Vapor Mass Flow Rate Research Articles

An experimental study on using natural vaporization for cooling of a photovoltaic solar cell

This study attempts to investigate a new way for cooling PV cell using natural vapor as coolant. The performance of solar cell was examined on simulated sunlight. The natural vapor encountered backside of PV cell vertically in various distribution and different mass flow rates. Also, the effect of natural vapor temperature in cooling performance was analyzed. Results indicated that the temperature of PV cell drops significantly with increasing natural vapor mass flow rate. In detail, the PV cell temperature decreased about 7 to 16°C when flow rate reaches 1.6 to 5grmin−1. It causes increasing electrical efficiency about 12.12% to 22.9%. The best performance of PV cell can be achieved at high natural vapor flow rate, low natural vapor temperature and the obtained optimum distribution condition.

Numerical investigation of mist flow regime in a vertical tube

In this research, the mist flow regime, consisting dispersed water droplets in vapor flow, is simulated numerically in a vertical tube; using a discrete phase model (DPM). In this method, in addition to solving transport equations for continuous phase, a discrete phase is simulated in a Lagrangian approach and the coupling between phases is modeled through interaction terms in the transport equations. The aims of this research are to investigate thermal equilibrium and evaluate the heat transfer coefficient of mist flow regime. The results show, when thermodynamic non-equilibrium takes happen, the rate of heat transfer from the vapor to the droplets is too slow that their presence is ignored, therefore by increasing the water mass flow rate in this case, due to reduction of vapor mass flow rate, the heat transfer coefficient decreases. But when complete thermodynamic equilibrium condition is established, the rate of heat transfer from the vapor to the droplets is too fast that the vapor temperature remains at the saturation temperature until all the droplets have been evaporated and by increasing the water mass flow rate, the heat transfer coefficient will increase. In order to simulate mist flow regime in thermal equilibrium and non-equilibrium conditions, water droplets with two different diameters are injected into steam flow. The numerical results of heat transfer coefficient and wall temperature in four different vapor qualities are investigated in each state, which show good agreement with experimental data and correlations.

F235 フィン及びねじり板導入によるPWR蒸気発生器蒸気量増大に関する研究(OS9 熱・流動(6))

Increasing the electric power generated by nuclear power plant is important for the economy and the environment. In this study, I focused on the steam generator of PWR. We have established a method to calculate the vapor mass flow rate of steam generator. Vapor mass flow rate of the steam generator with the axial economizer is also calculated and evaluated for performance. In order to generate more vapor mass flow rate than that of the current steam generator with the axial economizer, the heat transfer enhancement of the heat transfer tube is considered. Considering the introduction of the fin and the twisted tape, and were compared to calculate the vapor mass flow rate. Vapor mass flow rate has increased about 7 % by the combination of the external fin and internal fin.

Modeling and optimal control of an energy-efficient hybrid solar air conditioning system

Abstract The paper addresses the modeling and optimal control problem of a new hybrid solar-assisted air conditioning system developed for performance enhancement and energy efficiency improvement. To regulate the mass flow rate of the refrigerant vapor passing through a water storage tank for increasing the refrigerant's sub-cooling process at partial loads, we propose a new discharge bypass line together with an inline solenoid valve, installed after the compressor. In addition, to control the air flow rate, a variable speed drive is coupled with the condenser fan. For the control purpose, a lumped parameter model is first developed to describe the system dynamics in an explicit input–output relationship; then, a linear optimal control scheme is applied for the system's multivariable control. The system has been fully-instrumented to examine its performance under different operation conditions. The system model is then validated by extensive experimental tests. Based on the obtained dynamic model, an optimal controller is designed to minimize a quadratic cost function. Numerical algorithms, implemented in a simulation tool, are then employed to predict the energy performance of the system under transient loads. The experimental results obtained from implementation with PLC demonstrate that the newly-developed system can deliver higher system efficiency owing to amelioration of the refrigeration effect in the direct expansion evaporator and adjustment of its air flow rate. The development is thus promising for improvement of energy efficiency, enhancement of the system performance while fulfilling the cooling demand.

