Concentric Tube Research Articles

Investigation and performance analysis of solar milk pasteurisation system

ABSTRACT The main aim of this research work is to test and evaluate the performance of solar milk pasteurisation system. To evaluate the performance of solar milk pasteurisation system, a solar hot water system, concentric tube type heat exchanger, the cooling tank has used. To test the solar milk pasteurisation system, three different mass flow rate of hot water like 2, 3 and 5 l/min and cold milk 0.5, 0.7 and 1.0 l/min have been used. After the pasteurisation, the obtained milk from the concentric tube type heat exchanger has been tested in the laboratory and achieved satisfactory results. From the series of experiments, it has been found that the hot water flow rate of 5 l/m and milk flow rate of 0.5 l/min found the optimum for the pasteurisation system.

Local wall heat transfer coefficient measurement in a packed bed of cylinders using infrared (IR) thermography technique and application of random packing of cylindrical particles inside concentric tube heat exchangers with water as working medium

Heat transfer enhancement is challenging area in which different techniques are utilized to dissipate the generated heat during operation. Packed beds are devices which enhance heat transport while being compact and are used in several applications such as energy storage, heat exchange devices, catalysis, food processing etc. In the present study, the behavior of wall heat transfer coefficient with randomized packing of equal aspect ratio cylinders is investigated. In this work, the local wall heat transfer coefficient is calculated from local wall temperature data obtained using infrared (IR) thermography in packed beds with randomized packing of cylinders under steady state conditions with water as the working fluid. The randomized packing of cylinders is done inside a concentric tube heat exchanger and the heat transfer enhancement is studied. Experiments are conducted for bed to equivalent particle diameter ratio 2 using random packing of mono-dispersed glass cylinders (dcyl = 6 mm and lcyl = 6 mm). The local wall temperatures are measured using an infrared (IR) camera while the fluid flow takes place through the packed beds. In literature, it is found that wall region contribution to heat transfer is above 90%. The comparison of enhancement in heat transfer for both packing of spheres and cylinders inside concentric tube heat exchangers is done and it is observed that the random sphere packing is superior to cylinder packing.

Evaluation of ultimate bending moment of circular concrete–filled double skin steel tubes using finite element analysis

In this study, the ultimate bending moment of circular concrete-filled double skin steel tubes (CFDSTs) was investigated. A CFDSTs made of two concentric circular steel tubes with concrete infill and M16 shear connector system was fabricated. The four-point bending test of the 10 m long CFDST consisting of outer and inner steel tubes with 914.4 mm and 514.4 mm in diameter, respectively, was carried out and the ultimate bending moment of the CFDST was investigated. A finite element (FE) simulation of the CFDSTs subjected to bending was developed using the commercial software ABAQUS and the accuracy of the developed FE model was verified by comparing to the experimental result. The ultimate bending moment of CFDSTs was then evaluated with respect to different concrete infill compressive strengths and yield strengths of the steel tubes. The corresponding design ultimate bending moments of the CFDST with regard to the design codes AISC and EC4 were also computed. The results revealed that EC4 and AISC can accurately predict the ultimate moment capacities of the CFDST with shear connector.
 Keywords: ultimate bending moment; concrete-filled double skin tube; shear connector system; finite element analysis.
 Received 19 November 2018, Revised 04 January 2019, Accepted 04 January 2019

Transient Dean flow in a channel with suction/injection: A semi-analytical approach

The mathematical model responsible for fully developed laminar transient flow formation between the gaps of two stationary concentric porous tubes due to the imposition of azimuthal pressure gradient (Dean flow) is solved semi-analytically. The tubes walls are porous so that a radial flow can be superimposed. The solution of the momentum and continuity equations are obtained semi-analytically by using the combination of Laplace transform technique and a Laplace inversion method called Riemann sum approximation method. The solutions for skin friction at [Formula: see text] (outer surface of the inner porous tube) and [Formula: see text] (inner surface of the outer porous tube) are presented. The impact of suction/injection parameter and the ratio of the radii of the tubes are examined for the velocity profile and skin friction. Results show that the velocity profile decreases with increase in suction/injection parameter for various values of time, [Formula: see text] and at large value of time, ([Formula: see text]), the velocity and the skin friction attain a steady state.

