Aydın Durmuş

Geometric design of solar-aided latent heat store depending on various parameters and phase change materials

The cylindrical latent heat storage tanks considered here are part of a domestic heating system. In this study, the performances of such energy storage tanks are optimized theoretically. Two different models describing the diurnal transient behaviour of the phase change unit were used. The first is suited to tanks where the phase change material (PCM) is packed in cylinders and the heat transfer fluid (HTF) flows parallel to it (mode 1). The second is suited to tanks where pipes containing the fluid are embedded in the PCM (mode 2). The problem (treated as two-dimensional) is tackled with an enthalpy-based method coupled to the convective heat transfer from the HTF. A series of numerical tests are then undertaken to assess the effects of various PCMs, cylinder radii, pipe radii, total PCM volume in the tank, mass flow rates of fluid, and inlet temperatures of the HTF on the storing time. In addition, optimal geometric design of the store depending on these parameters and PCMs is presented.

Investigation of heat transfer and pressure drop in a concentric heat exchanger with snail entrance

Abstract In this study, in order to increase heat transfer in concentric double-pipe heat exchangers by passive method, snail which is mounted at inlet of the inner pipe and assumed as a swirl generator was used. In the experimental set-up, cold air in ambient conditions was passed through the inner pipe while hot water was flowing through the annulus. The effects of a snail on the heat transfer and pressure drop were investigated for parallel and counter-flow, and obtained Nusselt numbers (Nu) were compared with those found, using a standard correlation such as Dittus–Boelter equation given for axial flows in smooth pipes. The results were correlated in the form of Nusselt number as a function of Reynolds number, Prandtl number and the swirling angle. An augmentation of up to 120% in Nusselt number was obtained in the swirl flow for counter-flow and 45° swirling angle. Though the swirl flow effect of the snail caused some increase in pressure drop, this effect was unimportant compared with the improvement in heat transfer capacity.

Heat transfer and exergy loss in cut out conical turbulators

It would be misleading to consider only the construction costs of heat exchangers in their design because high service costs during their service life may also greatly increase total costs. Therefore, energy saving aspects are very important in the design, construction and operation of the heat exchangers. For this reason, various active or passive methods have been sought to save energy by increasing the heat transfer coefficients in the cold and warm fluid sides in the heat exchangers. In this study, the effect of cut out conical turbulators, placed in a heat exchanger tube at constant outer surface temperature, on the heat transfer rates was investigated. The air was passed through the exchanger tube, the outer surface of which was heated with saturated water vapor. The experiments were conducted for air flow rates in the range of 15,000 ⩽ Re < 60,000. Heat transfer, pressure loss and exergy analyses were made for the conditions with and without turbulators and compared to each other. Some empirical correlations expressing the results were also derived and discussed.

Heat Transfer and Friction Factor of Coil-Springs Inserted in the Horizontal Concentric Tubes

The goal of this investigation is to obtain definitive information about the heat transfer characteristics of circular coil-spring turbulators. This is achieved by measuring the wall temperatures on the inner tube of the exchanger. Also the inlet and outlet temperatures and pressure loss of the fluid are measured. These results are parametrized by Reynolds numbers (2500 <Re < 12, 000), outer diameters of the springs (D s = 7.2 mm, 9.5 mm, 12 mm, and 13 mm), numbers of the springs (n =4, 5, and 6), and the incline angles of the springs (θ=0 deg, 7 deg, and 10 deg). Additionally, another goal of this work is to quantify the friction factor f of the turbulated heat exchanger system with respect to aforementioned parametric values. As a result, it is found that increasing spring number, spring diameter, and incline angle result in significant augmentation on heat transfer, comparatively 1.5-2.5 times of the results of a smooth empty tube. By the way, friction factor increases 40-80 times of the results found for a smooth tube. Furthermore, as a design parameter, the incline angle has the dominant effect on heat transfer and friction loss while spring number has the weakest effect.