Thermal System Configuration Research Articles

3D MHD convection and entropy production in a rectangular cavity with localized heating: A study on conductive fluid dynamics

This study aims to investigate the magnetoconvection of an electrically conducting fluid within a rectangular enclosure through a comprehensive three-dimensional computational analysis. The enclosure has a hemispherical block for bottom heating and incorporates two elliptical sources with differing temperatures along its vertical sidewalls. The primary focus is to optimize heat transfer and fluid flow characteristics within this thermal system by analyzing various control parameters. The simulations were carried out with the relevant parameters of the problem, including the Rayleigh number [Formula: see text], Hartmann number [Formula: see text], the inclination of the magnetic field [Formula: see text], and the radius of the hemispherical block [Formula: see text]. Three distinct scenarios represent different positions for the localized heat sources. Among these configurations, the Middle–Middle (MM) arrangement is the most favorable, with the specific value for the radius [Formula: see text] yet to be determined. The findings highlight the effective control of heat transfer rate and irreversibility effects by manipulating the parameters [Formula: see text], [Formula: see text] and [Formula: see text]. It is demonstrated that selecting [Formula: see text] and [Formula: see text] values of [Formula: see text] and 15 allows for optimal thermal system configuration. A correlation with two variables [Formula: see text] expressing the rate of heat transfer through the cavity was established and verified. The analysis of the helicity confirms the predicted optimal case.

Enhancing the flexibility and stability of coal-fired power plants by optimizing control schemes of throttling high-pressure extraction steam

Regulating the thermal system configuration can improve the ramp-up rate of the coal-fired power plants during peak shaving transient processes, while it may bring penalties in the performance of the steam temperature control and thermal efficiency. This study simulated the load ramping up transient processes when throttling the extraction steam of high-pressure heaters. The results show that there is a gap between the needed energy and energy supply caused by drastic fluctuations of reheat steam flowrate. Control schemes of steam temperatures and fuel demands were revised considering the dispatch of the fuel and working medium. According to economic optimality, the order of throttling high-pressure heaters was optimized. By implementing the revised control strategies, the fluctuations of steam temperatures were diminished and the maximum deviation of live and reheat steam temperatures was reduced by 23.5 °C and 11.4 °C, respectively. The flexibility indicator was increased by up to double at most. The average standard coal consumption rate variations with and without the revised control schemes were compared and the maximum difference is 1.23 g kW−1 h−1 with 2.5 % Pe min−1. The flexibility and economic performance were both improved when adopting the revised control schemes.

Magneto-nanofluid flow in cylinder-embedded discretely heated-cooled annular thermal systems: Conjugate heat transfer and thermodynamic irreversibility

The present work investigates magnetohydrodynamics-driven thermal-fluid flow characterization in cylinder-embedded annular thermal systems subjected to peripheral differential heating. It explores Al2O3/water nanofluid flow-associated heat transfer and entropy generation in the presence of a magnetic field and a conducting cylindrical obstruction (block). The consequence of various obstruction sizes on thermo-fluid flow behavior is also analyzed. The transport equations are handled by a finite element-based solver. The thermal-flow analysis is carried out for the relevant vital parameters such as Rayleigh number (Ra), Hartmann number (Ha), magnetic field orientation (γ), and obstruction size. Through the investigation, it is found that Nusselt number (Nu) is greatest when the internal conducting block size is the least. It can thus be inferred that flow circulation plays a dominant role in determining the Nu value. Heat flow dynamics described by the heatlines, as well as flow structure examined by the streamlines, are found to vary depending upon the obstruction size, and the field orientation (γ). Furthermore, the total entropy generation figures out that when the buoyant forces within the thermal systems are low, the entropy generation is uniform along the periphery; however, when the buoyant forces take a significantly higher value, the contours of entropy generation are seen to be more concentrated near the discretely heated and cooled walls. It is seen that if the inner conducting body size increases, the overall entropy production significantly increases. Finally, a generalized single mathematical correlation is developed for both heat transfer and entropy generation. This thermal system configuration has practical relevance and the present findings could enrich the understanding of pre-existing concepts in the area of thermal systems pertaining to effective heat-exchanging devices.

