Plate Finned-tube Heat Exchangers Research Articles

Wet cooling of air oN plate finned tube heat exchangers

The objective of this paper is to provide the reliable calculation procedure for determining heat and mass flow rates for plate finned tube heat exchangers in dehumidification regimes that can be used easily in engineering practice. For this purpose, the experiments are conducted on two heat exchangers, and datasets for six more heat exchangers are used from literature. Comprehensive database is established with total of 637 sets of data, and it gathers 365 new measurement sets and 272 sets from open literature. The new calculation procedure predicts heat transfer rate and condensate flow rate where new methodology approach (based on the porous velocity, the ratio of characteristic surfaces and hydraulic diameter) is used. Predicted results show 5 to 10 % deviation for heat duty and up to 20 % for mass flow rate from experimental results, which is of importance to industrial practice.

Novel study on inverse convection–conduction heat transfer for plate-finned tube heat exchanger

Novel study on inverse convection–conduction heat transfer for plate-finned tube heat exchanger

Analysis of the thermal improvement of plate fin-tube heat exchanger with straight and curved rectangular winglet vortex generators

A novel combination of curved and straight rectangular winglet vortex generator (RWVG) pairs was arranged in a common-flow-up (CFU) configuration on plate fins for enhancing the comprehensive performance of the fin-tube heat exchanger. The effects of RWVGs were compared with those of non-RWVGs for flow streamline, temperature distribution, and pressure field. Then the thermohydraulic performance and the comprehensive performance were numerically investigated among the cases with varied locations and sizes of RWVGs. The results revealed that j for all cases with RWVGs was higher than non-RWVGs and the values of JF were greater than 1.0 for all cases except for case 4. Especially, apparent improvements in heat transfer characteristics and comprehensive performance were observed with the novel combination. Furthermore, it was found that the appropriate location and size of RWVGs were able to influence the thermohydraulic characteristic positively. The curved RWVGs with a smaller offset showed better comprehensive performance, and the larger attack angle of the straight RWVGs was accompanied by a higher heat transfer intensity and a greater flowing drag force. Moreover, the curved RWVGs with a larger arc angle performed better in the comprehensive performance, and the length of the straight RWVGs was larger and JF smaller.

Performance Prediction of Plate-Finned Tube Heat Exchangers for Refrigeration: A Review on Modeling and Optimization Methods

Finned tube heat exchangers are used in many technological applications in both civil and industrial sectors. Their large-scale use requires a design aimed at reaching high thermal efficiency as well as avoiding unnecessary waste of resources in terms of time and costs. Therefore, in the last decades, research in this area has developed considerably and numerous studies have been conducted on modeling in order to predict heat exchangers (HXs) performance and to optimize design parameters. In this paper, the main studies carried out on plate-finned tube HXs have been collected, analyzed, and summarized, classifying existing models by their scale approach (small, large, or multi-scale). In addition, the main methods of design optimization with a focus on circuitry configurations have been illustrated. Finally, future developments and research areas that need more in-depth analysis have been identified and discussed.

Experimental investigation of heat transfer and pressure drop of fin and tube heat exchanger under dry and wet conditions

The heat transfer and pressure drop characteristics of nine flat plate finned tube heat exchangers have been experimentally investigated under dry and wet conditions. The effect of five parameters is evaluated for wet conditions: number of tube row (2, 4, 6), fin pitch (2, 3, 4 mm), frontal air velocity (1, 2, 3 m/s), temperature (25, 30, 35 °C), and relative humidity (60, 70, 80). The Box-Behnken Design (BBD) is used to determine minimum candidate test points of the experimental studies, and more experiments have been carried out to determine the effects more sensitively. For nine heat exchangers, the effect of frontal air velocity (1, 2, 3 m/s) is evaluated for dry conditions. (The Reynolds number ranged from 300 to 2150 for both conditions.) Response Surface Model (RSM) has been used to evaluate the Colburn j factor and Fanning friction f factor for dry and wet conditions. The results show that the j factor decreases with increasing front air velocity and number of tube rows, while the j factor increases with increasing fin pitch, air temperature, and relative humidity for wet conditions. In addition, the f factor decreases with increasing front air velocity, number of tube rows and fin pitch, while the f factor increases with increasing air temperature and relative humidity. For dry conditions, the j factor decreases with increasing front air velocity and number of tube rows, while the j factor increases with increasing fin pitch. In addition, the f factor decreases with increasing front air velocity, number of tube rows, while the f factor increases with increasing fin pitch. The j factor and f factor values are higher under wet conditions than dry conditions.Three correlations are proposed for the j and f factors under dry and wet conditions. For wet conditions, the best mean deviation for the j factor is 8.3%, whereas the best mean deviation for the f factor is 10.9%. For dry conditions, the best mean deviation for the j factor is 8.3%, whereas the best mean deviation for the f factor is 8.2%. The experimental results are compared with the proposed and literature correlations.Compared to the correlations obtained in literature studies using similar geometric parameters in the study, the proposed correlation has gave better results. Even at the values of geometric parameters which literature correlations are failed, the proposed correlations has gave good results.

