Performance Of Tube Heat Exchangers Research Articles

Improvement of tube heat exchanger performance with perforated ring inserts, tube rotation and using nanofluids

Many engineering applications, such as waste heat recovery, air-conditioning and refrigeration systems, include heat exchangers. In this work, the performance of a double-tube heat exchanger with a rotating tube, perforated ring inserts and nanofluids as working fluids has been studied. After developing a 3D numerical model, verifying its discretization and validating it with experimental results, an optimal design for maximizing heat transfer while keeping a relatively low pressure drop was found (11 eight-holed rings with a 2.2 pitch ratio). Increasing the cold fluid Reynolds number to 4946 and the inner tube rotational speed to 500 rpm increased the heat transfer coefficient from around 7500 to 9500 W (m2 K)−1. Considering the nanofluids studied, the best performance was found with Cu nanoparticles, followed by Al2O3–Cu and Al2O3. With Cu nanoparticles at 3%, heat transfer coefficients above 12,100 W (m2 K)−1 were obtained, increasing heat exchanger effectiveness from 27 to 51%. Pressure drop levels increased up to 235 Pa, resulting in increasing pumping requirements by around 0.1 kJ kg−1. Hence, only very high flowrates would represent a problem when using the exchanger. Explanations for the underlying physical phenomena that cause the enhancement of heat transfer due to the rotational speed, the perforated rings and the nanofluids were provided. Turbulent kinetic energy contours, flow streamlines, and temperature contours were used to gain insight into the thermal and flow fields, identifying the mechanisms responsible for the enhancement of the heat exchanger effectiveness.

Experimental and numerical investigations on the effect of a novel internal surface micro-grooving toward improving convective heat transfer performance of tube heat exchangers

In the present work, the use of passive heat transfer enhancement technique through surface alteration was explored. The enhancement was achieved through internal conduit surface micro-grooving using a new apparatus that was developed by modifying a magnetic abrasive finishing technique. A new surface profile was created and later verified using optical and laser profiler measurements. The new profile was numerically investigated to compare the heat transfer and hydrodynamic performance against other profiles that have been studied in the literature. It was found from the results that the new profile shows much higher heat transfer improvement and comparable pressure loss to the previously investigated profiles (i.e., square, rectangular, trapezoidal, and circular). Overall, the new groove geometry provides the highest performance followed by the circular, triangular, curvy, square, and rectangular grooves. Also, the results indicate that designs with a smooth profile performs better than those with sharp edges, owing to the elimination of stationary fluid spots within the grooves. The effectiveness between the profiles was compared based on the level of heat transfer enhancement against the flow penalty. Experimental validation was further conducted for the experimentally generated groove. The results revealed that a relatively small surface temperature drop was obtained, corresponding to a slight improvement in heat transfer. This confirms the results generated by the simulation that groove size plays a major role in attaining significant improvement in heat transfer.

Sensitivity analysis of nanofluid flow over different flat tubes confined between two parallel plates using Taguchi method and statistical analysis of variance

In this research, the effect of simultaneous use of nanofluids and flat tubes to evaluate the efficiency of heat exchangers in the fluid flow over tandem tubes between two parallel plates is investigated and analyzed. The use of effective methods to reduce the number of numerical experiments and achieve accurate and reliable analysis with statistical techniques as well as the use of passive methods to improve the performance of tube heat exchangers are investigated in this study. The focus of the research is to achieve the optimal values of controlling factors, determine the effectiveness of each variable and evaluate the hydraulic and thermal behaviors of the flow structure. For this purpose, nanofluid containing aluminum oxide nanoparticles with volume fractions of 0–8%, flat tubes with 1.5, 2, 2.5 axial ratios, and square sections in comparison with circular tubes are used. Constant temperature boundary conditions are applied on the confining plates and the surface of the tubes. To perform sensitivity analysis, the Taguchi method with L25 orthogonal array and statistical analysis of variance (ANOVA) are utilized. The obtained results show that by changing the cross-section and further flattening, heat transfer and pressure drop decrease concurrently. Moreover, with increasing the volume fraction of nanoparticles, both parameters related to heat transfer rate and flow pressure drop increase. Examining the combination of the two output parameters of the flow and obtaining the efficiency evaluation criterion, it is determined that flattening the tubes, in contrast to increasing the volume fraction of nanoparticles, increases the efficiency of the heat exchanging modules. One of the important results obtained in utilizing the Taguchi method with ANOVA analysis, in addition to reducing the numerical calculations by 80%, is accurate and reliable findings that are confirmed by comparison with the full factorial method.