Diesel engine spray characteristics prediction with hybridized artificial neural network optimized by genetic algorithm

ANN (artificial neural network) modeling is adopted along GA (genetic algorithm) optimization method in order to investigate spray behavior as function of nozzle and engine variant parameters such as crank-angle, nozzle tip mass flow rate, turbulence, and nozzle discharge pressure. Spray quality is measured in SMD (Sauter mean diameter) and spray liquid tip penetration prospective. Experimental data were used at limited engine condition and elsewhere requisite data was acquired with the aid of curve fitting and extrapolation of CFD (computational fluid dynamics) numerical simulation results. Engine crank-angle, vapor mass flow rate, turbulence, and nozzle outlet pressure were taken as input layer while spray penetration and SMD were used as output layer. It is found out that Levenburg–Marquardt training algorithm has the least mean square error for ANN and ANN-GA (artificial neural network-genetic algorithm) at 24, 30 neurons in hidden layer with the amount of 0.8994, 0.3348, respectively. The coefficient of determination (R2) for penetration equals 0.994 whereas SMD yields lower amount of 0.992. By application of GA to optimize the network's interconnecting weights, R2 values have been enhanced to 0.999 for SMD and to 0.998 for penetration (both values are close to unity). Results indicate that the ANN-GA improved the spray specification modeling simply and with acceptable accuracy.

Numerical and experimental study on the heat and mass transfer of porous plate water sublimator with constant heat flux boundary condition

Water sublimators offer effective heat rejection for the spacecraft, which work in warm environments or with peak heat loads, by evaporating or sublimating water into the vacuum. In this study, the heat and mass transfer of porous plate water sublimator with constant heat flux boundary condition was investigated numerically and experimentally. The startup process of sublimator was divided into three continuous states to analyze its work characteristics: water evaporation in the feed water gap state, water evaporation in the porous plate state and the alternation of evaporation and sublimation in the porous plate state. The locations of evaporation/sublimation front and freezing/thawing interface in the micron porous plate associate with the rarefied water vapor flow through the porous plate were taken into consideration. The heat and mass transfer equations coupling with phase change and rarefied gas flow through the porous plate were established and solved to evaluate the sublimator temperatures, water and vapor mass flow rates, locations of phase change interfaces. In addition, experiments of a water sublimator test module were conducted to validate the numerical model. The experimental results obtained were consistent with the simulation results.

Output power analyses for the thermodynamic cycles of thermal power plants

Thermal power plant is one of the important thermodynamic devices, which is very common in all kinds of power generation systems. In this paper, we use a new concept, entransy loss, as well as exergy destruction, to analyze the single reheating Rankine cycle unit and the single stage steam extraction regenerative Rankine cycle unit in power plants. This is the first time that the concept of entransy loss is applied to the analysis of the power plant Rankine cycles with reheating and steam extraction regeneration. In order to obtain the maximum output power, the operating conditions under variant vapor mass flow rates are optimized numerically, as well as the combustion temperatures and the off-design flow rates of the flue gas. The relationship between the output power and the exergy destruction rate and that between the output power and the entransy loss rate are discussed. It is found that both the minimum exergy destruction rate and the maximum entransy loss rate lead to the maximum output power when the combustion temperature and heat capacity flow rate of the flue gas are prescribed. Unlike the minimum exergy destruction rate, the maximum entransy loss rate is related to the maximum output power when the highest temperature and heat capacity flow rate of the flue gas are not prescribed.

Measurement of the evaporation mass flow rate in a horizontal liquid layer partly opened into flowing gas

The dynamics of evaporation from a local surface of a horizontal liquid layer under a gas flow is studied experimentally. The average evaporation mass flow rate of a liquid layer (HFE-7100) induced by inert gas (nitrogen) is measured using two independent methods. The influence of the average gas flow rate, gas and liquid temperature, and the layer depth upon the evaporation rate and convection in the liquid layer is investigated. Correlation dependences of the evaporation rate vs. the inert gas flow rate and temperature are obtained. It is found that the average evaporation-rate curve has a local maximum with a growth of the liquid layer depth. With the growth of the gas and liquid temperature, the local maximum in an evaporation flow rate of the liquid layer is shifted to the larger value of the liquid depth.

