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MicroGroove Paper at ATMO Europe 2018, Lago di Garda, Italy: Sub-Zero and MTL Cool optimise MigroGroove copper-tube coils for use with natural refrigerants in equipment

Nigel Cotton, Anderson Bortoletto and Yoram Shabtay

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Hydrocarbons are highly attractive for use in refrigerator and freezer applications but their flammability necessitates strict “use conditions” with respect to refrigerant charge. Sub-Zero, Inc. makes high-end, built-in residential refrigerators, freezers and wine coolers. The company used a proprietary heat exchanger design and simulation software tool from Optimized Thermal Systems to identify feasible 5-mm inner-grooved copper tube coil designs. The baseline design used 6.35-mm copper tubes. For an R600a residential application, simulations identified 5-mm tube coil designs with significantly less internal tube volume than the baseline coil. One 5-mm design reduced the internal tube volume by as much as 41 percent as compared to the baseline, along with a potential 57 percent reduction in coil footprint, while maintaining a near equal airside pressure drop. Sub-Zero is reinventing its residential appliances to allow for more efficient use of natural refrigerants using MicroGroove smaller diameter copper tubes

In the Spotlight: MicroGroove Research at Purdue Herrick Conferences

Column in MicroGroove Update eNews reviews MicroGroove-related research presented at this renowned International Conference.

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The Seventeenth International Refrigeration and Air-Conditioning Conference included 41 sessions (R-01 through R-41) with hundreds of papers. PDF versions of all of these papers are now openly accessible and downloadable by searching for the paper number in the Conference Tool. (https://www.conftool.com/Purdue2018/sessions.php) Research relating to MicroGroove includes laboratory experiments, theory and modeling, and design case studies. The most pertinent papers relating to MicroGroove are highlighted in this article.

Optimization of MicroGroove Copper Tube Coil Designs for Flammable Refrigerants (Purdue 2018)

Paper 2532 by Nigel Cotton, Adam Rhoads, Anderson Bortoletto, and Yoram Shabtay presented at Purdue Conferences in 2018.

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The ultralow Global Warming Potential (GWP) of propane (R290) and isobutane (R600a) refrigerants make them highly attractive for refrigerator and freezer applications, although their flammability necessitates strict use conditions with respect to refrigerant charge. Copper tubes with smaller diameters are widely used to reduce refrigerant charge. The process of downsizing copper-tube diameters involves detailed simulations and prototype construction as well as testing and validation. A proprietary heat exchanger design and simulation software tool (Jiang et al., 2006) was used to evaluate the performance of and optimize the design of domestic refrigerator condenser coils made with 5-mm outer-diameter copper tubes. Optimization was accomplished through the use of reduced order models, meta-models and a multi-objective genetic algorithm (MOGA). Reducing refrigerant charge was the primary objective. Secondary objectives included the reduction of the total footprint and the total tube-andfin material mass. The baseline design used 6.35-mm O.D. copper tubes with a minimum wall thickness of 0.41 mm, i.e., quarter-inch tubes with 0.016-inch wall thickness. The new designs use wavy-herringbone fins with reduced fin thicknesses as compared to the baseline design. Other variables included the horizontal and vertical spacing of the tubes; number of tubes per bank; fin density; wavy fin pattern depth; tube length; and tube circuitry. For an R600a residential application, reduced internal volume was considered to be more important than the airside pressure drop. A Pareto chart is presented of optimized values from the design space. Compared to the baseline design, the best 5- mm design reduced the internal tube volume by 41 percent, along with a 57 percent reduction in coil footprint. Additionally, test data to validate the performance of prototype coils is presented with emphasis on the design, construction and manufacture of the heat exchanger coils.

Boiling Heat Transfer and Pressure Drop of R1234ze(E) inside a Small-Diameter 2.5 mm Microfin Tube (Purdue 2018)

Paper 2542 by Daisuke Jige, Shota Iizuka, and Norihiro Inoue presented at Purdue Conferences in 2018. Research performed at Tokyo University of Marine Science and Technology (TUMSAT).

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This study experimentally investigated the flow boiling heat transfer and pressure drop of R1234ze(E) in a horizontal small-diameter microfin tube with an outer diameter of 2.5 mm and equivalent diameter of 2.1 mm. The boiling heat transfer and pressure drop were measured in the mass velocity range of 100–400 kg/(m2 s) and in the heat flux range of 5–20 kW/m2 at a saturation temperature of 15 °C. The heat transfer coefficient increased as the quality increased because of increasing the forced convection in the pre-dryout region. The heat transfer coefficient increased as the heat flux increased in the low-quality region, but decreased when the heat flux increased past a certain point because the thin liquid film at the fin tips had dried. The heat transfer coefficient increased as the mass velocity increased and exhibited the highest value at a mass velocity of 200 kg/(m2 s). The measured heat transfer coefficient agreed well with previous correlations only in the dominant region of the forced convection evaporation. The frictional pressure drop increased as the mass velocity and vapor quality increased, and the measured values agreed well with previously reported correlations for conventional-diameter microfin tubes.

