Effects of two-phase flow friction factor correlations on the optimal pressure drop-martinelli parameter pair in a mini-channel

Substantial research has been completed with more on-going on the flow pattern and heat transfer associated with two-phase flows. Discrepancies reported may have been as much as agreements, due to the different models, approaches, flow regimes, correlations, and new working fluids being utilized. This paper reports the outcome of a study to look at the effects of applying two different friction factor correlations on the simultaneous minimization of the pressure drop and Martinelli parameter under optimized flow rate and vapor quality, using genetic algorithm. The homogeneous model is assumed with ammonia as the working fluid, the coolant being environmentally friendly and having recently discovered as a potential replacement for the current refrigerants in micro and mini-channels. Results show that significant differences in the frictional pressure drop and Martinelli parameter arise due to the different correlations used, and this is only the outcome from two different correlations currently being considered by researchers in pressure drop analysis for two-phase flows in mini-channels. Thus, absolute agreement is indeed not possible between theoretical, experimental, and numerical work in view of the many different available correlations being utilized today with differences between 10 to 100 percent that has already been established

Characteristics of two-phase flow heat transfer of R-22 and R-290 in horizontal circular small tube

Hydrocarbon refrigerants have been widely used to replace HFCs. As hydrocarbon, R- 290 has no ODP (Ozone Depletion Potential) and negligible GWP (Global Warming Potential). This paper presents flow boiling heat transfer in small tube with R-290 and R-22. The test tube has inner diameter of 7.6 mm and length of 1.07 m. In order to determine the heat transfer coefficient, experiments were carried out for heat fluxes ranging from 10 to 25 kW/m2K, mass fluxes ranging from 204 to 628 kg/m2s, and saturation temperatures ranging from 1.87 to 11.9o C. The study analyzed the heat transfer through the local heat transfer coefficient along the flow under the variation of these different parameters. In comparison with R-22, R-290 provides higher heat transfer coefficients. In the prediction of the heat transfer coefficients of R-22 and R-290, the correlation of Shah (1982) and Choi et.al. (2009) best fitted the present experimental result, respectively

Rheology Characteristics and Critical Velocity of Particle-laden Flow Affected by Three-lobed Spiral Pipe

The use of piping systems for fluid transportation is increasing because it is considered the most effective method. Newtonian and non-Newtonian fluid flows are suitable for piping systems, and non-Newtonian, particle-laden fluids are more complex due to various factors. Deposition is one of the problems that must continue to be investigated because of the effects of flow efficiency. The purpose of this study was to investigate the performance of the three-lobe spiral pipe effect. Working fluids in several variations of concentration weight (Cw 20%, 30%, and 40%) were used. Test pipe with a length of 1550 mm and consisting of spiral pipe P/Di = 7 and a circular pipe with an inner diameter of 25.4 mm were used. The circular pipe was used to investigate the rheological workings of fluid. Both pipes were used to investigate the particle effects. Using scanning electron microscopy, 1-?m to 5-?m slurry particles were obtained from the mud eruption source at Semau Island, Kupang, Indonesia. The critical velocity value of the spiral pipe was lower than the circular pipe, so the spiral pipe is highly effective for slurry transportation

Heat Transfer Coefficient Characteristic Study of Natural Refrigerant with Substitute for R-134a

The wide-spread use of halocarbon refrigerants are making negative impact on Earth. Natural Refrigerant, such as hydrocarbon, is one alternative of several option to use. Mixing hydrocarbon are develop to improve the heat transfer characteristic. For example is, Musicool-134 (MC-134) is a mixture with two major substance of propane and iso-butane. The experimental apparatus is using a microchannel with a diameter of 0.5 mm and length of 0.5 m. The evaporative process was conducted in the experiment. The result of the experiment is that if the high coefficient value then the heat flux value is also high

Thermofluids on Renewable Energy, Refrigeration and Air Conditioning, and Flame and Combustion

Increasingly limited sources of fossil energy are driving people to seek alternative energy resources. The use of photovoltaic (PV) and biogas for electric power generation continues to be accompanied by efforts to improve their system performance. Electrical ratings on PV systems, and the design of the digester in the biogas combustion process, are two of the relevant issues presented in this edition. Absorption cooling systems for buildings with solar power is one type of environmentally friendly system. In addition, the use of the natural refrigerant propane and a small channel can provide a higher heat transfer coefficient. In the heating and cooling process, the heat transfer characteristics are changed due to the phase change of the working fluids or material. Therefore, research on phase change material or working fluids has become an important way to support energy savings. Adsorption cooling systems that work with certain materials have shown better system performance, are environmentally friendly, and are energy-saving. System performance is determined by the properties of the material or the working fluid; it can be improved by modifying the serial or parallel stages of the process, which can be implemented in the dehumidification process. The pyrolysis process is another example of an application of thermofluids that uses flame and combustion; here, a carbonaceous solid is thermally degraded via heat in the absence of oxygen. For safety in flame and combustion, controlling the oxygen concentration can reduce the propensity for ignition and lower the fire propagation rate. Related applications on the engine and controlling the conditions of combustion in the engine room can improve engine performance

