Flow Rate Of Working Fluid Research Articles

Process integration and superstructure optimization of Organic Rankine Cycles (ORCs) with heat exchanger network synthesis

Low and medium temperature energy utilization is one way to alleviate the energy crisis and environmental pollution problems. In the past decades, Organic Rankine Cycles (ORCs) have become a very promising technology for low and medium temperature energy utilization. When an ORC is used to recover waste heat in chemical plants, heat integration between the ORC and the process streams should be performed to save more utilities and generate more power. This study aims to integrate an ORC into a background process to generate maximum electricity without increasing the hot utility usage. We propose a two-step method to integrate an ORC to a background process, optimally considering the modifications of the ORC to increase the thermal efficiency and heat recovered by the working fluid simultaneously. The first step is to determine the configuration (turbine bleeding, regeneration, superheating) and operating conditions (working fluid flowrate, evaporation and condensation temperatures, turbine bleed ratio, degree of superheat, bleeding pressure). The second step is to synthesize the heat exchanger network by minimizing the number of heat exchangers that keep the hot utility unchanged. A well-studied example from the literature is solved to demonstrate the effectiveness of the proposed model for industrial waste heat recovery. The net power output in this paper is improved by 13% compared with the best known previous literature design for this system. The proposed method is also useful for quickly screening working fluids while considering integration potential. Screening of several working fluids revealed that using R601 (n-pentane) in place of the original working fluid (n-hexane) can increase the power output of the example system by an additional 14%.

Экспериментальное исследование самостабилизации частоты вращения одноцилиндрового пневматического поршневого двигателя

Generation of electricity by standalone sources is one of leading-edge avenues in the development of modern power engineering. Good-looking prospects of developments in this field are stemming from the fact that the use of nothing else but centralized power grids and generating capacities in Russia becomes impossible under the conditions of market economy in the country. Wide use of stand-alone generation of electricity on the basis of well-known heat engines is held back by impossibility to ensure highly accurate stabilization of voltage frequency (at a 50 ±0.2 Hz level) unless expensive equipment is used. The article considers an approach to solving this problem by using a generating set equipped with an expansion piston (reciprocating) engine operating in the rotation frequency self-stabilization mode (RFSS). This phenomenon is studied by taking a pneumatic piston engine as an example. Air is considered as a modeling working fluid. Steam will be used as an actual working fluid in a real cogeneration plant. One of distinctive features pertinent to operation of a piston engine with RFSS is that the working fluid flowrate remains constant irrespective of the load power, which is a positive feature during its operation in a cogeneration mode. This feature eliminates the need to use an adjustable bypass line or a separate boiler and ensures normal operation of the heat supply system when the electrical load decreases. The main objective of the study is to compare the experimental data on the generating set operation with the theoretical data (the latter were obtained on a piston engine’s simplified dynamic model in transient modes). It has been shown that this model describes the real piston engine with accuracy sufficient for engineering purposes. Owing to this circumstance, taken in combination with simplicity of the dynamic model, it became possible to derive for the first time an engineering analytical formula for the overshoot of piston engines with RFSS at a step-wise variation of load. The study results opened the possibility to reliably determine how the rotation frequency of a piston engine with RFSS deviates in response to a step-like change of load. This quantity uniquely determines deviation of the frequency of voltage generated by the electrical generator driven by such engine. The authors have created prerequisites for determining the advisable application field of piston engines with RFSS in cogeneration power supply systems.

Modelling and Performance Analysis of U Type Evacuated Tube Solar Collector Using Different Working Fluids

Abstract This paper presents the mathematical modelling of a U type evacuated tube solar collector required for heating a working fluid. The developed mathematical model is used for predicting the outlet temperature and net heat gain by the working fluid. The model predictions are compared with experimental data and a good agreement is observed between them. Aqueous lithium chloride solution (LiCl-H2O), water and air are chosen as working fluids. The effects of working fluid flow rate and inlet temperature, collector length, ambient temperature and solar intensity on the performance of the system are investigated. It has been observed that collector length, working fluid flow rate and solar intensity have greater impact on performance of the collector. The working fluid inlet temperature doesn’t have significant effect. Also, a detailed analysis on aforementioned working fluids is carried out for U type copper tube and the results are presented in this paper.

