8.3 Applications of phase change materials for sustainable energy  (Page 6/26)

Vehicle applications

Studies on viability of PCM in vehicle applications are growing widely. For example, PCMs are studied with regard to refrigerated trucks, which are designed to carry perishable freight at specific temperatures. Refrigerated trucks are regulated by small refrigeration units that are placed outside the vehicle in order to keep the inside of the truck trailer at a constant temperature and relative humidity. They operate by burning gas, hence the cost of shipment is highly affected by the changes of temperature in the trailer. The use of PCM has helped in lowering peak heat transfer rates and total heat flows into a refrigerated trailer. Ahmed, Meade, and Medina (2010) modified the conventional method of insulation of the refrigerated truck trailer by using paraffin-based PCMs in the standard trailer walls as a heat transfer reduction technology. An average reduction in peak heat transfer rate of 29.1 percent was observed when all walls (south, east, north, west, and top) were considered, whereas the peak heat transfer rate was reduced in the range of 11.3 - 43.8 percent for individual walls. Overall average daily heat flow reductions into the refrigerated compartment of 16.3 percent were observed. These results could potentially translate into energy savings, pollution abatement from diesel-burning refrigeration units, refrigeration equipment size reduction, and extended equipment operational life.

Vehicles are mainly powered by gasoline    (i.e gas or petrol). Liquified petroleum gases and diesel    are other types of fluids used in vehicles. Lately, hybrid vehicles became popular among consumers as they significantly reduce the toxic exhaust gases if the vehicles run in electric mode. Li-ion batteries have been used in electronic devices for a long time (cell-phones, laptops, and portable devices). Many scientists, especially in the United States, have been working on the possibility of using Li-ion batteries for transportation applications in order to double the fuel efficiency and reduce emissions of hybrid vehicles. Li-ion battery    modules can be connected in order to meet the nominal voltage    of the vehicle to run the vehicle in the electric mode. However this brings a huge problem which keeps away the uses of Li-ion batteries in many applications: as a result of exothermic electrochemical reactions, Li-ion batteries release energy during discharge. The generated energy should be transferred from the body of the battery to environment. If the rate of the transfer is not sufficient, some of the gelled phase materials turn into gas phase    and increase the internal pressure of the cell. Therefore the energy should be released from the cell as soon as possible or the temperature of the cell should not lead to an increase. Sveum, Kizilel, Khader, and Al-Hallaj (2007) have shown that Li-ion batteries with thermal management using PCM eliminate the need for additional cooling systems and improve available power (Figure Application with PCM Technology ). The researchers maintained battery packs at an optimum temperature with proper thermal management and the PCM was capable of removing large quantities of heat due to its high latent heat of fusion.