This paper presents the effects of saturation temperature and inclination angle on convective heat transfer during condensation of R134a in an inclined smooth tube of inner diameter of 8.38 mm.Experiments were conducted for inclination angles ranging from -90° (vertical downwards) to

An experimental study of the pressure drops during the condensation of R134a in a smooth copper tube of inner diameter of 8.38 mm was carried out for vapour qualities ranging between 0.1 and 0.9, mass fluxes between 100 kg/m 2 s and 400 kg/m 2 s, and saturation temperatures between 30°C and 50°C. Inclination angles ranging from-90° (downward flow) to +90° (upward flow) were considered. The pressure drop was measured directly by means of calibrated differential pressure transducers connected to the inlet and the outlet of the test condenser. It was found that the pressure drop is significantly influenced by the inclination angle and saturation temperature. The void fraction and frictional pressure drop results also show that they are largely influenced by these parameters. While the highest and lowest measured pressure drops were obtained during the upward flow and downward flow respectively, the results obtained for the void fraction and the frictional pressure drop showed that the highest values were obtained during the downward flow while the lowest values were obtained during the horizontal and upward flows.

solar collectors, evaporators, condensers and relevant energy storage schemes during thermal charging and discharging. A brief overview of some energy storage options are also presented to motivate the inclusion of thermal energy storage into direct steam generation systems.

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.

Solar dryers are imperative for the tropical and sub-Saharan African countries, which are faced with the duo challenges of inadequate electrical energy supply, which has severely limited the application of conventional refrigeration as a means of preservation of agricultural produce, and the need to make produce competitive in the international market. In this study, a cost-effective natural convection solar dryer was developed; the thermal and drying analyses were done and tested to obtain some performance evaluation parameters for the system in order to examine its efficiency and effectiveness by drying some plantain fillets. The collector and system efficiencies are found to be 46.4% and 78.73%, respectively, while a percentage moisture removal of 77.5% was achieved at the 20th hour in order to give final moisture contents of 15.75% in the product, which still maintained its integrity. With a cost of about $195.00, it has been affordable for the small- and medium-scale enterprises as well as for private use in domestic applications.

Highlights Analytical approach is employed to solve the energy equations with convective boundary condition of the third kind.  The wall thickness, Bi and k pf significantly influence the interfacial heat flux, the wall and fluid bulk temperatures.  The fluid bulk and wall temperatures decrease with decreasing pipe wall thickness and increasing Bi number and k pf .  Increase in the convective heat loss corresponds to a decrease in wall thickness but increase in both Bi and k pf .  The thermal entrance length increases with pipe wall thickness while it decreases with increase in both Bi and k pf . ABSTRACTConjugate heat transfer in laminar tube flow with convective boundary conditions is considered analytically. The steady state problem involving two-dimensional wall and axial fluid conduction is solved using separation of variables for a thick walled cylindrical pipe. The effects of the wall thickness, external Biot number and wall-tofluid thermal conductivity ratio are investigated on the heat flux, fluid bulk and wall temperatures. Results are presented for the cases when the wall thickness is between 0.1 and 2, Biot number ranging between 0.1 and 10, and the ratio of wall-to-fluid thermal conductivity between 3 and 100. These parameters are found to significantly affect the heat transfer characteristics at the thermal entrance region, for instance, increase in wall thickness results in reduced heat flux while increase in Biot number and the ratio of the wall-to-fluid thermal conductivity result in increased heat flux. Decrease in wall thickness, increase in both Biot number and the ratio of the wall-to-fluid thermal conductivity correspond to decreased fluid bulk and wall temperature profiles.Keywords: thick-walled pipe; Biot number; Peclet number; wall-to-fluid thermal conductivity ratio; convective heat transfer characteristic eigen values or roots of pipe eq.

An experimental study of convective condensation heat transfer of R134a was conducted in an inclined smooth copper tube of inner diameter of 8.38 mm. The test condenser had a straight copper tube section with an effective length of 1.488 m and was cooled by water circulated in the surrounding annulus in a counter-flow arrangement. The rate of heat transfer was maintained at an average of 250 W throughout the experiment while the mean vapour qualities ranged between 0.1 and 0.9, mass flux between 200 kg/m 2 s and 400 kg/m 2 s for inclination angles varied between-90 o (vertical downward) and +90 o (vertical upward) covering the whole range of inclination at saturation temperature of 50 o C. The results show that the inclination angles and mean vapour qualities strongly influence the coefficient of heat transfer and an optimum inclination angle was found to be between-15 o and-30 o (downward flow). The developed correlation gave an average and mean deviations of-3.44% and 9.22% respectively for horizontal flow and, 5.25% and 19.41% respectively for vertical downward flow.

In oil and gas installations, whether on-shore or off-shore, pipes are the primary vessel for the conveyance of either crude or products from one location to another. Under use, the pipes are subjected to both internal and external temperature fluctuations while repeated operational start-up and shut-down procedures triggers vibrations of these pipes, propagates internal waves and results in finite and irreversible longitudinal extension of the pipe over time. This longitudinal extension which is sometimes accompanied by pipe buckling is known as ratcheting and has also been described by some as pipe walking. In view of the complicated and intractable nature of the problem, most attempts to study the behavior of these pipes have been limited to the analysis of some reduced problem based on heuristic arguments and idealizations. Within this context, the transverse vibration and stability of such pipes have been studied while the problem of undamped clamped-pinned pipe conveying fluid has also been tackled numerically. Keiper and Metrikine [2004] however pointed out that such numerical schemes sometimes lead to disputed or controversial results. More importantly, the coupling between the transverse vibration and longitudinal motion has been largely ignored or neglected altogether by most writers. The objective of this paper is to formally derive the governing equations of Euler-Bernoulli beam capturing various effects including temperature variations (within and without), Coriolis acceleration, transverse acceleration, pre-stress, pressurization, rotatory inertia, and cross-sectional area change. In particular, it is shown that the latter effect is what causes pipe walking phenomenon. Most of the other effects were either earlier accounted for by Semler, et al [1994] or recently captured by Reddy and Wang [2004]. Nonetheless earlier contributions neglected the effect of the cross-sectional area change completely, thereby omitting the pipe walking phenomenon. Simple examples are considered to demonstrate the importance of these terms.