Study of the Influence of the Lack of Contact in Plate and Fin and Tube Heat Exchanger on Heat Transfer Efficiency under Periodic Flow Conditions

Plate fin-tube heat exchangers are widely used in air conditioning and refrigeration systems and other industry fields. Various errors made in the manufacturing process can result in the formation of an air gap between the tube and fin. Several numerical simulations were carried out for a symmetric section of plate fin-tube heat exchanger to study the influence of air gap on heat transfer under periodic flow conditions. Different locations and sizes of an air gap spanning 1/2 circumference of the tube were considered for the range of airflow velocities. Velocity and temperature fields for cases with air gap were compared with ideal thermal contact cases. Blocking of heat flow by the gap leads to the reduction of heat transfer rate. Fin discontinuity in the front of the tube causes the smallest reduction of the heat transfer rate in comparison to the ideal tube-fin contact, especially for thin slits. The rear gap position is the worst in the smallest gap range. Therefore, reversing the flow direction can lead to up to a 15% heat transfer increase, if mainly the rear gaps are present. The introduction of a thin slit in the front of the tube leads to convective heat transfer enhancement, which should be further investigated.

Performance Evaluation of a Single-Stage Two-Bed Adsorption Chiller With Desalination Function

Abstract Energy efficiency is one of the most important topics nowadays. It is strictly related to the problem of energy demand, energy policy, environmental pollution, and economic issues. Because of the technological development, using more advanced processes in almost every part of industry and increasing demands both for a high standard of living and simplification of processes, the energy demand is growing. This can be observed, e.g., in the building sector—air conditioning is present in almost every new building and people expect high quality thermal conditions. At the same time, many technological processes result in dissipating energy to the environment. Energy efficiency can be increased and operation costs reduced by using waste heat in other processes. One of the possibilities is to use sorption chillers to produce cool and desalinated water. Low temperature waste heat is not easy to utilize because of low energy potential. Using adsorption chillers in low temperature conditions allows utilizing waste heat and producing useful products in many regions of the world. The paper presents the results of experimental study carried out on three-bed adsorption chiller with desalination, using silica gel and water as the working pair. The chiller was equipped with plate-fin tube heat exchanger filled with silica gel with a grain size of 0.5–1.5 mm. The laboratory test stand included one evaporator, one condenser, and three separate tanks for water, desalinated water, and brine, respectively. The test stand scheme and description were presented. All results were obtained during a few hours test with stable temperature conditions in the range of 55–85 °C for the heating water.

Optimizing Thermal Behavior of Flat Plate Heat Exchanger Tube by Varying Geometrical Configuration

A plate fin heat exchanger is a type of heat exchanger design that uses plates and finned chambers to transfer heat between liquids. It is often classified as a compact heat exchanger to emphasize the relatively high ratio between the heat transfer surface and the volume. The main objective of the present work is to investigation of optimum design of plate fin tube heat exchanger using Computational fluid dynamic approach and maximizing thermal performance. There are total five designs of plate fin and tube heat exchanger are used in present work and CFD analysis have been performed in it to get maximum heat transfer. It has been observed from CFD analysis that the maximum heat transfer can be achieved from plate fin and tube heat exchanger with elliptical tube arrangement inclined at 30o with 23.22% more heat transfer capacity as compared to circular tube plate pin heat exchanger. So that it is recommended that if the plate fins and tube heat exchanger with inclined elliptical tube used in place of circular tube arrangement, batter heat transfer can be achieved.

