A hollow electric heating cylinder is inserted inside a thermo-insulating cylindrical body of larger diameter, together representing a single cylindrical heating element. Three cylindrical heating elements, with an independent electrical source, are arranged alternately one after the other to form a heating duct. The internal diameters of the hollow heating cylinders are different, and the cylinders are arranged from the largest to the smallest in the nanofluid’s flow direction. Through these hollow heating cylinders passes nanofluid, which is thereby heated. The material of the hollow heating cylinders is a PTC (positive temperature coefficient) heating source, which allows maintaining approximately constant temperatures of the cylinders’ surfaces. The analytical analysis used three temperatures of the hollow heating cylinders of 400 K, 500 K, and 600 K. The temperatures of the heating cylinders are varied for each of the three cylindrical heating elements. In the same arrangement, the inner diameters of the hollow cylinders are set to 15 mm, 11 mm, and 7 mm in the nanofluid’s flow direction. The basis of the analytical model is the entransy flow dissipation rate. Furthermore, a new dimension irreversibility ratio is introduced as the ratio between entransy flow dissipation and thermal-generated entropy. This paper provides a suitable basis for optimizing the geometric and process parameters of cylindrical heating elements. An optimization criterion can be maximizing the new dimensionless irreversibility ratio, which implies minimizing thermal entropy and maximizing entransy flow dissipation.

No abstract

No abstract

Abstract:In this paper, a discussion of results is presented for the dimensionless analysis of generating irreversibility of vessels in which mixing and heating of fluid are done simultaneously. In the first case, the impeller inside the mixing vessel is the heating body, and in the second case heating body is a fixed ring and the impeller inside the vessel provides only mixing of the fluid. The paper presents a comparative analysis of typical irreversible dimensionless parameters in both cases. A mathematical model is established to describe the thermal-hydraulic irreversibility of heating-mixing vessel which indirectly gives them the ability to minimize and maximize the efficiency of such a system. Also, the paper established typical relations between the dimensionless entropic values and power number, as for the water heater impeller and also for impeller, combined with a heating ring, which will enable comparison of the required power numbers

No abstract