Countercurrent Exchange Research Articles

Nonlinear control of high duty counter-current heat exchangers using reduced order model

In this study, nonlinear control of high duty counter-current heat exchanger is considered. The dynamics of this system can be captured by first order hyperbolic partial differential equations (PDEs), which are stiff due to the high rate of heat transfer. The potential of multi-time scale dynamics is discussed, and model reduction is performed using singular perturbations to obtain non-stiff PDE models which are valid in each time scale. Three controllers are designed and compared in the simulation case study: input/output linearizing controllers on the basis of original model and reduced order model, and a proportional-integral controller. The nonlinear controller designed using the reduced order model showed a superior performance compared to the others, especially in the presence of large modeling errors and disturbances.

Dynamical Analysis and Model Predictive Control of an Auto-Thermal Reactor

This manuscript addresses the design of a model predictive controller for the autothermal reactor with internal counter current heat exchanger (ARICHE) modeled by the system of quasilinear hyperbol...

Development of thermal hydraulic design code for SFR steam generators

Sodium heated once-through steam generator (OTSG) is a critical component of Sodium cooled Fast Reactor (SFR). It is a counter current heat exchanger. It transfers heat from hot sodium to water. Therefore, the steam generator is a necessity for the operation of the plant. However, due to the phase change exists in water side, it becomes challenging to design a steam generator for SFR. After the successful construction of CEFR (China Experiment Fast Reactor), a power-up demonstration SFR is being developed in China. For the design and analysis of the steam generator of the demonstration SFR, a thermal hydraulic Design Code of Once-through Steam generator for Sodium cooled fast reactor (DeCOSS) has been developed based on the movable mesh method. The DeCOSS code has been benchmarked based on the design data of OTSGs reported. The tube lengths and temperature distributions calculated by DeCOSS showed general agreements with published data. The influences of tube diameters on heat transfer capacity have been analyzed. The results indicated that the heat transfer capacity is determined by the thermal resistance of tube wall under the condition of fixed heat transfer coefficient of water side. In addition, under the same flow area of water and sodium, the heat transfer capacity could be enhanced by decreasing the tube diameters with constant tube wall thickness. Hence, the code can be utilized to do the sensitivity analyses and optimum thermal design of OTSGs. Moreover, it can support the design work of once-through steam generator of SFR.

An experimental study on MWCNT–water nanofluids flow and heat transfer in double-pipe heat exchanger using porous media

This paper presents the results of an experimental investigation on the heat transfer characteristics of multi-walled carbon nanotube aqueous nanofluids inside a countercurrent double-pipe heat exchanger using porous media. Aluminum porous media (e = 67%) were used because of the construction of the medium, with porous plate media at the center of the inner tube and with three porous plates on the walls of the inner tube. The effects of operating parameters including flow rate (4600 < Re < 7600), mass fractions of nanofluids (0.04–0.25 mass%), and inlet temperature of nanofluids (Tin = 50 °C) on the heat transfer coefficient were investigated. The results indicate that imposing the plate porous media increases the heat transfer coefficient significantly, and the highest increase in the heat transfer coefficient is 35% which is obtained in the test of the lowest mass fraction (0.04 mass%) with three-plate porous media in the experiment range. As the mass fractions increased, the value of heat transfer enhancement assisted by porous media gradually decreased. Also the lower range 100 (L h−1) of the volume flow rate has a powerful enhancement on the enhancement coefficient, while the higher ranges 300 (L h−1) have low influence.

Thermoprotective adaptations are critical for arthropods feeding on warm-blooded hosts.

Blood feeding in arthropods has evolved in multiple lineages. This feeding preference provides a source of ample proteins and lipids for egg production and survival, but ingestion of a large warm blood-meal can boost the arthropod's body temperature 15°-20°C within seconds to minutes. This represents one of, if not the most, rapid thermal change documented under a natural setting. Here, we describe mechanisms of thermoregulation and thermotolerance in arthropods during blood feeding. The ability to prevent blood-induced thermal damage is a fundamental physiological adaptation linked to the use of warm-blooded vertebrates as food sources. Specific functional and comparative studies have identified unique and divergent mechanisms that suppress or repair thermal stress during blood feeding. These mechanisms include countercurrent heat exchange, evaporative cooling, and upregulation of stress associated proteins.

