A Pulsed Wire Probe for the Measurement of Velocity and Flow Direction in Slowly Moving Air

1984 ◽  
Vol 106 (1) ◽  
pp. 72-78 ◽  
Author(s):  
D. E. Olson ◽  
K. H. Parker ◽  
B. Snyder
Keyword(s):  
Heat Transfer ◽  
Theoretical Model ◽  
Spatial Resolution ◽  
Flow Direction ◽  
Three Dimensional ◽  
Velocity Fields ◽  
Transport Time ◽  
Wire Probe ◽  
Circular Pipes ◽  
Measured Flow

This report describes the theory and operation of a pulsed-probe anemometer designed to measure steady three-dimensional velocity fields typical of pulmonary tracheo-bronchial airflows. Local velocities are determined by measuring the transport time and orientation of a thermal pulse initiated at an upstream wire and sensed at a downstream wire. The transport time is a reproducible function of velocity and the probe wire spacing, as verified by a theoretical model of convective heat transfer. When calibrated the anemometer yields measurements of velocity accurate to ±5 percent and resolves flow direction to within 1 deg at airspeeds ≥10 cm/s. Spatial resolution is ±0.5 mm. Measured flow patterns typical of curved circular pipes are included as examples of its application.

Three-Dimensional Numerical Simulation on the Laminar Flow and Heat Transfer in Four Basic Fins of Plate-Fin Heat Exchangers

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
Yinhai Zhu ◽  
Yanzhong Li
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Heat Exchangers ◽  
Flow Direction ◽  
Three Dimensional ◽  
Entry Length ◽  
Flow And Heat Transfer ◽  
F Factor ◽  
The One ◽  
Data Reduction Method

In this paper, four basic fins of the plate-fin heat exchangers, rectangular plain fin, strip offset fin, perforated fin, and wavy fin, are modeled and simulated by taking account of fin thickness, thermal entry effect, and end effect. Three-dimensional numerical simulations on the flow and heat transfer in the four fins are investigated and carried out at laminar flow regime. Validity of the modeling technique is verified by comparing computational results with both corresponding experimental data and three empirical correlations from literatures. Global average Colburn factor (j factor) and friction factor (f factor) and their local 1D streamwise-average distributions along the fins are presented by introducing data reduction method. The heat transfer behaviors in both the developing and developed regions are analyzed by examining variations of the local Nusselt number along the flow direction. It is found that the thermal entry length of the four fins might be expressed in the format of Le=c1 Rec2 Pr Dh, which has the same form as the one in a circular tube.

Discussion on Finite Element Model for Three Dimensional Rolling Process Analysis

2014 ◽  
Vol 496-500 ◽  
pp. 452-455
Author(s):  
Chi Chih Shen
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Finite Element ◽  
Theoretical Model ◽  
Process Analysis ◽  
Three Dimensional ◽  
Element Model ◽  
Rolling Process ◽  
Strip Rolling ◽  
Rigid Matrix

A three dimensional numerical simulation model of metal rolling formation is developed from the theoretical model. In this theoretical model, the two variables of element deformation and temperature variation are placed in a variable matrix. The thermal elastic plastic rigid matrix and heat transfer rigid matrix are placed in the same expansion rigid matrix. Furthermore, the numerical simulation analytical model developed in this paper was used to simulate aluminum strip rolling.

Prediction of Turbulent Flow and Heat Transfer in a Ribbed Rectangular Duct With and Without Rotation

1993 ◽  
Author(s):  
C. Prakash ◽  
R. Zerkle
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Flow ◽  
Flow Direction ◽  
Three Dimensional ◽  
Stationary Case ◽  
Rectangular Duct ◽  
Wall Functions ◽  
Flow And Heat Transfer ◽  
Smooth Channel

The present study deals with the numerical prediction of turbulent flow and heat transfer in a 2:1 aspect ratio rectangular duct with ribs on the two shorter sides. The ribs are of square cross–section, staggered and aligned normal (90–deg) to the main flow direction. The ratio of rib height to duct hydraulic diameter equals 0.063, and the ratio of rib spacing to rib height equals 10. The duct may be stationary or rotating. The axis of rotation is normal to the axis of the duct and parallel to the ribbed walls (i.e., the ribbed walls form the leading and the trailing faces). The problem is three–dimensional and fully elliptic; hence, for computational economy, the present analysis deals only with a periodically–fully–developed situation where the calculation domain is limited to the region between two adjacent ribs. Turbulence is modelled with the k–epsilon model in conjunction with wall–functions. However, since the rib height is small, use of wall–functions necessitates that the Reynolds number be kept high. (Attempts to use a two–layer model that permits integration to the wall did not yield satisfactory results and such modelling issues are discussed at length). Computations are made here for Reynolds number in the range (30,000–100,000) and for Rotation number=0 (stationary), 0.06, and 0.12. For the stationary case, the predicted heat transfer agrees well with the experimental correlations. Due to the Coriolis induced secondary flow, rotation is found to enhance heat transfer from the trailing and the side walls, while decreasing heat transfer from the leading face. Relative to the corresponding stationary case, the effect of rotation is found to be less for a ribbed channel as compared to a smooth channel.

