Boiling heat transfer coefficient of R22 and an HFC/HC refrigerant mixture in a fin‐and‐tube evaporator of a window air conditioner

The commonly used refrigerant in unitary type air conditioners is R22 and its phase out schedule in developing countries is to commence from 2015. Many alternatives to R22 are found in published literature in which R407C has similar characteristics to those of R22 except for its zeotropic nature. However, R407C which is an HFC is made compatible with the mineral oil lubricant in the system compressor by the addition of 20% of HC. This HFC/HC mixture called the M20 refrigerant mixture is reported to be a retrofit refrigerant for R22. Though its latent heat value is greater than that of R22, its refrigerating capacity is lower when it is used to retrofit R22 window air conditioners. Hence, a heat transfer analysis was conducted in the evaporator of a room air conditioner, for practically realized heat flux conditions during standard performance testing. The tests were conducted as per the BIS and ASHRAE standards. Kattan–Thome–Favrat maps are used to confirm the flow patterns, which prevail inside the fin‐and‐tube evaporator in the tested operating conditions. It is revealed that the heat transfer coefficient/heat fluxes are poorer for M20 because of the lower mass flow rate and higher vapor fraction at the entry of the evaporator than that of R22 in the prevailing operating conditions. The heat transfer coefficients of the M20 refrigerant mixture under various test conditions are lower in the range of 14% to 56% than those of R22. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20299     

Applications of artificial neural networks for refrigeration, air-conditioning and heat pump systems—A review

In this paper, an attempt has been made to review the applications of artificial neural networks (ANN) for energy and exergy analysis of refrigeration, air conditioning and heat pump (RACHP) systems. The studies reported are categorized into eight groups as follows: (i) vapour compression systems (ii) RACHP systems components, (iii) vapour absorption systems, (iv) prediction of refrigerant properties (v) control of RACHP systems, (vi) phase change characteristics of refrigerants, (vii) heat ventilation air conditioning (HVAC) systems and (viii) other special purpose heating and cooling applications. More than 90 published articles in this area are reviewed. Additionally, the limitations with ANN models are highlighted. This paper concludes that ANN can be successfully applied in the field of RACHP systems with acceptable accuracy.     

Numerical analysis of an air condenser working with the refrigerant fluid R407C

As CFC (clorofluorocarbon) and HCFC (hydrochlorofluorocarbon) refrigerants which have been used as refrigerants in a vapour compression refrigeration system were know to provide a principal cause to ozone depletion and global warming, production and use of these refrigerants have been restricted. Therefore, new alternative refrigerants should be searched for, which fit to the requirements in an air conditioner or a heat pump, and refrigerant mixtures which are composed of HFC (hydrofluorocarbon) refrigerants having zero ODP (ozone depletion potential) are now being suggested as drop-in or mid-term replacement. However also these refrigerants, as the CFC and HCFC refrigerants, present a greenhouse effect.The zeotropic mixture designated as R407C (R32/R125/R134a 23/25/52% in mass) represents a substitute of the HCFC22 for high evaporation temperature applications as the air-conditioning.Aim of the paper is a numerical–experimental analysis for an air condenser working with the non azeotropic mixture R407C in steady-state conditions. A homogeneous model for the condensing refrigerant is considered to forecast the performances of the condenser; this model is capable of predicting the distributions of the refrigerant temperature, the velocity, the void fraction, the tube wall temperature and the air temperature along the test condenser. Obviously in the refrigerant de-superheating phase the numerical analysis becomes very simple. A comparison with the measurements on an air condenser mounted in an air channel linked to a vapour compression plant is discussed. The results show that the simplified model provides a reasonable estimation of the steady-state response and that this model is useful to design purposes.     

