Modeling the convective thermal heat transfer of nanofluids with carbon nanotubes in cylindrical minichannel

This paper is devoted to the development of an algorithm for numerical modeling convective thermal heat transfer of nanofluids with carbon nanotubes. The algorithm is based on a one-liquid description of a nanofluid with common macroscopic variables. The properties of the nanofluid are determined only by the concentration of carbon tubes, and it is assumed that their distribution is uniform and does not change during the flow. A nanofluid can have both Newtonian and non-Newtonian rheology. The fundamental point of this algorithm is the need to use real thermophysical data in solving specific problems, which depend on the concentration of carbon nanotubes naturally. The transport equations are solved using finite volume method. The algorithm was tested by comparing the simulation data with the experimental. The problem of convective thermal exchange of nanofluid with single-walled nanotubes is solved. The corresponding experimental data were previously obtained by the authors of this work. It is shown that the algorithm simulates the considered flow with high accuracy. In addition, its important advantage is the possibility of modeling the flow characteristics, which cannot be measured experimentally. As such example the data on the velocity and temperature profiles of the fluid in the channel are presented.

An approximate method for solving MHD boundary layer flow over a stretching sheet with Joule heating and convective thermal condition

In this paper, He’s homotopy perturbation method (HPM) is used, which is an approximate analytical method for solving numerically the problem of Newtonian fluid flow past a porous exponentially stretching sheet with Joule heating and convective boundary condition. The major feature of HPM is that it does not need the small parameters in the equations and hence the determination of classical perturbation can be discarded. Due to the complete efficiency of the HPM, it becomes practically well suited for use in this field of study. Also, the obtained solutions for both the velocity and temperature field are graphically sketched. The results reveal that the proposed method is very effective, convenient, and quite accurate to systems of nonlinear differential equations. Results of this study shed light on the accuracy and efficiency of the HPM in solving these types of nonlinear boundary layer equations.

An Experimental Investigation Into Frost Accumulation Over Vertical Finned and Unfinned Surfaces During Impinging Air Flow

Frost formation on evaporators negatively affects the cooling performance of refrigerators. It increases the thermal resistance between the refrigerant and air leading to a reduction in the system cooling capacity. In this study, the effect of frost accumulation over a bare and finned surface on the convective thermal resistances has been experimentally investigated under impinging flow conditions. The surfaces are vertically positioned in a horizontal wind tunnel. The convective resistances have been measured with an in-house developed heat flux measurement system. Finally, the effectiveness of the finned surface was derived from the measurements for dry, condensing flow and as well as for frosting conditions. Under frosting conditions, the effectiveness of the finned surface is measured as 1.4 that is by a factor of 2X lower compared to the effectiveness of the same finned surface operating under dry conditions. It has been observed that the frost accumulation initially takes place at the tip of the fins and leads to a 45% drop in the heat transfer rate when the fin tips are completely covered with frost. Further frost accumulation on the fin base does not result in an additional drop in the heat transfer rate. In this regard, the study emphasizes the importance of the fin tip design for the heat sinks operating under frosting conditions.