Marine power systems are facing the need for bringing an innovation to the recent regulatory requirements for greener transportation. The reduction of greenhouse gas emission is the most crucial challenge. Improvement in thermal efficiency of engine systems, without an increase in NOX emission rate, is strongly encouraged for lowering the CO2 emission. The use of low carbon fuels such as natural gas would be of great interest to reduce CO2 and NOX/SOX emissions. In the near future, a variety of alternative fuels would be within the scope of the marine transportation sector including hydrogen and ammonia, both with zero carbon content. Another important technical trend is information technology. Autonomous ships are now in focus as a future marine transportation to ensure a safer and more economical voyage, where power systems are required more controllable and with less maintenance. The presentation provides an overview of the urgent challenges to respond the requirements of the environmental regulations and to introduce advanced technologies.
To reduce SOx emission, it has been decided that a global cap for sulfur % of marine fuel, which limits the sulfur content of all marine fuel to within 0.5%, starts from 2020. Subsequently, conventional heavy fuel oil (HFO) will not be used for any ship that has not been fitted with an exhaust gas SOx scrubber.
On the EEDI or CO2 emission from ships, reduction by 20% for the newly built ships after 2020 must be implemented. The subject of energy-saving vessel and engine designs is currently being discussed and researched by various organizations representing government and industry. For example, the conversion of marine fuel into natural gas is a very effective solution, achieving the reduction of CO2 more than 20% while at the same time eliminating all the harmful emissions.
What kind of marine fuel will appear as an alternative to HFO should be discussed from the viewpoint of combustion quality, availability, cost (CAPEX and OPEX of ship), and ease of distribution in the world to allow proper preparations to be made before the afore-mentioned sulfur global cap and EEDI reduction become a reality.
This paper focuses how the alternative liquid and gaseous fuels will burn in a marine engine to support the above-mentioned discussion.
Among the energy sources nowadays, fossil fuels are the most popular being utilized but have a huge impact and contribute negatively on the environment. Along with vast economic benefit, maritime transportation industry and stakeholders in particular are facing a serious challenge of addressing environment pollution protection due to the impacts of engine emissions to populace in general. Currently, state authorities have also become more vigilant on the implementation of environmental pollution policies especially on the energy industry sector that plays a vital role.
The 71st session of the IMO MEPC was held in London from 3rd to 7th July 2017. Exhaust emissions such as CO2, PM and VOC have been discussed at the meeting and regulations will possibly be in effect in the near future. The first mandatory measure on energy efficiency was entered into force on 1 January 2013 while the Tier III NOx emission regulations became effective last 1st January 2016. This keynote speech describes the performance and emissions of Marine Diesel Engines as well as the results of MEPC 71st session.
The aim of this study was to develop the multi-zone diesel combustion model modified to apply for diesel combustion in lean mixture of gaseous fuel. The modified model uses a chemical kinetics simulation called Cantera for predicting combustion. The presented paper shows the effects of CH4 gas mixed into intake air on the diesel engine. Next, we show modified model behaviors respect to the number of dividing spray region and crank angle step resolution on the simulation. In addition, the predictions of heat release and cylinder pressure by the modified model are compared with the results obtained from experiments with a single-cylinder diesel engine. The results show that the predictions of heat release and cylinder pressure agreed with experimental data by adjusting the coefficients regarding of air entrainment of diesel spray in the modified model. We found that the modified model can estimate qualitative effects of mixing gaseous fuel into intake air on combustion.
This study is aimed at conducting an experimental study to find the macroscopic relationship between two-phase flow structure and frictional drag. The experiments were performed for two-phase flow in a horizontal rectangular channel which simulates the external two-phase flow. The local two-phase flow parameters including void fraction, gas chord length and interfacial velocity were measured by a double-sensor probe. Flow observation was also conducted using a high-speed camera. A correlation for prediction of drag coefficient ratio which expresses the drag reduction effect due to air injection was developed. Predictions by the correlation were compared with 161 data. The correlation could predict the measured data in horizontal rectangular channel with the average relative deviation of 8.8%.
