Halocarbon Refrigerants Research Articles

An Evaluation of Correlations for Predicting the Heat Transfer Coefficient during the Condensation of Saturated and Superheated Vapors Inside Channels

Condensation heat transfer is involved in many industrial applications. Therefore, it is important to know the relative accuracy of the available methods for predicting heat transfer. Condensation can occur with saturated as well as superheated vapors. Predictive methods for both conditions were evaluated using a wide range of data. Twelve well-known correlations for the condensation of saturated vapor, including the most recent ones, were compared with data for 51 pure fluids and mixtures from 132 sources in horizontal and vertical channels of many shapes. Channel hydraulic diameters were 0.08–49 mm, the mass flux was 1.1–1400 kg/m2s, and the reduced pressure range was 0.0006–0.949. The fluids included water, CO2, ammonia, hydrocarbons, halocarbon refrigerants, various chemicals, and heat transfer fluids. The best predictive technique was identified. The three most commonly used models for heat transfer during the condensation of superheated vapors were studied. They were first compared with test data using measured saturated condensation and forced convection heat transfer coefficients to select the best model. The selected model was then compared with test data using various correlations for heat transfer coefficients needed in the model. The best correlations to use in the model were identified. The results of this research are presented, as are recommendations for use in design.

Improved correlation for heat transfer during condensation in inclined tubes

Condensers with inclined tubes (i.e. inclinations other than horizontal and vertically downwards) are used in many applications. Hence accurate prediction of heat transfer in inclined tubes is needed. The author had earlier published a correlation which was in good agreement with the limited data available then. Data from many more experimental studies has become available now. A new correlation has been developed considering all available data which gives better quantitative and qualitative agreement than the author's earlier correlation. The data correlated includes 10 fluids (water, halocarbon refrigerants, and chemicals), tube diameters 0.5 mm to 40 mm, orientation −90° to +90°, reduced pressures 0.0046 to 0.886, mass flux 1 to 1360 kg m−2 s−1, and qualities 0.1 to 0,96. The data are from 15 studies. The 1645 data points are predicted with mean absolute deviation of 17.7%. The development of the new correlation is described and detailed comparison of data with the correlation is presented.

Detection of gaseous halocarbon refrigerants and extinguishing agent based on photoacoustic spectroscopy

A photoacoustic (PA) gaseous halocarbon refrigerants and extinguishing agent detector based on a mid-infrared broadband source was developed. H1301 (extinguishing agent), R134a and R410A (refrigerants) were the target gases. A mid-infrared thermal radiation source radiated along the longitudinal direction of the cylindrical PA cell and was reflected by a gold-plated mirror to excite PA signals. The concentrations of CO2 and H2O were measured to reduce their interference. The PA signals of H1301, R134a, R410A, CO2 and H2O were excited by using a thermal radiation source with five different optical filters, respectively. The fundamental-frequency intensity modulation (1f-IM) technique was used to measure the generated PA signals. The detection limits (1σ) of H1301, R134a and R410A were 49 ppb, 80 ppb and 211 ppb with an average time of 100 s, respectively. According to the absorption spectrum of the three target gases, there are strong cross interference around the wavelength of 8.5 µm. By using the proposed calculation method to obtain the concentrations of the target gases, the high cross interference among these gases is reduced to less than 2 %.

Effect of halocarbon refrigerants as working fluid of the heat pipe for thermoelectric power generation

This study investigates the effect of a refrigerant in a heat pipe for thermoelectric power generation (TEG). R22, R32, R134a, and R410a were used as working fluids. A water bath was used to heat the hot side of the TEG, and a heat pipe was used to cool the cool side of the TEG. Eight high-performance TEGs connected in series were used in this study. The heat-absorbing section of the heat pipe was the evaporator while at the top section was the condenser. The experiment tested ten conditions of the hot-side temperature of the TEG as 35, 40, 45, 50, 55, 60, 65, 70, 75, and 80 °C. In each testing condition, the necessary parameters were collected, such as the hot-side and cool-side temperature of the TEG, the inlet and outlet of the cooling air of the heat pipe condenser, the temperature of the heat pipe condenser and heat pipe evaporator, the voltage, and the current generated by the TEG. The necessary parameters were used to investigate the power generation of the TEG module, which is related to the hot-side temperature of the TEG. Multiple linear regression was used to investigate the relation of TEG power generation. The result was found that the power generation of the TEG was in direct relation to the hot-side temperature of the TEG, for which the correlations are reported. The average power generation of R410a, R22, R134a, and R32 is 45.4, 46.3, 49.5, and 62.7 mW, respectively. Finally, it can be concluded that the halocarbon refrigerant of the heat pipe has a significant effect on the TEG power generation.