Impact of variable fluid properties on forced convection of Fe3O4/CNT/water hybrid nanofluid in a double-pipe mini-channel heat exchanger

The objective of this study is to assess the hydrothermal performance of a non-Newtonian hybrid nanofluid with temperature-dependent thermal conductivity and viscosity compared with a Newtonian hybrid nanofluid with constant thermophysical properties. A counter-current double-pipe mini-channel heat exchanger is studied to analyze the effects of the hybrid nanofluid. The nanofluid is employed as the coolant in the tube side, while the hot water flows in the annulus side. Two different nanoparticles including tetramethylammonium hydroxide-coated Fe3O4 (magnetite) nanoparticles and gum arabic-coated carbon nanotubes are used to prepare the water-based hybrid nanofluid. The results demonstrated that the non-Newtonian hybrid nanofluid always has a higher heat transfer rate, overall heat transfer coefficient, and effectiveness than those of the Newtonian hybrid nanofluid, while the opposite is true for the pressure drop, pumping power, and performance evaluation criterion. Supposing that the Fe3O4-carbon nanotube/water hybrid nanofluid is a Newtonian fluid with constant thermal conductivity and viscosity, there leads to large error in the computation of pressure drop (1.5–9.71%), pumping power (1.5–9.71%), and performance evaluation criterion (18.24–19.60%), whereas the errors in the computation of heat transfer rate, overall heat transfer coefficient, and effectiveness are not considerable (less than 2.91%).

The heat transfer enhancement of concurrent flow and counter current flow concentric tube heat exchangers by using hexagonal boron nitride/water nanofluid

Heat exchangers are used in many applications including chemical, oil, and gas power generation, refrigeration, pharmaceuticals, and food processing. Because of their widespread usage, they have various types to serve at different working conditions. Increasing the performance of heat exchangers has become a very interesting field of study since the efficiency of various industrial and domestic systems depend on them. In this study, a coaxial double tube experimental set-up was prepared, and the effect of using nanohexagonal boron nitride nanofluid as hot working fluid on the heat transfer performance increase was investigated. The experiments were carried out in concurrent flow and counter flow conditions for various hot fluid-flow rates to obtain the heat transfer coefficients. Nanohexagonal boron nitride obtained in powder form was used to prepare the nanofluid by a two-step method. The 4 kg nanofluid containing 2% nanohexagonal boron nitride with 0.5% Triton X-100 as a surfactant in terms of mass ratio was prepared for the experiments. Heat transfer experiments were carried out three times by using the prepared nanohexagonal boron nitride/water nanofluid and pure water as hot fluid to reach more precise results. In the result of this study, the total heat transfer coefficient showed an average improvement of 48.78% for the concurrent flow heat exchanger, while an average improvement of 0.36% was observed in the counter flow conditions compared to the base fluid. This study shows the potential of application of nanohexagonal boron nitride/water nanofluid in heat management applications.

Numerical Simulation of Heat Transfer Characteristics between Liquid Lithium Lead and Oil

The liquid LiPb experimental loop is an essential device for studying the compatibility of LiPb with structural materials of the fusion reactor. The heat exchanger is one of the most important devices of the LiPb loop, which is used to control the temperature distribution and study the LiPb flow characteristics in the working condition of the LiPb loop. Based on the heat transfer theory, the liquid LiPb experimental loop cooler is designed at first, which is a tube-type countercurrent heat exchanger with YD-300 heat-conducting oil as the coolant. Numerical simulation analysis was carried out to verify the feasibility of the design scheme under the design condition and the normal operation by using the FLUENT software. The results show that the theoretical design parameters are in good agreement with the numerical simulation results and the average concentration deviation is less than 2%. Furthermore, the average volume temperature and film temperature of heat conducting oil under different working conditions are lower than 310℃ and 375℃ respectively, which indicates that the cooling effect of the LiPb fluid can be realized and the design scheme of the cooler is reasonable.

Microvasculature of the Guttural Pouch Mucosa and Relationship With the Internal Carotid Artery in Horses

The objectives of this study were to describe the microvasculature of the guttural pouch and consider its provable function. We suggest a working hypothesis that the guttural pouch is an additional organ of thermoregulation. Vascular corrosion casts were prepared for scanning electron microscopy by injecting acrylic resin via the common carotid artery, and tissue sections were prepared for histologic examination in 10 equine cadavers. The arteries supplying the guttural pouch originated from the external carotid artery and its branches, and the arteries formed a capillary network in the pouch mucosa. Some of the superficial arterioles and capillaries extended toward the internal carotid artery (ICA) after supplying the pouch mucosa and formed a fine, compact network in the tunica adventitia of the ICA. The capillaries formed two types of vascular plexuses surrounding the ICA: one with capillary bundles parallel to the ICA in the outer layer of the tunica adventitia (outer periarterial plexus) and the other with vein–artery–vein triads in the inner layer of the tunica adventitia (inner periarterial plexus). The microvascular arrangement and the ICA in the guttural pouch were closely related and consisted of a countercurrent heat exchanger. Such an arrangement supports the hypothesis that the guttural pouch participates in selective brain cooling. Results of the present study help provide a better understanding of the function of the guttural pouch in horses.