Gradually toughening requirements on reducing ships energy consumption and gas emissions raise the importance of adoption of various energy saving systems on engine and ship. However, a correct coupling of the various systems is of great importance in achieving the ultimate ship efficiency. One of the examples of such a coupling is the application of air lubrication for the ship hull resistance reduction, air for which is bled from the scavenging system of the main engine. This system has found an application on a real ship, the range of operation is limited though. This paper proposes the way of extending operation of air lubrication system by taking advantage of power take-in capabilities of recently developed assist systems for turbochargers. As was found experimentally and confirmed analytically the increase of air bleeding rate requires a proportional increase of compressor’s assist power and droop control of scavenging pressure can reduce assist power demand considerably.
Constantly tightening regulations and rules related to emissions and energy-efficiency lead to a more complex design of the ship systems where several new technologies are applied simultaneously. Since the scavenging process is the most important factor affecting the performance, efficiency and emission characteristics of a two-stroke engine, most of the technologies, somehow or other, relate to engine air supply system. Thus in order to ensure the optimal systems integration and operation, an intelligent air management of the engine is required. In this paper, the results of scavenging characteristics measurements and simulations are reported. The tests were performed on a two-stroke marine diesel engine varying scavenging air pressure, engine speed and exhaust valve close (EVC) timing, next the simulation software was used to get an insight of the scavenging process. The obtained results set prerequisites for the development a simple estimation model of the air excess ratio available for the combustion which can be used for the intelligent scavenging system control, furthermore, a simple correlation of the specific fuel consumption and the air excess ratio has also been found.
Engine power reduction is now regarded as the most efficient and easy realisable measure to improve the Energy Efficiency Design Index, introduced by the IMO. However, there is a concern regarding the sufficiency of propulsion power to maintain manoeuvrability of ship in the adverse sea, and so the IMO also set the interim guideline to assess Minimum Propulsion Power (MPP). As a result of these streams, it has never been more important to evaluate the performance of the ship in actual sea conditions, even including engine characteristics deeply. Here, as a method to validate or investigate designs of ship propulsion plant system in the initial design stage, the authors have developed an intelligent motor system for the ship model test, called as a Marine Diesel Engine Simulator (MDES). The MDES consists of the cycle mean value model of engine, a speed governor and motion equation of propeller shaft. The MDES simulates the response of the engine model in real time, based on the measured propeller torque and speed, and manage the rotational speed of the motor as the calculated response. In this way, the engine matching, requirement on MPP, speed governor settings, etc., can be easily validated at the design stage without the need for full-scale tests. This paper briefly introduces the tank test methodology and then discusses the test results of propulsion plant responses in regular waves at different speed governor settings in details.
The AC motor drive system is widely used in electric propulsion systems. This motor drive system has a far faster response time (by up to several milliseconds) than a conventional system. It is also possible to monitor the state (current, voltage, torque, rotational speed) of the motor accurately in real time. If bubbling in the vicinity of the propeller is detected by monitoring the motor state, an additional special device such as a torque meter can be omitted from the propulsion system. Furthermore, a faster response time allows advanced propeller control, enabling the suppression of bubble formation and the resulting effects in real time. This paper demonstrates the detection of bubbles and fluctuating thrust due to bubble entrainment by monitoring signals from the motor, as it is driven in constant torque control mode. A fluctuating thrust force can be detected and well correlated with any bubble interactions using the monitoring signal.
The ion eluted from the metal surface is expected to utilize as the scale inhibitor. In previous study, we found that the eluted phosphate ion from Ni-P coated steel prevents the adhesion amount of CaCO3 scale. However, its scale inhibiting mechanism is unclear. The scale formation process should be explained as the nucleation (the generation of crystal on the surface), its growth and transformation. In present study, we investigated the effect of nucleation and crystal growth on the adhesion amount of CaCO3 to understand the mechanism of inhibiting the adhesion by the eluted phosphate ion. Test materials are Ni, Ni-5%P, Ni-8%P, Ni-12%P, and Ni-14%P coated steels. CaCO3 scale adhesion testing was conducted to the Ni-P coated steels. The adhesion morphology of calcium carbonate was observed by scanning electron microscopy. There were four kinds of polymorphic crystal forms on the test materials: calcite, aragonite, vaterite, and irregular shape crystal. The adhesion amounts, the crystal numbers of their polymorphs, and their sizes were measured. There was almost no correlation between the adhesion amount and the crystal number of polymorphs. Inhibiting nucleation does not affect on the inhibiting adhesion amount. On the other hand, there was a strong correlationship between total adhesion amount and the size of irregular shape crystal. The reason why the scale adhesion amount became small may be that the crystal growth by the eluted phosphate ion has been suppressed.
