhance the heat transfer in the region behind the tube on both fin surfaces. The average Nusselt number increases with increasing the angle of attack θ. However, if the angle of attack is too large, the vortex may break down and decrease heat transfer enhancement. The optimum attack angle for heat transfer augmentation is about θ = 45 deg. Both the average Nu and friction factor decrease with an increase in the tube row numbers. When the Reynolds number is less than 9000, two tube rows are recommended, and when the Re is higher than 9000, the number of tube rows has a small effect on heat transfer performance.
A STUDY OF SPRAY-IMPINGEMENT COOLING ON SMOOTH AND PIN-FINNED SURFACES USING FC-72
375-387
Liang-Han
Chien
National Taipei University of Technology
Tung-Lu
Wu
Department of Energy and Refrigerating Air-Conditioning Engineering, National Taipei University of Technology, 1, Section 3, Chung-Hsiao E. Rd., Taipei 106, Taiwan
Shu-Che
Lee
Department of Energy and Refrigerating Air-Conditioning Engineering, National Taipei University of Technology, 1, Section 3, Chung-Hsiao E. Rd., Taipei 106, Taiwan
This manuscript presents the experimental results of the cooling performance of a pin-finned surface and a smooth surface in a spray-cooling device. Five orifices of either 0.23 or 0.56 mm diameter were made on the spraying device. dielectric fluid, FC-72, was used as the working fluid and the test section was maintained at 50° C saturation temperature. The total flow rate varied between 24.5 and 99.1 ml/min, and the heat flux varied from 60 to 800 kW/m2. The results showed that the larger orifices (0.56 mm) provided a thicker liquid layer on the surface, and resulted in a greater critical heat flux and higher performance at high heat fluxes than the smaller orifices (0.23 mm). The smaller orifices (0.23 mm diameter) of the liquid distributor created stronger impingement on the test surface, and yielded better heat transfer performance at low heat fluxes. Spray-impingement cooling yielded up to 50% greater heat transfer coefficients than pool boiling at low heat fluxes for both surfaces. The pin-finned surface yielded ∼10%−40% enhancement as compared with the smooth surface for heat flux > 200 kW/m2. A correlation of spray-impingement cooling heat transfer coefficient of the fully wetted smooth surface is proposed. The prediction of this correlation agrees with the experimental data within ±25%.
LOCAL HEAT TRANSFER OF JET IMPINGEMENT COOLING WITH FILM EXTRACTION FLOW IN A ROTATING CAVITY
389-401
Kai
Wang
Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200025, China
Guoqiang
Xu
National Key Laboratory of Science and Technology on Aero-Engines, School of Jet Propulsion, Beihang University, Beijing, 100191, China; School of Energy Science and Engineering, Harbin institute of Technology, Harbin, 150001, China
Zhi
Tao
National Key Laboratory of Science and Technology on Aero-Engine Aero-thermodynamics
The Collaborative Innovation Center for Advanced Aero-Engine of China
Beihang University
Beijing 100191, China
Jining
Sun
National Key Laboratory of Science and Technology on Aero-Engines, School of Jet Propulsion, Beihang University, Beijing, 100191, China
Hongwu
Deng
National Key Laboratory of Science and Technology on Aero-Engines, School of Jet Propulsion, Beihang University, Beijing, 100191, China
An experimental investigation was carried out to examine the heat transfer characteristics on impingement cooling with extraction flow in a rotating cavity. Two H/d configurations of 3.0 and 6.0 were conducted. The Reynolds number based on the inlet velocity of the jet air and the diameter of the impingement hole was fixed at 2000. The test model rotated at five different speeds, 0, 200, 400, 600, and 800 rpm, in two reversal directions, respectively. The local heat transfer coefficient on the target surface was measured by a transient method with thermochromic liquid crystal. Experimental result reveals that the jet flow could be bent by the Coriolis force and consequently the heat transfer would be weakened by rotation. The heat transfer coefficient of H/d = 3 configuration is higher than that of H/d = 6 configuration for either stationary or rotational conditions. For the structure of H/d = 6.0, the stagnation point has an offset of 1.5d due to the bending of the jet flow. Compared to the stationary results, the maximum of the local heat transfer coefficient is reduced by 38.3% and the averaged heat transfer coefficient is reduced by 44.5% at 800 rpm. For the structure of H/d = 3.0, the offset of the stagnation point is small, but the spreading rate of the jet core is enhanced by rotation. Although not as strongly as the structure of H/d = 6.0, the heat transfer is still weakened by rotation. The maximum of local heat transfer coefficient is decreased 29.2% and average heat transfer coefficient is decreased 27.8% at 800 rpm compared to those at 0 rpm.
