scholarly journals Performance Evaluation Criterion at Equal Pumping Power for Enhanced Performance Heat Transfer Surfaces

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Rajendra Karwa ◽  
Chandresh Sharma ◽  
Nitin Karwa
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Literature Survey ◽  
Evaluation Criterion ◽  
Rectangular Duct ◽  
Pumping Power ◽  
Design Constraints ◽  
Performance Evaluation Criterion

The existing equations for the thermal performance evaluation, at equal pumping power for the artificially roughened and smooth surfaced multitube and rectangular duct heat exchangers, have been critically reviewed because the literature survey indicates that a large number of researchers have not interpreted these equations correctly. Three of the most widely used equations have been restated with clearly defined constraints and conditions for their application. Two new equations have been developed for the design constraints not covered earlier.

scholarly journals Investigation of Overlapped Twisted Tapes Inserted in a Double-Pipe Heat Exchanger Using Two-Phase Nanofluid

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1656 ◽  
Author(s):  
Mehdi Ghalambaz ◽  
Hossein Arasteh ◽  
Ramin Mashayekhi ◽  
Amir Keshmiri ◽  
Pouyan Talebizadehsardari ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Performance Evaluation ◽  
Heat Exchanger ◽  
Evaluation Criterion ◽  
Twisted Tape ◽  
Performance Evaluation Criterion ◽  
Twisted Tapes ◽  
Double Pipe ◽  
Pipe Heat

This study investigated the laminar convective heat transfer and fluid flow of Al2O3 nanofluid in a counter flow double-pipe heat exchanger equipped with overlapped twisted tape inserts in both inner and outer tubes. Two models of the same (co-swirling twisted tapes) and opposite (counter-swirling twisted tapes) angular directions for the stationary twisted tapes were considered. The computational fluid dynamic simulations were conducted through varying the design parameters, including the angular direction of twisted tape inserts, nanofluid volume concentration, and Reynolds number. It was found that inserting the overlapped twisted tapes in the heat exchanger significantly increases the thermal performance as well as the friction factor compared with the plain heat exchanger. The results indicate that models of co-swirling twisted tapes and counter-swirling twisted tapes increase the average Nusselt number by almost 35.2–66.2% and 42.1–68.7% over the Reynolds number ranging 250–1000, respectively. To assess the interplay between heat transfer enhancement and pressure loss penalty, the dimensionless number of performance evaluation criterion was calculated for all the captured configurations. Ultimately, the highest value of performance evaluation criterion is equal to 1.40 and 1.26 at inner and outer tubes at the Reynolds number of 1000 and the volume fraction of 3% in the case of counter-swirling twisted tapes model.

Numerical Study on Heat Transfer and Resistance of a Tube Fitted With New Twisted Tapes for Lubricating Oil

2017 ◽  
Author(s):  
Xiaoya Liu ◽  
Ming Ding ◽  
Haozhi Bian ◽  
Changqi Yan ◽  
Chun Li
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Numerical Study ◽  
Evaluation Criterion ◽  
Lubricating Oil ◽  
Twisted Tape ◽  
Steam Turbines ◽  
Transition Flow ◽  
Performance Evaluation Criterion ◽  
Twisted Tapes

Oil coolers are widely-used in nuclear power plants which cool oil flowed through the bearing of steam turbines to a suitable temperature in order for the safe operation of steam turbines. Owing to the high viscosity, the flow state of oil is generally laminar flow or transition flow, which easily leads to poor heat transfer capability and thus a large volume of the oil coolers. The insertion of twisted tapes in circular tube is a passive method widely-used for enhancing heat transfer of laminar or transition flow. However, little research focuses on the heat transfer of highly-viscous fluids inside tube using the twisted tapes. The article will present the numerical simulations of the swirling flow induced by a new coaxial cross twisted tape inserts in a heat transfer tube with lubricating oil. The effects of the clearance ratios and twist ratios on oil side heat transfer coefficient, friction factor and performance evaluation criterion will be numerically investigated using CFD computer software STAR-CCM+. The clearance ratios are 0.077, 0.154 and 0.231. The twist ratios are 2.0 and 4.0. The boundary condition of simulation is constant wall temperature for the Reynolds number ranging from 200 to 1300. The results indicate that the new coaxial cross twisted tapes are efficacious in enhancing the heat transfer of the lubricating oil inside tube. When the clear ratio is 0.077, the effect of heat transfer enhancement of the coaxial cross twisted tapes is better than that of traditional twisted tapes. Furthermore, the highest performance evaluation criterion is up to 2.3.

