57 results for Atkins, Martin John

  • Internal fibre length concentration in a pressure screen

    Atkins, Martin John; Walmsley, Michael R.W.; Weeds, Zuben (2007)

    Journal article
    University of Waikato

    Localised axial consistency profiles within a pressure screen of a Pinus Radiata kraft pulp are reported. Axial Samples were also analysed using a Kajaani FS-200 to obtain fibre length distribution data. Localised consistency in the feed annulus was found to vary considerably and the consistency was found to be less than the feed consistency over some portions of the screen (annular dilution). Changes in consistency along the accept side was fairly constant although subtle changes were observed. Pulp passage ratios for both the bulk and individual fibre length fractions were calculated using the consistency profiles and fibre length data. In all cases fibre passage decreased along the screen length. Fibre passage was affected by a position effect which is comprised of two factors: flocculation effects, and flow and rotor effects. Fibre fractionation efficiency was found to increase along the length of the screen. Mechanisms that account for the observed annular dilution, passage ratio and efficiency changes are proposed. These involve flow of both fluid and fibre in the forward and reverse directions across the screen plate, increased flocculation in the feed annulus and the slip velocity between incoming pulp and the rotor tip.

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  • Pinch Analysis of an Industrial Milk Evaporator with Vapour Recompression Technologies

    Walmsley, Timothy Gordon; Walmsley, Michael R.W.; Neale, James R.; Atkins, Martin John (2015-08-24)

    Conference item
    University of Waikato

    The present study focuses on applying Pinch Analysis to an industrial milk evaporator case study. Modern milk evaporators are typically integrated using both mechanical and thermal vapour recompression technologies as the primary means for attaining a high level of energy efficiency. A significant step change in energy efficiency for milk evaporators is achieved in this study by modifying the set-up of the concentration processing pathway in combination with an improved heat exchanger network design. To effectively perform the Pinch Analysis, a validated mass and energy balance model of the milk evaporator case study has been implemented in an Excel spreadsheet from which appropriate stream data may be extracted. In particular the Grand Composite Curve plays a critical role in identifying where vapour recompression units, which are a type of heat pump, may be applied to reduce thermal energy use by as much as 67%, which represents an annual utility cost saving between $640 – 820k /y.

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  • Axial Variations and Entry Effects in a Pressure Screen

    Atkins, Martin John (2007)

    Doctoral thesis
    University of Waikato

    Pressure screens are used for contaminant removal and fibre length fractionation in the production of pulp and paper products. Axial variations and entry effects in the screen are known to occur and these variations have not been adequately quantified. This thesis describes a fundamental study of the axial variations of several factors that occur within an industrial pressure screen; namely, pulp consistency, fibre length distribution, rotor pressure pulse, and feed annulus tangential velocity. Axial variations of pulp consistency in the screen annulus and the accept chamber of the screen were studied using an internal radial sampling method. Localised pulp samples were taken and evaluated and common measures of screen performance such as fibre passage ratio and fractionation efficiency were calculated along the screen. Consistency generally increased along the length of the screen although under certain conditions the consistency toward the front of the screen was lower than the feed consistency. A two passage ratio model that incorporated forward and reverse passage ratio was derived to elucidate the flow of both fibre and fluid through the screen and their effects on overall screen performance. The passage of fibre through the screen decreased with screen length which generally had a positive effect on the fractionation efficiency toward the back of the screen. The passage of individual fibre length fractions was also studied and it was found that long fibre had a much lower passage than short fibre which caused the average fibre length in the annulus to increase. Rotor induced pressure pulse variations along the screen length were also investigated. The magnitude of the pressure pulse was significantly lower (up to 40 %) at the rear of the screen. The variation in pressure caused by the rotor is due to a Venturi effect and the shape of the rotor. The relative velocity of the fluid and the rotor, called the slip factor, also directly affects the size of the pressure pulse in the annulus. The slip factor decreases along the length of the screen due to the increase in tangential velocity of the fluid. Pressure pulse data was also used to estimate the instantaneous aperture velocity and back-flush ratio. The instantaneous aperture velocity was calculated to vary considerably from the superficial aperture velocity by up to 5 m/s in the forward direction and 10 m/s in the reverse direction. Computational Fluid Dynamics (CFD) was used to model tangential velocity changes in simplified screen annuli with axial through flow. For a smooth screen rotor the mean tangential velocity increased over the entire length of the annulus without reaching a maximum value. A step and bump rotor were modelled and the shape of the pressure pulses showed good agreement with experimentally measured pulses. The mean tangential velocity and the entrance length were found to be heavily dependant on the screen rotor used.

