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The competitiveness of hydrogen as a sustainable energy carrier depends greatly on its transportation and storage costs. Liquefying hydrogen offers advantages such as enhanced purity, versatility, and higher density, yet current industrial liquefaction processes face efficiency and cost challenges. Although various large-scale and efficient liquefaction concepts exist in the literature, they often overlook the economic and technical viability of such plants. Here, we addresses this issue by establishing a framework for modeling a large-scale hydrogen liquefaction concept and conducting both technical and economic assessments, with a specific focus on 125 tonnes per day (TPD) high-pressure hydrogen Claude-cycle concept. The technical analysis involves preliminary designs of key process components, while the economic assessment utilizes Aspen Process Economic Analyzer. Our findings indicate that at an electricity price of €0.1/kWh, the Claude-cycle liquefier concept yields a specific liquefaction cost (SLC) of €1.55/kg LH 2 . A sensitivity analysis was performed, which shows that electricity price has a significant influence on the economics. Further investigation on the compressors design shows that incorporating high-speed centrifugal compressors could reduce the SLC by 5.42% and potentially more. Scaling up to 250 and 500 TPD reveals further cost improvements, while cost projections indicate substantial declines as the technology matures. Ultimately, this paper presents novel cost-scaling and experience curves of hydrogen liquefaction technology, demonstrating the compelling economic viability of integrating large-scale hydrogen liquefaction into sustainable energy infrastructure. [Display omitted] • A process model of a large-scale Claude-cycle hydrogen liquefaction plant has been developed for both technical assessment and economic analysis. • The technical evaluation primarily centers on the preliminary design of key process equipment, such as compressors, turbo-expanders, and heat exchangers. • The techno-economic assessment is performed based on the process simulation and equipment preliminary design. • Capital cost estimation is carried out using the Aspen Process Economics Analyzer. • These cost estimations serve as the basis for predicting cost and experience curves of hydrogen liquefaction technology. [ABSTRACT FROM AUTHOR]

Heating in industrial processes is responsible for approximately 13% of greenhouse gas emissions in Europe. Switching from fossil-fuel based boilers to heat pumps can help mitigate the effect of global warming. The present work proposes novel high-temperature transcritical heat pump cycles targeted at heating air with a mass flow rate of 10 kg/s up to 200 °C for spray drying processes. Four low-GWP refrigerants, R1233zd(E), R1336mzz(Z), n-Butane, and Ammonia are considered as the candidate working fluids. The pressure ratio of the compressor is optimized to achieve a maximum coefficient of performance (COP) for the four working fluids. A shell & tube heat exchanger is considered as the gas cooler. Using a generalized version of the ϵ -NTU method, the gas cooler is sized and a second law analysis is conducted. Striking a balance between the first- and second-law performance and size of the gas cooler, the R1233zd(E) transcritical heat pump cycle with a COP of 3.6 is judged to be the most promising option. • Transcritical heat pump cycles designed to heat air up 200 °C are proposed. • Four working fluids, R1233zd(E), R1336mzz(Z), n-Butane and ammonia are compared. • Shell-tube heat exchangers are sized to be used as gas coolers. • R1233zd(E) cycle is found to be the most promising one. [ABSTRACT FROM AUTHOR]

Abstract: The operability limits of a supersonic combustion engine for an air-breathing hypersonic vehicle are characterized using numerical simulations and an uncertainty quantification methodology. The time-dependent compressible flow equations with heat release are solved in a simplified configuration. Verification, calibration and validation are carried out to assess the ability of the model to reproduce the flow/thermal interactions that occur when the engine unstarts due to thermal choking. quantification of margins and uncertainty (QMU) is used to determine the safe operation region for a range of fuel flow rates and combustor geometries. [Copyright &y& Elsevier]

The steady state behavior of thermodynamically supercritical natural circulation loops (NCLs) is investigated in this work. Experimental steady state results with carbon dioxide are presented for supercritical pressures in the range of 80–120 bar, and temperatures in the range of 20–65 ° C. Distinct thermodynamic states are reached by traversing a set of isochors. An equation for the prediction of the steady state of NCLs at supercritical pressures is presented, and its performance is assessed using empirical data. Changes of mass flow rate as a result of independent changes of thermodynamic state, heating rate, driving height and viscous losses are shown to be accurately captured by the proposed equation. Furthermore, close agreement between the predicted and measured mass flow rate is found when the measured equipment losses are taken into account for the comparison. Subsequently, the findings are put forward in aid of the development of safe, novel supercritical natural circulation facilities. • Experimental investigation of natural circulation loop (NCL) with supercritical CO 2. • A steady-state mass flow rate equation is proposed for supercritical pressure NCLs. • An experimental sensitivity analysis substantiates the validity of the equation. • The applicability of the equation to large-scale systems is elaborated on. [ABSTRACT FROM AUTHOR]

