Heat Exchanger Tube Bundles Research Articles

Effectively designed NTW shell-tube heat exchangers with segmental baffles using flow hydraulic network method

In the present study, performance analysis of a shell-tube heat exchanger by using hydraulic network modeling has been employed in order to enhance the performance of the heat exchanger. Since a major component of a shell-tube heat exchanger is tubes, the aim of this paper is to study the effect of using different tube count, tube layout and tube diameter at different baffle sections on heat transfer, pressure losses and exergy destruction rate of shell-tube heat exchangers with segmental baffles. Three different modified designs with a classical design of a specimen shell-tube heat exchanger have been taken into consideration for their thermo-hydraulic performances and the results are compared. It is revealed that the modified heat exchanger, even though the number of tubes is reduced compared to the conventional design version, has better thermo-hydraulic performance, improving the original design heat transfer performance, and having lower exergy destruction rate. Eliminating window section will allow the cross and window flow to mix better and will automatically increase the heat transfer performance. The results obtained from the present method show that by elimination window-section baffles, heat transfer performance (hs/ΔPs) increased about 25–48% at different mass flow rates. Also for a shell-tube heat exchanger requiring low pressure drop No Tube at Window section design (NTW) is an alternative. So application of NTW shell-tube heat exchangers is recommended and the results of these methods are directly applicable to real design. Also using this method provides the necessary database to refine the previous empirical flow rate methods for use in the prediction of the instabilities of industrial heat exchanger tube bundles.

Experimental study on cross-flow induced vibrations in heat exchanger tube bundle

Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement (60°) with P/D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 m/s. The free stream shell side velocity ranges from 0.8 m/s to 1.3 m/s, the reduced gap velocity varies from 1.80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range.

Heat transfer challenge and design evaluation for a multi-stage temperature swing adsorption process

Functionalized solid amine-based temperature swing adsorption (TSA) processes have recently been proposed as a potential way to reduce the energy-penalty of post-combustion carbon capture processes. Thereby, multi-stage fluidized bed contactors with immersed heat exchanger surfaces and counter-current flow of solids and gas phase may solve the heat transfer challenge while maintaining the thermodynamic process requirements. Hence, the present work develops design requirements for TSA stages based on achievable heat transfer rates in bubbling fluidized beds. The considered particles are Geldart Type B. It is shown that the pressure drop of multi-stage fluidized bed TSA units for flue gas CO2 capture is practically determined by the heat exchange requirement. Scalability, maintainability and durability of different heat exchanger geometries are considered. The net movement and mixing of particles within the bubbling bed stage must be maintained in spite of the immersed heat exchangers concerning possible dead zones in the area of the tube bundles. Comprehensive models are used to predict heat transfer coefficients for tubes immersed in fluidization. A heat transfer measurement test device for optimization of the heat exchanger geometry has been put into operation and heat exchange measurement results are compared to calculated heat transfer coefficients. It is shown that experimentally obtained heat transfer rates for single tubes are in good agreement with modeled values. A model proposed for Geldart A particles is used to estimate heat transfer rates for two particular tube bundles with a tube diameter of 25mm and horizontal tube spacing of 2.2 and 2.8. It is shown that the calculated results represent heat transfer rates qualitatively and quantitatively for tube bundle heat exchangers immersed in Geldart Type B particle fluidized beds. Although this article has been motivated by heat exchange in TSA, it may be of interest for other applications concerned with heat transfer between bubbling fluidized beds and immersed heat exchanger surfaces.

Seasonal thermochemical energy storage: Comparison of the experimental results with the modelling of the falling film tube bundle heat and mass exchanger unit

This paper focuses on the assessment of a heat and mass exchanger dedicated to an absorption/desorption seasonal thermal energy storage system. The closed sorption heat storage based on water vapour absorption in aqueous sodium hydroxide (NaOH-H2O) solution theoretically achieves a significantly higher volumetric energy density compared to conventional hot water storage systems. To this purpose, a prototype designed for a power output of 10 kW was built and operated in both absorption and desorption mode under steady state boundary conditions. In this work, the influence of two main parameters on the exchanged power is evidenced. Furthermore, a comparison with the results of the initial numerical model used to design the heat and mass exchanger is carried out. On one hand it is found that, for the absorption process, the measured exchanged power is much lower than the numerically predicted value. On the other hand, for the desorption process the numerical and experimental results have the same order of magnitude. Physical explications of the strongly diverging results encountered during the absorption process as well as an improved heat transfer coefficient model for the desorption process are proposed.

