Organic Rankine Cycle Optimization Performance Analysis Based on Super-Heater Pressure: Comparison of Working Fluids

The organic Rankine cycle (ORC) is widely accepted to produce electricity from low-grade thermal heat sources. In fact, it is a developed technology for waste-heat to electricity conversions. In this paper, an ORC made up of super-heater, turbine, regenerator, condenser, pump, economizer and evaporator is considered. An optimization model to obtain the maximum performance of such ORC, depending on the super-heater pressure, is proposed and assessed, in order to find possible new working fluids that are less pollutant with similar behavior to those traditionally used. The different super-heater pressures under analysis lie in between the condenser pressure and 80% of the critical pressure of each working fluid, taking 100 values uniformly distributed. The system and optimization algorithm have been simulated in Matlab with the CoolProp library. Results show that the twelve working fluids can be categorized into four main groups, depending on the saturation pressure at ambient conditions (condenser pressure), observing that the fluids belonging to Group 1, which corresponds with the lower condensing pressure (around 100 kPa), provide the highest thermal efficiency, with values around η=23−25%. Moreover, it is also seen that R123 can be a good candidate to substitute R141B and R11; R114 can replace R236EA and R245FA; and both R1234ZE and R1234YF have similar behavior to R134A.

Experimental Investigation of a Miniature Ejector Using Water as Working Fluid

This paper presents an experimental investigation of a miniature ejector using water as the working fluid. The investigated ejector cooling system can utilize the thermal energy to be removed to power the cooling system and maintain the temperature of an electronic component below ambient temperature. The effects of working conditions, nozzle exit position (NXP), and area ratio on the coefficient of performance (COP) of ejector performance were investigated. Experimental results show that the miniature ejector can function well when the temperature in the high-temperature evaporator (HTE) ranges from 55 °C to 70 °C and can achieve a COP (coefficient of performance) of 0.66. With an increase of the NXP, the COP decreases, while the critical condensing pressure first increases and then decreases. As the area ratio of the miniature ejector increases, the COP increases, and the critical condensing pressure decreases.

Enhanced Steam Condensation Heat Transfer on a Honeycomb-Like Microporous Superhydrophobic Surface Under Different Condensing Pressures

Steam condensation heat transfer was studied over a honeycomb-like microporous superhydrophobic surface under various pressures, in order to elucidate the effects of pressure on the jumping-droplet condensation behaviors. The condensing pressure was varied from 4 kPa to 13 kPa, based on the typical operating conditions of condensers in power plants. Stable coalescence-induced droplet jumping was realized on the honeycomb-like superhydrophobic surface over this range of pressure, leading to a great enhancement on the condensation heat transfer as compared to that on the common hydrophobic surface, especially at small degrees of subcooling (e.g., < 10 K). The frequency and number of jumping droplets were observed to decrease at lower pressures because of the less amount of condensate produced, and at higher degrees of subcooling due to the occurrence of surface flooding. The increasing condensing pressure was found to lead to a later onset of surface flooding. The results indicated that the honeycomb-like superhydrophobic surface has a great potential for industrial condensation equipment operating at multiple pressures owing to its superior performance and facile fabrication.

Performance analysis of heat accumulation of solar thermal generator units by computer numerical simulation

The core carrier working substances of heat accumulation of solar thermal generator units are analyzed through computer numerical simulation analysis and simulation experiments, including the selection criteria of working substances, the mechanism of heat accumulation system, the correlation between power generation efficiency and the evaporation temperature of working substance, the correlation between the condensing temperature and condensing pressure of working substance, and the influence of working substance velocity on heat accumulation capacity. The results show that under the same radiation intensity, the greater the flow velocity of the working substance is, the worse the heat accumulation and heat conduction of the working substance is. As the condensing temperature of the working substance increases, the condensing pressure also increases. As the evaporation temperature of the working substance increases, the power generation efficiency of the working substance also increases significantly. In summary, the heat accumulation system based on the high efficiency working substances is vital for the normal operation of solar thermal generator units. Once the solar radiation intensity cannot meet the needs of power generation, the heat accumulation system will output previously-stored thermal energy. Meanwhile, its collection and release of thermal energy depend on the photovoltaic intensity. The constructed hot-oil working substance-based heat accumulation system satisfies the normal operation needs for thermal generator units, which is significant for subsequent research.

Experimental Investigation of a Miniature Ejector Using Water As Working Fluid

This paper presents an experimental investigation of a miniature ejector using water as the working fluid. The investigated ejector cooling system can be used to keep the temperature of an electric chip below ambient temperature. The authors tested the effects of working conditions, the nozzle exit position (NXP), and the area ratio on the ejector’s performance. Experimental results show that the miniature ejector works well in the high-temperature evaporator (HTE) under temperatures ranging from 55 °C to 70 °C and can achieve a 0.66 coefficient of performance (COP). With the increase of the NXP, the COP decreased, while the critical condensing pressure first increased and then decreased. As the area ratio of the miniature ejector increased, the COP increased, and the critical condensing pressure decreased.