EFFECTS OF OUT OF PHASE AND INCLINATION ANGLES ON NATURAL CONVECTION HEAT TRANSFER FLOW OF AIR INSIDE A SINUSOIDAL CORRUGATED ENCLOSURE WITH SPATIALLY VARIABLE WALL TEMPERATURE
403-417
Salam Hadi
Hussain
Mechanical Engineering Department, College of Engineering, Babylon University
Rehab Noor
Mohammed
Mechanical Engineering Department, College of Engineering, Babylon University
In this paper, the effects of the variation of the out of phase and the inclination angles on natural convection heat transfer of air in a sinusoidal corrugated enclosure are investigated numerically. The present study is based on a configuration where the two vertical sinusoidal walls and the horizontal bottom wall are maintained at constant low temperature, whereas the flat upper wall temperature distribution of the enclosure is assumed to vary with a sinusoidal function. The governing equations of continuity, momentum, and energy are solved computationally using finite-volume techniques. The solution procedure is based on the SIMPLE algorithm and a nonorthogonal, nonuniform collocated grid system. The effects of various orientations on the heat transport process inside the sinusoidal corrugated enclosure are studied in detail. The computational results are presented in terms of isothermal lines and streamlines for different governing parameters. The values of the governing parameters are the inclination angle of the enclosure γ (0°−90° ), out of phase angle Ø (0°−180°), Rayleigh number (103−106), and Prandtl number (0.71). The main results of this investigation illustrate that the effect of γ on the streamlines and the isothermal lines is very important for all values of Ra and Nu. The centers of vortices will move upward into the upper surface with increasing Ra. The local Nusselt number along the cold left wavy sidewall is increased with increasing Rayleigh numbers at γ = 0°. For γ > 0° ,the average Nusselt number is decreased with increasing Ra along the left wavy sidewall, while the average Nusselt number is increased with increase of Ra along the right wavy sidewall. At γ = 0°, two vortices appear that control the flow inside the enclosure for all values of Ra, Nu, and the out of phase angle, while at γ = 90°, one vortex appears that controls the flow inside the enclosure for all values of Ra, Nu, and the out of phase angle.
FILM COOLING PERFORMANCE IN A LOW-SPEED 1.5-STAGE TURBINE: EFFECTS OF BLOWING RATIO AND ROTATION
419-432
Zhi
Tao
National Key Laboratory of Science and Technology on Aero-Engine Aero-thermodynamics
The Collaborative Innovation Center for Advanced Aero-Engine of China
Beihang University
Beijing 100191, China
Guoqing
Li
Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing, 100190, China; University of Chinese Academy of Sciences, Beijing, 100190, China
Hongwu
Deng
National Key Laboratory of Science and Technology on Aero-Engines, School of Jet Propulsion, Beihang University, Beijing, 100191, China
Jun
Xiao
National Key Laboratory of Science and Technology on Aero-Engines, Beijing University of Aeronautics and Astronautics, Beijing, 100191, China
Guoqiang
Xu
National Key Laboratory of Science and Technology on Aero-Engines, School of Jet Propulsion, Beihang University, Beijing, 100191, China; School of Energy Science and Engineering, Harbin institute of Technology, Harbin, 150001, China
Xiang
Luo
National Key Laboratory of Science and Technology on Aero-Engines, Beijing University of Aeronautics and Astronautics, Beijing, 100191, China
This paper presents experimental investigations on film cooling performance under rotation in a low-speed 1.5-stage turbine using the thermochromic liquid crystal (TLC) technique. The experiment was accomplished in a test facility which was recently established to study rotating film cooling performance in realistic turbine stages. Eighteen blades of chord length of0.1243 m and height of 0.099 m were installed in the rotor. A film hole with diameter of 0.004 m, angled 28° and 36° tangentially to the pressure surface and suction surface in streamwise, respectively, was set in the middle span of the rotor blade. All measurements were made at three different rotating speeds of 600, 667, and 702 rpm with the blowing ratios varying from 0.3 to 3.0. The Reynolds number based on the mainstream velocity of the turbine outlet and the chord length of the rotor blade was fixed at 1.89 × 105. Results show that on the pressure side, the film coverage and cooling effectiveness scaled up with the blowing ratio and the film deflected centrifugally; on the suction side, the maximum film coverage and cooling effectiveness were obtained at moderate blowing ratio and a centripetal deflection of the film was observed. The film deflection could be amplified by either decreasing the blowing ratio or increasing the rotation number on both sides. Overall, blowing ratio and rotation play significant roles in the film cooling performance.