New general correlation for heat transfer during saturated boiling in mini and macro channels

A new correlation is presented which was verified with a very wide range of data for plain mini and macro channels. The data include 42 fluids (water, halocarbon refrigerants, hydrocarbons, carbon dioxide, ammonia, cryogens, chemicals) in single and multi-channels of diameter 0.38 mm to 41 mm, of various shapes (round, rectangular, triangular), partly or fully heated, in horizontal and vertical orientations. Reduced pressures varied from 0.0046 to 0.787 and mass flux from 15 to 2437 kgm−2s−1. The 10387 data points from 111 sources were predicted with mean absolute deviation (MAD) of 18.8%. The same data were also compared to 17 other correlations. The present correlation was found significantly more accurate than others. The results of this research are presented and discussed.

Prediction of heat transfer in evaporation of saturated falling films on bundles of horizontal tubes

Falling film evaporators consisting of bundles of horizonal tubes are widely used in many applications including refrigeration, chemical processing, desalination, etc. While many experimental studies have been done, as yet there is no well-verified method for the prediction of heat transfer. The research reported here was done to fulfill this need. A correlation is presented for heat transfer before occurrence of CHF which has been verified with a wide range of data from 12 sources. The data include plain and enhanced tubes of many types and materials, diameters 15.9 to 25.4 mm, P/D 1.1 to 2.0, liquid film Reynolds number from 43 to 6449, and heat flux from 1 to 94 kWm −2 . Included are eight diverse fluids (water, halocarbon refrigerants) with reduced pressures from 0.000046 to 0.172. The correlation predicts 2708 data points with mean absolute deviation of 17.4%. The correlation and its verification are presented and recommendations are made for its use.

A general correlation for heat transfer during evaporation of falling films on single horizontal plain tubes

Falling film evaporators are widely used in many industries including desalination, petrochemical, and refrigeration. Hence ability to correctly predict heat transfer in these evaporators is important. While many prediction methods have been proposed, none has been validated with data from many sources covering a wide range of parameters. Hence there is a need for a well-verified general correlation. This research was done to fulfill this need. A correlation has been developed for heat transfer coefficient of single horizontal tubes with falling film evaporation. It is shown to be in good agreement with data from 22 sources that cover a very wide range of parameters. Included in the data are 11 fluids (water, ammonia, halocarbon refrigerants, hydrocarbons), tube diameters from 12.7 mm to 50.8 mm, heat flux from 1 to 208 kWm−2, and liquid film Reynolds number 19 to 10,734. A total of 1237 data points are predicted with a mean absolute deviation of 17.4%. The new correlation is presented together with details of its verification.

Heat transfer during condensation in corrugated plate heat exchangers

Abstract Prediction of heat transfer during condensation in plate heat exchangers is of much practical importance as they are widely used in many applications including refrigeration. While many correlations have been published, there has been no comprehensive evaluation by comparison with a wide range of data from many sources. The research reported here was done to fulfil this need. Analyzable data from 25 sources were collected and compared to 11 published correlations. The data included chevron angles from 30 to 75 degree, 18 fluids (water, ammonia, hydrocarbons, halocarbon refrigerants), reduced pressure from 0.0083 to 0.8, and mass flux from 2.3 to 165 kgm−2s−1. Two of the published correlations gave fairly good agreement while other correlations had much larger deviations. A new correlation was developed by modifying the Longo et al. correlation. The new correlation is more accurate and is easier to use. Its mean absolute deviation is 19.5% for chevron angles 40° to 65°.

