Search

Ferrofluids are type of colloidal systems which are known as an important group of smart materials. Their physical properties adaptively change with magnetic strength. These characteristics of ferrofluid must be applied for improving the efficiency. In this work, thermal performance of a type of ferrofluid with a viscosity correlation dependence on temperature, magnetic field and volume fraction was scrutinized. FVM is applied for solving momentum, conservation and heat transfer equation. To consider the effect of solid part in thermal behavior of system, the conjugate heat transfer was considered. The wire is placed in the bottom of channel, and the equation of non-uniform external magnetic field is defined as user function. The results indicated in a comparison of studied parameters as non-dimensional variables, it is demonstrated magnetic number and wave amplitude result in the maximum impact on improving Nu and the worst impact on friction coefficient and pressure loss correspondence to volume fraction and Reynolds number. The results also predicted significant changes in viscosity under influence of effective parameters, especially Kelvin force. [ABSTRACT FROM AUTHOR]

Utilizing passive methods is an efficient way in order to improve the thermal performance of heat exchangers. The novelty of the present paper is that two kinds of passive techniques for heat transfer enhancement, including a corrugated tube equipped with a coiled wire as turbulator, are combined in the present study. Heat transfer and pressure drop in a corrugated tube with a wire coil are analyzed numerically by a commercial CFD software. The range of the considered Reynolds number is 5000–20,000, which guarantees that the flow regime is fully turbulent. The effects of two different geometrical parameters and of two flow operating parameters, namely the Reynolds and Prandtl numbers, are numerically investigated. The conservative equations for momentum are closed using the k-ε realizable model. Results indicate that the geometrical and fluid flow parameters have significant effects on the thermal performance of the system. When one increases the pitch ratio of the wire coil (P/d), the heat transfer enhancement ratio NuER decreases. The maximum decrease is obtained for P/d = 5 with − 7.78% at Re = 20,000 in comparison with the baseline case P/d = 2. The maximum increase in the performance evaluation criterion (PEC) is observed at Re = 5000: + 11.16% and + 17.4% for P/d = 3 and P/d = 5, respectively. The configuration with a roughness height equal to e = 3 mm exhibits the best thermal performance with a maximum enhancement in terms of NuER of + 3.3% at Re = 10,000 in comparison with the baseline case e = 0.5 mm. By considering the PEC number, increasing the parameter e has a negative effect on the thermal performance of the proposed system. [ABSTRACT FROM AUTHOR]