Design sensitivity analysis of a plate-finned air-cooled condenser for waste heat recovery ORCs

The study is related to the design sensitivity analysis of a plate-finned tube bundle V-shaped air-cooled condenser design problem for a range of representative low-temperature waste heat recovery Organic Rankine Cycle (ORC) cases. An iterative design model is implemented which reveals the thermodynamic and geometric design error margins that occur when different in-tube prediction methods are used. 19 condensation heat transfer correlations are used simultaneously within arrays of geometric and thermodynamic variables. Through attained 19 different convective coefficients, a design sensitivity on the calculated overall heat transfer coefficient, total transferred heat, degree of subcooling, required tube and fin material amount, air- and refrigerant-side pressure drops is reported

Model predictive control of a free piston compressor/expander with an integrated linear motor/alternator

Linear positive displacement machines are becoming increasingly more attractive for applications that are normally known as unconquerable niches of rotary and scroll machines. Free-piston machines are characterized by the absence of a crank mechanism, since there is a direct transformation of electrical energy into the piston movement. From the point of view of manufacturing, these machines benefit from a higher robustness and reliability because of less mechanical components involved and reduced frictional losses associate with a conventional crank mechanism. However, the major challenge in replacing the rotary machines by linear ones is a lower efficiency at lower speeds which is unavoidable because of the nature of linear motion: continuous operation means a reciprocating movement within a stroke length with significantly long periods of acceleration and deceleration when the speed is far from its optimal value. However, the advantage of free-piston machines is the fact that the motion profile is freely configurable within physical constraints, which provides a possibility to optimize the speed given the efficiency map of particular linear motor. While the methods and results of the efficiency assessment for rotary machines are widely available, there is a lack of these analyses for linear machines. The current study provides in-depth analyses of a double-coil iron core linear motor also acting as a generator

Design sensitivity analysis of using various in-tube condensation correlations for an air-cooled condenser for ORCs

The study is related to the evaluation of using 19 condensation heat transfer correlations in an annular finned horizontal round tube V-shaped air-cooled condenser design problem for a representative low-temperature waste heat recovery Organic Rankine Cycle (ORC) case. The condensation is realized through cold air provided by the fan suction at a mass flow rate of 90,35 kg/s, whereas the working fluid mass flow rate is 7,8 kg/s. The considered condensation temperature is 40°C which corresponds to a saturation pressure of 1,17 bar. The ambient air is considered to be 15°C. The investigated working fluid is SES36. For a given set of geometrical constraints, an iterative condenser design model is implemented. All considered correlations are applied separately for the same boundary conditions. The design sensitivity on the overall heat transfer coefficient, total transferred heat, required fan power, air- and refrigerant-side pressure drops is assessed. By those means, the engineering error margin of using different calculation tools in designing air-cooled condensers for ORC is reported

A coupled BES-zonal model to predict stratification in a large building

C

Mapping of horizontal refrigerant two-phase flow patterns based on clustering of capacitive sensor signals

A

Experimental investigation at sub- and supercritical conditions of a helical coil heat exchanger particularly designed for a small-scale solar ORC

C

Performance potential of ORC architectures for waste heat recovery taking into account design and environmental constraints

The subcritical ORC (SCORC), sometimes with addition of a recuperator, is the de facto state of the art technology in the current market. However architectural changes and operational modifications have the potential to improve the base system. The ORC architectures investigated in this work are: the transcritical ORC (TCORC), the triangular cycle (TLC) and the partial evaporation ORC (PEORC). Assessing the potential of these cycles is a challenging topic and is brought down to two steps. First, the expected thermodynamic improvement is quantified by optimizing the second law efficiency. Secondly, the influences of technical constraints concerning volumetric expanders are investigated. In the first step, simple regression models are formulated based on an extensive set of boundary conditions. In addition a subset of environmentally friendly working fluids is separately analysed. In the second step, two cases are investigated with the help of a multi-objective optimization technique. The results of this optimization are compared with the first step. As such the effect of each design decision is quantified and analysed, making the results of this work especially interesting for manufacturers of ORC systems