Effect of Fin Geometries on Condensation Heat Transfer and Pressure Drop inside Horizontal Small-Diameter 4 mm Microfin Tubes (Purdue 2018)

Paper 2511 Norihiro Inoue, Masataka Hirose, Daisuke Jige presented at Purdue Conferences in 2018. Research performed at Tokyo University of Marine Science and Technology (TUMSAT).

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This study experimentally investigated the condensation heat transfer and pressure drop characteristics of R1234ze(E) inside horizontal small-diameter 4.0 mm OD microfin tubes having three different types of fin geometries. The specifications of the three fin geometries were 40 fins with a fin height of 0.18 mm and a helix angle of 18°, 50 fins with a fin height of 0.15 mm and a helix angle of 12°, and 50 fins with a fin height of 0.12 mm and a helix angle of 25°. The experiments were carried out for a range of mass velocities from 50 to 400 kgm-2 s -1 , and at a saturation temperature of 35 °C. The effects of fin geometries such as the number of fins, fin height, and helix angle on the heat transfer and pressure drop were investigated. The heat transfer coefficient increased as the number of fins increased for the lowest mass velocity. Fin height was most effective on heat transfer enhancement at higher mass velocities. The heat transfer coefficient and pressure drop of the microfin tubes were compared with those of smooth tube and were evaluated in terms of the enhancement factor of heat transfer. The measured heat transfer coefficient and pressure drop were compared with previous correlations, and the results were verified practical effectiveness of the previous correlations for small-diameter microfin tubes.

R134a And Its Low GWP Substitutes R1234yf And R1234ze(E) Flow Boiling Inside A 4mm Horizontal Smooth Tube

Paper 2204 by Giovanni Antonio Longo, Simone Mancin, Giulia Righetti, Claudio Zilio presented at Purdue Conferences in 2018. Research performed at University of Padova, Italy.

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This paper presents some new experimental data on R1234yf saturated flow boiling inside a 4 mm horizontal smooth tube: the effects of heat flux, refrigerant mass flux, and mean vapor quality are investigated separately to point out the different heat transfer mechanism contributions (i.e., nucleate boiling or/and forced convection boiling). The experimental tests were carried out at a saturation temperature equal to 10 °C, refrigerant mass flux from 200 to 600 kg m-2 s -1 , heat flux from 15 to 30 kW m-2 , and at increasing vapor quality up to incipient dryout. The measurements are here reported in terms of boiling heat transfer coefficient and frictional pressure drop. Furthermore, the R1234yf performance is compared against R1234ze(E) and R134a, since the substitution of R134a with low GWP refrigerants is one of the most important actual challenge for refrigeration and air conditioning, and R1234ze(E) and R1234yf seem to be very promising substitutes of it. Finally, the experimental heat transfer and frictional pressure drop data are used to assess some classical literature correlations.

R134a and its low GWP substitutes R1234yf and R1234ze(E) condensation inside a 4mm horizontal smooth tube (Purdue 2018)

Paper 2205 presented by Giovanni A. Longo, Siomone Mancin, Giulia Righetti, and Claudio Zilio at Purdue Conferences in 2018. Research performed at University of Padova, Italy.

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This paper presents the comparative analysis of HFC134a and its low GWP substitutes HFO1234yf, and HFO1234ze(E) in saturated vapour condensation inside a 4 mm ID horizontal smooth tube. The experimental tests were carried out at 30, 35, and 40°C of saturation temperatures, with refrigerant mass flux in the range 100 - 600 kg m-2s -1 at decreasing vapour quality. A transition point from gravity-dominated and forced convection condensation was found in the range of the equivalent Reynolds number 10,000  20,000. The experimental heat transfer coefficients in the forced convection condensation regime were very well predicted by the Akers et al. (1959) model, whereas the Friedel (1979) correlation was able to reproduce the frictional pressure drop data in the whole experimental range. HFO1234yf and HFO1234ze(E) exhibit heat transfer coefficients and frictional pressure drops similar to those of HFC134a and both the HFO refrigerants seem to be very promising as long-term low GWP substitutes for HFC134a.

