A comprehensive review of the Maisotsenko-cycle based air conditioning systems

Abstract not availableHamed Sadighi Dizji, Eric Jing Hu, Lei Che

Development and validation of an analytical model for perforated (multi-stage) regenerative M-cycle air cooler

Maisotsenko cycle based coolers are able to reduce the air temperature below the wet-bulb temperature of the inlet air without adding any moisture to the product air and without the use of any compressor or refrigerant (CFC). These positive features of M-cycle have encouraged the researchers to enthusiastically consider the thermal-fluid characteristics of M-cycle cooler via numerical, analytical and experimental techniques. In this paper attempts are made to present an analytical solution for thermal behavior of perforated (multi-stage) regenerative M-cycle exchanger which has not been carried out before. Indeed, all previous analytical solutions of M-cycle have been provided for the simplest structure of M-cycle exchanger (single-stage, without perforation) and the perforated M-cycle cooler (multistage) has been investigated only via experimental and numerical techniques (including finite difference method, numerical ε-NTU technique, statistical design tools all of which are sophisticated and require high computational time). However, the precision aspect and analysis speed of analytical approach is undeniable and it is considered as the priority in most engineering problems. Hence, in this study, an analytical model is developed for three-stage regenerative M-cycle exchanger which can be developed for any number of perforations. All modeling process is described in detail (step by step) to make it ease understanding for readers. Evaluation methods of all required parameters are described in detail as well. Finally, the model is verified with numerical results.Hamed Sadighi Dizaji, Eric Jing Hu, Lei Chen, Samira Pourhedaya

A critique of effectiveness concept for heat exchangers; theoretical-experimental study

In this study attempts are made to clarify some hidden features of effectiveness concept (the ratio of ac- tual heat transfer to maximum possible heat transfer) of heat exchangers and provide a critique viewpoint and comprehensive description about that. It is shown in present paper that the effectiveness parame- ter requires much more attention when it is used in fluid-flow parametric or sensitivity studies of heat exchangers and lack of consideration of its hidden features may lead to incorrect or imperfect decision- makings on curve behavior of effectiveness. Indeed, it is shown that the curve trend of effectiveness against the Reynolds number of one side of heat exchanger can be ascending, descending, or ascending- descending depending on the mass flow rate ( Re number) of the other side fluid. Although this critique viewpoint is not considered as a weakness of the effectiveness definition for heat exchangers, inattention may lead to wrong or imperfect inferences in sensitivity analysis of effectiveness parameter. Moreover, it is not logical to provide empirical correlation for effectiveness against flow parameters without the con- sideration of described features of effectiveness in this study. In order to support the described viewpoint some experiments are performed on double helical tube heat exchanger to evaluate the related thermal parameters and describe the mentioned features of effectiveness statistically. However, the provided anal- ysis is valid for any other type heat exchanger as well.Shu-Rong Yan, Hazim Moria, Samira Pourhedayat, Mehran Hashemian, Soheil Asaadi, Hamed Sadighi Dizaji, Kittisak Jermsittiparser

Experimental investigation of heat transfer and exergy loss in heat exchanger with air bubble injection technique

The main aim of this study is to evaluate thermal performance and exergy analysis of a shell-and-tube heat exchanger with a new technique called air bubble injection. The study has been carried out with different parameters such as flow rate, fluid inlet temperature, and different air injection techniques. The air has been injected at different locations such as the inlet of pipe, throughout the pipe, and in the outer pipe of the heat exchanger. Based on the results, the performance of the heat exchanger enhances with an increase in the flow rate and the fluid inlet temperature. The exergy loss and dimensionless exergy loss increase with a rise in the flow rate. The maximum and dimensionless exergy losses are obtained at a maximum flow rate of 3.5 l min−1. With the air bubble injection in the heat exchanger, it has been observed that the temperature difference increases, which leads to an increase in the exergy loss. The injecting air bubbles throughout the tube section shows that minimum dimensionless exergy is 27.49% concerning no air injection.http://link.springer.com/journal/109732021-08-28am2020Mechanical and Aeronautical Engineerin