This paper presents a critical review of heat transfer applications of nanofluids. The effects of nanoparticle concentration, size, shape, and nanofluid flow rate on Nusselt number, heat transfer coefficient, thermal conductivity, thermal resistance, friction factor and pressure drop from numerous studies reported recently are presented. Effects of various geometric parameters on heat transfer enhancement of system using nanofluids have also been reviewed. Heat transfer devices covered in this paper include radiators, circular tube heat exchangers, plate heat exchangers, shell and tube heat exchangers and heat sinks. Various correlations used for experimental validation or developed in reviewed studies are also compiled, compared and analyzed. The pros and cons associated to the applications of nanofluids in heat transfer devices are presented in details to determine the future direction of research in this arena.

Recent advances in application of nanofluids in heat transfer devices: A critical review

The increasing need for thermal comfort has led to a rapid increase in the use of cooling systems and, consequently, electricity demand for air-conditioning systems in buildings. Heat-driven ejector refrigeration systems appear to be a promising alternative to the traditional compressor-based refrigeration technologies for energy consumption reduction. This paper presents a comprehensive literature review on ejector refrigeration systems and working fluids. It deeply analyzes ejector technology and behavior, refrigerant properties and their influence over ejector performance and all of the ejector refrigeration technologies, with a focus on past, present and future trends. The review is structured in four parts. In the first part, ejector technology is described. In the second part, a detailed description of the refrigerant properties and their influence over ejector performance is presented. In the third part, a review focused on the main jet refrigeration cycles is proposed, and the ejector refrigeration systems are reported and categorized. Finally, an overview over all ejector technologies, the relationship among the working fluids and the ejector performance, with a focus on past, present and future trends, is presented.

https://re.public.polimi.it/bitstream/11311/984261/1/2016_RSER_BesagniMereuInzoli.pdf

Ejector refrigeration: A comprehensive review

Advanced computational modelling for drying processes – A review

Electronics cooling with nanofluids: A critical review

Previous reviews on ejectors for expansion work recovery have provided detailed discussions of operating characteristics and control of ejector cycles, zero-dimensional ejector modeling, ejector geometry effects, and alternate ejector cycles. However, important advances in the field of ejector technology have occurred since previous reviews were written. Several focuses of recent ejector research are the development of multi-dimensional CFD ejector models, investigation of alternate ejector cycles and uses of the work recovered by the ejector, implementation of effective control strategies for ejector cycles, and application of ejectors in real systems. The objective of this paper is to present a review of developments in the use of ejectors for expansion work recovery in vapor-compression systems focusing on the past several years. Although the first commercial applications are being introduced to the market, it is suggested that future works continue in these areas in order to make ejectors more suitable for additional applications.

Review of recent developments in advanced ejector technology

A computational model of a transcritical R744 ejector based on a homogeneous real fluid approach

CFD-based shape optimisation of a CO2 two-phase ejector mixing section

A CFD-based numerical analysis of the flow irreversibility in R744 ejectors is presented. A validated CFD tool was used to investigate three cases that were differentiated by the mass flow rate per unit area (mass flux) that passed through the mixer, which represented three dissimilar flow patterns. The mixer mass flux was found to significantly affect the ejector performance both locally and globally. An original approach was introduced to assess the contribution of the local irreversibilities to the overall entropy increase. A new factor was proposed to evaluate the ejector performance based on the reference entropy increase in a classic expansion valve. In addition, the influence of the mixer diameter and length on the ejector performance was numerically analysed, which showed that the effects of both geometric parameters may be significant. Namely, in the conditions considered, both enlargement of the mixer cross section area by 17.4% as well as shortening the mixer length by 33.3% resulted in the increase of the overall entropy growth rate by 8.9% and 5.4%, respectively.

A CFD-based investigation of the energy performance of two-phase R744 ejectors to recover the expansion work in refrigeration systems: An irreversibility analysis

Investigation on the CPU nanofluid cooling

A test facility for the experimental investigation of the R744 vapour compression rack equipped with a multi-ejector expansion work recovery module was designed and manufactured. A comparison of the R744 multi-ejector refrigeration system with the R744 parallel compression system at the same test facility was carried out based on the energy performance characteristics of refrigeration capacity, power consumption, COP, and exergy efficiency. Apart from the system performance comparison, the influence of the pressure level in the flash tank on the system performance for the two alternatives was analysed. The experimental results indicate COP and exergy efficiency improvements of the multi-ejector refrigeration system up to 7% and 13.7%, respectively. The highest values of COP and exergy efficiency were obtained by a multi-ejector refrigeration system with the tank pressure lift close to the maximum value possible to operate the multi-ejector expansion module. The values of the effective compressor efficiencies were significantly different, depending on the operation module (cooling load and heat rejection conditions).

/pdf/experimental-analysis-of-the-r744-vapour-compression-rack-567jwph6cs.pdf

Jacek Smolka

Papers

A computational model of a transcritical R744 ejector based on a homogeneous real fluid approach

CFD-based shape optimisation of a CO2 two-phase ejector mixing section

A CFD-based investigation of the energy performance of two-phase R744 ejectors to recover the expansion work in refrigeration systems: An irreversibility analysis

Investigation on the CPU nanofluid cooling

Experimental analysis of the R744 vapour compression rack equipped with the multi-ejector expansion work recovery module