Refrigerant Vapor Research Articles

Indoor Room Air Conditioning Using External Enclosure

This paper presents a new air conditioning system using an external air chamber enclosure. The system is based on evaporative refrigeration technique humidifying hot air from the environment by means of a new design humidifier. Temperature at the air chamber is set up according to the required comfort conditions. The air chamber plays the role of a heat collector from indoor room radiative energy. This new system avoids thermal gradient inside the room improving the comfort because of a more homogeneous temperature distribution. Maximum thermal amplitude at the air chamber and indoor room is of 2°C. Theoretical analysis has been developed to determine the refrigeration energy consumption matching values with literature data. Experimental tests have shown a good correlation with theoretical prediction, within accuracy of 7.8%, close to the 8.2 % uncertainty of experimental measurements. A significant reduction in energy consumption has been achieved with COP values up to 4.8 for 31.5°C of ambient temperature. COP increases linearly with ambient temperature and enhances efficiency of air conditioning compression units above 31.5°C, although shows poorer performance below 29°C, what makes the new system especially suitable for hot climates. The result of the evaporative refrigeration at the air chamber has permitted the reduction of daily thermal amplitude from 17°C at the outside, to only 2°C, at the inside. COP of the new system moves from 1.1 to 4.8 within ambient temperature limits, 25.5°C to 31.5°C. Maximum amplitude of temperature at the indoor room has been of 2°C, with a maximum thermal gradient that has not exceeded 0.5°C/m.

Experimental analysis of R410A flow in helically rib-roughened tubes

In this study, an experimental setup was built to investigate the two-phase flow characteristics of R410A refrigerant fluid inside a horizontal internally micro-fin helical coiled tube made of copper. The experimental measurements are carried out with a fixed refrigerant fluid evaporation with temperature equals to 10˚C for eleven mass fluxes values varied from 0.00635 (kg/s) to 0.02150 (kg/s), and the Reynolds number ranged from 6998 to 23,695 covering turbulent flow regime. The heat flux supplied to the micro finned test section was fixed in 10 (kW/m2) and mixture quality at 30% of the vapor phase. The experimental results were accurately measured under the diabatic condition. Friction factor and heat transfer coefficient were obtained experimentally and compared with available literature correlations for smooth and finned tube configurations. Results showed that the presence of internal helical-rib roughness increased friction factor by 27% when compared with a smooth wall, and 5.3% when compared with finned tubes correlation. New correlation to predict the friction factor of R410A refrigerant fluid inside the micro-fin helical coiled tube was developed based on flow patterns and it agrees with experiment data within the deviation of ±0.4%. The heat transfer coefficient shows a minimum average deviation of 10.5% when compared with literature.

Theoretical investigations on the cycle performance of a single-pressure diffusion absorption heat transformer with LiBr–H2O-R134a-TEGDME

A simulation model using the first thermodynamic law is first proposed to estimate the performance of diffusion absorption heat transformer, which could potentially improve energy utilization efficiency and reduce CO2 emission. Thermodynamic analyses are performed to investigate the cycle performance when H2O is employed as refrigerant, LiBr as absorbent for H2O, R134a as diffusion gas and TEGDME as absorbent for R134a. Analyses aim to optimize system COP under specified temperature of two generators, two absorbers, evaporator and condenser, and compare the influence of the six temperatures on COP. The results under design conditions show that larger generation efficiency of R134a and smaller mass fraction of LiBr in H2O–LiBr solution are beneficial to COP improvement, but they are limited by the operating conditions. There is an optimal ratio of H2O–LiBr solution mass flow rate to R134a mass flow rate for an optimal COP, and the optimal ratio decreases with the increase of LiBr mass fraction in H2O–LiBr solution. The highest COP of 0.1701 is reached with the optimal ratio of 1.743. In addition, under design-off conditions, the temperatures of refrigerant generator and evaporator have the greatest influence on COP while the temperature of diffusion gas generator has the least influence. The diffusion absorption heat transformer will provide a new way to lift temperature of low grade heat without electricity input which can further improve the energy utilization efficiency and reduce the CO2 emission.