Performance of SDHW systems with fully mixed and stratified tank operation under radiative regimes with different degree of stability

In this paper we investigate whether, and to what extent, the radiative regime has an influence on the performance of a solar domestic hot water system. We compared the results of two mathematical models (a more accurate model with stratification in the storage tank and a simple, less accurate, fully mixed model), simulating the dynamic behaviour of a system with two flat-plate solar collectors, under three commonly used tapping cycles. Four summer and four winter days with different radiative regimes have been selected for simulations. For the less stable winter day of 19 January (relative sunshine σ = 0.4–0.7), when the system operates with a constant working fluid flow rate of 0.01 kg/(s m2) and hot water is extracted according to a medium consumption tapping cycle, the mean value predicted by the more accurate, stratification model, for the useful heat gain by the solar collector is 388.87 W. Using this value as a reference, the MBE and RMSE values of the results predicted by the less accurate model are 41.54 W and 293.28 W, respectively. This proves that approximation models may not be used successfully for simulation. For variable working fluid mass flow rate, depending on the level of incoming solar irradiation and collecting surface area, the simplified model accuracy increases with the increase of the radiative regime stability.

Experimental investigation on the performance of ORC power system using zeotropic mixture R601a/R600a

An experimental study on the practical performance of organic Rankine cycle (ORC) system using zeotropic mixture is performed by using a small scale ORC power generation experimental setup. R601a/R600a is selected as the working fluid. The effects of mixture composition, heat source temperature, and working fluid flow rate on the performance of ORC system are investigated. The experimental results indicate that the net power output first increases and then decreases as the R600a concentration increases. The optimal mixture composition with the maximum net power output is 0.6/0.4 (mass fraction) at the heat source temperature of 115°C. The net power output of R601a/R600a (0.6/0.4) is higher than that of R601a by 25%, indicating that the performance of ORC system can be clearly improved by using the zeotropic mixture. For a fixed working fluid flow rate, both net power output and thermal efficiency first decrease slowly and then drop sharply with the decrease of the heat source temperature. The appropriate superheat degree of R601a/R600a is in the range of 15 to 20°C when the heat source temperature has a small variation. In addition, the optimal working fluid volume flow rates yielding the maximum net power output are obtained for different compositions of R601a/R600a. The experimental results in the study can be of great significance for the design and operation of ORC power system using zeotropic mixture. Copyright © 2016 John Wiley & Sons, Ltd.

Thermal Performance of the U-Tube Solar Collector Using Computational Fluid Dynamics Simulation

In this paper, we propose a numerical study of a tubular solar collector with a U-tube. A three-dimensional numerical model is developed. It was first used in order to study the efficiency of the solar collector and to evaluate the validity of the developed computational fluid dynamics (CFD) model by comparison with experimental results from the literature. For the numerical simulations, the turbulence and the radiation were, respectively, modeled using the standard k–ε model and the discrete ordinates (DO) model. This numerical model was then used to carry out a parametrical study and to discuss the effect of selected operating parameters such as the fluid mass flow rate, the absorber selectivity, and the material properties. Numerical results show that with the increase of the working fluid flow rate from 0.001 kg/s to 0.003 kg/s, the efficiency of the solar collector is improved (from 30% to 35%). Numerical results also show that the filled-type evacuated tube with graphite presents a best result in comparison with those found using the copper fin tube (η increases from 54% to 64%). Finally, we noted that the use of a high selective absorber surface adds to better performance in comparison with the black absorber tube. This is mainly due to the radiation losses reduction.

Experimental Study of the Influence of Light Intensity on Solar Organic Rankine Cycle Power Generation System

A low-temperature (<120 °C) solar organic Rankine cycle (ORC) power generation experimental facility is designed and built. The influence of light intensity on the system performance is investigated using the experimental facility. The results indicate that the system efficiency can reach 2.2%. The temperature of heat transfer fluid (HTF) decreases linearly with light intensity (I). However, both system efficiency and thermoelectric efficiency first decrease linearly and then drop sharply as I decreases at working fluid flow rates (Vwf) of 200 and 160 L/hr, while they only decrease slightly with I at Vwf of 120 L/hr. The light intensity of the turning point is 824 W/m2 at Vwf of 200 L/hr, which corresponds to an HTF temperature of 75 °C. In addition, it is found that the influence of light intensity on the performance of ORC becomes stronger for higher working fluid flow rate. Moreover, the light intensity and HTF temperature at the turning point increase with working fluid flow rate. The experimental results are of great significance for the design and operation of low-temperature solar ORC power generation system.