Performance comparison of CFCs with their substitutes using artificial neural network

In order to decrease global pollution due to chlorofluorocarbons (CFCs), the usage of HFC‐ and HC‐based refrigerants and their mixtures are considered instead of CFCs (R12, R22, and R502). This was confirmed by an international consensus (i.e. Montreal Protocol signed in 1987). This paper offers to determine coefficient of performance (COP) and total irreversibility (TI) values of vapour‐compression refrigeration system with different refrigerants and their mixtures mentioned above using artificial neural networks (ANN). In order to train the network, COPs and TIs of refrigerants and their some binary, ternary and quartet mixtures of different ratios have been calculated in a vapour‐compression refrigeration system with liquid/suction line heat exchanger. In the calculations thermodynamic properties of refrigerants have been taken from REFPROP 6.01 which was prepared based on Helmholtz energy equation of state. To achieve this, a new software has been written in FORTRAN programming language using sub‐programs of REFPROP, and all related calculations have been performed using this software using constant temperature method as reference. Scaled conjugate gradient, Pola–Ribiere conjugate gradient, and Levenberg–Marquardt learning algorithms and logistic sigmoid transfer function were used in the network. Mixing ratios of refrigerants, and evaporator temperature were used as input layer; COP and TI values were used as output layer. It is shown that R² values are about 0.9999, maximum errors for training and test data are smaller than 2 and 3%, respectively. It is concluded that, ANNs can be used for prediction of COP and TI as an accurate method in the systems. Copyright © 2004 John Wiley & Sons, Ltd.     

Determination of a Vapor Compression Refrigeration System Refrigerant Charge

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Experimental evaluation of the internal heat exchanger influence on a vapour compression plant energy efficiency working with R22, R134a and R407C

Internal or liquid-suction heat exchangers are used in many refrigeration and air conditioning systems based on the vapour compression cycle, with the basic objective of assuring the entrance of refrigerant in liquid phase to the expansion device. This purpose is achieved by exchanging energy between the cool gaseous refrigerant leaving the evaporator and warm liquid refrigerant exiting the condenser. These devices can have positive or negative influences on the plant overall energy efficiency, depending on the working fluid and the operating conditions. In this paper the experimental results obtained from a refrigeration test facility with and without the presence of an internal heat exchanger, using R22, R134a and R407C as working fluids, are presented and analyzed, including the impact of pressure drops and variations of refrigerant mass flow rate. A comparison between experimental and theoretical results is also enclosed.     

Effect of saturation‐temperature on the performance of a vapour‐compression refrigeration‐cycle working on different refrigerants using exergy method

In this study, the behaviour of a vapour‐compression refrigeration cycle, for different refrigerants such as NH₃, R‐12, R‐22 and HFC‐134a was investigated using the exergy method. The cooling load of the plant and the saturation‐temperature of the cold chamber were held constant, whereas the saturation‐temperatures of the evaporator and the condenser were varied from 303 to 313 K and 258 to 248 K, respectively. The irreversibility rates (or exergy destruction rates) of sub‐regions for the whole cycle, using energy and exergy analysis, were determined for each refrigerant. The effects of changes in the saturation‐temperature in the condenser and evaporator on the irreversibility rate of the cycle were obtained for each refrigerant. The relations between the total irreversibility rate of the plant and the irreversibility rate of the condenser and the evaporator were determined for different values of saturation temperatures of the condenser and the evaporator. The COP of the cycle and the rational efficiency were determined for each of the refrigerants and compared with each other. Among the refrigerants used, R‐12 was found to be the most economical refrigerant as compared with the others. Copyright © 2005 John Wiley & Sons, Ltd.     

Energy and exergy analyses of a two‐stage vapour compression refrigeration system