Numerical Study of Shell and Tube Heat Exchanger Performance Enhancement Using Nanofluids and Baffling Technique

The aim of this work is to investigate the forced convective heat transfer phenomena and fluid flows of water-based Al2O3 nanofluids in the baffled shell and tubes heat exchanger (STHE). Water as a hot fluid flows in the side of the tubes, and Al2O3 nanofluids as cooling fluid flow in the shell side. Numerical investigations have been carried out based on the continuity, momentum, and energy equations which are solved by using the finite element method with the help of the COMSOL 5.4 CFD software. The obtained results were presented by average Nusselt number, streamlines, isotherms, and various physical parameters which are a volumetric fraction of nanoparticles (1%? Cv ?3%). The results are found that the heat transfer increases with the rise of inlet velocity and volume fraction. In addition, the presence of baffles inside tubular heat exchangers can create a better mixture of fluids which is augmenting heat transfer execution. The choice of these parameters is important to get the maximum improvement of heat transfer with minimum entropy consumption.

Thermal and flow performance of tilted oval tubes with novel fin designs

We studied the thermal and flow performance of tube heat exchangers with novel fin designs for tube tilt angles of 0°, 20°, 30° and 40° to the horizontal. The novel fin designs target to enhance the conduction heat transfer within the fin and the convective heat transfer along the fin surface simultaneously. Tubes with three different fin designs, the circular plain fin (CPF), the circular integrated pin fin (CIPF) and the serrated integrated pin fin (SIPF), were additively manufactured by selective laser melting and experimentally investigated in an air flow channel for Reynolds number between 1800 and 7800. We analysed the performance evaluation criterion, the volumetric heat flux density and the global performance criterion. It was found, that the SIPF achieves highest performance evaluation criterion and the CPF performs worst. Thus, the SIPF is recommended, when the required surface area, the material cost and the weight of the finned tube heat exchanger are relevant. Highest heat transfer per volume heat exchanger and temperature difference was achieved for the CIPF at highest tube tilt angle. The value of the global performance criterion strongly depends on the fin design and the tube tilt angle. For the horizontal orientation the CPF reaches highest global performance and for the 40∘ tube tilt angle the CIPF gives best performance. From the experimental data we derived appropriate heat transfer correlations for Reynolds number, Prandtl number, tube tilt angle and fin designs.

쉘-튜브 열교환기에서의 쉘쪽 유체의 특성에 따른 열교환기 성능 변화 예측 사례

쉘-튜브 열교환기에서의 쉘쪽 유체의 특성에 따른 열교환기 성능 변화 예측 사례

3D dynamic numerical programming and calculation of vertical buried tube heat exchanger performance of ground-source heat pumps under coupled heat transfer inside and outside of tube

Targeting the underground vertical buried tube heat exchangers (BTHEs) of ground-source heat pumps, a physicomathematical model of heat and mass transfer that couples the turbulent flow field in the tube with the groundwater seepage in the surrounding soil was established in this study. FORTRAN language was used to design a 3D dynamic numerical calculation program for this model, and the geotechnical thermal response test data was used to verify the reliability of this program. It also used the program to comparatively analyze the error influence of the assumption of uniform velocity flow field in the tube on heat transfer performance analysis. Considering the turbulent flow field in the tube, the influence of groundwater seepage and inlet flow velocity in buried tube on the heat transfer performance of BTHEs was further explored. The results show that the assumption of uniform velocity flow field in the tube caused a relatively significant error with the heat transfer performance analysis on buried tube, and both the soil seepage velocity and flow velocity in the tube influenced the heat transfer performance of buried tube. This study aimed to provide a programming method for the in-depth study of buried tube heat transfer performance.

