Degree Of Superheat Research Articles

Influence study of bottom cycle ratios and superheat for vessels waste heat cascade recovery based on TEG-ORC combined cycle system employing R245fa

ABSTRACT The vessel’s waste heat has the characteristics of a large temperature gradient, huge recoverable volumes, and various properties. TEG-ORC combined cycle is a promising method for multiple vessels waste heat cascade utilization. Keeping the evaporation pressure at 0.7Mpa, R245fa of low toxicity and environmental friendly is employed for the research under the conditions of different bottom cycle ratios(₣) and superheating. The interaction between essential parameters and system performance is explored. As the ₣ gets larger, the system net power output (W net ), the system thermal efficiency (η s ) and the waste heat utilization of main engine flue gas (f g ) gradually increase, the power-production cost (C g ) of the system gradually decreases. When the degree of superheat increases from 3.36K to 9.23K, the output power of the expander increases synchronously. The results show that superheating improves the combined cycle W net and f g while reducing theC g . The stability and safety of the ORC unit are further enhanced by expanding the ₣. When the ₣ is 0.885 and superheat is 11.28 K, W net is 965.18 W, η s is 8.74%, and the C g of the system is 0.5363 $ k Wh−1, and the rate of f g is 85.07%.

An investigation on near-field and far-field characteristics of superheated ammonia spray

Ammonia is an attractive alternative fuel for internal combustion engines because it has an octane number above 110 and produces zero carbon oxide emissions compared to traditional fossil fuels. Due to its low boiling point, liquid ammonia is highly susceptible to flash boiling even at high ambient pressures under engine-like conditions. However, the characteristics of superheated ammonia spray are not fully understood due to the combined effects of bubble explosion in the near-field and strong aerodynamic interactions during its penetration process. In this study, the spray characteristics of ammonia under different fuel temperatures and ambient densities were investigated in a constant volume chamber to cover a wide range of superheat degrees. High speed diffused back-illumination method was adopted to measure both micro-and macroscopic features of ammonia spray. A non-dimensional analysis was established for the near-field characteristics to correlate critical factors to quantified bubble explosion intensity of ammonia as well as methanol and n-hexane for a comparison. It is found that both superheat degree and fuel viscosity play a significant role in the entire flashing region. For the far-field characteristics, the evolution of penetration is divided into three stages, and the dominant factor in each stage is investigated systematically. These experimental data would provide insightful information for understanding the breakup mechanism and developing simulation models of ammonia sprays.

Visualization study on oil retention and flow characteristics of R32/PVE oil in suction lines with different flow orientations

Oil retention characteristic and flow patterns of R32/PVE lubricant oil mixture in compressor suction lines were investigated. Smooth copper tubes with 10.7mm inner diameter and four tube orientations including horizontal flow, vertical upward flow and inclined upward flow with 45° and 60° inclined angles, were utilized as test samples. Saturation temperature and superheat degree were maintained at 7.5°C and 12°C, respectively. The operation conditions of refrigerant mass flux and nominal oil mass fraction covered ranges of 48.5−230 kg•m−2•s−1 and 1−5%, respectively. The oil retention amount was measured by the remove and weight technique. Based on the visualization technique, flow patterns of R32/oil mixture were also observed, identified and analyzed. The characteristic of flow patterns was greatly influenced by the thermophysical properties of refrigerant-oil mixture. Comparisons of existing flow pattern maps and wet wall fraction correlations were conduct to investigate the applicability. The experimental result showed that oil retention in suction lines increased with the decrease in refrigerant mass flux and increase in oil mass fraction. The oil retention amount of 60° inclination suction line was slightly higher than that for 45°. Additionally, the difference of oil retention among the four configurations becomes limited at high mass flux conditions.

