When a liquid undergoes sudden reduction in the surrounding pressure below its saturation pressure, the liquid then enters in a metastable state. In order to regain equilibrium, part of the liquid evaporates quickly i...When a liquid undergoes sudden reduction in the surrounding pressure below its saturation pressure, the liquid then enters in a metastable state. In order to regain equilibrium, part of the liquid evaporates quickly in a phenomenon called ＂flash evaporation＂, and the excess sensible heat contained in the liquid is converted into latent heat of vaporization. Therefore, temperatures of both the liquid and the generated vapor decline to the saturation temperature for the reduced pressure. As the heat and mass transfer occur in direct contact between the liquid and its own vapors, the process involves a very high heat transfer rate which makes it suitable for exchanging heat between sources of relatively small temperature difference. Moreover, dispensability of the heat exchange surfaces in this process is a considerable advantage as these surfaces constitute major part of the total system expenses in addition to the associated maintenance problems, especially when dealing with corrosive fluids such like seawater in the thermal desalination processes and in the OTEC （ocean thermal energy conversion） systems. This paper reports on the heat flux variation profiles during the flash evaporation of superheated water jets at various flow conditions. Heat flax was found to grow with time attaining a peak value before it starts to decrease monotonically.展开更多
Numerical simulation of complex systems and components by computers is a fundamental phase of any modern engineering activity. The traditional methods of simulation typically entail long, iterative processes which lea...Numerical simulation of complex systems and components by computers is a fundamental phase of any modern engineering activity. The traditional methods of simulation typically entail long, iterative processes which lead to large simulation times, often exceeding transient real time. Artificial neural networks （ANNs） may be advantageous in this context, the main advantage being the speed of computation, the capability of generalizing from the few examples, robustness to noisy and partially incomplete data and the capability of performing empirical input-output mapping without complete knowledge of underlying physics. In this paper, the simulation of steam generator is considered as an example to show the potentialities of this tool. The data required for training and testing the ANN is taken from the steam generator at Abott Power Plant, Champaign （USA）. The total number of samples is 9600 which are taken at a sampling time of three seconds. The performance of boiler （drum pressure, steam flow rate） has been verified and tested using ANN, under the changes in fuel flow rate, air flow rate and load disturbance. Using ANN, input-output mapping is done and it is observed that ANN allows a good reproduction of non-linear behaviors of inputs and outputs.展开更多
文摘When a liquid undergoes sudden reduction in the surrounding pressure below its saturation pressure, the liquid then enters in a metastable state. In order to regain equilibrium, part of the liquid evaporates quickly in a phenomenon called ＂flash evaporation＂, and the excess sensible heat contained in the liquid is converted into latent heat of vaporization. Therefore, temperatures of both the liquid and the generated vapor decline to the saturation temperature for the reduced pressure. As the heat and mass transfer occur in direct contact between the liquid and its own vapors, the process involves a very high heat transfer rate which makes it suitable for exchanging heat between sources of relatively small temperature difference. Moreover, dispensability of the heat exchange surfaces in this process is a considerable advantage as these surfaces constitute major part of the total system expenses in addition to the associated maintenance problems, especially when dealing with corrosive fluids such like seawater in the thermal desalination processes and in the OTEC （ocean thermal energy conversion） systems. This paper reports on the heat flux variation profiles during the flash evaporation of superheated water jets at various flow conditions. Heat flax was found to grow with time attaining a peak value before it starts to decrease monotonically.
文摘Numerical simulation of complex systems and components by computers is a fundamental phase of any modern engineering activity. The traditional methods of simulation typically entail long, iterative processes which lead to large simulation times, often exceeding transient real time. Artificial neural networks （ANNs） may be advantageous in this context, the main advantage being the speed of computation, the capability of generalizing from the few examples, robustness to noisy and partially incomplete data and the capability of performing empirical input-output mapping without complete knowledge of underlying physics. In this paper, the simulation of steam generator is considered as an example to show the potentialities of this tool. The data required for training and testing the ANN is taken from the steam generator at Abott Power Plant, Champaign （USA）. The total number of samples is 9600 which are taken at a sampling time of three seconds. The performance of boiler （drum pressure, steam flow rate） has been verified and tested using ANN, under the changes in fuel flow rate, air flow rate and load disturbance. Using ANN, input-output mapping is done and it is observed that ANN allows a good reproduction of non-linear behaviors of inputs and outputs.