Tube-Fin Heat Exchanger Circuitry Optimization Using Integer Permutation Based Genetic Algorithm (Purdue 2018).

Paper 2598 presented by Zhenning Li, Jiazhen Ling, Vikrant Aute at Purdue Conferences in 2018. Research performed at the Center for Environmental Energy Engineering, University of Maryland.

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Tube-fin heat exchangers (HXs) are widely used in air-conditioning and heat pump applications. The performance of these heat exchangers is strongly influenced by the refrigerant circuitry, i.e. the refrigerant flow path along the different tubes in the HX core. Since for a given number of tubes, the number of possible circuitries is exponentially large, neither the exhaustive search nor traditional optimization algorithms can be used to optimize the circuitry for a given application. Researchers have previously used Genetic Algorithms (GAs) coupled with a learning module or other heuristic algorithm to solve this problem, but there is no guarantee that the resulting circuitry can be manufactured in a cost-effective manner. In this paper, we present an integer permutation-based GA approach for solving the circuitry optimization problem. A finite volume heat exchanger simulation tool is used to simulate the performance of different circuitries generated by the optimizer. The novel genetic operators are designed such that all chromosomes generated by GA can be mapped to a valid circuitry design. As a result, the proposed approach can explore the solution space more efficiently than a conventional GA. The manufacturability aspect is handled using a constraint-dominated sorting technique in the fitness assignment stage. The analyses of several case studies show that the constrained integer permutation-based GA can generate circuitry designs with capacities superior to those obtained manually and meanwhile guarantee good manufacturability. Overall, a 2.4-14.6% increase in heat exchange capacity is observed by applying the new optimization method to an evaporator from a A-type indoor unit. Comparison with other optimization methods in literature shows that the proposed approach exhibits higher quality optimal solutions than other methods.

Alternative Defrost Strategies for Residential Heat Pumps (Purdue 2018)

Paper 2258 presented by Cara Martin, Paul Oppenheim, John Bush, and Hal Stillman at the Purdue Conferences in 2018. Research performed at Optimized Thermal Systems, the University of Florida, the Electric Power Research Institute, and the International Copper Association.

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Heat pumps are an energy efficient way to provide adequate heating to an indoor space. In contrast to electric or gas heating, a heat pump works to draw the “free” heat from the cold outdoor ambient and transfer thermal energy to the heated space. When the outdoor ambient is cold and humidity conditions are right, however, frost will start to develop on the heat pump’s outdoor coil. Frost on the coil surface blocks air flow through the coil thus reducing the heat pump’s efficiency and overall performance. Control of frosting and defrosting is particularly important to the successful use of heat pumps in cold climates.

To restore the unit’s heating capacity and efficiency, a defrost cycle is needed to remove the accumulated frost developed on the coil. While defrosting restores heat pump efficiency, this period of operation itself requires additional power and ultimately results in an energy penalty. Improving defrost performance and/or reducing the number and duration of required defrost periods would significantly improve heat pump operation.

Heat pump researchers and manufacturers have spent a great amount of effort on the topic of defrosting. A comprehensive review of efforts within the last 15 years was conducted to summarize existing defrosting technologies and identify those solutions that may be more feasible or readily commercialized to reduce the defrost penalty. This summary highlights technologies that may reduce or eliminate the negative impacts of the defrosting period including approaches using hot gas bypass, coil coatings and advanced control strategies. The potential impact of the identified technologies is energy and demand savings, improved performance for comfort, and removal of a significant barrier to widespread adoption of air-source heat pumps in all climates

MicroGroove Presentation at ATMO America 2018, Long Beach, California: Performance Testing of MicroGroove Heat Exchangers with Natural Refrigerants

Yoram Shabtay with MTL Cool presented at ATMO America, Long Beach MicroGroove Paper at ATMO America 2018, Long Beach, California (2018)

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Reduced internal volume of coils made with smaller-diameter copper tubes allows for a reduction in refrigerant charge compared to conventional heat exchangers. Especially for propane and isobutane systems, the smaller refrigerant volume allows for the desired cooling capacities to be reached without exceeding refrigerant charge limitations.

Recently obtained system test data results provided by a North American manufacturer of light-commercial refrigeration equipment are presented. MicroGroove copper-tube heat exchangers are used along with natural refrigerants. Performance comparisons are made for several models of cooling cabinets currently sold to end-users in North America. For ambient temperatures of 75 ºF and 55% RH, conventional designs using R134a and R404A refrigerants are compared with new designs using R290 (propane) and R600a (isobutane) refrigerants, respectively. The effects of variables such as heat exchangers size, refrigerant charge and energy efficiency are also examined.

