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Fly ash generated during boiler combustion are carried away with hot flue gas and deposited over the heat exchanger surfaces. This study was motivated by the decline in the thermal efficiency of the heat exchangers in thermal power plants due to ash fouling. The paper discusses a new computational procedure that has been attempted to identify the best statistical model for predicting heat exchanger fouling and also to choose the most strongly linked covariates. In this context, three different statistical models including multiple linear regression, sliced inverse regression, and random forests regression are used to estimate the cleanliness factor of the heat exchanger. The variables and model are chosen solely on the basis of analytical procedures. Heat exchanger metal tube temperature that highly influences the cleanliness factor is selected using a measure of importance based on random perturbations. Metal temperature above a threshold is selected as a strongly linked covariate. The R package modevarsel is used here to perform the statistical analysis. The value of root mean square error for the cleanliness factor from sliced inverse regression and random forest is 0.0002, indicating that as more feasible in predicting ash fouling. [ABSTRACT FROM AUTHOR]

Nanofluids are generally utilized in providing cooling, lubrication phenomenon, and controlling the thermophysical properties of the working fluid. In this paper, nanoparticles of Al2O3 are added to the base fluid, which flows through the counterflow arrangement in a turbulent flow condition. The fluids employed are ethylbenzene and water, which have differing velocities on both the tube and the shell side of the cylinders. A shell tube-type heat exchanger is used to examine flow characteristics, friction loss, and energy transfer as they pertain to the transmission of thermal energy. The findings of the proposed method showed that the efficiency of a heat exchanger could be significantly improved by the number, direction, and spacing of baffles. With the inclusion of nanoparticles of 1% volume, the flow property, friction property, and heat transfer rate can be considerably improved. As a result, the Nusselt number and Peclet numbers have been increased to 261 and 9.14 E +5. For a mass flow rate of 0.5 kg/sec, the overall heat transfer coefficient has also been increased to a maximum value of 13464. The heat transfer rate of the present investigation with nanoparticle addition is 4.63% higher than the Dittus–Boelter correlation. The friction factor is also decreased by about 17.5% and 11.9% compared to the Gnielinski and Blasius correlation. The value of the friction factor for the present investigation was found to be 0.0376. It is hence revealed that a suitable proportion of nanoparticles along with the base fluids can make remarkable changes in heat transfer and flow behavior of the entire system. [ABSTRACT FROM AUTHOR]

The most common type of heat exchanger used in a variety of industrial applications is the shell-and-tube heat exchanger (STHE). In this work, the impact of graphene nanoplate (GNP)/water nanofluids at 0.01 wt.%, 0.03 wt.%, and 0.06 wt.% on the thermal efficiency, thermal performance factor, pressure drop, overall heat transfer, convective heat transfer coefficient (CVHTC), and heat transfer characteristics of a shell-and-tube heat exchanger was examined. For these experiments, a new STHE was designed and built. The novelty of this study is the use of GNPs/water nanofluids in this new STHE for the first time and the fully experimental investigation of the attributes of nanofluids. GNP properties were analysed and confirmed using analyses including XRD and TEM. Zeta potential, DLS, and camera images were used to examine the stability of nanofluids at various periods. The zeta potential of the nanofluids was lower than -27.8 mV, confirming the good stability of GNP/water nanofluids. The results illustrated that the experimental data for distilled water had a reasonably good agreement with Sieder-Tate correlation. The maximum enhancement in the CVHTC of nanofluid with 0.06 wt.% of GNP, was equal to 910 (W/m2K), an increase of 22.47%. Also, the efficiency of the heat exchanger for nanofluid at 0.06 wt.% improved by 8.88% compared with that of the base fluid. The heat transfer rate of the nanofluid at maximum concentration and volume flow rate was 3915 (J/kg.K), an improvement of 15.65% over the base fluid. The pressure drops increased as the flow rate and concentration of the nanofluid increased. Although increasing the pressure drop in tubes would increase the CVHTC, it would also increase the power consumption of the pump. In conclusion, nanofluid at 0.06 wt.% had good performance. [ABSTRACT FROM AUTHOR]

This paper designed a platelet heat exchanger in the solar thermal thruster and analyzed the unsteady-state conjugate heat transfer characteristics between heat exchanger and propellant. The conjugate heat transfer (CHT) computational fluid dynamics (CFD) simulation of the 3D model of the platelet under steady-state conditions was carried out with different mass flow rates to find the empirical correlation between the average Nusselt number and the average Reynolds number. The unsteady-state 1D simplified model of the heat exchanger was established using a loose coupling algorithm based on quasi-steady flow domain and finally verified by experiments. The results show that the platelet structure could heat the working medium to more than 2380 K with the heat transfer efficiency of 87% and produce a peak thrust of 0.57 N and specific impulse of 2200 m/s; in steady state, the outlet temperature and heat transfer efficiency of the heat exchanger were stable at 1950 K and 69%. Moreover, 1D model could accurately reflect the real heat exchange situation to a certain extent, the simulation error was less than 5% compared with the 3D model, and the calculation time was greatly shortened, making it more convenient to adjust the heat exchange strategy. The experimental results were consistent with the simulation results at the initial stage of heat exchange, and the difference was mainly reflected in the steady-state stage, which might be caused by the lack of precision of the experimental equipment. [ABSTRACT FROM AUTHOR]