Heat Transfer Effectiveness and Coefficient of Pressure Drop on the Shell Side of a Staggered Elliptical Tubes Bank

2014 ◽  
Vol 493 ◽  
pp. 134-139 ◽  
Author(s):  
Utomo Kukuh W. Budi ◽  
Kamal Samsul ◽  
Suhanan ◽  
I. Made Suardjaja
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Equivalent Diameter ◽  
Shell Side ◽  
Low Reynolds Numbers ◽  
Wind Velocities ◽  
Low Reynolds ◽  
Tube Banks

The effectiveness of heat transfer and the pressure drop coefficient of staggered elliptical tube banks are studied experimentally. The bank consists of 11 elliptical tubes of 0.75 equivalent diameter in an arrangement of 4-3-4. The major and the minor sub-axis of each tube are 24.70 mm and 12.35 mm respectively, and therefore the aspect ratio (AR) of the tube is 2.0. The geometric parameters of the bank are ST = 24.70 mm, SL = 37.00 mm and minimum frontal area B = 12.35 mm. Seven mid-tubes are internally heated by electrical heater of 69.6 Watt each. Experiment is conducted in a sub sonic wind tunnel and run with the wind velocities of 1 m/s 12.6 m/s which correspond with Reynolds number of = 346-6904. The results show that the effectiveness (ε) varied from 2144.44 to 15.26. It decreases exponentially at low Reynolds numbers and tended asymptotically at higher Reynolds number. The coefficient of pressure drop (CΔp) ranges from 7.21 to 4.41 decreases continuously at low Reynolds number and asymptotic at higher one.

Low Reynolds number heat transfer from a circular cylinder

1968 ◽  
Vol 32 (1) ◽  
pp. 21-28 ◽  
Author(s):  
C. A. Hieber ◽  
B. Gebhart
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Number Theory ◽  
Circular Cylinder ◽  
Prandtl Number ◽  
Experimental Work ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Theoretical Results

Theoretical results are obtained for forced heat convection from a circular cylinder at low Reynolds numbers. Consideration is given to the cases of a moderate and a large Prandtl number, the analysis in each case being based upon the method of matched asymptotic expansions. Comparison between the moderate Prandtl number theory and known experimental results indicates excellent agreement; no relevant experimental work has been found for comparison with the large Prandtl number theory.

Local and Average Heat Transfer Characteristics for Turbulent Airflow in an Asymmetrically Heated Tube

1979 ◽  
Vol 101 (4) ◽  
pp. 635-641 ◽  
Author(s):  
G. R. Knowles ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Tube Wall ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Average Heat ◽  
Local Coefficients ◽  
Fluid Convection ◽  
Turbulent Airflow ◽  
Low Reynolds

Turbulent airflow experiments were performed with a specially fabricated test section tube which facilitated nonuniform heat transfer around the tube circumference. Heating was accomplished by passing electric current axially through half the tube wall (subtending a 180 deg arc), while the other half of the wall was not directly heated. Measurements were made both in the thermal entrance region and the fully developed region, and the Reynolds number was varied from about 4400 to 64,000. The results of the experiments underscored the strong interaction between circumferential tube-wall conduction and fluid convection when a gas flowing in a tube is heated nonuniformly around its circumference. The effects of the wall conduction were shown to be significant at low Reynolds numbers but diminished as the Reynolds number increased. Owing to the circumferential nonuniformities, the thermal development was much slower than that for a uniformly heated pipe flow. By use of a suitably defined circumferential average heat transfer coefficient, the present fully developed results agreed well with a literature correlation for uniformly heated flows. At any cross section, the local coefficients varied around the tube circumference, with the smallest value at the mid-point of the heated arc. Buoyancy effects at low Reynolds numbers were investigated and found to be undetectably small.

Effect of Louver Angle in Multi-Louvered Fins at Low Reynolds Numbers

2003 ◽  
Author(s):  
Dahai Guo ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Maximum Flow ◽  
Reynolds Numbers ◽  
Dominant Mode ◽  
Favorable Effect ◽  
Low Reynolds Numbers ◽  
Impingement Heat Transfer ◽  
Low Reynolds ◽  
Face Velocity

The paper studies the effect of large louver angles on the performance of large pitch multilouvered fins at low Reynolds numbers. The Reynolds number based on face velocity and louver pitch is varied between 50 and 300. Louver angles are varied from 20° to 60° for fin pitch ratios of 1.5 and 2.0. It is found that increasing louver angle has a favorable effect on flow efficiency up to a certain point, beyond which the flow efficiency decreases. The maximum flow efficiency is realized at smaller louver angles as the Reynolds number increases. The drop in flow efficiency is attributed to the development of recirculation zones which act as blockages. In spite of the decrease in flow efficiency, the heat transfer coefficient increases with louver angle for all the cases studied. It is found that as louver angle increases, impingement heat transfer at the leading surface of louvers becomes a dominant mode of heat transfer. Friction factors also increase with louver angle, primarily due to an increase in form drag.

