• Energy Research

AbstractFlash processes have been investigated several times [1–4]. This study focuses on the flash process taking place in a cyclone. The separated and extracted steam expands directly into a cylinder of a piston engine. In contrast to known flash expanders, the pressure drops continuously within a short time. Of special interest is the efficiency of phase separation which is critical to the feasibility of the piston process with internal flash evaporation.

Abstract Heat engines transfer high-temperature heat into mechanical and electrical energy using the Clausius Rankine Cycle (CRC). Low temperature applications primarily use the Organic Rankine Cycle, in which mainly waste heat, geothermal heat and solar heat are transferred into mechanical energy. The exergy of a low temperature heat source can be transferred into electricity in so-called triangle (or trilateral) cycles. By applying batch processes in heat engines, it is possible to reach an exceptionally high approximation to triangle cycles and thus to build up high exergy-efficient heat engines. In an example case the calculated exergy efficiency is 71% higher compared to a CRC. The proposed process is not limited to specific working media and can therefore be adapted to a wide range of temperatures. The required setup is rather simple and is derived from setups ranging from basic to more and more advanced. The thermodynamic performance of an example plant is derived from T-s-diagrams.

Abstract A Triangle Cycle with a piston engine expansion unit is used to convert low temperature heat into electrical energy. In this process, the isentropic efficiency of the expansion unit is considered to be unknown, and a theoretical approach for the calculation of isentropic efficiency is presented. A number of influences are taken into account – dead volume, residual mass, liquid injection performance and wall heat transfer. Various working fluids are investigated in a wide range of temperatures (333K–573K), engine speeds (5 Hz–30 Hz) and stroke volumes (0.1 L–50 L). The isentropic efficiency of water as working fluid is in the range of 0.75–0.88 and drops significantly for high stroke volumes and engine speeds. In general, injection mass has the most impact on isentropic efficiency because it influences dead volume and injection performance. The injection mass increases with vapor density and therefore is significantly influenced by working fluid and temperatures. The Triangle Cycle is compared with Organic Rankine Cycles by using determined isentropic efficiency. The exergetic efficiency of the Triangle Cycle using water is up to 35–70% higher than that of supercritical Organic Rankine Cycles in situations with a heat source temperature of up to 450K.

Abstract This article presents a new design for the edge-seal of multiple-glazings with spacers made of foamglass and a new concept for frameless windows to reduce the heat loss through windows significantly. Thus the energy demand for heating is reduced or covered by solar energy gains through the window to a higher extent. The thermal performance of window assemblies with foamglass spacers and with and without frames is compared with that of the common window design. For the calculations of the heat flux a finite element analysis computer program has been used to account for the 2D-effects in the glazing, edge-seal and frame heat transfer patterns. The total heat transfer through an example window with a glazing 1 m×1 m is reduced by 45% using the window design presented. The objective of this article is not only to quantify the heat fluxes for different combinations of glazing, edge-seal and frame. The major part of the article focuses on practical aspects that are important for the durability of edge-seals, such as mechanical stress within the materials, water vapour and gas tightness, as well as on new design concepts of window–wall joints. A frameless window construction is an important aspect to enhance the thermal performance of windows. The costs for this kind of frameless windows are estimated to be less than or equal to windows commonly used now.

Abstract Trapezoid Cycles are thermodynamic cycles, mainly vapour compression cycles, which simply spoken adapt to the heat source curve and the heat sink curve in the temperature – entropy – diagram (T-S-diagram). The name of the cycles refers to the case of sensible heat, where the shapes of these cycles is similar to trapezoids. It was shown before that trapezoid cycles are feasible by adding storage devices to the cycle setup. In this article exact and simplified theoretic equations for the calculation of the COP of different cases of Trapezoid Cycles both with and without influence of dissipation are presented. These equations allow a mathematically simple prediction of the COP with very small error. Further the use of Trapezoid Cycles in the well-known Pinch Analysis is derived on a graphical basis (T-S-diagram). Heat which is usually lost in the Pinch Analysis will become usable with the highest thermodynamic possible efficiency.