Research Frontiers in Energy, Materials, Production, and Transportation

The growth of research in various areas highlights the increasing needs of human life, such as in the fields of energy, materials, production, and transportation. Research in the field of fluid flow for energy savings is now very advanced, and research on the fluid flow pattern with a micro-scale is performed to obtain a high heat transfer with a low pressure drop. The use of microorganisms, biomass, and the Organic Rankine Cycle (ORC) is employed to stimulate heat transfer and fluid flow to produce energy through a more efficient and more environmentally friendly process. Furthermore, research on the designs and processes of air-conditioning systems is essential in view of energy consumption, which has exhibited a significant rise. Air conditioning is included in the future of transportation, namely electric cars, to achieve energy efficiency in vehicles. In addition to vehicle systems, attention should also be given to the precision of the routes and schedules of vehicles, particularly for public transport, so research on transportation modeling has also become very important. Another increasing requirement, which in the past has not been very well thought out, is the level of human comfort in driving. The challenge is to align the needs of driving comfort with energy efficiency requirements. The effort to reduce fuel consumption is also applied in marine transport modes by reducing the drag of ships. Moreover, cost efficiency related to energy consumption is an important issue in the production process. The management of manufacturing processes, including the production arrangement layout area, will greatly affect efficiency. This special edition presents the current manufacturing research in relation to various technologies associated with materials, automation, semiconductor, and nano devices

Optimization of the Friction Factor and Frictional Pressure Drop of R22 and R290

Today, the air-conditioning and refrigeration industry is still searching for environmentally friendly refrigerants that could replace hazardous, ozone-depleting coolants – refrigerants that behave similarly, if not better, than the present ones. The present study examines optimization of the frictional pressure drop of R22 and R290 using genetic algorithm. Outcomes are compared against the measured pressure drop obtained from a horizontal 7.6 mm channel with a length of 1.07 meters. Three equations have been used for calculating the Darcy friction factor and two-phase flow pressure drop for both laminar and turbulent flow regimes in smooth and rough tubes. The effects of the different correlations for the friction factor and pressure drop utilized are demonstrated. The results illustrate that the differences between values of the Darcy friction factor are very small for the two refrigerants examined, with the frictional pressure of R-290 higher than R-22. Use of a smaller channel induced a much higher frictional pressure drop, as well

Performance of natural refrigerants in two phase flow

The search for alternative environmentally friendly refrigerants have never been so crucial with the increasing demand for effective cooling of increasing miniaturization of our heat exchanging devices in the ever expanding air-conditioning and refrigeration industry. Although propane (R290) and ammonia (R717), natural refrigerants, have been around for decades, their two-phase thermal performance in small channels has yet to be fully investigated. Predictions of the heat transfer using correlations developed based on past experimental data have shown poor agreements, with more correlations being developed to date. This research was done to investigate the optimized conditions for the two-phase boiling heat transfer coefficient of R290 and R717 where the contributions from nucleate boiling and forced convective are represented explicitly. Multi-objective Genetic Algorithm (MOGA) is utilized for the simultaneous maximization of nucleate boiling and forced convective, two conflicting phenomena-the former generally significant in the low vapor quality region while the latter in the high quality region. A superposition correlation is used as it sums up both contributions. Two phased-out refrigerants, R134a and R22 are also being research here for comparison purposes. The range of MOGA design parameters set for mass flux, G, is between 100-300 kg/m2.s, heat flux q between 5-30 kW/m2 and vapor quality, × for 0.0009-0.9. The optimization is done for 3 mm channel diameter with saturation temperature at 10˚C. The optimized results showed a strong contribution of each nucleate boiling and forced convective for R717 with increasing vapor quality, compared to the other three refrigerants. The optimized value of the total heat transfer coefficient for R717 could reach up to 90 kW/m2.K and for R290 up to 12 kW/m2.K compared to R134a and R22 at 6 kW/m2.K and 5 kW/m2.K respectively. At lower vapor quality, the nucleate boiling contributes more to the total heat transfer coefficient, and suppressed due to forced convective as the vapor quality reaches middle range. The theoretical results indicate the potential of R717 and R290 as replacement refrigerants for R22 and R134a with further verifications to be done with correlations not using the superposition method

Effect of Liquid Reynolds Number on Pressure Drop of Evaporative R-290 in 500µm Circular Tube

Due to certain advantages, natural refrigerants have recently become more popular. Environmental issues motivate this study, focused on the characteristics of propane (R-290) as a replacement for conventional refrigerants. The aim of the present research is to characterize the pressure drop of evaporative R-290 in a microchannel of 500µm diameter and 0.5 m length. The variables of the experimental conditions are mass flux between 155 and 1071 kg/m2s and vapor quality between 0 and unity. The results show a laminar flow for liquid R-290 and a turbulence flow for vapor. Some existing correlations of two-phase flow viscosity were used to predict the pressure drop. For homogeneous model, Dukler et al.’s (1964) prediction viscosity correlation best predicted the present experimental pressure drop

Experimental Investigation of a Large Scale-oscillating Heat Pipe at Different Inclinations

As a family of heat pipes, oscillating heat pipes have many additional unique operating parameters. This paper examined the heat transfer characteristics of an oscillating heat pipe that has an effective length (leff) of 500 mm and uses methanol as the working fluid. The effective length of 500 mm is not typically used in previous experimental setups. This structural dimension of the oscillating heat pipe is widely used as a heat recovery device. The heat pipe was tested with various heat supplies and inclinations. The results show that the inclination makes a substantial contribution to the heat transfer capability for large scale heat pipes. Decreasing the degree of inclination reduces the capability of the heat pipe in handling the heat load. Reducing the inclination also decreases the oscillatory motion, which is an obvious “heat carrier” from the evaporator to the condenser