scholarly journals Simulation of the operation of the car radiator with a laminar, transitional, and turbulent regime of liquid flow in the tubes

2019 ◽  
Vol 23 (Suppl. 4) ◽  
pp. 1311-1321
Author(s):  
Dawid Taler
Keyword(s):  
Nusselt Number ◽  
Friction Factor ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Water Flow Rate ◽  
Linear Interpolation ◽  
Turbulent Regime ◽  
Heat Flow Rate ◽  
Transition Flow ◽  
Calculation Results

The results of the simulation of car radiator operation with a large range of changes in the volume flow rate of liquid inside the tubes were presented. The change of the flow regime from laminar through transitional to turbulent flow was taken into account. Semi-empirical and empirical relationships for the Nusselt number on the liquid-side in the laminar, transitional, and turbulent range were used. The Nusselt number on the air side was determined using empirical power-type correlation. The friction factor in the transition flow range was calculated by linear interpolation between the values of the friction factor for the Reynolds number equal to 2100 and 3000. The water and air temperature at the outlet of the heat exchanger were calculated using effectiveness-number of transfer units method. The heat-flow rate from water to air was calculated as a function of the water-flow rate to compare it with the experimental results. The calculation results agreed very well with the results of the measurements.

scholarly journals Performance of Air-Cooled Heat Exchanger with Laminar, Transitional, and Turbulent Tube Flow

2018 ◽  
Vol 240 ◽  
pp. 02012
Author(s):  
Dawid Taler
Keyword(s):  
Nusselt Number ◽  
Heat Exchanger ◽  
Heat Flow ◽  
Friction Factor ◽  
Flow Rate ◽  
Empirical Relationship ◽  
Heat Flow Rate ◽  
Transition Flow ◽  
Water Side ◽  
Wide Range

Some air-cooled heat exchangers, especially in air conditioning and heating installations, heat pumps, as well as car radiators, work in a wide range of loads when the liquid flow in the tubes can be laminar, transitional or turbulent. In this paper, a semi-empirical and empirical relationship for the Nusselt number on the liquid-side in the transitional and turbulent range was derived. The friction factor in the transition flow range Rew,trb ≤ Rew ≤ Rew,tre was calculated by linear interpolation between the values of the friction factor for Rew,trb =2,100 and Rew,tre =3,000. Based on experimental data for a car radiator, empirical heat transfer relationships for the air and water-side were found by using the least squares method. The water temperature at the outlet of the heat exchanger was calculated using P-NTU (effectiveness-number of transfer units) method. The heat flow rate from water to air was calculated as a function of the water flow rate to compare it with the experimental results. The theoretical and empirical correlation for the water-side Nusselt number developed in the paper were used when determining the heat flow rate. The calculation results agree very well with the results of the measurements.

Investigation of Circular Water Jet Impingement Heat Transfer

2011 ◽  
Author(s):  
Cuicui Liu ◽  
Zeyi Jiang ◽  
Xinxin Zhang ◽  
Qiang Ma ◽  
Yusheng Sun
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Rate ◽  
Water Flow Rate ◽  
Jet Impingement ◽  
Water Jet ◽  
Nozzle Diameter ◽  
Constant Flow Rate ◽  
Impingement Heat Transfer

Mathematical model combining theoretical analysis approach and differential numerical solving techniques has been set up to predict the free surface water jet impingement heat transfer. Heat transfer properties are obtained and validated by comparison with experiments. The characteristic of Nu-r/d distribution is discussed and the effect of nozzle diameter is analyzed. In addition, nozzle arrangements are studied for water jet equipment designation purpose. The results show that: Reynolds number is the dominate parameter in Nu-r/d distribution and area-averaged Nusselt number increases with increasing nozzle diameter. The best heat transfer effect appears when the aspect ratio of rectangular surface equals to 1. Fewer nozzles and bigger single impinged area could get larger Nusselt number under a given total water flow rate and given total impinged area. At a constant flow rate, larger nozzle diameter and smaller Reynolds number present a larger Nusselt number.