Internal Groove Influenced Thermohydraulic Performance on an Air-Channel

2018 ◽  
Author(s):  
Gazi I. Mahmood ◽  
Aasa Samson
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Constant Heat Flux ◽  
Pumping Power ◽  
Transfer Coefficients ◽  
Flux Boundary Condition ◽  
Smooth Channel

Internal fins, protrusions, and porous foams enhance the local convective heat transfer at the channel walls in the heat exchangers, electronic chips for cooling, and solar panels for cooling and heating by promoting the local turbulence in flow. However, the fluid pumping power in the channel suffers due to the blockage and high pressure drop caused by the fins, protrusions, and foams. The present article reports the experimental friction factors and Nusselt numbers in a rectangular channel with an array of internal grooves in one wall. The grooves provide the minimum flow blockage, but still promote the local turbulence to enhance the surface heat transfer. The cylindrical grooves are machined at 45° to the mean air-flow direction in one of the wide walls of the channel of aspect ratio of 40.6:1. The ratio of groove print-diameter to depth is 2.83:1. The objectives are to investigate the effects of groove pitch on the thermal performance in the channel as the flow Reynolds number (Re) varies between 600 and 15000. Two ratios of groove-pitch to print-diameter are employed — 3.2:1 and 4.5:1. The measurements include the distributions of the wall staticpressure and heat transfer coefficient along the channel wall having the grooves. The pressure distributions are obtained at the adiabatic condition. The heat transfer coefficients are obtained with the constant heat flux boundary condition from the grooved surface. The measurements are also obtained in the smooth channel when the grooved wall is replaced by a smooth wall for comparisons with the grooved channel. The results indicate the ratio of Darcy friction factor (f/fo) for the grooved channel (f) to that for the smooth channel (fo) increases with the Re by 27% and 41% at the maximum for the two grooves. The f/fo ratios are slightly higher for the grooves with the smaller pitch. The fully developed Nusselt number ratio (Nu/Nuo) for the grooved channel (Nu) to that for the smooth channel (Nuo) increases with the Re by 37% at the maximum for the two grooves. However, the thermal performance quantified by the ratio (Nu/Nuo)/(f/fo)1/3 is higher for the smaller pitch grooves for most of the Reynolds numbers > 2000. The results thus contribute to the design of heat exchangers and cooling channels for high thermal performance with the ratio (Nu/Nuo)/(f/fo)1/3 > 1.0 based on the smaller surface area, pumping power, and heat duty.

scholarly journals Numerical Investigation of Forced Convective Heat Transfer and Performance Evaluation Criterion of Al2O3/Water Nanofluid Flow inside an Axisymmetric Microchannel

Symmetry ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 120 ◽  
Author(s):  
Misagh Irandoost Shahrestani ◽  
Akbar Maleki ◽  
Mostafa Safdari Shadloo ◽  
Iskander Tlili
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Evaluation Criterion ◽  
Forced Convective Heat Transfer ◽  
Performance Evaluation Criterion ◽  
Macro Scale ◽  
The Heat Transfer Coefficient

Al2O3/water nanofluid conjugate heat transfer inside a microchannel is studied numerically. The fluid flow is laminar and a constant heat flux is applied to the axisymmetric microchannel’s outer wall, and the two ends of the microchannel’s wall are considered adiabatic. The problem is inherently three-dimensional, however, in order to reduce the computational cost of the solution, it is rational to consider only a half portion of the axisymmetric microchannel and the domain is revolved through its axis. Hence. the problem is reduced to a two-dimensional domain, leading to less computational grid. At the centerline (r = 0), as the flow is axisymmetric, there is no radial gradient (∂u/∂r = 0, v = 0, ∂T/∂r = 0). The effects of four Reynolds numbers of 500, 1000, 1500, and 2000; particle volume fractions of 0% (pure water), 2%, 4%, and 6%; and nanoparticles diameters in the range of 10 nm, 30 nm, 50 nm, and 70 nm on forced convective heat transfer as well as performance evaluation criterion are studied. The parameter of performance evaluation criterion provides valuable information related to heat transfer augmentation together with pressure losses and pumping power needed in a system. One goal of the study is to address the expense of increased pressure loss for the increment of the heat transfer coefficient. Furthermore, it is shown that, despite the macro-scale problem, in microchannels, the viscous dissipation effect cannot be ignored and is like an energy source in the fluid, affecting temperature distribution as well as the heat transfer coefficient. In fact, it is explained that, in the micro-scale, an increase in inlet velocity leads to more viscous dissipation rates and, as the friction between the wall and fluid is considerable, the temperature of the wall grows more intensely compared with the bulk temperature of the fluid. Consequently, in microchannels, the thermal behavior of the fluid would be totally different from that of the macro-scale.