Comparative investigations on dynamic characteristics of basic ORC and cascaded LTES-ORC under transient heat sources

In order to overcome the thermal power fluctuations of transient heat sources and improve the safety performance of organic Rankine cycles (ORC), a novel combined system that latent thermal energy storage (LTES) using phase change material (PCM) is integrated into an ORC is proposed in this study. In the proposed system, LTES and evaporator have a cascaded configuration where the transient heat source first flows through LTES and then flows into the evaporator, with the fluctuating amplitude largely buffered. To validate the superiorities of the proposed cascaded LTES-ORC system, effects of PCM thermophysical properties including thermal conductivity and melting temperature are evaluated on the dynamic performance of LTES-ORC system, and they are comprehensively compared with that of basic ORC system under step-change and cyclic heat sources. Results indicate that proposed LTES-ORC system achieves significantly smaller fluctuating range of evaporating pressure and superheat degree than basic ORC system under both step-change and cyclic heat sources. Especially, LTES-ORC system has a larger maximum allowable fluctuating limitation range of heat sources and improves the safety performance under fluctuating heat source. In detail, under small-period fluctuating heat sources, LTES-ORC system can bear 15%–20% higher fluctuating amplitude ratio than basic ORC system under the same period of heat source. When the period is within the range of 600–3600 s, about 33%–42% higher fluctuating amplitude ratio can be resisted by LTES-ORC system. In addition, a correlation is proposed and validated to fast predict the maximum allowable fluctuation limitation for LTES-ORC system.

System integration for combined heat and power (CHP) plants with post-combustion CO2 capture

Based on a typical 1000 MWe coal-fired power plant with ultra-supercritical parameters, this study proposes a new integration scheme for the combined heat and power (CHP) plant with post-combustion CO2 capture. By introducing a back-pressure heat supply (BPHS) turbine and a back-pressure CO2 capture (BPCC) turbine, the superheated degree of the extraction steam is effectively retrieved for parameter matching of CO2 capture and heat supply. With 90% CO2 capture efficiency and 785.06 MWth heat supply, the total efficiency penalty for the CHP plants with solid amine-based CO2 capture reaches 19.32%. To optimize the proposed integration scheme, over 90% of the waste heat in the CO2 capture is recovered by applying the absorption heat exchanger (AHE) to increase the heating capacity of the integrated system. Energy analysis results show that the heating capacity of the integrated system is increased by 64.18%. Exergy analysis results reveal that the exergy destruction of the CO2 capture process and the heat exchange between the primary and secondary heating networks is reduced by 40.27 MWex and 10.33 MWex. Economic analysis results show that the cost of electricity (COE) and the cost of CO2 avoided (COA) are reduced by 2.59 $/MWh and 4.19 $/t CO2.

Experimental analysis of saturated pool boiling of acetone and isopropanol with added surfactant sodium lauryl sulfate over aluminum surface

AbstractThe present article reports a detailed experimental study to know the effect of adding surfactants to different base fluids. For this purpose, an aqueous solution of different concentrations of surfactant with base fluids was formed and then heated at varying heat flux in a pool boiling apparatus. Acetone and isopropanol have been used as base/boiling fluids with anionic surfactant sodium lauryl sulfate (SLS) of 200, 400, 600, 800, and 1000 PPM concentration. The data obtained by heating surfactant‐based fluids has been compared to the data of heating pure base fluids to establish the role of surfactants and the importance of surfactant concentration, that is, critical micelle concentration (CMC) in pool boiling augmentation. CMC value was found in the case of pool boiling of acetone with an SLS concentration of 400 PPM. However, the CMC value is found to be a lower value of SLS concentration of 200 PPM in the pool boiling process of isopropanol. Therefore, it is interesting to investigate the possible causes of such heat transfer phenomena with different values of surfactant concentration. Variations in heat flux change the degree of superheat of the aluminum heater substrate. The heat transfer performance is studied, and finally, a semi‐empirical correlation is proposed to know the heat transfer coefficient and its dependency over the concentration of surfactant.