Development of experimental Nusselt number and friction factor correlations for condensation of R-1233zd(E) in plate heat exchangers

R-1233zd(E), a kind of HCFO refrigerants, has a negligible ODP and a GWP of 1-7, and it is classified as the ASHRAE classification A1 level, which means stable and safe to use in the refrigeration industry. In this study, condensation heat transfer and frictional pressure drop of R-1233zd(E) in three different plate heat exchangers, two brazed types (BPHE-30 and BPHE-60) and a shell-and-plate type (SPHE) are experimentally investigated. Condensation heat transfer coefficient and frictional pressure drop are estimated by varying heat flux from 1.5 kW/m2 to 4.5 kW/m2, saturation pressure from 200 kPa to 300 kPa, mass flux of refrigerant from 13.0 kg/m2s to 26.7 kg/m2s, and mean vapor quality between the inlet and outlet of heat exchanger from 0.25 to 0.9. It is confirmed that the condensation heat transfer coefficient increases with increasing heat flux, mass flux of refrigerant, and mean vapor quality while it decreases with increasing the saturation pressure of refrigerant. Frictional pressure drop increases with increasing the mass flux of refrigerant and mean vapor quality while it decreases with increasing the saturation pressure of refrigerant. On the other hand, the heat flux doesn't have significant effect on the frictional pressure drop. It was found that the BPHE has a higher Nusselt number and lower friction factor than the SPHE, so that the SPHE having excessively high friction factor against Nusselt number is not recommended as a condenser with R-1233zd(E). Finally, experimental correlations for Nusselt number and friction factor are developed with ±25% error range for the BPHE.

Experimental studies on vapour compression refrigeration system using Al2O3/mineral oil nano-lubricant

ABSTRACT Nowadays, in many developing countries like India they are facing the shortage of energy. The Refrigeration system has become the major consumer of energy for many industrial as well as household applications. So, it is the need to enhance the energy efficiency of the refrigeration systems. Performance of the refrigeration system can be improved either by increasing the rate of heat absorption in evaporator or by reducing the compressor power. Use of efficient lubricant oil can help to remove the heat generated in the compression process which leads to less power consumption. Development in Nanotechnology makes it possible to develop a new class of lubricant called nanolubricant, in which nanoparticles are added in base lubricant oil to enhance the thermal properties. The two step technique with ultrasonic agitation force is used to synthesise stable nanolubricant.The present study investigates the performance of a R-134a refrigerant vapour compression refrigeration system using nanolubricant with different volume concentrations (0.05%, 0.075%, 0.1% and 0.2%) of Al2O3 to mineral oil (MO) experimentally. The result shows maximum enhancement in COP approximately as 85% for 0.075 % volume fraction Nano lubricant as compared to base fluid. Use of nanolubricant saves approximately 27% compressor power.

Investigation on the fractional nature of a refrigeration evaporator

The frequency response of an evaporator for commercial refrigeration is investigated to develop a control-oriented model which balances simplicity with accuracy. The dynamics of such devices is highly nonlinear; the response curve was experimentally identified around an operating point by recording the output of the system for several sinusoidal input signals. Among the possible linear approximating models, the collected data turn out to be best fitted with a fractional order transfer function. The proposed identification and process model allow for online tuning at different operating points for an efficient control design.

Condensation heat transfer and pressure drop characteristics of Isobutane in horizontal channels with twisted tape inserts

• Using twisted tapes augmented the heat transfer and pressure drops. • The heat transfer rate enhanced by giving rise to vapor quality and mass flux. • The pressure losses increased by giving rise to vapor quality and mass flux. • The performance factor varied between 0.39 to 1.05 using inserts. The enhancement of heat transfer rate in heat exchangers has been considered a major concern. In this research, the impacts of inserting twisted tapes in horizontal two-phase flow heat exchangers are discussed, and different values of vapor qualities (in the range of 0.1 to 0.7) and mass velocities (in the range of 119 to 367 kgm −2 s −1 ) are considered during forced convective condensation of R600a (Isobutane). The test case is a pipe made from copper with an inner diameter of 8.1 mm and a length of 1000 mm. Furthermore, three twisted tape inserts with various twist ratios (defined as the ratio of the twisted tape pitch to the test pipe inner diameter) of 4, 10, and 15 are used. The results illustrated that installing twisted tapes results in the increment of pressure drops and the rate of heat transfer in comparison to the smooth case. Furthermore, the pressure drops and heat transfer rates augment as the refrigerant mass velocity and vapor quality increase. Depending on the inserts type and operating conditions, the performance factor (a criterion to assess the performance modification compared to the primary test case) between 0.39 to 1.05 was obtained. It was also observed that there exists an optimum amount of the refrigerant mass velocity at which the performance factor is higher. Results showed that generally using twisted tapes in heat exchangers is not instrumental unless when the main concern is to improve the heat transfer rate or when the augmented power consumed by pump can be justified.