CFD Application on Shell and Double Concentric Tube Heat Exchanger

This work is concerned with the design and performance evaluation of a shell and double concentric tubes heat exchanger using Solid Works and ANSY (Computational Fluid Dynamics).
 Computational fluid dynamics technique which is a computer-based analysis is used to simulate the heat exchanger involving fluid flow, heat transfer. CFD resolve the entire heat exchanger in discrete elements to find: (1) the temperature gradients, (2) pressure distribution, and (3) velocity vectors. The RNG k-ε model of turbulence is used to determining the accurate results from CFD.
 The heat exchanger design for this work consisted of a shell and eight double concentric tubes. The number of inlets are three and that of outlets are also three for all the fluids that pass through the heat exchanger.
 A comparison was made for the numerical and experimental results and it was found that the percentage error for the hot oil outlet temperature was (6.8%) and the percentage error was (- 21%) for cold water outlet temperature.

Heat transfer behaviour on influence of an adiabatic section on concentric tube shell assisted heat pipe heat exchanger

ABSTRACT Thermal performance of the concentric tube shell assisted heat-pipe heat exchanger with and without adiabatic section has been experimentally investigated. Water is used as a heat-carrying fluid and methanol is used as a working fluid in the heat pipe. Mass flow rates of hot water range from 30 to 70 lph and those of cold water from 15 to 35 lph and during the investigation the temperature of the hot water at inlet ranges from 50to –60°C. For various mass flow rates and inlet temperatures, the heat transfer coefficient, heat transfer rate and effectiveness of the heat exchanger are reported. The mass flow rate of hot and cold water is 70 and 35 lph, respectively, and that of the inlet hot water is 60°C, the effectiveness of heat pipe without adiabatic section is 26.9%. The investigation reveals that there is an increase in effectiveness by 11.2% in non-adiabatic section, compared with adiabatic section.

Quantifying the carbon conversion efficiency and emission indices of a lab-scale natural gas flare with internal coflows of air or steam

To better understand the effect of air- and steam-assist on flaring operations on carbon conversion efficiency and pollutant emissions, a lab-scale coflow burner constructed of two concentric circular tubes was used. Natural gas at 20 SLPM flowed through the annular space and increasing amounts of air or steam were added through the inner tube until flame extinction was invoked. The combustion products were captured by an exhaust hood and analyzed using a gas chromatograph to measure the concentrations of CH4, C2H6, C3H8, C4H10, CO and CO2. A photoacoustic extinctiometer and a NOx analyzer were used to measure black carbon and NOx concentrations, respectively. A challenge associated with the experiments was to accurately resolve stark transitions in conversion efficiency and orders of magnitude change in key emissions. Results indicated that the addition of air or steam to a natural gas jet diffusion flame caused a sudden collapse in carbon conversion efficiency, occurring at a coflow-fuel gas mass flow ratio of 1.8 for steam and 5.0 for air. As was expected, the CO2 emission indices for both air and steam coflow followed their respective carbon conversion efficiency trends. Conversely, the total unburned hydrocarbon emission indices increased with the reduction in carbon conversion efficiency. NOx emission indices for air and steam coflow were shown to decrease by an order of magnitude compared to the unassisted flame. For air coflow this occurred before the collapse in carbon conversion efficiency, while for steam coflow this occurred concurrently. Black carbon emission indices decreased rapidly by three orders of magnitude for both air and steam coflow. For both these lab-scale air and steam assisted flares there was a range of mass flow rates of the assist fluid that resulted in high combustion efficiency and low pollutant emissions.

