Pipe Heat Exchanger Research Articles

ЭКСПЕРИМЕНТАЛЬНЫЕ ИССЛЕДОВАНИЯ ПЕРСПЕКТИВНЫХ СПОСОБОВ ИНТЕНСИФИКАЦИИ ТЕПЛОПЕРЕДАЧИ В ТРУБЧАТОМ ТЕПЛООБМЕННИКЕ

Актуальность работы обусловлена необходимостью повышения интенсивности теплоотдачи в аппаратах трубчатого типа химической и нефтехимической промышленности. Аппараты данного типа, как правило, громоздки, характеризуются высокой металлоемкостью, занимают большие производственные площади. Интенсификация теплоотдачи позволит снизить габариты теплообменного оборудования, уменьшить потери теплоты в окружающую среду и повысить технико-экономические показатели производства. Экспериментально полученные критериальные уравнения могут быть использованы при разработке интенсифицированных теплообменников. Цель: экспериментально определить зависимость критерия Nu от критерия Re в лабораторных теплообменникахтипа «труба в трубе», реализующих следующие способы интенсификации теплоотдачи: 1) использование сетчатого и спирального турбулизаторов; 2) использование псевдоожиженного слоя сферических металлических частиц; 3) вращение теплообменной трубы за счет кинетической энергии потока теплоносителя. Методы: экспериментальное определение зависимости критерия Nu от критерия Re в лабораторных интенсифицированных теплообменниках типа «труба в трубе», инструментальное определение температуры и расхода жидкости, высоты псевдоожиженного слоя; видеосъемка. Результаты. Экспериментально определена зависимость критерия Nu от критерия Re в лабораторных интенсифицированных теплообменниках типа «труба в трубе». Для исследованных турбулизаторов при 10000<Re<25000 получены эмпирические критериальные зависимости в пределах погрешности ±5%. Исследование способа интенсификации теплоотдачи за счет использования псевдоожиженного слоя в вертикальной теплообменной трубе показало, что наилучшие гидродинамические условия для интенсификации теплоотдачи достигаются в псевдоожиженном слое из свинцовых сферических частиц диаметром d=0,002м. Для псевдоожиженного слоя сферических свинцовых частиц d=0,002м при 5000<Re<15000 получена эмпирическая критериальная зависимость в пределах погрешности ±6%. Установлено, что во вращающейся охлаждаемой горизонтальной теплообменной трубе с постоянной частотой 2,0 об/с повышается критерий Nu в среднем 1,24 раза в интервале 10000<Re<40000. Анализ показал, что увеличение интенсивности теплоотдачи в исследованных теплообменниках обеспечено за счет улучшения перемешивания потока жидкости, а также за счет турбулизации пристеночного слоя. Результаты экспериментальных исследований позволяют сделать вывод, что рассмотренные методы интенсификации процесса теплоотдачи являются перспективными для дальнейшего исследования и использования на химическом и нефтехимическом производстве.

A novel method for designing thermo-active retaining walls using two-dimensional analyses

Thermo-active retaining walls are geotechnical structures employed as heat exchangers to provide low carbon dioxide heating and cooling to buildings. To assess the thermo-mechanical response of such structures, finite-element (FE) analyses are typically carried out. Due to the presence of heat exchanger pipes, the temperature distribution along the width of the wall is not uniform, implying that these problems are three-dimensional (3D) in nature. However, performing 3D FE analyses including elements to model the heat exchanger pipes to simulate the advective conductive heat transfer as well as thermo-hydro-mechanical coupling to reproduce the non-isothermal soil response accurately requires considerable computational effort. In this work, a novel approach to simulate thermo-active walls in 2D analyses was developed, which requires the sole use of thermal boundary conditions. This approach was found to reproduce average wall behaviour computed in 3D to a high degree of accuracy for numerous wall geometries, a wide range of thermal properties of soil and concrete, and different thermal boundary conditions along the exposed face of the wall. In addition, out-of-plane effects recorded in 3D analyses were assessed and an accurate simplified procedure to account for these when performing 2D analyses was developed.

Finite-Element Modeling of Heat Transfer in Ground Source Energy Systems with Heat Exchanger Pipes

Abstract Ground source energy systems (GSES) utilize low enthalpy geothermal energy and have been recognized as an efficient means of providing low carbon space heating and cooling. This study focu...

CFD Analysis of Heat Pipe Heat Exchanger to Predict the Temperature Distribution.