Cascade refrigeration system with environment friendly refrigerants as R290 and ammonia

Many industrial applications need low-temperature cooling which single-stage refrigeration systems are unable to produce efficiently due to specific limitations of refrigerants used. Therefore, a cascade refrigeration system is one of the paramount substitutes in such applications. This paper presents a simulation of a cascade refrigeration system with hydrocarbon refrigerant, R290 in a low-temperature circuit (LTC) and natural refrigerant, ammonia in a high-temperature circuit (HTC). Both the refrigerants in this refrigeration system have low GWP and zero ODP, hence, eco-friendly with the environment. The main thrust of this study is to determine various performance parameters of the cascade refrigeration system and carry out exergy analysis as well as parametric analysis of the system. In this simulation the cascade refrigeration system achieves low temperature as -30°C in low temperature evaporator and cooling capacity 15 kW with COP of 6.024. It is observed that the work of compressors in LTC and HTC are 2.49 kW and 11.21 kW respectively, whereas total work of the cascade system is 13.7 kW at these operating conditions. It is considered to utilise refrigerant gas discharge superheat for heating of water to enhance overall performance of the system. The parametric analysis of cascade refrigeration system involves parameters like evaporator temperature, condenser temperature, degree of superheat, sub-cooling after condenser and utilisation of degree of gas discharge superheat for heating of water to determine effect on the system performance.

Optimization Study on Regenerative Organic Rankine Cycle (ORC) with Heat Source of Low-Grade Steam

Aiming at improving the performance of Organic Rankine Cycle (ORC) system with low-grade steam as heat source, this work studied and optimized the main operating parameters of the ORC system. The effects of evaporation temperature, superheat degree, condensation temperature and regenerator pinch temperature difference on the system performance were obtained. The optimization for the operating parameters is based on the indicators of specific net power output, waste heat pollution, cycle exergy efficiency, and total UA value (the product of overall heat transfer coefficient and heat transfer area of heat exchanger). The results show that the increase of the evaporation temperature and the superheat degree, and the decrease of the condensation temperature and regenerator pinch temperature difference can improve general system performance but lead to weaker economic performance. The optimal evaporation temperature, superheat degree, condensation temperature and regenerator pinch temperature difference are determined as 139°C, 4°C, 36°C and 8°C, respectively, reaching net power output of 114.73 kW, exergy efficiency of 37.10%. Besides, it is indicated that the regenerative ORC system can reach 13.6% additional net power output compared to the ORC system without the regenerator.

Boiling-up of a jet of superheated water discharged through a nozzle of small diameter

An experimental investigation of the boiling-up dynamics of a jet of superheated water being discharged through a short nozzle of a small diameter (d=0.2 mm) has been conducted. A change in the shape of a boiling-up jet has been traced at various degrees of superheat. A complete flow opening has been established in the temperature range of T=493-583 K. The instability of a complete breakup has been revealed. On the basis of experimental data, the dependence of variations in the jet opening angle on the saturation pressure has been plotted in dimensionless coordinates. Low-frequency pulsations with a power spectrum inversely proportional to the frequency (1/f-spectrum) have been found under changes of shapes of the boiling-up flow. Keywords: complete jet opening, superheated liquid, explosive boiling-up, short nozzle, 1/f-spectrum.

Вскипание струи перегретой воды при истечении через канал малого диаметра

An experimental investigation of the boiling-up dynamics of a jet of superheated water at the discharge through a short nozzle of small diameter (d=0.2 mm) has been conducted. A change in the shape of a boiling-up jet has been traced at various degrees of superheat. A complete flow opening has been established in a temperature range T=493 – 583K. The instability of a complete breakup has been revealed. On the bases of experimental data the dependence of a change of an opening jet angle on the saturation pressure has been plotted in dimensionless coordinates. Low-frequency pulsations with a power spectrum inversely proportional to the frequency (1/f - spectrum) have been found under changes of shapes of a boiling-up flow.

Super-Heating Degree Responsive Control Strategy of Variable Refrigerant Flow Air Conditioning System for Energy Saving and Stable Operation

Super-Heating Degree Responsive Control Strategy of Variable Refrigerant Flow Air Conditioning System for Energy Saving and Stable Operation

Effects of fuel properties and aerodynamic breakup on spray under flash boiling conditions

