Upgrading Waste Heat Research Articles

Energy Performance Analysis of Isobutene/Water/ tert-Butanol Chemical Heat Pump

A chemical heat pump cycle for upgrading waste heat from ≈ 70°C to ≈ 110°C has been proposed, which utilizes the reaction of isobutene/water/tert-butanol. The thermal performance was analysed by process simulation, based on experimental data. A flow cycle of the heat pump is proposed. The reaction conditions for the model were optimized. The performance of the proposed heat pump was evaluated in order to compare its coefficient of performance (COP) with that of the conventional compression heat pump. The proposed heat pump system has a COP of 6.4 when operating between 70 and 110 °C, which is higher than the COP of the conventional compression heat pump of 4.0 under the same conditions. In addition, the proposed heat pump has a higher exergy efficiency than the conventional compression heat pump.

Industrial heat recovery by absorption/compression heat pump using TFE–H 2O–TEGDME working mixture

The thermodynamic performance of a single-stage absorption/compression heat pump using the ternary working fluid Trifluoroethanol–Water–Tetraethylenglycol dimethylether (TFE–H 2O–TEGDME) for upgrading waste heat has been studied. A simulation program has been developed using a mathematical model based on mass and energy balances in all components of the cycle and thermodynamic equilibrium considerations. In order to establish the optimum operating conditions of the cycle for various thermal conditions, sensitivity studies of the coefficient of performance ( COP), the flow rate of the weak solution and the compressor volumetric displacement, both per unit of upgraded energy, were carried out versus of water content in the vapour phase. The results obtained show that the operation of the cycle with this ternary system is still more advantageous than the TFE–TEGDME binary working pair. So, it is possible to upgrade thermal waste heat from 80 to 120°C, with a COP of about 6.4, with a compression pressure ratio of 4 at a low pressure of 100 kPa, the water mole fraction in the vapour being 42%. At these operating conditions, the necessary weak solution mass flow rate is about three times lower than the corresponding binary one. The performance comparison of such a cycle with other absorption cycles like the heat transformer or the single-effect heat pump, both of them using the ternary system, shows its interest and potential.

Investigation of the Working Cycle of a Metal Hydride Heat Transformer for Upgrading Waste Heat

This paper presents an investigation of the working cycle of a metal hydride heat transformer for upgrading waste heat. A mathematical model for calculation of the heat and mass transfer processes in the metal hydride heat transformer is suggested. The method for balancing the heat and mass exchanges in the thermodynamic cycle is developed. This method essentially takes into account the pressure drop inside a reacting hydride bed.

History and prospects of heat transformation

Following a short description of some historic events the basic theory of heat transformation published 50 years ago by Nesselmann is presented. Here the heat transformation is discussed primarily with respect to house heating. Firstly, single stage plants and their COP are discussed, then problems of multi-stage processes are looked at. One of the main problems today is to identify new and suitable working pairs for absorption heat pumps. Only a few substances seem to be suitable. Finally inverse heat pumps (for upgrading waste heat) as well as a new single substance heat transformer are discussed.