Anti-freezing prediction model for different flow patterns of air-cooled heat exchanger

Water heat load may get lower than the huge cooling capacity of air for air-cooled heat exchanger in winter, resulting in the freezing risk of finned tube bundles, so the water temperature distribution inside the tube under various working conditions stands the premise issue for the security and energy efficiency of dry cooling system. Based on the energy balance and heat transfer analyses, the anti-freezing prediction model of air-cooled heat exchanger is developed and experimentally validated at different low ambient temperatures with the maximum deviation of 16%. Taking a six-row plate finned tube heat exchanger as the research object, the water temperature distribution in any tube and the critical anti-freezing parameters are obtained with different air/water flow patterns at various ambient temperatures, air face velocities, inlet water temperatures, and water flow rates. The results show that the finned tube bundle with slotted fins is superior to the flat fins in heat transfer performance, but faces more serious freezing risks in cold winter. In the baseline case, the average outlet water temperature of the slotted finned tube bundle decreases by 3.9 °C compared to the flat finned tube bundle. For the air/water cross-counter flow pattern, the critical freezing position is fixed and appears at the water exit of upwind row. While for the air/water cross-cocurrent flow, the minimum water temperature varies with operating conditions, but it always happens at the row 1 or row 4. The anti-freezing of air-cooled heat exchanger can be realized by reasonably matching the air/water heat capacity as well as transforming the air/water flow patterns. The proposed anti-freezing prediction model is of potential benefit to the real-time temperature distribution forecast, freezing analyses, and control strategies for air-cooled heat exchanger in winter.

Natural convection of plate finned tube heat exchangers with two horizontal tubes in a chimney: Experimental and numerical study

This study uses a hybrid method of computational fluid dynamics (CFD) and inverse heat conduction analysis (IHCA) combined with experimental temperatures to investigate the natural convection of plate finned tube heat exchangers with two horizontal tubes located in a chimney. The influence of the position of the two heated tubes on the results obtained is considered. IHCA combined with experimental temperatures is used to estimate h¯ and h¯b. Subsequently, the CFD commercial software combined with the obtained inverse results and experimental temperatures is employed to get the present results. The results reveal that the zero-equation turbulence model can be applied to determine more accurate results than the other two flow models. Therefore, the appropriate flow model for this study is the zero-equation turbulence model. The fringe pattern for each heated tube is mainly aligned in the vertical direction and the two plumes are slightly inclined toward the inward direction. The obtained velocity pattern and air temperature contour are consistent with existing interferometric images or isotherms. The proposed correlation between Ra and Nu agrees with the obtained inverse and CFD results.

Air side heat transfer coefficient in plate finned tube heat exchangers

ABSTRACTIn order to establish a reliable procedure for estimation of heat transfer coefficient, experiments on plate finned tube heat exchangers have been conducted on five exchangers. Using own and previously published experimental data databank of 969 working regimes, a new correlation was formed. Correlation is based on hydraulic diameter and porous velocity and on the ratio of characteristic surfaces of the finned tube bundle. Statistical parameters of a new correlation for estimation of heat transfer coefficient are very good, and correlation covers a wide range of geometrical and other parameters of heat exchangers that are industrially important.

Optimization Performance on Plate Fin Tube Heat Exchanger

The main objective of the present work is to investigation of optimum design of plate fin tube heat exchanger using Computational fluid dynamic approach and maximizing thermal performance. There are total five designs of plate fin and tube heat exchanger are used in present work and CFD analysis have been performed in it to get maximum heat transfer. It has been observed from CFD analysis that the maximum heat transfer can be achieved from plate fin and tube heat exchanger with elliptical tube arrangement inclined at 30o with 23.22% more heat transfer capacity as compared to circular tube plate pin heat exchanger. So that it is recommended that if the plate fins and tube heat exchanger with inclined elliptical tube used in place of circular tube arrangement, batter heat transfer can be achieved.

Experimental Studies on Performance Parameters of Finned Tube Heat Exchanger for Waste Heat Recovery.