The environmental pollution with exhaust gases of fuel combustions is one of the serious global problems. IMO (International Maritime Organization) has issued the NOx emission rules, Tier I started from 2011, and Tier III from 2016. As a result, technologies to reduce NOx concentration, and also PM concentration, have been developed around the world. At the same time, rules to reduce PM and SOx have been issued by limiting sulfur content in fuel oils used on board. At ECA (Emission Control Area), fuel with a sulfur content of no more than 0.1% must be used from 2015. Outside ECA, the sulfur limitation will be reduced from 3.5% to 0.5% in 2020. However, at present, despite of recent advances in technologies, So we combine treatment technologies, regulation must be satisfaction. Improvement of suction air and Fuel is before treatment technology, such as EGR (Exhaust Gas Recirculation) and water emulsified fuel. Reduction of NOx concentration is SCR (Selective Catalytic Reduction), Reduction of PM concentration is DPF (Diesel Particulate Filter), and they are after treatment technology. However, new regulation is severe restriction, we must develop new technology. UFB (Ultrafine Bubble) water is included bubbles of less than 1μm, and it has several radical. ·OH radical is improved combustion, such as spark purge. The objective of this study is to reduce the pollutants from diesel exhaust gas and improve the fuel consumption by mixed with ·OH radical into the fuel. The authors developed a device and extracting radical element from Ultrafine Bubbles (UFB) water and mixing the extracted ·OH radical with special loop. This study is to reduce the pollutants from diesel exhaust gas and improve the fuel consumption by mixed with ·OH radical into the fuel. The outcomes of the results are summarized as follows: (1) We obtained the following conclusion from the above experiment condition; mixing ·OH radical into the fuel by atomization of UFB water. (2) Atomization of UFB water into the fuel can reduce NOx of 25% and PM of 70%, and be able to be improved fuel consumption of 10% by diesel engine. (3) Atomization of UFB water into the water emulsified fuel can reduce NOx of 55% and PM of 85%, and be able to be improved fuel consumption of 20% by diesel engine.
Within the IMO regulations, NOx Tier II (from 2011), ECA (from 2016), and EEDI (from 2013) have been effective, and restriction of sulfur content in fuel oil (from 2020), expansion of the scope of restrictions of ECA (from 2021), and the restriction of black carbon (BC) are now being examined. Marine diesel engines that will be designed in the future must have performances that satisfy all these restrictions. Therefore, for the present study, a system that satisfies all of the restrictions relative to NOx, EEDI, and BC was constructed by using newly developed water mixture fuel (WMF) technologies without additives. For this experiment, a small four-stroke high-speed marine diesel engine was used as a real engine model. To clarify the influence of WMF technologies on engine performance and exhaust emissions, the following experiments were performed. (1) Confirmation of the NOx-SFOC (specific fuel oil consumption) trade-off: The variations in NOx and SFOC when the fuel injection timing was advanced by 1 degree to 3 degree (crank angle) were clarified. (2) Influence of WMF technologies on the NOx-SFOC trade-off: The variations in NOx and SFOC when water was mixed with the fuel were clarified at each injection timing. (3) Influence of WMF technologies on BC: The ratio of PM when water was mixed with the fuel was measured by using a highly accurate PM measurement system, in addition to clarifying the ratio of BC in PM. (4) Combustion analysis: The cylinder pressure and fuel injection pressure obtained from each experiment were analyzed, clarifying the ignition period, highest pressure and its period, heat release rate, combustion speed, and combustion ratio. Analysis of the results revealed that (1) NOx increases by about 25%, while SFOC is improved by 3%, when fuel injection timing is advanced by a 3 degree crank angle. (2) NOx can be decreased without increasing SFOC by mixing water with the fuel. For instance, NOx can be decreased by about 20% by mixing water with the fuel at a 20% W/FO ratio. (3) PM and BC can be decreased by mixing water with the fuel. For instance, PM and BC can be reduced by half by mixing water with the fuel at a 20% W/FO ratio. (4) NOx, SFOC, and BC can be decreased at the same time by using WMF technologies and effectively combining the other results. Most importantly, WMF technologies allow most IMO regulations to be met.