Case study of a [formula omitted]He evaporation refrigerator for polarized target experiments

In this work, we propose the use of Computational Fluid Dynamics (CFD) as a useful design tool for the construction and improvement of a vertical 4He evaporation refrigerator. This approach provides a cost-effective solution for improving the performance of such systems designed through the use of traditional heat transfer and fluid mechanics-based relations. To this effect, we applied COMSOL Multiphysics to model an existing refrigerator, which had been built and extensively tested at the University of New Hampshire (UNH). This allowed us to firstly validate our methodology through contrast with reliable empirical data and subsequently to evaluate which modifications can contribute to improved performance. Our CFD based model accurately predicts the cooling power of the UNH design and provides insight into its operation. Moreover, the CFD case study we present here allowed us to propose and evaluate design modifications aimed at minimizing the heat load on the refrigerator.

Energy efficient multiejector CO2 cooling system for high ambient temperature

Experimental evaluation of a multiejector CO2 cooling system of 33 kW cooling capacity is conducted for an Indian supermarket at high ambient temperature context. The test-rig is designed to depict the actual supermarket cooling requirements in India with three different cooling temperature levels simultaneously; freezing, medium refrigeration and air-conditioning. The rig is equipped with a novel design consisting of two multiejectors; low ejection ratio ejector (LERE) and high ejection ratio ejector (HERE), in a series configuration. It is observed that the maximum pressure lift of 5.5 bar is obtained with this new design. Moreover, improvement in the overall system performance with the support of the internal heat exchanger (IHX) is evaluated. Enhancements observed in the maximum COP and PIR are 7.2% and 6.2% respectively. Furthermore, the test-rig performance with the flooding and non-flooding of the medium temperature evaporator (refrigeration) is evaluated. It is observed that the evaporator flooding reduces its superheat at the exit by 83.84%, leading to the overall reduction of PIR by 6.51%. The performance of the proposed system is also compared with the reported field data obtained at a low ambient temperature context. The results projected that the proposed cooling system with series multiejector configuration is a reliable choice for higher ambient temperatures and it is expected to outperform the existing systems at lower ambient temperatures.

Virtual Flow Meter with Energy Balance Method

Keeping the chiller performance at an optimum level is desirable because chiller is one of the energy-consuming equipment in buildings. Chiller is responsible for 40% to 70% of building energy consumption. Therefore, monitoring chiller performance is essential to keep its performance at a desirable level. Knowing chiller performance needs information about the water flow rate. Unfortunately, not every chiller is equipped with the water flow meter. Fortunately, in the last decade, some researchers have been developing virtual flow meters (VFM) to eliminate the need for flow meter equipment. One of the well-known methods of VFM is the energy balance method. There are two types of energy balance methods. Firstly, using theoretical work input to a compressor in calculating energy balance to estimate the flow rate. However, this method needs free-fault data from manufacturer or field measurement to obtain the theoretical compressor work input from a regression analysis. The second method uses actual compressor work input in energy balance analysis. This method needs trend data generated from the building automation system (BAS) for the energy balance analysis. Our research proposes the use of isentropic compressor work input to estimate the water flow rate. The proposed method may eliminate the need for manufacturer or field measurement data or trend data from BAS. The result shows that the comparison with the measurement values indicates that the use of isentropic work to estimate the water flow rate has good accuracy. However, it is sensitive to a low temperature difference in evaporator and condenser and refrigerant overcharged fault.

(Invited) Surface Acoustic Wave Sensors for Refrigerant Leak Detection

Advanced sensors for detection of gases and vapors are required for energy and environmental monitoring. For example, detection of refrigerant leaks from HVAC equipment specifically difluoromethane at low concentrations in air is required. When a refrigerant leak occurs from a HVAC system, there are several consequences, i) reduction in cooling efficiency and ii) higher greenhouse gas emissions to the atmosphere. Sensing refrigerant leaks requires sorbents with high affinity at low partial pressures. Having a highly effective sorbent sensitive to fluorocarbon refrigerant vapors provides a means to develop a sensing device for leak detection. In this regard, Pacific Northwest National Laboratory is exploring novel classes of materials including metal organic frameworks (MOFs), covalent organic frameworks and porous organic cages as a thin film on surface acoustic wave sensor for detection of refrigerant leaks. The structure and selectivity of these materials can be tailored by the selection of various organic bridging ligands used in the synthesis. Further these materials shown to have high surface area and shown to have high gas mobility higher than many other sorbent materials. These characteristics are highly favorable for development sorptive materials for sensing refrigerant molecules from air. Our work in this area suggest these materials reflect a range of sorbent properties from high uptake capacity (over 170 wt%) at high vapor pressures to very high sorption affinities at very low vapor pressures. I will discuss methods to use these materials as a thin film on surface acoustic wave sensor for detection of refrigerant molecules

Assessment of design constraints for the Duplex Stirling Refrigerator with imperfect regeneration

