A numerical investigation of the heat transfer characteristics of water-based mango bark nanofluid flowing in a double-pipe heat exchanger.

In this study, the heat transfer characteristics of a new class of nanofluids made from mango bark was numerically simulated and studied during turbulent flow through a double pipe heat exchanger. A range of volume fractions was considered for a particle size of 100 nm. A two-phase flow was considered using the mixture model. The mixture model governing equations of continuity, momentum, energy and volume fraction were solved using the finite-volume method. The results showed an increase of the Nusselt number by 68% for a Reynolds number of 5,000 and 45% for a Reynolds number of 13 000, and the heat transfer coefficient of the nanofluid was about twice that of the base fluid. In addition, the Nusselt number decreased by an average value of 0.76 with an increase of volume fraction by 1%. It was also found that there was a range of Reynolds numbers in which the trend of the average heat transfer coefficient of the nanofluid was completely reversed, and several plots showing zones of higher heat transfer which if taken advantage of in design will lead to higher heat transfer while avoiding other zones that have low heat transfer. It is hoped that these results will influence the thermal design of new heat exchangers.

Effects of the timing of antigen stimulation on parasitaemia profile and subsequent immunodepression in an experimentally induced Trypanosoma brucei infection.

The influence of administering sheep red cells (SRC) as antigens, either after or before a trypanosome challenge, on parasitaemia profile and antibody response was assessed in albino Wistar rats. High levels of parasitaemia associated with significantly depressed antibody response and packed cell volume (PCV) values were observed when trypanosome challenge preceded antigen stimulation. In contrast, a clear delay in the onset and development of parasitaemia occurred when antigen priming preceded trypanosome challenge. At the beginning, PCV values and antibody response to the antigen were in the range of levels found in control rats. However, as infection progressed, parasitaemia rose and significant immunological hyporesponsiveness developed which at least reached levels found in rats that had received trypanosome challenge prior to antigen stimulation. These findings should be taken into consideration when evaluating serological tests used for assessing responses to specific vaccinations, or for the diagnosis of infections based on rising antibody titres in the host.