Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
11
1
2004
Professor Paul J. MartoOn the Occasion of His 65th Birthday
vi-vii
10.1615/JEnhHeatTransf.v11.i1.01
Raj M.
Manglik
Thermal-Fluids and Thermal Processing Laboratory, Mechanical and Materials Engineering, University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45220, USA
Ralph L.
Webb
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802, USA
Increase in Mass Transfer by the Onset of Taylor-Couette-Wise Vortices
1-12
10.1615/JEnhHeatTransf.v11.i1.10
Laurent
Gbahoue
Laboratoire d’Etudes Thermiques UMR CNRS 6608, ESIP, 40, avenue du Recteur Pineau, 86022 Poitiers cedex, France
An experimental study on the enhancement of transfer phenomena is conducted in a thin fluid film in order to better understand the influence of the turbulence of the mean flow on the local wall transfer. Primarily, the influence of the coherent structures is investigated. Another purpose lies in what could be the convenient condition of being aware of the transfer improvement. The thin fluid film gap is commonly encountered in rotor-stator rotating engines in turbo machinery or in journal bearings in tribology [Frene, 1973]. The experiments are conducted in a simple physical model made of two coaxial cylinders with the inner one rotating. Indeed, this well-known Couette-Taylor-like apparatus [Taylor, 1923] easily provides the film flow with vortices with very accurate conditions. The Sherwood number is shown to increase as a third power of the Taylor number in the fully azimuthal laminar flow regime Sh ~ Ta1/3. The onset of the Taylor vortices from the transition regime clearly corresponds to an increase in the slope of the previous relation.
Turbulent Heat Transfer Enhancement of Microencapsulated Phase Change Material Slurries with Constant Wall Heat Flux
13-22
10.1615/JEnhHeatTransf.v11.i1.20
Wang
Xin
Department of Building Science, Tsinghua University, Beijing, 100084, P.R.China
Zhang
Yinping
Department of Building Science, Tsinghua University, Beijing, 100084, P.R.China
Hu
Xianxu
Department of Building Science, Tsinghua University, Beijing, 100084, P.R.China
This article presents a novel insight as to the turbulent heat transfer enhancement of microencapsulated phase change material slurries flowing through a circular tube with constant wall heat flux. A turbulent heat transfer model, based on the effective specific heat model, for microencapsulated phase change slurries is presented. Its numerical calculation results agree well with the previously published experimental data. For microencapsulated phase change slurries through a circular tube with constant wall heat flux, the main factors influencing turbulent heat transfer enhancement, Ste, Reb, Mr, ML, and the types of cp curves, are clarified and analyzed in detail.
Enhancement of Pool Boiling on Structured Surfaces Using HFC-4310 and Water
23-42
10.1615/JEnhHeatTransf.v11.i1.30
Liang-Han
Chien
National Taipei University of Technology
C. C.
Chang
Department of Thin Film Engineering, AU Optronic Corp., Lung-Tang, Taiwan
This experimental study investigated the effects of geometric parameters of boiling on structured surfaces. The structured surfaces were created by bending fins having triangular cuts of specific size and pitch. The tunnels between the fins were made by electrical discharge machining. The surface geometric parameters include the pore geometry (pore angle = 30 or 60° and pore length = 0.3 or 0.5 mm), pore pitch (0.6 or 1.0 mm), and tunnel height (0.7 or 1.0 mm). Water or HFC-4310 was used as the working fluid, and the tests were performed at a 60 or 70 °C saturation temperature. The heat flux varied between 30 and 550 kW/m2. For boiling in water, the larger pore pitch (1.0 mm) yields better performance than a 0.6 mm pitch for the same type of pores, and a smaller fin height (0.7 mm) is preferred to the 1.0 mm fin height. However, these parameters have no significant influence for boiling in HFC-4310, whose latent heat and surface tension are much smaller than water. The best structured surface yields about sixfold boiling heat transfer enhancement over the plain surface in water and fivefold in HFC-4310. This enhanced boiling surface yields 0.03 K/W evaporation resistance at 91W heat input for water on a 16 mm diameter circular heating area.
