scholarly journals Graphing Behaviour of Heat Transfer In Terms of Nusselt and Reynolds

2021 ◽  
Vol 6 (2) ◽  
pp. 41-52
Author(s):  
Mohd Rahimie Md Noor ◽  
Nur Syafiqah Hidayah Mohd Fauzi ◽  
Siti Nur Fadhilah Masrom ◽  
Mohd Azry Abdul Malek ◽  
Muhammad Firdaus Mustapha ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Volume Flow Rate ◽  
Convection Heat Transfer ◽  
Heat Transfer Process ◽  
Two Fluids ◽  
The Relationship

Heat exchangers are tools used to transfer thermal energy between two fluids (liquid or gas) by convection and conduction at different level of temperatures. Heat exchangers are the common equipment and employed in many different applications because of ability to withstand high temperatures and compactness. There are no intermixing or leakage occurred between two fluids during the heat transfer process as fluids are separated by walls of heat exchanger. The main objective of this project is to determine the heat exchanger effectiveness in heat transfer performance. This will be done by investigating the performance of five different angles of heat exchanger which are 150,300, 450, 600 and 750. The effectiveness of heat exchanger depends on the convection heat transfer coefficient of the fluid. Besides that, this project also aims to develop some parameters such as Nusselt number, Reynolds number and Prandtl number for evaluating the heat transfer. It is found that the Nusselt Number at angle of 150 is lower compared to angle of 750. Meanwhile, Reynolds number for angle 150 is higher than angle 750 which means that the type of flow produced by angle 150 is turbulent flow while for 750 angle is laminar flow. Hence, the overall result of this project proved that 150 is the best angle for heat exchanger in chimney because of higher velocity, higher volume flow rate, higher density of gas and higher LMTD. The relationship between Nusselt number and Reynolds number between different angles can be observed by plotting the graph using Maple Software.

Heat Transfer by Mixed Convection Opposing Laminar Flow From the Inside Surface of Uniformly Heated Inclined Circular Tube

2006 ◽  
Author(s):  
H. Mohammed ◽  
T. Yusaf
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Flow Direction ◽  
Convection Heat Transfer ◽  
Heat Transfer Process ◽  
Secondary Flows ◽  
Opposed Flow ◽  
Wide Range

This paper aims to investigate the effect of the flow pattern on the mixed convection heat transfer. A 28 thermocouples wire were installed along a 900mm copper tube to measure the temperature distribution. Three insulation layers of fiber glass, asbestos and gypsum were used to minimize to heat lost to the surrounding. A forced convection at the entrance region of a fully developed opposing laminar air flow was investigated to evaluate the flow direction effect on the Nusselt number. The investigation covered a wide range of Reynolds number from 410 to 1600 and heat flux varied from 63W/m2 to 1260W/m2, with different angles of tube inclination of 30°, 45°, 60°, and 90°. It was found that the surface temperature variation along the tube for opposed flow higher than the assisted flow but lower than the horizontal orientation. The Reynolds number has a significant effect on Nusselt number in opposed flow while the effect of Reynolds number was found to be small in the case of assisted flow. The Nusselt number values were lower for opposed flow than the assisted flow. The temperature profiles results have revealed that the secondary flows created by natural convection have a significant effect on the heat transfer process. The obtained average Nusselt number values were correlated by dimensionless groups as Log Nu against Log Ra/Re.