Numerical Analysis of Triple Concentric Tube Heat Exchanger using Dimpled Tube Geometry

Computational Fluid Dynamic (CFD) is a useful tool in solving and analyzing problems that involve fluid flows, while triple tube concentric tube heat exchanger is the most common type of heat exchanger and widely use in chemical and food processes. In this current research to studying the Numerical Analysis of Triple Concentric Tube Heat Exchanger Using spherical shape of the Dimpled Tube Geometry, it's to create modeling and meshing the Plain and spherical dimpled geometry of triple tube concentric tube heat exchanger using the CFD package Gambit 2.4 and the boundary condition to be set before been simulate in Fluent 6.2 based on the parameters. The Hot water is flowing through in an Intermediate tube and Cold water is flowing through in an inner tube and outer tube at different Reynolds numbers. Triple Concentric tube heat exchanger performance is compared with plain and spherical shape dimpled triple concentric tube heat exchanger using CFD. From this result the simulation of in triple concentric tube heat exchanger enhancing spherical dimpled tube model to increasing the overall heat transfer coefficient, effectiveness and heat transfer rate compare to plain tube, and also calculate the flow characteristics of velocity, Nusselt number, pressure drop and Friction factor of the triple concentric tube heat exchanger spherical dimpled tube.

Numerical Investigation on Heat Transfer of Al<sub>2</sub>O<sub>3</sub>/Water Nanofluid in a Shell and Tube Heat Exchanger

In the present work, the effect of nanofluid in a shell and tube heat exchanger was studied numerically. The effects of Reynolds number, volume concentration of suspended nanoparticles on the heat transfer characteristics were investigated using CFD software. Finally, the effect of the nanofluid on Shell and tube heat exchanger performance was studied and compared to that of a conventional fluid (i.e., water).

Influence of nanofluids and rotation on helically coiled tube heat exchanger performance

The effects of using various types of nanofluids and rotation on heat transfer and fluid flow characteristics in a helically coiled tube heat exchanger (HCTHE) are numerically investigated. Mainly, the effects of nanoparticles type (Al2O3, SiO2, CuO, ZnO), its concentration (1–4%), and particle diameter (25–80nm), base fluid type (water, ethylene glycol, engine oil), towards the heat transfer and fluid flow characteristics are comprehensively analyzed. The three-dimensional steady, laminar flow and conjugate heat transfer governing equations of a balanced HCTHE are solved using the finite volume method. The results reveal that nanofluids can enhance the thermal properties and performance of the HCTHE but it is accompanied with a slight increase in pressure drop. It is found that the Nusselt number is highest using CuO–water nanofluid in this study. In addition, rotation can be used to enhance the heat transfer rates.

Experimental analysis of an air–water heat pump with micro-channel heat exchanger

A multi-port extruded (MPE) aluminium flat tube air heat exchanger was compared to a round tube finned coil (FC). The MPE heat exchanger has parallel flow vertical tube configuration with headers in horizontal position and conventional folded louvred fins. The two heat exchangers were mounted on a 10 kW cooling capacity R410A packaged air heat pump. They were sized to approximately obtain the same cooling and heating capacities in chiller and heating mode, respectively. Climatic room steady state tests without frosting phenomena occurring during heat pump operation, demonstrated that the round tube and the flat tube heat exchanger performance are comparable. The MPE heat exchanger was tested with different refrigerant inlet distributor/outlet tubes configurations to investigate the effect of liquid refrigerant distribution. Cycling frosting/defrosting operations were tested with two equivalent machines placed in parallel outdoor and working at full load condition, one of the units was equipped with the MPE heat exchanger while the other mounted a standard finned coil. Penalization factors were analytically introduced to evaluate frosting associated heating energy and energy efficiency degradation. Test results indicate that both the heat pumps are penalized by frost formation but both the penalization factors are higher for the MPE-unit than the FC-unit one in the −6 to 4 °C air dry bulb temperature range. For the two units, a roughly linear dependence of the heating energy penalization factor and of the energy efficiency factor from the difference between outdoor air and saturated air at the evaporation temperature humidity ratio can be pointed out.

Effect of tube-to-tube conduction on plate-fin and tube heat exchanger performance

We study the effect of heat transfer between the tubes of a plate-fin and tube heat exchanger by conduction through the fins. Fin conduction not only enhances heat transfer to the over-tube fluid, but also increases tube-to-tube conduction. A continuum model to evaluate this conduction is developed and conditions under which it may or may not be neglected are determined. The effect of parametric variation on the performance of a single-row plate-fin and tube heat exchanger is considered in some detail. Tube-to-tube conduction is found to degrade the performance of the heat exchanger. It is found that the same heat transfer area distributed in a different number of tubes affects its performance.