Internally grooved copper tubes, also known as "microfin tubes", are a small diameter coil technology for modern

air conditioning Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...

and

refrigeration The term refrigeration refers to the process of removing heat from an enclosed space or substance for the purpose of lowering the temperature.International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.phpASHRAE Terminology, ht ...

systems. Grooved coils facilitate more efficient

heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...

than smooth coils. Small diameter coils have better rates of heat transfer than conventionally-sized condenser and

evaporator An evaporator is a device used to turn the liquid form of a chemical substance, such as water, into a vapor. Uses Air conditioning and refrigeration Some air conditioners and refrigerators use a compressed liquid with a low boiling point, ...

coils with round copper tubes and aluminum or copper fin that have been the standard in the

HVAC Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...

industry for many years. Small diameter coils can withstand the higher pressures required by the new generation of environmentally friendlier refrigerants. They have lower material costs because they require less refrigerant, fin, and coil materials. They enable the design of smaller and lighter high-efficiency air conditioners and refrigerators because the evaporator and condenser coils are smaller and lighter. With MicroGroove technology, heat transfer is enhanced by grooving the inside surface of the tube. This increases the surface to volume ratio, mixes the

refrigerant A refrigerant is a working fluid used in the heat pump and refrigeration cycle, refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Ref ...

, and

homogenize Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...

s refrigerant temperatures across the tube.Hipchen, John (2010). “Small Tubes of Copper in ACR Applications," Webinar presented by ''ACHR News and Appliance Design.''Ding, Guoliang ''et al.'' (2010). “Condensation Heat Transfer Characteristic of R410A-oil Mixture Inside Small Diameter Smooth Copper Tubes,” ''ASME-ATI-UIT Conference on Thermal and Environmental Issues in Energy Systems'', Sorrento, Italy, May 2010.Ding, Guoliang ''et al.'' (2010). “Two-phase Heat Transfer Characteristics of R410A-oil Mixture Flow Condensation Inside Small Diameter Microfin Copper Tubes,” ''Conference on Thermal and Environmental Issues in Energy Systems'', Sorrento, Italy, May 2010. Tubes with MicroGroove technology can be made with copper or aluminium. Copper fins are an attractive alternative to aluminium due to the better corrosion resistance of copper and its antimicrobial benefits.

Design

To use smaller tubes instead of conventional-sized tubes in air conditioners, heat exchangers must be redesigned including the fin and tube circuits. Design optimization requires the use of computational fluid dynamics to analyze airflow around the tubes and fins, as well as computer simulations of refrigerant flow and temperatures inside the tubes. This is important because the overall heat transfer coefficient of a coil is a function of the

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

of the

inside the tube to the tube wall, conduction through the tube wall, and dissipation through the fins. Engineering considerations for using Microgroove include: # Determining the best ratio of transverse tube pitch to longitudinal tube pitch by fin efficiency analysis.New Research Underscores Best Practices in Coil Design; Microgroove™ Update Newsletter: Volume 2, Issue 3, June 2012; http://www.microgroove.net/sites/default/files/microgroove_nl_june2012b.pdf # Optimizing transverse and longitudinal tube pitch by performance analysis and material cost. # Optimizing fin pattern by comparing performances of fins with different patterns through computational fluid dynamics-based simulations. # Testing the performance of heat exchangers with smaller diameter tubes. # Developing empirical equations for predicting performance of heat exchangers with smaller diameter tubes. Published experiments on MicroGroove coil performance and energy efficiency take into account the effects of fin spacing and fin design, tube diameter, and tube circuitry. Tube circuitry is substantially different than for conventional coils. Coils should be optimized with respect to the number of paths between the inlet and outlet manifolds. Typically, smaller diameter tubes require more paths of shorter lengths. Published research on tube circuitry and fin design for heat exchangers made with 4 mm tubes are available. Research on a heat exchanger redesign with 5-mm diameter tubes demonstrated a 5% greater heat exchange capacity than that of the same size heat exchanger with 7 mm diameter tubes. Also, the refrigerant charge of the 5 mm diameter tubes was less than the 7 mm diameter tubes. In China, Chigo, Gree, and Kelon are producing air conditioners with coils that have 5 mm diameter tubes. A variety of fin designs have been developed for use with small-diameter copper tubes. The performance of slotted and louvered fin designs have been evaluated and compared as a function of various fin dimensions. Simulations have been used to optimize fin design performance.