Numerical investigation on synthetical performance of heat transfer of planar elastic tube bundle heat exchanger

This paper studied the synthetical performance of heat transfer in the shell-side of planar elastic tube bundle heat exchanger using numerical simulation. The temperature distribution in shell-side was studied. The relation of average heat transfer coefficient, pressure drop and comprehensive heat transfer performance were also discussed considering varying Reynolds number and geometry parameters. Results demonstrate that the temperature distribution provides a possibility to improve heat transfer by arranging the tube bundle layout to produce a fully heated fluid within full-scale shell-side. For the effect of geometry parameter, tube pitch has a greater effect on heat transfer compared to the tube-row spacing. However, Reynolds number dominates the heat transfer and fluid flow in shell-side. As a result, a prediction correlation of average Nusselt number is developed based on Reynolds number using the multiple-regression analysis of MATLAB software. A quite outstanding comprehensive heat transfer performance can be obtained in the case of tube pitch 20mm. However, the high Reynolds number is more acceptable in the industry to enhance the heat transfer rate without considering the heat transfer difference caused by geometry parameter.

Research on Performance of Finned Tube Bundles of Indirect Air-cooled Heat Exchangers

Research on Performance of Finned Tube Bundles of Indirect Air-cooled Heat Exchangers

Innovative Design and Manufacturing Technology of High Temperature Air Combustion (HTAC) Municipal Solid Waste Incinerator

Incineration is a Thermal Treatment Technology (3Ts) that could be expressed as the way to get rid of waste effectively with the reduction of its mass and volume. However, to control the combustion process efficiently, especially combustion temperature, with low energy content in Municipal Solid Waste (MSW), an additional fuel is needed and leads to increase of operating cost compared with other disposal option. High Temperature Air Combustion (HTAC) has been successfully demonstrated in a lab-scale incinerator for energy saving and pollutant reduction, especially NOx. This article has the objective to design and manufacture the prototype scale High Temperature Air Incinerator with a capacity to treat MSW of 12 Ton per day. The system consists of an automatic feeding machine to feed the waste into the primary combustion chamber (PCC) where the combustion takes place. The push ram is used to push the burning waste and fall down to the lower hearth. Primary combustion air is supplied into PCC at the amount lower than the stoichiometric requirement to produce the combustible gas which is flown into the Secondary Combustion Chamber (SCC) located above PCC. Secondary combustion air is injected to react with combustible gas to convert to the product of complete combustion. A part of hot flue gas which is flew out from SCC is reverted and mixed with fresh air, in order to reduce oxygen concentration, before passing through the heat exchanger tube bundle which is placed inside SCC in order to exchange heat with hot flue gas. To manufacture the designed incinerator, the detail of materials used as well as the frabication method is explained. It has been shown that HTAC can be applied for thermal destruction of waste successfully, in term of energy saving and pollutant free. Benefits of this research work will promote the using of thermal treatment technology of dispose of MSW with lower operating cost and lower pollutants.

Experimental evaluation of pairs of inline tubes of different size as components for heat exchanger tube bundles

A passive heat exchanger design for process intensification, reduced flow fluctuations, pressure-drop and fouling is evaluated experimentally. A primal geometry of two unequally sized cylinders placed in tandem arrangement under cross-flow is initially examined in order to establish the effect on the wake fluctuations, compared to the single cylinder case. Three pairs of cylinders were considered with a diameter ratio of d/D=0.5 and at different longitudinal pitches, SL/D=1.5, 2.0 and 2.5, at the subcritical Reynolds number of ReD=3900. The streamwise velocity fluctuations in the wake of the cylinders were found to be lower for the cylinder pairs as compared to the case of the single cylinder. The preferred primal arrangement with unequally sized cylinders was extended to form a heat exchanger tube bundle, where the effect of the transverse distance between the tubes (ST/D) was also studied. Three tube bundle configurations were examined with d/D=0.5, SL/D=1.5 and ST/D=3.6 and ST/D=2.5, and a common arrangement with d/D=1.0, SL/D=2.5 and ST/D=3.6. Measurements were performed with regard to the heat transfer on the external surface of the tubes and the pressure drop across each configuration. When compared to the conventional tube bundle arrangement, the arrangement with d/D=0.5, SL/D=1.5 and ST/D=3.6 led to specific (per unit volume) heat transfer enhancement by 40% with indications of a negligible penalty in pressure drop.