The demand for energy is rising significantly due to growth of nations. The use of diesel engines for the purpose of transportation is increasing because of their high efficiency and robustness. Around 30% of the input energy is carried by the engine exhaust gas, which in turn reduces thermal efficiency and increases environmental pollution. With an objective of waste heat recovery and reduction in pollution due to engine exhaust, this work focuses on the theoretical and experimental analysis of performance parameters of continuous plate fin-tube heat exchanger for waste heat recovery at simulated engine conditions. From the experimental data it was observed that fin tube heat exchanger is one of the best heat exchangers for recovery of waste heat at lower fluid flow rates and higher inlet temperatures. The heat recovered is calculated to be 110W, 60W and 52W at hot gas flow rates of 150, 170 and 190LPM respectively.

Air side pressure drop in plate finned tube heat exchangers

Previous researches have proved that newly introduced parameters such as void velocity and others can be successfully used for correlating the heat transfer and pressure drop parameters. In order to establish a reliable procedure for estimation of air pressure drop, experiments on plate finned tube heat exchangers have been conducted, as well as the extensive investigation of the open literature. Using own and previously published experimental data, new correlation for estimation of air pressure drop have been established, covering a wide range of parameters of industrial importance. New correlation is comprehensive and statistically superior to any other pressure drop correlation.

A hybrid numerical-experimental analysis of heat transfer by forced convection in plate-finned heat exchangers

A hybrid numerical-experimental approach to obtain the thermal performance of heat exchangers is presented. The proposed methodology combines numerical simulation with wind tunnel experimental data to predict the average convective heat transfer coefficient and overall finned surface efficiency. The technique is applied to a plate-finned tube heat exchanger with in-line arrangement. Validation of the present methodology is performed by comparing the results against empirical correlations for the Nusselt number available in the literature. A parametric study is performed aiming to evaluate the influences of the airflow velocity (Reynolds number) and fin materials (aluminium, carbon steel and copper) upon the heat transfer characteristics. The main results indicate an increase of the average convective heat transfer coefficient with air velocity; whereas the overall fin surface efficiency presents an opposite behaviour. Furthermore, the Nusselt number based on the overall heat transfer coefficient is larger for higher conductive fin materials. In addition, aluminium and steel fins are found to be the most weight and cost-effective fin materials, respectively.

Reconsideration of data and correlations for plate finned-tube heat exchangers

This paper deals with heat exchangers having plain finned tubes in staggered (triangular) pattern. The objective of this paper is to provide the heat transfer and friction factor correlation which can be used in engineering practice. For this purpose, the experimental data of several (most cited) authors who deal with this type of heat exchangers are used. The new correlations are established to predict the air-side heat transfer coefficient and friction factor as a function of the Reynolds number and geometric variables of the heat exchanger – tube diameter, tube pitch, fin spacing, tube rows, etc. In those correlations the characteristic dimension in Reynolds number is calculated by using the new parameter – volumetric porosity. Also, there are given the errors of those correlations.

An experimental, computational and flow visualization study on the air-side thermal and hydraulic performance of louvered fin and round tube heat exchangers

The aim of this study is to determine heat transfer and pressure drop characteristics in different louvered fin geometries for manufacturing of commercial louvered fin and round tube heat exchangers. Numerical simulations were carried out for various louver angles, louver lengths (pitches), fin pitches and frontal air velocities. The heat transfer and pressure drop characteristics of the louvered fin and round tube heat exchangers, Colburn and friction factors, were respectively normalized with Colburn and friction factors of the flat plate fin and round tube heat exchangers operating under the same conditions and they were presented as the relative Colburn factor j∗ and the relative friction factor f∗. Thermal & hydraulic performance was presented as JF∗. Temperature and local Nusselt number contours, and streamline patterns were provided to reveal the mechanisms behind the heat transfer enhancement. Among different heat exchangers for which heat transfer and pressure drop characteristics were obtained, one was chosen to manufacture a real size heat exchanger. Flow visualization studies were also conducted with a PIV system in an open water channel to determine whether the flow structure is louvered directed or not. The louvered fin heat exchanger tested in the PIV system was a five times scaled up model of the real size louvered fin heat exchanger and made from a transparent plexiglas material. PIV results were presented and evaluated based on streamlines and velocity vectors. Furthermore, a numerical analysis was performed using exactly the same dimensions and conditions of the model tested in the PIV system. The comparison between numerical and experimental results was done to validate the numerical model. Consequently, the performance of the fabricated real size heat exchanger was tested at different air velocities in a wind tunnel in a conditioned room. The experimental results were compared with numerical analyses and found to be compatible with each other. Finally, thermal and hydraulic performance of the louvered fin and round tube heat exchanger was compared with a wavy fin and round tube heat exchanger with identical size and specifications. It was found that the thermal and hydraulic performance of the louvered fin and round tube heat exchanger is higher than that of the wavy fin and round tube heat exchanger. The Colburn factor j, friction factor f and JF of the louvered fin and round tube heat exchanger are higher about 16.8–7%, 19.9–8.2% and 10–4.3% than that of the wavy fin and round tube heat exchanger depending on the Reynolds number, respectively.