The Computational Fluid Dynamic (CFD) Analysis of Heat Pipe Heat Exchanger (HPHE) is done to predict the temperature distribution using ANSYS-ICEM modular/meshing and FLUENT solver. In this study, HPHE is modeled in four different cases with and without fillet near the inlet and outlet sections including (standard HPHE, with enlarge inlet and outlet sections, with horizontal plate near the entrance zone, using three different cone of angles (36.03 degree, 30 degree and 45 degree)). The mass flow rate 3.75kg/sec of hot air or gas as given at the inlet section. The Standard k- -Realizable turbulence model was used for fluid flow in simulations. The magnitude and location of the temperature distribution, velocity, and turbulence kinetic energy are influenced by prescribed conditions. However, pressure drop is reduced up-to certain extent (due to change in turbulence kinetic energy) for all the cases in which round corner/fillet at the inlet and outlet section was made in the model. At the same time jet type flow is also reduced because of reduction in axial velocity and increment of Y & Z directional velocity which tends to expansion of flow toward the y and z direction.

Performance enhancement of gas turbine units by retrofitting with inlet air cooling technologies (IACTs): an hour-by-hour simulation study

In the present research, a yearly performance of a gas turbine unit and the unit with the added inlet air cooling technologies (IACTs) was investigated in terms of performance and output power using TRNSYS software. The existing system was retrofitted with five different IACTs, namely Config. A: existing system integrated with an evaporative media, Config. B: existing system integrated with a fogging unit, Config. C: existing system integrated with a mechanical chiller, Config. D: existing system integrated with an absorption chiller, and Config. E: existing system integrated with a thermal energy storage. The configurations were examined to determine the most proper configuration. The study revealed that Config. C was superior and was the optimal configuration for the gas turbine unit and it was recommended for the existing system. The study showed that Config. C was capable of enhancing the yearly output power with about 10.62%. After determining the proper configuration, a method benefiting a passive energy technology of heat pipe structure was also proposed. In the proposed method, a water-to-air heat pipe heat exchanger (HPHX) consisting of single heat pipe tubes was planned to be added to Config. C as a pre-cooling equipment. To this end, the mathematical performance of the water-to-air HPHX was derived to be defined in TRNSYS studio. It was shown that a considerable amount of energy could be obtained after adding the water-to-air HPHX to Config. C. The exergy analysis also proved that application of IACT improves the exergy efficiency of the whole system.

Investigation of the three-dimensional structure, pressure drop, and heat transfer characteristics of the thermohydraulic flow in a circular pipe with different twisted-tape geometrical configurations

The effect of inserting twisted tapes with various configurations and parameters inside a circular pipe on the flow field is studied. The pressure drop and turbulent heat transfer are investigated using the computational fluid dynamics (CFD) technique. Ten cases of heat exchanger pipes are considered numerically. The 3D Navier–Stokes, continuity, momentum, and energy equations are solved using Fluent software. To study the impact of the turbulent flow on the heat transfer performance, a scheme with the semi-implicit method for pressure-linked equations (SIMPLE) algorithm is adopted. Water is applied as the working liquid, with constant heat flux boundary conditions. The results show that insertion of a twisted tape has a strong effect on all the flow properties inside the pipe, such as the pressure, velocity, vorticity, and temperature. Moreover, the turning induced by the twisted tape can provide more effective mixing of the fluid and enhance the turbulent intensity, leading to a thermal boundary layer. It is reported that the maximum dynamic pressure occurs midway between the surface of the twisted tape and the pipe outlet. Such use of a twisted tape could lead to a greater pressure drop and make the flow in the pipe more unstable, due to influences of the stronger swirling flow and vortex flow as well as the effect of the increased turbulent intensity. The resulting strong swirling flow leads to an improvement in the heat transfer performance. The numerical results reveal that the introduction of a twisted tape efficiently increases the pressure drop and heat transfer, as well as improving the heat transfer performance by about 46.0%. Furthermore, the results indicate that insertion of a twisted tape can improve the thermal performance of the system.

