pocketTHERM: a web-based tool for teaching non-ideal thermodynamic cycles

pocketTHERM is a set of web-based calculators intended to be used as a teaching tool to introduce basic principles related to thermodynamic cycles operating with non-ideal fluid flows, namely organic Rankine cycle (ORC) power systems and heat pumps. The tool enables these technologies to be introduced interactively to students from a wide range of backgrounds, and at different stages of their education, without requiring any programming knowledge or installation of software. pocketTHERM contains design tools for both ORC and heat pump systems, suitable for carrying out single- and parametric design exercises, alongside self-paced lessons. The underlying model is written in Python, and the PyScript framework is used to call the Python code directly from HTML. Alongside detailing pocketTHERM’s capabilities, this paper puts forward a vision of how it can be used in an engineering curriculum, and serves as an example of how existing Python research codes can be converted into web-based educational tools.</p

Non-equilibrium CFD simulation of the wet-to-dry expansion of the siloxane MM in a converging-diverging nozzle

Wet-to-dry organic Rankine cycles could generate 30% higher power outputs in the temperature range of 150 to 250°C compared to existing single-phase cycles. Since the expansion is only partially wet, turboexpanders could potentially be applied provided that the wet portion of the expansion is confined to the stator to avoid erosion in the rotor. To assess the feasibility of achieving complete evaporation in the stator, two-dimensional non-equilibrium numerical simulations of the wet-to-dry expansion of siloxane MM in a covering-diverging nozzle are performed for the first time. The simulation setup is first validated against published experimental data, and a sensitivity study is conducted concerning the selected interphase models. The model is then applied to simulate expansions from inlet pressures ranging from 478 to 1250 kPa and vapour qualities from 0.1 to 0.5. Moreover, the droplet number density was varied between 1010 and 1014. The results show that the evaporation rate, the extent of non-equilibrium effects and the flow’s spatial uniformity are predominantly dependent on the droplet size. Expansions beginning with droplets smaller than 20 μm resulted in complete mixture evaporation and negligible non-equilibrium effects in almost all investigated cases. For larger droplets, ranging from 40 to 100 μm, full evaporation could only be achieved for inlet pressures above 750 kPa and inlet qualities above 0.3, whereas for lower pressures, the outlet vapour quality varied between 80 and 90%. For droplets larger than 200 μm, there is a significant delay in evaporation resulting in outlet quality typically between 40 and 70%. Larger droplet flows are characterised by substantial velocity slip, temperature difference, phase separation and lateral velocity variations. Having said this, droplet breakup analysis indicates that droplets larger than 100 μm are likely to undergo breakup, which could enhance the evaporation rate; however, this requires further investigation. In conclusion, high inlet pressures and high inlet qualities are preferred from the perspective of ensuring dry-vapour conditions at the nozzle outlet

Non-equilibrium CFD simulation of the wet-to-dry expansion of the siloxane MM in a converging-diverging nozzle

Wet-to-dry organic Rankine cycles could generate 30% higher power outputs in the temperature range of 150 to 250°C compared to existing single-phase cycles. Since the expansion is only partially wet, turboexpanders could potentially be applied provided that the wet portion of the expansion is confined to the stator to avoid erosion in the rotor. To assess the feasibility of achieving complete evaporation in the stator, two-dimensional non-equilibrium numerical simulations of the wet-to-dry expansion of siloxane MM in a covering-diverging nozzle are performed for the first time. The simulation setup is first validated against published experimental data, and a sensitivity study is conducted concerning the selected interphase models. The model is then applied to simulate expansions from inlet pressures ranging from 478 to 1250 kPa and vapour qualities from 0.1 to 0.5. Moreover, the droplet number density was varied between 1010 and 1014. The results show that the evaporation rate, the extent of non-equilibrium effects and the flow’s spatial uniformity are predominantly dependent on the droplet size. Expansions beginning with droplets smaller than 20 μm resulted in complete mixture evaporation and negligible non-equilibrium effects in almost all investigated cases. For larger droplets, ranging from 40 to 100 μm, full evaporation could only be achieved for inlet pressures above 750 kPa and inlet qualities above 0.3, whereas for lower pressures, the outlet vapour quality varied between 80 and 90%. For droplets larger than 200 μm, there is a significant delay in evaporation resulting in outlet quality typically between 40 and 70%. Larger droplet flows are characterised by substantial velocity slip, temperature difference, phase separation and lateral velocity variations. Having said this, droplet breakup analysis indicates that droplets larger than 100 μm are likely to undergo breakup, which could enhance the evaporation rate; however, this requires further investigation. In conclusion, high inlet pressures and high inlet qualities are preferred from the perspective of ensuring dry-vapour conditions at the nozzle outlet

Binary interaction uncertainty in the optimisation of a transcritical cycle: consequences on cycle and turbine design