In this paper exergy analysis of two‐stage vapour compression refrigeration (VCR) system has been carried out with an objective to evaluate optimum inter‐stage temperature (pressure) for refrigerants HCFC22, R410A and R717. A thermodynamic model based on the principles of mass, energy and exergy balances is developed for this purpose. The computed results illustrate the effects of evaporation and condensation temperatures, isentropic efficiencies of compressors, sub‐cooling of refrigerant and superheating of suction vapour on optimum inter‐stage saturation temperature (pressure). The optimum inter‐stage saturation temperatures (pressures) for HCFC22 and R410A are proximate to arithmetic mean of evaporation and condensation temperatures (AMT) when assuming superheating of suction vapour and non‐isentropic compression processes in low‐pressure and high‐pressure compressors. The optimum inter‐stage saturation temperatures (pressures) for HCFC22 and R410A are near to geometric mean of evaporation and condensation temperatures (GMT) when it is assumed that cycle involves the effects of sub‐cooling, superheating of suction vapour and non‐isentropic compression of the suction vapour. The optimum inter‐stage saturation temperature (pressure) for R717 is close to GMT irrespective of sub‐cooling, superheating of suction vapour and non‐isentropic compression in the cycle. The efficiency defects, computed corresponding to optimum inter‐stage temperature in condenser is higher in comparison to the other components. Finally, it is deduced that R717 is a better alternative refrigerant to HCFC22 than R410A in two‐stage VCR system. Copyright © 2009 John Wiley & Sons, Ltd.     

Applications of nanorefrigerant and nanolubricants in refrigeration,air-conditioning and heat pump systems: A review

Nanorefrigerants are a special type of nanofluids which are mixtures of nanoparticles and refrigerants and have a broad range of applications in diverse fields for instance refrigeration, air conditioning systems, and heat pumps. In this paper thermal–physical properties of nanoparticles suspended in refrigerant and lubricating oils of refrigerating systems were reviewed. The effects of nanolubricants on boiling and two phase flow phenomena are presented as well. Based on results available in the literatures, it has been found that nanorefrigerants have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional refrigerant. This can be considered as one of the key parameters for enhanced performance for refrigeration and air conditioning systems. Because of its superior thermal performances, latest up to date literatures on this property have been summarized and presented in this paper as well. The results indicate that HFC134a and mineral oil with TiO₂ nanoparticles work normally and safely in the refrigerator with better performance. The energy consumption of the HFC134a refrigerant using mineral oil and nanoparticles mixture as lubricant saved 26.1% energy with 0.1% mass fraction TiO₂ nanoparticles compared to the HFC134a and POE oil system.     

A performance comparison of vapour-compression refrigeration system using various alternative refrigerants

A theoretical performance study on a traditional vapour-compression refrigeration system with refrigerant mixtures based on HFC134a, HFC152a, HFC32, HC290, HC1270, HC600, and HC600a was done for various ratios and their results are compared with CFC12, CFC22, and HFC134a as possible alternative replacements. In spite of the HC refrigerants' highly flammable characteristics, they are used in many applications, with attention being paid to the safety of the leakage from the system, as other refrigerants in recent years are not related with any effect on the depletion of the ozone layer and increase in global warming. Theoretical results showed that all of the alternative refrigerants investigated in the analysis have a slightly lower performance coefficient (COP) than CFC12, CFC22, and HFC134a for the condensation temperature of 50 °C and evaporating temperatures ranging between − 30 °C and 10 °C. Refrigerant blends of HC290/HC600a (40/60 by wt.%) instead of CFC12 and HC290/HC1270 (20/80 by wt.%) instead of CFC22 are found to be replacement refrigerants among other alternatives in this paper as a result of the analysis. The effects of the main parameters of performance analysis such as refrigerant type, degree of subcooling, and superheating on the refrigerating effect, coefficient of performance and volumetric refrigeration capacity are also investigated for various evaporating temperatures.     

Evolving an optimal composition of HFC407C/HC290/HC600a mixture as an alternative to HCFC22 in window air conditioners