CFD Analysis of Heat Transfer Characteristics of Helical Coil Heat Exchangers

2015 ◽  
Vol 787 ◽  
pp. 172-176
Author(s):  
R. Maradona ◽  
S. Rajkumar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Helical Coil ◽  
Cfd Analysis ◽  
Compact Size ◽  
Coil Diameter ◽  
Coil Heat

The applications of heat exchangers are vast and the enhancement of heat transfer and compact size are the key factors for designing the heat exchangers in order to achieve energy savings. In the field of tubular heat exchangers one of the possible ways for reducing the space occupied by the exchanger is by bending tube axis in helical shape. This option is particularly suitable when construction simplicity is needed and the geometry of the place in which the exchanger has to be housed is the cylindrical one. In this paper, an attempt is made to enhance the heat transfer rate without application of any external power. This is achieved by providing the helical tube in tubes. The parameters influencing the nature of flow in a helical coil heat exchanger are the tube geometry namely pitch coil diameter, pitch and tube diameter. CFD analysis is carried out to study these geometry effects on heat transfer and hydraulic characteristics by varying Reynolds number (hot fluid). The CFD results of velocity and temperature distribution in the heat exchanger are used to estimate the Nusselt number and heat transfer coefficient. This helps to arrive at an optimum value of Reynolds number and Nusselt number for the corresponding tube-to-coil diameter ratios.

Experimental study for Convection Heat Transfer from Helical Coils with the Same Outer Surface Area and Different Coil Geometry

2021 ◽  
pp. 1-17
Author(s):  
Amr M. Hassaan ◽  
Hesham Mohamad Mostafa
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Surface Area ◽  
Outer Surface ◽  
Convection Heat Transfer ◽  
Heat Transfer Process ◽  
Convection Heat ◽  
Helical Coils

Abstract An experimental study is done to study the convection heat transfer from the outer surface of a group of helical coils that have the same external surface area which is (0.1 m2). These coils are wrapped to form different helical coils with different geometrical dimensions. Five pipe diameters are used in this study also; the pipes are wrapped by different values of coil diameter ranges from 75- 300 mm. The effect of the coil pitch on the heat transfer process has been studied, to reach the value that gives the best performance for each coil. The heat source is steam flowing inside the coil. These coils are tested at different air speeds inside the wind tunnel, which made the Reynolds number (Re) changes from 239 - 3990. The obtained results showed that the Nusselt number enhances with the increase of D/do and P/do to reach the maximum value at the optimum values of D/do and P/do then the Nusselt number begins to decrease. Nusselt number increases with the increase of Reynolds number under all conditions. A correlation for Nusselt number as a function of Reynolds number and the other studied operating parameters reported. By comparing this work with literature, one can find an acceptable agreement in the results.

Experimental Study on Air Cooling via a Multiport Mesochannel Cross-Flow Heat Exchanger

2011 ◽  
Author(s):  
Sarbadaman Dasgupta ◽  
Faisal A. Siddiqui ◽  
Md. Abdul Quaiyum ◽  
Serena A. Al-Obaidi ◽  
Amir Fartaj
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Exchangers ◽  
Cross Flow ◽  
Uniform Temperature ◽  
Flow Channels ◽  
Flow Heat