Doping CO2 with an additional fluid to produce a CO2-based mixture is predicted to enhance the performance of the super critical CO2 power cycle and lower its cost when adapted to Concentrated Solar Power plants. A consistent fluid mixture modelling process is necessary to reliably design and predict the performance of turbines operating with CO2-based working fluids. This paper aims to quantify the significance of the choice of an Equation of State (EoS) and the uncertainty in the binary interaction parameter (Kij) on the cycle and turbine design. To evaluate the influence of the thermodynamic model, an optimisation study of a 100 MWe simple recuperated transcritical CO2 cycle is conducted for a combination of three mixtures, four equations of state, and three possible values of the binary interaction parameter. Corresponding multi-stage axial turbines are then designed and compared based on the optimal cycle conditions. Results show that the choice of the dopant fraction which yields maximum cycle thermal efficiency is independent from the fluid model used. However, the predicted thermal efficiency of the mixtures is reliant on the fluid model. Absolute thermal efficiency may vary by a maximum of 1% due to the choice of the EoS, and by up to 2% due to Kij uncertainty. The maximum difference in the turbine geometry due to EoS selection corresponded to a 6.3% (6.6 cm) difference in the mean diameter and a 18.8% (1.04 cm) difference in the blade height of the final stage. On the other hand, the maximum difference in turbine geometry because of Kij uncertainty amounted to 6.7% (5.6 cm) in mean diameter and 27.3% (2.73 cm) in blade height of the last stage.</p

Loss analysis in radial inflow turbines for supercritical CO2 mixtures

Recent studies have indicated the potential of CO2-mixtures to lower the cost of concentrated solar power plants. Based on aerodynamic and cost considerations, radial inflow turbines (RIT) can be a suitable choice for small to medium sized sCO2 power plants (about 100 kW to 10 MW). The aim of this paper is to quantify the effect of doping CO2 on the design of RITs. This is achieved by comparing the 1D mean-line designs and aerodynamic losses of pure sCO2 RITs with those of three sCO2 mixtures containing tetrachloride (TiCl4), sulphur dioxide (SO2), and hexaflourobenzene (C6F6). Results show that the optimal turbine designs for all working fluids will have similar rotor shapes and velocity diagrams. However, factors such as the clearance-to-blade-height ratio, turbine pressure ratio, and the difference in the viscosity of the fluids cause variations in the achievable turbine efficiency. Once the effects of these factors are eliminated, differences in the total-to-static efficiency amongst the fluids may become less than 0.1%. Moreover, if rotational speed limits are imposed, then greater differences in the designs and efficiencies of the turbines emerge amongst the fluids. It was found that limiting the rotational speed reduces the total-to-static efficiency in all fluids; the maximum reduction is about 15% in 0.1 MW CO2 compared to the 3% reduction in CO2/TiCl4 turbines of the same power. Among the mixtures studied, CO2/TiCl4 achieved the highest performance, followed by CO2/C6F6, and then CO2/SO2. For example, 100 kW turbines for CO2/TiCl4, CO2/C6F6, CO2/SO2, and CO2 achieve total-to-static efficiencies of 80.0%, 77.4%, 78.1%, and 75.5% respectively. Whereas, the efficiencies for 10 MW turbines are 87.8%, 87.3%, 87.5%, and 87.2%, in the same order

CO2-based power cycles: what effect does additive molecular complexity have on the cycle layout?

Since their inception, CO2 power cycles have gained prominence for their superior performance and compactness. However, the efficiency of the simple supercritical CO2 cycle is hindered by relatively large temperature differences in the recuperator, leading to increased exergy destruction. Although complex cycles like the recompression or precompression cycles can reduce recuperator irreversibility, their higher complexity and additional equipment requirements raise the cost of the power plant. This paper aims to demonstrate that recuperator irreversibility in a simple recuperated transcritical cycle can be alleviated using CO2-based mixtures, without resorting to complex cycles. This is achieved by comparing the efficiencies of simple and recompression cycles using CO2-based mixtures with nine additives of various molecular complexities: H2S, SO2, C3H8, C4H10, C5H12, C6H6, C4H4S, TiCl4, and C6F6. The effect of additive molar fraction (ranging from 0.05 to 0.5) on the efficiency of both cycles is examined. Thermal efficiency optimisation reveals a correlation between the efficiency difference of the simple and recompression cycles and the molecular complexity of the working fluid. The reduction in recuperator irreversibility is attributed to the decrease in the difference in the isobaric specific heat capacities between the streams in the recuperator with the use of complex additives. Consequently, the advantage of a recompression cycle diminishes as the aggregate molecular complexity of the working fluid increases. Simple additives like H2S, SO2, and C3H8 result in recompression cycles outperforming simple recuperated cycles by 4% to 8% in terms of absolute thermal efficiency, depending on the additive and its molar fraction. Conversely, more complex additives like C4H4S, TiCl4, and C6F6, exhibit thermal efficiencies in simple recuperated cycles comparable to those of recompression cycles. The additive molar fraction at which both cycles achieve similar performances depends on the molecular complexity of the additive; the more complex the additive, the lower the additive molar fraction required to create a complex working fluid. Moreover, the split fraction in recompression cycles exhibits a similar correlation with molecular complexity as observed in the efficiency difference, suggesting that recompression cycles will morph into simple recuperated cycles as molecular complexity increases. In conclusion, the use of additives provides an additional dimension through which the efficiency of CO2 cycles can be optimised, enabling improved performance without the need for complex cycles.</p