Highlights: [•] Bayesian calibration is applied to power plant performance prediction. [•] Measurements from a plant in operation are used for model calibration. [•] A gas turbine performance model and steam cycle model are calibrated. [•] An integrated plant model is derived. [•] Part load efficiency is accurately predicted as a function of ambient conditions. [Copyright &y& Elsevier]

Organic Rankine cycle (ORC) systems are a readily available technology to convert thermal energy from renewable- and waste heat sources into electricity. However, their thermal performance is relatively low due to the low temperature of the available heat sources, but more importantly, due to the low efficiency of the employed expander. Designing the turboexpander is exceptionally challenging, because the flow field is highly supersonic and unsteady, and since the expansion takes place in the highly non-ideal dense-vapor region. In this work, we perform unprecedented three-dimensional unsteady simulations of several high-expansion cantilever ORC turbines to highlight distinctive loss mechanisms. The simulations indicate strong unsteady effects in the rotor blade passage, as a result of unsteady propagating shock waves interacting with viscous wakes and boundary layers. Moreover, the flow field in the rotor blade passage is strongly affected by three-dimensional secondary flow features and a sharp expansion in the shroud region at the inlet of the rotor blade. These span-wise mechanisms and unsteady flow interactions introduce irreversible losses which must be taken into account for designing highly efficient ORC expanders. • Two high-expansion ORC turbines are evaluated employing unsteady 3D simulations. • The simulations indicate substantial unsteady and 3D effects in the rotor passage. • The stator-rotor interactions increase the irreversibilities at the rotor inlet. • Strong 3D effects in the rotor passage modify the pressure between stator and rotor. • The optimized turbine improves performance by decreasing the kinetic energy wasted. [ABSTRACT FROM AUTHOR]

Highlights • Semi-local scaling analysis is used to modify RANS models for variable density flows. • The modification substantially improve turbulence model with respect to wall friction and heat transfer. • The modifications are simple to implement to existing CFD codes. • The generated methodology is applicable to generic eddy viscosity models. • The modifications can also be applied to wall-modeled LES. Abstract This paper presents a novel methodology for improving eddy viscosity models in predicting wall-bounded turbulent flows with strong gradients in the thermo-physical properties. Common turbulence models for solving the Reynolds-averaged Navier–Stokes equations do not correctly account for variations in transport properties, such as density and viscosity, which can cause substantial inaccuracies in predicting important quantities of interest, for example, heat transfer and drag. Based on the semi-locally scaled turbulent kinetic energy equation, introduced in [Pecnik and Patel, J. Fluid Mech. (2017), vol. 823, R1], we analytically derive a modification of the diffusion term of turbulent scalar equations. The modification has been applied to five common eddy viscosity turbulence models and tested for fully developed turbulent channels with isothermal walls that are volumetrically heated, either by a uniform heat source or viscous heating in supersonic flow conditions. The agreement with results obtained by direct numerical simulation shows that the modification significantly improves results of eddy viscosity models for fluids with variable transport properties. [ABSTRACT FROM AUTHOR]

Direct numerical simulations (DNS) of a heated turbulent pipe flow with a fluid at supercritical pressure are performed at a Reynolds number of Re τ = 360 , based on pipe diameter and friction velocity at the inlet. A constant wall heat flux is applied and the temperature range within the flow domain incorporates the thermodynamic region where large variations in thermophysical properties occur. The contribution of these property variations on the mean flow is studied. As compared to ideal gas heat transfer, additional terms appear in the mean flow governing equations. These terms can significantly affect the energy balance, because they modify the averaged wall heat flux and the enthalpy diffusion close to the pipe wall. Furthermore, the averaged thermophysical properties, especially the isobaric heat capacity c p , deviate significantly from those evaluated using the mean temperature or enthalpy. This is due to an averaging artifact called the Jensen inequality, caused by the enthalpy fluctuations and the non-linear dependence of thermophysical properties with respect to enthalpy. Turbulent statistics for one forced convection and two mixed convection cases in an upward flow are discussed. A decrease in turbulent kinetic energy is observed for the forced convection and the low buoyancy case, which cause heat transfer deterioration indicated by high wall temperatures. For the high buoyancy case the turbulence activity first reduces (heat transfer deterioration) and then increases due to turbulence recovery. [ABSTRACT FROM AUTHOR]