## 1 Introduction  
Fine solid-liquid phase-change material (PCM) particles can be dispersed in a carrier or suspended in a working fluid to form PCM slurries or suspensions. The latent heat of absorption and release of the PCM can be used to reduce the maximum temperature and increase heat transfer in a loop. PCM particles can be prepared by microencapsulation technology [1; 2; 3; 4] or emulsion technology [6; 7; 8]. In microencapsulation, polymer materials cover the PCM to create a barrier between the dispersed phase (PCM) and the dispersion medium (such as water and glycerol) that results in the suspension of PCM particles in the dispersion medium. The prepared PCM particles have a relatively fixed size and shape and relatively stable physical properties compared to particles prepared by other methods. However, these materials have the disadvantages of high cost, a difficult manufacturing process, reduced heat transfer efficiency from the polymer surface coating, and expansion and cracking after repeated heating. In emulsion technology, the addition of appropriate emulsifiers reduces the surface tension between the dispersed phase and the dispersion medium to produce a stable emulsion of PCM particles uniformly suspended in the dispersion medium. Heat transfer enhancement using PCM suspensions as the working fluid has been demonstrated in forced convection. [PERSON] et al. [9] proposed a numerical simulation and an experiment on an isothermal outer wall. The results show that the heat transfer for a working fluid containing PCM microparticles is 1.6-2.5 times higher than that of pure water. The highest overall heat transfer is obtained for 20% PCM particles by volume. [PERSON] et al. [10] used numerical analysis to investigate the influence of the wall thickness of a circular tube on the heat transfer characteristics of a PCM suspension. For low Peclet numbers, the forward propagation of heat along the tube wall results in the complete melting of the PCM microparticles before entrance into the heating section. [PERSON] et al. [11] conducted experiments on the laminar forced convection of a hybrid water-based suspension of Al\({}_{2}\)O\({}_{3}\) nanoparticles and microencapsulated PCM (MEPCM) particles through a circular tube. The effective cooling by the hybrid suspension is significantly higher than that of the pure PCM suspension, the pure nanofluid, or water. [PERSON] and [PERSON] [12] investigated heat transfer in water-based MEPCM suspensions in laminar flow through rectangular copper mini-channels. The MEPCM suspensions perform better than water for only a certain range of parameter combinations, over which the latent heat can be exploited to a high degree. [PERSON] et al. [13] conducted experiments to compare the effect of substituting pure water with water-based Al\({}_{2}\)O\({}_{3}\) nanoparticle suspensions (nanofluids) and an MEPCM suspension in the laminar forced convective cooling of an iso-flux heated circular horizontal tube. The forced convective cooling from the hybrid suspension is significantly higher than that of the pure PCM suspension, the pure nanofluid, or pure water. [PERSON] et al. [14] experimentally investigated the laminar forced-convection heat transfer characteristics of a circular tube heated at a constant heat flux. A phase change nanofluid (eicosane-in-water nano-PCM emulsion (particles)) was used as the working fluid under the following operating conditions: volume flow rate = 12.5-180 cm\({}^{3}\)/min, heating power applied at the outer wall of the tube = 20, 30, 40, 50, 60 W, and an inlet fluid temperature of approximately 27 \({}^{\circ}\)C. The results showed that when the flow rate and the heat flux are in a proper range, the tube wall temperature along the heated section can be effectively suppressed with increasing mass fraction of the nano-PCM particles in the water-based phase-change nanofluid compared with that of the pure water. Moreover, the penalty of the pressure drop increases when phase-change nanofluids are used. [PERSON] et al.