Analysis on optimal working fluid flowrate and unstable power generation for miniaturized ORC systems

For efficient utilization of a limited geothermal resource in practical projects, the cycle parameters were comprehensively analyzed by combining with the heat transfer performance of the plate heat exchanger, with a variation of flowrate of R245fa. The influence of working fluid flowrate on a 500W ORC system was investigated. Adjusting the working fluid flowrate to an optimal value results in the most efficient heat transfer and hence the optimal heat transfer parameters of the plate heat exchanger can be determined. Therefore, for the ORC systems, optimal working fluid flowrate should be controlled. Using different temperature hot water as the heat source, it is found that the optimal flowrate increases by 6-10 L/h with 5 °C increment of hot water inlet temperature. During experiment, lower degree of superheat of the working fluid at the outlet the plate heat exchanger may lead to unstable power generation. It is considered that the plate heat exchanger has a compact construction which makes its bulk so small that liquid mixture causes the unstable power generation. To avoid this phenomenon, the flow area of plate heat exchanger should be larger than the designed one. Alternatively, installing a small shell and tube heat exchanger between the outlet of plate heat exchanger and the inlet of expander can be another solution.

Optimization of a modified double-turbine Kalina cycle by using Artificial Bee Colony algorithm

Owing to appropriate performance of ammonia-water as a working fluid over two-phase region when exploiting low-temperature heat sources, a modified low-temperature double-turbine Kalina cycle system is designed to boost thermal efficiency. Due to low pressure after the second turbine, it is not affordable to use more than two turbines. Input mass flow rate of the second turbine is supplied by adding heat to the output liquid ammonia-water mixture from the first separator, separating the vapor at the outlet of the first turbine before blending the two streams. In order to reach the optimum thermal efficiency of the cycle, ABC (Artificial Bee Colony) algorithm is implemented as a novel powerful multi-variable optimization algorithm. Considering the structure of the algorithm, convergence speed and accuracy of solutions have been considerably enhanced when compared to those of GA, PSO and DE algorithms. Such a relative enhancement is indicated by limit parameter and reducing probability of occurrence of local optimum problem. In this paper, thermal efficiency is selected as the objective function of ABC algorithm where its optimum value for the suggested Kalina cycle is found to be 26.32%. Finally, effects of the first separator inlet pressure and temperature, basic ammonia mass fraction and mass flow rate of the ammonia-water working fluid on net power output, required heat energy for the cycle and thermal efficiency are investigated.

Design and experimental analysis of a mini ORC (organic Rankine cycle) power plant based on R245fa working fluid

ORC (organic Rankine cycles) represent a sound solution for the exploitation of thermal energy available at low temperature.The prototype of a small ORC power plant has been realized at the Energy Systems Laboratory of Cassino University. In this paper, the plant design, the experimental methodology and the thermodynamic analysis of the work cycle have been illustrated. The aim of the work is to assess the feasibility of small-scale ORC plants.The basic idea is to analyze the performance of a small ORC plant able to exploit low-temperature heat sources.Thus, a simple organic Rankine cycle has been analyzed and R245fa as working fluid has been selected. Due to the small working fluid flow rates, a volumetric machine, in particular a scroll expander, has been chosen for mechanical power generation.The hot source temperature has been varied in the range 75–95 °C and the cold sink temperature ranged between 20 °C and 33 °C. The R245fa vapor maximum pressure varied from 6 up to 10 bar. In this operating range, the best obtained results were: electric power equal to 1.2 kW, specific work about 20 kJ/kg and cycle efficiency slightly greater than 9 percent.

Nanorefrigerants application possibilities study to increase the equipment ecological-energy efficiency

The results of experimental and theoretical studies of the TiO 2 and Al 2 O 3 nanoparticle additives in the working fluid R600a / mineral oil on the eco-energy efficiency of the compressor system have been considered. The experimental setup (refrigeration compressor system) and the experimental methodology have been described. Following working fluids have been selected for compressor refrigeration system: R600a / compressor oil; R600a / compressor oil / nanoparticle TiO 2 (1,0 and 0,48 wt%.) and R600a / compressor oil / nanoparticles Al 2 O 3 (0,52 and 0,08 wt.%). The results of experimental studies of cooling capacity, compressor power and coefficient of performance at the different values of working fluid flow rate in the compressor refrigeration system have been reported. It was shown that the nanoparticle additives may lead to increase in energy consumption of the compressor system up to 23% at flow rate of the working fluid equal to 0.00025 kg/s at the evaporator temperature 258 K. The method of eco-energy analysis has been proposed to science-based evaluation of an expediency of nanoparticle additives to the refrigeration equipment working fluids. This method is based on assessment of total equivalent greenhouse gases emissions on the equipment life cycle (TEGHGE). Expressions to assessment the value of TEGHGE and the specific eco-indicator have been proposed. The values of TEGHGE and eco-indicator on the life cycle of the compressor system based on experimental data obtained for the cooling capacity and compressor power for different working fluids have been analyzed. It was shown that Al 2 O 3 nanoparticle additives with 0.52 % mass concentration provide the best eco-energy effect.

