Mass Flow Rate Of Working Fluid Research Articles

Research on the Performance Characteristics of a Waste Heat Recovery Compound System for Series Hybrid Electric Vehicles

In this paper, a waste heat recovery compound system for series hybrid electric vehicles is established. The existing components of vehicle air conditioning are used in the organic Rankine cycle (ORC) to realize miniaturization. The waste heat recovery compound system is constructed using GT-SUITE, and the objective of the analysis is to increase the power output and engine thermal efficiency increase ratio (ETEIR). The effects of the expander speed, pump speed, working fluid mass flow rate, and working fluid type on the waste heat recovery compound system are analyzed. The simulation results show that the optimal schemes for the ORC system and compound system corresponding to the expander speed and pump speed are 1000 pm, 2500 rpm, 1200 rpm, and 2500 rpm, respectively. Compared with the ORC system, the maximum power output of the compound system with the same working fluid in three states (1500 rpm, 2500 rpm, and 3500 rpm) of the engine is increased by 21.67%, 24.05%, and 28.23%, respectively. Working fluid supplies of 0.4 kg/s, 0.4 kg/s, and 0.6 kg/s in the three engine states are also considered the best solutions. The working fluid R1234yf and R1234ze are the preferred choices for a waste heat recovery compound system, which have a high system power output and ETEIR and are environmentally friendly.

Comparative analysis of geothermal binary ORC systems: performance and environmental considerations for CO2 andwater as geofluids

This study considers the process simulation of geothermal binary Organic Rankine Cycle (ORC) systems which utilizes CO2 and water as geofluids for electricity generation. The simulation was performed using Hysys v11 software by using Peng Robinson’s fluid property package. Two dry working fluids including isopentane and n-pentane, were used. The effects of geofluid temperature and working fluid mass flowrate on power generation, as well as the maximum pressure of working fluids were evaluated. The result showed that power generation increases with higher geofluid temperature due to enhanced heat transfer. Isopentane outperformed n-pentane, attributed to its superior thermodynamic properties. CO2 showed better performance as geofluid than water highlighting its superiority, observed in the increased power generation. The unique characteristics of CO2 enable efficient heat transfer at lower temperatures, making it an environmentally friendly and effective choice. Contrarily, the use of water as a geofluid poses some implications for local ecosystems and water resources. From an environmental perspective, CO2 shows greater potential for reduced environmental impact, which aligns with the transition to cleaner energy sources. However, the economic considerations suggest a trade-off, as CO2 projects may entail higher upfront costs compared to water-based systems. Regulatory factors and economic feasibility, therefore, play a crucial role in the choice of geofluid for geothermal power generation.

Multi-condition operating characteristics and optimization of a small-scale ORC system

The multi-condition operating characteristics of an organic Rankine cycle (ORC) are crucial to the development of the practical unit. This work developed a steady-state model of a small-scale ORC prototype built and tested in the lab. The influence of heat source/sink parameters, component design, and operation strategies are analyzed. It is found that the optimal output power and thermal efficiency correspond to the similar expander rotating speed but diverse working fluid mass flow rate. The higher mass flow rate is beneficial to the output power whereas deteriorates the thermal efficiency. Heat source temperature and flow rates mainly affect the unit output power while the ambient temperature and humidity influence both the output power and thermal efficiency. The condenser fouling resistance leads to a significant reduction of expander output power and system thermal efficiency. However, the effect of the evaporator fouling resistance could be neglected due to its sufficient redundant area. The long-term climate conditions and operating strategies profoundly impact the unit's off-design performance. The annual constant output power operation can be achieved by adjusting the working fluid mass flow rate. The thermal efficiency of the unit is damaged while pursuing the output power stability in winter and spring.

