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.

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.

Heat and Mass Transfer to Air in a Cross Flow Heat Exchanger with Surface Deluge Cooling

2016 ◽  
Vol 24 (01) ◽  
pp. 1650002 ◽  
Author(s):  
Andrea Diani ◽  
Luisa Rossetto ◽  
Roberto Dall’Olio ◽  
Daniele De Zen ◽  
Filippo Masetto
Keyword(s):  
Heat Exchanger ◽  
Heat Flow ◽  
Flow Rate ◽  
Data Center ◽  
Heat Dissipation ◽  
Cross Flow ◽  
Critical Conditions ◽  
Heat Flow Rate ◽  
External Temperature ◽  
Flow Heat

Cross flow heat exchangers, when applied to cool data center rooms, use external air (process air) to cool the air stream coming from the data center room (primary air). However, an air–air heat exchanger is not enough to cope with extreme high heat loads in critical conditions (high external temperature). Therefore, water can be sprayed in the process air to increase the heat dissipation capability (wet mode). Water evaporates, and the heat flow rate is transferred to the process air as sensible and latent heat. This paper proposes an analytical approach to predict the behavior of a cross flow heat exchanger in wet mode. The theoretical results are then compared to experimental tests carried out on a real machine in wet mode conditions. Comparisons are given in terms of calculated versus experimental heat flow rate and evaporated water mass flow rate, showing a good match between theoretical and experimental values.

scholarly journals Thermal Calculations of Four-Row Plate-Fin and Tube Heat Exchanger Taking into Account Different Air-Side Correlations on Individual Rows of Tubes for Low Reynold Numbers

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6978
Author(s):  
Mateusz Marcinkowski ◽  
Dawid Taler ◽  
Jan Taler ◽  
Katarzyna Węglarz
Keyword(s):  
Nusselt Number ◽  
Heat Exchanger ◽  
Heat Flow ◽  
Least Squares Method ◽  
Heat Output ◽  
Optimum Number ◽  
Heat Flow Rate ◽  
Cfd Modelling ◽  
Tube Heat Exchanger ◽  
Average Value

Currently, when designing plate-fin and tube heat exchangers, only the average value of the heat transfer coefficient (HTC) is considered. However, each row of the heat exchanger (HEX) has different hydraulic–thermal characteristics. When the air velocity upstream of the HEX is lower than approximately 3 m/s, the exchanged heat flow rates at the first rows of tubes are higher than the average value for the entire HEX. The heat flow rate transferred in the first rows of tubes can reach up to 65% of the heat output of the entire exchanger. This article presents the method of determination of the individual correlations for the air-side Nusselt numbers on each row of tubes for a four-row finned HEX with continuous flat fins and round tubes in a staggered tube layout. The method was built based on CFD modelling using the numerical model of the designed HEX. Mass average temperatures for each row were simulated for over a dozen different airflow velocities from 0.3 m/s to 2.5 m/s. The correlations for the air-side Nusselt number on individual rows of tubes were determined using the least-squares method with a 95% confidence interval. The obtained correlations for the air-side Nusselt number on individual rows of tubes will enable the selection of the optimum number of tube rows for a given heat output of the HEX. The investment costs of the HEX can be reduced by decreasing the tube row number. Moreover, the operating costs of the HEX can also be lowered, as the air pressure losses on the HEX will be lower, which in turn enables the reduction in the air fan power.

scholarly journals Energy analysis of heat exchanger in a heat exchanger network

2018 ◽  
Vol 22 (5) ◽  
pp. 1999-2011 ◽  
Author(s):  
Martina Rauch ◽  
Antun Galovic
Keyword(s):  
Mathematical Model ◽  
Heat Exchanger ◽  
Heat Flow ◽  
Flow Rate ◽  
Local Extremum ◽  
Heat Flow Rate ◽  
Fluid Stream ◽  
Heat Exchanger Network ◽  
Maximum Heat ◽  
The Given

For many years now, heat exchanger optimization has been a field of research for a lot of scientists. Aims of optimization are different, having in mind heat exchanger networks with different temperatures of certain streams. In this paper mathematical model in dimensionless form is developed, describing operation of one heat exchanger in a heat exchanger network, with given overall area, based on the maximum heat-flow rate criterion. Under the presumption of heat exchanger being a part of the heat exchanger network, solution for the given task is resting in a possibility of connecting an additional fluid stream with certain temperature on a certain point of observed heat exchanger area. The connection point of additional fluid stream determines the exchanging areas of both heat exchangers and it needs to allow the maximum exchanged heat-flow rate. This needed heat-flow rate achieves higher value than the heat-flow rate acquired by either of streams. In other words, a criterion for the existence of the maximum heat-flow rate, as a local extremum, is obtained within this mathematical model. Results of the research are presented by the adequate diagrams and are interpreted, with emphasis on the cases which fulfill and those which do not fulfill the given condition for achieving the maximum heat-flow rate.

scholarly journals Heat Transfer and Friction Factor Characteristics of Heat Exchanger using Aluminium Oxide and Titanium Oxide

2019 ◽  
Vol 8 (3) ◽  
pp. 2950-2952
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Flow ◽  
Titanium Oxide ◽  
Flow Rate ◽  
Liquid Flow ◽  
Aluminium Oxide ◽  
Plain Water ◽  
Heat Flow Rate ◽  
Nano Fluids

t A heat flow and fluid flow investigation of double tube heat exchanger by means of warped tape insert under the mixing water based nano fluids. In this article Aluminium oxide and Titanium oxide was used to get better performance heat exchanging device. A different mass flow rate of fluids used to conduct the experiment and gathered various surface temperature for analyses the heat flow augmentation. A heat flow rate Nano fluids 10 to 12% was enhanced compare with the plain base water. A heat flow with liquid flow Aluminum oxide was enhanced with +8% compare with the plain base water. A heat transfer characteristics titanium oxide were augment with raise of Re and 12% was augmented compare with the plain water. However heat flow and liquid flow heat exchanging device was increasing with volume of Nano fluids increased and leading to friction facto

CFD SIMULATION OF A PLATE HEAT EXCHANGER WITH TRAPEZOIDAL CHEVRON

2016 ◽  
Vol 78 (8-4) ◽  
Author(s):  
Chin Yung Shin ◽  
Normah Mohd-Ghazali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Friction Factor ◽  
Cfd Simulation ◽  
General Pattern ◽  
Plate Heat Exchanger ◽  
Plate Heat ◽  
Flow Configuration ◽  
Heat Transfer Capacity

In this research, the trapezoidal shaped chevron plate heat exchanger (PHE) is simulated using computational fluid dynamics (CFD) software to determine its heat transfer capacity and friction factor. The PHE is modelled with chevron angles from 30° to 60°, and also the performances are compared with the plain PHE. The validation is done by comparing simulation result with published references using 30° trapezoidal chevron PHE. The Nusselt number and friction factor obtained from simulation model is plotted against different chevron angles. The Nusselt number and friction factor is also compared with available references, which some of the references used sinusoidal chevron PHE. The general pattern of Nusselt number and friction factor with increasing chevron angle agrees with the references. The heat transfer capacity found in current study is higher than the references used, and at the same time, the friction factor also increased. Besides this, it is also found that the counter flow configuration has better heat transfer capacity performance than the parallel flow configuration.

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