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  • Total site methodology as a tool for planning and strategic decisions

    Nemet, Andreja; Klemeš, Jiri Jaromir; Varbanov, Peter; Atkins, Martin John; Walmsley, Michael R.W. (2012)

    Journal article
    University of Waikato

    A Total Site (TS) is defined as a set of processes (industrial plants, residential, business and agriculture units) linked through the central utility system. The utility system incorporates a number of operating units such as boilers, steam turbines, gas turbines and letdown stations. Many sites are using the TS system representation. Heat Integration at TS level has been well developed and successfully implemented. However, sites typically develop with time and even minor changes/extensions can affect TS heat recovery significantly. It is beneficial to plan their strategic development in advance, to increase or at least not to decrease the rate of heat recovery when integration of additional processes takes place. Even when this has not been done at the initial stage, the TS methodology can still be used as a tool for the strategic planning decision making. This work illustrates how the TS methodology can contribute to the strategic development and the extension planning of already existing TS. The aim is to reveal the potentials for Heat Integration, when new units or processes are considered for the inclusion in the TS. Moreover, some operating parameters (e.g. temperature or capacity) of the unit can be proposed to achieve the best possible heat recovery. The degrees of freedom for TS changes can be on two levels: (i) only adding an operating unit to the current utility system (the Total Site Profiles remain the same) or (ii) changing of the TS by including more processes (the Total Site Profiles are changed). The first group of changes includes the integration of heat engines to produce electricity utilising heat at higher temperature and returning it to the system at lower temperature, which is still acceptable for the heat recovery and simultaneously for the electricity production. The second group of changes is more complex. For evaluating these changes a plus/minus principle is developed allowing the most beneficial integration of new units to the TS. Combinations of both types of changes are also considered.

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  • The challenge of integrating non-continuous processes-milk powder plant case study

    Atkins, Martin John; Walmsley, Michael R.W.; Neale, James R. (2009)

    Journal article
    University of Waikato

    The integration of non-continuous processes such as a milk powder plant present a challenge for existing process integration techniques. Current techniques are generally based on steady and continuous operation which for some industries is not the case. Milk production varies considerably during the year as dairy cows in New Zealand are grazed on pasture, which affects the scheduling and operation of plants on site. The frequency and duration of cleaning cycles and non-productive operating states can have a major affect on energy demand and the availability of heat sources and heat sinks. In this paper the potential for indirect heat transfer between the several plants using a heat recovery loop and stratified tank at a typical New Zealand dairy factory is investigated. The maximum amount of heat recovery is calculated for a range of recirculation loop temperatures. The maximum amount of heat recovery can be increased considerably if the temperature of the hot fluid in the recirculation loop is varied depending on which condition the site is operating under.

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  • WinGEMS modelling and pinch analysis of a paper machine for utility reduction

    Atkins, Martin John; Morrison, Andrew S.; Walmsley, Michael R.W.; Riley, Joseph (2010-09)

    Journal article
    University of Waikato

    A multi-ply paper machine process model was developed using WinGEMS and the stream data produced was used to conduct a pinch analysis. The product stream was excluded from the analysis and the composite curves display the enthalpy contained only in the inputs and outputs to the various sections of the paper machine. The pinch point for the overall paper machine was 55.9 C while the minimum hot utility target was 170 MW. Occurrences of cross pinch heat transfer were identified and discussed. Heat recovery options for heating of the fresh water showers, using waste heat streams were investigated. Steam savings of over 14 MW could be achieved by recovering heat from two waste streams that currently go directly to drain with no heat recovery taking place. The use of pinch analysis for utilities targeting under non-continuous conditions was examined. Finally, the feasibility of integrating non-conventional technologies, such as heat storage, is discussed.

