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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Model-based Design Optimization to Achieve the Performance Goals (16.0 SEER/9.5 HSPF), Developing Heat Pump by Using Low-GWP Refrigerants and 5 mm Diameter Tubes

Usage of low-GWP refrigerants can reduce the Green House Gas (GHG) emission of HVAC systems. Our research in previous milestone report has shown that using heat exchangers with 5 mm diameter tubes instead of 9 mm diameter tubes is a promising solution to meet the performance goals of heat pump using low-GWP refrigerants. In addition, the 5mm tube heat exchangers can lead to lower system refrigerant charge and as a result, reduce environmental impact further. However, shifting to small tube diameters requires in-depth heat exchanger design optimization to adapt to the transition to low-GWP refrigerants. In the 2nd quarter of FY21, we conducted multi-objective optimizations using Particle Swarm Optimization algorithm on a residential 5-ton air source heat pump to investigate the potential system performance improvements and material savings. 4 low-GWP refrigerants, ARM20A, ARM20B, R454A and R454C are investigated in this study. The objectives of the optimization are to minimize the heat pump material cost and to maximize the system performance simultaneously. As a result, the HXs material cost is reduced by up to 77% according to the copper and aluminum material price in current market. Under heating mode operation, the smart 4-way valve guarantees that the optimal low-GWP systems maintain or outperform the heating performance of the R410A baseline system. The model-based design optimization yields 18.3-18.9 SEER and 10.6-11.9 HSPF for optimal systems using different low-GWP refrigerants. The initial performance goals (16.0 SEER/9.5 HSPF) are achieved. Furthermore, up to 50% system refrigerant charge reduction is possible in the optimized low-GWP heat pump system using ARM20B. And 91%-95% predicted life-time direct CO 2 emission reduction is achieved by using the optimal 5mm tube low-GWP heat pumps. The significant material saving, charge reduction and direct CO 2 emission reduction help in reducing the environmental impacts of heat pump systems. The optimal heat exchangers resulting from this research can fit into the original baseline indoor and outdoor fan-coil unit. This can reduce the retrofitting effort by minimizing the change in manufacturing and installation of the heat pumps and guarantee the compatibility with end-users’ house structure. Finally, the new products can be easily accepted by manufacturers and end-users.

42 ENGINEERING↗
DOE OSTI2021

Perform Life Cycle Energy and GHG Emission Analysis, Select Candidate Refrigerant(s), Developing Heat Pump by Using Low-GWP Refrigerants and 5 mm Diameter Tubes

Reducing environmental impacts from the energy conversion systems has been an important research topic due to recent severe global climate changes. In residential buildings, the space heating and cooling are main energy consumers, which are relying on vapor compression based heat pumps. To mitigate the environmental impacts of residential systems, the heat pumps using low-GWP refrigerants and 5mm-tube heat exchangers are proposed to replace the conventional 9 mm or 7 mm tube heat exchangers. This research uses a simulation-based design method to optimize the refrigerant circuitries of a 5-ton low-GWP refrigerant heat pumps whose indoor and outdoor heat exchangers adopt 5 mm tubes. Heat pump systems using four commercially available low-GWP refrigerants (R454A, R454C, ARM20A and ARM20B) are optimized and compared with the baseline R410A system. The results indicate that directly replacing 9 mm tubes into 5mm tubes in the baseline systems induces heat pump performance degradation; by optimizing the 5 mm tube heat pumps with added tube rows, the system refrigerant charge is reduced up to 33% compared with the baseline; the optimized low-GWP 5 mm tube heat pumps offer the same or higher performance under both cooling and heating mode; that under cooling mode, the EER improvement is up to 10.7% and under heating mode the COP improvement is up to 3.4%; and a smart flow control device to maintain counter-flow circuitry pattern on both operating modes can improve the heating performance of 5 mm tube optimized system by up to 3.0%. In an effort to better understand the environmental impacts of these systems, life cycle climate performance (LCCP) evaluation method is used to assess the baseline and optimized systems. LCCP considers the direct and indirect emissions of the system over the course of its lifetime from manufacturing to disposal. Our analyses indicate that the optimized systems using 5mm tubes and low-GWP refrigerants can reduce life-cycle CO 2 emission significantly. And improving system efficiency is the most effective way to reduce the emission of low-GWP refrigerant systems. This report shows that using 5 mm diameter tubes in heat exchangers is a feasible approach to develop heat pumps with low-GWP refrigerants. Using the proposed design approach can yield higher system efficiency with lower environmental impact.

42 ENGINEERING↗
DOE OSTI2018

Extending ORNL HPDM capabilities for design and optimization of new refrigerant blends - FY18 3rd quarterly milestone: a trial version published online for modeling and design ac units using low GWP refrigerants

Based on exhaustive literature survey, we updated the DOE/ORNL HPDM to include most up-to-date heat transfer and pressure drop correlations suitable for modelling low GWP HFO blends and built up a comprehensive refrigerant property database including all the emerged HFO refrigerants. The upgraded HPDM has been released online, containing a desktop version for free download. The new release includes five system examples of room and commercial air conditioner (AC) units, which facilitates modelling and designing AC units using low GWP refrigerants. Geometry and configurations of the units were obtained from ORNL’s low-GWP refrigerant drop-in investigations [1] [2]. The published models have been calibrated to match the measured data. The new public-domain, free-to-use tool will help the US industry design their AC units using the new refrigerants and shorten the learning curve.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2017

