• Energy Research

Abstract During the last few decades, low-grade energy sources such as solar energy and wind energy have enhanced the efficiency of the advanced renewable technologies such as the combined Rankine. Furthermore, these heat sources have contributed to a reduction in CO2 emissions. To address the problem of the intermittent nature of such renewable sources, energy storage technologies have been used to balance the power demand and smooth out energy production. In this study, the direct expansion cycle (open Rankine cycle) is combined with a closed loop Rankine cycle to generate power more efficiently and address the problem of discontinuous renewable sources. The topping cycle of this system is a closed looped Rankine cycle and propane is used as a hydrocarbon fluid, while the direct expansion cycle is considered to be the bottoming cycle utilizing nitrogen as cryogen fluid. Small-scale expanders are the most important parts in many thermal power cycles, such as the Rankine cycle, due to the significant impact on the overall cycle’s efficiency. This work investigated the effect of using a number of blade configurations on the cycle’s performance using a small-scale axial expander. A three-dimensional Computational Fluid Dynamic (CFD) simulation was used to examine four proposed blade configurations (lean, sweep, twist, bowl) with three hub- tip ratios (0.83, 0.75, 0.66). In addition, a numerical simulation model of the hybrid open expansion- Rankine cycle was designed and modeled in order to estimate the cycle’s performance. The results show that when the expander’s efficiency increases, the hybrid open Rankine cycle’s thermal efficiency increases, where each 10% improvement in the expander efficiency will increase the cycle’s efficiency by 5.0%. The blade sweep configuration achieved the optimum expander efficiency of up to 75.5% using a hub to tip ratio of 0.83 and an expansion ratio of 1.5 with stator sweep −20° and a rotor sweep of 20°.

Abstract In this study, a novel method for integrating adsorption cooling system with ORC to simultaneously generate cooling and electricity utilising low grade heat source is developed by incorporating a steam expander to the adsorption side, so that the system has two expanders in order to increase the amount of power generated. Four different configurations are developed, where in configuration 1 the adsorption system (topping cycle) is powered by an external heat source, while ORC (bottoming cycle) is driven by recovering the heat of adsorption. Configuration 2 is similar to configuration 1 but the ORC is powered using the same heating fluid leaving the adsorption side. In configuration 3, an adiabatic mixer is used to power ORC with the mixture of the leaving heating and cooling fluids, while in configuration 4; the adsorption system (bottoming cycle) is powered using the heating fluid leaving ORC (topping cycle). In this work, advanced adsorption pairs (AQSOA-ZO2/water, Aluminium-Fumarate MOF/water) are investigated and compared to Silica-gel/water while CPO-27(Ni) MOF/water is used in the experimental facility to validate the simulation model. For the ORC side, R245fa, R365mfc, and R141b are used as working fluids. Results show that using configuration 1 can achieve maximum value of the equivalent system COP of 1.17 using Silica-gel/water and R141b and 0.79 using AQSOA-ZO2/water and R141b. In addition, the maximum Specific Power (SP) achieved is 288 W/kg ads using AQSOA-ZO2 in configuration 4 and the maximum Specific Cooling Power (SCP) achieved is 552 W/kg ads utilizing AQSOA-ZO2 and R141b in configuration 2 and 4. Maximum adsorption power efficiency achieved is 4.3% in configuration 2, while the maximum ORC power efficiency achieved is 18.3% in configuration 4. This work highlights the feasibility of generating cooling and electricity simultaneously from integrated adsorption-ORC system using two expanders.

Abstract In this study, different multi-bed water adsorption systems have been used to generate cooling and electricity at the same time using 9 different cases including 7 bed configurations and 7 time ratios (R = total switching and adsorption time /the total switching and desorption time) utilizing advanced adsorption materials such as AQSOA-Z02 and MOF Aluminium-Fumarate additionally to traditional Silica-gel. A MATLAB Simulink program of multi-bed adsorption system for cooling and power generation has been developed to investigate the effect of using different cases on the overall system performance. Results showed that using three-bed configuration with time ratio of (R = 1/2) produced the highest specific cooling power (SCP) and specific power (SP) for Silica-gel (for all heat source temperature range), Aluminium-Fumarate (for heat source temperature higher than 120 °C) and AQSOA-Z02 (at heat source temperature of 160 °C). Moreover, using two-bed configuration with time ratio of (R = 1) generates the highest coefficient of performance (COP) for all adsorption materials within the range of heat source temperature used in this study. Results also, showed that maximum COP of 0.64 can be achieved using Silica-gel, while maximum SCP, SP and adsorption power efficiency of 650 W/kg ads , 64 W/kg ads , 4.6% can be achieved using AQSOA-Z02.

Abstract Adsorption system is a promising technology that can exploit the abundant low grade heat sources (∼150 °C) from renewables like solar, geothermal and industrial waste heat leading to reduction of fossil fuel consumption and CO2 emissions. In this work, the effect of using advanced adsorbent materials like AQSOA-Z02 zeolite (SAPO-34) and Metal Organic Framework (MOF) like MIL101Cr and Aluminium fumarate on power and cooling performance compared to that of commonly used silica-gel was investigated using water as refrigerant. A mathematical model for a two bed adsorption cooling cycle has been developed with the cycle modified to produce power by incorporating an expander between the desorber and the condenser. Results showed that it is possible to produce power and cooling simultaneously without affecting the cooling output. Results also showed that for the four pairs used as the heat source temperature increases, the cooling capacity and power generated increase. As the condenser cooling temperature increases, the cooling effect and power output will decrease while for the chilled water temperature, the cooling capacity and power generated increased as the chilled temperature increased. Also, it is shown that SAPO-34 achieved the maximum average specific power generation (SP) and specific cooling power (SCP) of 67 W/kgads and 622 W/kgads respectively. A detailed CFD modelling has shown that a small-scale steam radial inflow turbine with mass flow rate of 0.0046 kg/s generated using 8.55 kg/bed of SAPO-34 adsorbent with heat source temperature of 160 °C can achieve efficiency of 82% and power output of 785 W.

Abstract Globally there is abundance of low grade heat sources (around 150 °C) from renewables like solar energy or from industrial waste heat. The exploitation of such low grade heat sources will reduce fossil fuel consumption and CO 2 emissions. Adsorption technology offers the potential of using such low grade heat to generate cooling and power. In this work, the effect of using advanced adsorbent materials like AQSOA-Z02 (SAPO-34) zeolite and MIL101Cr Metal Organic Framework (MOF) at various operating conditions on power and cooling performance compared to that of commonly used silica-gel was investigated using water as refrigerant. A mathematical model for a two bed adsorption cooling cycle has been developed with the cycle modified to produce power by incorporating an expander between the desorber and the condenser. Results show that it is possible to produce power and cooling at the same time without affecting the cooling output. Results also show that for all adsorbents used as the heat source temperature increases, the cooling effect and power generated increase. As for increasing the cold bed temperature, this will decrease the cooling effect and power output except for SAPO-34 which shows slightly increasing trend of cooling and power output. As the condenser cooling temperature increases, the cooling effect and power output will decrease while for the chilled water temperature, the cooling load and power generated increased as the temperature increased. The maximum values of average specific power generation (SP), specific cooling power (SCP) and cycle efficiency are 73 W/kg ads , 681 W/kg ads (using SAPO-34) and 67% (using Silica-gel) respectively. However, MIL101Cr can generate SP and SCP of 95 W/kg ads and 1367 W/kg ads respectively, but this case cannot consider to be practical operating conditions, because of using relatively low cooling source temperature, but this material still offers potential of generating power.