Transient performance and intelligent combination control of a novel spray cooling loop system

Effective thermal control systems are essential for the reliable working of insulated gate bipolar transistors (IGBTs) in many applications. A novel spray cooling loop system with integrated sintered porous copper wick (SCLS-SPC) is proposed to meet the requirements of higher device level heat fluxes and the harsh environments in some applications such as hybrid, fuel cell vehicles and aerospace. Fuzzy logic and proportional-integral-derivative (PID) policies are applied to adjust the electronic temperature within a safe working range. To evaluate the thermal control effect, a mathematical model of a 4-node thermal network and pump are established for predicting the dynamics of the SCLS-SPC. Moreover, the transient response of the 4 nodes and vapor mass flowrate under no control, PID and Fuzzy-PID are numerically investigated and discussed in detail.

친환경 프레온 냉매를 이용하는 단압축 단팽창 냉동시스템의 성능예측

In this paper, cycle performance analysis of two-stage compression and two-stage expansion refrigeration system using alternative freon refrigerants is presented to offer the basic design data for the operating parameters of the system. Alternative freon refrigerant for freon refrigerant R22 were used as working fluids in this study. The operating parameters considered in this study included evaporation temperature, condensation temperature, subcooling degree, superheating degree, and mass flow rate ratio of inter-cooler. The main results were summarized as follows : The COP of two-stage compression and two-stage expansion refrigeration system increases with the increasing subcooling degree and mass flow rate ratio of inter-cooler, but decreases with the increasing evaporating temperature, condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and two-stage expansion refrigeration system using alternative freon refrigerants have an effect on COP of this system.

Modelling and Design of Indirect Solar Dryers for Batch Drying

A model is developed to study the influence of design parameters (dimensions, air mass flow rate) in the performance of an indirect solar drier for batch drying. The aim of the work is to cover a wide range of configurations and sizes with a simple model. The model covers the air heating in the collector and the vapour mass transfer in the drying chamber. Constant rate controlled by convection mass transfer is assumed. The results, still preliminary, show the relevance of using a solar collector and the evolution of the drying process in the drying chamber. The obtainable vapour mass flow rate is calculated for a variety of configurations, showing the incidence of the air mass flow and the dimensions of the collector and the drying chamber. Performance parameters such as temperatures during the process and the efficiency of the drying chamber are also depicted.

A study on flow and heat transfer characteristics for saturated falling-film evaporation of liquid oxygen in a vertical channel

In this study, a mathematical model for the laminar falling film is presented in order to simulate the evaporation heat transfer characteristics in falling liquid oxygen films. The model takes into account the effect of the interfacial shear. The values of the film thickness, the heat transfer coefficient as well as the interfacial shear are obtained under given conditions by solving the model with an iteration method. The influences of the inlet Reynolds number, channel length and the interfacial shear on the flow and heat transfer characteristics of the falling film evaporation are analyzed in detail. Effects of key factors on the circulation ratio of the inlet fluid mass flow rate to the generated vapor mass flow rate, an important design parameter for reboilers/condensers, are particularly analyzed. In addition, the variations of the average vapor velocity and interfacial film velocity are also discussed. The analysis results could provide theoretical guidance for the simulation and design of downflow reboilers/condensers applied in air separation units.