Experimental Investigation of Heat transfer and Friction Factor Characteristics with Triangular-cut Twisted Tape (TCTT) Inserts

An experiment was conducted to investigate the heat transfer characteristics and friction factor characteristics of a concentric tube fitted with triangular-cut twisted tape (TCTT) insert with a twist ratio Y of 5.4 and depth of triangular cut of 1.2 cm, which were studied for laminar flow. This investigation also is used to find the heat transfer coefficient, Nusselt number and Reynolds number. The heat transfer enhancement was caused with the flow of fluid between the plain twisted tapes and TCTT. The experimental value of plain tube and triangular-cut twisted tube obtained from the experimental work and these two statistical data were compared with the results. The results show that the enhancement of heat transfer rate induced with plain and TCTT inserts increases with the increase in Reynolds number. The Reynolds numbers were varied in the range of 5710–18,366. The Reynolds number in the tube with triangular- cut twisted tape insert were enhanced by 1.1–1.3 times compared with smooth twisted tape inserts. The configuration of TCTT insert offered higher heat transfer rate and friction factor than that of the plain twisted inserts.

Total costs of shell and tube heat exchangers with concentric helical tube coils

The paper deals with the manufacturing costs of shell and tube heat exchangers with concentric helical tube coils. The most common correlations for calculating prices of shell and tube heat exchangers found in accessible literature were tested using the market data for a comparison and they have shown significant deviations. A new correlation for estimating prices of heat exchangers with concentric helical tubes (when the shell is made of carbon steel and the helical tube of copper) was determined in the following form: Cin = 614?S0.627/hts

Numerical simulation of a phase change material melting process

Storage processes are usually integrated in solar energy systems applications due to daily variation of this energy source availability. Among different thermal storage solutions, phase change materials (PCM) lately became more extensively used covering a wide range of operating temperatures. In this regard, a numerical simulation of a PCM melting process is performed under ANSYS CFD environment. A particular configuration is considered consisting in a 2m length annular tube having a 5.48 cm external diameter. The tube is filled with paraffin chosen as PCM. A concentric interior tube of 2.54 cm diameter is used for transporting the heat transfer fluid (HTF) from the solar collector. Heat is transferred through the 1 mm thick pipe wall to the PCM placed all around the HTF tube. The numerical results reveal the melting process of the PCM at different instances and tube sections. The time variation of the PCM liquid fraction is emphasized. The results describe the dynamic behavior of a PCM melting process and might be further integrated in any solar power plant storage charging process simulation.

Evaluation of antimicrobial properties of Solanum xanthocarpum and Pistacia lentiscus extracts on Streptococcus mutans, Lactobacillus species and Actinomyces viscosus: An in vitro study.

Introduction:The Ayurvedic system of medicine is popular in India and has gone through various change and remains as the mainstay of medical relief to a large population. Dental caries is the one of the major issue in the recent time, and there is no definite caries prevention method so far apart from Topical fluoride application, regular oral hygiene measures, pit and fissure sealants and diet measure. In spite of the above mentioned preventive measures the people are still prone to dental caries. In order to find a better solution the present study evaluates the antimicrobial properties widely available and cost effective herbal extracts of Solanum xanthocarpum and Pistacia lentiscus extract on cariogenic oral microbial flora.Aim:To Evaluate the Antimicrobial properties of Solanum xanthocarpum and Pistacia lentiscus extracts on cariogenic oral microbial flora.Methodology:The antimicrobial properties of Solanum xanthocarpum and Pistacia lentiscus extracts on cariogenic oral microbial flora (streptococcus mutans, lactobacillus, actinomyces viscosus) by different culture techniques to estimate the zone of inhibition (well diffusion method) and minimum inhibitory concentration (tube dilution method).Results:The antimicrobial efficacy of Solanum xanthocarpum and Pistacia lentiscus on test bacteria were analysed using kurskal wallis test and values of 0.003 and 0.002 were obtained respectively, since the p values were less than 0.005, indicating that both herbal products possess statistically significant antimicrobial properties.Conclusion:The antimicrobial effects of the herbal extracts were almost on par with commercially available allopathic agents like chlorhexidine on oral cariogenic microbes. The efficacy should be further validated in a large scale studies and can be utilized for caries prevention in the form of mouth rinses, dentifrices and topical application in the future.

Computational Fluid Analysis of Triple Concentric Copper Tube Heat Exchanger

Computational Fluid Analysis of Triple Concentric Copper Tube Heat Exchanger

Thermo-fluid dynamic design optimization of a concentric tube heat exchanger

Thermo-fluid dynamic design optimization of a concentric tube heat exchanger

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.