Researchers are moving forward to provide energy efficient, compact and inexpensive heat exchangers. Main focus is being deployed to the heat exchangers comprising narrow size flow channels such as mesochannels and microchannels for their augmented heat transfer characteristics, compactness and energy efficiency compared to conventional heat exchangers with the same heat exchange duty. Air to water cross-flow heat exchangers are encountered in many engineering applications. While numerous investigations were performed to characterize the heat transfer and fluid flow in mesochannels and microchannels, the literatures examining the air side heat transfer and flow behaviors in the cross-flow mesochannel heat exchangers are inadequate. In the current study air side heat transfer and flow characteristics of cross-flow cooling of air through a multiport slab mesochannel heat exchanger were investigated experimentally. The major components of experimental setup are the closed loop integrated thermal wind tunnel, liquid circulation network with heat add or removal system arrangement, sets of measuring instruments, data acquisition system, and multiport slab mesochannel heat exchanger as the test specimen. The multiport slab mesochannel heat exchanger consists of 15 finned aluminum slabs with 304 mm × 304 mm size frontal area and 100 mm flow length across the direction of air flow. Each slab contains 68 flow channels of 1mm circular diameter. Cold deionized (DI) water at a constant mass flow rate (0.0196 kg/s) was forced to flow through the mesochannels whereas the hot air at different velocities was allowed to pass through the finned passages of the heat exchanger core in cross-flow orientation. The inlet air temperature was changed in three levels (28°C, 33°C and 38°C) while maintaining a constant inlet water temperature of 8° C. The air velocity was varied in four steps (3.5m/s, 5.5m/s, 7.5m/s, and 9.5 m/s) at each temperature level. In the present study heat transfer and fluid flow key parameters such as heat transfer rate (Q˙), number of transfer units (NTU), effectiveness (ε), overall thermal resistance (Rtotal), and the air side Nusselt number (Nua) as well as Reynolds number (Rea) were examined in the region of the air side Reynolds number at the range of 972–2758, with a constant water side Reynolds number of 135. Heat balance performance of the experiment was found to be 4% for all operating conditions. The air side thermal resistance was found to be dominating over the overall thermal resistance ranging from 85% to 91% of the overall thermal resistance. The effect of air side Reynolds number on air side Nusselt number was examined and a general correlation of Nusselt number with Reynolds number was obtained as Nua = 0.3972(Rea)0.3766. The Nusselt number value was found to be higher in comparison with other research works for the corresponding Reynolds number range. The multiport mesochannel flat slab has offered uniform temperature distribution into the core. This uniform temperature distribution leads to higher heat transfer over standalone inline flow tube bank.

Heat Transfer Investigation of a Tube Partially Wrapped by Metal Porous Layer as a Potential Novel Tube for Air Cooled Heat Exchangers

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
M. Mohammadpour-Ghadikolaie ◽  
M. Saffar-Avval ◽  
Z. Mansoori ◽  
N. Alvandifar ◽  
N. Rahmati
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Rate ◽  
Porous Layer ◽  
Transfer Rate ◽  
Metal Foam ◽  
Convection Heat Transfer ◽  
Darcy Number ◽  
High Heat Transfer

Laminar forced convection heat transfer from a constant temperature tube wrapped fully or partially by a metal porous layer and subjected to a uniform air cross-flow is studied numerically. The main aim of this study is to consider the thermal performance of some innovative arrangements in which only certain parts of the tube are covered by metal foam. The combination of Navier–Stokes and Darcy–Brinkman–Forchheimer equations is applied to evaluate the flow field. Governing equations are solved using the finite volume SIMPLEC algorithm and the effects of key parameters such as Reynolds number, metal foam thermophysical properties, and porous layer thickness on the Nusselt number are investigated. The results show that using a tube which is fully wrapped by an external porous layer with high thermal conductivity, high Darcy number, and low drag coefficient, can provide a high heat transfer rate in the high Reynolds number laminar flow, increasing the Nusselt number almost as high as 16 times compared to a bare tube. The most important result of thisstudy is that by using some novel arrangements in which the tube is partially covered by the foam layer, the heat transfer rate can be increased at least 20% in comparison to the fully wrapped tube, while the weight and material usage can be considerably reduced.

scholarly journals 3D Numerical simulation of turbulent heat transfer and Fe3O4/nanofluid annular flow in sudden enlargement

2021 ◽  
Vol 321 ◽  
pp. 04014
Author(s):  
Hussein Togun
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transport ◽  
Annular Flow ◽  
Volume Concentration ◽  
Convection Heat Transfer ◽  
Turbulent Heat Transfer ◽  
Recirculation Region ◽  
Convection Heat

