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In this article, detailed work on the heat transfer and fluid flow behavior of carbon-based hybrid nanofluid (multi-walled carbon nanotubes + graphene nanoplatelets/H2O) was studied numerically. The carbon-based hybrid nanofluids have been prepared experimentally and their measured properties were used for this study. The numerical study was carried out by passing the nanofluids under laminar flow through the tube side of the microchannel heat sink (MCHS). A constant heat flux on the heat sink base was applied and a single-phase model approach was used for analyzing the heat transfer. The nanofluid volume concentration varied from 0.01% to 0.2%. The improvement in the heat transfer coefficient is observed to be a maximum of 73%, with a maximum of 18% pressure drop variation across the MCHS for 0.2 vol%. The pressure drop variation across the MCHS is minimal for all the considered volume fractions of the nanomaterials. The results confirmed that the hybrid nanofluid possesses a remarkable heat transfer characteristic for transporting heat effectively. [ABSTRACT FROM AUTHOR]

A widely used hydrochlorofluorocarbon (HCFC) refrigerant HCFC‐22 in the split air conditioner (AC) is being phased out in all countries under the Montreal Protocol. Propane (HC‐290) is a favorable substitute for HCFC‐22. The performance, environment impact and cost‐benefit analysis of a split AC unit operated with HCFC‐22 and HC‐290 has been carried out experimentally under different test conditions prescribed by IS 1391. The results showed that the variation in system performance was more significant for HCFC‐22 than for that of HC‐290 while varying the refrigerant charge. The experienced optimum charges that represent the maximum coefficient of performance (COP) was varied with the working environment and it was realized that, generally the optimum charge for HC‐290 was 50% lesser than that of HCFC‐22. The COP of the AC unit with HC‐290 was observed to be 5% more than that of HCFC‐22. However, the system capacity diminished by 7.8%. The operation of a split AC unit with HC‐290 produced up to 15.9% lesser CO2 emission than that of HCFC‐22 under all the test conditions. The use of HC‐290 in an existing HCFC‐22 split AC system can save up to 12.22% of the life time total cost. Finally, it was inferred that the replacement of HCFC‐22 with HC‐290 in the split AC unit showed dominance in all aspects such as performance, emission, and life time total cost. [ABSTRACT FROM AUTHOR]

HC-290 is a promising alternative for HCFC-22, which is an ozone depleting substance under Montreal Protocol. However, HC-290 charge is to be reduced because of its flammability. The objective of this study was to reduce the charge quantity of HC-290 in a split air conditioner, which was originally designed for HCFC-22. The effect of charge reduction on the performance of the HC-290 split air-conditioning system was studied experimentally by varying condenser tube diameter, length of capillary tube, and condenser air face velocity. Initially, simulation study was conducted using ART simulation software. In accordance with the simulation results, a 5.25 kW split air conditioner was modified and experimentally tested with HC-290 in a psychrometric test facility under standard test conditions as per IS 1391 part 2. The condenser tube diameter was reduced from 12.7 mm to 6.35 mm, while the length of capillary tube was increased from 650 mm to 820 mm with enhanced condenser air face velocities. It was found that with 300 g of HC-290 charge, the performance parameters such as cooling capacity, power consumption, and coefficient of performance were better than the baseline test with HCFC-22 in all conditions tested. [ABSTRACT FROM AUTHOR]

The performance comparison of two automotive air conditioning systems was experimentally studied under two typical cabin conditions viz; 27°C dry bulb temperature / 40% relative humidity and 40°C dry bulb temperature /40% relative humidity in a bench test rig for different blower speeds of the evaporator. Two mobile air conditioning systems viz; enhanced system having minichannel evaporator with integrated receiver-dryer condenser, and baseline system having conventional serpentine evaporator with parallel flow condenser were considered for the study. The compressor was the same for both the systems. The charge quantity, compressor speed, condenser air flow rate were suitably modified to maintain similar suction / discharge pressures, suction super heat and sub-cooling at all test conditions. The percentage of condensate retention during the dehumidification for both the evaporators were also compared. The comparison indicates that the average coefficient of performance of the enhanced system is higher in both low and high cabin temperature condition by about 15% and 8% respectively. The percentage of condensate retention in the evaporator of the enhanced system is lesser in the range of about 17–31% as compared to the base line system evaporator. It is also expected that a specific design of compressor for the enhanced system can yield better performance at all conditions. [ABSTRACT FROM AUTHOR]

Polyalkaline glycol is used as the lubricant with R134a in automobile air conditioning systems and it is well known that polyalkaline glycol oil is highly hygroscopic in nature. Presence of moisture in the system may deteriorate the system and its performance. Hence polialkaline glycol oil is replaced with conventional mineral oil. In the present study, a new refrigerant blend R134a/R290/R600a with mineral oil as lubricant has been tested in an experimental test rig with R12 as base line and compared with the published results. Pull down test from an average cabin temperature of 50 °C is performed while the compressor speed is varied successively from 1500-2250-3000-800 rpm with a constant heat load of 2500 W, and held at that speed for duration of 30 minutes. Both R12 and the HFC-HC blend is tested in an experimental test rig and it has been found that this new mixture is almost in par with R12, However, a slight loss in system performance is encountered. But, considering the service issues associated with R134a and polyalkaline glycol oil, this new mixture can have better performance than R134a and polyalkaline glycol combination. [ABSTRACT FROM AUTHOR]