Flow Heat Exchanger Research Articles

Active Turbulence Grid-Controlled Inflow Turbulence and Replication of Heat Exchanger Flow Fields in Fan Applications

A novel active turbulence grid of the Institute of Fluid Mechanics at FAU Erlangen-Nuremberg is introduced. The focus of this grid is not on basic investigations of fluid mechanics, as is usually the case with active turbulence grids, but the generation of defined inflow conditions for axial fans. Thus, by means of the active turbulence grid, individual turbulence characteristics in the flow to the fan can be changed; therefore, fundamental interactions between the flow mechanics at the axial fan and the sound radiation can be analyzed. In addition, the replication of the flow fields of heat exchangers by the active turbulence grid is the focus of the investigations. The investigations showed that it is possible to use the active turbulence grid to generate defined inflow conditions for axial fans. It was also possible to reproduce the heat exchanger flow fields both for the mean turbulence values and for the spatial distributions. It was found that the grid induces tonal components due to the drive motors, but also that the inherent noise has no significant influence on the spectrum of the fans under investigation. Based on selected turbulence characteristics, direct correlations were found between the spatial distribution of the turbulence level and sound radiation at the first blade passing frequency of the axial fan. As the variance of the turbulence level increases, the sound radiation of the tonal components becomes more pronounced. The total sound pressure level, however, is mainly determined by the low-frequency broadband sound. A linear relationship between the spatial mean value of the turbulence level and the total sound pressure level was found for the investigated axial fan.

The process of heat exchange of steam-water flow in a geothermal pipe of a vertical well

The main purpose of the work is mathematical modelling of heat exchange of steam-water flow in a geothermal pipe of a vertical well. Within the framework of the hydraulic approximation, a numerical study of the steady isothermal motion of a thermodynamically equilibrium steam-water mixture in a vertical well has been carried out, taking into account heat losses into the surrounding rocks. In this task, the process of coolant movement along the borehole and its thermal interaction with its wall is considered. Because of the implementation of the described model, the values of specific heat losses in the rock mass for various initial conditions for wells were obtained.

Shell-side flow study and structural optimization of a double helical-like flow heat exchanger

A double helical-like flow heat exchanger model was built, its shell-side flow state was studied by the CFD method, and the difference in heat transfer performance between it and the torsional flow heat exchanger was compared. From the numer?ical simulation results, it is found that the heat transfer coefficient and pressure drop are improved by 7.07-8.93% and 15.50-18.22%, respectively at the same flow rate, and the comprehensive performance expressed as Nu/f 1/3 is improved by 21.84-24.08%. Using the orthogonal test method to optimize the shell-side struc?ture, it is found that the comprehensive performance is influenced by the two factors of spacing/groups and angle of baffles, and the influence of the deflection angle of two adjacent groups of baffles is very small, and the optimal structural combi-nation of comprehensive performance is 30-0-70/11 (the angle of baffles is 30?, the deflection angle of two adjacent groups of baffles is 0?, the spacing between two adjacent sets of baffles is 70 mm, and the number of baffle groups is 11). The reliability and feasibility of the simulation method were verified by experiments.

Design and experimental study of an outdoor portable thermoelectric air-conditioning system

This study aims to identify suitable microclimate cooling systems to reduce heat stress and improve human thermal comfort. A portable thermoelectric air conditioner was developed for local cooling of the human body. Effects of core components thermoelectric refrigerators (TECs), hot end heat dissipation, intake flow and cold end heat exchangers on TEAC performance. It is shown that, remarkably, this operating voltage can be distinguished from the optimal voltage for the maximum operational performance of TEAC. When the TECs operating voltage is 4V, the maximum COP is 2.2, and the best operating voltage is 10V, the maximum cooling capacity is 26.7 W (COP=0.92). Simulation data show that the area of the diffuser can effectively control the contact between the air and the cooling surface with an error of less than 10% compared to the experimental results. The fans and radiators attached to the hot side of the TEM play an important role in keeping the temperature difference on the hot side of the TECs as small as possible, by dissipating the heat generated on the hot side of the TEM to the external environment. In addition, the experimental refrigeration capacity is greater than 26.7 W and the new system has ultra-quiet operation at large refrigeration capacity, which has promising potential for advanced refrigeration, building air conditioning, ventilation systems and other applications. • Thermalelecrtic air conditioner (TEAC) can achieve a cooling capacity of 26.7W and a cooling coefficient of 0.92, enabling local cooling of the human body. • The maximum cooling capacity of thermoelectric refrigerator varies nonlinearly with the surface area and height of thermoelectric leg. • The increase of cooling capacity decreases with the increase of intake flow rate. • Increasing the strength of heat dissipation at the hot end of the thermoelectric cooler has a larger effect on the TEAC cooling capacity than on the cooling coefficient.