Understanding the market need for skills in alternative refrigerants with low global warming potential in the EU region – A comprehensive survey on Refrigerant Emissions And Leakage (REAL) alternatives programme

The widespread adoption of low GWP alternative refrigerants across Europe is critical to achieving long-term carbon reduction emissions from the Refrigeration, Air Conditioning and Heat Pump (RACHP) sector. The RACHP sector has been identified as being responsible for significant greenhouse gas emissions through direct emission (leakage of high GWP refrigerants) and indirect emissions (energy use). The changes to EU's Fluorinated greenhouse gases (F-gas) regulation No 517/2014, which came to force since 1st January 2015, has enacted restrictions on the use of halocarbon refrigerants in certain applications with the intent of reducing the F-gas associated emissions in the EU region. There are currently inconsistent levels of knowledge and awareness of how alternative refrigerants can be sustainably procured and utilised. This paper provides an understanding of the needs for skills in some European countries, specifically covering the general overview of the “as installed“ RAC use, the current training provision, the potential use and status of alternative refrigerants and recommendations on procurement process. Furthermore, the paper discusses the availability of skills and existing training materials and template in specific European countries.

HFO1234ze(e) As an Alternative Refrigerant for Ejector Cooling Technology

The paper presented a mathematical assessment of selected refrigerants for the ejector cooling purpose. R1234ze(e) and R1234yf are the well-known refrigerants of hydrofluoroolefins (HFOs), the fourth-generation halocarbon refrigerants. Nature working fluids, R600a and R290, and third-generation refrigerant of halocarbon (hydrofluorocarbon, HFC), R32 and R152a, were selected in the assessment. A detail mathematical model of the ejector, as well as other components of the cycle, was built. The results showed that the coefficient of performance (COP) of R1234ze(e) was significantly higher than R600a at the same operating conditions. R1234yf’s performance was compatible with R290, and both were about 5% less than the previous two. The results also indicated that R152a offered the best performance among the selected refrigerants, but due to the high value of global warming potential, it did not fulfill the requirements of the current European refrigerant regulations. On the other hand, R1234ze(e) was the most suitable working fluid for the ejector cooling technology, thanks to its overall performance.

A correlation for heat transfer during boiling on bundles of horizontal plain and enhanced tubes

A dimensionless correlation is presented for calculation of local heat transfer coefficients during saturated boiling in bundles of plain and enhanced tubes. It has been verified with a wide range of data that include 12 fluids (water, ammonia, halocarbon refrigerants, and hydrocarbons), plain and a variety of enhanced tubes of many materials, inline and staggered arrangements, pitch to diameter ratios 1.17 to 2.0, reduced pressures from 0.005 to 0.2866, mass flux from 0.17 to 1391 kgm−2s−1, heat flux from 1 to 1000 kWm−2, and vapor quality from 0 to 0.98. A total of 2173 data points from 51 data sets from 28 sources are predicted with mean absolute deviation of 15.2%.

Unified correlation for heat transfer during boiling in plain mini/micro and conventional channels

A correlation is presented for predicting heat transfer coefficients during saturated boiling prior to critical heat flux in mini/micro channels as well as channels of conventional sizes in horizontal and vertical upward flow. The correlation is verified with a database that includes channels of various shapes (round, rectangle, triangle), fully or partially heated, horizontal and vertical downflow, diameters 0.38 to 27.1 mm, 30 fluids (water, CO2, ammonia, halocarbon refrigerants, organics, cryogens), reduced pressure 0.0046 to 0.787, and mass flux 15 to 2437 kg m−2s−1. The new correlation predicts the 4852 data points from 137 data sets from 81 sources with a mean absolute deviation of 18.6 %. Several other correlations were also compared with the same database; all had significantly higher deviations.