Heat transfer area optimization of intermediate heat-exchange cycle system for aero engines

The present study constructs an intermediate heat-exchange cycle system for aero engines. To explore the impact of circulation parameters on the cycle, a mathematical model has been developed. Based on the mathematical model, a novel and convenient approach to determining intermediate working fluid (IWF) mass flow rate and temperature, achieving the minimum total system heat transfer area, has been proposed. A two-stage heat exchanger combined intermediate heat-exchange cycle system with Chinese aviation kerosene RP-3, high-pressure water, and air as working fluids is taken as an example to verify the analytical results through numerical calculations. The deviation between the analytical and numerical results is relatively small, below 0.03%. For the situation of a given higher intermediate temperature, a wide range of IWF mass flow rates can be selected as the design point without significantly affecting the total heat transfer area. For the situation where both intermediate temperature and IWF mass flow rate are variable, an optimal area exists where the total heat transfer area is very low and does not differ much with each point. Overall, the present findings can serve as reasonably accurate preliminary guidelines for designing and optimizing the intermediate heat-exchange cycle system.

Optimization of a solar-based PEM methanol/water electrolyzer using machine learning and animal-inspired algorithms

This contribution scrutinizes the performance of the integrated photovoltaic thermal (PVT) system with the proton exchange membrane methanol electrolyzer (PEMME) and water electrolyzer (PEMWE) as sustainable ways to produce hydrogen. Artificial neural networks (ANNs), are adopted to evaluate the effect of various operating parameters on the performance of the systems. The adopted ANNs are radial basis function (RBF), extreme learning machine (ELM), long short-term memory (LSTM), and gated recurrent unit (GRU). Moreover, to obtain the optimum performances of the systems, the multi-objective whale optimization algorithm (MOWOA) and multi-objective bat algorithm (MOBA) are implemented. It is found that solar radiation is the most influential parameter on the hydrogen production rate of the systems, followed by ambient temperature, inlet temperature, working fluid mass flow rate, and wind speed. According to the machine learning outputs, the highest hydrogen production rate for the PVT-PEMWE and PVT-PEMME systems are around 2.45 mol h−1 m−2 and 5.44 mol h−1 m−2, respectively. Moreover, the MOBA shows that the hydrogen production rate and electrical efficiency of the PVT-PEMWE and PVT-PEMME systems are 2.29 mol h−1 m−2 and 18.74%, and 5.06 mol h−1 m−2, and 18.77%, respectively, at their global optimum point by considering hydrogen production rate and electrical efficiency as the objective functions. This study reveals that although at the same working conditions, the electrical and thermal output of the water-based PVT system is superior to that of the water/methanol-based PVT system, the PVT-PEMME system outperforms the PVT-PEMWE system from the hydrogen production viewpoint, due to the higher efficiency of the PEM methanol electrolyzer.

A parametric study on the efficiency of a solar evacuated tube collector using phase change materials: A transient simulation

Evacuated solar collectors are renewable systems that provide a considerable quantity of heat during test time. However, this system is unable to provide energy in the absence of sunlight. Thus, this study attempted to numerically study a Solar Evacuated Tube Collector (ETC) performance using phase change materials (PCM). PCM can store considerable thermal energy during the day and release it to the system at night. In order to simulate the ETC-PCM system, an accurate three-dimensional model considering all the layers is designed. In the present numerical investigation, the effect of various properties of the PCM, including enthalpy, melting point, and thermal conductivity, on the outputs of the ETC-PCM system are evaluated separately. Also, the effects of some other factors, such as MWCNT nanoparticles dispersion in the base fluid and working fluid mass flow rate, on the performance of the ETC-PCM system are studied. Furthermore, to evaluate the performance of the system and model the behavior of the PCM during the day, the system is simulated under the weather condition of Hing Kong from sunrise until sunset. According to the results of the simulations, a reduction in PCM melting point from 50 °C to 35 °C can elevate the efficiency of the ETC-PCM device. PCM with a high melting point remains solid during the day. Thus, its effect on the output of the system cannot be revealed. Moreover, it is found that the system using PCM with the latent heat of 160 kJ/kg has the best performance among the studied cases. Besides, it is illustrated that raising the mass flow rate of working fluid and mass fraction of nanoparticles can enhance the system's performance.