Ship exhaust gas emission becomes one of the main sources of marine environment pollution. This imposes significantly on the health risk along the area which has densely traffic of ship. The aim of this paper is to conduct an estimation of emission distribution of ships in the Madura Strait which is one of the busiest access channels in Indonesia. Vessel activity based approach is utilized for estimating the emission of ships by inputting the power of main engine (ME), auxiliary engine (AE) and auxiliary boiler(AB), engine load factor, time in mode and emission factor. Operation mode of ships are categorized as maneuvering, fairway cruising, low cruising and hoteling. Automatic Identification System (AIS) is used to identify all data of ships which are operated in the Madura Strait both the static and dynamics data. The static data includes MMSI (Maritime Mobile Service Identity), IMO number, type of ship, call sign and ship dimension, while dynamics data such as ship speed, position and navigation status. Ship information from AIS is used as input for ship database for knowing the engine power, actual and design speed which are needed to estimate the ship emission, including carbon monoxide (CO), Nitrogen oxides (NOX), sulfur oxides (SOX) and particulate matter (PM). In this study, ships operation data obtained from AIS and the emission estimation are combined to do a simulation using Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model to generate emission map which shows the inventory of emission distribution. Result shows that the emission of SO2 and NOX are much higher than the other pollutant. The total emission of AE is higher than that of ME because most of ships are in the mode of hoteling. The dispersion model reveals that the pollutant reaches location of resident around the Madura Strait. Output of this study can be used as consideration for the government to regulate an effective policy regarding the ships emission to control the marine pollution at sea for better environmental health.
The authors have investigated on a ship installed some conventional marine diesel engines and lean burn gas engines, and have proposed a C-EGR (combined exhaust gas recirculation) system to reduce the slipped methane from the gas engines and the Nitrogen oxides (NOx) from the marine diesel engines. This system can consist of a marine diesel engine and a lean burn gas engine, and the exhaust gas emitted from the lean burn gas engine is provided to the intake manifold of the marine diesel engine. This system thus could reduce both the NOx from the marine diesel engine and the slipped methane from the lean burn gas engine simultaneously because of the EGR effect and the re-burning of the slipped methane. This paper introduces the effects of the intake gas compositions on the combustion characteristics of diesel engine simulated as our C-EGR system. In the experiments, oxygen(O2), methane(CH4) and carbon dioxide (CO2) concentration of the intake gas was changed by mixing nitrogen(N2), CH4, and CO2, the cylinder pressure and gas temperature of the diesel engine were thus investigated at the high and low load conditions. From the results, it was confirmed that, when CH4 concentration was increased or O2 concentration was decreased, NOx emission was decreased and CH4 emission was increased because the cylinder gas temperature was decreased, especially in low load condition. The reason can be decreased of cylinder gas temperature. On the other hand, the increase of CO2 concentration did not influence to the CH4 emission. These results might show that the reductions of slipped methane and NOx are trade-off depending on the O2 or CH4 concentration in intake gas as well as the load condition.
The harmful exhaust emissions from marine diesel engines are NOx, SOx, and PM (Particulate Matter). In recent years, there are problems of global warming and rising sea levels. When the BC (Black Carbon) in the PM falls on sea ice in the high-latitude region, an albedo of the sea ice surface decreases and its absorption of solar radiation increases. This promotes sea ice melting. Then marine diesel engines are strongly required to reduce the PM emission in the exhaust gas. However, the actual state of the PM emission from marine diesel engines has been not entirely cleared. In this paper, particle size distribution and mass concentration of PM from a high speed four-stroke engine (3L13AHS, 73.55 kW) were measured by hot dilution method. In the hot-dilution method, exhaust gas from the engine is diluted by the rotary disk type diluter with high temperature air. This method allows exhaust gas dilution while preventing condensation of volatile component in the PM. PM particle size distribution in the diluted exhaust gas was measured by the SMPS (Scanning Mobility Particle Sizer). The effect of the dilution ratio on the particle size distribution and mass concentration of the PM was examined. In the experiment, the test engine was operated according to a propeller load curve and a constant speed with four load conditions (25%, 50%, 75% and 100%). Furthermore, the change of the number concentration of the PM in the sampling tube was examined. The results of this experiment are as follows: The particle diameter distributions obtained by the hot dilution show the mono-modal distribution and the bi-modal distribution depending on the operating condition of the engine. The mode diameters are 100 to 120 nm, except for the low load condition. It is found that the dilution ratio has a great effect on production of nucleation mode particles of small size region at the low engine load under constant speed operation. Therefore, it can be understand that volatile components are contained at a high concentration on exhaust gas. For the total number concentration measured by the SMPS, the maximum value is obtained at 75% load of the propeller load operation. The number concentration of the PM in the diluted exhaust gas decreases in the sampling tube for transfer from the diluter to the SMPS. The decrease rate of number concentration of the PM becomes higher for smaller particle sizes. While the dilution ratio of exhaust gas does not affect the decrease rate, the decreases rate increases as the tube length increases.