Efficiency of counter flow heat exchange in copper tube using APISN and XTRA KOOL oils

Abstract We all know that heat exchanger is one of the equipment to transfer the heat between the fluids. Heat will transfer from one side of fluid to another side of fluid. In this project we use counter flow heat exchanger. In this heat exchanger one kind of fluid will come from one side and another kind of fluid will come from another side. Both fluids will be sending inside to the tube in opposite direction. Here we are using two medium one is hot fluid and another one is APISN (American Petrol Institution of Super Natural) with B grade oil. Inside of apparatus we are using copper tube, to enhance the heat transfer. Because that copper is having higher thermal conductivity (385 W/m K). When we compared to the carbon steel (19 W/m K), copper is having more thermal conductivity. The reason for choosing copper tube is not only higher thermal conductivity; it's also having properties like corrosion resistance, max allows able stress and internal pressure. Hot fluid will be send through the way of inside of the copper tube. Over the copper tube will send APISN oil, both will be send in an opposite manner. In a setup of counter flow heat exchanger, we put two holes with some dimension. When the fluid goes inside of the tube we insert the digital thermo-meter to note down the temperature of both inlet and outlet. After taking all reading we will evaluate the counter flow heat exchanger with term of efficiency.

Effect of louver angle on performance of parallel flow heat exchanger

In order to study the influence of the louver angle on the heat transfer and flow resistance characteristics of a parallel flow heat exchanger, this paper establishes five calculation models including a uniform angle model and four variable angle models for comparing and analyzing the temperature, velocity, and pressure fields, and evaluates their comprehensive performance. The results show that the suitable choice of the v louver angle can lead to an optimal heat transfer effect and a best comprehensive performance.

A design model for spiral wound heat exchangers which accounts for property variation, longitudinal heat conduction, and heat-in-leak

• A combined analytical-numerical design model for cryogenic SWHE is developed. • Analytical sizing module finds the optimum configuration of SWHE. • The effects of property variation, LHC, and heat-in-leak are investigated. • LHC impact is negligible compared to property variation and heat-in-leak. • A sensitivity analysis on the input constraint is performed. Spiral Wound Heat Exchangers (SWHEs) can be a good and reliable choice for serving as the main heat exchanger in the cryogenic gas liquefaction cycles using throttling process such as the Linde-Hampson cycle. In this application, a high pressure hot gas stream has to be cooled down via transferring heat to a low pressure cold gas in a high-effectiveness heat exchanger. Present research has been organized to develop a design model which is able to find the optimum SWHE configuration for gas liquefaction cycles. The model has to be capable of considering the important physical phenomena in the cryogenic temperature ranges, including variation of fluid properties with temperature, longitudinal heat conduction (LHC) through separating walls, and heat-in-leak. Therefore, a combined analytical-numerical design model has been developed in the present study. The design model is essentially composed of two stand-alone modules, i.e. an analytical sizing module and a numerical performance evaluation module. To develop the design model, first, the geometrical characteristics of SWHE are studied and primary geometrical parameters are recognized. Then, the analytical sizing module is developed which is able to determine the optimum values of primary geometrical parameters of SWHE minimizing the heat transfer surface area based on the input design requirements. Afterwards, a 1D finite difference numerical module is presented in which important physical phenomena can be considered in the evaluation of the thermo-hydraulic performance of all types of counter flow or parallel flow heat exchangers as well as SWHEs. Finally, the two modules are combined to construct a design model. Two examples in which the low pressure superheated vapor helium is intended to cool down the high pressure supercritical helium flowing inside the tubes are also provided to demonstrate the applicability of the proposed combined model, and also, to elucidate its sensitivity to the input constraints. It was concluded that while variations of fluid properties and the external heat fluxes due to the radiation and convection have significant influence on the performance of cryogenic SWHE, the LHC is of minor importance and can be neglected. Moreover, decreasing the shell-side allowable pressure drop from 10 kPa to 2 kPa, causes the heat exchanger length and its outside diameter to increase by 79% and 48%, respectively.

