New type of graphite composite for heat exchange applications

This study of new thermally conductive composite was conducted as a part of EU project: ˶Development of new generation of Eco Smart products for Oprema d.d. KK.01.2.1.0104.” Main objective was to develop a composite material that would replace existing cast aluminium heat exchanger dry blocks used in beer dispenser cooling units with satisfying multiple demands set on material properties such as: thermal conductivity comparable to the aluminium, lower material cost and suitability for company' s production line capabilities. Aluminium blocks currently used, faced major issues due to casting process applied which firstly caused incomplete block interior infiltration due to complex pipe arrangement in the block. Secondly casting process at high temperature made usage of copper pipes in the block itself impossible so austenitic corrosion resistant steel pipes were used which would then have to be joined with copper pipes outside of the block by soldering, yielding extra production costs. All that taken in consideration implied that obtaining heat conductive yet cost and production effective composite material without high temperatures needed for production was crucial. Natural graphite was chosen as a basis of composite to be developed. The investigation was conducted in two major iterations, first regarding choice of the optimal mixture of different graphite powder granulations with heat conductivity set as key demanded property in laboratory conditions. In the second phase of study chosen graphite powder mixtures with defined weight ratios of each granulation were used along with wide array of different biding agents. Obtained materials were casted in real dry blocks with identical geometry of piping used so far in aluminium blocks. Detailed investigation of heat transfer properties in real life conditions conducted on all mixtures and compared to the reference Al block. The testing was conducted on Pro Event equipment provided by Oprema d.d. Along with thermal properties consistency changes during drying of the composite in order to check if any cracking occurred which would strongly reduce heat transfer in the block. All the obtained results showed ability of produced graphite- based composite to substitute aluminium.