International Journal of Air-Conditioning and Refrigeration

In hot climatic conditions, increased energy consumption toward cooling has led to the development of evaporative coolers. The performance of evaporative cooler depends on the various material and operating parameters. Type of material selected for cooling pad is the most important factor among them. In this study, various types of cooling pad materials have been discussed based on their potential benefits, influence on the cooling performance like characteristics wettability, porosity, water holding capacity and cost. It is seen that organic- and fiber-based materials have been extensively used, whereas the studies related to materials based on plastics and metals are limited. Ideal material properties to be possessed by a good pad material have been discussed. Prospects and future scope for further research have been identified. Hence, this review paper certainly throws some light on the selection criteria for a potential alternative evaporative cooling pad material that shows the maximum cooling performance and helps achieve sustainable cooling in buildings.

The phenomenon of supercooling, which prevents freezing of water below the freezing point, is an obstacle to the production of inexpensive ice. In the case of ice heat storage systems using bio-preservation, low-temperature refrigeration of food and ice capsules in the HVAC industry, the supercooled water in capsules that indirectly come into contact with the outside is one of the problems that must be solved to maintain energy costs and the quality of food or organs. To improve this, experimental evaluation of additives that serve as crude nuclear agents is needed. However, research on this area needs to be supported because the types of additives are limited and their physical properties are unstable. In this paper, the effect of distilled water containing an additive of average diameter nanometer size on solution (frozen) supercooled below the freezing point was investigated. The supercooling time and supercooling level of each specimen were analyzed after addition of kaolin, strontium hydroxide, oxidizing mineral and nano-sized single-wall carbon nanotubes (SWCNT) as mineral fine particles in the distilled water. As a result, it has been confirmed that kaolin and SWCNT can be used as nuclear materials to release supercooling of water. In addition, when kaolin, a mineral fine particle, is used as a nuclear material, its size affects the performance of nuclearization. This confirmed the impact of nuclear material particle size and structure on overcooled emissions.

The tendency of renewable energies is one of the consequences of changing attitudes towards global energy issues. As a result, solar energy, which is the leader among renewable energies based on availability and potential, plays a crucial role in thoroughly filing global needs. Significant problems with the solar thermal power plants (STPP) are the operation time, which is limited by daylight and is approximately half of the power plants with fossil fuels, and the capital cost. In the present study, a new suggested sketch of adding latent heat storage (LHS) filled with commercial phase change material (PCM) to a 500-kW STPP case study has been investigated. Solar system details and irradiation amounts for a case study, including total and beam radiation have been determined. Also, the theoretical energetic and exergetic analysis of adding PCM storage to STTP is conducted, which showed a 19% improvement in the exergetic efficiency of the power plant to reach 30%. Besides, an optimized storage tank and appropriate PCM material have been investigated and selected concerning the practical limitations of the case study. By designing a new cycle, the LHS will be charged during daylight and will be discharged at night, doubling power plant operation time up to 2500h. Finally, exergoeconomic survey of STPP hybrid with PCM storage was carried out using Engineering Equation Solver (EES) program with genetic algorithm (GA) for three different scenarios, based on eight decision variables, which led us to decrease final product cost (electricity) in optimized scenario up to 30% compared to base case scenario from 28.99 to 20.27 $/kWh for the case study. Also, a comparison is made to demonstrate the effectiveness of the proposed new cycle on 250, 500, 1000, and 2000 kW STTPs.

In this study, the performance of a window-type air-conditioning unit with an alternative, ozone-friendly refrigerant was enhanced by incorporating a nozzle instead of a capillary tube as an expansion device. An experimental evaluation was adopted on a 1.5 RT window-type air-conditioning unit with a controlled environmental zone. According to operating conditions, an ANSYS-Fluent program was used to predict an appropriate nozzle size for a lower pressure ratio. The refrigeration cycle model was simulated using the Engineering Equation Solver (EES).²⁷ The results showed that using a nozzle of 30mm length and inner and outer diameters of 9 and 2mm, respectively instead of the capillary tube with R404A reduces compressor power consumption by 7.7% and increases the coefficient of performance (COP) by 7.4%.

Short-fiber reinforced polymer composites have been widely used in industrial applications due to high strength-to-weight ratio, versatile manufacturing process, and etc. The alignment of fiber type additives plays an important role in the mechanical properties of a composite material. In this paper, an injection molding process was imitated with a liquid polymer composite flow inside a $90^{\circ }$ elbow channel. We performed a flow visualization experiment and analyzed the additive alignment of carbon fiber flowing in the polydimethylsiloxane (PDMS) medium. By analyzing the flow visualization images, the angle changes at the corner region of the elbow channel were calculated. At the corner region, the change of passage direction leads to the change of fiber orientation. It was observed that near to the convex region, fibers have angle change values larger than the fibers traveling near to the concave region.

In this work, the performance of an existing algebraic solution for adiabatic coiled capillary tubes, in subcritical cycles, is investigated. However, the C-M&N friction factor, commonly used, was replaced by Schmidt friction factor, which is less complex. Two existing dimensionless correlations were also evaluated for comparison. To assess the effect of altering the friction factor, experimental data collected in the literature were used as reference. Analyzing the present results and that with C-M&N friction factor, it was observed that adopting the Schmidt friction factor does not cause a relevant impact on the solution. The deviations of the predicted versus experimental mass flow rates were comprised in a range between –8% and 12%, with average deviation (AD), absolute average deviation (AAD) and root mean square (RMS) error of –0.1%, 2.7% and 3.4%, respectively. The empirical correlations presented unsatisfactory results, with maximum deviation around 40%. Therefore, it was concluded that using the Schmidt friction factor is adequate to reduce the complexity of the algebraic solution and to maintain the accuracy.