Countries that have ratified Montreal Protocol have to phase out HCFC22 in the near future due to its ozone depleting potential (ODP) and hence new eco-friendly refrigerants are being evolved as substitutes. At Present HFC407C is one of the promising drop-in substitutes for HCFC22. But it is immiscible with mineral oil and hence polyol ester (POE) oil is recommended. Since POE oil is highly hygroscopic in nature it is not user friendly. However such oil immiscibility issue of HFC134a has been overcome [M. Janssen, F. Engels, The use of HFC134a with mineral oil in hermetic cooling equipment, Report 95403, No. 07, presented in the 19th International Congress of Refrigeration, The Hague, 1995] by the addition of HC blend to it, which also resulted in performance improvements. In the present work an attempt has been made to study the possibility of using HFC407C/HC290/HC600a refrigerant mixture as a substitute for HCFC22 in a window air conditioner and to evolve an optimal composition for the mixture. Experiments were carried out in a room calorimeter setup fitted with 1050 W capacity window air-conditioner. Condenser inlet air temperatures were held constant at 30, 35, 40 and 45 °C, while evaporator inlet air temperatures were varied over a range viz. 21, 23, 25, 27 and 29 °C during the experimentation. The HC percentage was also varied from 10 to 25% in steps of 5%. The new refrigerant mixtures demand longer condenser length to decrease the high discharge pressure matching with HCFC22 systems and hence the length has been increased while testing the mixtures. This also resulted in better heat transfer in condenser. The performance analysis revealed that the new refrigerant mixture performed better than that of HCFC22. It has in fact been found that the new mixture can improve the actual COP by 8 to 11% and hence it can reduce the energy consumption by 5 to 10.5%. The overall performance has proved that the new refrigerant mixture could be an excellent substitute for HCFC22.     

Performance evaluations of refrigeration systems with air‐cooled,water‐cooled and evaporative condensers

This paper compares the performance characteristics of refrigeration systems employing three types of condensers, namely the air‐cooled, the water‐cooled and the evaporative condensers. Experimental studies were conducted in the same vapour‐compression refrigeration unit operating with a different condenser in each test. It was found that the system with water‐cooled condenser had a higher refrigeration capacity by 2.9–14.4%, and a higher COP by 1.5–10.2% than the one with evaporative condenser. However, the refrigeration capacity and COP of the unit with evaporative condenser were higher than those of the one with air‐cooled condenser by 31.0 and 14.3%, respectively. Copyright © 2004 John Wiley & Sons, Ltd.     

Nanorefrigerant effects in heat transfer performance and energy consumption reduction: A review

The heat transfer performance and energy consumption of various thermal devices may be augmented by active and passive techniques. One of the passive techniques is the addition of nanoparticles to the common heat transfer fluids so that the thermal transport properties of the prepared suspension (called nanofluid) will be enhanced as compared to the base fluid. Nanorefrigerants are a special type of nanofluids which are mixtures of nanoparticles and refrigerants and have a broad range of applications in diverse fields for instance refrigeration systems, air conditioning systems, and heat exchangers. This review is performed in order to clarify the effect of nanorefrigerant properties on heat transfer and pressure drop compared to pure refrigerant. Moreover, studies related to the thermophysical properties, and applications of nanorefrigerants to some specific areas such as domestic refrigerators, heat pipes and air conditioners are also summarized.     

Thermodynamic studies on HFC134a–DMA double effect and cascaded absorption refrigeration systems

The double-effect vapour absorption refrigeration system working with HFC134a as refrigerant and dimethyl acetamide as absorbent is analysed. Cooling coefficients of performance in the range of 0·5–0·9 could be obtained depending on the operating conditions. However, sub-zero temperatures are difficult to obtain at typical heat source and heat rejection temperatures. Hence, cascaded systems are suggested for achieving low temperatures. © 1998 John Wiley & Sons, Ltd.     

Influence of magnetic field on two‐phase flow convective boiling of some refrigerant mixtures

In this paper, an experimental study on the influence of magnetohydrodynamic (MHD) on heat transfer characteristics of two‐phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of MHD on the heat transfer characteristics such as average heat transfer coefficients, and pressure drops of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition. It was also evident that the proposed correlations for predicting the heat transfer characteristics were applicable to the entire heat and mass flux, investigated in the present study. The deviation between the experimental and predicted value using new and improved correlations for the heat transfer coefficient and pressure drop were less than ±20%, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd.     