MicroGroove Presentation at ATMO America 2017, San Diego, California: Select case studies of copper heat exchanger coils for natural refrigerants

Yoram Shabtay with SPIROTECH, LORDAN, BURR OAK AND OTS

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The use of natural refrigerants in refrigeration equipment necessitates the redesign of heat exchangers. In particular, R744 heat exchangers must withstand high pressure because of the extraordinary high operating pressures of R744 systems; and R290 heat exchangers must minimize refrigerant volume because of the R290’s Level-3 flammability rating.

In this paper, several case studies are presented from various coil makers and refrigeration equipment makers to illustrate the design principles and manufacturing methods. Successful designs have been realized using high strength copper tube alloys and the development of new manufacturing equipment for smaller diameter copper tubes. Recent development in design simulations as well as real world applications will be presented.

MicroGroove Presentation at ATMO America 2016, Chicago, 2016: New copper-tube technologies for heat exchangers: R290 condenser coil and R744 gas cooler

Yoram Shabtay, Dr. Jian Yu and Nigel Cotton

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Comparing various diameters of copper tubes with the same wall thicknesses, burst pressures are much higher for the smaller diameter tubes.

Copper tubes up to ten feet in length with wall thicknesses of 0.040 inches (about one millimeter) have been hydraulically expanded to obtain a mechanical fit against aluminum fins with 10 fins per inch.

This presentation will describe the performance R744 gas coolers and evaporators currently produced in North America for real-world commercial and industrial applications and will discuss the practicality of manufacturing such systems in volume. It will also present new high-strength tube alloys and research on new copper tube technologies.

A Review of the Influence of Microfin Enhancements on the Condensation Heat Transfer Coefficient for Small Diameter Tubes

White Paper by Burr Oak Tool Inc. and Optimized Thermal Solutions (2015)

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This white paper reviews the relationship between condenser coil tube diameter, internal tube enhancements, and the resultant influence on heat transfer coefficient (HTC). Helical microfins are the primary enhancement of interest, specifically for condenser applications for tube diameters ranging from 9.5 mm to 3 mm outer diameter (OD). Several other tube enhancements, such as herringbone fins and surface microstructures, are also considered.

New Copper-Based Heat Exchangers for R744 Refrigerant, Part I: New Technologies for Tubes and Coils

Yoram Shabtay et al. (Presented at Ohrid 2015.)

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The replacement of current refrigerants with zero ozone depletion potential (ODP) and virtually zero global warming potential (GWP) refrigerants has important implications for heat exchangers, heat pumps, air conditioners and refrigeration system design, and the materials choices in these designs. The use of CO2 as a refrigerant requires components to withstand higher pressures compared to conventional refrigerants. Part I presents critical information about smaller-diameter copper tubes and other heat-exchanger technologies, and Part II discusses design principles and presents example case studies for CO2. Seamless copper tubes with or without inner-grooves can be fabricated from a high-strength copper-iron alloy, reducing wall thickness and thus cost. Coil processing can usually be performed with existing manufacturing equipment since the high strength alloys are brazeable and weldable. Corresponding fittings made from the high strength alloys are also available. Since the volume of CO2 required to achieve the same cooling effect is much lower than for HFCs, components and tubing can be smaller than in conventional installations. In practice, accommodating the high pressures of CO2 systems is advantageous because the smaller diameter tubes used to withstand higher pressures also reduce system size and materials requirements. CuFe2P alloy tubes at small diameters are further advantageous for use in high-pressure CO2 cascade, transcritical and secondary-loop refrigeration systems due to their high strength without increasing wall thickness in the transmission lines.

New Copper-Based Heat Exchangers For R744 Refrigerant, Part II: System Design and Case Studies.

Yoram Shabtay et al. (Presented at Ohrid 2015.)

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Part I presented critical information on how round inner-grooved small-diameter copper tube and newly developed flat copper microchannel tube can be used with alternative refrigerants and especially CO2. Seamless copper tubes with or without inner-grooves can be fabricated from a high-strength copper-iron alloy, reducing wall thickness and thus cost. Corresponding fittings made from the high strength alloys are also available. Part II examines and presents critical information and case studies relating to system design. Since the volume of CO2 required to achieve the same cooling effect is much lower than for HFCs, components and tubing can be smaller than conventional installations. In practice, accommodating the high pressures of CO2 systems is advantageous because the smaller diameter tubes used to withstand higher pressures also reduce system size and materials requirements. CuFe2P alloy tubes at small diameters are further advantageous for use in high-pressure CO2 cascade, transcritical and secondary-loop refrigeration systems due to their high strength without increasing wall thickness in the transmission lines.