Design and analytical investigation on air-to-air cross flow heat exchanger of an industrial heat recovery ventilation system

Design and analytical investigation on air-to-air cross flow heat exchanger of an industrial heat recovery ventilation system

The Phenomenon of Flow and Heat Transfer in Annular Heat Exchanger on Plain Tube Condition

Advanced industrial development in technology necessitates using equipment that can effectively and efficiently transfer heat energy. A heat exchanger is the most common device used in industry to transfer heat energy. The Annular Heat Exchanger is one of the heat exchangers used in industry that is simple to manufacture and inexpensive to finance. The annular heat exchanger is commonly found in the food, beverage, chemical process, pharmaceutical, and refrigeration technology industries. This type of heat exchanger is used due to its simple design, easy to manufacture, and low cost. The presence of a heater in a concentric pipe with a straight construction is the general form. Experimentation was carried out in this study. A heater is used to transfer the heat, and there is a cold fluid flow through the annulus. The heater is linked to an AC Voltage Regulator and has five heat settings ranging from 400 W to 600 W. Simultaneously, cold fluid flows in the annulus via a closed system with six flow variations ranging from 2.5 GPM to 5 GPM. A cooling system is used to keep cold fluids at a constant temperature. The purpose of this research is to demonstrate the flow and heat transfer phenomena in an annular heat exchanger. This study obtained the average heat transfer convection coefficient, h, and Nusselt number, Nu. The steady-state conditions for the heat variations of 400 W, 500 W, and 600 W are 2400 s, 3600 s, and 5400 s, respectively. The flow calibration results in this apparatus experiment have an error of 0.05%. At a heat variation of 500 W and Reynolds number 10669, the highest average heat transfer convection coefficient (h) reaches 6703 W/m2K, and the average Nusselt number (Nu) of 314 is obtained. The Reynolds number of critical transition points for heat variations of 400 W, 450 W, 500 W, 550 W, and 600 W are 6986, 7125, 8444, 8616, and 10009, respectively.

KINERJA GAS PENUKAR PANAS ALIRAN BALIK SHELL AND TUBE UNTUK PENGERING PERTANIAN

Abstract—One of the important post-harvest processes of rice is drying. Drying is divided into two, namely natural drying (using sunlight) and artificial drying (using tools). In this study drying utilizes heat from a biomass furnace and a configuration of heat exchanger pipes. Where the utilization of heat and the configuration of heat exchanger pipes in the design can increase thermal efficiency because the exhaust hot air mixed with smoke can still be used for drying. The configuration of the heat exchanger pipe greatly influences the expected moisture content level. The purpose of this study was carried out to determine the performance of the shell and tube counter flow heat exchanger for agricultural dryer gases with a heat source from biomass and to find the effect of the configuration of the heat exchanger pipe arrangement on the working process of the drying machine. This research is an experimental test of the performance of heat exchange pipes with a heat source from a biomass furnace. The exchange pipe performance parameters that must be known are temperature and time. The method used in this study refers to experimental and descriptive methods, namely research conducted in a systematic, factual and accurate manner. The results of this study are that the heated air flow rate affects LMTD, heated air outlet temperature, heat transfer coefficient, and efficiency, with variations in the heated air flow rate of 0.11 kg/s, 0.16 kg/s, 0.20kg/s, 0.24kg/s. Highest efficiency of 94% at a heated air flow rate of 0.24 kg/s. and the smallest efficiency of 74% is found in the value of the heated air flow rate of 0.11 kg/s.
 Keywords : dewatering, biomass, pipe configuration, heat exchanger pipe

