A review of multi-phase and single-phase models in the numerical simulation of nanofluid flow in heat exchangers

Various types of heat exchangers have many applications in industrial and engineering fields to improve heat transfer rate (HTR). The techniques of heat transfer enhancement which are active, passive, and hybrid are discussed in the present review paper. One of passive methods to enhance HTR is the use of nanofluids. This article provides the governing equations of nanofluid flows and discusses their modeling methods, including single-phase and two-phase. Advanced investigations considered single-phase and two-phase flow regimes are summarized. Comparing single-phase models (SPMs) and two-phase models (TPMs), most researchers concluded that numerical modeling based on TPMs experiences a better prediction compared to the SPMs. However, there are conflicting results among the researchers and it is not confirmed which model is better. This review paper aims to analyze the examinations on SPMs and TPMs in heat exchangers to assess the impact of these approaches on the prediction of the characteristics of nanofluids in these devices.