Heat transfer from a sphere at low Reynolds numbers

1973 ◽  
Vol 60 (2) ◽  
pp. 273-283 ◽  
Author(s):  
S. C. R. Dennis ◽  
J. D. A. Walker ◽  
J. D. Hudson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Viscous Incompressible Fluid ◽  
Reynolds Numbers ◽  
Experimental Measurements ◽  
Low Reynolds Numbers ◽  
Nusselt Numbers ◽  
The Mean ◽  
Low Reynolds ◽  
Prandtl Numbers

The heat transfer due to forced convection from an isothermal sphere in a steady stream of viscous incompressible fluid is calculated for low values of the Reynolds number and Prandtl numbers ofO(1). The mean Nusselt number is compared with the results of experimental measurements. At very low Reynolds numbers, both the local and mean Nusselt numbers are compared with the results obtained from the theory of matched asymptotic expansions.

Thermal Performance of Pin Fins at Low Reynolds Numbers in Mini-Micro-Channels

2007 ◽  
Author(s):  
A. Rozati ◽  
D. K. Tafti ◽  
N. E. Blackwell
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Thermal Performance ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
High Density ◽  
Low Reynolds Numbers ◽  
Micro Channels ◽  
Low Reynolds

The computational study investigates different pin fin arrangements at low Reynolds numbers, which would typically be prevalent in mini-micro-channels used in enhancing heat as well as mass transfer. The effect of pin density, span-wise pitch, and stream-wise pitch is investigated on friction and heat transfer over a range 5<ReD<400. High density pins with small span-wise pitches were found to provide the highest augmentation in heat transfer capacity (conductance), whereas low density pins with or without a large stream-wise pitch were found to provide the least heat transfer benefits in the low Reynolds number range studied. Friction factor decreases considerably as the pin density decreases. The effect of decreasing span-wise pitch increases the friction factor in the low Reynolds number regime (ReD<200) but decreases it beyond ReD = 200 by delaying wake instabilities and the associated increase in form drag. Increasing the stream-wise pitch decreases the friction factor at low ReD<200, but increases it at ReD>200 due to the formation of larger recirculating wakes. Overall it is concluded that a high density arrangement with a small span-wise pitch provides the best thermal performance.

The Development of a Closed Loop High Speed Cascade Wind Tunnel for Aerodynamic and Heat Transfer Testing at Moderate to Low Reynolds Numbers

2013 ◽  
Author(s):  
M. P. Mihelish ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Speed ◽  
Closed Loop ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Low Reynolds Number Flows ◽  
Low Reynolds ◽  
Reynolds Number Flows ◽  
Very High

Engine companies typically emphasize research which has been conducted at conditions as close to engine conditions as possible. This focus on engine relevant conditions often causes difficulties in University research laboratories. One particularly difficult testing regime is high speed but low Reynolds number flows. High speed low Reynolds number flows can occur in both low pressure turbines under a normal range of engine operating conditions and in high pressure turbines run at very high altitudes. This paper documents a new steady state closed loop wind tunnel facility which has been developed to study high speed cascade flows at low Reynolds numbers. The initial test configuration has been representative of a first stage vane configuration for a UAV turbofan which flies at a very high altitude. The initial test section was configured in a three full passage four-vane linear cascade arrangement with upper and lower bleed flows. Both heat transfer and aerodynamics loss measurements were acquired and are presented in this paper. Heat transfer measurements were taken at a Reynolds number of 720,000 based on true chord and exit conditions at Mach numbers of 0.7, 0.8, and 0.9. Exit survey measurements were conducted at a chord exit Reynolds number of 720,000 over a similar range in Mach numbers. However, this facility has the capability to run at chord Reynolds numbers of 90,000 or below in the present configuration which uses an approximately three times scale test vane.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

scholarly journals Parametric optimization of a stamped longitudinal vortex generator inside a circular tube of a solar water heater at low Reynolds numbers

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Felipe A. S. Silva ◽  
Luis Júnior ◽  
José Silva ◽  
Sandilya Kambampati ◽  
Leandro Salviano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

AbstractSolar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.

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