ANFIS based effectiveness and number of transfer units predictions of MWCNT/water nanofluids flow in a double pipe U-bend heat exchanger

In this study, the heat transfer coefficient, Nusselt number, effectiveness and number of transfer units of water mixed multi-walled carbon nanotubes nanofluids passes through a tube-in-tube heat exchanger was experimentally investigated. Investigations were performed in the operating conditions of Reynolds number ranging from 3500 to 12000 and volume concentrations ranging from 0% to 0.3%, respectively. The obtained four parameters were predicted using adaptive neuro fuzzy inference system (ANFIS). The Reynolds number and particle volume loadings are the input data in artificial neural network analysis and heat transfer coefficient, Nusselt number, effectiveness and number of transfer units is output or target. The Nusselt number, heat transfer coefficient, effectiveness, and number of transfer units was enhanced to 31.3%, 44.17%, 2.51% and 2.76% at φ = 0.3% and at a Re of 10005, against base fluid. Implementation of ANFIS with various quantities of neurons in the mid layer provides 1–10−6 with the correlation coefficient (R2) of 0.9978, and 0.9998 and root mean square error of 0.0018581, and 0.0014159 for heat transfer coefficient and Nusselt number, respectively. The above developed structure has been successful in predicting 96% of variation in all the parameters.

CFD analysis of heat transfer enhancement in a concentric tube counter flow heat exchanger using nanofluids (SiO2/H2O, Al2O3/H2O, CNTs/H2O) and twisted tape turbulators

A concentric tube, counter flow heat exchanger with nanofluids under turbulent flow conditions has been examined using a computational fluid dynamics model. The proposed model consists of Twisted Tape Turbulators (TTT) on the annular side and inside the tube along with different nanofluids. Twisted Tape Turbulators produce a swirl motion within the fluids to increase heat transfer. Al2O3/H2O, SiO2/ H2O, and CNTS/ H2O nanofluids (with varying volume concentrations of 1 %, 2 %, and 3 %) with the turbulent flow (Reynold number Re = 2000 to 10000) were considered to determine three major parameters i.e., heat transfer rate (Q), overall heat transfer coefficient (U) and Nusselt number (Nu). This study resulted in 6.03 %, 16.74 %, and 6.74 % enhancement of overall heat transfer coefficient (U) with a 3 % volume concentration of CNTS/H2O nanofluid, Al2O3/H2O nanofluid, and SiO2/H2O nanofluid, respectively, when equated to without twisted tape tabulators. This analysis shows the maximum value of Nusselt number as 143,136.68 and 140.12 for CNTS/H2O, Al2O3/H2O, and SiO2/H2O, respectively, for the twisted tape tubular arrangement. It is concluded that when using twisted tape turbulator, the heat transfer rate (Q), overall heat transfer coefficient (U), and Nusselt Number (Nu) increase with increasing Reynolds number (turbulent flow conditions) and volume concentrations of nanofluid.Novelty statement: Twisted Tape Turbulators (TTT) arrangement with different concentrations and types of nanofluids combined are infrequent in the study of concentric tube heat exchanger with turbulent flow to obtain enhanced heat transfer.

Metallic foam with cross flow heat exchanger: A review of parameters, performance, and challenges

AbstractThe cross‐flow heat exchanger involves a tractor moving between two fluids that flow in a direction perpendicular to each other, and one of the fluids is often a liquid and the other is a gas. This type of heat exchanger has been studied in many previous studies for its importance in air conditioning applications and many industrial applications. In this type of heat exchanger, the surface area for heat transfer is very large. Therefore, many techniques have been used to improve the thermal and dynamic performance of this type of heat exchanger. In this study, previous studies that used metallic foam as one of the ways to improve the performance of heat exchangers were reviewed. The most important techniques that were used in previous studies during the process of evaluating the thermal performance of a cross‐flow heat exchanger in the presence of different types of metal foam were clarified. The use of metal foam depends on important factors, including (1) the type of material, where copper and aluminum were used in most of the previous studies, due to their availability and ease of foam formation using these materials, in addition to the good thermal properties, (2) porosity, where the porosity value of metal foam ranged between 0.85 and 0.98 in the previous studies, (3) the density of pores, most of the studies ranged between 10 and 40 PPI.

