Experimental Investigation on Heat Transfer Enhancement by Transversal Ribs in Channels

2017 ◽  
Author(s):  
Bernardo Buonomo ◽  
Luca Cirillo ◽  
Oronzio Manca ◽  
Sergio Nardini
Keyword(s):  
Heat Flux ◽  
Experimental Investigation ◽  
Test Section ◽  
Heated Wall ◽  
Heated Plate ◽  
Rectangular Section ◽  
Convergent Channel ◽  
Number Range ◽  
Transversal Section ◽  
Experimental Apparatus

In this paper an experimental investigation is carried out on forced convection in channels with the lower ribbed wall heated with a uniform heat flux. The fluid is air. The experimental apparatus is made up of a channel with a transversal rectangular section, a test section, a convergent channel, to reduce the rectangular transversal section in a circular section and a fan between circular tubes. The unheated rectangular channel is long 2.50 m, the transversal rectangular section is 27.8 mm high and 250 mm wide. The test section is 300 mm long and it has the same rectangular transversal section of the unheated channel. In the test section the lower plate is in aluminum and is heated by two electrical resistances whereas the upper plate and the lateral walls are in glass. The experiments are carried out employing a smooth or a ribbed plate. The ribs are transversal and can be squared or triangular. In both cases the ribs are 5.0 mm wide and 5.0 mm high. The rib pitch is 40 mm and along the heated plate there are 7 ribs. Results are obtained in a Reynolds number range from 5000 to 15000 and wall heat flux of 3000 W/m2 and 5000 W/m2. In the experiments two heated wall emissivity values are considered, 0.05 and 0.95. Results are given in terms of wall temperature profiles, air temperature, average Nusselt numbers and pressure drops.

Experimental Investigation on the Effect of Longitudinal Aspect Ratio on Natural Convection in Inclined Channels Heated Below

2006 ◽  
Author(s):  
Assunta Andreozzi ◽  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Sergio Nardini
Keyword(s):  
Heat Flux ◽  
Experimental Investigation ◽  
Natural Convection ◽  
Flow Visualization ◽  
Inclination Angle ◽  
Flow Separation ◽  
Heated Wall ◽  
Uniform Heat Flux ◽  
Heated Plate ◽  
Inclined Channels

In this paper an experimental investigation on natural convection in air in inclined channels with rectangular transversal section and lower wall heated at uniform heat flux is carried out. Wall temperature measurements and flow visualization are presented. The results allow investigating on the effect of the distance between the two principal parallel walls and of the inclination angle. The experiments are accomplished for two channel gap values: 20 and 40 mm. The inclination angle is equal to 80° and 88°. The flow development and the shape of flow transitions along the channel are visualized. Flow visualization allows to describe the secondary motion inside an inclined channel. Flow separation region along the lower heated plate begins at lower axial coordinate as the wall heat flux, the inclination angle and the channel gap are greater. The flow separation depends also on transversal coordinate. The detected secondary structures pass from thermals to plumes and vortices. Along the plane parallel to the heated wall, the visualization shows that thermal plumes split in V-shaped structures. For the largest considered channel gap value the instability phenomena in the channel are stronger and chaotic motion in the channel outlet zone is observed. When the channel gap value increases wall temperatures become lower because the higher distance between the walls determines a greater mass flow rate and an increase in the heat transfer.

scholarly journals Experimental investigation on evaporation of R407C in a single horizontal smooth tube

2017 ◽  
Vol 7 (2 (S)) ◽  
pp. 266
Author(s):  
M. D. Hambarde ◽  
Ramakant Shrivastava ◽  
S.R. Thorat ◽  
O.P. Dale
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Investigation ◽  
Mass Flux ◽  
Test Section ◽  
Flow Boiling ◽  
Horizontal Tube ◽  
Operating Conditions ◽  
Montreal Protocol ◽  
Vapor Quality

