Contents lists available at ScienceDirect Journal of Energy Storage journal homepage: www.elsevier.com/locate/est Pressure drop in large volumetric heat storage tank radial plate diffuser Lino Kocijel ⁎ , Vedran Mrzljak, Vladimir Glažar University of Rijeka, Faculty of Engineering, Vukovarska 58, 51000 Rijeka, Croatia ARTICLE INFO Keywords: Thermal energy storage Radial plate diffuser pressure drop Numerical analysis Geometry and process parameters ABSTRACT In this paper a number of numerical simulations were performed to determine the geometry and the process parameters influence on the large volumetric heat storage tank radial plate diffuser pressure drop. The tank is used in district heating systems. To reduce the possibility of a pressure drop in the diffuser below the water saturation pressure, three basic diffuser types were tested sharpe edge joint (SEJ), conical element (COE) and curved element (CUE). The analysis shows the differences and similarities between the diffuser types and their influence on the static and total diffuser pressure drop. The geometric similarity of the hermetic compressor radial valve with heat storage tank radial plate diffuser was used to validate the numerical model. The numerical calculation results were compared with the experimental measurements of the air pressure drop on the radial valves front plate taken from the literature. Good correlation between the calculation results and experimental measurements has been achieved. Along with mentioned, the diffuser model similarity effect is also presented and analyzed. The obtained results showed that, the static pressure drop remains the same for different diffuser sizes, when the geometric similarity of the diffuser is preserved. 1. Introduction Heat storage tanks are today an integral part of many plants such as: refrigeration plants used for building air conditioning [1–3], three- generating systems for heating, cooling and electricity production [4,5], cogeneration systems that integrate with renewable energy sources [6–9], etc. Heat storage tanks that are installed in the district heating networks, which serve for the supply of heat energy, contribute to the optimized operation of the cogeneration plant [10]. The effectiveness of thermal storage depends on many factors in- cluding temperature ranges [11], the shape of the tank (the ratio be- tween the height and the diameter) and charging flow rates [12–14], thermal diffusion from the hot layer to the cold layer [15] and many others. Also, one of the key factors for the correct and efficient opera- tion of storage tanks is the diffuser type that is arranged in the tank and through which the fluid, which is the energy carrier, enters and exits the tank. Flow diffusers are used to reduce turbulence at the water inlet in the tank in a way that slows the flow in the charging or discharge process of the tank. The fluid flow that they produce creates a high temperature stratification in the tank [16]. In [17,18], the influence of geometric and process parameters on the quality of temperature stratification and the width of thermocline thickness is analyzed. By reducing the surface through which fluid enters and exits the tank, reducing the distance between the diffuser and the top or bottom of the tank and reducing the inlet velocity of the water have a positive effect on the temperature stratification and the thermocline width reduction. The effect on temperature stratification and thermocline width of different diffuser types and shapes such as conical elements and elbows [19], flexible polyethylene tube [20], different shapes of perforated tubes, perforated disks, spirals and manifolds [21–29] by experimental and computational fluid dynamics (CFD) methods, are analyzed. In [30–32], Findeisen et al. simulated the fluid flow through the diffuser connection pipes and the radial plate diffuser itself. Particular attention was given to the boundary layer treatment with different methods of computational fluid dynamics (CFD). The flow effect on the development of temperature stratification in the tank was also in- vestigated. In the first of the three papers, the flow in the pipe con- nected to the diffuser is analyzed. To simulate realistic pipeline con- ditions, one elbow is placed on the pipe at the distance of 700 mm from the diffuser and the elbow influence on the flow in the pipe and the diffuser itself is analyzed. The analysis showed that the elbow in- stallation influences the occurrence of turbulence in the water flow, and concluded that setting a uniform velocity distribution as a boundary condition when entering the diffuser is not suitable for this case. It should be noted here that such designs occur in heat storage tanks with multiple radial plate diffusers arranged at a certain height within the tank or in the case of a single lower diffuser where shortly before https://doi.org/10.1016/j.est.2020.101350 Received 27 December 2019; Received in revised form 23 February 2020; Accepted 5 March 2020 ⁎ Corresponding author. E-mail addresses: lkocijel@riteh.hr (L. Kocijel), vedran.mrzljak@riteh.hr (V. Mrzljak), vladimir.glazar@riteh.hr (V. Glažar). Journal of Energy Storage 29 (2020) 101350 2352-152X/ © 2020 Elsevier Ltd. All rights reserved. T