Optimization of multistage vapour compression systems using genetic algorithms. Part 1: Vapour compression system model

The vapour compression cycle is the most common type of refrigeration cycle in use today. Most vapour compression systems are simple, having only four major components: a compressor, a condenser, an expansion device and an evaporator. Multistage vapour compression systems are more complex with, for example, extra compressors, aftercoolers, intercoolers, flash tanks and liquid‐to‐suction heat exchangers. The study performed here considers 121 different configurations operating at condensing and evaporating temperatures that range from ?50 to 50°C. The refrigerants used are ammonia, R‐22, R‐134a, R‐152a and R‐123. The basis of comparison for the systems is multistage effectiveness. Multistage effectiveness is a novel term defined as the ratio of the coefficient of performance of a multistage system to the collective coefficient of performance of an equivalent group of basic single‐stage systems operating at the same cooling capacities and evaporating and condensing temperatures. Equivalency here is defined on the basis of achieving the same cooling capacity at their respective temperatures as dictated by the multistage systems. The vapour compression system model presented here was put through genetic optimization with interesting results. Copyright © 2001 John Wiley & Sons, Ltd.     

Influence of liquid injection on two‐phase flow convective boiling of refrigerant mixtures

In this paper, an analytical study on the influence of liquid injection on heat transfer characteristics of two‐phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the liquid injection the thermophysical properties of refrigerant mixtures as well as the heat transfer characteristics such as average heat transfer coefficient of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow boiling inside enhanced surface tubing. It was also evident that the proposed correlations and the experimental data that the liquid injection has significant impact on the heat transfer coefficient. In addition, the proposed correlations were applicable to the entire heat and mass flux, investigated in the present study under the liquid injection conditions. The deviation between the experimental and predicted under liquid injection were less than ±20, for the majority of data. Copyright © 2004 John Wiley & Sons, Ltd.     

Two‐phase flow boiling characteristics of alternatives to R‐22 inside air/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two‐phase flow boiling of alternative zeotropic refrigerant mixtures to R‐22, on air/refrigerant horizontal enhanced surface tubing is presented. The new alternatives considered in this study are: R‐507, R‐404A, R‐408A, R‐407C, and R‐410A. The experimental data showed that R‐22 has the highest heat transfer rate compared to the other blends in the range investigated. Furthermore, it was also quite evident from these data that R‐410A has the highest pressure among the blends under investigation for Reynolds number greater than 3.5×10⁴. However, for Reynolds number less than 3.6×10⁴, it appears from the data that R‐22 has the highest pressure drop compared to other refrigerants under investigation. Copyright © 2000 John Wiley & Sons, Ltd.     

Performance evaluation of heat exchanger using alternative refrigerant R407C

R22 (HCFC22) has been widely used as the refrigerant in air conditioners. According to the Montreal protocol for ozone layer protection, the total production of HCFCs has been capped since the beginning of 1996. Zeotropic refrigerant mixture R407C and nearly azeotropic refrigerant mixture R410A have been selected as alternatives to R22. We examined refrigerant passages in heat exchangers used in heat pump‐type room air conditioners using zeotropic refrigerant R407C through simulation, and obtained the following conclusions. In an indoor heat exchanger, a counter flow configuration when operating as a condenser has higher temperature efficiency. When an outdoor heat exchanger operates as an evaporator, a configuration that suppresses the temperature glide by partially reducing the refrigerant passage not only produces high efficiency, but also reduces the frost formation on fins. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 626–638, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10064     

Modelling of an ethanol‐water distillation column assisted by an external heat pump

This paper presents a simulation of an ethanol–water distillation column assisted by a vapour‐compression heat pump. The heat pump is of the external type, i.e., it uses a working fluid (refrigerant) different from that of the column. A simulation model was developed and four different working fluids were studied: R‐11 and R‐114 and, as substitutes, the column own fluids, water and ethanol. Results from the simulation model have shown that considerable reduction in energy consumption can be achieved with the installation of a heat pump. Copyright © 2002 John Wiley & Sons, Ltd.