Surface modification of several materials was conducted to improve the tribological properties and corrosion resistance to develop friction materials for marine applications. The surface modification method included various processes, the most important of which was the friction reforming process with powder. The modified layer of previously modified materials with superior properties was examined in terms of thermodynamics. Modified titanium and modified chrome-molybdenum were examined as specimen materials. Electron probe microanalysis (EPMA) and thermodynamic database software were used for the examination. The results indicated the formation of chrome oxides, a lack of Cr and diffusion of Mo, which were considered to be due to a higher affinity between Cr and O.
Battery-powered prime mover vehicles, i.e., electric vehicles (EVs) and hybrid electric vehicles (HEVs), of which drive train system shall be applied for traction drive type gantry cranes at the port and harbor facilities. The battery has a chemical degradation both cycle and preservation time. The battery verification shall be done in both aspect of the battery cycle lifetime experiment and the battery preservation lifetime experiment. Though it is a fact that the most of the experiment which does not verify the battery preservation lifetime but the battery cycle lifetime prior to the battery mass production. Owing to an allowable research and development span, there is not enough time to verify the battery preservation lifetime experiment which makes hard to estimate the battery total life in actual usage. This study investigates a possibility extent that an AC impedance response analysis, which method can verify the battery deterioration condition in progress of cycle lifetime experiment which was previously reported , and also apply to verify the battery deterioration condition in progress of preservation periods and the estimation life time. The battery is focused on a Nickel-metal hydride (Ni-MH) battery which is widely used as traction energy storage in HEVs. The AC impedance response analysis is an appropriate method which can be detected easily to measure the battery deterioration level of an amount of the battery's self-discharge, a nominal type of Ni-MH battery called AB5 alloy type. The final objective of this study is verified that the AC impedance response with a statistical analysis is an effective method to verify the battery deterioration level in progress of preservation easily and to estimate the battery total life time.
The application of polymer electrolyte fuel cells (PEFCs) for marine vessels will be an effective means of reducing the environmental impact and solving energy crisis problems. The diagnosis of abnormal operational conditions is an important aspect of improving the reliability and durability of marine PEFCs, and helps to ensure long-term safe and stable operation. Electrochemical impedance spectroscopy (EIS) is a technique suitable for the real-time diagnosis of operational PEFCs. EIS analyses are performed using an equivalent circuit model consisting of several resistances and capacitances, associated with ohmic, activation and concentration overpotentials. The present work investigates the effects of abnormal variations in the cell temperature as well as the flow rate and relative humidity values of supplied gases on the cell resistance and capacitance values using EIS analysis. The detection of sea salt (NaCl) contamination in the cathode air stream is also evaluated by injecting a NaCl solution into the cathode inlet gas.
It is a fact that the correct and safe operation of machinery by engineers, is of paramount importance for safe navigation of vessels. Added to this fact is the effective communication and clear manifestation of intentions by engineers while managing the engine room resources at their disposal. Proper communication is an essential requirement in engine room in special situations such as maneuvering, starting up or machinery cooling down situations. Further, it can also be situations such as carrying out main engine repairs and maintenance work in port or during a normal passage at sea. In those situations, the senior engineer in the control room order various operational tasks to be carried out by the younger engineer or engine support staff in the engine room.
In this research task, a pair of transceivers is used for communication of operational order or other request in engine room under the noisy environment. Under the prevailing circumstances of operation, it will be difficult for the engineers communicate and establish a clear perception due to noisy environment and other factors such as age differences, language barriers, cultural and religious differences. A further compounding effect will be the stress levels of the engineers, especially when they work in unfamiliar environment.