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  • Importance of understanding variable and transient energy demand in large multi-product industrial plants for process integration

    Walmsley, Michael R.W.; Atkins, Martin John; Morrison, Andrew S.; Neale, James R. (2011)

    Journal article
    University of Waikato

    There have been some news releases claiming that Professor Henle in Germany has found the chemical identity of UMF, and that in future chemical analysis will be used instead of assays of antibacterial activity to indicate the level of UMF in manuka honey. Both of these claims are misleading. Because the level of active substance in manuka honey is an unreliable indication of the level of antibacterial activity and can be very misleading, it is hard to see any commercial advantage for it to be used to indicate antibacterial activity other than if someone wanted to fool the consumer into thinking that the higher numbers are giving them a level of antibacterial activity that is far higher than they are really getting.

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  • Carbon Emissions Pinch Analysis (CEPA) for emissions reduction in the New Zealand electricity sector

    Atkins, Martin John; Morrison, Andrew S.; Walmsley, Michael R.W. (2010)

    Journal article
    University of Waikato

    Carbon Emissions Pinch Analysis (CEPA) is a recent extension of traditional thermal and mass pinch analysis to the area of emissions targeting and planning on a macro-scale (i.e. economy wide). This paper presents an extension to the current methodology that accounts for increased demand and a carbon pinch analysis of the New Zealand electricity industry while illustrating some of the issues with realising meaningful emissions reductions. The current large proportion of renewable generation (67% in 2007) complicates extensive reduction of carbon emissions from electricity generation. The largest growth in renewable generation is expected to come from geothermal generation followed by wind and hydro. A four fold increase in geothermal generation capacity is needed in addition to large amounts of new wind generation to reduce emissions to around 1990 levels and also meet projected demand. The expected expansion of geothermal generation in New Zealand raises issues of GHG emissions from the geothermal fields. The emissions factors between fields can vary by almost two orders of magnitude making predictions of total emissions highly site specific.

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  • Ensuring cost-effective heat exchanger network design for non-continuous processes

    Morrison, Andrew S.; Atkins, Martin John; Walmsley, Michael R.W. (2012)

    Journal article
    University of Waikato

    The variation in stream conditions over time inevitably adds significant complexity to the task of integrating non-continuous processes. The Time Averaging Method (TAM), where stream conditions are simply averaged across the entire time cycle, leads to unrealistic energy targets for direct heat recovery and consequently to Heat Exchanger Network (HEN) designs that are in fact suboptimal. This realisation led to the development of the Time Slice Method (TSM) that instead considers each time interval separately, and can be used to reach accurate targets and to design the appropriate HEN to maximise heat recovery. However, in practise the HENs often require excessive exchanger surface area, which renders them unfeasible when capital costs are taken in to account. An extension of the TSM that reduces the required overall exchanger surface area and systematically distributes it across the stream matches is proposed. The methodology is summarised with the help of a simple case study and further improvement opportunities are discussed

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  • Integrating heat recovery from milk powder spray dryer exhausts in the dairy industry

    Atkins, Martin John; Walmsley, Michael R.W.; Neale, James R. (2011)

    Journal article
    University of Waikato

    Heat recovery from milk powder spray dryer exhausts has proven challenging due to both economic and thermodynamic constraints. Integrating the dryer with the rest of the process (e.g. evaporation stages) can increase the viability of exhaust recovery. Several potential integration schemes for a milk powder plant have been investigated. Indirect heat transfer via a coupled loop between the spray dryer exhaust and various heat sinks were modeled and the practical heat recovery potential determined. Hot utility use was reduced by as much as 21% if suitable heat sinks are selected. Due to high particle loading and operating temperatures in the particle sticky regime, powder deposition in the exhaust heat exchanger is perhaps the greatest obstacle for implementing heat recovery schemes on spray dryers. Adequate cleaning systems are needed to ensure continuous dyer operation.

