Investigation of the Maisotsenko Cycle Based Air Conditioning Systems

Abstract

Water evaporative based air coolers become more and more popular because of their lower energy consumption compared to the compressor-refrigerant based coolers. Low cooling capacity (theoretically wet-bulb temperature at 100% relative humidity), adding moisture to the product air and probable health issues due to the contaminated water droplets are the main shortcomings of direct evaporative air coolers. Although conventional indirect evaporative air cooler (which is direct evaporative cooler + a heat exchanger) overcomes some of the mentioned shortcomings (i.e. adding no moisture to the product air), the minimum achievable temperature would even be increased and remains as the main weakness of the indirect evaporative air coolers. Maisotsenko-cycle (M-cycle) based indirect evaporative cooler (IEC) overcomes all mentioned problems as it is able to provide lower air temperature (below the wet-bulb temperature towards the dew point temperature) without adding moisture to the product air and without further energy consumption. Besides, M-cycle cooler does not have any negative impact on environment and it does not have any potential health issue due to the probable contaminated water droplets. However, the research on M-cycle IEC is limited. No potential analytical model has been provided before for M-cycle IEC, and cumbersome timeconsuming numerical simulations have been employed for design and analysis purposes. Hence, this research aims to develop better understanding on the thermalexergetic behaviour of M-cycle cooler by developing new high-accurate quick analytical models for different working conditions. Experimental set-up is developed to validate the results of the programmed analytical models and then the models are employed to perform a comprehensive sensitivity analysis of the key operation and design parameters of the M-cycle IEC. Two high accurate quick solving analytical models are developed and presented for two main different working conditions of multi-stage Maisotsenkocycle based indirect evaporative coolers termed water-spray mechanism and wetsurface mechanism. The models are able to generate cooling characteristics of the cooler very quick (compared to the numerical solutions) and accurate. The models are also able to provide temperature/humidity distribution (as a function of the locations inside the cooler) in addition to the outlet characteristics. Thus, the models can be considered as a strong research and design tool for M-cycle coolers. The models are further expanded to analyse the exergetic characteristics of the M-cycle cooler as well. Although M-cycle IEC was first developed as the air conditioning system, other potential applications of M-cycle is proposed in this research as a novel air pre-cooling technology for gas turbine based power plants which suffer lower output power problem in summers (due to hot intake air temperature). The proposed system is based on a hybrid cycle of M-cycle and absorption chiller. The absorption chiller is powered by the released heat from the exhaust gas of the turbine, and the required water of M-cycle could be provided by the condensed water of the saturated air which make the system as an efficient air pre-cooling technology. This thesis is presented in the form of a collection of the published papers which are the results of research. These five papers have been chosen to best demonstrate the study of M-cycle based air coolers. Additional background information is also provided in order to establish the context and significance of this work.