Thermal and hydraulic performance of a compact plate finned tube air-fuel heat exchanger for aero-engine

The article presents a novel compact plate finned-tube air-fuel heat exchanger which is designed by means of using logarithmic mean temperature difference method (LMTD) and both thermal and hydraulic performance of the heat exchanger are experimentally investigated. Worldwide, due to the harsh working condition, both aviation industry and aerospace industry department are in badly need of compact heat exchanger with light weight and high efficiency. In this paper, the design, manufacture and tests of a prototype, plate finned tube heat exchanger are presented. The stainless-steel heat exchanger weights 1.207kg and by using the fuel RP-3 as the coolant, it can cool the high-temperature air from high pressure compressor in aircraft engine in a very limited space. The study of flow resistance in air-fuel flow allows determining the flow friction factor. Experimental values of heat transfer for the heat exchanger are also calculated. In addition, obtained values of heat transfer coefficient show some differences with literature correlations. Based on these differences, an empirical correlation for the outside heat transfer of compact finned tube heat exchanger is established, which will be helpful for the researchers to design similar heat exchangers.

Impacts of geometric structures on thermo-flow performances of plate fin-tube bundles

Continuous plate fin-tube heat exchangers are commonly applied to natural draft dry cooling system in power plants due to their excellent thermo-flow performances, but the effects of geometrical structures on the air-side flow and heat transfer characteristics have not been thoroughly clarified yet. In this study, the air-side flow and heat transfer models of plate fin-tube bundles are developed, and the numerical modeling and methods are validated by the experimental test. The thermo-flow characteristics of the plate fin-tube bundles at various parameters of air face velocity, fin oblique angle, fin spacing, fin thickness and tube external diameter are numerically simulated. The buoyancy effect due to natural convection is also investigated. The results show that the performance evaluation criterion (PEC) varies little with the fin oblique angle. As the fin spacing increases, the average PEC will increase despite of a considerable heat transfer reduction. The increased fin thickness and tube external diameter are both beneficial to the thermo-flow characteristics, but the buoyancy effect on the flow and heat transfer performances can be neglected. The fin oblique angle of 30°, fin spacing of 10 mm, fin thickness of 0.3 mm and tube external diameter of 18 mm are recommended within the scope of investigation. The correlations between the Nusselt number, friction factor and the Reynolds number and geometrical parameters are recommended using the orthogonal experimental design method, which can be used to the optimal design of air-cooled heat exchanger in power plants.

Development of cooling system for 66/6.9kV-20MVA REBCO superconducting transformers with Ne turbo-Brayton refrigerator and subcooled liquid nitrogen

We developed a turbo-Brayton refrigerator with Ne gas as a working fluid for a 3 ϕ- 66/6.9kV-2MVA superconducting transformer with coated conductors which was bath-cooled with subcooled LN2. The two-stage compressor and expansion turbine had non-contact magnetic bearings for a long maintenance interval. In the future, we intend to directly install a heat exchanger into the Glass-Fiber-Reinforced-Plastics cryostat of a transformer and make a heat exchange between the working fluid gas and subcooled LN2. In this paper we investigate the behaviour of subcooled LN2 in a test cryostat, in which heater coils were arranged side by side with a flat plate finned-tube heat exchanger. Here a He turbo-Brayton refrigerator was used as a substitute for a Ne turbo-Brayton one. The pressure at the surface of LN2 in the cryostat was one atmosphere. Just under the LN2 surface, a stationary layer of LN2 was created over the depth of 20 cm and temperature dropped from 77 K to 65 K with depth while, in the lower level than that, a natural convection flow of LN2 was formed and temperature was almost uniform over 1 m depth. The boundary plane between the stationary layer and the natural convection region was visible.