Numerical Study of Air Forced Convection in a Rectangular Channel Provided With Ribs

2010 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Numerical Study ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Longitudinal Axis ◽  
Three Dimensional Model ◽  
Orthogonal Direction ◽  
Inclination Angles

Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications, like heat exchangers for refrigeration, automotives, process industry, solar heater etc.. Convective heat transfer may be enhanced passively by adopting different solutions. A possibility for increasing the heat transfer is to employ rough surfaces. When a fluid flows in a channel, ribs break the laminar sub-layer and create local turbulence, due to flow separation and reattachment between consecutive ribs, which reduce thermal resistance and augment heat transfer. This behaviour overcomes the effect linked to the increased heat transfer area due to the ribs. However, higher friction losses are expected and turbulence must be created only in the region very close to the heat transferring surface and the core flow should not be unduly disturbed. In this paper a numerical investigation is carried out on air forced convection in a rectangular channel with constant heat flux applied on the bottom and upper external walls. Properties of fluid are considered temperature-dependent and flow regime is turbulent. The investigation is accomplished by means of the commercial code Fluent. A three-dimensional model is developed in order to study the effect of the angle between the fluid flow direction and the ribbed surfaces. In fact, secondary turbulence is promoted in the orthogonal direction to the channel longitudinal axis. Three different inclination angles of the ribbed surfaces have been considered and the channel is provided with rectangular ribs. Simulations have shown that Nusselt numbers as well as the pressure drops increase as the inclination angles increase.

Numerical Simulation and Experimental Validation of Flow and Heat Transfer in Flat-Tube Heat Exchangers

2007 ◽  
Author(s):  
Jiuyang Yu ◽  
Wenwu Xia ◽  
Xingkui Feng
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Three Dimensional ◽  
Flat Tube ◽  
Flow Energy ◽  
Flow Parameters ◽  
Flow And Heat Transfer ◽  
Measured Flow

A three dimensional numerical simulation study has been carried out to predict air flow and temperature distribution in flat-tube heat exchangers. Due to the symmetry in geometrical construction, a section of heat exchanger has been considered for CFD analysis by using PHOENICS software. The k-ε turbulence model has been used to solve the transport equations for turbulent flow energy and the dissipation rate. In order to check the validity of the computational modeling, the results were compared with the measured flow parameters such as pressure and velocity distribution. It is found that both the heat transfer coefficient and the pressure drop for the shell-side are in good arrangement with experimental results. Comparing with circular-tube heat exchangers, the simulation result shows that the pressure drop of flat-tube heat exchangers decreases 12%∼20%, and the coefficient of integral performance Nu/ζ0.29 has an increment, which is between 22%∼34%.

Influence of Thermo-Physical Properties on the Flow and Heat Transfer in Rectangular Micro-Channels

2011 ◽  
Vol 347-353 ◽  
pp. 2640-2644 ◽  
Author(s):  
Xue Tao Duan ◽  
Bin Xu ◽  
Hao Luo
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Flow Direction ◽  
Three Dimensional ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Flux Boundary Condition ◽  
Flow And Heat Transfer ◽  
Friction Factors ◽  
Micro Channels

This paper investigated the behaviors of flow and heat transfer of single-phase in rectangular micro-channels with three-dimensional numerical analysis. The single micro-channel is 200μm deep, 50μm wide. Deionized water was used as the working fluid. The fluid physical properties varying with temperature and Re number were studied. Comparisons were made among the results obtained from experiments, numerical simulations, and from those in the literature. The results indicated that the friction factors decreasing along the flow direction were ascribed to the fluid temperature rising under the unified heat flux boundary condition. It was found that influence of viscosity variation with temperature and viscous dissipation effect could be too significant to be neglected.

