• Energy Research

Abstract In this paper, natural convection due to two heated cylinders inside a rhombus enclosure with lower temperature with respect to the cylinders is investigated. Here, Cu-water is the working nanofluid. The numerical algorithm is based on an iterative direct immersed boundary method (IBM). The focus of this article is on stability, instability, symmetry as well as asymmetry of nanofluid flow pattern in three different Rayleigh (Ra) numbers, i.e. 104, 105 and 106. The effects of important parameters such as cylinder diameters, nanoparticle volume fraction and distance between two cylinders are analyzed. The results of this study disclose that at both Ra = 104 and 105, nanofluid flow is symmetric and stable, while at Ra = 106 four different flow regimes including steady-symmetric, steady-asymmetric, unsteady-asymmetric with periodic oscillations and unsteady-asymmetric with irregular oscillations are observed. In addition to geometrical parameters, nanoparticle volume fraction has a considerable impact on the flow regime. Furthermore, the possibility of unsteady-asymmetric flow increases considerably by increasing the distance between two cylinders.

Abstract In hot and humid regions, vapor-compression cooling systems impose high power demand to grid and increase peak of the load. While thermally activated cooling systems can be a sustainable solution, they are even more beneficial when driven by waste heat. In this paper, a multi-generation system including gas engine, desiccant cooling system and thermal desalination system is studied under three different weather conditions. In the desiccant system, two innovative cycles are applied in which the humidity of regeneration air is higher than conventional systems. Therefore, dew point temperature will be high enough for water condensation. The results show it can compensate for 121% of consumed water in humid areas. Moreover, thermal COP is within range of 0.61–1 in studied cities. While the cooling system uses the jacket water heat, desalination system is powered by the flue gasses. It can annually desalinate 1,122 and 1,817 m3 water by heats of the engines with powers of 33 and 55 kVA. Economic investigation shows levelized cost of cooling is within range of 1.5 to 20 US cents depending on the system size and weather conditions. Besides the water price, the difference between electricity and gas prices plays a key role in system economic feasibility.

AbstractIn this study, the numerical investigation of the natural convection heat transfer around a hot elliptical cylinder inside a cold rhombus enclosure filled with a nanofluid in the presence of a uniform magnetic field is conducted. An immersed boundary method as a computational tool has been extended and applied to solve the problem. The influence of various parameters such as cylinder diameters (a, b), Hartmann number (Ha = 0, 50 and 100), nanofluid volume fraction ($$\varphi = 0 , 2.5\% and 5\%$$ φ = 0 , 2.5 % a n d 5 % ), and Rayleigh number (Ra = 103, 104, 105, 106, and 107) has been studied. Streamlines and isotherms contours as well as average Nusselt number have been specified for different modes. An equation for the average Nusselt number as a function of mentioned parameters is presented in this paper. The results show that at lower Ra numbers of Ra = 103 and 104, the magnetic field effect is negligible. However, at higher Rayleigh numbers, the average Nusselt number (Nuave) decreases with the increasing Ha number. The maximum decrease in Nuave at Ra = 105, 106 and 107are calculated −8.15%, −23.4% and −27.3%, respectively. An asymmetry-unsteady flow is observed at $${\text{Ra}} = 10^{7}$$ Ra = 10 7 for Ha = 0. However, at higher Ha numbers a steady-symmetrical flow is formed.

Abstract The cogeneration systems as an effective solution are recommended to make fresh water through heat recovery system and thermal distillation units. The usage of extra heat from gas engines are considered in this article to generate fresh water through a novel thermal Distillation (Single Effect) and the Conventional MED unit. For this purpose, a numerical simulation of single effect thermal distillation unit is done. Then, the results are compared with the experimental investigation. Finally, technical and economic analyses are performed for both configurations. Different sizes of system and sensitive analyses of economic parameters are also considered in this part. Results show that the generated fresh water through novel thermal distillation unit and 33 kVA gas engine is 1982 L per day. According to the economic analyses, period of return and levelized cost of fresh water for the proposed system are 4.2 years and 0.0296 US$ per cubic meter respectively. It also shows that by increasing the size of system up to 4 MW gas engine, the period of return decreases to 2.3 years which confirms that the suggested configuration (thermal desalination and gas engine) is economically feasible.