Optimal design of a sleeve-type steam methane reforming reactor for hydrogen production from natural gas

The three-dimensional computational fluid dynamics (CFD) model was used in a sleeve-type steam methane reforming (SMR) reactor for H2 production of 2.5 Nm3/h from natural gas. The feed and combustion gases acted as a counter-current heat exchange owing to a narrow sleeve equipped between the combustor and catalyst-bed. The CFD results were validated against the experimental data of the SMR reactor with a sleeve gap size of 3 mm. The effect of the sleeve gap size and the flame shape on process performances such as H2 production rate, thermal efficiency, and uniformity of catalyst-bed temperature was investigated using the CFD model. The sleeve gap size influenced the gas velocity inside the sleeve gap and the convective heat transfer. The SMR reactor with a sleeve gap size of 7 mm showed the highest H2 production rate and thermal efficiency when comparing six sleeve gap sizes ranging from 2 to 10 mm. A new flame shape for the SMR reactor with the sleeve gap size of 7 mm was proposed to improve the process performances.

Computational fluid dynamics and experimental validation of a compact steam methane reformer for hydrogen production from natural gas

A three-dimensional (3D) computational fluid dynamics (CFD) model of an annulus steam methane reforming (SMR) reactor was developed for producing 2.5 Nm3/h of H2 from natural gas. The feed and combustion gases played a role in a counter-current heat exchange owing to a narrow sleeve equipped between the combustor and catalytic reactor. The momentum, energy, and mass conservation equations were integrated with a realizable k–ε turbulence model, discrete ordinates radiation model, and reversible SMR reaction kinetics. The CFD results such as axial temperature profiles and producer gas compositions were validated against the experimental data measured in this study. The thermal efficiency of the compact SMR reactor was 60%, and the heat flux through the reactor wall was 39 kW/m2. The overall heat transfer coefficient from the sleeve to the catalytic reactor was 158 W/m2/K. The sleeve-type SMR reactor flattened the temperature profile along the reactor length.

Effect of employing a new biological nanofluid containing functionalized graphene nanoplatelets on thermal and hydraulic characteristics of a spiral heat exchanger

In this study, thermal and hydraulic attributes of an ecofriendly graphene nanofluid flowing within a countercurrent spiral heat exchanger are evaluated. The cold water flows in one side while the hot nanofluid or hot base fluid moves in the other side of heat exchanger. The heat transfer rate and overall heat transfer coefficient enhance with increasing either Reynolds number or concentration. The effect of adding nanoparticles becomes more important at higher Reynolds numbers. At great Reynolds number, the higher heat transfer occurs in the end sections of the heat exchanger whereas at low Reynolds number, the chief heat exchange happens at the initial sections. The results show that the value of effectiveness is much great (higher than 0.85) in all cases under investigation. Moreover, the effectiveness and number of transfer units decrease by increasing the Reynolds number. The pressure drop intensifies with the Reynolds number increment, and the nanofluid demonstrates a greater pressure drop than the base fluid especially at higher Reynolds numbers. Meanwhile, the cold fluid demonstrates a higher pressure drop compared with the hot fluid due to the greater viscosity. The performance index, i.e. the ratio of heat transfer rate to pressure drop, enhances with increase in either Reynolds number or concentration, which is a promising result. Thereby, the performance index for the nanofluid increases almost 142% by increasing the Reynolds number from 1000 to 3000.

Retinal oximetry and systemic arterial oxygen levels.

Retinal oximetry and systemic arterial oxygen levels.