Effects of heat transfer medium flow field changes on the heat storage and discharge performance of phase change heat accumulators

In this study, a numerical simulation was employed to assess the heat storage and exothermic behaviour of a phase change unit with different heat flow channel configurations, height-to-diameter ratios, inlet flow rates, and addition of different rib structural parameters. Thus, we aimed to explore the heat storage and exothermic behaviour of the phase change accumulator under changes to the heat transfer medium flow field. By analysing the variation in the velocity and temperature fields of the heat transfer medium and using the field synergy principle, the structure of the cylindrical phase change accumulator was optimised, and the liquid fraction, field synergy angle, and Nu number in different structures were compared. The results revealed that the H-type heat exchanger flow channel could effectively improve the heat exchanger field synergy and increase the heat storage rate by 6.3 %. Increasing the inlet flow velocity could accelerate the heat storage rate; however, the flow velocity caused the flow field synergy to fluctuate and the heat storage efficiency to increase gradually. On increasing the height-to-diameter ratio, the heat exchanger field synergy ‘increased first and then decreased’, reaching the optimal heat transfer effect when D = 1.932. Under the heat storage and release condition, the straight rib heat transfer was superior to that for the ring rib. The change in the built-in straight rib length played a dominant role in the heat storage rate. Accordingly, for optimal heat transfer, the rib length was set to >45 mm, rib thickness to 1.5–2 mm, and number of ribs to 10. Meanwhile, the heat release efficiency initially increased as the length of the external straight rib increased and subsequently decreased. For optimal heat transfer, the rib length was set between 15 and 25 mm, rib thickness to >1.5 mm, and the number of ribs to >10 ribs. Therefore, we determined the ranges of structural parameters that would provide appropriate references for this phase change accumulator in fields such as thermal energy storage and waste heat recovery.

Thermo-fluidic characteristics of ice slurry flows in U-bend pipes for cold thermal energy storage

Thermal energy storage plays an important role in improving the efficiency of refrigeration systems. Ice slurries have a high potential for thermal energy storage due to their high latent energy storage properties and almost uniform temperature field. Ice slurry flows in heat exchangers can assist in peak load conditions of refrigeration systems. In the present study, the thermo-hydraulic behavior of ice slurry in U-Bend pipes as a component of heat exchangers was investigated. Numerical simulations were perforfemd using multiphase two-fluid model. Kinetic theory of granular flows were used for modeling the viscosity of ice particles. The effect of geometry of U-Bend pipes on heat transfer rate, pressure drop and ice slurry phase change were investigated. Numerical results were in good agreement with the experimental data. The results showed that heat transfer coefficient and pressure drop increase with Reynolds number, ice volume fraction and ice particle diameter. Tripling the particle diameter leads to the Nusselt number increase by 76 %. It was also found that by reducing the radius ratio, the heat transfer coefficient and the average skin friction coefficient increase, but overally it improves the performance. With a 100 % increase in Reynolds number, the average Nusselt number increases by 80 %, and by decreasing the radius ratio to 50 %, the Nusselt number increases by <1 %.

Experimental and numerical study of stator end-winding cooling with impinging oil jet

As an efficient cooling technology, impinging jet was utilized to reduce end-winding temperature of electric machine stator in this study. Infrared imaging and numerical simulation technologies were applied to investigate heat dissipation efficiency of silicone oil jet on a real electric machine stator. Infrared camera is possible to measure end-winding temperature without influence on flow pattern and heat exchange. Numerical simulation results for end-winding temperature were validated by comparing to experimental results. Then heat transfer coefficient was calculated by inverse method, which is very difficult to be obtained by experimental method. The testing stator had three configurations, among which one was covered by aluminum foil at external surface and the other one had extra internal surface in order to lead oil flow to contact all the end-windings. Moreover, effect of dissipated heat quantity and oil flow rate were considered in present study. According to experimental and simulation results, the configuration with internal surface reveals best cooling performance by impinging oil jet. For this stator configuration, the minimum and the most cost-effective oil flow rates were found which will provide insight for impinging jet system.