• Sprays of four single component fuels under flash boiling conditions were studied. • Spray collapses at R p of 0.28 for isooctane, hexane and ethanol, and 0.18 for pentane. • Ethanol has relatively larger near-field angle, far-field angle and SMD. • Aerodynamic breakup still plays an important role under low flash boiling conditions. • Isooctane, hexane and pentane under R p of 0.28 show a similar SMD value of 10 µm. The main purpose of this work is to conduct detailed comparisons of spray behavior among four important components of gasoline and to investigate the effects of fuel properties and aerodynamic breakup on spray behavior under flash boiling conditions. Isooctane, hexane, pentane, and ethanol were used as test fuels. Pressure ratio ( R p ) was used as an indicator for the superheated degree and varied from 0.14 to 1.1 by adjusting the ambient pressure. Both Diffused Backlight Imaging (DBI) and Phase Doppler Anemometry (PDA) measurements were used to obtain macroscopic and microscopic characteristics of sprays. Four dimensionless numbers were used to evaluate the aerodynamic breakup processes. The results showed that as the reduction of R p , the flash boiling intensity increased, leading to dramatic spray morphology changes and smaller droplet size, regardless of fuel type. Spray plumes merged into the spray center when lowering R p from 1.0. Spray collapsed at an R p of 0.28 for isooctane, hexane, and ethanol, and at an R p of 0.18 for pentane. Fuel properties also had significant effects on spray behaviors. Spray with pentane had the smallest penetration length, and a dramatic far-field angle reduction was observed at R p between 0.2 and 0.4, due to its higher vapor pressure and lower latent heat of vaporization. Under the same R p , ethanol sprays had relatively larger near-field angles, far-field angles, and Sauter mean diameter (SMD), due to its high latent heat of vaporization. All the dimensionless numbers showed that the spray with pentane had the largest aerodynamic breakup intensity, followed by hexane and isooctane, while ethanol had the lowest aerodynamic breakup intensity under the tested conditions. Aerodynamic breakup still played an important role under low flash boiling intensity conditions ( R p over 0.8). Microscopic results showed that SMD of isooctane, hexane, and pentane under an R p of 0.28 had a similar value of 10 µm.

Thermodynamic and Techno‐economic Analysis of a Triple‐pressure Organic Rankine Cycle: Comparison with Dual‐pressure and Single‐pressure ORCs

AbstractInvestigation of a triple‐pressure organic Rankine cycle (TPORC) using geothermal energy for power generation with the net power output of the TPORC analyzed by varying the evaporation pressures, pinch temperature differences (tpp) and degrees of superheat (tsup) aimed to find the optimum operation conditions of the system. The thermodynamic performance of the TPORC was compared with a dual‐pressure organic Rankine cycle (DPORC) and a single‐pressure ORC (SPORC) for geofluid temperatures ranging from 100°C to 200°C, with particular reference to the utilization of a hot dry rock (HDR) geothermal resource. Thermodynamic performances of the TPORC system using eight different organic working fluids have also been investigated in terms of the net power outputs. Results show that a higher geofluid mass flow rate can make a considerable contribution to shortening the payback period (PBP) as well as to decreasing the levelized electricity cost (LEC), especially when the geofluid temperature is low. For the temperature range investigated, the order from high to low based on thermodynamic and techno‐economic performances is found to be TPORC > DPORC > SPORC. In terms of using geothermal resources within the given temperatures range (100°C–200°C), the TPORC system can be a better choice for geothermal power generation so long as the wellhead geofluid temperature is between 140°C and 180°C.

Experimental study on operating parameters matching characteristic of the organic Rankine cycle for engine waste heat recovery

The organic Rankine cycle (ORC) is a promising engine waste heat recovery (WHR) technology. However, with a change in the engine operating conditions, the choice of ORC-WHR system operating parameters have great influence on system performance. Therefore, this study investigated the changing law of ORC-WHR system operating parameters optimal value and the sensitivity of the system to the operating parameters under eight different engine operating conditions. That is, the research on operating parameters matching characteristic. The two key operating parameters selected were expander speed (Sexp_shaft) and superheat degree (SD). The performance indexes of the system included expander shaft efficiency (ηexp_shaft), thermal efficiency (ηth), evaporator heat exchange (Qeva), expander output work (Wexp_shaft), pump work consumption (Wpump), and net power output (Wnet). The results showed that Sexp_shaft was the most significant parameter affecting the system performance. As engine load increased from 1000 rpm, 300 Nm to 1350 rpm, 650 Nm, the best Sexp_shaft of Wnet increased from 1200 to 1600 rpm. As the engine load increased, the sensitivity of the system to Sexp_shaft and SD gradually decreased. The influence of the Sexp_shaft on Wnet decreased from 90.28% to 7.78%. The effect of the SD on the Qeva decreased from 11.26% to 5.16%.

