International Journal of Air-Conditioning and Refrigeration

Conventionally, the CFC-type refrigerants were used until Montreal Protocol which stated that CFC refrigerants cause ozone depletion and should be replaced with alternative refrigerants. The alternative refrigerants are safe for ozone but they have comparatively high flammability, toxicity and global warming potential. Thus they need careful handling. In Kyoto Protocol, it was stated that the currently used refrigerants with high global warming potential need to be replaced with yet other alternative refrigerants with low global warming potential. This paper comprehensively reviews those recent studies that focused on the possible replacement of currently in-use refrigerant with a comparatively more environmental-friendly alternative refrigerant. Initially, the progression of refrigerants through different generations has been described and discussed. A list of currently in-use refrigerants has been presented. Then, the scientific developments for the replacement of listed refrigerants are thoroughly reviewed and critically analyzed. From the comprehensive review, it was found that R1234yf has the most potential to be a suitable low-flammable replacement for R134a for domestic refrigeration and automotive air-conditioning systems. Also, R32 has the most potential to be a suitable alternative of R410A.

Air conditioning is one of the large energy consuming sectors, as it comforts the human in closed environment. Especially, in coastal regions where both temperature and humidity are high, it demands for air conditioning. Usually, in such cases, cooling and dehumidification of outside air is done by cooling coils. Such cooling and dehumidification coils requires relatively large amount of energy. In the era of energy saving technologies, Liquid desiccant system (LDS) has proved to be one of the best alternatives for controlling the humidity, economically and efficiently. Different liquid desiccants are available for dehumidification purpose with their own advantages and disadvantages. This paper summarizes the different liquid desiccants used by researchers in their study and the performances analysis of dehumidification process. An attempt is also made to summarize the characteristics of the different hybrid or composite desiccants developed by researchers in order to improve the desiccant properties for the better dehumidification process.

Thermoacoustic refrigeration, a novel technology, uses eco-friendly gases like helium, air or the mixture of noble gases as working substances in the absence of moving parts. The design, optimization and analysis of thermoacoustic refrigerators using helium and air as oscillating gases are discussed. Pure helium is chosen since it is proven as the best and economical working gas compared to the alternate pure or the mixture of noble gases. Air is chosen since it is abundant in nature and the least cost of the pressurized dry air cylinders. The design optimization strategies discussed in this paper serve as a guide for aspiring researchers in the design and development of thermoacoustic coolers. Cooling power as a function of stack diameter is discussed. Theoretical results of the optimized coolers are compared with DeltaEC simulation results for validation and are in agreement with each other.

Three design enhancement options for a vertical gravitational flash tank separator were proposed and investigated in this work. Computational Fluid Dynamic (CFD) was used to assess the optimum configurations of the vertical gravitational flash tank separator. A series of experiments were performed to test the CFD proposed configurations of the enhancement design options. This paper also assessed the usefulness of CFD in flash tank design, and this is achieved through experiments and simulations on a range of relevant configurations using water as the working fluid. The results revealed that the combination of the inlet flow direction and extractor had a significant effect on the performance of the vertical flash tank separator which increased by 2%. The results also revealed that there was a good agreement between the CFD simulations and experiments; the CFD simulations underestimated the liquid separation efficiency by approximately 0.02 over the range of conditions tested.

Considering the new issues human society faces now, environmental issues, and climate change is one of the primary and most essential phenomena which have been caused by the unsustainable lifestyle of men over the last two centuries. Power and energy are some of the leading role players of today’s human lifestyle and one of the most effective in which the environment is affected. This article represents the results of research over the possibility of recovering waste heat and determination of design parameters of a waste heat steam generator for medium speed set of diesel generators, with the rated 42MW capacity and are used for power generation. The main goals of this study are to manage the waste heat of the engines and to help the severe water leakage of the power plant. In this paper, for managing the waste heat, a combined steam cycle is being designed for this process. This system added 19MW the overall electricity generation, and the exergy and energy efficiencies of the system are being increased by 29.2% and 32.8%. Moreover, finally, a geothermal condensing system (GCS) is designed to control the water shortages of the steam power unit condensing system. The GCS condensing system developed in this paper helps to reduce the water evaporation losses in the cooling water by more than 79% compared to the wet cooling towers.

This work presents a technique to improve the thermal performance of an R-32 air conditioner by using ultrasonic waves. Two 1-TR air conditioners — one with and one without 40kHz/50W ultrasonic generators — were tested under controlled conditions in a 3.6m $\times 3.6$m $\times 2.5$m room. The air temperature and humidity conditions entering the condenser and evaporator coils were controlled under 12 conditions to mimic the climate of Thailand. The testing results indicated that the average energy efficiency ratio (EER) of the modified ultrasonic R-32 air conditioner unit was 3.685kW_th/kW_e and the normal R-32 unit without the ultrasonic generators was 3.375kW_th/kW_e. The testing conditions also indicated that the cooling efficiency of the modified system could be increased by approximately 7.69%. Moreover, the convective heat transfer coefficient of the modified ultrasonic R-32 unit was approximately 17.36% higher than that of the normal R-32 unit without the ultrasonic generators because the ultrasonic waves could increase the turbulence in the refrigerant flow and decrease the condensed water at the fan coil unit. In terms of economic results, the payback period of the modified unit based on the climate of Thailand ranged from 0.8–1.2 y, leading to a savings in power consumption of approximately 400–620kWh/y.