Duplex Stirling refrigerators are the alternative cycles to the conventional vapor refrigeration cycles with their high efficient, low noise, and low emission characteristics. It consists of a Stirling heat engine and a Stirling refrigerator in a mono-block construction that operates by a power piston. In this particular study, the effect of imperfect regeneration on the performance of the duplex Stirling refrigerator is determined analytically while helium is the working fluid. The polytropic heat transfer processes are chosen instead of isothermal processes to get a more realistic approach. Various temperature and compression ratios are taken into account for the refrigerator side of the duplex system and the required compression ratio of the heat engine is determined by using the work equality constraint. The combined effects of the regenerator effectiveness, temperature and compression ratios on the performance of the duplex system are assessed. The results of the parametric analysis are presented in terms of heat removal from the refrigerated space, coefficient of performance of the refrigerator side, work consumed by the system, heat addition to the engine side, thermal efficiency and overall system performance.

Superstructure-Based Optimization of Vapor Compression-Absorption Cascade Refrigeration Systems.

A system that combines a vapor compression refrigeration system (VCRS) with a vapor absorption refrigeration system (VARS) merges the advantages of both processes, resulting in a more cost-effective system. In such a cascade system, the electrical power for VCRS and the heat energy for VARS can be significantly reduced, resulting in a coefficient of performance (COP) value higher than the value of each system operating in standalone mode. A previously developed optimization model of a series flow double-effect H2O-LiBr VARS is extended to a superstructure-based optimization model to embed several possible configurations. This model is coupled to an R134a VCRS model. The problem consists in finding the optimal configuration of the cascade system and the sizes and operating conditions of all system components that minimize the total heat transfer area of the system, while satisfying given design specifications (evaporator temperature and refrigeration capacity of −17.0 °C and 50.0 kW, respectively), and using steam at 130 °C, by applying mathematical programming methods. The obtained configuration is different from those reported for combinations of double-effect H2O-LiBr VAR and VCR systems. The obtained optimal configuration is compared to the available data. The obtained total heat transfer area is around 7.3% smaller than that of the reference case.

Energy performance evaluation of R600a/MWCNT-nanolubricant as a drop-in replacement for R134a in household refrigerator system

Vapour compression refrigerator systems working with R134a are associated with high energy demand and environmental problems and refrigerator consumers’ prioritise energy consumption in choosing their choice of refrigerator systems. Therefore, this research work investigated R600a in MWCNT-nanolubricant (0.4 g/L and 0.6 g/L) as a drop in replacement for R134a refrigerant in a household refrigerator system with varied mass charge of R600a (50, 60 and 70 g). The refrigerator was instrumented at the inlet and outlet of the refrigerator compressor, condenser, expansion valve and evaporator. Two bourdon type pressure gauges were connected to the compressor inlet and outlet of the system. The results were taken and evaluated and compared with the result obtained through R134a refrigerant in the system. The result showed that R600a perform better in terms of COP, power consumption and cooling capacity compared to R134a in the system with lower evaporator temperature of −11°C and power consumption of 0.0639 kW and highest COP in the system. Therefore, R6000a/MWCNT- nanolubricant can serve as a drop in replacement for R134a in the household refrigerator.

PERBANDINGAN COP AC SPLIT KAPASITAS 1 PK MENGGUNAKAN REFRIGERANT R410a DAN R32 DENGAN VARIASI KECEPATAN FAN EVAPORATOR

Air Conditioning Split or AC Split is one of the air conditioning system that works by using a vapor compression system. The vapor compression system is one of the most cycles used for mechanical refrigeration systems, while the vapor refrigerant will be compressed by the compressor as the main component in addition to other components such as condensers, expansion valves and evaporators. This research focuses on AC Split Coefficient of Performance (COP) with Comparison of Refrigerants R410a and R32 with variations speed based on the Evaporator Fan speed. This analysis method uses two AC Split each capacity is 1PK with two different of refrigerants R32 and R410a, as well as varying in Low, Medium and High-level speed with air flow velocity in each mode respectively 1.2 m/s, 1.5 m/s and 1.9 m/s. From the result that COP on R410a refrigerant is 8.13 and COP on R32 refrigerant is 5.3. And also, the efficiency of R410a is 72.8% and R32 is 70.67%. So, AC Split with refrigerant R410a has better COP compared with AC Split with refrigerant R32. Keywords: COP, AC Split, Refrigerants, R410a, R32, Efficiency

Efficiency of the thermodynamic cycle of absorption lithium bromide refrigerating unit with two-stage absorption and three-stage generation of the refrigerant vapor with bound mass flow