Evaluation of thermoelectric power generated through waste heat recovery from long ducts and different thermal system configurations

This paper presents the impact of Thermoelectric Generator (TEG) performance for recovering waste heat from long flue gas ducts with different thermal system configurations such as constant fluid temperature, counter flow, parallel flow and cold heat sink exposed to ambience. The counter flow configuration showed a good agreement with reference study for 2 m length of the duct at a high heat transfer coefficient of 100 W/m2K. The increase in duct length showed an adverse effect on TEG power generation due to the temperature drop of fluid along the duct rather than a constant temperature and hence the efficiency of TEG decreased in comparison with a constant fluid temperatures of flue gas and fresh air. Analyzing the performance of different thermal system configurations, results showed that cold heat sink exposed to ambient configuration has a potential to generate maximum TEG power output of 172.34 kW with an efficiency of 4.3% which are 40.22%, and 20.74% lower than the constant fluid temperature configuration respectively for 50 m duct length at a practical heat transfer coefficient of 25 W/m2K. The cold sink exposed to ambient configuration is economical whereas counter flow configuration is recommended for regenerative purposes after TEG power generation.

Increasing operational flexibility of supercritical coal-fired power plants by regulating thermal system configuration during transient processes

The operational flexibility of traditional coal-fired power generators has played crucial parts in many countries given the continuous integration of intermittent and fluctuant renewable power resources in their power system. This study is aimed at improving the short-term operational flexibility of thermal power units. The transient simulation models of a 660 MW supercritical coal-fired power system are developed by using the GSE software, and the six measures of regulating thermal system configuration, which can rapidly activate thermal storages in thermal systems, are introduced and compared. The greatest potential mode in each measure of regulating thermal system configuration is obtained on the basis of the utilization degree of the internal thermal storages. The dynamic characteristics of the thermal parameters of the selected measures are compared, and the results reveal that the measures of regulating extraction steam from low-pressure heaters has less negative effects on the live and reheat steam parameters but greater negative effects on the deaerator and condenser parameters than the measures of regulating extraction steam from high-pressure heaters. Moreover, the performance indexes of operational flexibility are also evaluated for all the measures of regulating thermal system configuration. Among five measures applied in the power-up process, the values of power ramp rate are from 1.26% to 6.31% of rated power per minute, the values of power capacity are from 12.87 to 48.35 MW, and the values of energy capacity during the regulating time of 120 s are 1009.73 to 5048.93 MJ. However, the measure of condensate water increasing of low-pressure heaters is an only way suitable for the power-down regulation process, and the value of power ramp rate is 0.61% of rated power per minute, the power capacity is −5.65 MW, and the energy capacity is −483.84 MJ. The best regulating measures are obtained on the basis of the different perspectives of operational flexibility. The findings of this study can help determine the best operational control strategies in different situations.

Impact of Thermal Interface Materials for Thermoelectric Generator Systems

A primary challenge still exists in the field of thermoelectric generators (TEG) for practical applications in which a thermal system of the TEG is a crucial factor in TEG power generation. The material development for TEG has contributed significantly towards advancement in TEG applications over a decade, the need for a thermal system configuration is inevitable considering the applications. The thermal efficiency of TEG depends upon the temperature difference across its modules (between the hot and cold surfaces). Thermal design of the thermoelectric system is important to ensure that there exists a maximum temperature difference across the hot and cold surfaces of the TEG. Thermal Interface Material (TIM) in thermoelectric systems plays a main role in improving the efficiency of thermoelectric systems by reducing the temperature difference between the heat source and the hot surface of the TEG and similarly, the temperature difference between the cold surface of TEG and the heat sink. This review paper predominantly focuses on the thermal interfaces between the TEG modules which reduces the performance of a thermoelectric system. The characteristics of TIM in a TEG system (contact pressure, surface roughness and thermal conductivity) were analyzed with a mathematical model to emphasize the importance of TIM in a TEG system. This paper also highlights the existing challenges for Thermal Interface Materials in TEG applications and concludes with a brief discussion on future directions of TIM in TEG thermal systems.