New Copper-based Heat Exchangers for Alternative Refrigerants

Yoram Shabtay et al. (Presented at Purdue 2014, paper 2570).

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The ongoing global effort to replace current refrigerants with zero Ozone Depletion Potential (ODP) and virtually zero Global Warming Potential (GWP) refrigerants has important implications for heat exchangers, air conditioning system design, and the materials choices in these designs. Natural refrigerants with higher flammability, CO2, HFOs, and HFC – HFO blends each place different requirements on the heat exchanger design, whether it be for higher equipment efficiency, to reduce refrigerant charge, to operate to much higher operating pressures or temperatures, to prevent corrosion or to avoid leakage. This paper presents critical information on how heat exchangers based on round inner-grooved small-diameter copper tube and newly-developed flat copper microchannel tube can be applied in air conditioning equipment using new alternative refrigerants. These technologies have synergies with key refrigerant performance characteristics enabling multiple application opportunities, and they address operating energy efficiency degradation from mold growth on total Life Cycle Climate Performance (LCCP).

Investigation of Application of Suction Line Heat Exchanger in R290 Air Conditioner with Small Diameter Copper Tube

Tao Ren et al. (SJTU and ICA, Presented at Purdue 2014, paper 2231).

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The use of small diameter copper tube is an effective way to reduce refrigerant charge for R290 air conditioner, but may reduce system performance. To improve the performance of R290air conditioner with small diameter copper tube, this paper presents an investigation of application of a suction line heat exchanger. A theoretical analysis is proposed to investigate the effect of the suction line heat exchanger on capacity and coefficient of performance, and a simulation based analysis is processed to investigate the effect of suction line heat exchanger on refrigerant charge of condenser. To verify the results of analysis, experiments on a prototypeR290 air conditioner are carried out, and the results show that the suction line heat exchanger improves the cooling capacity by 5.3%and system efficiency by4.5%, and reduces the refrigerant charge by 6%, which agree well with that of the theoretical and simulation based on analysis.

Influence of Oil on Heat Transfer Characteristics of R410A Flow Boiling in Conventional and Small Size Microfin Tubes

Haitao Hu et al. (SJTU and ICA, Presented at Purdue 2014, paper 2347).

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In order to extend the existing heat transfer coefficient correlation of R410A-oil mixture flow boiling in conventional size (7.0 mm) microfin tube to be suitable for widely used small diameter tubes (4.0~5.0 mm), the experiments of R410A-oil mixture flow boiling inside three small diameter microfin tubes with different outside diameters of 4.0~5.0 mm and different microfin structures were performed. For the tested tubes with different diameter, the decrease of tube diameter may weaken the deterioration effect of oil on heat transfer at intermediate and high vapor qualities. For the fixed outside diameter microfin tubes with different microfin structures, larger fin height and contact area of liquid with tube wall may enhance the heat transfer for oil-free R410A, but result in smaller enhancement effect of oil at low vapor qualities and smaller deterioration effect of oil at intermediate and high vapor qualities for R410A-oil mixture. A general correlation to predict the heat transfer coefficients of R410A-oil mixture flow boiling inside conventional size and small diameter microfin tubes was developed, and it agrees with 94% of the experimental data of R410A-oil mixture in 4.0 mm ~ 7.0 mm microfin tubes within a deviation of ±30%.

Diffluence Characteristics Investigation of Distributors Used in Heat Pump Type Air Conditioner with Microgroove Tubes

Guoliang Ding et al. (SJTU and ICA, Eleventh IEA Heat Pump Conference 2014, Montréal (Québec) Canada, Paper AO-119093.

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Well design and application of a distributor is important to obtain a reasonable distribution of refrigeration flow among the multi paths of a heat exchanger in heat pump type air conditioner. In this paper, theoretical and experimental studies on the diffluence characteristics of distributors used in heat pump type air conditioners with microgroove tubes were done. The main factors influencing diffluence performance of distributors were summarized by theoretical analysis. The effects of the main factors on diffluence performance of typical distributors were investigated by experiments with air and water as the working fluid instead of actual refrigerants. Based on the theoretical analysis and experimental results, improvement methods for the existing distributors were proposed, and the improvement effects were verified by experiments

Stefano Filippini – List of Papers

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Fin Design for Fin-And-Tube Heat Exchanger with Microgroove Small Diameter Tubes For Air Conditioner

Yifeng Gao et al. (SJTU and ICA, Paper No. TP-071 presented at IIR-TPTPR 2013)