Due to higher ozone layer depletion potential of HCFC refrigerant, R22 which has been mostly used in house hold refrigeration will be phased out by 2020 as per Montreal Protocol and UNFCCC Regulations. R407C, a zeotropic refrigerant from HFC category is a promising refrigerants in place of R22. Performance evaluation of R407 is required to enhance its application in house hold refrigeration. Hence an experimental investigation is carried out to understand the heat transfer characteristics during flow boiling of R407C in a smooth horizontal tube of 13.386 mm inner diameter and 2m length. The experiment is performed under the operating conditions; (i) mass flux range 100 to 300 kg s-1m-2; (ii) heat flux within range 2 to 7 kWm-2; (iii) temperature range at inlet to test section -100C to +100C; (iv) average vapor quality within test section from 0.05 to 0.95.The effect of heat flux, mass flux, vapor quality, temperature glide on heat transfer coefficient, during evaporation of R407C are examined.

Experimental Study of Uniform and Non-Uniform Transverse Heat Flux Distribution Effect on the Onset of Nucleate Boiling

2017 ◽  
Author(s):  
Omar S. Al-Yahia ◽  
Taewoo Kim ◽  
Daeseong Jo
Keyword(s):  
Heat Flux ◽  
Power Distribution ◽  
Test Section ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
The Other ◽  
Heated Plate ◽  
Heated Section ◽  
Other Hand ◽  
The One

An experiment study is conducted to investigate the effect of transverse power distribution on the Onset of Nucleate Boiling (ONB) through a one-side heated narrow rectangular channel. Two test section are used to perform the experiment; uniform and non-uniform heated suction. The demineralized water is flowing in upward direction through the coolant channel with a thickness of 2.35 mm, a width of 54 mm, and a length of 300 mm. The experiment is carried out under different thermal power (0.5 kW – 6.5 kW) for the both test section. As well as, a wide variety of inlet subcooling and flow velocity are used as; 65−35 °C and 0.1–1.0 m/s, respectively. The wall temperature distribution of the heated plate is measured by 10 TCs for the uniformly heated test section, and 20 TC for the non-uniformly heated section. On the other hand, the ONB location is visualized via high speed camera, in which the ONB occurs near the edges for the non-uniformly heated section and occurs at the center of the heated surface for the uniformly power distribution. The results of the ONB heat flux and temperature in the non-uniformly heated section are compared against the one in the uniformly heated power. The results show the variety of the ONB location, ONB heat flux with the different power distribution. With the increase of the power, the ONB is shifted toward the inlet. On the other hand, the ONB for the non-uniform power distribution occurs near the edges at power lower than that the one in the uniformly power distribution. Also, the results are compared against the available correlations, such as Bergles and Rohsenow (1965), Jens and Lottes (1951), and Thom et al. (1965), as well as other experimental results done by several research institutes.

scholarly journals Experimental Investigation of Heat Transfer Rate Using Twisted Tape with Elliptical Holes

2017 ◽  
Vol 7 (2 (S)) ◽  
pp. 105
Author(s):  
K. R. Gawande ◽  
A. V. Deshmukh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Test Section ◽  
Smooth Tube ◽  
Twisted Tape ◽  
Transfer Enhancement ◽  
Nusselt Numbers

An experimental investigation was carried for measuring tube-side heat transfer coefficient, friction factor, heat transfer enhancement efficiency of water for turbulent flow in a circular tube fitted with rectangular-cut twisted tape insert. A copper tube of 26.6 mm internal diameter and 30 mm outer diameter and 900 mm test length was used. A stainless steel rectangular-cut twisted tape insert of 5.25 twist ratio was inserted into the smooth tube. The rectangular cut had 8 mm depth and 14 mm width. A uniform heat flux condition was created by wrapping nichrome wire around the test section and fiber glass over the wire. Outer surface temperatures of the tube were measured at 5 different points of the test section by T-type thermocouples. Two thermometers were used for measuring the bulk temperatures. At the outlet section the thermometer was placed in a mixing box. The Reynolds numbers were varied in the range 10000-19000 with heat flux variation 14 to 22 kW/m2 for smooth tube, and 23 to 40 kW/m2 for tube with insert. Nusselt numbers obtained from smooth tube were compared with Gnielinski correlation and errors were found to be in the range of -6% to -25% with r.m.s. value of 20%. At comparable Reynolds number, Nusselt numbers in tube with rectangular-cut twisted tape insert were enhanced by 2.3 to 2.9 times at the cost of increase of friction factors by 1.4 to 1.8 times compared to that of smooth tube. Heat transfer enhancement efficiencies were found to be in the range of 1.9 to 2.3 and increased with the increase of Reynolds number.