A review of multi-phase and single-phase models in the numerical simulation of nanofluid flow in heat exchangers

Various types of heat exchangers have many applications in industrial and engineering fields to improve heat transfer rate (HTR). The techniques of heat transfer enhancement which are active, passive, and hybrid are discussed in the present review paper. One of passive methods to enhance HTR is the use of nanofluids. This article provides the governing equations of nanofluid flows and discusses their modeling methods, including single-phase and two-phase. Advanced investigations considered single-phase and two-phase flow regimes are summarized. Comparing single-phase models (SPMs) and two-phase models (TPMs), most researchers concluded that numerical modeling based on TPMs experiences a better prediction compared to the SPMs. However, there are conflicting results among the researchers and it is not confirmed which model is better. This review paper aims to analyze the examinations on SPMs and TPMs in heat exchangers to assess the impact of these approaches on the prediction of the characteristics of nanofluids in these devices.

Heat transfer enhancement for corrugated facing step channels using aluminium nitride nanofluid - numerical investigation

The present work carries out a three-dimensional numerical analysis study of Aluminium Nitride (AlN)-water hybrid nanofluid enhanced heat transfer in laminar forced convection flow heat exchanger with four different channels, flat, backward facing step, triangle and trapezoidal facing step channels. The influence of different Reynolds number (100≤ Re ≤1500) and different solid nanoparticles volume fraction (1% and 4%) on the heat transfer and fluid flow were numerically investigated. The numerical analysis was carried out by using a laminar model of ANSYS-Fluent CFD code and the governing equations were resolved using the finite volume method. The results indicate that the thermal conductivity of the nanofluids increases with the increase values of both the nanoparticles volume fractions and Reynolds number, compared with base fluids. Likewise, the pressure drop showed slightly increased due to the increased of both parameters. The use of high nanoparticles volume fractions (4% volume) nanofluid corresponded with the use of four different channel designs resulted in heat transfer augmentation about 30% when compared to that pure water for the trapezoidal channel.

Multi-Objective Optimization of Plate-Fin Heat Exchangers via Non-Dominated Sequencing Genetic Algorithm (NSGA-II)

The rules of heat transfer and fluid flow in plate-fin heat exchanger are intricate and complex, and the selection of boundary conditions is the key to giving full play to the performance of heat exchanger. In this paper, a multi-objective optimization based on computational fluid dynamics (CFD) and non-dominated sequencing genetic algorithm (NSGA-II) was carried out to obtain the optimal performance of a plate-fin heat exchanger for an extended-range hybrid vehicle engine. The angle of serrated staggered fin, oil flow rate, and water flow rate were taken as input parameters, and the heat transfer quantity, oil pressure drop, and oil outlet temperature were taken as objective functions to perform the optimization analysis of the heat exchanger. Support vector machine regression (SVR) was used to establish the objective function, and the NSGA-II algorithm was adopted to obtain the Pareto optimal solution set. The optimal solution was determined in the Pareto optimal solution set by comprehensive evaluation based on technique for order preference by similarity to an ideal solution (TOPSIS). The results showed that the best comprehensive performance of the heat exchanger was achieved at a fin angle of 63.01°, an oil flow rate of 9.7 L/min, and a water flow rate of 6.45 L/min. At this time, the heat transfer quantity was 9.79 kW, the oil pressure drop was 13.63 kPa, and the oil outlet temperature was 65.11 °C.

Design Analysis of Heat Sink Using the Field Synergy Principle and Multitarget Response Surface Methodology

This study describes a novel heat sink design approach employs the field synergy concept and multitarget response surface methodology (RSM). The multiobjective response surface methodology can be used to determine the simulation equations that will maximize the heat transfer of fins at various fin heights, fin angles, and fin circumferences, when considering the impact of jet flow heat exchange. The goal of the response value was to maintain the minimum possible average field coangle and fin temperature. The results show that the ideal heat sink size would be the following: fins with a height of 50 mm, an angle of 60 degrees, and the number of fins equal to five. We examined the impact of wall speed on the heat transfer caused by the field synergy angle. Our findings suggest that with the synchromesh of the display field, heat-dissipation efficiency rises.