In this paper, 3D Simulation of turbulent Fe3O4/Nanofluid annular flow and heat transfer in sudden expansion are presented. k-ε turbulence standard model and FVM are applied with Reynolds number different from 20000 to 50000, enlargement ratio (ER) varied 1.25, 1.67, and 2, , and volume concentration of Fe3O4/Nanofluid ranging from 0 to 2% at constant heat flux of 4000 W/m2. The main significant effect on surface Nusselt number found by increases in volume concentration of Fe3O4/Nanofluid for all cases because of nanoparticles heat transport in normal fluid as produced increases in convection heat transfer. Also the results showed that suddenly increment in Nusselt number happened after the abrupt enlargement and reach to maximum value then reduction to the exit passage flow due to recirculation flow as created. Moreover the size of recirculation region enlarged with the rise in enlargement ratio and Reynolds number. Increase of volume Fe3O4/nanofluid enhances the Nusselt number due to nanoparticles heat transport in base fluid which raises the convection heat transfer. Increase of Reynolds number was observed with increased Nusselt number and maximum thermal performance was found with enlargement ratio of (ER=2) and 2% of volume concentration of Fe3O4/nanofluid. Further increases in Reynolds number and enlargement ratio found lead to reductions in static pressure.

scholarly journals The Effect of Nanofluid Volume Concentration on Heat Transfer and Friction Factor inside a Horizontal Tube

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Adnan M. Hussein ◽  
K. V. Sharma ◽  
R. A. Bakar ◽  
K. Kadirgama
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Thermal Properties ◽  
Friction Factor ◽  
Volume Concentration ◽  
Convection Heat Transfer ◽  
Horizontal Tube ◽  
Maximum Deviation ◽  
Flat Tube

The additives of solid nanoparticles to liquids are significant enhancement of heat transfer and hydrodynamic flow. In this study, the thermal properties of three types of nanoparticles (Al2O3, TiO2, and SiO2) dispersed in water as a base fluid were measured experimentally. Forced convection heat transfer turbulent flow inside heated flat tube was numerically simulated. The heat flux around flat tube is 5000 W/m2and Reynolds number is in the range of5×103to50×103. CFD model by finite volume method used commercial software to find hydrodynamic and heat transfer coefficient. Simulation study concluded that the thermal properties measured and Reynolds number as input and friction factor and Nusselt number as output parameters. Data measured showed that thermal conductivity and viscosity increase with increasing the volume concentration of nanofluids with maximum deviation 19% and 6%, respectively. Simulation results concluded that the friction factor and Nusselt number increase with increasing the volume concentration. On the other hand, the flat tube enhances heat transfer and decreases pressure drop by 6% and −4%, respectively, as compared with circular tube. Comparison of numerical analysis with experimental data available showed good agreement with deviation not more than 2%.

Natural Convective Flow and Heat Transfer in a Collector Storage with an Immersed Heat Exchanger: Numerical Study

2005 ◽  
Vol 127 (3) ◽  
pp. 324-332 ◽  
Author(s):  
Yan Su ◽  
Jane H. Davidson
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Numerical Study ◽  
Storage System ◽  
Fluid Motion ◽  
Heat Transfer Process ◽  
Strong Mixing ◽  
Scale Analysis ◽  
Three Dimensional Model

A three-dimensional model and dimensionless scale analysis of the transient fluid dynamics and heat transfer in an inclined adiabatic water-filled enclosure with an immersed cylindrical cold sink is presented. The geometry represents an integral collector storage system with an immersed heat exchanger. The modeled enclosure has an aspect ratio of 6:1 and is inclined at 30deg to the horizontal. The heat exchanger is represented by a constant surface temperature horizontal cylinder positioned near the top of the enclosure. A scale analysis of the transient heat transfer process identifies four temporal periods: conduction, quasi-steady, fluctuating, and decay. It also provides general formulations for the transient Nusselt number, and volume-averaged water temperature in the enclosure. Insight to the transient fluid and thermal processes is provided by presentation of instantaneous flow streamlines and isotherm contours during each transient period. The flow field consists of two distinct zones. The zone above the cold sink is nearly stagnant. The larger zone below the sink is one of strong mixing and recirculation initiated by the cold plume formed in the boundary layer of the cylindrical sink. Correlations for the transient Nusselt number and the dimensionless volume-averaged tank temperature predicted from the model compare favorably to prior measured data. Fluid motion in the enclosure enhances heat transfer compared to that of a cylinder in an unbounded fluid.

