International Journal of Air-Conditioning and Refrigeration

The refrigeration system based on the conventional compression cycle consumes an enormous amount of high-grade energy. Using fossil fuels as the energy sources results in the addition of CO₂ into the atmosphere and consequently stimulating higher greenhouse effect. The ejector refrigeration systems powered by renewable energy sources would be an effective alternative without increasing global CO₂ footprint. In this study, the performance characteristics of a solar ejector refrigeration system working with R718 are analytically calculated by using a one-dimensional flow model. At the critical mode, the solar ejector-refrigeration system is analyzed at various working conditions such as condenser temperature, evaporator temperature, generator temperature, and ejector area ratio. The critical system performance is analyzed to meet any designated working conditions with a wide range of condenser temperatures. It is found that during the critical mode of operation, higher area ratio, higher evaporator temperature and lower generator temperature enhance the performance of the system. The minimum evaporator temperature, and the maximum generator temperature designed to acquire the required coefficient of performance value are also calculated.

Desiccant cooling mechanism is one of the alternate methods to control the humidity of air and temperature, compared to the conventional vapor compression method of air conditioning. Desiccant cooling doesn’t use harmful chemicals which effect the ozone layer and it saves lots of energy. Summer air condition system can use this technology since it removes the latent heat load from the room effectively and this process is economical. Selection of the appropriate liquid desiccant and packing material is very vital to obtain maximum dehumidification. This paper focuses on the different desiccants and packings used by different researchers to enhance the dehumidification. Simple and hybrid systems are also reviewed, and their comparison are presented based on the construction and dehumidification performance.

Three hydrocarbons are considered as refrigerants for solar absorption air-conditioner. The cooling plant is composed essentially of the absorption chiller and the solar system is simulated with three working pairs: propane/octane, butane/octane and iso-butane/octane. Results are compared to those of ammonia/water mixture at the same fixed operating conditions and assumptions. The main advantages of the investigated refrigerants are their similar cooling effect compared to ammonia with a coefficient of performance reaching 0.63 and their relatively low working pressures. Nevertheless, the circulation ratio for hydrocarbon mixture is higher compared to ammonia. Propane/octane working mixture seems to be suitable for solar absorption air-conditioners with some particular precautions. The heat required to drive the absorption system is provided by evacuated tubes solar collectors of 90m², a value in agreement with commercialized solar absorption air-conditioner operating with ammonia.

The utilization of ice slurry as a pumpable phase-change material has been getting a lot of attention in research and development discourses. This study attempted to investigate the rheological characteristics of ice slurry at different freezing-point depressants through experiments. Ice slurry was formed by mixing water and different freezing-point depressants (monoethylene glycol, ethanol, and sodium chloride) at a 20% initial concentration. Rheology tests were conducted on the transition from laminar to turbulent flows in a circular pipe. The inner dimension of the pipe was 12.7mm in diameter, while the ice mass fraction varied in between 0–28% depending on storage time of ice slurry. Experimental results showed sodium chloride ice slurry to have a higher pressure drop and friction factor compared to those of monoethylene glycol and ethanol ice slurry ones at the same initial concentration and ice mass fraction level. In general, ice slurry was discovered to behave as a Newtonian fluid at 10–15% ice mass fractions, as a shear thinning fluid at 15–20% ice mass fractions, and a shear thickening fluid at 20–28% ice mass fractions. Later, experimental data of shear stress were compared to Ostwald–deWaele and Herschel–Bulkley models based on Mellari method. In fact, a modified Herschel–Bulkley model for monoethylene glycol ice slurry showed a close agreement with experimental data with 4.7% mean deviation. In addition, the experimental viscosity data were compared to the Einstein, Jeffrey, Kunitz, Guth, Steimour, Vand, Mooney, Simha, Happel, Ford, Thomas dan Morio–Ototake models. The best fit was only produced with Morio model for values at low ice mass fraction ($X_{\mathrm{\text{is}}}<15$%).

The fast evolving Electric vehicles (EVs) have become popular due to their zero-emission, fuel economy and better technology. However, the performance and life of batteries are very sensitive to temperature, it is important to maintain the proper temperature range. The battery thermal management system (BTMS) plays an important role in the performance of EVs. In this context, this study is conducted to evaluate the thermal performance of a battery with a parallel system using an induction heater. The GT-Suite software is used for simulation and evaluation. Mixture of water and ethylene glycol 50:50 is used as a working fluid and controlled by pump and valves. The heating rate of battery was analyzed by changing the capacity of induction heater 2, 4 and 6kW and the flow rate of fluid was 2, 3, 5, 7, 10 and 27 LPM. The simulation work predicts that the battery heating rate increases with the increase in fluid flow. The study concluded that the battery heating rate is maximum with a flow rate of 27 LPM which is the highest amount of LPM, indicating that the rise in flow rate causes the increase in heating rate of the system which is also affected by induction heater capacity.