A comparative energy analysis of idealized cycles using an ammonia-water mixture for combined power/cooling

The Goswami combined power/cooling cycle is an appropriate way to convert energy efficiently. However, in the conventional Goswami cycle (CGC), the refrigeration is not available when the absorber temperature is high. In the present study, a mechanically driven compressor is used to compress the vapors leaving the turbine. This design creates a line independent of the absorber temperature. An idealized cycle approach was used with the assumptions adopted by Goswami. As a result, under the same typical operating conditions, the thermal efficiency of the novel cycle is 27.52% with a net useful effect of 135.2 kW, while the thermal efficiency of CGC is 23.54% with a net useful effect of 99.47 kW. Moreover, at equal total heat input, the working fluid mass flowrate in the novel cycle is less than the CGC. Ultimately, the refrigeration limits highlighted in the CGC were overcome in the novel cycle which allows the availability of refrigeration regardless of the increase in absorber temperature. This advantage, combined with the improved thermal efficiency, suggests a short-to-medium-term payback time of the additional investment cost of the added components and a long-term profitability of the system.

Numerical transient modeling of a flat plate solar collector

The present study deals with numerical simulation of a typical flat plate solar collector. The transient two-dimensional governing differential equations of absorber plate, working fluid and glass cover were formulated to describe the thermal problem of the collector. The governing differential equations were solved numerically using Finite Differences Method and the transient problem was formulated using implicit scheme which gives a stable solution for any grid size and time step. The two-dimensional temperature distribution in absorber plate was achieved at 2211 nodes at every 10 s of the simulation period that extended for 1800 s. The variation of fluid exit temperature and glass cover temperature were also estimated. The estimation of top heat loss coefficient and collector efficiency becomes possible using the temperature distributions of absorber plate and working fluid along with cover temperature. The variations of mean plate temperature, fluid exit temperature, cover temperature, top heat loss coefficient and collector efficiency were drawn during the simulation period. Temperature distribution contours were also drawn at selected time intervals and irradiance values. It was concluded that the top heat loss coefficient of the solar collector is a strong function of the irradiance and working fluid mass flow rate. Increasing the value of mass flow rate shortened the transient period of the solar collector and rendered the transient curves of the collector parameters more flat. The study can be useful for further understanding the complex transient two-dimensional thermal problem occurring in flat plate solar collectors.

Dynamic Modeling and Comparison Study of Control Strategies of a Small-Scale Organic Rankine Cycle

The control strategy is crucial for the effective and safe operation of the ORC system. A transient model of the ORC system was developed in the present work and validated by the experimental data of a 4 kW ORC prototype. Then, the effect of heat source temperature on the dynamic response and operation characteristics of the ORC system were analyzed. Five control strategies were compared: the constant working fluid mass flow rate mode, constant vapor superheat mode, constant vapor temperature mode, constant evaporation pressure mode and constant output power load mode. Under the constraint that the working fluid at the expander inlet should be superheated, we found that the constant vapor superheat mode enabled the safe operation with the largest range of heat source temperature, while the other four modes were only available for a certain temperature range. Apart from the constant output power mode, the constant evaporation pressure mode can also provide a relatively stable performance for the ORC unit. The variation of the thermal efficiency was limited when the heat source temperature was higher than 125 °C, except for the constant vapor temperature mode. Considering the high performance and stable operation of the ORC system, it is necessary to have different operation modes combined in the control strategy according to the specific working scenarios.