A Borehole Thermal Resistance Correlation for a Single Vertical DX U-Tube in Geothermal Energy Application

The ground source coupled heat pump is considered as one of the most important technologies utilized in the field of sustainable energy. The borehole thermal resistance has a great impact on the total thermal resistance between the fluid that flows inside the buried U-tube and ground. This issue is related directly to the heat transfer efficiency of the ground part of the heat pump and the effective coefficient of performance of the heat pump system. The capability of the ground heat exchanger to dissipate or absorb energy to or from the ground determines the size and geometry configuration of these heat exchangers. The present research represents a model for the prediction of the borehole thermal resistance of a ground heat exchanger. The U-tube heat source or sink was replaced by a single equivalent concentric tube in the borehole possessing equal thermal resistance as that of the original U-tube heat exchanger. The model was applied for four different U-tube/borehole configurations, the test U-tubes were (9.52) mm, (12.7) mm, (15.88) mm, and (19.05) mm for a borehole to U-tube diameter ratios range of (3.94) to (7.88). The correlation showed a nonlinear dependency for the equivalent tube diameter and hence the thermal resistance of the filling on the U-tube diameter. It has also shown that for the same U-tube/borehole configuration, increasing of the U-tube legs spacing reduces the thermal resistance and approaching a minimum as the tube legs are located close to the borehole wall. Further, for the same borehole size, the thermal resistance exhibited a decrease as the U-tube size was increased and vice versa. At a borehole size of (75) mm, shank spacing to tube diameter ratio of (2), and a grout thermal conductivity of (0.78) W/m.K, the borehole total thermal resistance of the (9.52) mm U-tube size was higher than that of the (19.05) mm by (74)%. The model revealed that the grout thermal conductivity plays an important role in the thermal resistance assessment; the latter showed a decrease as the thermal conductivity increases to the highest test value of 1.9 W/m.K. The predicted thermal resistance was compared with other available correlations in the open literature and found to be consistent in the data trend and magnitudes with acceptable margin.

Design and Optimization of Concentric Tube Robots Based on Surgical Tasks, Anatomical Constraints and Follow-the-Leader Deployment

Many neurological disorders are characterized by the focal and anatomically definable lesions within the brain parenchyma. Traditional treatment may introduce major trauma in neurosurgery and conventional medical devices can only trace straight trajectories. To overcome these problems, a design and optimization method for a patient-specific concentric tube robot (CTR) satisfying the constraints of anatomy, surgical tasks and follow-the-leader (FTL) deployment is proposed in this paper. CTR is a tentacle like continuum robot that can work inside confined and complex biological chambers with the ability of tracking complex 3D trajectories. It consists of pre-curved superplastic tubes with hollow cavities to accommodate the surgical tools. These merits make the CTR well suitable for minimally invasive surgeries. This paper introduces a design framework that utilizes preoperative MRI data to configure patient-specific CTR for single and multiple tasks with the minimum number of tubes. A constant curvature circular arc model is built to solve the problem of inverse kinematics. Two iterative optimization methods for single and multiple tasks are proposed to optimize the parameters of the CTR. Initial waypoints of the CTR are produced based on the FTL deployment. The waypoints are then refined using a Follow Shape Rapidly-exploring Random Tree algorithm (FSRRT) for cases that the initial configurations of the CTR cannot completely satisfy the FTL deployment. Simulations and experiments are carried out on a human brain model to validate the proposed methods. The parameters of CTR including the entire length, curvature, radius angle, number, diameter, arc length and the waypoints are obtained. The errors of the FTL deployment are found to be within 2.1mm.

Acoustic measurement of additive manufactured concentric tube reverse flow resonators

This study investigates acoustic properties of additive manufactured (AM) concentric tube reverse flow (RF) resonators where acoustic attenuation with smaller sample length is achieved by increasing effective travel length of acoustic waves within a structure. The theoretical modeling based on narrow tube theory has been proposed to predict absorption coefficient, while numerical estimation of absorption coefficient is carried out using finite element method (FEM). The predicted theoretical and numerical results are found to be in good agreement with measured results in impedance tube, thus demonstrating its potential in achieving low frequency attenuation with compact size structures.

