## 1 Introduction  
Miniature heat exchangers have received considerable attention, given potential for high heat transfer removal and the success of this device in high heat-flux, as developments in electronic equipment with the advent of modern technology. In such devices, a huge amount of heat is produced during their operation, which results in reduced reliability, normal performance, and their prognosed work. Therefore, a proper cooling mechanism is of great importance when designing miniature electronic components. The heat dissipation capabilities associated with minichannel heat sinks have been developed because they have a good potential for effectiveness and are still promising. Quite a few studies have developed various aspects of applications of mini heat exchangers, including theoretical perspectives and practical aspects. There is still a demand for an improvement in overall thermal performance of miniature heat transfer exchangers when both heat transfer and hydrodynamic characteristics are considered. Currently, heat transfer, with the change of state during flow refrigerants in minichannel heat sinks, has been studied extensively. Meanwhile, only a few studies have been devoted to investigating different methods of heat transfer calculations regarding miniature heat transfer devices, and it remains inconclusive whether similar results are expected. Many recent studies have concentrated on enhancement of heat transfer in minichannel heat sinks. Several of these studies have focused on the effects of heat flux,mass flow rate or fluid velocity, Reynolds number, mass flux, pressure, inlet liquid subcooling, channel dimensions and spatial orientation on improving the cooling performances of miniature heat exchangers. In the current computational age, heat transfer analysis, using numerical methods, has become a common mode to reduce time, cost, and material. In-depth analysis and study of flow behaviour and pattern in the flow domain can be obtained very quickly with the aid of commercial software and by developing computer codes. Heat transfer analysis in the minichannel heat sink using the numerical method is generally needed to be carried out by either reliable data upload in the calculation methods. However, numerical analysis conducted in commercial software, based on experimental data, is more valuable because it ensures verification of the simulation results. In this work, an experimental study of subcooled flow boiling was conducted for FC-72 flow in a minichannel heat sink, comprising of five channels. The boiling heat transfer characteristics were investigated, and the effect of the mass flow rate on the heat transfer coefficient was studied. The results achieved on different calculation methods were also explored with an emphasis on the impact of the mass flow rate on the heat transfer intensity. The research reported in the literature confirms the importance of different flow and thermal parameters in the flow boiling heat transfer. Different criteria for predicting the transition from macro-channels to mini-/microchannels were proposed. The classification of channels, taking into account their hydraulic dimension according to Kandlikar and [PERSON] [1], is common, that is, it has been stated that microchannel in minichannel transition occurs at a hydraulic diameter of 3 mm. The effect of low heat and mass fluxes on the boiling heat transfer coefficient of R-245 fa was examined in [2]. In the test section, a smooth horizontal tube, with an inner diameter of 8.31 mm and a heated length of 0.8 m, was provided. The steady-state experiments were carried out in a wide range of vapour qualities (from 0.05 to 0.90) for mass fluxes of 40, 60 and 80 kg/(m\({}^{2}\)s) and heat fluxes of 2.5, 5.0 and 7.5 kW/m\({}^{2}\). The authors stated that the heat transfer coefficient was influenced by both the mass and the heat fluxes. An increase in the mass flux resulted in an increase in the heat transfer coefficient.