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  • Thermocline management of stratified tanks for heat storage

    Walmsley, Michael R.W.; Atkins, Martin John; Riley, Joseph (2009)

    Conference item
    University of Waikato

    Stratified tanks are useful for maximising the thermal energy efficiency of non-continuous and semi-continuous processes. Liquid at two or more dissimilar temperatures is stored within the same tank to provide a buffer for variations in heating and cooling loads. Control of the thermocline between the hot and cold fluid regions is needed to minimise thermocline growth and maximise operation of the storage tank. An experimental programme using a scale model of an industrial stratified tank (aspect ratio 3.5) and Perspex tank (aspect ratio 8.2) is reported. The behaviour and growth of the hot-cold thermocline under various operating conditions is presented. A siphoning method to re-establish the thermocline without interrupting the use of the tank is tested. Siphoning of the thermocline region from either 20%, 50% or 80% of the tank height is an effective strategy for uninterrupted interface re-establishment. However, the rate and position of siphoning and the load balance of the exit streams are critical variables for minimising the time for effective re-establishment of the two temperature zones.

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  • Total site targeting with stream specific minimum temperature difference

    Fodor, Zsófia; Klemeš, Jiri Jaromir; Varbanov, Peter; Walmsley, Michael R.W.; Atkins, Martin John; Walmsley, Timothy Gordon (2012)

    Journal article
    University of Waikato

    The paper focuses on extending traditional Total Site Integration methodology to produce more meaningful utility and heat recovery targets for the process design. The traditional methodology leads to inadequate results due to inaccurate estimation of the overall Total Site heat recovery targets. The new methodology is a further development of a recently extended traditional pinch methodology. The previous extension was on the introduction of using an individual minimum temperature difference (δTmin) for different processes so that the δTmin is more representative of the specific process. Further this paper deals with stream specific δT min inside each process by setting different δT contribution (δTcont) and also using different δTcont between the process streams and the utility systems. The paper describes the further extended methodology called stream specific targeting methodology. A case study applying data from a real diary factory is used to show the differences between the traditional, process specific and stream specific total site targeting methodologies. The extended methodology gives more meaningful results at the end of the targeting with this avoiding the over or under estimated heat exchanger areas in the process design.

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  • Optimal waste stream discharge temperature selection for dryer operations using thermo-economic assessment

    Walmsley, Timothy Gordon; Walmsley, Michael R.W.; Atkins, Martin John; Fodor, Zsófia; Neale, James R. (2012)

    Journal article
    University of Waikato

    A typical drying process that has liquid and gas discharge streams has been analysed and the impact of selecting various combinations of soft temperatures on heat recovery, utility targets, area targets, capital cost and total cost is reported. The method is based on the plus-minus principle and traditional pinch analysis methods for utility, area and capital cost targeting with the modification of using a ΔT contribution. Results show that there is significant benefit from optimising discharge temperatures for total cost. To achieve minimum energy consumption and total cost, heat recovery from the dryer exhaust air is necessary. Heat recovery from liquid heat sources is shown to be preferable over gas streams due to a higher film coefficient resulting in less heat exchanger area and capital cost. There is also value in making process modifications, such as combining streams or removing small streams to be solely heated by utility, to reduce the number of network heat exchangers. For the best case, the discharge temperatures of the leaving streams are 18.0 °C for water condensate (liquid stream) and 52.4 °C for the exhaust air (gas stream).