ІНТЕНСИФІКАЦІЯ ТЕПЛООБМІННИХ ПРОЦЕСІВ ШЛЯХОМ ВИКОРИСТАННЯ ПОВЕРХНЕВО-АКТИВНИХ РЕЧОВИН

This paper deals with the issue of increasing the heat transfer coefficient of cooling and heating in processing plants. In the context of rising energy prices intensification of heat exchange processes is a challenge for the food industry. The article analyzes the modern methods of intensifying the process of heat exchange, and also provides a low-cost method of heat transfer when using surface-active agents (surfactants). Intensifying effect of surfactants - this change in physico-chemical properties of the technological environment, namely a decrease of the surface tension of the liquid at the boundary wall of the heat exchanger, heat exchange operating fluid, dynamic viscosity liquid cosine of the contact angle. The heat transfer coefficient of heat exchange equipment is determined by the components of the thermal resistance of the regenerative thermal resistance wall and laminar boundary layers. Adding the optimum concentration of the surfactant to the coolant provides a decrease in the average thickness of the boundary laminar (L) layer in the wall of the heat exchanger-flow and improving the overall heat transfer coefficient of heat exchange equipment. In this paper the example of normalized tube heat exchanger shown that the addition of a concentration (0.05 ... 0.15) masses. %. nonionic calculated heat transfer coefficient of heat exchanger tube bundle grows by 23%, while its flow resistance is not increased

Numerical Simulation of Finned Tube Bank Across a Staggered Circular-Pin-Finned Tube Bundle

In this paper, fluid flow and heat transfer over a three-dimensional staggered circular-pin-finned tube bundle heat exchanger surface have been numerically investigated. The effects of six geometric parameters and pin-fin arrangement in the flow direction on the thermo-hydraulic performance are investigated in details by adopting the performance evaluation plot of enhanced heat transfer oriented for energy-saving. The results show that the pin-fin diameter d, pin-fin length H, and pin-fin number around the tube N have positive effects on improving thermo-hydraulic performance, but the transverse tube pitch S1 and the fin axial pitch S1,pf have negative effects, whereas the longitudinal tube pitch S2 and the fin arrangement in flow direction (in-line or staggered) have little effects.

Numerical investigation on prevention of fouling in the horizontal tube heat exchanger: Particle distribution and pressure drop

To improve the performance of fouling prevention in liquid–solid fluidized bed heat exchanger with the horizontal tube bundle, parametric study of particle distribution and pressure drop in the heat exchanger was numerically conducted. Eulerian multiphase fluid model was used to calculate the flow of liquid–solid two phase in heat exchanger by means of the commercial software Fluent. In the simulation result, it was demonstrated that more particles occurred in the lower tubes of the horizontal tube bundle in low velocity due to the lack of full fluidization. Relative to that in low velocity, uniformity distribution of particle was obtained in high velocity which was accompanied with greater dynamic pressure drop. The particle with the greater density and diameter was inclined to sediment in the lower tubes due to larger sediment velocity and difficulty in the realization of full fluidization. Meanwhile an increase in size and density of particle would bring about greater pressure drop originating from more particle kinetic energy consumed. Effect of volume fraction of solid phase on particle distribution and pressure was discussed. It showed that an increase in volume fraction of solid phase led to significant rise of pressure drop. It was because consumed kinetic energy and collision energy of particles were greatly amplified with the increasing volume fraction of solid phase. Therefore greater volume fraction of solid phase, especially for the particle with the greater diameter and density, would not be recommended in the performance of fouling prevention in the horizontal tube bundle heat exchanger.

A Non-Dimensional Lattice Boltzmann Method for direct and porous medium model simulations of 240-tube bundle heat exchangers in a solar storage tank

An improved Non-Dimensional Lattice Boltzmann Method (NDLBM) is developed and a uniform computational code is compiled to fit into both direct and porous medium model simulations. Comparison studies based on natural convection of 240 cylindrical tube bundle heat exchangers immersed in a thin rectangular solar storage tank show the computational efficiency and accuracy of both direct simulations and porous medium model simulations achieved by using NDLBM. The governing parameters in the macroscopic, microscopic, and mesoscopic length scales corresponding to the enclosure width, tube diameter, and mesh size are obtained. Transient isotherms, streamlines, Nusselt numbers, and CPU time of nine models have been simulated for various pitch, porosity, and distributions of tubes. Given the same grid number and simulation time, the CPU time of the porous medium model simulations by using NDLBM is about 1/60 of that of porous medium simulations by using finite difference based on projection method, and 1/20 of that of the direct simulations with the uniform code based on NDLBM. The porous medium simulations can only obtain Darcy velocity and volume averaged temperature, while the direct simulations can obtain both macroscopic and microscopic velocity and temperature.