Modelling a molten salt thermal energy system – A validation study

Thermal energy storage (TES) plays a crucial role improving the efficiency of solar power utilization. Molten salt (MS) has gained a strong position as a thermal fluid in applications where solar power is stored and used overnight to provide dispatchable energy production. Novel process and operating concepts are being developed for TES systems that require reliable engineering tools. System-wide dynamic simulation provides a virtual test bench and analysis tool for assisting in process and control design and operational issues. Proper characterization of the thermal fluids in simulation tools is critical for successful simulation studies. In this paper, we report the experimental and modelling work related to counter-current heat exchange and free drainage test runs in CIEMAT’s multi-purpose MS test loop at Plataforma Solar de Almería in Spain. We present a general method to define MS and non-condensable gas within a homogeneous pressure-flow solver. We present modelling of an indirect MS TES system connected to a thermal oil loop through TEMA type heat exchangers, model calibration with half of the experimental data, and finally, validation simulations against rest of the data. All these experimental data are previously unpublished. The model predicts the system behaviour with good agreement regarding temperatures, pressures, flow rates and liquid levels. The simulations suggest that the heat exchangers’ shell sides suffer from trapped non-condensable gas which significantly affects heat transfer, heat loss to ambient air and hydrodynamic losses. Our results contribute to thermal-hydraulic, system-wide modelling and simulation of MS processes. Furthermore, the results have practical implications for MS TES facilities with respect to system design, analysis and operation.

On Modernization of Air Supply Systems for Improvement of Gas Distribution in Shaft Furnaces

The paper presents a developed method for assessment of gas distribution over the cross section of a shaft furnace working in the countercurrent conditions. This method is scientifically based on the fundamental principles of the countercurrent heat exchange theory in shaft furnaces, i.e. dependences of the temperature field throughout the burden bed height on the ratio between heat capacities of gas and burden flows. The ratio between the gas flow heat capacity and burden flow heat capacity at the stock line level is determined by the averaged gas temperature at the burden bed output. By comparing these data, we estimated directions for improving the gas distributing system. Efficiency of this method was assessed when analyzing the system of air supply to the shaft furnace at one of the Ural plants. The analysis showed the main drawbacks of the existing gas distributing system and enabled to determine the main directions for reconstruction of this system. On the basis of the analysis results related to operation of the tuyeres and distribution manifold, we proposed more efficient options of their parameters, i.e. manifold cross-section area, tuyere number and diameter, angle of tuyere inclination to the horizontal. These changes provided a uniform distribution of gases across the furnace and improved conditions for melt flow in the furnace. Thus, we established virtually equal conditions for development of heat and mass transfer processes in the work space of the shaft furnace. The modernized system of air supply to MMSK’s shaft furnace increased the furnace performance by 14.14% in terms of burden, by 23.27% in terms of matte, by 15.15% in terms of slag and by 6.65% in terms of thermal efficiency. At the same time, the following parameters were reduced: specific fuel consumption (anthracite) by 17.46% and dust discharge by 40.5%. When supplying air to the furnace through the inclined tuyeres, it became possible to reduce formation of accretions and provide new working conditions for operating personnel due to a more uniform gas distribution across the horizontal section of the furnace. Within six months of furnace operation the personnel had no problems related to its operation.

Modeling the Operation of a Cooling System for Return Ethylene in the Production of High-Pressure Polyethylene

The authors have presented a mathematical description of the process of cooling of ethylene in countercurrent heat exchangers of the ″double-pipe″ type, where the ethylene gas is flowing in the inner tube, and water is moving countercurrently in the intertubular space. Such a system belongs to the basic cycle of polymerization of ethylene by the high-pressure method. Basic properties of heat-exchange apparatuses of a cooling system and its parameters have been described. The interrelation between such physical quantities as pressure, temperature, flow rates of coolants, and heat-transfer surfaces of circulating water and return ethylene has been determined. The proposed model takes account of the ″sticking″ of a liquid polymer onto interior tube walls.

Fault tolerant system based on non-integers order observers: Application in a heat exchanger

This work presents a fault-tolerant (FT) scheme based on the application of non-integer order observers also called fractional observers, the case of study is a double pipe countercurrent heat exchanger (HE). The aim of the FT is to detect sensors faults as soon as possible, and to provide a healthy signal in order to replace the faulty sensor signal by the fractional observer estimation. To develop the FT scheme a bank of high gain fractional order observers (HGFOO) is proposed. The Riemann-Liouville (RL) fractional derivative definition is used to solve each fractional observer. Experimental measures from a HE were used to test the performance of the fractional observers and the control scheme. The results show the robustness of the proposed observers.