Optimization of the finned double-pipe heat exchanger using nanofluids as working fluids

The heat exchanger pipe diameter has a significant effect on the flow characteristics as well as on the initial investment, operation and overall cost. Increasing fin dimensions increases the annulus hydraulic diameters. Even though the total volume of the heat exchanger remains unchanged between the finned and bare designs, the heat duty increases with increased heat transfer area for the finned design. The fins should be designed, and the dimensions should be calculated with special attention for different flow rates and heat exchanger dimensions. In this study, number, geometry and dimensions of the fins are determined using the algorithms available in the literature. The operational condition optimization is carried out accompanied with the cost analysis. In addition, the effects of the types of working fluids and fouled and clean cases are investigated for the total heat transfer enhancement in parallel with performance, lifetime and cost issues. A detailed analysis is presented for finned and unfinned double-pipe heat exchanger models for pure engine oil and its nanofluid mixtures with Ti, TiO2, Cu, CuO, Al and Al2O3 nanoparticles, multi-wall carbon nanotubes and graphene nanosheet having a constant particle concentration in the liquid phase. The nanofluid is flowing in annulus side, whereas the seawater is flowing in the tube side. It is observed that both the pressure drop and the pumping power increase with the increasing fin number and decrease with the cleanliness factor, whereas the total tube number decreases with increasing fin number. It is found that different types of nanofluids affect the cost and optimum annulus side velocity significantly. The results are summarized in several figures that consider the increasing Reynolds number with the cleanliness factor, the heat transfer coefficient and the pressure drop, the friction factor with changing mass flow rate and the cost values with corresponding annulus side velocities. Finally, the overall characteristics of the trend lines are provided in the figures.

A Model of a Diaphragm Wall Ground Heat Exchanger

Ground thermal energy is a sustainable source that can substantially reduce our dependency on conventional fuels for heating and cooling of buildings. To exploit this source, foundation sub-structures with embedded heat exchanger pipes are employed. Diaphragm wall heat exchangers are one such form of ground heat exchangers, where part of the wall is exposed to the basement area of the building on one side, while the other side and the further depth of the wall face the surrounding ground. To assess the thermal performance of diaphragm wall heat exchangers, a model that takes the wall geometry and boundary conditions at the pipe, basement, and ground surfaces into account is required. This paper describes the development of such a model using a weighting factor approach, known as Dynamic Thermal Networks (DTN), that allows representation of the three-dimensional geometry, required boundary conditions, and heterogeneous material properties. The model is validated using data from an extended series of thermal response test measurements at two full-scale diaphragm wall heat exchanger installations in Barcelona, Spain. Validation studies are presented in terms of comparisons between the predicted and measured fluid temperatures and heat transfer rates. The model was found to predict the dynamics of thermal response over a range of operating conditions with good accuracy and using very modest computational resources.

Mathematical Modeling of Flow and Heat Exchange in Pipes with Surface Turbulators with a Square Cross-Section (S/H = 1) and Edges (S/H << 1) Based on the Low-Reynolds Mentor Model

Mathematical Modeling of Flow and Heat Exchange in Pipes with Surface Turbulators with a Square Cross-Section (S/H = 1) and Edges (S/H << 1) Based on the Low-Reynolds Mentor Model

The Effect of Heat Transfer Fluid Velocity on Heat Exchange Efficiency in Cold Energy Storage Tank: A Numerical Simulation Study

Developing a cold thermal energy storage (CTES) technology is one of the most effective methods to solve energy shortage and environmental pollution all over the world. The current study deals with the modelling and simulation of a cold thermal energy storage tank consisting of an polyvinyl chloride pipe (PVC) heat exchanger partially filled with a phase change material (PCM). Water, as the heat transfer fluid (HTF), flows through the inner tubes and the outer one while propylene glycol as the phase change material fills. This paper focuses on studying the effect of the velocity characteristics on the heat transfer efficiency of polyvinyl chloride pipe (PVC) heat exchanger in cold thermal energy storage system by the numerical simulation. In this paper, the detail of heat transfer performance within the heat exchanger is numerically solved using computational fluid dynamics (CFD), for various velocity as well as different heat transfer for optimal design. Several results of changes in the temperature field at the outlet of the cold thermal energy storage tank are presented when the inlet water velocity changes from 1 m/s to 1.4 m/s. The results indicate that low input water velocity will provide better heat exchange efficiency. However, it is required to make sure that the flow inside the heat exchanger is the turbulent flow because the study uses turbulent flow modules.

Use of kinetic flow energy liquids for vibration of local turbulizers in pipe heat exchangers

This issue of using certain part of the kinetic energy of the flow for imparting vibration for special local turbulators (LT), consisting of an elastic thread with strung on it through a certain distance volume elements (made of a special material) of various geometric configuration installed in the tubes of the heat exchanger with fixing one end of the thread at the inlet, and the other end remains free. The results of numerical and experimental studies are presented, which show the effectiveness of the use of LT for intensifying the processes of hydrodynamics and heat transfer.