Loss analysis in radial inflow turbines for supercritical CO2 mixtures

Recent studies have indicated the potential of CO2-mixtures to lower the cost of concentrated solar power plants. Based on aerodynamic and cost considerations, radial inflow turbines (RIT) can be a suitable choice for small to medium sized sCO2 power plants (about 100 kW to 10 MW). The aim of this paper is to quantify the effect of doping CO2 on the design of RITs. This is achieved by comparing the 1D mean-line designs and aerodynamic losses of pure sCO2 RITs with those of three sCO2 mixtures containing tetrachloride (TiCl4), sulphur dioxide (SO2), and hexaflourobenzene (C6F6). Results show that the optimal turbine designs for all working fluids will have similar rotor shapes and velocity diagrams. However, factors such as the clearance-to-blade-height ratio, turbine pressure ratio, and the difference in the viscosity of the fluids cause variations in the achievable turbine efficiency. Once the effects of these factors are eliminated, differences in the total-to-static efficiency amongst the fluids may become less than 0.1%. Moreover, if rotational speed limits are imposed, then greater differences in the designs and efficiencies of the turbines emerge amongst the fluids. It was found that limiting the rotational speed reduces the total-to-static efficiency in all fluids; the maximum reduction is about 15% in 0.1 MW CO2 compared to the 3% reduction in CO2/TiCl4 turbines of the same power. Among the mixtures studied, CO2/TiCl4 achieved the highest performance, followed by CO2/C6F6, and then CO2/SO2. For example, 100 kW turbines for CO2/TiCl4, CO2/C6F6, CO2/SO2, and CO2 achieve total-to-static efficiencies of 80.0%, 77.4%, 78.1%, and 75.5% respectively. Whereas, the efficiencies for 10 MW turbines are 87.8%, 87.3%, 87.5%, and 87.2%, in the same order

Loss analysis in radial inflow turbines for supercritical CO2 mixtures

Recent studies suggest that CO2 mixtures can reduce the costs of concentrated solar power plants. Radial inflow turbines (RIT) are considered suitable for small to medium-sized CO2 power plants (100 kW to 10 MW) due to aerodynamic and cost factors. This paper quantifies the impact of CO2 doping on RIT design by comparing 1D mean-line designs and aerodynamic losses of pure CO2 RITs with three CO2 mixtures: titanium tetrachloride (TiCl4), sulfur dioxide (SO2), and hexafluorobenzene (C6F6). Results show that turbine designs share similar rotor shapes and velocity diagrams for all working fluids. However, factors like clearance-to-blade height ratio, turbine pressure ratio, and fluid viscosity cause differences in turbine efficiency. When normalized for these factors, differences in total-to-static efficiency become less than 0.1%. However, imposing rotational speed limits reveals greater differences in turbine designs and efficiencies. The imposition of rotational speed limits reduces total-to-static efficiency across all fluids, with a maximum 15% reduction in 0.1 MW CO2 compared to a 3% reduction in CO2/TiCl4 turbines of the same power. Among the studied mixtures, CO2/TiCl4 turbines achieve the highest efficiency, followed by CO2/C6F6 and CO2/SO2. For example, 100 kW turbines achieve total-to-static efficiencies of 80.0%, 77.4%, 78.1%, and 75.5% for CO2/TiCl4, CO2/C6F6, CO2/SO2, and pure CO2, respectively. In 10 MW turbines, efficiencies are 87.8%, 87.3%, 87.5%, and 87.2% in the same order.</p

ACC-PH: a comprehensive framework for adopting cloud computing in private hospitals

The healthcare sector is of paramount importance as it provides necessary medical services to sustain human lives. In the private healthcare sector, organisations place equal emphasis on profits as on providing essential medical services. Thus, to offer optimal health aids at low cost, private healthcare organisations try to acquire the best technologies available. Cloud computing offers a solution to cutting business expenses while boosting productivity because it supplies computing services through third parties more cost-effectively. Nonetheless, recent studies have shown that adopting cloud computing services in private healthcare facilities in Saudi Arabia is behind when compared to other sectors. This study presents an optimal data collection and framework validation methodology, combining qualitative and quantitative approaches to examine proposed factors influencing Adopting Cloud Computing in Private Hospitals (ACC-PH) in Saudi Arabia. Accordingly, this research is expected to enhance the implementation of cloud computing in Saudi private hospitals

Exploring M-Commerce vendors’ perspectives in post-Saudi vision 2030: a thematic analysis

Despite the popularity of mobile commerce (m-commerce) services in developing countries, their adoption in Saudi Arabia has been limited. Vision 2030, launched in 2016, has triggered substantial transformations in the country, prompting the need to examine its impact on the adoption of m-commerce. This paper investigates the vendors’ perspective in regard to the adoption of m-commerce in Saudi Arabia. Through a thematic analysis of semi-structured interviews with ten Saudi vendors, the study explores the vendors’ views on the status of m-commerce in the country and their intentions to adopt it. The findings suggest that m-commerce services are still immature in Saudi Arabia, primarily due to government regulations and technological infrastructure</p