Experimental Investigation of Coil Curvature Effect on Heat Transfer and Pressure Drop Characteristics of Shell and Coil Heat Exchanger

2014 ◽  
Vol 7 (1) ◽  
Author(s):  
M. R. Salem ◽  
K. M. Elshazly ◽  
R. Y. Sakr ◽  
R. K. Ali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Average Nusselt Number ◽  
Transfer Coefficients ◽  
Nusselt Numbers ◽  
Fanning Friction Factor ◽  
Coil Heat

The present work experimentally investigates the characteristics of convective heat transfer in horizontal shell and coil heat exchangers in addition to friction factor for fully developed flow through the helically coiled tube (HCT). The majority of previous studies were performed on HCTs with isothermal and isoflux boundary conditions or shell and coil heat exchangers with small ranges of HCT configurations and fluid operating conditions. Here, five heat exchangers of counter-flow configuration were constructed with different HCT-curvature ratios (δ) and tested at different mass flow rates and inlet temperatures of the two sides of the heat exchangers. Totally, 295 test runs were performed from which the HCT-side and shell-side heat transfer coefficients were calculated. Results showed that the average Nusselt numbers of the two sides of the heat exchangers and the overall heat transfer coefficients increased by increasing coil curvature ratio. The average increase in the average Nusselt number is of 160.3–80.6% for the HCT side and of 224.3–92.6% for the shell side when δ increases from 0.0392 to 0.1194 within the investigated ranges of different parameters. Also, for the same flow rate in both heat exchanger sides, the effect of coil pitch and number of turns with the same coil torsion and tube length is remarkable on shell average Nusselt number while it is insignificant on HCT-average Nusselt number. In addition, a significant increase of 33.2–7.7% is obtained in the HCT-Fanning friction factor (fc) when δ increases from 0.0392 to 0.1194. Correlations for the average Nusselt numbers for both heat exchanger sides and the HCT Fanning friction factor as a function of the investigated parameters are obtained.

Numerical Study of Shellside Performance of Heat Transfer and Flow Resistance for Heat Exchanger with Trefoil-Hole Baffles

2012 ◽  
Vol 557-559 ◽  
pp. 2141-2146
Author(s):  
Yong Hua You ◽  
Ai Wu Fan ◽  
Chen Chen ◽  
Shun Li Fang ◽  
Shi Ping Jin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Pressure Loss ◽  
Transfer Rate ◽  
Numerical Study ◽  
Shell Side ◽  
Tube Heat Exchanger

Trefoil-hole baffles have good thermo-hydraulic performances as the support of heat pipes, however the published research paper is relatively limited. The present paper investigates the shellside thermo-hydraulic characteristics of shell-and-tube heat exchanger with trefoil-hole baffles (THB-STHX) under turbulent flow region, and the variations of shellside Nusselt number, pressure loss and overall thermo-hydraulic performance (PEC) with Reynolds number are obtained for baffles of varied pitch with the numerical method. CFD results demonstrate that the trefoil-hole baffle could enhance the heat transfer rate of shell side effectively, and the maximal average Nusselt number is augmented by ～2.3 times that of no baffle, while average pressure loss increases by ～9.6 times. The PEC value of shell side lies in the range of 16.3 and 73.8 kPa-1, and drops with the increment of Reynolds number and the decrement of baffle pitch, which indicates that the heat exchanger with trefoil-hole baffles of larger pitch could generate better overall performance at low Reynolds number. Moreover, the contours of velocity, turbulent intensity and temperature are presented for discussions. It is found that shellside high-speed jet, intensive recirculation flow and high turbulence level could enhance the heat transfer rate effectively. Besides good performance, THB-STHXs are easily manufactured, thus promise widely applied in various industries.

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