Evaporation characteristics during decompression of liquified CO2 from a conical-shaped vessel

Safe transport of pressurized CO2 requires a profound knowledge of the processes' effect during the phase transition on catastrophic failure of a tanker filled with liquid CO2. This study presents experimental results and analyses associated with the characteristics of expansion waves during depressurization of liquified CO2 in a divergent cross-section vessel. It explores the rarefaction and evaporation waves velocities analyzed in different three vessel's regions based on the pressure records. Results showed that the evaporation wave velocity increased downward with decreasing cross-section and increased liquid volume fraction. Also, the upstream state properties after the isentropic expansion in the metastable region were determined. The results were compared with previously achieved outcomes of CO2 decompression from a constant cross-section rectangular duct.Comparisons indicated significant differences in the wave pattern. So, expansion waves velocities varying in different vessel regions while they were nearly constant for the duct. The evaporation wave velocities were nearly identical for the duct and the upper conical vessel's regions. But their divergence increased as the evaporation wave propagated downwards. Furthermore, the downstream two-phase flow in the conical vessel propagated in an increased cross-section toward the exit. In comparison, there was non-spontaneous two-phase propagation behind the evaporation wave due to the small exit cross-section in the rectangular duct. Additionally, during the isentropic expansion, the degree of superheat was higher for the conical vessel than the duct, resulting in significant discrepancies in the upstream flow properties.

Numerical Investigation of Pool Boiling Under Ocean Conditions with Lattice Boltzmann Simulation. Part Ⅰ: Heaving Condition

Pool boiling is the heat-transfer mechanism of many heat exchangers inside ocean nuclear power plants working under the complex marine circumstances. Also, ocean conditions will create a new acceleration field other than gravity for the fluid, which induces some unique thermal–hydraulic characteristics. In this study, pool boiling under heaving conditions is numerically simulated using multiple relaxation time phase change lattice Boltzmann method. Firstly, the simulated results under static condition have been validated with recognized empirical equations, such as Rohsenow’s correlation at nucleate boiling, Zuber’s model, and Kandlikar’s model about critical heat flux (CHF). Then, pool boiling patterns, the boiling curve of time-averaged heat flux, transient heat flux, and heaving effects on different pool boiling regions are investigated. The results show that pool boiling curves of time-averaged heat flux between heaving conditions and static conditions with middle superheat degrees are similar. Heat transfer under heaving conditions at low superheat is somewhat enhanced, and it is weakened at high superheat, which leads to a slightly smaller critical heat flux with larger superheat compared with that under static conditions. Moreover, distinct fluctuation of the transient heat flux of pool boiling under heaving conditions is found for all boiling regimes. Furthermore, the heaving condition shows both positive and negative effects on pool boiling heat transfer at high-gravity and low-gravity regions, respectively. Besides, both the larger heaving height and shorter period time bring out more violent heaving motion and make a greater impact on pool boiling heat transfer.

Energy analysis and optimization of a small-scale axial flow turbine for Organic Rankine Cycle application

Increasing the cycle efficiency of Organic Rankine Cycles is an important R&D area. In this study, an effort has been made to optimize various parameters related to the axial flow turbine to maximize an ORC's efficiency. First, a numerical model for a small-scale single-stage axial flow turbine was developed and coupled with a 1D model of an existing ORC system. Then, a parametric study was undertaken for the system working under various turbine inlet conditions, such as turbine pressure ratios and working fluids. An optimization study was undertaken for the turbine flow profile using a low computational intensity Artificial Neural Network coupled with Genetic Algorithm optimization. Investigating the turbine losses revealed that the Mach Number is the most influential factor, which depends on the molar mass of the working fluid. Our study revealed that increasing the degree of superheat by up to 200% enhanced the turbine and overall cycle efficiency by 11% and 5%, respectively. Increasing the turbine total-to-static pressure ratio from 3 to 10 improved the turbine and cycle efficiency by up to 41% and 15%, respectively. Optimizing the turbine's flow profile enhanced the overall loss coefficient by 13.7%, the turbine's total-to-static efficiency by 5.2%, and the overall cycle efficiency from 8.78% to 9.02%.