Surrogate-Assisted Multi-Objective Optimization of a Liquid Oxygen Vacuum Subcooling System Based on Ejector and Liquid Ring Pump

As an important combustion aid for aerospace vehicles, subcooled liquid oxygen of high density can be used to increase loading capacity of a spacecraft. Providing a large amount of cryogenic propellant in a short time with a strict energy consumption limitation is a challenge in the design of the fuel filling system. The authors proposed a vacuumed subcooling system combined with an ejector and liquid ring pump to vacuum a liquid oxygen tank and obtain subcooled liquid oxygen. After the liquid oxygen tank is vacuumed to an intermediate pressure by the ejector, it is further vacuumed to 10 kPa using the liquid ring pump. The infinitesimal method was used to simulate the thermodynamic processes involved. Taking the ejector working fluid mass flow rate, jet pressure, intermediate pressure, initial tank liquid level, and liquid ring pump speed as optimizing variables, optimization was conducted to determine the optimal vacuuming time, remaining liquid level in the tank, pumping speed difference, and nitrogen consumption. The sample set was generated by the optimal Latin sampling algorithm. The surrogate assisted Non-dominated Sorting Genetic Algorithm (NSGA-III) multi-objective algorithm was used to construct a system optimization framework. The non-dominated solutions were added to the sample set to improve the generalization ability of the Gaussian Process Regression (GPR) in the Pareto front. A convergent Pareto solution set was obtained after multiple iterations. The influence of different optimization variables on each optimization objective was analyzed using the Pearson correlation coefficient method. The optimization results show that the trade-off scheme can obtain the subcooled liquid oxygen at 10 kPa and 73 K with a remaining liquid level of 74.84% in a total vacuum time of 19.93 h. The efficiency of the liquid oxygen vacuum subcooling system can be improved significantly.

Multi-objective performance optimization of regenerative S-CO2 Brayton cycle based on neural network prediction

• A finite time thermodynamic model for regenerative S-CO 2 Brayton cycle is set up. • Artificial neural networks and multi-objective optimization are used. • Four different optimization objectives are considered. • The thermal efficiency and net power output are increased by 31.15% and 43.29%. • The exergy efficiency is increased by 33.75%. The regenerative supercritical CO 2 Brayton cycle (RSCBC) has great development potential in waste heat recovery and utilization, and it is necessary to carry out performance analysis and optimization. This article first applies the theory of finite time thermodynamics to establish a RSCBC model with finite temperature difference heat transfer, irreversible compression, irreversible expansion and other irreversible factors under variable temperature heat source conditions, and then uses the data samples to construct the corresponding neural network model. Based on the NSGA-Ⅱ algorithm, the working fluid mass flow rate, the pressure ratio, the heat conductance distribution ratios of the regenerator and the heater are chosen as optimization variables, multi-objective optimization is carried out with the goals of cycle thermal efficiency, net power output, ecological function and exergy efficiency. The results show that the use of neural network models to predict cycle performance can save a lot of calculation time compared to traditional calculation methods; after optimization, the positive ideal point is not on the Pareto front, which shows that the four optimization objectives are mutually restricted and affect each other. The results by using Shannon Entropy method for decision-making have a lower deviation index, and those by using TOPSIS and LINMAP methods for decision-making are consistent with each other; for the results by using Shannon Entropy method for decision-making, the cycle thermal efficiency and net power output can reach 38.4% and 12.047 MW respectively, which can be increased by 31.15% and 43.29% compared to those for the initial design point respectively, and the ecological function and exergy efficiency can reach 7.6274 MW and 73.2% respectively, which are 4.2588 times and 33.75% higher than those for the initial design point respectively. The obtained results can provide some guidance for the optimal design of the RSCBC in real engineering.