Heat Transfer and Fluid Flow in Rectangular Fin and Elliptic Tube Heat Exchangers under Dry and Dehumidifying Conditions
43-60
10.1615/JEnhHeatTransf.v11.i1.40
Shin-Li
Chen
Department of Mechanical Engineering, National Cheng-Kung University, Tainan, Taiwan 70101
Jiin-Yuh
Jang
Department of Mechanical Engineering, National Cheng-Kung University, Tainan, Taiwan
Experimental and numerical analyses were carried out to study the thermal-hydraulic and mass transfer characteristics of four-row rectangular fin and elliptic tube heat exchangers having a major/minor axis ratio of 2.83. Four types of rectangular finned configurations have been investigated for various inlet frontal velocities ranging from 1 to 6 m/s under dry and dehumidifying conditions: two staggered tube arrangements with fin heights of 7 mm and 10 mm, respectively; and two in-lined tube arrangements with fin heights of 7 mm and 10 mm, respectively. The results indicated that the sensible Colburn factor js and the friction factor f for the wet coils are, respectively, 56-71% and 2-16% higher than those for dry coils. In addition, a two-dimensional fin efficiency analysis for rectangular fins with elliptic tubes was presented for a wide range of air relative humidities and Biot numbers. It is shown that the fully wet fin effciency is lower than that of the dry fin by 20% and 31% with respect to fin heights of 7 and 10 mm.
Numerical Analyses of Effects of Tube Shape on Performance of a Finned Tube Heat Exchanger
61-74
10.1615/JEnhHeatTransf.v11.i1.50
Jingchun
Min
Department of Engineering Mechanics, Tsinghua University, Beijing, 100084,
China
Ralph L.
Webb
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802, USA
This article discusses the effects of tube geometry on the performance of a multi-row finned tube heat exchanger having herringbone wavy fins. The air-side heat transfer and pressure drop characteristics of the heat exchanger were predicted numerically and the tube-side heat transfer coefficient and pressure drop were calculated using commonly adopted equations for turbulent flow in a smooth tube. The numerical calculations were performed in three dimensions for three frontal air velocities of 1.0, 2.0, and 3.0 m/s, yielding hydraulic diameter Reynolds numbers from 297 to 999. Investigated were five tube geometries, including a round tube, three elliptical oval tubes, and a flat oval tube. The round tube has a 15.875 mm (5/8") outside diameter and serves as the baseline tube. The four oval tubes were made by reforming the baseline round tube and have the same perimeter as that of the round tube. The aspect ratios of the three elliptical tubes are 2.00, 3.00, and 4.29, respectively, and the aspect ratio of the flat oval tube is 3.00. As the tube aspect ratio is increased, the air-side heat transfer coefficient and pressure drop decrease, but the water-side heat transfer coefficient and pressure drop increase. At 2.0 m/s frontal velocity, the 3.00 aspect ratio elliptical tube yields a 6.9% lower air-side heat transfer coefficient and a 45.9% lower air pressure drop than the round tube. As compared to the 3.00 aspect ratio elliptical tube, the same aspect ratio flat tube has a 0.6% higher air-side heat transfer coefficient and a 2.5% higher air pressure drop.
Mechanistic Modeling of Steam Condensation onto Finned Tube Heat Exchangers in Presence of Noncondensable Gases and Aerosols, under Cross-Flow Conditions: Aerosol Fouling and Noncondensable Gases Effects on Heat Transfer
75-86
10.1615/JEnhHeatTransf.v11.i1.60
J. L.
Munoz-Cobo
Polytechnic University of Valencia, Department of Chemical and Nuclear Engineering, Camino de Vera 14, 46022 Valencia, Spain
A.
Escriva
Polytechnic University of Valencia, Department of Chemical and Nuclear Engineering, Camino de Vera 14, 46022 Valencia, Spain
Luis E.
Herranz
CIEMAT, Department of Nuclear Fission, Avenida Complutense 22, 28040 Madrid, Spain
In this article, a mechanistic model to predict the steam condensation on containment finned tube heat exchangers in the presence of noncondensable gases (NC) and aerosols is presented. The total thermal resistance from the bulk gas to the coolant is formulated as a parallel combination of the convective and condensation gas resistances coupled in series to those of the condensate layer, the aerosol fouling layer, the wall, and the coolant. The condensate layer thermal resistance is calculated by means of an Adamek-based model. The fouling layer resistance is estimated from the thickness of the particle deposit; removal mechanisms such as diffusiophoresis, settling, and impaction are taken into account. Finally, the gas mixture thermal resistance is formulated based on diffusion layer modeling. The model results are compared with available experimental data for condensation in the presence of NC gases and aerosols. The results show a good performance for the thermal-hydraulic part of the model and a sound consistency when estimating the role of aerosols in the scenario. A satisfactory explanation of the experimental differences concerning aerosol depletion onto finned surfaces has been provided through the model predictions.