Dynamic test on waste heat recovery system with organic Rankine cycle

Dynamic performance is important to the controlling and monitoring of the organic Rankine cycle(ORC) system so to avoid the occurrence of unwanted conditions. A small scale waste heat recovery system with organic Rankine cycle was constructed and the dynamic behavior was presented. In the dynamic test, the pump was stopped and then started. In addition, there was a step change of the flue gas volume flow rate and the converter frequency of multistage pump, respectively. The results indicate that the working fluid flow rate has the shortest response time, followed by the expander inlet pressure and the expander inlet temperature. The operation frequency of pump is a key parameter for the ORC system. Due to a step change of pump frequency (39.49–35.24 Hz), the expander efficiency and thermal efficiency drop by 16% and 21% within 2 min, respectively. Besides, the saturated mixture can lead to an increase of the expander rotation speed.

Semi-dynamic Simulation of ORC Based Diesel Engine WHR System

Organic Rankine Cycle (ORC) based engine waste heat recovery (WHR) has been recognised as a promising technology as it can potentially improve the total engine efficiency significantly and has no noticeable effect on engine operation. In this paper, a model based investigation in this technology has been presented. A semi-dynamic model has been developed which consists of a detailed 1-D engine acoustic model, an ideal ORC thermodynamic model and a bridging model that couples the two sub-models and enables a dynamic data transfer between these two models, thus enables a semi-dynamic simulation. A parametric analysis has been carried out for working fluid selection that allows the best match of the engine working conditions. Water, R134a and R245fa were selected as working fluid candidates, and the simulation results suggest that despite water has the highest cycle efficiency, it is unsuitable to use it because as a wet fluid, water cannot be heated to superheated steam in most of the conditions. For the two organic refrigerants, R245fa is superior to R123a in terms of cycle efficiency. A cyclic simulation following a WHSC engine operation cycle suggests that the control of working fluid flow rate is necessary to maintain a high ORC cycle efficiency. A preliminary optimal control can achieve 8.1% fuel economy improvement throughout the whole cycle.

On the efficient use of a lowtemperature heat source by the organic Rankine cycle

Abstract The evaporation temperature is regarded as one of the major parameters influencing the organic Rankine cycle (ORC) efficiency. Majority of contributions in literature for ORC cycle analyses treat the heat source as if it had an infinite heat capacity. Such analyses are not valuable as the resulting temperature drops of the heat source needs to be small. That leads to the fact that the heat source is not well explored and in the case of waste heat utilization it can prove the poor economics of the ORC. In the present study cooperation of the ORC cycle with the heat source available as a single phase or phase changing fluids is considered. The analytical heat balance models have been developed, which enable in a simple way calculation of heating fluid temperature variation as well as the ratio of flow rates of heating and working fluids in ORC cycle. The developed analytical expressions enable also calculation of the outlet temperature of the heating fluid.

Heat losses from parabolic trough solar collectors

SUMMARY Parabolic trough solar collector usually consists of a parabolic solar energy concentrator, which reflects solar energy into an absorber. The absorber is a tube, painted with solar radiation absorbing material, located at the focal length of the concentrator, usually covered with a totally or partially vacuumed glass tube to minimize the heat losses. Typically, the concentration ratio ranges from 30 to 80, depending on the radius of the parabolic solar energy concentrator. The working fluid can reach a temperature up to 400°C, depending on the concentration ratio, solar intensity, working fluid flow rate and other parameters. Hence, such collectors are an ideal device for power generation and/or water desalination applications. However, as the length of the collector increases and/or the fluid flow rate decreases, the rate of heat losses increases. The length of the collector may reach a point that heat gain becomes equal to the heat losses; therefore, additional length will be passive. The current work introduces an analysis for the mentioned collector for single and double glass tubes. The main objectives of this work are to understand the thermal performance of the collector and identify the heat losses from the collector. The working fluid, tube and glass temperature's variation along the collector is calculated, and variations of the heat losses along the heated tube are estimated. It should be mentioned that the working fluid may experience a phase change as it flows through the tube. Hence, the heat transfer correlation for each phase is different and depends on the void fraction and flow characteristics. However, as a first approximation, the effect of phase change is neglected. Copyright © 2013 John Wiley & Sons, Ltd.