Assessment and working fluid comparison of steam Rankine cycle -Organic Rankine cycle combined system for severe cold territories

In this work, organic Rankine cycle (ORC) is employed to expand the available temperature region of the conventional steam Rankine cycle (SRC) in severe cold territories. The feasibility of the proposed steam Rankine cycle -Organic Rankine cycle combined system is investigated and verified. Working fluids are compared and screened, the matching scheme of different working fluids suitable for different working conditions and objects (thermodynamic or economic performance) are obtained. The results show that the net power increment (NPI) of the combined system increases with the decrease of the condenser outlet temperature (CT). The NPI of ORC system can be effectively improved by adding a regenerator. For wet working fluids, when the evaporating pressure of ORC system is close to the critical pressure of working fluid, there exists an optimal superheat degree with maximum NPI of the system. The combined system using ammonia and R600 as working fluid has the largest NPI values. When the CT of SRC is higher than 90 °C, the Rankine cycle using ammonia as working fluid has better performance. When the CT of SRC is less than 90 °C, the regenerative ORC system using R600 as working fluid has a better performance.

Research on the characteristics of the refrigeration, heating and hot water combined air-conditioning system

Air source heat pump (ASHP) and heat pump water heater (HPWH) have the advantages of convenience and high efficiency. The newly proposed refrigeration, heating and hot water combined air-conditioning system (RHHAC) combines traditional ASHP with HPWH. The demands of users for cooling, heating and hot water are effectively satisfied with this equipment. In this study, five groups of experiments were conducted to study the starting and operating characteristics of the system. Besides, two sets of experimental cases were carried out to explore the operating characteristics of the system under the frosting process. Results show that the maximum superheat degree is 11°C when the system starts in hot water mode, while the maximum superheat degree is more than 22°C when the system starts in the other modes. As the temperature of hot water rises when the system runs in hot water mode, the maximum value of the discharge pressure can reach 3.7MPa. Besides, the analysis parameters will have regular pulsations when the system is in cooling mode. For example, in the experimental case 5, the fluctuation range of the superheat degree is 5.1°C-16.2°C.

A Waste Energy Recovery Management for Electricity Generation from Two Temperature Grades of Energy Sources in Subcritical Organic Rankine Systems

Waste energy represents one of the most critical issues for the economic utilization and management of energy in modern industrial fields. This article outlines a scheme to utilize two different source temperature levels within the envelope of higher than 200 °C zones. Two regenerative organic Rankine cycles (RORC) were implemented to construct a compound regenerative organic Rankine cycle (CRORC) to improve the energy management of the sources. These two mini-cycles were integrated throughout an intermediate economizer circuit to extract a certain amount of energy from the high-temperature level mini-cycle. R-123 was circulated in the high-temperature cycle due to its high critical temperature at evaporation and condensation temperatures of 160 °C and 50 °C, respectively. R-123, R-21, and hydrocarbon R-600 were used as working fluids for the low-temperature cycle at evaporation and condensation temperatures of 130 °C and 35 °C, respectively. The R-123 fluid in the high-temperature mini-cycle was superheated to 170-240 °C, whereas the fluid in the low-temperature level was superheated to 180 °C. The results showed that the independent system (IRORC) requires more energy recovery than the compound system by a maximum of 2% to achieve the same net power output. This corresponds to the enhancement of 2% for the system net thermal efficiency of the compound (CRORC) system compared to the independent (IRORC) one. The compound (CRORC) system revealed a net thermal efficiency in the range of 14% and 15.6% for the test conditions. The mini-cycle net thermal efficiency of the low-temperature in the compound system was enhanced by a range of 2.5-5% compared to that of the independent arrangement. R-123/R-123 and R-123/R-21 systems exhibited higher net thermal efficiencies than the R-123/R-600 one by 3% and 2%, respectively. Increasing the superheat degree of the high-temperature mini-cycle from 10 °C to 80 °C for the compound system has improved the thermal efficiency by 7.6-7.9% for the examined fluid pairs and operating conditions. Keywords: compound cycle, regenerative, energy management, energy recovery, organic fluids