Evaluating the impact of different pipe arrangements on the thermal performance of thermo-active piles

Thermo-active piles are widely utilised for low carbon heating and cooling, and their uses are further encouraged in cities where there are obligations for developments larger than a certain threshold to generate a portion of their estimated energy use on site in a renewable manner. It is therefore important to model accurately the thermal performance of the designed thermo-active piles to ensure that such obligations are complied with. In this paper, the thermal performance of a thermo-active pile is quantified by the evolution with time of the power that can be harnessed from the pile, obtained from 3D thermo-hydro-mechanically coupled finite element analyses which include the simulation of a hot fluid flowing through heat exchanger pipes. Different pipe arrangements are considered in this study, in order to demonstrate the potential gains in efficiency arising from the installation of multiple U-loops within the pile. Furthermore, detailed analysis of the heat fluxes resulting from pipe-pile-soil interaction is carried out, illustrating the contribution of the different components of the system (concrete, near-field and far-field) to the overall storage of thermal energy.

Numerical analysis of a heat exchanger pile response in a Brazilian subtropical region

Ground-coupled heat exchanger systems have been used as acclimatization systems for residential and commercial buildings in many countries. Brazil is the ninth largest consumer of electrical energy in the world, for this reason, local researchers are investigating the use of the energy piles in order to reduce the consumption of electricity. Thermal response tests have been carried out on a heat exchanger pile at the geotechnical experimental site of the University of São Paulo in São Carlos city, a region of subtropical climate. Simultaneously, using the thermal properties obtained in these tests, numerical analysis has been performed to investigate the heat exchange performance of energy piles installed in this site. For this numerical analysis, the effect of soil and concrete properties, pile geometry and the flow rate on the pile thermal response were evaluated. The current paper presents the results obtained by the analysis of 67 models tested to found an optimal configuration of an energy pile through the software COMSOL, using Heat Transfer and Non-Isothermal Pipe Flow modules. From this work, it was observed that the optimal configuration was obtained for a turbulent flow condition in piles in the heat exchanger pipes.

Simplified methods for designing thermo-active retaining walls

Thermo-active retaining structures are geotechnical structures employed to provide thermal energy to buildings for space heating and cooling through heat exchanger pipes embedded within the concrete structure. Consequently, the design of these structures needs to consider both the long-term energy efficiency as well as the thermo-mechanical response in terms of stability and serviceability. Transient finite element analyses can be carried out to evaluate the behaviour of thermo-active walls, where the heat exchanger pipes are explicitly modelled, thus requiring three-dimensional (3D) analyses. However, performing long-term 3D finite element analyses is computationally expensive. For this reason, in this study, new approaches are presented that allow the thermal or thermo-mechanical design of thermo-active walls to be carried out by performing two-dimensional (2D) plane strain analyses. Two methods, which are based on different design criteria, are proposed and their performance in replicating the three-dimensional behaviour is assessed. Furthermore, the factors affecting the 2D approximations for the two modelling approaches are evaluated, where particular emphasis is given to the influence of the simulated boundary condition along the exposed face of the retaining wall.

Thermal response of energy foundations installed in unsaturated residual soils

This study focuses on the thermal response of energy foundations with different piping geometries installed in unsaturated soil. Energy foundations are an efficient alternative to traditional space heating and cooling approaches and can reduce energy demand for air conditioning in Brazil, where unsaturated residual soil deposits are abundant. A three-dimensional numerical model for heat transfer and subsurface flow is first validated against field data from a thermal response test at the University of São Paulo. The model is then used to compare the performance of triple and quadruple U-tube piping geometries and helical piping geometries of equivalent length. The helical geometries resulted in initial less uniformly heated foundations and lower heat flux at the foundation boundary compared with the U-tubes, but the differences between the U-tube geometries and their equivalent length helices were less than 1°C. All piping geometries exhibited increased heat output as the length of heat exchanger piping increased. The infinite line source solution was compared with the model results. The infinite line source solution underestimated the thermal response of the system during the first 25-30 days and overestimated it afterwards.