Vaporization and collision modeling of liquid fuel sprays in a co-axial fuel and air pre-mixer

Droplet collision occurs frequently in regions where the droplet number density is high. Even for Lean Premixed and Pre-vaporized (LPP) liquid sprays, the collision effects can be very high on the droplet size distributions, which will in turn affect the droplet vaporization process. Hence, in conjunction with vaporization modeling, collision modeling for such spray systems is also essential. The standard O’Rourke’s collision model, usually implemented in CFD codes, tends to generate unphysical numerical artifact when simulations are performed on Cartesian grid and the results are not grid independent. Thus, a new collision modeling approach based on no-time-counter method (NTC) proposed by Schmidt and Rutland is implemented to replace O’Rourke’s collision algorithm to solve a spray injection problem in a cylindrical coflow premixer. The so called “four-leaf clover” numerical artifacts are eliminated by the new collision algorithm and results from a diesel spray show very good grid independence. Next, the dispersion and vaporization processes for liquid fuel sprays are simulated in a coflow premixer. Two liquid fuels under investigation are jet-A and Rapeseed Methyl Esters (RME). Results show very good grid independence in terms of SMD distribution, droplet number distribution and fuel vapor mass flow rate. A baseline test is first established with a spray cone angle of 90° and injection velocity of 3m/s and jet-A achieves much better vaporization performance than RME due to its higher vapor pressure. To improve the vaporization performance for both fuels, a series of simulations have been done at several different combinations of spray cone angle and injection velocity. At relatively low spray cone angle and injection velocity, the collision effect on the average droplet size and the vaporization performance are very high due to relatively high coalescence rate induced by droplet collisions. Thus, at higher spray cone angle and injection velocity, the results expectedly show improvement in fuel vaporization performance since smaller droplet has a higher vaporization rate. The vaporization performance and the level of homogeneity of fuel–air mixture can be significantly improved when the dispersion level is high, which can be achieved by increasing the spray cone angle and injection velocity.

Development of porous plug phase separator and superfluid film flow suppression system for the Soft X-ray Spectrometer onboard ASTRO-H

ASTRO-H is the sixth Japanese astronomy satellite scheduled for launch in 2014. The Soft X-ray Spectrometer instrument is onboard ASTRO-H. This is a 6×6 array of X-ray microcalorimeters with an energy resolution of <7eV at 0.5–10keV. Superfluid liquid helium is utilized as a part of the cooling system. To retain the liquid helium in the tank under zero-gravity, a porous plug phase separator made of sintered stainless is used. Since the vapor mass flow rate is only 29μg/s, any additional superfluid film loss influences the lifetime of the liquid helium. Therefore, a film flow suppression system consisting of an orifice, a heat exchanger, and knife edge devices is adopted based on the design used for the X-ray Spectrometer onboard Suzaku. The film flow will be suppressed to <2μg/s, sufficiently smaller than the vapor flow rate. In the present investigation, the design and ground experiments of a helium vent system composed of the porous plug and film flow suppression system are presented. The results show that the phase separation and the film flow suppression are satisfactorily achieved.

C123 燃焼場を用いたSiO_2ナノ粒子生成に関する研究(OS-5: これからの燃焼研究(2))

The temperature from the tip of the methane premixed flame along the flow direction decreased dramatically at low mass flow rate of the Hexamethyldisiloxane (HMDSO) vapor while the temperature was almost constant along the flow direction at high mass flow rate of the HMDSO vapor. From the SEM images, the size of the agglomerates of silica nanoparticles had a maximum at a certain mass flow rate of the HMDSO vapor due to not only the temperature distribution along the flow direction from the tip of the premixed flame but also the temperature. Furthermore, when the concentration of the oxygen in the premixed flame increased, the size of the agglomerates decreased.

Effect of Condenser Temperature and Speed on one A/C System

This study describes the results on the performance of one vehicle air conditioning system. The coefficient of performance, evaporator cooling capacity, compressor power consumption, total mass flow rate, vapor mass flow rate, liquid mass flow rate and oil in circulation, pressures and temperatures of refrigerant at every component (inlets and outlets) are measured and analyzed with the variation of the outside temperatures at the evaporator and condenser, the speed of the compressor, refrigerant charge and oil charge. The systematical experimental results obtained from this real-size test system depict the relations between the above parameters in a vehicle air conditioning system, which constitute a useful source for vehicle air conditioning systems design and analysis. The vapor quality (two-phase flow) measurements realized in this work provide an extremely important tool for diagnosing the system performances.