Thermodynamic analysis of two micro CHP systems operating with geothermal and solar energy

Micro combined heat and power (CHP) plants operating through an organic Rankine cycle (ORC) using renewable energy are analyzed. The reference system is designed to produce 50kWe. The heat sources of the system are geothermal energy at low temperature (80–100°C) and solar energy. Two different system layouts, a single and a double stage arrangement, are presented. The first uses a solar field composed only by evacuated solar collectors, and work is produced by a single turbine. In the double-stage system, a field of evacuated solar collectors heats the working fluid up to an intermediate temperature. After this first stage, only a part of the working fluid flow rate is heated in a second solar field, composed of direct-steam parabolic through collectors (PTCs), up to the maximum temperature of the cycle. The mechanical work is then produced in two turbo-expanders arranged in series. For the investigations, different working fluids (e.g. R134a, R236fa, R245fa) are considered. The results of the simulation in terms of efficiencies, heat and electricity production and the main characteristics of the system (i.e. heat exchanger surface, solar collector area) are presented and discussed.

Evacuated tube solar heat pipe collector model and associated tests

In this paper, an evacuated solar heat pipe collector is investigated theoretically and experimentally. Heat transfer formulas were used for theoretical modeling, and a test method was adopted from ISO 9806-1 to compare the theoretical model with the experimental results. The collector efficiency and useful heat gain were compared between the theoretical and experimental methods. The effect of the working fluid flow rates and collector area were also investigated and discussed. The comparison shows that the theoretical model is in good agreement with the experimental results and is capable of predicting the efficiency, useful heat gain, and working fluid outlet temperature of an evacuated heat pipe collector with good accuracy.

An experimental study on the recuperative low temperature solar Rankine cycle using R245fa

An experimental study is conducted to investigate the performance of a low-temperature solar recuperative Rankine cycle system using working fluid R245fa. The experimental setup consisted of typical Rankine cycle components, such as throttling valves, working fluid pumps, air cooled condensers, and a flat plate collector for gathering solar energy. Prior to boiler, the working fluid is typically preheated; this process is simulated in the experiment using an electric tracing ribbon. Experiments conducted during typical winter weather conditions in Tianjin, China. Results showed that for conditions of constant working fluid flow rates, the introduction of a recuperator did not improve the thermal efficiency of the experimental system obviously, which remained constant at about 3.67%. Furthermore, preheating caused the collector inlet temperature to increase, which led to lower collector efficiencies and ultimately, lower overall system efficiencies. Results also showed that both thermal and collector efficiencies could be improved significantly by adjusting the working fluid flow rate to an appropriate level based on the solar heat flux. Significant improvements in thermal efficiency can also be achieved with an improved expander.

Heat transfer in a low latitude flat-plate solar collector

Study of rate of heat transfer in a flat-plate solar collector is the main subject of this paper. Measurements of collector and working fluid temperatures were carried out for one year covering the harmattan and rainy seasons in Port Harcourt, Nigeria, which is situated at the latitude of 4.858oN and longitude of 8.372oE. Energy balance equations for heat exchanger were employed to develop a mathematical model which relates the working fluid temperature with the vital collector geometric and physical design parameters. The exit fluid temperature was used to compute the rate of heat transfer to the working fluid and the efficiency of the transfer. The optimum fluid temperatures obtained for the harmattan, rainy and yearly (or combined) seasons were: 317.4, 314.9 and 316.2 [K], respectively. The corresponding insolation utilized were: 83.23, 76.61 and 79.92 [W/m2], respectively, with the corresponding mean collector efficiency of 0.190, 0.205 and 0.197 [-], respectively. The working fluid flowrate, the collector length and the range of time that gave rise to maximum results were: 0.0093 [kg/s], 2.0 [m] and 12PM - 13.00PM, respectively. There was good agreement between the computed and the measured working fluid temperatures. The results obtained are useful for the optimal design of the solar collector and its operations.

Performance analysis of the Chena binary geothermal power plant

In this paper, the IPSEpro model of the Chena Geothermal ORC Power Plant had been developed and validated using the real data. The validated model was used to investigate the effect of variation in the geothermal source temperature on plant performance. The analysis showed that the variation of the geothermal source temperature affects the plant behaviour. Increase in the geothermal source temperature above the design point increases the working fluid flowrate, decreases the working fluid degree of superheat at the inlet of the turbine (evaporator exit), increases the plant net power output and reduces the efficiency while decrease in the geothermal source temperature lower than the design point increases the degree of superheat up to a certain maximum beyond which it starts to reduce. It also causes a decrease in the net power output and an increase in the plant efficiency.