This study introduces the design of a novel condenser for air conditioning systems. Enhancement of performance of the system was manifested by increasing the coefficient of performance (COP), decreasing the pressure drop and the power consumed by the refrigerant compressor and the cooling water pump. The design consists of an adiabatic double-pipe heat exchanger with longitudinal rectangular fins. This model can enhance heat transfer coefficient and expose more area per unit length. This novel design supersedes other conventional condenser designs by 4.7% higher COP, 8.2% lower water pressure drop, 4.68% lower compressor power. Two refrigerants have been examined in the study; R-134a which is used in commercial and industrial chillers and R-1234ze which has low global warming potential.

The borehole thermal energy system, KINTEX, located in Ilsan, South Korea was simulated using TRNSYS. The effect of the depth and spacing of the boreholes in this Borehole Thermal Energy Storage (BTES) system on the average stored energy and ground temperature were investigated over three years of its operation. Borehole thermal energy storage was simulated using the Duct Ground Heat Storage Model built in TRNSYS. The BTES system is composed of solar collectors, a heat exchanger, borehole thermal energy storage, and a thermal storage tank. The effects on the internal energy of the system were investigated by varying borehole depth and spacing while the volume and number of boreholes were kept constant. The total number of boreholes is 90 and all boreholes are connected in series. The borehole depths varied from 40 to 47.5m with steps of 2.5m, and the borehole spacing varied from 2.5 to 4.0m while the total volume of the BTES was maintained at 21,236 m³. The internal energy stored ranged from 1528.91 GJ to 1618.69 GJ over three years of calculations. With an increase of borehole depth and associated decrease of borehole spacing, the internal energy increased and ground temperatures approached 35^∘C over a simulation period of three years.

A thermodynamic steady-state model for a single-effect lithium bromide–water (LiBr-H₂O)-based vapor absorption refrigeration system of 17.5kW capacities has been presented using the first and second laws of thermodynamics. The mass, energy and exergy balance equations in each component of the vapor absorption cycle have been fitted into a computer program to carry out the calculation using the thermo-physical properties of the working fluid. The performance parameters such as coefficient of performance (COP), exergy coefficient of performance (ECOP), total exergy destruction (TED), etc. have been evaluated considering different temperatures in generator and evaporator, different LiBr concentrations in the weak and strong LiBr-H₂O solution and different solution heat exchanger effectiveness. The model evaluated the optimum performance parameters like COP, ECOP, TED, etc. of the vapor absorption system by using Design Expert-12 software for an application like on-farm cooling or transit storage of fruits and vegetables.

The coefficient of performance (COP) and relative coefficient of performance (COPR) of the standing wave thermoacoustic refrigerator (SWTAR) were investigated. The components of the SWTAR are a resonator tube, a stainless-steel bowl-shaped resonator cone, a commercial loudspeaker, a spiral stack, a cold side heat exchanger (CSHX) with miniature heat pipes (MHPs) and a hot side heat exchanger (HSHX). An operating frequency of 163Hz was used in this study, with an acoustic power (AP) supply of 10, 20 and 30W. Cooling loads were heat provided from a thermoelectric module (TEM) by joining the hot side of the TEM to the copper heat absorber and transferring heat to the CSHX through MHPs. The COP of the SWTAR increased with increasing cooling load. The slopes of the COP curves decreased with increasing AP. The COPR of the SWTAR increased with increasing cooling load until it was approximately 30% of AP.

Inverter air conditioners are being widely used in the air conditioning sector for energy saving purposes. These air conditioners use an inverter or a variable frequency drive (VFD) to control the compressor operating speed based on cooling or heating load fluctuations. If the heat generated by the electronic components of the VFD is not dissipated properly, it can lead to failure of the VFD. In general, a heat sink is used for dissipating the heat generated by the electronic components of the VFD. The heat sink can be either air cooled or liquid cooled. Using computational fluid dynamics (CFD), this paper deals with optimization of the thermal performance of an air cooled plate-fin heat sink with rectangular fins used in a residential split inverter air conditioner. Commercially available CFD tool has been used for simulations. It has been observed that enhancing fluid flow around the heat sink and improving heat transfer area of the fins significantly improve the thermal performance of the heat sink. By using heat sink with rectangular fins having a stepped profile, it has been possible to improve the heat transfer from the baseline case by 27%. Whereas, by using hollow fins, heat transfer improvement of 20% has been achieved.

A conditioning dehumidifier system is a simple technology to improve air quality and also reduces air conditioning costs. This experimental study evaluated the performance of a liquid desiccant system by adding copper oxide nanoparticles (NPs). The effect of operating parameters, such as inlet air humidity ratio and desiccant flow rate on air dehumidification rate, was also investigated. The desiccant solution contained 48wt.% CaCl₂ and 0.35vol.% of CuO NPs. Comparison of liquid desiccants demonstrated a mean difference of 4.5g/s$\cdot$m² in the air dehumidification rate by solutions with and without CuO NPs.