scholarly journals Influence of Nanoparticle Shape Factor on Convective Heat Transfer of Water-Based ZnO Nanofluids. Performance Evaluation Criterion

2011 ◽  
pp. 106-112
Author(s):  
S. Ferrouillat ◽  
A. Bontemps ◽  
O. Poncelet ◽  
J. A. Gruss ◽  
O. Soriano
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Colloidal Suspensions ◽  
Evaluation Criterion ◽  
Transfer Coefficients ◽  
Nanoparticle Shape ◽  
Nusselt Numbers ◽  
Performance Evaluation Criterion

The convective heat transfer of ZnO/water colloidal suspensions is investigated experimentally to appreciate the influence of two shapes of nanoparticles. Pressure drop and heat transfer coefficients have been measured at two different inlet temperatures (20, 50°C) in heating and/or cooling conditions at various flow rates (200 < Re < 15,000). The Reynolds and Nusselt numbers have been determined by using thermal conductivity and viscosity measured in the same conditions as those in tests. The results obtained are compared with classical correlations. An energetic Performance Evaluation Criterion (PEC) has been defined to compare heat transfer rate to pumping power.

Design and testing of energy-efficient heat exchangers for Newtonian and non-Newtonian fluids – A review

2021 ◽  
pp. 095765092110470
Author(s):  
Jayesh P ◽  
Mukkamala Y ◽  
Bibin John
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Internal Surface ◽  
Surface Modifications ◽  
Newtonian Fluids ◽  
Tube Surface ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
The Impact

Heat transfer enhancement, pumping power and weight minimization in enhanced heat exchangers has long been achieved by deploying tubes with internal surface modifications like microgrooves, ribs, fins, knurls, and dimples with and without tube inserts. This article presents a very extensive review of experimental and computational studies on heat transfer enhancement, which covers convectional and unconventional working fluids under different fluid flow conditions. Compound augmentation with tube surface modifications and inserts has yielded enhancements in the overall heat transfer coefficient of over 116% in the fully developed turbulent flow regime. Exotic fluids like nano-coolants deployed in spiral grooved mircofin tubes yielded 196% enhancement in tube side heat transfer rate for concentrations as low as 0.5% by volume, while the thermal efficiency index measuring the overall enhancement in relation to the pumping power was 75%. However, reviews that address the combined effect of unconventional fluids, surface modifications and tube inserts on the overall thermo-hydraulic performance of annular heat exchangers seem to be limited. Further, nano-coolants aren’t frequently used in the process industry. The goal of this study is to document and evaluate the impact of cost-effective and energy-saving passive enhancement techniques such as tube surface modifications, tube inserts, and annular enhancement techniques on annular heat exchangers used in the process industries with Newtonian and non-Newtonian fluids. This review should be useful to engineers, academics and medical professionals working with non-Newtonian fluids and enhanced heat exchangers.

scholarly journals Execution of a Smart Prediction Tool to Evaluate Thermal Performance in a heat exchanger by using Single Elliptical Leaf Strips with altered Angle

2019 ◽  
Vol 8 (11) ◽  
pp. 123-131
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Industrial Applications ◽  
Generalized Regression Neural Network ◽  
Prediction Tool ◽  
Pressure Drops ◽  
Transfer Rates ◽  
Mass Flow Rates

Heat exchangers are prominent industrial applications where engineering science of heat transfer and Mass transfer occurs. It is a contrivance where transfer of energy occurs to get output in the form of energy transfer. This paper aims at finding a solution to improve the thermal performance in a heat exchanger by using passive method techniques. This experimental and numerical analysis deals with finding the temperature outlets of cold and hot fluid for different mass flow rates and also pressure drop in the tube and the annular side by adding an elliptical leaf strip in the pipe at various angles. The single elliptical leaf used in experiment has major to minor axes ratios as 2:1 and distance of 50 mm between two leaves are arranged at different angular orientations from 0 0 to 1800 with 100 intervals. Since it’s not possible to find the heat transfer rates and pressure drops at every orientation of elliptical leaf so a generalized regression neural network (GRNN) prediction tool is used to get outputs with given inputs to avoid experimentation. GRNN is a statistical method of determining the relationship between dependent and independent variables. The values obtained from experimentation and GRNN nearly had precise values to each other. This analysis is a small step in regard with encomiastic approach for enhancement in performance of heat exchangers

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