A Simplified CFD Model With Multi-Periodic Boundary Conditions for Cross Wavy Channels

2011 ◽  
Author(s):  
L. X. Du ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Periodic Boundary ◽  
Flow Direction ◽  
Wave Length ◽  
Three Dimensional ◽  
Periodic Boundary Conditions ◽  
Navier Stokes ◽  
The Cross ◽  
Wavy Channels

The compact and efficient primary surface heat exchangers are often used as recuperators in microturbine regenerative cycle systems. In the present study, the flow and the heat transfer performance of the cross wavy (CW) ducts have been simulated by three-dimensional models. The hydrodynamic diameters of the models are 1.689mm. Navier-Stokes and energy equations are solved by COMSOL3.5. Because one single wavy cell will overlap more than one adjacent channel, multi-periodic boundary conditions are especially adopted to simplify the calculations. Multi-periodic boundary conditions have been proved to have more reasonable flow field and heat transfer coefficient compared with the literature results. A dimensionless parameter L/A (wave length L, internal height of the corrugation in flow direction A) is defined as the optimization target. The numerical results indicated that when L/A = 6, the CW channel has the best comprehensive performance in all the cases. The comprehensive performances of the CW ducts are evaluated by the j/f (heat transfer factor j and friction factor f). The flow and heat transfer characteristics are much more complex in the cross wavy channels, especially when L/A is small.

Numerical Study on Heat Transfer Characteristics in Rectangular Ducts With Pin-Fins

2011 ◽  
Author(s):  
Xinjun Wang ◽  
Xiaowei Bai ◽  
Jiangbo Wu ◽  
Rui Liu ◽  
Ding Zhu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Numerical Study ◽  
Flow Direction ◽  
Three Dimensional ◽  
Heat Transfer Characteristics ◽  
Pin Fin ◽  
Transfer Characteristics ◽  
Pin Fins

By using the CFX software, three-dimensional flow and heat transfer characteristics in rectangular cooling ducts with in-line and staggered array pin-fins of gas turbine blade trailing edge were numerically simulated. The effects of in-line and staggered arrays of pin-fins, flow Reynolds number as well as density of cylindrical pin-fins in flow direction on heat transfer characteristics were analyzed. Both in the cases of in-line and staggered arrays of pin-fins, the results show that the pin-fin surface averaged Nusselt number increases with the increasing of Reynolds number. In the case of the same Reynolds number, the mean Nusselt number of pin-fin surface decreased with the increasing of X/D (the ratio of streamwise pin-pitch to pin-fin diameter) value. The Nusselt number increases gradually before the first pin-fin row and then reached the fully developed value at fourth or fifth row. The pin-fin Nusselt number at flow direction is larger than that at back flow direction. Along the height direction of pin-fin, the Nusselt number in middle area is larger.

From Macro to Micro Scales: Identifying and Measuring Scaling Effects

2006 ◽  
Author(s):  
H. Herwig ◽  
D. Gloss
Keyword(s):  
Heat Transfer ◽  
Theoretical Model ◽  
Navier Stokes ◽  
Scaling Effects ◽  
Continuum Approach ◽  
First Law Of Thermodynamics ◽  
Flow And Heat Transfer ◽  
Micro Channels ◽  
Macro Scale ◽  
Measured Flow

Scaling effects in continuum flows can be identified that characterize flow and heat transfer in small, micro-sized devices compared to the same geometries but on a macro-sized scale, when the underlying continuum equations (Navier-Stokes and first law of thermodynamics) are subject to a dimensional analysis. In order to identify micro scaling effects experimentally, measured flow quantities are compared to numerically calculated results, based on a theoretical model that is appropriate for macro scale channels (no scaling effects, continuum approach). They have to be interpreted carefully, including a thorough error analysis of experiments as well as the theoretical model. Instead of trying to experimentally identify scaling effects in fixed geometries we suggest to combine macro parts in a way that micro channels emerge. Then, continuously adjustable sizes of the channels can be realized that go from macro to micro dimensions. Equally important, the surfaces of the channels are freely accessible when the macro parts are disjoined. Two such facilities are shown and discussed.

scholarly journals Influence of the Gap Size Between Side Walls and Ribs on the Heat Transfer in a Stationary and Rotating Straight Rib-roughened Duct

2000 ◽  
Vol 6 (4) ◽  
pp. 253-263 ◽  
Author(s):  
R. Kiml ◽  
S. Mochizuki ◽  
A. Murata
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Flow Direction ◽  
Three Dimensional ◽  
Side Wall ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Wall Region ◽  
Side Walls ◽  
Cooling Passage

The objective of this study is to investigate a heat transfer phenomenon in a straight ribroughened duct which represents a cooling passage of a modern gas turbine blade. Experiments were performed for ribs mounted perpendicularly to the main flow direction on two opposite sides of the duct for the following cases: (1) with no gaps, (2) with gaps=0.33hand (3) with gaps=1hbetween the side walls and ribs (wherehis the rib height). The heat transfer results revealed significant differences among these three cases, showing that the existence of gaps increases the heat transfer. Particularly, the local heat transfer on the wall between the consecutive ribs is higher in the near-side wall region than in the central region. To shed some light on this phenomenon, flow visualization was conducted using the particle tracer method. The flow visualization results revealed the effect of gaps on the three-dimensional flow structure between the ribs. It was concluded that this structure caused the heat transfer enhancement in the near-side wall region.

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