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  • Minimising energy use in milk powder production using process integration techniques

    Atkins, Martin John; Walmsley, Michael R.W.; Walmsley, Timothy Gordon; Fodor, Zsófia; Neale, James R. (2012)

    Journal article
    University of Waikato

    Spray drying of milk powder is an energy intensive process and there remains a significant opportunity to reduce energy consumption by applying process integration principles. The ability to optimally integrate the drying process with the other processing steps has the potential to improve the overall efficiency of the entire process, especially when exhaust heat recovery is considered. However, achieving the minimum energy targets established using pinch analysis results in heat exchanger networks that, while theoretically feasible, are impracticable, unrealistic, contain large number of units, and ultimately uneconomic. Integration schemes that are acceptable from an operational point of view are examined in this paper. The use of evaporated water is an important factor to achieve both energy and water reductions. The economics of additional heat recovery seem favourable and exhaust heat recovery is economically justifiable on its own merits, although milk powder deposition should be minimised by selecting an appropriate target temperature for the exhaust air. This will restrict the amount of heat recovery but minimise operational risk from heat exchanger fouling. The thermodynamic constraints caused by the operating temperatures of the dryer and the poor economics exclude the use of heat pumps for exhaust heat recovery in the short to medium term.

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  • Methods for improving heat exchanger area distribution and storage temperature selection in heat recovery loops

    Walmsley, Michael R.W.; Walmsley, Timothy Gordon; Atkins, Martin John; Neale, James R. (2013)

    Journal article
    University of Waikato

    Inter-plant Heat Integration across a large site can be achieved using a HRL (Heat Recovery Loop). In this paper the interrelationship between HRL storage temperatures, heat recovery and total HRL exchanger area is investigated. A methodology for designing a HRL based on a ΔTmin approach is compared to three programming optimisation approaches where heat exchangers are constrained to have the same NTU (Number of Heat Transfer Units), LMTD (Log-Mean Temperature Difference) or to find the absolute MTA (Minimum Total Area) for a given heat recovery level. Analysis is performed using time-averaged and transient mass flow rate data and temperature data. The actual temperature driving force of the HRL heat exchangers is compared to the apparent driving force as indicated by the Composite Curves. Results for the same heat recovery level show that the ΔTmin approach is effective at minimising total area to within 5% of the minimum area approach. Allocation of individual heat exchanger areas can vary widely depending on the optimisation method, the characteristics of the transient stream data and the differences in the approach and exit stream temperatures. Results suggest that using the ΔTmin method for selecting storage temperatures in combination with sizing exchangers based on the time average CP values (for while the process is running) gives a near optimal solution without requiring lots of data input or computing resources

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  • Improving energy recovery in milk powder production through soft data optimisation

    Walmsley, Timothy Gordon; Walmsley, Michael R.W.; Atkins, Martin John; Neale, James R. (2013)

    Journal article
    University of Waikato

    Milk powder production is highly energy intensive and can benefit from the application of Pinch analysis techniques to develop better methods for integrating the process. In this study, process stream data is extracted from an industrial plant and Pinch analysis applied to calculate utility and heat recovery targets. Some of process data is also varied, within small ranges that do not harm product quality or violate environmental regulation, to minimise utility use targets. Using the Pinch design method and the targets as a guide, Maximum Energy Recovery (MER) networks are developed for two cases, where the condenser in the evaporator section of the plant may be directly or indirectly integrating into the reminder of the process. The two MER networks are compared to two heat exchanger network structures commonly found in industry. Results show that there is potential to increase specific heat recovery by over 30%, while reducing total cost by almost 10%, in the best case. To achieve maximum energy recovery, spray dryer exhaust air heat recovery is necessary and should be matched to preheat the dryer inlet air stream.

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  • Fouling and pressure drop analysis of milk powder deposition on the front of parallel fins

    Walmsley, Timothy Gordon; Walmsley, Michael R.W.; Atkins, Martin John; Neale, James R. (2013)

    Journal article
    University of Waikato

    One method to reduce the energy consumption of industrial milk spray dryers is to recover waste heat from the exhaust dryer air. A significant challenge associated with this opportunity is the air contains a small amount of powder that may deposit on the face and surfaces of a recuperator. This paper introduces a novel lab based test that simulates powder deposition on a bank of parallel plate fins at exhaust dryer air conditions. The fin bank acts like the face of a typical finned tube row in a recuperator. The aim of this study is to look at how deposition on the front of fins is affected by the air conditions. Results show similar characteristics to other milk powder deposition studies that exhibit a dramatic increase in deposition once critical stickiness levels are reached. As powder deposits on the face of the fins, the pressure drop across the bank increases until eventually an asymptote occurs, at which point the rates of deposition and removal are similar. For very sticky conditions, deposition on the face of the fins can cause a rise in the pressure drop by as much as 65%. The pressure drop has also been successfully related to the percentage of open frontal area of the fins with and without deposition. Deposition inside and at the rear of the fin bank was found to be minimal.

