Recent Developments of Heat Transfer Enhancement and Thermal Management Technology

New thermal management technology is widely developed in new energy industries, such as electric vehicles, IoT sensors, photothermal energy conversion, ground thermal energy utilization and propulsion systems. Associating with thermal management technology, some advanced heat transfer enhancement methods are proposed by combining different kinds of convection heat transfer methods or using new thermal transportation mediums, such as nanofluids. In this editorial paper, some new developments of heat transfer enhancement and thermal management technology within the applications of energy system and propulsion systems are provided.

Nanofluids have drawn a lot of research attention because they exhibit many beneficial thermo-physical properties. By nanofluids, the capability of heat transfer efficiency, thermal conductivity and light absorption is enhanced and can be adjusted by the concentration of nanofluids, which are widely applied in energy conversion and storage systems. For the application in the photothermal energy conversion process, Boldoo et al. [1] compared the performance of different nanofluids to search for the suitable nanofluid in thermal conversion systems.

Impingement cooling by droplets has also drawn attention of researchers for decades and the potential heat transfer enhancement were furtherly realized by nanofluids in the past decades. From the previous literature, using coolants with high thermal conductivity, such as nanofluids, is an effective way to improve the efficiency of impingement cooling [2]. This improvement on cooling efficiency is caused by some physical mechanisms within heat transfer and fluid flow which includes degree of stabilization, the nanofluids’ rheology and the interaction of nanoparticles with the droplet/substrate dynamics.

The application of nanofluids is also found in heat pipes for heat transfer enhancement. Esmaeilzadeh et al. [3] developed a model of a phase change heat transfer in a heat pipe using both experimental and numerical methods. Effects of three parameters of nanofluid, input heating power and inclination angles of heat pipe are considered in the model. In this work, the working fluids in the heat pipe are distilled water and 1-pyrene carboxylic-acid -functionalized graphene nanofluid.

Some new advanced thermal management systems are designed in electric vehicles, propulsion engine [4], ground thermal energy system and et al. Behi et al. [5] proposed a hybrid thermal management system which combined an air cooling assisted heat pipe, natural convection and a normal heat pipe for electric vehicles. By a fast-discharging process, experimental tests and numerical calculations were both performed to investigate thermal behaviors for a lithium titanate oxide battery cell.

Radchenko et al. [6] proposed a logical analysis method of the actual operation efficiency of turbine intake air cooling systems in real environment, which is verified by the numerical calculation. The cooling air efficiency at the turbine inlet in temperate climatic conditions and the enhancement effect through deep cooling were investigated. They proposed a novel trend in engine intake air cooling to 7 or 10 °C by two-stage cooling in combined cycle chillers. The new trend provides an annual fuel saving of 50% compared to traditional air cooling to about 15 °C in absorption lithium-bromide in a simple cycle chiller.

Thermal management technology is also used in outdoor IoT sensors and an energetically autonomous IoT sensor is designed which is powered by thermoelectric harvesting [7]. Thermal harvesting operates at a temperature gradient more than 26.31 K between the two sides of the thermoelectric-generator. The hot side of the thermal harvesting is a metal plate, and the cold side is attached with a phase-change material which works as passive dissipative material. For the specified temperature gradient, it can realize conversion efficiencies of about 26.43% without efficiency loss.

As a sustainable source, ground thermal energy can reduce our dependency on conventional fuels which can be used for the heating and cooling in urban buildings. The source is exploited by foundation of sub-structures associated with embedded heat exchanger pipes. Bohan et al. [8] investigated the application of several types of ground heat exchangers and more attention is focused on direct expansion systems and deep vertical borehole heat exchangers. They provide a review of the developments in ground heat exchangers in recent years, including design aspects of pipe arrangement, structure materials and working fluids.

As one kind of ground heat exchanger, one side of diaphragm wall heat exchangers is exposed to the basement region of the building, while the other side and the further depth of the wall are embedded into the surrounding ground. Shafagh et al. in [9] designed a model to assess the thermal performance of diaphragm wall heat exchangers, which considered the wall geometry and boundary conditions at the pipe, basement, and ground surfaces.

Gluesenkamp et al. [10] investigated the effects of components thermal masses on the performance of several adsorption heat pump systems. The original measurements of thermal masses are provided in this work by an experimental sorption heat exchanger hardware. The contribution degree of heat transfer fluid on overall effective thermal mass is analyzed and a calculation model is developed. This work built a knowledge framework for future research of experimental thermal masses. This framework also enriches the database for model validation which has benefits for a more thorough evaluation of adsorption heat pumps.