• Energy Research

Abstract This work deals with the probability of using a counter-flow M-cycle in Arab Gulf cities. The system is applied for weather conditions for the main cities in the region, which are Riyadh, Dammam, and Jeddah in Saudi Arabia; Abu Dhabi and Dubai in the United Arab Emirates; Kuwait, the capital of Kuwait; Doha, the capital of Qatar; and Muharraq in Bahrain. Heat and mass transfer models for the air flow in channels are developed and solved. The present model of the counter-flow M-cycle shows good agreement with the previous experimental and numerical works. The literature review shows that the critical value of ambient relative humidity is 70%. Below that value, the M-cycle could be used. This value is only exceeded sometimes in Jeddah, reaching 72.77%. The obtained results show that the supply conditions of air leaving the counter-flow M-cycle are more convenient than that can be achieved by the evaporative cooler. The M-cycle system consumes water more than the evaporative cooler. However, it uses less electrical energy than the vapor-compression refrigeration system, for the same cooling capacity. The M-cycle sometimes supplies air with conditions that do not meet the comfort condition. However, these conditions are still more convenient than those provided by the conventional evaporative cooling systems (DECs and IECs). In conclusion, the M-cycle is suitable for all selected cities and should be considered as an alternative to conventional HVAC systems in Arab Gulf Countries.

Abstract The Maisotsenko cycle (M-cycle), which is a dew-point air-cooling system, has been identified as a promising alternative to conventional air conditioning systems. Previous works have focused on conducting feasibility studies of using the M-cycle in various applications in different climates while the optimization of the process and the impact of important design and operational aspects received few interests. In the present work, the impacts of various geometrical and operational aspects on the M-cycle performance were theoretically investigated. Six configurations of the counter-flow M-cycle were studied and compared numerically. These configurations included a circle, a rectangle with different aspect ratios (width-to-height ratio), and a triangle with various angles. In the circle and triangle configurations, the dry and wet channels were considered to be concentric, where the dry channel was surrounded by the wet channel. However, the plates were put on each other in rectangular geometries. A heat and mass transfer model of the counter-flow M-cycle was developed and validated using the previous numerical and experimental results of Riangvilaikul and Kumar. The influences of the hydraulic diameter and the length of the channel were investigated. Furthermore, the impacts of operating conditions, such as intake air temperature, intake relative humidity, intake air velocity, and water temperature, on the overall M-cycle performance were also examined. The system's performance was expressed in terms of dew-point effectiveness, wet-bulb effectiveness, coefficient of performance, cooling capacity, and water consumption. The obtained results show that it is preferable to maintain the intake air velocity between 2 and 3 m/s for all the considered cases. The triangular geometry with a 60° angle appears to be the best geometry. In addition, the circular shape was found to be preferable to the rectangular geometries.

In this paper, energy and exergy analysis of typical gas turbines is performed using average hourly temperature and relative humidity for selected Gulf cities located in Saudi Arabia, Kuwait, United Arab Emirates, Oman, Bahrain and Qatar. A typical gas turbine unit of 42 MW is considered in this study. The electricity production, thermal efficiency, fuel consumption differences between the ISO conditions and actual conditions are determined for each city. The exergy efficiency and exergy destruction rates for the gas turbine unit and its components are also evaluated taking ISO conditions as reference conditions. The results indicate that the electricity production losses occur in all cities during the year, except in Dammam and Kuwait for the period between November and March. During a typical day, the variation of the power production can reach 4 MW. The rate of exergy destruction under the combined effect of temperature and humidity is significant in hot months reaching a maximum of 12 MW in July. The presented results show also that adding inlet cooling systems to the existing gas turbine units could be justified in hot periods. Other aspects, such as the economic and environmental ones, should also be investigated.

Abstract This work focuses on theoretical investigation of the performance of a multistage vapor-compression refrigeration system using energy, exergy and economic analysis. The system was modeled using Engineering Equation Solver (EES) software and the model was validated against published data with maximum error of 1.14%. System optimization was carried out using Conjugate Directions Method. Optimization objective function was maximizing the coefficient of performance (COP) of the multistage vapor-compression refrigeration system by varying four optimization variables. Those variables are sub-cooling, de-superheating parameters, and evaporator and condenser temperatures of the system. Eight refrigerants were used in the investigation. They are: R717, R22, R134a, R1234yf, R1234ze(E), R410A, R404A, and R407C. Results show that COP increases with increasing the sub-cooling parameter. The maximum COP of 6.17 was achieved with ammonia while minimum COP of 4.95 was achieved with R407C. The optimization results give also that, R717 is a best option compared with all refrigerants, while R407C is not recommended to use.

Riyadh is a desert region characterized by large daily and seasonal ambient temperature variations. Air cooling using mechanical vapor compression requires high energy rates resulting in negative environmental impacts. The use of non-conventional cooling methods such as evaporative cooling is attractive and needs further investigations particularly in such critical weather conditions. This paper deals with the analysis of the performance of a direct evaporative cooling in hot and arid weather conditions. Theoretical models using heat and mass transfer, exergy and cost analysis are first developed and presented. Such models have been systematically validated using available experimental and theoretical results from previous studies. The second part of the work concerns the analysis of the performance of a direct evaporative cooler under a metropolitan central Arabian Peninsula (Riyadh, KSA) weather conditions using average hourly temperature and relative humidity of the month of July. The optimum operating parameters of the cooler have been then selected. The analysis shows that the effect of the cooler effectiveness on the exergy efficiency is not significant. The suitable value of the effectiveness of the evaporative cooler working under summer weather of the studied location is found to be between 0.7-0.8. Such a value achieves comfortable conditions at low cost.