Experimental determination of the heat transfer and cold storage characteristics of a microencapsulated phase change material in a horizontal tank

In the present paper, the performance of a microencapsulated phase change material (in 45% w/w concentration) for low temperature thermal energy storage, suitable for air conditioning applications is studied. The results are compared to a sensible heat storage unit using water. Thermo-physical properties such as the specific heat, enthalpy variation, thermal conductivity and density are also experimentally determined. The non-Newtonian shear-thickening behavior of the phase change material slurry is quantified. Thermal energy performance is experimentally determined for a 100l horizontal tank. The heat transfer between the heat transfer fluid and the phase change material was provided by a tube-bundle heat exchanger inside the tank. The results show that the amount of energy stored using the phase change material is 53% higher than for water after 10h of charging, for the same storage tank volume. It was found that the heat transfer coefficient between the phase change material and the tube wall increases during the phase change temperature range, however it remains smaller than the values obtained for water.

Flow Optimization of Gas Quenching Processes Using Perforated Plates

Abstract Industrial gas quenching is a cost-effective, environmental-friendly alternative to conventional fluid-based quenching processes used for the heat treatment of workpieces mainly in the automotive industry. The influence of the heat exchanger geometry in a novel gas quenching chamber on the gas flow was investigated through measurement in parallel to CFD-simulations. With reduced quenching chamber dimensions, a flow guiding system utilizing a perforated plate placed between the heat exchanger and the batch has been found to play a significant role on the velocity and turbulence distribution of the gas flow. The use of various perforated plates in this gas quenching process focuses on the exploration of two main parameters: plate porosity and perforation hole diameters. By combining in situ flow and CFD-simulations of heat and fluid flow, optimized parameters have been determined indicating improved uniformity and intensity of the velocity distribution in the quenching chamber, thus obtaining the potential of an overall improvement of the gas quenching process. Geometric parameters of perforated plates introduced into the gas quenching chamber facility are investigated as, e.g., the distance between the plate and the batch. More generally, the use of a perforated plate system to optimize gas flows may be extended to other applications where tube bundle heat exchangers in gas flow processes are involved.

Parametric study of particle distribution in tube bundle heat exchanger

Fluidized particles in liquid–solid fluidized bed exchangers are able to remove deposits from walls and thus are able to prevent fouling or scaling. Particle distribution is an important parameter for the performance of fouling prevention. In this paper, the Eulerian multiphase fluid model was adopted to simulate the particle distribution in the fluidized bed heat exchanger incorporating tube bundle arranged in parallel. The porous media model was applied in the zone of the tube bundle to analyze the pressure loss through the vertical tube. Factors influencing the particle distribution including the velocity, volume fraction of the solid phase and the property of the particle were discussed respectively. Particle distribution became more uniform in the high velocity due to the full fluidization of particle in each tube. With the increase in density or diameter of particle, particle maldistribution took place because the sedimentation velocity of these particles was so great that particles could not run into the tubes on both sides. With the increasing of volume fraction of solid phase, particle distribution became slightly more uniform. However increment of particle would bring about greater flow resistance and reduce the usage life of particle and devices. Therefore amount of injected particle should be adjusted according to parameters such as effect of fouling prevention, pressure drop etc. A comparison of the simulation results with the experimental measurements was carried out, showing good agreement.

Research Progress in Natural Frequency Calculation of Heat Exchanger Tube Bundles

Natural frequency in tube bundles is the basis of vibration analysis in the heat exchanger. The calculation methods of the natural frequency are summarized in four type of tube bundles: straight tube, U-bend tube, finned tube and tube-fin. The influence of structure, temperature and fluid on the natural frequency are analyzed. Some anti-vibration measures are also put forward. The research direction of vibration analysis in tube bundles of heat exchanger in the future has good prospects.

A Comparison Between the Separated Flow Structures Near the Wake of a Bare and a Foam-Covered Circular Cylinder

The flow structures behind bare and aluminum foam-covered single circular cylinders were investigated using particle image velocimetry (PIV). The experiments are conducted for a range of Reynolds numbers from 2000 to 8000, based on the outer cylinders diameter and the air velocity upstream of the cylinder. The analysis of the PIV data shows the important effects of the foam cover and the inlet velocity on the separated structures. The results show a considerable increase in the wake size behind a foam-covered cylinder compared to that of a bare cylinder. Furthermore, the turbulence intensity is found to be around 10% higher in the case of the foam-covered cylinder where the wake size is approximately doubled for the former case compared to the latter. The turbulence kinetic energy, however, is found to be less Reynolds dependent in the case of the foam-covered cylinder. In addition, small scale structures contribute to the formation of the flow structures in the foam-covered cylinder making them a more efficient turbulent generator for the next rows when used in a heat exchanger tube bundle. On the other hand, a higher energy level in such separated structures will translate into increased pressure drop compared to bare cylinders. Finally, the results of this study can be used as an accurate set of boundary conditions for modeling the flow field past such cylinders.

