Alexander Anderson

A hybrid gas turbine cycle (Brayton/Ericsson) : an alternative to conventional combined gas and steam turbine power plant

Abstract A hybrid gas turbine cycle is proposed based on the conventional Brayton cycle for the high-temperature heat addition process while adopting the Ericsson cycle for the low-temperature heat rejection process. It thus incorporates the thermodynamic advantages of a combined gas and steam turbine (CCGT) cycle without the irrevcrsibilities of the boiler and the ancillarics of the steam turbine/condenser plant. Thermodynamic analysis shows that a similar overall thermal efficiency as current CCGT plant (i.e. 0.54) would be achieved at a maximum gas temperature of 1311 °C if polytropic efficiencies of 0.90 for compression and expansion could be realized and if a maximum temperature of 77 °C was obtained during isothermal compression in the bottoming Ericsson cycle. A novel method of achieving multistage isothermal compression using heat pipe technology is proposed.

A comparison of the operating performance of alternative refrigerants

This paper provides a comparison of the operating performance of three alternative refrigerants for use in a vapour compression refrigeration cycle. The refrigeration capacity and COP of R401A, R290 and R134A were compared with those of R12 when used in a propriety vapour compression refrigeration unit initially designed to operate with R12. The results indicate that the performance of R134a is very similar to that of R12 justifying the claim that it is a drop in replacement for R12 but of the refrigerants tested it gave the poorest performance. When viewed in terms of green house impact however R290 showed the best performance.

Simulation of combined Brayton and inverse Brayton cycles

This paper presents the results of an optimization study of combined Brayton and reversed Brayton cycles. The optimization has been performed using the commercial process simulation package IPSE Pro and has been carried out by varying the upper cycle pressure ratio, the expansion pressure of the bottom cycle and using variable, above atmospheric, bottom cycle inlet pressure. This study indicated that optimum results can be obtained when the inlet pressure to the bottom cycle is above atmospheric pressure.

Experimental investigation on rapid filling of a large-scale pipeline

This study presents the results from detailed experiments of the two-phase pressurized flow behavior during the rapid filling of a large-scale pipeline. The physical scale of this experiment is close to the practical situation in many industrial plants. Pressure transducers, water-level meters, thermometers, void fraction meters, and flow meters were used to measure the two-phase unsteady flow dynamics. The main focus is on the water-air interface evolution during filling and the overall behavior of the lengthening water column. It is observed that the leading liquid front does not entirely fill the pipe cross section; flow stratification and mixing occurs. Although flow regime transition is a rather complex phenomenon, certain features of the observed transition pattern are explained qualitatively and quantitatively. The water flow during the entire filling behaves as a rigid column as the open empty pipe in front of the water column provides sufficient room for the water column to occupy without invoking air compressibility effects. As a preliminary evaluation of how these large-scale experiments can feed into improving mathematical modeling of rapid pipe filling, a comparison with a typical one-dimensional rigid-column model is made.

Emptying of large-scale pipeline by pressurized air

AbstractEmptying of an initially water-filled horizontal PVC pipeline driven by different upstream compressed air pressures and with different outflow restriction conditions, with motion of an air-water front through the pressurized pipeline, is investigated experimentally. Simple numerical modeling is used to interpret the results, especially the observed additional shortening of the moving full water column due to formation of a stratified water-air “tail.” Measured discharges, water-level changes, and pressure variations along the pipeline during emptying are compared using control volume (CV) model results. The CV model solutions for a nonstratified case are shown to be delayed as compared with the actual measured changes of flow rate, pressure, and water level. But by considering water-column mass loss due to the water-air tail and residual motion, the calibrated CV model yields solutions that are qualitatively in good agreement with the experimental results. A key interpretation is that the long air...

Optimisation of a steady-flow Carnot cycle with external irreversibilities for maximum specific output

A steady-flow two-phase Carnot cycle is optimised for maximum specific work output for the case in which temperature differences exist between the cycle isotherms and the external reservoirs for a given heat exchanger standard (defined as the product of the surface area A and the heat transfer coefficient h0). When the heat transfer process between the cycle and the reservoirs is by convection obeying Newtons law the optimum efficiency is shown to be n(opl) = 1 − TcTh in which Th and Tc are the temperatures of the hot and cold reservoirs, respectively. The efficiency is independent of the heat transfer process and is identical to the same expression for a similar non-flow irreversible Carnot cycle as derived by Curzon and Ahlborn and ideal Joule-Brayton and Otto cycles when optimised for the same maximum work condition. For the case of both the heat transfer processes following the Stefan-Boltzmann law of thermal radiation the efficiency is dependent upon characteristics of the heat transfer process and can be greater than the Curzon-Ahlborn cycle efficiency. Results are also presented of an analysis of several cycles with the heat transfer processes being different combinations of radiation, condensation and convection processes.

Validation of simulation model for cogeneration power and water desalination plant

Cogeneration power and MSF water desalination plant has been modelled using the IPSEpro software package based on plant operational scenarios and validated against measured recorded data from the plant. The relative differences between the model results and measured plant data vary from 1.1% to 3.7% for the power plant and 1.0 % to 1.8 % for MSF desalination. The model uncertainties could be attributed to either modelling assumptions or to input data uncertainties, with measured plant performance uncertainties due to measurement device precision and effects of external factors.

A finite time analysis of combined Carnot driving and cooling cycles optimised for maximum refrigeration effect with applications to absorption refrigeration systems

Abstract A finite time analysis of an ideal refrigeration cycle with the objective of maximising refrigeration effect has been performed. The optimised refrigeration cycle has then been combined with an optimised power cycle to produce a combined cycle. The general matching requirements of the two cycles are discussed. The cycles are then combined in a specific way such that they become a model for an ideal absorption refrigeration cycle. The influence of the design parameters on the performance of the combined cycle is analysed. The performance of an experimental absorption unit is compared with the predictions made by the analysis.

Optimization of an air-cooled hybrid gas turbine cycle (Brayton/Ericsson)

Abstract The performance of a Brayson cycle, a hybrid gas turbine cycle, has been examined to establish the effect of air cooling and heat exchanger effectiveness on the cycle efficiency and specific power. The air-cooled heat exchanger was optimized to produce the maximum net efficiency for the specified minimum cycle temperature. The cycle performance was shown to be adversely influenced by the air cooling as it reduced both the specific power and efficiency. The heat exchanger effectiveness was shown to have a secondary impact on the performance parameters. An additional optimization of the heat exchanger at minimum volume is also presented to act as a benchmark against which the performance of the heat exchanger in the optimized cycle can be compared.