New experimental Nusselt number correlation for spiral plate heat exchanger optimized using a code

A system of a spiral plate heat exchanger and its required auxiliaries was built. The pitches of heat exchanger were built differently to provide almost two geometrically different heat exchangers in a single package. Several experiments were done and working parameters of the heat exchanger were measured. A code was written to find a new optimised correlation that could approximate the Nusselt Number based on the obtained experimental data from 51 reliable experiments. As an advantage, that correlation was valid for low Reynolds Numbers. Also, in most of previous works, the correlation for Nusselt Number in one side of the heat exchanger was supposed to be known and the correlation for the other side was determined. But, in this study, the equation was found using calculations for both sides simultaneously. The overal heat transfer coefficient calculated from the proposed correlation, made an average error of 3.65% to the experimental data. A complete uncertainty analysis was done and revealed that the results from the new correlation for the Nusselt Number lies between [Formula: see text] around the real Nusselt Number.

Algal Biomass Harvesting Using Low-Grade Waste Heat: Evaluation of Overall Heat Transfer Coefficient in a Heat Exchanger

This study is part of a broader study on a novel method for harvesting algae by evaporation, and it investigated the feasibility of heating algal biomass using low-grade waste heat in a heat exchanger. Computational fluid dynamic (CFD) analysis was performed with ansysfluent, and the results were verified with experiments. The results of CFD analysis showed the overall heat transfer coefficient increased by 4, 13, and 100% as inlet gas temperature increased from 150 to 245 °C, liquid mass flow rate increased from 1.82 to 9.1 g/s, and gas mass flow increased from 2.2 to 13.2 g/s, respectively. It was also observed the overall heat transfer coefficient was not significantly affected with variations of properties of the liquid (thermal conductivity, density, and viscosity), thermal conductivity of the tube wall, and thickness of the tube banks, but it was sensitive to thermal conductivity of the gas. The experimental data were analyzed with logarithmic mean temperature difference (LMTD), number of transfer units (NTU), and Nusselt number correlation methods. There was an excellent agreement between the overall heat transfer coefficient calculated with the LMTD and NTU methods. The coefficients calculated with the LMTD method and Nusselt number correlation exhibited slight variations. This is likely because the LMTD is a theoretical method covering all experimental conditions and material properties, but Nusselt number correlation is an empirical approach based on correlations. The overall heat transfer coefficient calculated by CFD was slightly overestimated because the CFD analysis assumed complete insulation.

Experimental Investigation on Heat Losses From Differentially Heated Cylindrical Cavity Receiver Used in Paraboloid Concentrator

In the present study, an experimental testing facility is created to analyze the heat losses from the cylindrical solar cavity. Tests are carried out under the temperature range from 225 °C to 425 °C for a cavity inclination from θ = 0–90 deg in steps of 30 deg. It is observed that for off-flux investigation of solar cavity receiver, near isothermal wall temperature condition can be realized with the differential heating arrangement. The total loss is found to be the highest when the cavity aperture is positioned at sideways (θ = 0 deg). It decreases by 43–51% when the cavity is inclined (θ = 90 deg). The conduction loss is found to be accounted for up to 32–34% of the total heat loss, whereas the cavity radiative loss is estimated to be 13%, 16%, and 20% of the total heat loss, respectively, for cavity wall temperature 225 °C, 325 °C, and 425 °C. The investigation of convective losses showed significant change with cavity tilt angles. It is 46–54% of the total heat loss when the cavity aperture is facing sideways (θ = 0 deg), whereas its value reduces up to 4% of the total heat loss when the cavity aperture is facing downward (θ = 90 deg). A Nusselt number correlation has been developed for predicting the convective heat loss from a open cavity. The Nusselt number correlation correlates 100% of data within ± 20% deviation.