Efficiency of the thermodynamic cycle of absorption lithium bromide refrigerating unit with two-stage absorption and three-stage generation of the refrigerant vapor with bound mass flow

KARAKTERISTIK REFRIGERAN MUSICOOL DALAM MESIN REFRIGERASI KOMPRESI UAP MENGGUNAKAN EVAPORATOR GANDA

Musicool is an alternative refrigerant developed as a working fluid in a steam compression refrigeration system. Musicool has many advantages compared to conventional refrigerants, the advantage is that it is environmentally friendly. This study aims to determine the characteristics of musicool 134 on a steam compression refrigeration machine using a double evaporator. The test is done by comparing the characteristics of a single evaporator refrigeration machine and a double evaporator using musicool 134. The research variable is the air flow through the evaporator that is equal to 0.022 kg / s, 0.027 kg / s, 0.033 kg / s. The test data is taken by measuring the temperature and pressure of each component in the refrigeration machine, then using the P-h diagram musicool 134, to determine the performance of the refrigeration machine. The results of the study provide information that the use of a double evaporator will give rise to an improved refrigeration system performance compared to using a single evaporator.

Experimental analysis of magnetic field effects on compressor energy saving cooling system

A research on different refrigerants with and without influence of the magnetic field is provided in this paper. The magnetic field degree viz is four gauss. The condenser exit row was 3000, 6000, 9000 and 12000 gauss. Magnetic fields at condenser exit lines are found to reduce the consumption of the compressor energy. Through applying magnet fields on R134a, compressor energy savings was observed up to 1.35%, 6.23%, 5.40% and 4.19%, respectively, in gauss levels of 3000, 6000, 9000 and 12000, while R152a savings in energy levels were up 13.10%, 15.59% and 25.86% and R407a saving in power up to 7.3%, 9.19%, 13.05% and 12.40%. The coolant R152a saves energy in contrast to other coolant compressors. As the magnetic field strength increases, a vapor refrigeration system decreases the energy consumption of the compressor.

Development of cooling systems using the night-radiation effect

The analysis of the possibilities to use the effect of night radiation (ENR) for additional heat removal from the elements of the cooling system is carried out. The energy prospects of ENR technology for autonomous cooling systems are shown mainly in rural and peasant farms remote from electric energy sources. To increase the energy efficiency of autonomous cooling systems, it is proposed to use absorption water-ammonia refrigeration machines (WARM) and vapor compression refrigeration machines. It is proposed to use the thermal energy of solar radiation for the WARM operation.

Quest for Suitable Storage Condition for Sustainable Processing Quality of Potato Tubers

Processing quality of potato tubers depend on the physico-chemical properties which changes within the time in long-term storage period. The present study was conducted to find out a suitable storage condition that could be able to maintain the processing quality of potatoes. Three potato varieties namely Asterix (BARI Alu-25), Courage (BARI Alu-29) and Lady Rosetta (BARI Alu-28) and three different storage conditions viz. Bamboo chamber (BC), earthen chamber with evaporative cooler (EC) and refrigerator (RF) were used in this study. Data were recorded monthly-basis on the physico-chemical processing qualities of the potato tubers. Potato tubers stored in RF was able to maintain higher dry matter content and lower weight loss, shrinkage and energy content than BC and EC. Though the physical qualities of the refrigerated tubers were well-maintained, but produced considerably higher amount of mean reducing sugars (2.69 mg/g FW) which was 11.6 and 17.9% higher than the mean of BC (2.41 mg/g FW) and EC (2.28 mg/g FW), respectively; and higher mean sucrose contents (2.46 mg/g FW) which was 6.5 and 18.8% higher than the mean of BC (2.31 mg/g FW) and EC (2.07 mg/g FW), respectively. EC maintained significantly lower amount of mean glucose (0.17 mg/g FW), fructose (1.96 mg/g FW) and total soluble sugar (4.20 mg/g FW) contents than BC and RF. Compared to pre-storage, mean reducing sugar content was increased by 1.5, 1.7 and 2.0 times in EC, BC and RF, respectively until 90 days of storage and the increase in mean sucrose content was 1.7-, 2.1- and 2.3-fold in EC, BC and RF, respectively. Among the varieties, Courage and Lady Rosetta were suitable for long-term storage for processing than Asterix. Chips produced from the potatoes stored in the EC acquired significantly higher scores for sensory attributes than that of BC and RF. Results clearly depicted that potatoes stored in EC were more suitable for processing due to moderate retention of dry matter content (22.13%) and lower accumulation of different sugars and were able to retain processing quality up to 90 days of storage than that of BC and RF.
 Ann. Bangladesh Agric. (2019) 23(2) : 61-78