NUMERICAL INVESTIGATION OF A MANTLE HEAT EXCHANGER

The following work deals with numerical investigation of a storage tank equipped with a mantle annular cavity surrounding it. Heat is transferred via the working fluid flowing in the mantle side to the inner storage tank. Water at constant temperature of 60 oC enters the mantle to heat the tank and exits at a lower temperature. The study is carried out using the commercial software Ansys−Fluent to track the change of water temperature in the tank and mantle side during the simulated period of 60 minutes. Temperature contours of tank water and mantle water are drawn at several time intervals during the simulated period. The effects of changing working fluid mass flow rate were taken into account through three values, namely; 0.0077, 0.015 and 0.02 kg/s. Three values of mantle gap thickness; 10, 15 and 20 mm, and three values of mantle length; 250, 300 and 350 mm were applied in the simulation program and their effects were monitored and displayed. Results show that increasing the value of mass flow rate causes more heat transfer rate to the storage tank. The gap thickness of 10 mm which is the smallest value among the three applied values gave the best heat transfer rate and the mantle length of 300 mm was the optimum among the applied values. The heat transfer rate to the tank was studied in terms of tank mean temperature. The maximum mean tank temperature achieved at the end of the simulated period was 42oC.

Performance prediction of a cryogenic organic Rankine cycle based on back propagation neural network optimized by genetic algorithm

In this paper, a performance prediction model of the cryogenic ORC was presented based on the back propagation neural network optimized by the genetic algorithm (BPNN-GA). Firstly, an experimental setup was established to obtain the database for BPNN-GA model training and test. Then, the expander output power, working fluid mass flow rate, and the cold energy efficiency were selected as the BPNN-GA model outputs and the model structure was determined as 9-12-3. Finally, the accuracy of the BPNN-GA model was verified, and the parametric study was further conducted. The mean absolute relative errors (MARE) are 1.1876%, 0.9037%, and 2.6464%, the root mean square errors (RMSE) are 5.3789 W, 1.0260 kgh−1, and 0.3151%, and the correlation coefficients (R) are 0.9974, 0.9977, and 0.9665 for the expansion work, the working fluid mass flow rate, and the cold energy efficiency, respectively. The BPNN-GA is proved as a promising methodology, which could provide direct guidance for the determination of relevant parameters in experimental analysis and control strategy optimization.

Experimental evaluation of an innovative radial-flow high-temperature packed bed thermal energy storage

High-temperature packed-bed thermal energy storage represents an economically viable large-scale energy storage solution for a future fossil-free energy scenario. The present work introduces first-of-a-kind experimental setup of a radial packed-bed TES, and its performance assessment based on experimental investigations. The storage performance is analyzed based on a set of dimensionless criteria and indicators. The laboratory-scale prototype has an energy capacity of 49.7 kWhth and working temperatures between 25 °C and 700 °C with a non-pressurized dry airflow. The influence of different working fluid mass flow rates and inlet temperatures during charge and discharge is assessed. The proposed storage design ensures limited pressure drop, lower than 1 mbar, and thermal losses, about 1.11 % during dwell after charging at 700 °C until a state of charge of 55.8 %. A maximum overall thermal efficiency of 71.8 % has been recorded and trade-offs between efficiency, thermal uniformity, and thermocline thickness are highlighted. This work testifies that reduced pressure drops are the key advantage of radial-flow packed-bed designs. Thermocline degradation is shown to be the main weak point of this thermal energy storage design.

Performance comparison of single and double pass PV/T solar collectors integrated with rectangular plate fin absorber

Solar panel can act as a medium for transforming sunlight into electrical energy. Nevertheless, not all of the sunlight received on this device can be converted into electrical energy and the remainder will be dissipated into thermal energy. If a solar panel is continuously exposed to the sun, so its temperature will increase and thereby reduce its electrical efficiency. To deal with the issue, it may combine a PV panel with a thermal collector which is called a hybrid PV/T collector. Furthermore, in the present study the effects of fluid flow direction and mass flow rate on the thermal and electrical efficiency of the PV/T collectors are extensively analyzed. Single and double pass collectors with rectangular plate fin absorber were attached to backside of the PV panel. They were tested using a solar simulator with different flow rate ranging between 0.01 and 0.05 kg/s of the working fluid. The results show that the use of double pass PV/T air collector increase its performance compared with the single pass one. The highest values obtained from this type collector are found to be 73.23% in the thermal efficiency and 10.16% in the electrical efficiency with the working fluid mass flow rate of 0.048 kg/s.