In this study, speakers installed under the aluminum metal plates similar to engine room floor plates create a noisy environment. The sounds created by the speakers reproduce the running sound of the real generators, motors and other machinery. The output sound level was adjusted 85 dB by using volume control of amplifier tuner, which connects with speakers. The two subject engineers communicate each other under noisy environment in experiment by using transceivers. For the experiment, we employed two students from the Kobe University.
We measured the biological responses of the subjects, under noisy environment. The data was then compared with the changes of their responses under experimental environment differences. The outcome of the research was to find ways to reduce stress levels of engineers and create an optimal working environment in engine rooms.
The authors are considering a system to assist a lookout on ships using cameras. In this research, we propose a method of tracking offshore vessels continuously by using a PT (Pan-Tilt) camera. Radar and AIS (Automatic Identification System) are mounted on the ship as equipment to assist a lookout. Radar is essential and widely used in order to obtain information around own ship and find other vessels. However, it is not a perfect device and has some faults, for example, non-detection small vessels under the influence of the noise caused by sea clutter and so on. Also, AIS is not mounted on all vessels and information on AIS is not always trustworthy. In view of these reasons, a lookout by crews is indispensable. But there is a possibility of overlooking and many marine accidents with an insufficient lookout have occurred. We believe that a system that assists a lookout using cameras is thought to be effective in suppressing marine accidents. Previous studies have dealt with wide-angle images when monitoring offshore vessels. On the contrary, zoom images are effective on gazing at a specific vessel or obtaining detailed information, such as bow direction and moving direction. However, the orientation of the camera is necessary to be controlled because the field of view becomes narrow when it zooms. Furthermore, when gazing at the vessels continuously, the orientation of the camera must be directed to the target vessel. Therefore, we propose a fundamental method of controlling the orientation of the camera so that the vessel is located at the center of the image continuously. In this paper, we mainly describe a method to track a vessel on the image sequence, control theory of the camera orientation and the experimental results of real-time camera control to track a vessel.
Rader is essential and widely used in order to obtain information around own ship and find other ships. And GPS and Gyro sensors indicate the location and attitude of own ship but not estimate other ones. These systems are not perfect to prevent marine accidents. One of the major causes of the marine accidents is improper lookout. The authors have proposed a stereo vision system which detected ships and other obstacles and measured their 3D locations in order to improve the navigational safety. To apply the proposed methods to watching ships in the wide sea area such as a straight or port, this paper shows a method to automatically determine the arrangement of the camera system that is set up on land to monitor all over the target sea area.
Biofuel might be one of the good candidate of future marine fuel where 30% reduction of EEDI (Energy Efficiency Design Index) from 2025 and more in the future will be required. Today Biofuel of FAME (Fatty Acid Methyl Ester ) made from various source is already mixed to some extent in gas oil or diesel oil for land use. This paper focuses on the use of Biofuel both with and without methyl esterification treatment to marine diesel engines where the fuel heating system can be easily applied. We obtained FAME and CPO (Crude Palm Oil) from Indonesia and conducted engine combustion experiment on the 4 stroke cycle medium speed marine diesel engine. We investigated the effect of mixing ratio of CPO or FAME in MDO (Marine diesel oil) on combustion and exhaust emission characteristics. The combustion of both Biofuel showed good except CPO at low load, which could be improved by the pre-injection. The results of experiments not only combustion but also other problem like the clogging of filter are discussed and the possibility of usage both CPO and FAME by mixing into MDO with some care of heating and filtering for the marine diesel engine are shown.
This study experimentally investigated the boiling flow heat transfer and two-phase frictional pressure drop characteristics of the refrigerant R32 in a horizontal multiport tube with circular minichannels. The boiling heat transfer coefficients and two-phase pressure drops were measured at a saturation temperature of 15 °C for mass velocities that ranged from 50 to 400 kgm-2s-1 and heat fluxes that ranged from 5 to 40 kWm-2. The effects of mass velocity, heat flux, and vapor quality on the boiling heat transfer characteristics were clarified. The measured boiling heat transfer coefficients and two-phase frictional pressure drops were compared with previous correlations. Under the low mass velocity and low heat flux conditions, the boiling heat transfer characteristics differed from the previous correlations for conventional large diameter tubes. The two-phase frictional pressure drops were in good agreement with previous correlation, except for the mass velocity of 50 kgm-2s-1.