Effect of turbulence intensity on the pressure drop and heat transfer in a staggered tube bundle heat exchanger

This paper investigates experimentally the correlation and the effect of the turbulence intensity on the pressure drop and the heat transfer mechanism of a heat exchanger with elliptic tubes in a staggered arrangement. The heat exchanger studied in this work is an air–water cross flow heat exchanger with air being the external fluid and water the internal one. The heat exchanger consists of 144 elliptic tubes placed in a staggered arrangement. The experiments were carried out for two setups. The first setup was referring to isothermal conditions for which only air was used, flowing around the tubes. The second setup was referring to non-isothermal conditions with air as the external fluid and water as the internal working fluid, flowing inside the tubes. The Reynolds number for the external air for the isothermal experiments ranged between 3100 and 5200 based on the maximum velocity between the elliptic tubes. The turbulence intensity values varied between 0.9% and 3%. For the non-isothermal measurements the Reynolds number took values from 3100 to 7700 and the turbulent intensity ranged from 0.9% to 3%. The measurements showed that the increase of turbulent intensity led to a decrease in the total pressure drop of the external flow of the heat exchanger together with an enhancement of the heat transfer mechanism.

Experimental investigation on powder conductivity for the application to double wall heat exchanger (NACIE-UP)

The double wall tube bundle heat exchanger is generally constituted by two or three (called double wall bayonet) concentric tubes. It is based on the concept to provide a double physical separation between two fluids: the coolant (i.e. water) and the hot fluid (i.e. lead).There are two primary reasons for the separation of the fluids. The first is to maintain a given temperature drop between the hot fluid and the coolant. The second is to increase the safety margin of the unit by reducing the probability of interaction between the coolant and the hot fluid. Furthermore, this configuration allows the possibility to monitor eventual leakages from the coolant or from the hot fluid by pressuring the separation region. On the other hand, if it is necessary to achieve high thermal performance of the unit, the annular space that separates the fluids should be filled with a heat transfer enhancer (i.e. sintetic diamond powder, stainless steel-SS powder).Several applications of the double wall and double wall bayonet tube heat exchangers have been designed and constructed at ENEA CR Brasimone. In particular, there are four facilities (NACIE and NACIE-UP, HELENA and HERO) whose heat exchanger is based on this concept and make use of SS powder (AISI-304 or AISI-316) to provide a temperature drop or to accommodate monitoring and heat transfer enhancement.In this framework, the Tubes for Powders (TxP) facility has been designed and constructed during 2012 and has been operating since the beginning of 2013 to investigate the conductivity of porous materials for their application in double wall heat exchangers. The facility consists of three concentric tubes and it allows to estimate the conductivity of a porous material by measuring the temperature drop across its borders and the removed power. It has the capability to introduce helium and to pressurize it up to 5bar.The present paper focuses on the experimental campaigns carried out in TxP to characterize AISI-316 powder in support to the qualification of the NACIE-UP heat exchanger. The main goals of the experiments are to assess the conductivity of AISI-316 powder, to highlight the effects of the procedure adopted to load the powder in the facility on its conductivity and to investigate the influence of thermal cycling. The experimental findings are finally compared to the results obtained from experimental campaigns performed in NACIE and applied to NACIE-UP to develop and discuss the pre-tests calculations carried out by means of computational fluid dynamic code.

Evaluation of the Integrity of Steam Generator Tubes Subjected to Flow Induced Vibrations

Flow-induced vibrations (FIV) continue to affect the operations of nuclear power plant components such as heat exchanger tube bundles. The negative effect of FIV is in the form of tube fatigue, cracking, and fretting wear at the supports. Fretting wear at the supports is the result of tube/support impact and friction. Fluidelastic and turbulence forces are the two main excitation mechanisms that feed energy into the system causing these violent vibrations. To minimize this effect all support clearances must be kept at a very small value. This paper investigates the consequences of losing the effectiveness of a particular support as a result of corrosion or excessive fretting wear. A full U-bend tube subjected to both fluidelastic and turbulence forces is utilized in this work. The performance of countermeasures such as the installation of additional flat bars in the U-bend region is thoroughly investigated. The investigation utilized both deterministic and probabilistic techniques.