The ability to engineer enhanced thermal properties by adding small amounts of nanoparticles to liquids is especially attractive in the case of heat transfer fluids, which find applications in many types of power and heat generation. The specific heat capacity of nanofluids is an important parameter in the design of these systems, especially in the case of thermal energy storage. As with many nanofluid properties, the nature and extent of the modification of the specific heat capacity with the addition of nanoparticles is not well established, and many publications report conflicting experimental data. In contrast to thermal conductivity enhancements, it is yet unclear whether the specific heat capacity of a nanoparticle suspension can increase with respect to the base fluid value. In order to help determine the magnitude, nature, and theory of specific heat capacity modification with the addition of nanoparticles, published experimental heat capacity data for nanofluids was compiled and analyzed to investigate any trends or biases in the data. The objective of this meta-analysis is twofold: 1) to clarify in what cases an enhancement of specific heat capacity can be expected, and 2) to understand the mechanisms responsible for this behavior. It is hypothesized that reported anomalous specific heat enhancements are related to the ionic nature of the base fluid and, therefore, to particle-fluid interactions. Theories of nanofluid heat capacity are discussed in the context of the compiled data. Other factors are also discussed, including the effect of the heat capacity measurement technique, nanofluid synthesis methods, aggregation and dispersion and the characterization thereof, and the effect of base fluid, nanoparticle size, shape, and material. Finally, recommendations are made for improving the reliability and consistency in synthesizing and characterizing nanofluids and their thermal properties.
展开▼