The influence of fresh water production rate on the economics of two dual-purpose power/water plants: a case study

ABSTRACT The technical and economic analysis of the dual-purpose power/water Solar Rankine Cycle (SRC) coupled with Multi-Effect Desalination (MED) system was investigated. The influence of using Thermal Vapor Compression (TVC) on the unit costs of the generated power and water was also studied. Due to the population increase in the southern touristic coastal region of Iran and decreasing trend of the fuel price subsidy over the recent years, the government interest is shifting to the use of solar thermal energy and integrating the MED or MED-TVC desalination units with the conventional Rankine cycles, and to apply the solar thermal energy to reduce the fuel consumption. The water production rate of the MED or MED-TVC plants integrated into the SRC can significantly affect the electrical performance and consequently the fresh water and electricity unit of costs which has been rarely reported in the literature. In this regard, a comparison was made between the SRC-MED and SRC-MED-TVC configurations under two different scenarios of 6 and 12 hours of thermal energy storage. The output temperature of the LF solar field was considered to be regulated by defocusing the field mirrors and changing the working fluid mass flow rate. The unit costs of electricity (COE) and fresh water (COW) for both plants were determined under different scenarios of the water production capacities. Based on the results, COE and COW range from 0.20$/kWh to 0.25$/kWh and from 1.25$/to 3$/, respectively, for different water production rates. Also, for water production rates of more than 80,000/day, the SRC-MED plant has lower COE and COW as compared to the S‌RC-MED-TVC plant. While the COE and COW of the SRC-MED-TVC plant are less than those of the other plant for water production rates of less and equal to 36,000/day.

Model based control of the inlet pressure of a sliding vane rotary expander operating in an ORC-based power unit

• Experimental analysis on Sliding Vane Rotary Expander in ORC plant. • Development of a new approach for volumetric losses calculation. • Inlet pressure control strategy based on expander speed variation. • Effectiveness assessment of the proposed control strategy. • Performance optimization through the proposed regulation strategy. Sliding vane rotary expanders (SVREs) are widely used in organic Rankine cycle (ORC)-based power units for low-grade heat recovery because of their capability to deal with severe off-design working conditions. In particular, the speed of SVREs is a very effective operating parameter, together with the speed of the pump, to regulate the recovery unit and to lead the involved components in an acceptable operating behaviour when they are far from the design conditions. In this study, a control strategy based on the variation in revolution speed of a SVRE was developed, where the inlet pressure of the expander is the main controlled property, which must be verified when the flow rate of the working fluid is changed to match the thermal power recovery at the hot source. In fact, pressure level control is a key point of the recovery unit for thermodynamic reasons and for the safety and reliability of the expander and, more generally, of the whole recovery unit. The proposed control strategy is based on an original theoretical procedure that relates the expander speed, inlet pressure, volumetric efficiency, and working fluid mass flow rate in an analytical form. This analytical formulation is widely nonlinear and is simplified for use as a tool for the model-based control of the inlet expander pressure. An experimental activity performed on a SVRE operating in an ORC-based power unit, fed by the exhaust gases of a supercharged diesel engine, was the base of the analytical formulation. This provided the possibility of deriving a simplified model-based control of the expander inlet pressure and assessing its effectiveness and limits during off-design conditions. Higher expander global efficiencies were obtained (up to 45%), allowing a greater mechanical energy recovery (up to 2 kW).