The Utilization of Rice Husk with Furnace Modification Based on the Heat Exchanger Pipe Type for Sustainable Energy of Traditional Drying

The Utilization of Rice Husk with Furnace Modification Based on the Heat Exchanger Pipe Type for Sustainable Energy of Traditional Drying

Experimental Study of Heat Transfer Enhancement by Inserting Metal Chain in Heat Exchanger Tube

Heat transfer augmentation in heat exchangers is important in many large industrial applications and many studies have been conducted on this subject. In this paper, an experimental study was used to verify the increased heat transfer of a circular heat exchanger tube with the insertion of metal chains, under turbulent flow conditions. A rig was designed and fabricated to investigate the effects of using the metal chain as turbulators inside the heat exchanger pipe, on heat transfer performance and on fluid flow behavior. The metal chains used were of different lengths of chain ring and different diameters of ring wire. Five ring length/tube diameter ratios (P/D) were used, (1, 2, 3, 4 and 5). Two wire diameter/tube diameter ratios (t/D) were used in this work (0.1 and 0.15). Heavy fuel oil (HFO) was used inside the tube, flowing at 30 °C with uniform tube wall temperature. The Reynolds numbers tested were between 5,000 and 15,000. The results showed the thermal enhancement factor (η) decreased with increasing Reynolds number for all cases, depending on lengths of chain ring (P) and thickness the weir chain (t) values. A maximum thermal enhancement factor (η) was found with a metal chain at P/D=3 and t/D=0.15. The results also show that P/D=1 and t=4mm, give the highest Nusselt number.

Group effects in urban shallow geothermal energy

Since the 1980’s, shallow geothermal solutions have been developed whose principle is to attach heat exchange pipes to the reinforcing cages of geotechnical structures. These low energy solutions combining a structural and a thermal role allow the fulfilling of the heating and cooling needs of buildings for a very low carbon cost. Energy geostructures are often placed in a groundwater flow. On one hand, it is a good way to avoid any multiyear thermal shift since the heat excess or default is tempered through the advection. This advection creates a thermal plume and heat waves in the soil can interact with downstream structures whose behaviour can be affected. The understanding of these interactions is essential for a smart management of the shallow geothermal development at the city scale. To study these interactions, a group of nine energy piles has been studied in Sense City, a mini city where a specific climate can be imposed and the underground water flow can be controlled. A numerical hydraulic-thermal coupled model was developed with the FEM software CESAR-LCPC to extrapolate the results. The combination of experimental and numerical models provides helpful results for the definition of guidelines concerning the prevention of interactions.

Thermal Analysis on Hydrothermal Performance of Double Pipe Heat Exchanger with Single and Double Helical Tape

Double pipe heat exchanger has wide applications in industrial process. Thermo-hydro performance plays an important role from the economic point of view. Different enhancement techniques are available for the improvement of heat transfer. In this study the hydrothermal performance of double pipe heat exchanger with single and double HTI on inner pipe of double pipe heat exchanger were experimentally examined. Two types of inner tubes with single and double helical tape was fabricated. Experiments were performed by different mass flow rate of annulus side in the range of 0.072-0.21 kg/s varied. In order to validate the result three dimensional CFD simulations are performed, using Fluent software. CFD simulations analysis was done under turbulent flow conditions. Key design parameters such as heat transfer coefficient and Nusselt number are evaluated in order to predict the performance of DPHE. Findings from this study shows that hydrothermal performance of double pipe heat exchanger with double helical tape is better than single HTI. Moreover both the results of CFD simulation & experimental one are in good agreement. Therefore, the present study will help the manufacturers in providing the better thermal performance of DPHE.

TESTS OF ARRANGEMENTS IN A PROTOTYPE OF A STEAM GENERATOR IN AN ABSORPTION REFRIGERATION SYSTEM

This paper presents a proposal to optimize the prototype II of a steam generator, developed by the Cooperativa de Pesquisa Norte/Nordeste de Gas Natural, RECOGÁS - UFPB, which is a component of an absorption refrigeration system of water and lithium bromide triggered by direct burning of natural gas. The optimization was carried out through changes in the arrangement, geometry, and number of the heat exchanger pipes. It was developed a computational code using F-Chart software Engineering Equation Solver® (EES), applying the principles of heat transfer to all the different geometries. As a result, their respective coefficients of heat transfer, heat flow rate and other parameters of the process were obtained. The findings are organized in a table and represented in graphs generated by the EES software, allowing to verify which factors had a greater influence on the process, as well as the most efficient geometries. Internal convection was identified as the governing factor in the heat transfer process. Some of the geometries presented satisfactory values to the product of overall heat transfer coefficient and surface area (UA) and also to the heat transfer rate in the steam generator. Other ones presented a better thermal efficiency relation with the amount of volume occupied in the steam generator. Some geometries did not present satisfactory values under any aspect.