Refrigerants

The phasing out of

CFC CFC, cfc, or Cfc may stand for: Science and technology * Chlorofluorocarbon, a class of chemical compounds * Cardiofaciocutaneous Syndrome, a rare and serious genetic disorder * Subpolar oceanic climate (''Cfc'' in the Köppen climate classific ...

and

HCFC Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and propan ...

refrigerants (e.g.,

HCFC-22 Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). This colorless gas is better known as HCFC-22, or R-22, or . It was commonly used as a propellant and refrigerant. These applications were phased out under ...

, also known as

R22 R22 may refer to: Roads * R22 road (Belgium) * R-22 regional road (Montenegro) * R22 highway (Russia) * R22 (South Africa) Vessels * , a destroyer of the Royal Navy * , an aircraft carrier of the Indian Navy * , a submarine of the United ...

) due to

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

concerns has helped to spur innovations in cooling technologies.Microgroove™ Update Newsletter: Volume 2, Issue 1, January 2012: http://www.microgroove.net/sites/default/files/4600_microgroove_nl_jan2012_2.pdf Natural refrigerants such as

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

( R744) and

propane Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used a ...

( R290), as well as R-410A, have become attractive replacements for

and

applications. Higher pressures are typically required to condense these new environmentally friendly refrigerants compared to those that are being phased out. Small diameter copper tubes are more desirable in applications with higher pressures. For tubes of the same thickness, smaller diameter tubes can withstand higher pressures than larger diameter tubes.FAQs: Thirty Questions with Answers about Economical, Eco-friendly Copper Tubes for Air Conditioner Applications; http://www.microgroove.net/sites/default/files/overview-ica-questions-and-answers-qa30.pdf Hence, as tube diameters decrease, burst pressures increase. This is because working pressure is directly proportional to wall thickness and inversely proportional to diameter. By designing coils with shorter tube lengths, less work is required to circulate the refrigerant. Therefore, refrigerant pressure drop factors due to small diameter tubes can be offset. Carbon dioxide (R744) refrigerants are used in modern

vending machine A vending machine is an automated machine that provides items such as snacks, beverages, cigarettes, and lottery tickets to consumers after cash, a credit card, or other forms of payment are inserted into the machine or otherwise made. The fir ...

s, refrigerated

supermarket A supermarket is a self-service Retail#Types of outlets, shop offering a wide variety of food, Drink, beverages and Household goods, household products, organized into sections. This kind of store is larger and has a wider selection than earli ...

display cases,

ice-skating rink An ice rink (or ice skating rink) is a frozen body of water and/or an artificial sheet of ice created using hardened chemicals where people can ice skate or play winter sports. Ice rinks are also used for exhibitions, contests and ice shows. The ...

s, and other emerging applications.Microgroove™ Update Newsletter: Volume 1, Issue 3, December 2011: http://www.microgroove.net/sites/default/files/4473_ica_microgroove_nl_final.pdf Microgroove's smaller diameter copper tubes have the strength to withstand the very high gas cooler and burst pressures of R744 while allowing for lower overall refrigerant volumes. Propane ( R290) is an eco-friendly refrigerant with outstanding

thermodynamic Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of ther ...

properties. The pressure requirements for R290 are much less than for carbon dioxide, but R290 is extremely flammable. Research has demonstrated that MicroGroove is suitable for R290-charged room air conditioners because the refrigerant charge requirement is dramatically reduced with smaller diameter copper tubes. The risk of tube explosions is dramatically reduced as well. Research conducted with

in MicroGroove has implications for heat exchanger coils used in

refrigerators A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...

heat pumps A heat pump is a device that can heat a building (or part of a building) by transferring thermal energy from the outside using a refrigeration cycle. Many heat pumps can also operate in the opposite direction, cooling the building by removing h ...

and commercial

systems.