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Optimal louver fins suitable for 5 mm diameter tubes are designed by Computational Fluid Dynamic-based method in this study. Based on the design result, a set of fin-and-tube heat exchangers with 5 mm diameter tubes are tested to develop correlations to predict the performance of new fin-and-tube heat exchanger. According to the experimental results, it is found that water bridge occurs at the bottom of fin with hydrophilic coating, which did not occur in fin-and-tube heat exchangers with 7 mm or 10.33 mm diameter tubes in previous studies. Based on the data, correlation of j is developed to predict the heat transfer rate of fin-and-tube heat exchanger with 5 mm diameter tubes. The mean deviations of the proposed j correlation are 6.5%.

Step-by-Step Coil Design: Principle of Designing Fin-and-Tube Heat Exchanger with Smaller Diameter Tubes for Air Conditioner

Wei Wu et al. (SJTU and ICA, presented at Purdue 2012)

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Several useful design principles as applied to smaller diameter copper tubes are described in this paper. In particular, the knowledge-based evolution method (KBEM) has been developed into a step-by-step procedure that simulates and optimizes every aspect of the heat exchanger design, from tube spacing to fin type to tube circuitry. A methodical approach to the design of heat exchangers using smaller diameter copper tubes is summarized by the following steps: 1) Determine the best ratio of transverse tube pitch to longitudinal tube pitch by fin efficiency analysis; 2) Optimize transverse tube pitch and longitudinal tube pitch by analysis of performance and material cost; 3) Optimize fin pattern by comparing performances of fins with different patterns through CFD-based simulations; 4) Test the performance of heat exchanger with smaller diameter tubes; 5) Develop empiric equations for predicting performance of heat exchanger with smaller diameter tubes.

Copper v Aluminum: Simulation-Based Comparison of Optimized AC Coils Using Small Diameter Copper and Aluminum Micro-Channel Tubes

John C. Hipchen et al. (Copper Alliance and OTS, presented at Purdue)

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New research compares an RTPF heat exchanger with a brazed-aluminum multichannel (BAM) heat exchanger. Until now, there have been few studies comparing MicroGroove technology directly with aluminum MicroChannel technology. For that reason, the ICA sponsored a research project that allows for meaningful comparisons of the performance of these disparate systems. The method of comparison is simple. A search was made for a state-of-the-art, best-in-class BAM heat exchanger. The performance specifications were then identified and set as a target for the RTPF heat-exchanger. The design space was searched for candidate RTPF designs that met the performance specification.

Propane as a Refrigerant: Developing Low Charge R290 Room Air Conditioner by Using Smaller Diameter Copper Tubes

Guoliang Ding et al. (Copper Alliance and SJTU, presented at Delft 2012)

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The research describes a new case study on an R290 room air conditioner with 5 mm tubes. R290 is considered an eco-friendly natural refrigerant R290 because it has zero ozone depletion potential (ODP) and virtually zero global-warming potential (GWP). Moreover, it does not give out any toxic decomposing agents on combustion and is compatible with the materials and lubricants used in air conditioning. In the case study, the refrigerant charge for systems using 5-mm tubes was decreased in comparison to systems using 7-mm or 9.52-mm diameter tubes; and the cooling capacity was enhanced by optimization of heat exchanger as well as the matching of the entire system. Experimental results confirm the simulation results.

Optimization of Heat Exchanger: Simulation-Based Design Method for Room Air Conditioner with Smaller Diameter Copper Tubes

Guoliang Ding et al.  (SJTU and ICA, presented at IIR-ICR-2011)

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Smaller diameter copper tubes are beneficial in reducing the weight of tube and fin materials and the volume of refrigerant charge in room air conditioners while maintaining performance. This paper presents a simulation-based design method for air conditioners with smaller diameter tube. The new method combines heat exchanger simulator and knowledge-based evolution method optimizer to design and optimize air conditioner heat exchangers with smaller diameter tubes. The design method is illustrated in detail through an example of an air conditioner in which 5 mm tubes replace 7 mm tubes in the evaporator and replace 9.52 mm tubes in the condenser. The cost reduction is estimated at 17 percent while the performance deviation is less than one percent.

Copper Coils For R744: Air Cooled Heat Exchangers For CO2 Refrigeration Cycles

Stefano Filippini, Umberto Merlo,  (LU-VE, presented at IIR-ICR-2011, paper 295)

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The article illustrates first the key points of air cooler unit design, the differences compared to HFC products, and underlines the necessity of having low internal volume. DX air coolers and pump air coolers are analyzed.