Modelling an unconventional closed-loop deep borehole heat exchanger (DBHE): sensitivity analysis on the Newberry volcanic setting

Alternative (unconventional) deep geothermal designs are needed to provide a secure and efficient geothermal energy supply. An in-depth sensitivity analysis was investigated considering a deep borehole closed-loop heat exchanger (DBHE) to overcome the current limitations of deep EGS. A T2Well/EOS1 model previously calibrated on an experimental DBHE in Hawaii was adapted to the current NWG 55-29 well at the Newberry volcano site in Central Oregon. A sensitivity analysis was carried out, including parameters such as the working fluid mass flow rate, the casing and cement thermal properties, and the wellbore radii dimensions. The results conclude the highest energy flow rate to be 1.5 MW, after an annulus radii increase and an imposed mass flow rate of 5 kg/s. At 3 kg/s, the DBHE yielded an energy flow rate a factor of 3.5 lower than the NWG 55-29 conventional design. Despite this loss, the sensitivity analysis allows an assessment of the key thermodynamics within the wellbore and provides a valuable insight into how heat is lost/gained throughout the system. This analysis was performed under the assumption of subcritical conditions, and could aid the development of unconventional designs within future EGS work like the Newberry Deep Drilling Project (NDDP). Requirements for further software development are briefly discussed, which would facilitate the modelling of unconventional geothermal wells in supercritical systems to support EGS projects that could extend to deeper depths.

Thermodynamic analysis of serial dual-pressure organic Rankine cycle under off-design conditions

As a novel and promising cycle architecture, the serial dual-pressure organic Rankine cycle (STORC) is proved with higher thermodynamic performance than the basic organic Rankine cycle (BORC) in design condition. Nevertheless, system thermodynamic performance may severely deteriorate when the heat source and ambient temperature fluctuate. Thus the performance of STORC under off-design conditions is still unclear and needs further discussion. Besides, the serial layout of evaporators in STORC makes the mass and energy flow between different pressure levels coupled together, which presents new challenges for off-design analysis. This study proposes a design and off-design model of STORC using R1234ze(E) as the working fluid. Fluctuations of the heat source and ambient temperature are analyzed and their effects on the off-design performance and stability of STORC are explored. The net power output is maximized in each operation condition and the optimized results are compared with BORC. Results show that, compared with BORC, STORC exhibits better thermodynamic performance in both design and off-design conditions. On the one hand, under all calculated operation conditions, STORC achieves higher net power output and exergy efficiency, which are up to 24.3% and 21.4% higher than BORC, respectively. On the other hand, STORC better adapts to external fluctuations and runs closer to the design point in underload state with less thermodynamic performance degradation. Besides, it’s revealed that the variation of heat source characteristic mainly affects the evaporation process and working fluid mass flow rates, while the ambient temperature mainly affects the condensation process and has little effects on the evaporation process. Moreover, the low-pressure turbine accounts for 70% of the overall net power output, but its performance degradation is more serious than that of the high-pressure turbine. Thus the enhancement of the low-pressure turbine is expected to further improve the off-design performance of STORC in practical operation conditions.

Experimental investigation of heat transfer characteristics and performance of smooth and wicking surfaces in spray cooling for high heat flux applications

In this work, studies have been conducted on heat transfer performance of both smooth and modified wicking surfaces in a spray cooling experiment for high heat flux applications. The heat transfer performance of the two surfaces in terms of critical heat flux (CHF) and heat transfer coefficient (HTC) were determined in an experiment using a two-phase thermal loop, operating with de-ionized water as the working fluid in a pressure range of 101.45–165.80 ​kPa and working fluid mass flow rates of 0.84–1.26 ​g per second. The result shows that the modified wicking surface has higher CHF of 225 ​W/cm2 at cooling temperature difference of 130 ​°C compared to 160 ​W/cm2 at cooling temperature difference of 180 ​°C for the smooth surface. Further analysis of the results indicates that, maximum HTC enhancement of 8500 ​W/m2-K is achieved at cooling temperature difference of about 100 ​°C for the modified wicking surface over the smooth surface. Using a high speed camera set at 10,000 frames per second, it was observed that there was increased surface wettability on the modified surface due to fluid wicking and spreading, with reduced Leidenfrost effect at the onset of CHF. This effect resulted in lower surface temperatures and higher CHF for the modified surface compared to the smooth surface.