CFD Simulation of Installation Angle for Axial Flow Fan of a Motor

2013 ◽  
Vol 274 ◽  
pp. 212-215
Author(s):  
Jia Dong Tang ◽  
Yi Ping Lu ◽  
Xue Mei Sun ◽  
Wan Quan Zhang
Keyword(s):  
Flow Rate ◽  
Cfd Simulation ◽  
Volume Flow Rate ◽  
Axial Flow ◽  
Volume Flow ◽  
Hydraulic Efficiency ◽  
Axial Flow Fan ◽  
Installation Angle ◽  
Calculation Results ◽  
Blade Model

To analyze the effect of the installation angle on the performance of axial flow fan, single blade model and whole model was established, steady flow in the axial flow fan of the 7500KW air-cooled motor was simulated by software FLUENT. Volume flow rate and hydraulic efficiency of the fan with different installation angle under specific outlet pressures were analyzed, the effect of different turbulence model on the numerical simulation results was discussed, and the effect of the single blade model, the whole model and lengthened flow passage model on the numerical calculation results was compared. The results show that the fan volume flow rate and hydraulic efficiency is higher with the installation angle of 30°, the results simulated by standard k-ε model are close to the results simulated by k-ω-SST model, calculation results of these three methods have a good agreement with each other, and the result coincides well with experimental measured values.

Assessing Uncertainties in Friction Factor Measurement as a Tool in Devising Experimental Set-Ups

2007 ◽  
Author(s):  
Marco Lorenzini ◽  
Gian Luca Morini ◽  
Torsten Henning ◽  
Juergen J. Brandner
Keyword(s):  
Pressure Drop ◽  
Friction Factor ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Reynolds Numbers ◽  
Laminar Regime ◽  
Total Uncertainty ◽  
Low Reynolds Numbers ◽  
More Care ◽  
Factor Measurement

The promising performance of microchannels has given rise to intensive research on pressure drop and heat transfer characteristics of flows at the small- validate new ones, experiments need to be conducted, which are particularly difficult given the characteristic dimensions involved and the magnitude of the fluxes to be measured. Although more care has been devoted lately to the design of experiments in terms of control of geometry and boundary conditions, the uncertainties which inevitably affect each measurement do not seem to have been given the proper consideration. Correctly calculating uncertainties not only allow to a correct assessment of the experimental data obtained, but can also be used to decide which measurements need to have the highest precision to achieve a certain accuracy, thus saving money on the others. In this paper, a quantitative criterion is given to assess the accuracy achievable in the determination of the friction factor in the laminar regime for the flow of a fluid in a circular microtube. The influence of the six quantities (pressure drop, outlet pressure, temperature, length, pressure and volume flow rate) measured to determine f in the laminar regime are studied separately and when combined. It is found that at low Reynolds numbers flow rate and pressure drop measurements are determinant for the final value of the uncertainty, while at larger Reynolds numbers the influence of the accuracy in measuring the hydraulic diameter prevails and also limits the minimum value that the total uncertainty can take.

Performance Testing of Pico Hydro Generator for Electricity Generating

2013 ◽  
Vol 860-863 ◽  
pp. 1491-1494
Author(s):  
Yuttachai Keawsuntia
Keyword(s):  
Electric Power ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Water Flow Rate ◽  
Performance Testing ◽  
Gear Ratio ◽  
Volume Flow ◽  
Gear Up ◽  
Water Turbine ◽  
Water Wheel

This research paper presents the testing results of the electricity generating from the pico hydro generator, for save in a battery 12 V. A testing of pico crossflow turbine with 0.6 m diameter of wheel and a 20 blades water turbine which has a semi-circle shape at 0.1 m diameter of blade, connected with the generator at gear up ratio of 1:3 and 1:5 respectively, was undertaken. The results from the test run of pico hydro generator by varying flow rate from 60 to 120 L/min at 0.0127, 0.0190 and 0.0254 m diameter of nozzle respectively, showed that the gear ratio between the water wheel and the generator, the diameter of nozzle and the volume flow rate are important variables that affect the electric production. A combination of water flow rate at 120 L/min, 0.0127 m diameter of nozzle and gear ratio of 1:3 gives the maximum electric power of 121.68 watts.