Reduced Refrigerant Volume: New Finned Heat Exchanger Development With Low Refrigerant Charge

Stefano Filippini, Umberto Merlo, (LU-VE, presented at IIR-ICR-2011, paper 296)

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Many types of air cooled heat exchangers are used in the HVACR sector. The paper presents the results of development in new compact finned tube geometry 20x17.32mm. The technology employs 5.0 mm diameter copper tubes and advanced louvered fins for condenser applications.

MicroGroove Overview: Benefits of Reduced Diameter Copper Tubes in Evaporators and Condensers

Robert Weed et al. (Copper Development Association, presented at ASHRAE-2011)

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The heat transfer characteristics of smooth and inner-grooved tubes are compared and the benefits of smaller diameter copper tubes reviewed. Various sizes of conventional tubes are compared with smaller diameter tubes, using simulated and actual performance data as well as energy-efficient design options. Copper components also offer antimicrobial properties. Data from bacteria studies supports the use of copper components where antimicrobial properties are required. Recent registration of copper alloys with the U.S. Environmental Protection Agency is discussed as well.

Tube Circuitry Simulations: Development of Small-diameter Tube Heat Exchanger: Circuit Design and Performance Simulation.

Wei-kun Ding et al. (XJTU and ICA, presented at ASME-ATI-UIT-10)

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The performance of condensers made from small diameter tubes was modeled and simulated at the School of Energy & Power Engineering, Xi'an Jiao Tong University, Xi'an, China. Separate papers were published on the tube circuitry and on fin design. The tube-circuitry research compared conventional-diameter (F7mm) tubes with small-diameter (F5mm) tubes. Simulations predict higher refrigerant pressure drops for small-diameter tubes. Nonetheless, by increasing the number of circuit branches, decreasing the single branch length and adding more tubes in the circuit design, refrigerant pressure drop could be kept within a factor of two for almost the same heat exchange rate and a significant saving in tube materials. Reducing the refrigerant pressure drop is a key issue for practical applications.

Fin Design Simulations: Development of Small-diameter Tube Heat Exchanger: Fin Design and Performance Research.

Ju-fang Fan et al. (XJTU and ICA, presented at ASME-ATI-UIT-10).

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Researchers studied fin designs for heat exchangers made with small-diameter (F4mm) tubes. For reference, numerical simulations were conducted on reference fins with conventional-diameter (F7mm) tubes, including various louvered and slotted-fin heat transfer surfaces. Then, based on nearly optimized values, new louvered-fin and slotted-fin structures were proposed and simulated for small-diameter (F4mm) tubes. The fin designs with the small-diameter tubes matched the heat transfer requirements for the reference louvered fin while greatly reducing the copper tube material in the new heat exchanger.

HTCs for Smooth Tubes: Condensation Heat Transfer Characteristic of R410A-oil Mixture inside Small Diameter Smooth Copper Tubes.

Guoliang Ding et al. (SJTU and ICA, presented at ASME-ATI-UIT-10).

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The condensation heat-transfer characteristics of an R410A-oil mixture inside small-diameter smooth copper tubes was investigated experimentally by researchers from the Institute of Refrigeration and Cryogenics at Shanghai Jiao Tong University, Shanghai, China. The heat-transfer coefficient (HTC) was found to decrease with the increasing oil concentration. For small diameter smooth tubes, it decreased by a maximum of 28.5 percent at an oil concentration of five percent. A correlation was proposed between the heat transfer coefficient and oil concentration for R410A-oil mixture flow condensation inside smooth copper tubes. The proposed correlation agreed with all experimental data within a deviation of –30 percent to +20 percent.

HTCs for Inner-Grooved Tubes: Two-phase Heat Transfer Characteristics of R410A-oil Mixture Flow Condensation inside Small Diameter Microfin Copper Tubes.

Guoliang Ding et al. (SJTU and ICA at ASME-ATI-UIT-10)

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The two-phase heat-transfer characteristics for flow condensation of an R410A-oil mixture inside small-diameter, inner-grooved copper tubes were investigated experimentally by researchers from the Institute of Refrigeration and Cryogenics at Shanghai Jiao Tong University, Shanghai, China. Effects on heat transfer were negligible at one percent nominal oil concentration but the heat transfer coefficient deteriorated by 25.1 percent at five percent nominal oil concentration. The correlation of Yu and Koyama is recommended to predict the local condensation heat transfer coefficient of R410A-oil mixture inside small diameter microfin tubes.

Less Tube Material in Evaporator Application for Residential AC: Application of Small Diameter Inner-Grooved Copper Tubes in Air-Conditioning Systems.

