Sliding flow method for exergetically efficient packed bed thermal storage Hitesh Bindra a, c, * , Pablo Bueno b , Jeffrey F. Morris c, d a CUNY Energy Institute, City College of New York, NY 10031, USA b Southwest Research Institute, San Antonio, TX 78238, USA c Levich Institute, City College of New York, NY 10031, USA d Department of Chemical Engineering, City College of New York, NY 10031, USA highlights  The effect of pressure drop on fractional exergy destruction in packed bed thermal storage is quantified, that is 2e6%.  Sliding flow method (SFM) decouples the thermal behavior and pressure drop effects in packed bed thermal storage.  The SFM significantly improves the exergy efficiency and also reduces the design constraints on thermal storage systems. article info Article history: Received 18 July 2013 Accepted 13 December 2013 Available online 24 December 2013 Keywords: Packed bed Thermal storage Exergy Pressure drop abstract The feasibility of a thermal energy storage method is highly dependent on its exergetic efficiency. The two major components which cause exergy destruction in packed bed thermal energy storage methods are pressure drop and temperature dispersion. It is difficult to prevent exergy destruction with existing packed bed type thermal storage systems because the effect of most physical parameters on the pressure drop is opposite to that on the mixing or axial dispersion. We propose a new sliding flow strategy in which fluid inlet and outlet ports change as the temperature front in the bed moves. In this design the typical distance between two simultaneously active inlet and outlet ports will be approximately equal to twice the axial dispersion length. The computations presented in this paper show that the sliding flow method (SFM) is expected to perform significantly better than existing methods and will result in substantial reduction in exergy destruction. The major advantage of the SFM is its ability to decouple thermal behavior and pressure drop effects, thus reducing the design constraints. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Economical energy storage is currently in high demand for matching the grid demand curve and providing dispatchability to intermittent renewable energy sources. The existing electrical en- ergy storage, i.e. batteries, is not an economically viable option; therefore, other alternatives are being considered. There are many on-going efforts to develop energy storage ideas e chemical, elec- trical, mechanical, and thermal methods. Thermal energy is the most common form used in power production so it makes sense to find efficient ways to store it. As thermal energy has limited capacity to do mechanical work, it is essential to know the amount of useful energy that can be recovered from its storage. The best possible parametric method to evaluate the performance of thermal energy storage is by calcu- lating the fractional exergy recovery or exergy efficiency. Therefore, to achieve higher exergetic performance, several high temperature energy storage ideas are being investigated and improved today. Most of these ideas can be broadly classified as phase change, reversible thermochemical, and sensible heat methods. Phase change and reversible thermochemical methods operate favorably only over limited temperature ranges at which the phase change and chemical reactions occur respectively. Among the sensible heat methods, molten salt tank storage and packed bed solid storage are * Corresponding author. CUNY Energy Institute, City College of New York, New York, NY 10031, USA. E-mail addresses: hbindra@che.ccny.cuny.edu, nuchembins@gmail.com (H. Bindra). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.applthermaleng.2013.12.028 Applied Thermal Engineering 64 (2014) 201e208