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  • A derivative method for minimising total cost in heat exchanger networks through optimal area allocation

    Walmsley, Timothy Gordon; Walmsley, Michael R.W.; Morrison, Andrew S.; Atkins, Martin John; Neale, James R. (2013)

    Journal article
    University of Waikato

    This paper presents a novel Cost Derivative Method (CDM) for finding the optimal area allocation for a defined Heat Exchanger Network (HEN) structure and stream data, without any stream splits to achieve minimum total cost. Using the Pinch Design Method (PDM) to determine the HEN structure, the approach attempts to add, remove and shift area to exchangers where economic benefits are returned. From the derivation of the method, it is found that the slope of the ε-NTU relationship for the specific heat exchanger type, in combination with the difference in exchanger inlet temperatures and the overall heat transfer coefficient, are critical to calculating the extra overall duty each incremental area element returns. The approach is able to account for differences in film coefficients, heat exchanger types, flow arrangements, exchanger cost functions, and utility pricing. Incorporated into the method is the newly defined “utility cost savings flow-on” factor, θ, which evaluates downstream effects on utility use and cost that are caused by changing the area of one exchanger. To illustrate the method, the CDM is applied to the distillation example of Gundersen (2000). After applying the new CDM, the total annual cost was reduced by 7.1 % mainly due to 24 % less HEN area for similar heat recovery. Area reduction resulted from one exchanger having a minimum approach temperature (ΔTmin) of 7.7 °C while the other recovery exchangers had larger ΔTmin values. The optimum ΔTmin for the PDM was 12.5 °C. The CDM solution was found to give a comparable minimum total area and cost to two recently published programming HEN synthesis solutions for the same problem without requiring the increased network complexity through multiple stream splits.

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  • Design and operation methods for better performing heat recovery loops

    Walmsley, Michael R.W.; Walmsley, Timothy Gordon; Atkins, Martin John; Neale, James R. (2012-09-23)

    Conference item
    University of Waikato

    Inter-plant integration via a heat recovery loop (HRL) is an economic method for increasing total site process energy efficiency of semi-continuous processes. Results show that both the constant storage temperature approach and variable storage temperature approach have merit. Depending on the mix of source and sink streams attached, it may be advantageous to change the operation of an existing HRL from a constant temperature storage to a variable temperature storage. To realise the full benefits of this change in operation, a redistribution of the existing heat exchanger area may be needed.

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  • Tube shape selection for heat recovery from particle-laden exhaust gas streams

    Walmsley, Timothy Gordon; Walmsley, Michael R.W.; Atkins, Martin John; Neale, James R.; Hoffmann-Vocke, Jonas (2011-12-01)

    Conference item
    University of Waikato

    Heat recovery from exhaust gas streams is applicable to a wide variety of industries. Two problems encountered in exhaust gas heat recovery are: the high heat transfer resistance of gases and the presence of entrained particulate matter, which can limit the use of extended surface area. Standard heat exchangers use round tube. This study uses Computational Fluid Dynamics (CFD) to investigate whether round or another shape is the best tube selection for exhaust heat recovery. Tube shape rankings are based on taking into account heat transfer, gas flow resistance and foulability. Foulability is inferred from the average wall shear stress around the front or back of each shape. An estimated asymptotic fouling resistance is used to calculate an equivalent fouled j factor, jf. CFD results suggest the best tube for exhaust heat recovery is an elliptical tube. The ellipse shape produced j/f and jf/f ratios (where f is the tube bank friction factor) over 1.5 times larger than that of standard round tube. A flattened round tube is also promising and may be the practical and economic optimum.

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