Numerical Investigation of Flow and Heat Transfer in Microchannels

2008 ◽  
Author(s):  
Emrah Deniz ◽  
I. Yalcin Uralcan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Experimental Studies ◽  
Numerical Results ◽  
Turbulent Regime ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Micro Channels

Mini and microchannel applications have become an important and attractive research area during the past decades. For micro systems design purposes, numerical and experimental studies have been conducted on flow and heat transfer characteristics of mini and microchannels and various friction factor and Nusselt number correlations have been proposed. Some researchers have tried to apply conventional tube correlations to mini and micro channels, rather than deriving new correlations. In this study, using commercial CFD software, flow and heat transfer characteristics in laminar and turbulent flow through circular channels are analyzed numerically. The applicability of conventional correlations in calculating the friction factor and Nusselt number is investigated. It is concluded that, in laminar regime conventional correlations can be used to calculate the friction factor for the channel sizes considered. In turbulent regime, however, numerical results for friction factor yielded greater values than those calculated by the conventional correlations. Numerical Nusselt numbers are found to be closer to the conventional values in laminar and turbulent regimes. In turbulent regime, on the other hand, Nusselt number values calculated with the microchannel correlations are determined to be greater than the numerical results and the values calculated with the conventional correlations.

scholarly journals Comparative study of the thermal performance of four different parallel flow shell and tube heat exchangers with different performance indicators

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 1121-1135
Author(s):  
Chulin Yu ◽  
Haiqing Zhang ◽  
Youqiang Wang ◽  
Jin Wang ◽  
Bingjun Gao ◽  
...  
Keyword(s):  
Nusselt Number ◽  
Comparative Study ◽  
Friction Factor ◽  
Entropy Generation ◽  
Performance Indicators ◽  
Heat Exchangers ◽  
Parallel Flow ◽  
Turbulent Regime ◽  
Entransy Dissipation ◽  
Shell And Tube

Abstract Round rod baffle (RRB), plain plate baffle (PPB), wavy-shaped plate baffle (WSB) and polygonal-shaped plate baffle (PSB) are four commonly used baffles in parallel flow shell and tube heat exchangers (STHXs). Comparative study of these four different baffles are numerically carried out using different performance indicators including Nusselt number, friction factor, performance evaluation criterion, entropy generation ratio, and entransy dissipation ratio for flow in full turbulent regime. Heat transfer mechanism has also been discussed. Correlations for Nusselt number and friction factor are fitted and the cost estimation using Hall’s method is compared. It is found that the Nusselt number of STHX-PPB, STHX-WSB, and STHX-PSB increased by 20.9%, 15.2%, and 23.9% averagely compared with STHX-RRB, respectively. The friction factor can be increased on average by 142.0%, 154.5%, and 242.4%, respectively. However, the overall performance of them is only 90.1%, 84.4%, and 82.3% that of STHX-RRB, respectively. The sequence of entropy generation and entransy dissipation is STHX-RRB > STHX-WSB > STHX-PPB > STHX-PSB. The inlet Re and baffle distance have significant effects on different performance indicators while the baffle width does not. Finally, the results show that the STHX-PSB can reduce the total cost as it has better ability on heat enhancement.

Natural Convective Coutte Flow in a Vertical Parallel Plate Microchannel

2014 ◽  
Vol 705 ◽  
pp. 182-187 ◽  
Author(s):  
Marneni Narahari ◽  
Rajashekhar Pendyala
Keyword(s):  
Nusselt Number ◽  
Flow Rate ◽  
Parallel Plate ◽  
Volume Flow Rate ◽  
Fluid Velocity ◽  
Volume Flow ◽  
Grashof Number ◽  
Dimensionless Velocity ◽  
Vertical Heat ◽  
Vertical Heat Flux

In the present paper, the exact analysis of steady state fully developed natural convective Couette flow in a vertical parallel plate microchannel is performed. Exact solutions are derived for the dimensionless velocity, temperature, volume flow rate, vertical heat flux and Nusselt number. The effects of Grashof number, wall-ambient temperature difference ratio and Knudsen number on the velocity, volume flow rate and Nusselt number have been discussed through graphs. The study revealed that the fluid velocity and volume flow rate increases with increasing Grashof number whereas the Nusselt number decreases with increasing Grashof number.