MIXED CONVECTION HEAT TRANSFER FLOW OF AIR INSIDE A SINUSOIDAL CORRUGATED CAVITY WITH A HEAT-CONDUCTING HORIZONTAL CIRCULAR CYLINDER
433-447
Salam Hadi
Hussain
Mechanical Engineering Department, College of Engineering, Babylon University
Qusay Rashid
Abd-Amer
Mechanical Engineering Department, College of Engineering, Babylon University
Two dimensional, steady-state, and laminar mixed convection in a vented sinusoidal corrugated cavity with a heat conducting horizontal circular cylinder filled with air is studied numerically for the case when the horizontal walls and the left sidewall of the cavity are kept adiabatic, while the right vertical sinusoidal corrugated wall is heated at a constant hot temperature. A finite volume method with the structured nonuniformly collocated grid system is used to solve the governing equations. The following governing parameters are investigated: the effects of different values of Richardson number and Reynolds number in the ranges 0−10 and 50−200, respectively; thermal conductivity ratio changes from 0.2 to 10; and the diameter of inner solid cylinder (0 ≤ D ≤ 0.6) and its location (0.25 ≤ LX ≤ 0.75, 0.25 ≤ LY ≤ 0.75) on flow and thermal fields. The computational results indicate that the average Nusselt numbers at the heated wall are strongly affected by the Reynolds and Richardson numbers, and the diameter of the inserted cylinder. In addition, the variation of the thermal conductivity ratio becomes insignificant for the flow and thermal fields.
EXPERIMENTAL AND NUMERICAL STUDIES ON SHELL-SIDE PERFORMANCE OF THREE DIFFERENT SHELL-AND-TUBE HEAT EXCHANGERS WITH HELICAL BAFFLES
449-463
Gui-Dong
Chen
MOE Key Laboratory of Thermo-Fluid Science and Engineering, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, 710049, China
Min
Zeng
Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, 710049, China
Qiu-Wang
Wang
Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, P.R. China
Shell-and-tube heat exchangers (STHXs) have been widely used in many industrial processes. In the present paper, shell-side flow and heat transfer characteristics of shell-and-tube heat exchanger with continuous helical baffles (CH-STHX) is experimentally studied. Correlations for heat transfer and pressure drop, which are estimated by the Nusselt number and the friction factor, are fitted by experimental data for thermal design. The computational fluid dynamic (CFD) method is also used to compare the shell-side heat transfer and flow performance of the CH-STHX, STHX with combined helical baffles (CMH-STHX), and STHX with discontinuous helical baffles (DCH-STHX). The numerical results show that, for the same Reynolds number, the shell-side Nusselt numbers of the CMH-STHX and CH-STHX are ∼37.6% and ∼78.2% higher than that of the DCH-STHX, and shell-side friction factors of the CMH-STHX and CH-STHX are ∼104.1% and ∼177.0% higher than that of the DCH-STHX. Reasonable maximal velocity ratio design can make the CMH-STHX and DCH-STHX have higher heat transfer coefficients than the CH-STHX for the same mass flow rate in the shell side.