The flow characteristics of CO₂ refrigerant are numerically studied for an adiabatic spirally coiled capillary tube employing choked flow conditions. The mass, momentum and energy conservation equations are used to develop a numerical model. The existing model is verified with the published results. The choked flow behavior at various geometric parameters viz. tube diameter and spiral pitch is studied. Similarly, the influence of these parameters on the mass flow rate through the tube is observed. A significant change in mass flow rate is due to a change in tube diameter, whereas a minimal variation is observed with the change in surface roughness and spiral pitch. Moreover, it is observed that the coiling effect has a significant influence on the flow behavior of the spiral capillary tube. As the pressure decreases, from unchoked to the choked pressure in the evaporator by 63.46%, the mass flow rate increases by 9.46% only. The capillary tube choking is circumvented by increasing spiral pitch, tube diameter and decreasing the length of the tube. A unique nomogram is developed that gives the best understanding of choked and unchoked flow conditions, that graphical representation is useful to design the spirally coiled capillary tube. By using that, the choked length is identified for the known mass flow rate, even more, the choked mass flow rate is known for a given tube length. Moreover, for the given tube length and evaporator temperature, a nomogram is useful to the known choked values of mass flow rate and exit values of the evaporator pressure and quality of refrigerant.

This study aims to design an absorption refrigeration system and estimate the heat energy demand. Moreover, this paper investigates the opportunity of using alteration of energy resources such as solar energy. The trough parabolic solar collectors TPC system is suggested and analyzed as a heat energy resource. Actual data of TPC are presented in this work to evaluate the size needed to guarantee enough heat sources that is running the refrigeration system. The outcome of this calculation proved that each 1T.R needs about 11.1kW of heat energy. The COP of the refrigeration system is found to be about 0.313. Moreover, the TPC generates about 100W/m². However, the optimum TPC may generate about 380W/m² in Iraqi climate. This value of heat generated represents the maximum energy at clear sky. The calculations are validated based on experimental and proven data.

This paper presents the performance of a single effect absorption cooling system under three different climates in Saudi Arabia. The considered system capacity is 10.5kW and uses LiBr/water pair. The study results indicated that considering the dynamic response of the cooling cycle significantly increases (close to 30%) the time taken to reach steady-state operations and that the sensitivity of the system to form precipitation of LiBr also increases. Also, the dynamic performance was investigated under different heat inputs and resulted in shorter transient period with increasing the heat input. In addition, the performance of the solar absorption system was investigated for a representative summer day in different climatic regions in Saudi Arabia. The results indicated the requirement of different areas of collectors to meet the absorber heating demand from 09:00 a.m. to 04:00 p.m. if there is no auxiliary heating. Auxiliary heating is required from 04:00 p.m. to 09:00 a.m. Finally, the results indicated that the system performs better in Riyadh city than in Dhahran and Jeddah. This study emphasizes the importance of taking into consideration the thermal inertia of the system components when analyzing the performance of such systems.

An experimental and numerical assessment of multilayer active magnetic regenerators (AMR) composed of gadolinium (Gd) and gadolinium–yttrium (Gd–Y) alloys (Gd${}_{97.34}$Y${}_{2.66}$, Gd${}_{95.98}$Y${}_{4.02}$ and Gd${}_{94.79}$Y${}_{5.21}$) is presented. First, by calculating the adiabatic temperature change and the isothermal entropy change from the experimental data for the above materials, we show that, with reasonable accuracy for engineering design purposes, these properties can be determined by shifting the properties of pure Gd to the Curie temperature of the Gd–Y alloy — a common but not yet validated assumption in the design of Gd–Y AMRs with a low Y content. Next, we show that the optimal Gd–Y layer fraction in multilayer AMRs can be determined using the figure of merit known as the material refrigerant capacity (RC), which agrees well with the results from a more complex one-dimensional thermal non-equilibrium porous medium AMR model. Finally, the performance of the latter model is verified against the experimental cooling power data for two- and three-layer Gd–Y regenerators at temperature spans of 25, 30 and 35K.

Phase change thermal storage is an innovative and promising technology for saving energy. It is one of the new areas of research because it provides the solution to problems related between the provided and the required energies. Paraffin is a common phase change material (PCM) that used in many applications in thermal energy storage (TES) systems. However, the main disadvantage is their low thermal conductivities. However, using metallic additives to improve effective thermal conductivity of PCM can lead to decreasing effective heat capacity and the thermal energy stored. An experimental study is carried out to analyze the thermal behavior of the paraffin melting in a thermal cavity integrating different metals (zamak, aluminum and copper) with different configuration. The originality of study is to try to predict the best duo that respects both the improvement of thermal conductivity and energy stored. The experiments show that adding aluminum perforated plate in paraffin accelerates the melting process by about 19% and increases the energy stored by 5.18%.