Numerical Investigation of Turbulence Models for Minichannels

2010 ◽  
Author(s):  
Emrah Deniz ◽  
Nur Pehlivanoglu
Keyword(s):  
Nusselt Number ◽  
Friction Factor ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Turbulent Regime ◽  
Diameter Range ◽  
Micro Channels ◽  
Flow Through ◽  
Conventional Models ◽  
Stress Models

Due to having considerably small diameters compared to the macro channels; validation of conventional models and correlations and, examination of heat transfer and flow characteristics for mini/micro channels have been an attractive subject for last decades. In this study, classical turbulence models are compared and applicability of the conventional correlations is investigated for the flow through minichannels having diameter range between 1.2 and 0.25 mm. For the flow considered, fluid (R134a) enters the horizontal channel with a prescribed temperature and velocity, absorbs heat from the surrounding and then leaves the channel. Reynolds number is chosen in a range between 5000 and 20000 in order to cover the turbulent regime. For the first step of the study, in order to investigate the use of conventional turbulence models, Standard k-ε, RNG k-ε, Realizable k-ε, Standard k-w and Reynolds Stress models are employed to estimate friction factor and Nusselt number values for 0.5 mm diameter channel. These numerical results are compared with those calculated by conventional correlations existing in the literature. According to the comparison, none of the models create a dramatically deviation and Standard k-ε is determined as the model giving the closest results to the conventional values. As second step of the study, Standard k-ε model is applied for the flow through the minichannels having diameter of 1.2, 1, 0.8, 0.5 and 0.25 mm, respectively. Friction factor and Nusselt number values estimated numerically via Standard k-ε model are compared with those calculated by conventional correlations and existing relevant experimental data. According to the study, it is concluded that the numerical friction factor values are found to be close to the conventional values. The most discrepancy exists when diameter is less than and equal to 0.5 mm. Furthermore, numerical Nusselt number values are found to be close to conventional values estimated with the correlation proposed by Gnielinski (1976) while they are lower estimated for channels having diameter of 1.2, 1 and 0.8 mm and over estimated for 0.5 and 0.25 mm diameter channels. As a result, conventional correlations and turbulence models are found to be applicable for the diameter range and the flow investigated.

scholarly journals Heat Transfer and Pressure Drop in Wavy-Walled Tubes: A Parameter-BASED CFD Study

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 202
Author(s):  
Malik Muhammad Nauman ◽  
Muhammad Sameer ◽  
Murtuza Mehdi ◽  
Asif Iqbal ◽  
Zulfikre Esa
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Experimental Comparison ◽  
Turbulent Regime ◽  
Qualitative Comparison ◽  
Laminar And Turbulent Flow ◽  
Order Of Magnitude

Co-relations of friction factor and Nusselt number for plain tubes have been widely developed, but less analysis has been done for tubes with wavy surfaces. This paper uses the Computational Fluid Dynamics (CFD) tool for the analysis of heat transfer and pressure drop in wavy-walled tubes, which can be utilized as a heating element for fluids. An investigation was done for the effect of Reynolds number (Re) and wavy-walled tube geometry on friction factor and Nusselt number of laminar and turbulent flow inside wavy-walled tubes. The numerical results and experimental comparison indicate that heat transfer and pressure drop for water are significantly affected by wavy-walled tube parameters and flow Reynolds number. These wavy-walled tubes are capable of increasing the heat transfer to or from a fluid by an order of magnitude but at an expense of higher pumping power. This ratio was found to remain at the minimum at a wave factor of 0.83 for 34 < Re < 3500 and maximum at a wave factor of 0.15 for 200 < Re < 17,000. New correlations of friction factor and Nusselt number based on wavy-walled tube parameters are proposed in this paper, which can serve as design equations for predicting the friction factor and heat transfer in wavy-walled tubes under a laminar and turbulent regime with less than 10% error. The quantitative simulation results match the experimental results with less than 15% error. The qualitative comparison with the experiments indicates that the simulations are well capable of accurately predicting the circulation zones within the bulgy part of the tubes.

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