Passive thermal management of compressed hydrogen storage tank
Publication Date: 2016-Jan-19
The IP.com Prior Art Database
Passive thermal management in compressed hydrogen storage tank by enhancing heat transfer of Phase change Materials (PCM) integrated in the storage tank.
FIELD OF THE INVENTION
This invention relates to the field of compressed hydrogen storage. Compressed hydrogen gas at 700 bars at room temperature is considered today as the practical limit for a passenger car to run for 500 km without refueling. Today storage tanks made of reinforced polymer liners and metallic bottle necks are available commercially. However the long-term stability is an issue due to ageing of the polymer matrix of the liner. In order to support pressures of 700 bars and even higher with practically no permeability of the hydrogen, and to be able to maintain stability of performances in time the quality and time evolution of the polymer should be carefully controlled. As a matter of fact the temperature variation over 80-85°C that are currently obtained during rapid compression of the hydrogen tank are the principal cause of structural variations and ageing of the polymer liner implying an increase of the Hydrogen permeability due to free volume evolution of the polymer matrix.
The solution is an improvement of an earlier solution claiming the use a Phase Change Material (PCM) for passive management of temperature variation during the refilling and use (discharging) of Hydrogen tank using the Latent Heat Storage (LHS) concept. The material that is integrated to the storage tank PCM contributes to the protection of the polymer matrix of the liner as the PCM is positioned in the inner part of the bottle in contact with the polymer liner. PCM are materials that undergo phase change (melting and freezing) in the desired temperature range to store and release thermal energy. The PCM materials are selected to intercept the temperature variation for both refilling and discharge processes. Several configurations of metallic envelopes filled with adequate PCM materials have been described that are installed inside the hydrogen storage tank. It is to note that the LHS concept is based on absorption or release of heat when a storage material undergoes a phase change. For applying this concept paraffin have been predominantly used as PCM due of the following reasons, easy availability, large latent heat per unit volume, low melting temperature, low vapour pressure, small volume changes on phase transformation, unaltered properties after cyclic operation and retrieving the stored energy during discharging. One identified problem of paraffin used as PCM is its low thermal conductivity. The surface heat flux decreases due to the increasing thermal resistance of the growing thickness of the molten paraffin. In the case of solidification, conduction is the only transport mechanism, and in most cases, it is very poor. In the case of melting, natural convection can occur in the molten layer and this generally increases the heat transfer rate compared to the solidification process.