You Shunyi et al. (Chigo, presented at IIR-RCR-2010)

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Researchers at the Guangdong Chigo Air Conditioning in Foshan, Guangdong, compared the performance of conventional diameter (F7mm) and small-diameter

(F5mm) inner-grooved copper tubes in an evaporator application for a residential air conditioner. Heat-transfer coefficients, fluid pressure drops and system performance were compared. For the F5mm tube, copper usage was lowered by more than 43 percent and cost reduced by around 40 percent while increasing the cooling capacity, energy efficiency ratio (EER) and air volume.

Less Refrigerant in Split AC system: Experimental Research for Lowering Refrigerant Charge with 4mm Tube Heat Exchanger

Jia Qingxian et al. (Midea, presented at IIR-RCR-2010)

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Researchers at the Refrigeration Research Institute of Guangdong Midea

Refrigeration Appliances Group in Shunde, China conducted R410A and R290 performance experiments on split air conditioners with small diameter (F4mm) heat exchanger tubes. Without sacrificing any performance, the 4mm tubes reduced the volume and cost of the heat exchanger and significantly lowered the refrigerant charge.

Performance and Cost Analysis: Performance and Cost Analysis and Research of Air-Cooled Heat ExchangerUsing Small Diameter Copper Tubes

Wu Yang et al. (Tube Supplier, presented at IIR-RCR-2010)

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Researchers reported performance results and a cost analysis for conventional diameter (F9.52mm) and small diameter (F5mm) inner-grooved copper tubes as well as for heat exchangers made with these two tube types. For the same experimental conditions and volume flow, the heat exchange coefficient is about 15% higher for the F5mm inner-grooved copper tube than the F9.52mm inner-grooved copper tube. For the same operating conditions the same windward dimensions, comparing a F5mm copper tube heat exchanger with a F9.52mm copper tube heat exchanger, the former uses 41.8 percent less copper material for the tubes and 50 percent less aluminum foil material in the fins.

Microgroove vs Microchannel:A New Heat Exchanger Geometry for Next Condenser Generation with Ultra Low Refrigerant Charge

Stefano Filippini (LU-VE, presented at IIR-RCR-2010)

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A new coil geometry based on smaller-diameter copper tubes is compared with aluminum microchannel coils. The new design appears to be the best way to lower the internal volume and consequently the refrigerant charge, an issue that is more and more requested in order to ensure environmental sustainability of ACR products.

Abbreviations

ASHRAE 2011: ASHRAE Annual Conference, Montreal, Quebec Canada, June 25-29, 2011.

ASME-ATI-UIT-10: Conference on Thermal and Environmental Issues in Energy Systems, Sorrento, Italy, May 2010. The American Society of Mechanical Engineers (ASME), the Associazione Termotecnica Italiana (ATI), the Unione Italiana di Termofluidodinamica (UIT) and International Centre for Heat and Mass Transfer (ICHMT).  http://www.ichmt.org/asme-ati-uit-10/.

CDA = The Copper Development Association, US regional member of the Copper Alliance. www.coppper.org

Delft 2012 = The Tenth IIR Gustav Lorentzen Conference on Natural Refrigerants at the Delft University of Technology in the Netherlands. www.gl2012.nl

ICA: International Copper Association Ltd., Shanghai Office, Shanghai, China

IIR-ICR-2011: 23rd IIR International Congress of Refrigeration, Prague, Czech Republic, August 2011.

IIR-RCR-2010: Second IIR Workshop on Refrigerant Charge Reduction, Stockholm, Sweden, June 2010.

IIR TPTPR 2013: Fourth IIR Conference on Thermophysical Properties and Transfer Processes of Refrigerants, Delft, The Netherlands, 2013

Ohrid = 6th IIR Conference: Ammonia and CO2 Refrigeration Technologies, Ohrid, 2015.

OTS = Optimized Thermal Systems, College Park, Maryland. www.optimizedthermalsystems.com

Purdue 2012 = Fourteenth International Refrigeration and Air Conditioning Conference at the Purdue Conferences in West Lafayette, Indiana on July 16-19, 2012. https://engineering.purdue.edu/Herrick/Events/2012Conf

SJTU: Shanghai Jiao Tong University, Institute of Refrigeration and Cryogenics, Shanghai, China.

The Copper Alliance = The Copper Alliance® brand represents a network of regional copper centers and their industry-leading members, led by ICA. www.copperalliance.org

XJTU: Xi'an Jiao Tong University, School of Energy & Power Engineering, Xi'an, China