Weight savings

In a design study of functionally equivalent 5 kW

heat exchangers, tube materials in the coils weighed 3.09 kg for 9.52 mm diameter tube, 2.12 kg for 7 mm diameter tube, and 1.67 kg for 5 mm diameter tube. Tube weight was reduced by 31% when copper tube diameters were downsized from 3/8 inch to 7 mm. Tube weight was reduced by 46% when copper tube diameters were downsized from 3/8 inch to 5 mm. The weights of the fin materials in the coils was 3.55 kg for the 9.52 mm coils, 2.61 kg for the 7 mm coils, and 1.55 kg for the 5 mm coils.

Antimicrobial

Copper is an

antimicrobial An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ar ...

material. Bio buildup can be reduced with copper coils. This helps to maintain high levels of energy efficiency for longer periods of time and avoids energy efficiency drop off over time. The use of copper coils to inhibit the growth of

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

and

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

is a recent development in innovative air conditioning and refrigeration products.

OEM An original equipment manufacturer (OEM) is generally perceived as a company that produces non-aftermarket parts and equipment that may be marketed by another manufacturer. It is a common industry term recognized and used by many professional or ...

companies, such as Chigo in China and Hydronic in France, are now manufacturing all-copper antimicrobial air conditioning systems to improve indoor air quality.

Materials

Smaller diameter refrigerant paths can also be realized with extruded aluminium tubes. These have been designed with several microchannels in one flat, ribbon-like tube. Aluminium microchannel technology offers significant advantages over conventional copper-aluminium round tube plate fin coil, including improved heat transfer performance and reduced refrigerant charge. However, copper MicroGroove offers higher heat transfer efficiencies than aluminium microchannel tubes and it enables smaller refrigerant volumes because the tube ends of MicroGroove are connected by small U-joints rather than large headers.

Manufacturing

Copper tubes are often produced by a cast and roll process. Copper

ingot An ingot is a piece of relatively pure material, usually metal, that is cast into a shape suitable for further processing. In steelmaking, it is the first step among semi-finished casting products. Ingots usually require a second procedure of sh ...

s are cast into mother tubes and these tubes are then drawn to a final shape, annealed, and enhanced with an inner surface texture to improve heat transfer performance. The production of small diameter copper tubes requires only the addition of one or two additional drawing passes to achieve 5 mm tube diameters.Shabtay, Yoram and Cotton, Nigel (2015). Trends in the Design and Manufacture of Round-Tube Plate-Fin Coils from Smaller Diameter Copper Tubes; ''International Appliance Manufacturing;'' October. Existing air conditioner coils made of round copper tubes and aluminium fins (CTAF coils) typically are mechanically assembled using tube expansion. The equipment used in manufacturing Microgroove products expands the tubes circumferentially (i.e., the circumference of the tube is increased without changing the length). This "non-shrinkage" expansion allows for better control of tube lengths in preparation for subsequent assembly operations. Tubes are inserted, or laced, into the holes in a stack of precisely spaced fins. Expanders are inserted into the tubes and the tube diameters are increased slightly until mechanical contact is achieved between the tubes and fins. The high ductility of copper allows for this process to be performed accurately and precisely. Heat exchanger coils made in this manner have excellent durability and heat transfer properties. The small-diameter tube project in China involves manufacturers who together account for more than 80 percent of

production of approximately 75 million units. Several

s in North America are marketing residential air-conditioner products with copper tubes. Air-conditioner OEMs, including Guangdong Chigo Air Conditioning, the Refrigeration Research Institute of Guangdong Midea Refrigeration Appliances Group, and Shanghai Golden Dragon Refrigeration Technology Co., Ltd. have described the benefits of small-diameter copper tubes versus the standard for various designs and diameters. ACR coils from original equipment manufacturers (OEMs) Gree, Haier, Midea, Chigo and HiSense Kelon are also available.The China Refrigeration Expo (CR-2011) in Shanghai, China; in Microgroove™ Update Newsletter: Volume 1, Issue 1, May 2011: http://www.microgroove.net/sites/default/files/microgroove_nl_issue_1.pdf

References

{{Reflist, 2 Heat exchangers Heat transfer Heat conduction Heating, ventilation, and air conditioning Copper