Applicability of General Correlations for Critical Heat Flux in Conventional Tubes to Mini/Micro Channels

There is presently great interest in use of mini/micro channels with boiling in heat exchangers and for heat dissipation from microelectronic systems. Design of such devices requires the ability to predict critical heat flux (CHF). It is therefore desirable to know the applicability of general correlations for CHF in conventional tubes to minichannels. The most verified general correlations are those of Katto and Ohno and of Shah. In this study, these correlations were compared to an extensive database with 55 data sets from 30 sources, which included single tubes and multichannels with diameters from 0.13 mm to 3.0 mm, 15 diverse fluids (water, halocarbon refrigerants, hydrocarbons, and cryogens), reduced pressures from 0.009 to 0.887, and flow rates from 10 to 41810 kg/m2-s. The correlations of Shah and of Katto and Ohno gave mean absolute deviations of 18.9 and 33.2%, respectively. To put the performance of these general correlations in perspective, the same database was also compared to two of the best correlations specifically developed for minichannels.

A correlation for heat transfer during condensation in horizontal mini/micro channels

A correlation is presented for heat transfer during condensation in horizontal mini/micro channels. It has been verified with data for 13 fluids (water, CO2, halocarbon refrigerants, and hydrocarbons) in single and multi channels of many shapes, with hydraulic diameter from 0.10 to 2.8 mm, aspect ratio from 0.14 to 13.9, reduced pressure from 0.0055 to 0.94, and mass flux from 20 to 1400 kg m−2s−1. This correlation predicts 1017 data points from 67 data sets from 31 sources with a mean absolute deviation of 15.5%. The same data are also compared with some other correlations.

Sustainability with prospective refrigerants

This paper first presents a brief historical summary of the recent past and current status of refrigerants, and then proceeds to suggest a simple Second Law-based approach using the ideal vapor compression refrigeration cycle to estimate a refrigerant's performance potential. The resulting performance rankings are then supplemented by additional rankings of the exergy losses in the compressor and in the condenser. These methodologies are then applied to several refrigerants: three natural refrigerants (ammonia, propane, and isobutane), five conventional single-component halocarbon refrigerants, two conventional blends of halocarbon refrigerants, and three newer refrigerants (fluorinated propene isomers). Generally speaking, the lower pressure refrigerants have better COP and lesser volumetric cooling capacity than the higher pressure refrigerants; whereas, the lower pressure refrigerants have higher penalty factor (measure of condenser exergy losses) than the higher pressure refrigerants. The analyses presented in this paper suggest that to minimize a refrigeration system's overall impact on the environment, the choice of refrigerant should not necessarily be based on a single criterion but rather should be chosen based on the particular application. Copyright © 2013 John Wiley & Sons, Ltd.

A method for the calculation of the adsorbed phase volume and pseudo-saturation pressure from adsorption isotherm data on activated carbon

We propose a new method for evaluating the adsorbed phase volume during physisorption of several gases on activated carbon specimens. We treat the adsorbed phase as another equilibrium phase which satisfies the Gibbs equation and hence assume that the law of rectilinear diameters is applicable. Since invariably the bulk gas phase densities are known along measured isotherms, the constants of the adsorbed phase volume can be regressed from the experimental data. We take the Dubinin-Astakhov isotherm as the model for verifying our hypothesis since it is one of the few equations that accounts for adsorbed phase volume changes. In addition, the pseudo-saturation pressure in the supercritical region is calculated by letting the index of the temperature term in Dubinin's equation to be temperature dependent. Based on over 50 combinations of activated carbons and adsorbates (nitrogen, oxygen, argon, carbon dioxide, hydrocarbons and halocarbon refrigerants) it is observed that the proposed changes fit experimental data quite well.