The present study investigates the water retention behavior in two different types of porous media, i.e., porous metal — a type of metallic foam and ideal geometry. The present study uses computational fluid dynamics (CFD) to model a decreasing water level in a reservoir consisting of a stationary porous medium beneath the water surface at initial stage. It mimics the setup of dynamics dip-testing which measures the amount of retained water for different types of fins-tubes heat exchangers. The study varies parameters like static contact angle (${\theta }_s$) and drainage velocity ($U$). The literature review summarizes the unique water retention behaviors for different types of heat exchangers and the findings of the present study. Furthermore, the present study proposed new parameters for evaluating the structural variations in porous metal that explains the water saturation distribution in detail. The evaluation method could provide an insightful idea for performing the quality control check on metallic foam.

Ordinary refrigeration systems such as vapor-compression refrigerators are the commonly used devices in industry, mostly for their high efficiencies. However, they make a significant contribution to the depletion of Ozone and global warming due to their operational refrigerants. Hence, thermoacoustic refrigeration can be a great alternative candidate which uses inert gases such as air, helium and nitrogen as the primary refrigerant. Thermoacoustic refrigerators convert the acoustic power (sound waves) into a thermal effect (cooling power). Thermoacoustics can be counted as a new technology that has a strong potential toward the development of the thermal applications. This study aims to design and fabricate miniaturized traveling wave thermoacoustic refrigerator which can be driven by an ordinary loudspeaker. The optimized numerical design of the refrigerator shows an overall efficiency (cooling power over input electricity) of nearly 66% at a temperature difference of 25K (between cold and ambient heat exchangers). The maximum estimated cooling power is 65W at coefficient of performance (COP) of 2.65.

This work conceives the performance of vapor compression cascaded refrigeration system (CRS) from the exergy, safety and thermal inventory points of view employing the theory of effective temperature ($T_{\mathrm{\text{eff}}})$ than environment temperature ($T_o)$ in Gouy–Stodola equation. Comparative results show that the actual irreversible loss in CRS is 8.1% higher. Further, advanced exergy analysis results showed that 17.985kW irreversible loss (out of 33.737kW irreversible loss) in the system is evadable with improvement in the system design. Besides, the vulnerability of toxic fluid R717 is reported in terms of the total risk level. Moreover, the economy matter is expressed in terms of its total thermal inventory. At the base case, total risk level and total thermal inventory are determined to be 454.3 US$ and 48.86kW/K, respectively. First, sensitivity analysis is carried out to evaluate the variation in irreversible loss, total risk level and thermal inventory at different evaporator and condenser temperatures with different degrees of overlap (decision variables). A total of nine simulations are designed using the Taguchi technique. Later, multi-objective optimization is employed. The optimization process reduced the total irreversibility and annual risk level of CRS by 10.2% and 8.9%, respectively, with 6.8% increase in thermal inventory.

Small rotary compressors are used in domestic heat pump appliances, for example, in domestic dehumidifiers and heat pump clothes dryers. Compressor performance curves provided by the manufacturer can be based on testing at relatively high ambient temperatures, in some cases as high as 35^∘C. This can be much higher compared with the ambient temperature in which the compressor operates when, for example, it is installed in a domestic dehumidifier which can operate in ambient temperatures as low as 10^∘C.

We have developed a compressor calorimeter to test a small R134a rotary compressor extracted from a commercial domestic dehumidifier and use this to measure compressor performance parameters including the isentropic and volumetric efficiencies and the compressor heat loss fraction. The performance testing has been carried out at ambient temperatures 10^∘C, 15^∘C, 20^∘C and 25^∘C for a fixed relative humidity of 70% to compare how the compressor performance varies with the ambient temperature, and to determine how well the compressor performs outside of the performance envelope provided by the manufacturer. The results show that isentropic and volumetric efficiency of these small compressors is relatively insensitive to variation in ambient temperature, even outside of the performance envelope provided by the manufacturer. However, the compressor heat loss fraction can, on average, double from 15% to 30%, between operation at ambient 25^∘C and ambient 10^∘C.

The data obtained in this work is used to construct compressor sub-models for certain ambient temperatures. We show how these sub-models can be used to improve a domestic dehumidifier model for operation at low ambient conditions within the evaporator frosting regime and good agreement is obtained between experimental and simulated data. The authors are not aware of a domestic dehumidifier model designed to work at ambient temperatures within the frosting regime.

This paper presents the analysis of a modified vapor compression cooling system which uses an ejector as an expansion device. Expanding refrigerant in an ejector enhances the refrigeration effect and reduces compressor work. Therefore, it yields a better coefficient of performance. Thermodynamic analysis of a constant area ejector model has been done to obtain primary dimensions of the ejector for given condenser and evaporator temperature and cooling capacity. The proposed model has been used to design the ejector for three refrigerants; R134a, R152a and R1234yf. The refrigerant flow rate and the diameters at various sections of the ejector have been obtained by doing numerical modeling in Engineering Equation Solver (EES). Refrigerant R1234yf demanded the highest diameter requirements at a fixed 5^∘C evaporator temperature and 40^∘C condenser temperature for a given range of cooling load. Both primary and secondary refrigerants flow rates are higher for R1234yf followed by R134a and then R152a.