Field test on energy performance of medium-depth geothermal heat pump systems (MD-GHPs)

This paper introduces the practical energy performance of medium-depth geothermal heat pump systems (MD-GHPs), which use vertical concentric tube as ground heat exchangers (GHEs) to extract heat from the medium-depth geothermal energy for space heating in buildings. Hereby the medium-depth geothermal energy refers to heat embodied in rocks nearly 2–3 km underground with temperature around 70–90 °C. The operation performance and energy efficiency of MD-GHPs is tested in five residential buildings in Xi'an, North China. According to the short-term and annual field test results, the energy performance of MD-GHPs as well as the heat transfer performance of GHEs are introduced and analyzed. Results show that the average temperature of the outlet water from the ground can reach 33.0 °C, promoting the performance of whole systems greatly, with the COP (Coefficient of Performance) of the heat pump reaching 5.43 and the COPhs of heat source reaching 4.58. Therefore, the energy saving rate (ESR) of the MD-GHPs can reach 41.0%, 29.3% and 47.5% compared with air source heat pump systems (ASHPs), conventional ground source heat pump systems (SD-GHPs) and gas boilers.

Concentric annular heat pipe characterisation analysis for a drying application

We present a new configuration of concentric annular heat pipe (CAHP). A CAHP consists of two concentric tubes, with the smaller diameter tube positioned inside the larger one so that an annular space is created by sealing the ends whilst the inner space of the smaller tube is open to the surroundings. Evaporation and condensation take place along the length of the annular space. Unique to our CAHP design, the entire inner space of the central tube was designated as the condenser where wet ceramic slurries were to be conveyed through for moisture reduction. A 515 mm-long stainless steel CAHP was constructed for the present study with 76.2 and 38.1 mm outer and inner tube diameters, respectively. A screen wick was attached only to the inner wall of the outer tube. Several experimental parameters were investigated for their effects on axial temperature profile and thermal resistance: 11–43% filling ratios (a measure of fluid inventory inside the annular space), 0–90° angular orientations and 272–302 W heat inputs. An 11% filling ratio was found to be optimum, giving sufficient fluid inventory for wick saturation and compatible with all orientations and heat inputs. For the 11% filling ratio, vapour temperature differentials between heat pipe extremities were 0.4–1.3 K, showing an excellent isothermal condition. Global thermal resistances were calculated to be 0.08–0.31 K/W. As the wet loads were conveyed through the inner tube, vapour was condensed all along the outside surface of the inner tube, releasing thermal energy to the loads through radial heat transfer. The moisture content of the ceramic slurries was reduced from 33 wt% to 21 wt%, at the highest CAHP heat input of 302 W within 35 s residence time, demonstrating the promising potential of the CAHP as an efficient moisture removal technology.

Comparison of sludges produced from two different recirculating aquaculture systems (RAS) for recycle and disposal

Sludges from Submerged Biofilter (SBF) and Aerobic Three Phase Airlift Fluidized Bed Reactor with Circulation in Concentric Tubes (AAFBR-CT) wastewater treatment of recirculating aquaculture systems (RAS) were evaluated by thermogravimetric analysis. It was considered a microstructural analysis by SEM-EDX and XRD to identify the sample composition. SBF and AAFBR-CT sludge, presented three stages for both combustion and pyrolysis. The first stage to 180 °C was characterized by loss of water, low-stability organic compounds, the second stage, between 235 °C and 385 °C was characterized by decomposition of carbohydrate, lipids, and proteins. The third stage, between 420 °C and 540 °C represents a decomposition of monounsaturated, polyunsaturated fatty acids and amino groups. This sludge had a high ash content and is not viable to use for energy purposes. Presence of granular material was revealed by SEM. XRD analysis only identified SiO2. The sludges generated by RAS could be used in brick and ceramic manufacture, adsorbent material or for phosphorus recovery.