Evaluation of flow patterns and elongated bubble characteristics during the flow boiling of halocarbon refrigerants in a micro-scale channel

In the present study, quasi-diabatic two-phase flow pattern visualizations and measurements of elongated bubble velocity, frequency and length were performed. The tests were run for R134a and R245fa evaporating in a stainless steel tube with diameter of 2.32 mm, mass velocities ranging from 50 to 600 kg/m 2 s and saturation temperatures of 22 °C, 31 °C and 41 °C. The tube was heated by applying a direct DC current to its surface. Images from a high-speed video-camera (8000 frames/s) obtained through a transparent tube just downstream the heated sections were used to identify the following flow patterns: bubbly, elongated bubbles, churn and annular flows. The visualized flow patterns were compared against the predictions provided by Barnea et al. (1983) [1], Felcar et al. (2007) [10], Revellin and Thome (2007) [3] and Ong and Thome (2009) [11]. From this comparison, it was found that the methods proposed by Felcar et al. (2007) [10] and Ong and Thome (2009) [1] predicted relatively well the present database. Additionally, elongated bubble velocities, frequencies and lengths were determined based on the analysis of high-speed videos. Results suggested that the elongated bubble velocity depends on mass velocity, vapor quality and saturation temperature. The bubble velocity increases with increasing mass velocity and vapor quality and decreases with increasing saturation temperature. Additionally, bubble velocity was correlated as linear functions of the two-phase superficial velocity.

An Improved and Extended General Correlation for Heat Transfer During Condensation in Plain Tubes

An improved version of the authors's published correlation (Shah 1979), extended to a wider range of parameters, is presented. The new correlation has been shown to be in good agreement with data ranging from highly turbulent flows to the laminar flow conditions of Nusselt's analytical solutions. The data used for the correlation's validation includes 22 fluids (water, halocarbon refrigerants, hydrocarbon refrigerants, and organics) condensing in horizontal, vertical, and downward-inclined tubes. The range of parameters includes tube diameters from 2 to 49 mm, reduced pressure from 0.0008 to 0.9, flow rates from 4 to 820 kg/m2·s, all liquid Reynolds numbers from 68 to 85,000, and liquid Prandtl numbers from 1 to 18. A total of 1189 data points from 39 sources are predicted with a mean deviation of 14.4%. Comparisons are also made with some other well-known correlations.

Boiling heat transfer enhancement with carbon nanotubes for refrigerants used in building air-conditioning

In this study, the effect of carbon nanotubes (CNTs) on nucleate boiling heat transfer is investigated. Two halocarbon refrigerants of R123 and R134a for building chillers were used as working fluids and 1.0 vol.% of CNTs was added to them to examine the heat transfer enhancement with CNTs. The experimental apparatus was composed of a stainless steel vessel and a 152.0 mm long plain horizontal tube of 19.0 mm outside diameter heated by a cartridge heater. All data were obtained at the pool temperature of 7 °C in the heat flux range of 10–80 kW m −2. Test results showed that CNTs increase nucleate boiling heat transfer coefficients for these refrigerants. Especially, large enhancement up to 36.6% was observed at low heat fluxes of less than 30 kW m −2. With increasing heat flux, however, the enhancement was suppressed due to vigorous bubble generation. Fouling on the heat transfer surface was not observed during the course of this study. Optimum dispersion of CNTs should be examined for their commercial application to enhance nucleate boiling heat transfer in building air-conditioning applications.

The commercial feasibility of the use of water vapor as a refrigerant

This paper investigates the economic feasibility of a water-based vapor compression chiller with a nominal capacity of 3520 kW (1000 ton). Simplified models of potential cycle configurations are developed and used as a screening tool to identify a baseline cycle, the most attractive configuration for a water-based refrigeration machine. More detailed component-level models are developed to accurately size equipment and predict both the performance and cost of the baseline chiller. These component models address issues that are particularly crucial when water is used in refrigeration cycles, such as compression ratio, compressor discharge superheat and refrigerant-side pressure drop. Where possible, these component models are verified through comparison against the current state-of-the-art technology for large chillers that use R-134a as the refrigerant. The capital cost and expected operating costs are determined in order to quantify the payback and life-cycle costs associated with using water as a refrigerant, relative to traditional halocarbon refrigerants currently in use. Other issues that may have an economic impact on the feasibility of water as a viable alternative to traditional synthetic refrigerants are discussed, including purging and condensation within the compressor. The results show that water-based vapor compression refrigeration systems will not be economically attractive without substantial and successful efforts to develop low-cost, high capacity compressors. The paper provides an indication of the cost targets that must be met in order to make water vapor refrigeration systems practical.