The size of a cooling inventory is generally designed based on which size can endure the excessive heat load situations that occur sporadically. As a result, cooling systems are often too large for most normal driving modes. There have been numerous efforts to downsize the automotive engine cooling system using novel concepts and strategies (e.g. THEMIS cooling system, CoolMaster, UltimateCooling). However, in terms of the system design, preserving the passive cooling strategy may be simpler and more practical than implementing any major changes. Vetrovec (2008) proposed the use of a heat accumulator that has a phase change material (PCM) within the automotive cooling system. Excessive heat generated during severe operating conditions is stored in the heat accumulator, and it is dissipated during periods of low heat load. The heat dissipation capacity of the radiator and the amount of coolant in the cooling system are normally designed such that the system can sustain itself at peak heat load during acceleration and hill ascents in hot summer periods. Therefore, the unnecessarily large cooling inventory creates an overloaded vehicle which increases the fuel consumption rate. A heat accumulator which averages out the peak heat loads can reduce the entire cooling system remarkably in terms of both its volume and weight. Effective cooling in automobiles is beneficial in reducing harmful emissions as well as improving fuel economy. A simulation was conducted to validate the feasibility of using a novel cooling strategy that utilized the heat load averaging capabilities of a phase change material (PCM). Three prototypes were designed: full size, down sized, and a down sized prototype with a heat accumulator containing the PCM inside. When the full size of the cooling inventory was downsized by 30%, this smaller design failed to dissipate the peak heat load and consequently led to a significant increase in the coolant temperature, around 25 °C greater than that in the full size system. However, the peak heat load was successfully averaged out in the downsized system with a heat accumulator. Experimental study is also on-going to validate the simulation results and find more suitable PCM for the application.
On Efficiency of Air-Phase Change Material Heat Exchanger for Free Cooling System