Reduction of chloride in amine from gas sweetening unit using a continuous virtual countercurrent ion exchange setup

In this work, continuous chloride reduction was studied using a Continuous Virtual Countercurrent Ion Exchange setup (CVCIE). With this new laboratory scale setup constructed, ion exchange process which is inherently batchwise was conducted continuously. Lewatit Monoplus M800 OH and Amberjet 4500 OH resins were used for the first time for amine reclamation. According to the resins’ critical properties, Lewatit Monoplus M800 OH showed a better performance in chloride separation. The resin performance is pH-dependent. In this regard, amine-to-resin ratio at different influent chloride concentrations showed that Lewatit Monoplus M800 OH has the potential for higher chloride exchange at a pH of 10.5–11. During several experiments, the optimum amount of caustic needed for regeneration of the saturated resins was determined. Setup results showed that chloride concentration in amine tank was reduced to 50 ± 10 ppm and the pH increased to 11.85 ± 0.15 which were the averages of three different tests.

Convective heat transfer behaviour of water-ethylene glycol-mixture with silver nanoparticles under laminar flow conditions

In this work, we report the forced convective heat transfer performance and pressure drop of aqueous ethylene glycol seeded with silver nanoparticles for low temperature applications. Experiments were performed in a tube in tube counter-current heat exchanger using silver nanofluid as the hot fluid under laminar flow conditions. In this study, water-ethylene glycol mixture with 70:30 volume percent was used as the base medium. Silver nanofluid was allowed to flow through inner tube of the heat exchanger for varying nanofluid mass flow rates from 5 g/s to 30 g/s and three inlet temperatures of nanofluid viz. 2 °C, 5 °C and 10 °C. The increments in thermal diffusivity and viscosity are found to be ~37 % and ~69 % at 0.45 vol%, respectively. The enhancement in heat transfer coefficient at highest mass flow rate is found to be ~94 % for 0.45 vol%. The pressure drop in the silver nanofluid increases with respect to increase in volume percentage of nanoparticles due to increase in viscosity.

Selective Brain Cooling with Transnasal Flow of Ambient Air for Pediatric Resuscitation

Discharge rates and neurologic outcome from out‐of‐hospital pediatric cardiac arrest remains poor. The recent THAPCA trial for out‐of‐hospital pediatric cardiac arrest reported only a small, non‐significant favorable outcome with hypothermic treatment. A major limitation of this study was the median 5.9‐hour delay in inducing hypothermia, as studies in animals show loss of efficacy with this delay in initiation of hypothermia. To minimize this delay, we developed a simple yet innovative technique of transnasal cooling. Air at ambient temperature is passed through standard nasal cannula and out of the mouth to produce evaporative cooling of the nasal passages and a countercurrent heat exchange with cephalic arterial blood. We determined whether an age‐dependent effect exists in the ability to cool the brain because of potential differences in air humidification capacity during development. We studied piglets at 2–5 days of age (1.8 kg; 40 g brain weight), 2 weeks of age (4 kg; 45 g brain weight) and 6 weeks of age (16 kg; 75 g brain weight; adult brain = 110 g). The corresponding nasal turbinate surface area was estimated to be 3176±243, 4847±417, and 8651±1234 mm2. In anesthetized 1.8‐kg piglets with mechanical ventilation and an open mouth to permit airflow exit, institution of nasal airflow of 4 L/min through nasal cannula decreased brain temperature from 38.0±0.4°C to 36.4±0.9, 35.6±1.2, and 34.4±1.7°C at 30, 60, and 120 min, respectively. In 4‐kg piglets, nasal airflow of 32 L/min decreased brain temperature from 38.3±0.3°C to 35.0±0.6, 33.8±0.6, and 31.9±0.6°C at 30, 60, and 120 min, respectively. In 16‐kg piglets, nasal airflow of 32 L/min decreased brain temperature from 38.5±0.4°C to 35.1±1.6, 34.1±1.8, and 32.9±1.6°C at 30, 60, and 120 min, respectively. No further benefit was seen by increasing airflow to 48 L/min. No substantial spatial temperature gradients were seen among the sensory cortex, putamen, thalamus, cerebellum and olfactory bulb in any age group, suggesting that heat transfer is via blood convection rather than direct conduction from the airway wall. Decreases in rectal temperature lagged brain temperature by 30–60 min at all three ages. The rapid and selective brain cooling indicates that a high humidifying capacity of the nasal turbinates is present early in life. Because of its simplicity, portability, and low cost, transnasal cooling potentially could be deployed in the field by emergency medical technicians, in both community hospital emergency rooms, and in low resource areas for early initiation of brain cooling prior to maintenance with standard surface cooling after pediatric cardiac arrest.Support or Funding InformationSupported by NIH NS095036This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.