Effect of Refrigerant Charge and Inlet Air Temperature on One A/C System

This study describes the results on the performance of one vehicle air conditioning system. The coefficient of performance, evaporator cooling capacity, compressor power consumption, total mass flow rate, vapor mass flow rate, liquid mass flow rate and oil in circulation, pressures and temperatures of refrigerant at every component (inlets and outlets) are measured and analyzed with the variation of the outside temperatures at the evaporator and condenser, the speed of the compressor, refrigerant charge and oil charge. The systematical experimental results obtained from this real-size test system depict the relations between the above parameters in a vehicle air conditioning system, which constitute a useful source for vehicle air conditioning systems design and analysis. The vapor quality (two-phase flow) measurements realized in this work provide an extremely important tool for diagnosing the system performances.

Effect of thermal convection on frequency response of a perturbed vaporizing pastille-shaped droplet

We study the dynamic response to small acoustic oscillations of a vaporizing droplet in shape of a pastille (a small liquid cylinder, called “pastille” in the sequel, the height of which being smaller than the radius of the base). Contrary to some previously proposed models, where the thermal convection effect inside the droplet is often neglected, the continuously fed pastille-shaped model takes into account the effects of both thermal convection and conduction. Curves related to different heat exchange coefficients are presented for the frequency response of the vaporization rate. The case where the feeding process at the bottom of the pastille is assumed isothermal (isothermal bottom regime) is compared to the one where the feeding process at the bottom of the pastille is adiabatic (adiabatic bottom regime). The response factor curves for the pure conduction model of the spherical droplet and for the present model of the “equivalent pastille” are also compared. The temperature field perturbation is then examined. As well as for the evaporation mass flow rate perturbation, comparisons are made between the regime with an isothermal bottom and the one with an adiabatic bottom. We find that, in spite of some divergences observed between the various cases, the frequency response of a droplet submitted to acoustic oscillations presents also some common points. It is shown that the life time (or residence time), the thermal diffusion time, and the period of the harmonic perturbation do intervene strongly in the behaviour of the vaporizing pastille. The liquid propulsion is a possible application of this basic study conducted as part of a thesis.

Heat transfer during reflux condensation of an R134a/R123 mixture in vertical and inclined narrow tubular and rectangular channels

Heat transfer during reflux condensation in a narrow tube (0.007 m inner diameter, 0.5 m length) and a rectangular channel (0.007 m hydraulic diameter, 0.5 m length) was investigated. The basic mechanism of this process, i.e. removing high boiling point components from a stream of a more volatile fluid or even from inert gases, is still not sufficiently understood. The study presents experimental results with the zeotropic mixture of R134a and R123 at a constant composition of the incoming vapour of 50 mol%. The results show that both, gas side heat and mass transfer resistances and the resistances in the liquid film influence the condensation process. Channel inclination is less important in mixture condensation than in pure fluid condensation but not negligible, and increasing vapour mass flow enhances mixture condensation. Contrary to pure fluid results heat transfer in the rectangular channel with the same hydraulic diameter is much smaller than in the tube at the same vapour mass flow rate.

Numerical Modelling of Flow Boiling Heat Transfer in Horizontal Metal‐Foam Tubes

AbstractThe flow boiling heat transfer performance in horizontal metal‐foam tubes is numerically investigated based on the flow pattern map retrieved from experimental investigations. The flow pattern and velocity profile are generally governed by vapour quality and mass flow rate of the fluid. The porous media non‐equilibrium heat transfer model is employed for modelling both vapour and liquid phase zones. The modelling predictions have been compared with experimental results. The effects of metal‐foam morphological parameters, heat flux and mass flux on heat transfer have been examined. The numerical predictions show that the overall heat transfer coefficient of the metal‐foam filled tube increases with the relative density (1‐porosity), pore density (ppi), mass and heat flux.