Validation Study on Forced and Mixed Convection in the Rotatable Buoyancy Tunnel

2013 ◽  
Author(s):  
Blake W. Lance ◽  
Jeff R. Harris ◽  
Jared M. Iverson ◽  
Robert E. Spall ◽  
Richard W. Johnson ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Mixed Convection ◽  
Test Section ◽  
Fluid Velocity ◽  
Heated Wall ◽  
Data Sets ◽  
Heated Plate ◽  
Validation Data ◽  
Opposed Flow ◽  
High Level

The Rotatable Buoyancy Tunnel (RoBuT) at Utah State University, built for validation measurements incorporating a high level of data completeness, is described along with the results from validation data sets for forced and mixed convection. One wall of the tunnel test section is heated while the other three are transparent for optical access. All boundary conditions, including geometry, wall temperature and inflow temperature and velocity, are measured and their uncertainties are reported. The tunnel’s design is unique in that the test section can be inverted by rotating the entire facility to generate mixed convection with either buoyancy aided or buoyancy opposed flow. The RoBuT can also produce forced or natural convection, either steady or transient. Measurements for forced and buoyancy-aided mixed convection over a vertical heated plate are described. The RoBuT allows for simultaneous measurements of velocity, wall and inlet air temperature, heat flux measurements on the heated wall, and pressure drop across the test section. The fluid velocity is measured by time-averaged particle image velocimetry (PIV). The first validation case is forced convection since this flow is well understood. Both forced and mixed convection results are compared to published correlations and computational fluid dynamics (CFD) studies. The CFD is steady and 3-D using as-built measurements of the geometry. Experimental wall and inlet temperatures are used for CFD boundary conditions, as well as the inlet velocity and turbulence profiles. Three research groups perform simulations with varying levels of knowledge of the experimental results.

Mixed Convection Heat Transfer in a Convergent Vertical Channel With a Moving Plate

2006 ◽  
Author(s):  
Assunta Andreozzi ◽  
Nicola Bianco ◽  
Giovanni Lacasa ◽  
Vincenzo Naso
Keyword(s):  
Heat Flux ◽  
Mixed Convection ◽  
Vertical Channel ◽  
Wall Heat Flux ◽  
Heated Wall ◽  
Maximum Temperature ◽  
Channel Spacing ◽  
Moving Plate ◽  
Number Range ◽  
Converging Angle

A numerical investigation of mixed convection in air in a convergent vertical channel, due to the interaction between a buoyancy flow and a moving plate induced flow, is presented. The plate moves at a constant velocity along the buoyancy force direction and the principal inclined walls of the channel are heated at uniform heat flux. The numerical analysis is carried out by means of the finite volume method, using the commercial code Fluent. The effects of the channel spacing, wall heat flux, moving plate velocity and converging angle are investigated. Heated wall temperature increases at increasing converging angle, except for natural convection in a 10 mm minimum channel gap. The effect of the converging angle on the wall temperatures is less marked at the larger channel spacing. Maximum temperature of the moving plate is attained in the parallel wall channel for a 30 W m−2 wall heat flux, both in the 10 mm and 40 mm channel, whereas for a 220 W m−2 wall heat flux in the 40 mm channel in mixed convection, maximum wall temperatures are exhibited for a 10° angle. Nusselt, Reynolds and Richardson numbers are correlated by a monomial equation for each converging angle and a unique monomial correlation for all investigated angles in the 2.1·10−2 – 5.1·105 Richardson number range is presented.

Sign in / Sign up

Export Citation Format

Share Document