Experimental Investigation on Performance of an Organic Rankine Cycle System Integrated with a Radial Flow Turbine

An experimental method is used to investigate the performance of a small-scale organic Rankine cycle (ORC) system which is integrated with a radial flow turbine, using 90 °C hot water as a heat source. The considered working fluids are R245fa and R123. The relationship between cycle performance and the operation parameters is obtained. With constant condensing pressure (temperature), the outlet temperature of the hot water, the mass flow rate of the hot water and the evaporator heat transfer rate increase with increasing evaporating pressure. Turbine isentropic efficiency decreases and transmission-generation efficiency increases with rising evaporating pressure. In the considered conditions, the maximum specific energy is 1.28 kJ/kg, with optimal fluid of R245fa and an optimal evaporating temperature of 69.2 °C. When the evaporating pressure (temperature) is constant, the outlet temperature of the cooling water increases, and the mass flow rate of the cooling water decreases with increasing condensing pressure. Turbine isentropic efficiency increases and transmission-generation efficiency decreases with the rise of condensing pressure. In the considered conditions, the maximum specific energy is 0.89 kJ/kg, with optimal fluid of R245fa and an optimal condensing temperature of 29.1 °C. Turbine efficiency is impacted by the working fluid type, operation parameters and nozzle type.

PERFORMANCE CORRECTION FACTORS FOR VAPOR COMPRESSION REFRIGERATION AND HEAT PUMP SYSTEMS TESTED WITH UNCONTROLLED CONDENSER CONDITIONS

A method for experimental data adjustment consisting of correction equations for the performance parameters of the refrigeration/heat pump vapor compression cycle, when operation conditions depart from those established in testing standards, is here presented. A basic thermodynamic model allowed for a methodology to be developed so as to correct vapor compression cycle performance to a desirable operating condition. Correction factor equations are proposed for refrigerant mass flow rate, compressor specific enthalpy gain and evaporator refrigeration effect, for situations when condensing pressure has not followed standards conditions or has not been properly controlled during experiments. The method was verified against experimental data from a vapor compression water-to-water heat pump with controlled condensing temperatures of 30oC, 40oC and 50oC. In spite of the purposely excessive correction, ±10oC, a relatively good smoothness, as well as a good agreement among all conversions, was obtained with the standardized points. The model was also applied to a refrigeration system running with water-SWCNT nanofluid (single walled carbon nanotube with water as the base fluid) as the secondary fluid. It contributed to a better discernment of the actual influence of the nanofluid in the system performance.

The Impact of Condensing Pressure on the Performance of Solar Solid Adsorption Refrigeration System

A new solar solid adsorption refrigeration system is established in this paper, and the variation relationship between the adsorbent bed temperature and pressure with time are analyzed, and the effects of adsorbent bed condensing pressure on the system performance is researched. Results show that, under the same working conditions, when the condensing pressure is 39 kPa, the daily ice-making capacity of system reach to 5.5 kg with the refrigerating capacity of 2.26 MJ; And when the condensing pressure is 63 kPa, the ice-making capacity of system is only for 3 kg with the refrigerating capacity of 1.48 MJ; The refrigerating capacity of the former is 1.5 times of the latter.

Study of Ground – Water Heat Pump Parameters during 3 Years of Operation

The manuscript presents results of a 3 years experiment, concerning in the monitoring of working parameters of a ground – water heat pump with horizontal collectors. The measured working parameters of the refrigerant circuit are: evaporating pressure, condensing pressure, superheating temperature, discharge temperature, sub cooling temperature. There were also measured the flow rate and the temperatures on the heating circuit of water and on the horizontal collectors circuit with antifreeze. The methodology of data processing, described in the manuscript, allowed calculation of evaporating temperature and condensing temperature, based on measured corresponding pressures. The main obtained results consist in a complete set of working and performance parameters and their variation in 3 years of operation. Details are presented for operating conditions characteristic for different cases: middle of heating season, end of heating season, middle of non-heating season, beginning of heating season. Some practical conclusions of the study are also presented in the manuscript. It was indicated how the outside temperature is influencing the values of working and performance parameters, but mainly on the effective number of running periods.

Analysis of the evaporative towers cooling system of a coal-fired power plant

The paper presents a theoretical analysis of the cooling system of a 110 MW coal-fired power plant located in central Serbia, where eight evaporative towers cool down the plant. An updated research on the evaporative tower cooling system has been carried out to show the theoretical analysis of the tower heat and mass balance, taking into account the sensible and latent heat exchanged during the processes which occur inside these towers. Power plants which are using wet cooling towers for cooling condenser cooling water have higher design temperature of cooling water, thus the designed condensing pressure is higher compared to plants with a once-through cooling system. Daily and seasonal changes further deteriorate energy efficiency of these plants, so it can be concluded that these plants have up to 5% less efficiency compared to systems with once-through cooling. The whole analysis permitted to evaluate the optimal conditions, as far as the operation of the towers is concerned, and to suggest an improvement of the plant. Since plant energy efficiency improvement has become a quite common issue today, the evaluation of the cooling system operation was conducted under the hypothesis of an increase in the plant overall energy efficiency due to low cost improvement in cooling tower system.