R1234yf and R1234ze(E) as low-GWP refrigerants for residential heat pump water heaters; Le R1234yf et le R1234ze(E) comme frigorigènes à faible GWP pour des chauffe-eau domestiques à pompe à chaleur

Owing to the growing concerns about the relatively high global warming potential (GWP) of current refrigerants, a serious effort is currently in progress to find lower-GWP substitutes. The hydrofluoroolefin (HFO)-based refrigerants R1234yf and R1234ze(E) are being considered for use in multiple heating, ventilation, air conditioning, and refrigeration applications because of their very low GWP. A study was conducted to model a residential heat pump water heater using these HFOs. A system model was calibrated using experimental data and the calibrated model was used to evaluate the potential of HFOs to replace R134a. A series of parametric analyses were used to investigate the impacts of condenser wrap pattern, condenser tube size, evaporator size, and heat loss factor from the storage tank. It has been shown that both R1234yf and R1234ze(E) can be substituted for R134a with comparable performance and no substantial modifications to the original system. Finally, this study presents a detailed feasibility analysis for successful replacement of high-GWP refrigerants with low-GWP refrigerants with acceptable performance.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Microchannel Geometries for Improved Heat Transfer with Low-GWP refrigerants

Due to efforts aimed at decarbonizing industries, the use of refrigerants with low global warming potential (GWP) is highly recommended in the air-conditioning and refrigeration sectors. Despite possessing low-GWP values of less than 150, hydrofluoroolefins (HFO) exhibit relatively lower heat transfer performance compared to conventional hydrofluorocarbons (HFC) under certain operating conditions. In contrast to HFCs, there is a high demand for enhanced surfaces to meet the needs of heat transfer systems utilizing low GWP refrigerants. Accordingly, this study analyzes the pool boiling performance of low-GWP refrigerants in microchannel geometries. The experiments were carried out at various heat flux levels on both smooth and enhanced surfaces. The pool boiling behavior of low-GWP refrigerant R1234yf was compared to that of R-134a refrigerant in terms of heat transfer coefficient and wall superheat. The results indicate that the heat transfer coefficients of the enhanced surface are significantly higher than those of the smooth surface. Furthermore, the microchannel geometry demonstrated a lower wall superheat compared to the smooth surface. Additionally, a visualization study was performed using a high-speed camera to understand the pool boiling mechanism of low-GWP refrigerants on both smooth and enhanced surfaces.

Murugan, Muneeshwaran↗
DOE OSTI2024

Mitigation of Safety and Environmental Challenges Posed by Low and Ultra-low GWP Refrigerants

The abatement of safety and environmental burden associated with low and ultra-low Global Warming Potential (GWP) refrigerants is a critical undertaking. As the industry shifts towards more environmentally friendly alternatives, mitigating the potential risks and ensuring safety standards becomes paramount. The adoption of low GWP and ultra-low GWP refrigerants contributes significantly to minimizing the greenhouse gas impact on the environment, aligning with global climate and sustainability goals. However, it is essential to address safety concerns and potential environmental implications associated with the end use of these refrigerants.A method to mitigate the safety risk in a flammable refrigerant based HVACR system is the primary focus of this paper. Advent of A2L and A3 refrigerants as replacements to high GWP refrigerants requires careful handling of leak episodes to lower or eliminate the risk associated with creating flammable mixtures capable of fire/explosion hazard. Solid materials tailored to target the molecule of interest (i.e., refrigerant.) by engineering the microporous structure as well as chemically functionalizing the surface to attract and hold on to the chemical compound being removed from the gas stream was realized. Additionally, a chromatic transformation technique is investigated for rapid on-site analysis of refrigerant blends. Preliminary results demonstrating the feasibility of both of these methods for successful deployment of low-GWP refrigerants are presented.

Cheekatamarla, Praveen↗
DOE OSTI2017

Max Tech Efficiency Electric HPWH with low-GWP Halogenated Refrigerant

A scoping-level analysis was conducted to determine the maximum performance of an electric heat pump water heater (HPWH) with low GWP refrigerants (hydroflouroolefins (HFO), hydrofluorocarbons (HFC), and blends). A baseline heat pump water heater (GE GeoSpring) deploying R-134a was analyzed first using the DOE/ORNL Heat Pump Design Model (HPDM) modeling tool. The model was calibrated using experimental data to match the water temperature stratification in tank, first hour rating, energy factor and coefficient of performance. A CFD modeling tool was used to further refine the HPDM tank model. After calibration, the model was used to simulate the performance of alternative refrigerants. The parametric analysis concluded that by appropriate selection of equipment size and condenser tube wrap configuration the overall performance of emerging low GWP refrigerants for HPWH application not only exceed the Energy Star Energy Factor criteria i.e. 2.20, but is also comparable to some of the most efficient products in the market.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

Challenges and Recommended Policies for Simultaneous Global Implementation of Low-GWP Refrigerants and High Efficiency in Room Air Conditioners

Increasing incomes, electrification, and urbanization—as well as a warming world—are driving up the global stock of air conditioners (ACs), particularly in emerging economies with hot climates. AC energy consumption is expected to increase substantially as the global stock of room ACs rises to 1.5 billion in 2030 and 2.5 billion in 2050. Hence, improving AC energy efficiency will be critical to reducing AC energy, cost (consumer lifecycle cost, electricity generation cost, etc.), peak load, and emissions impacts. The 2016 Kigali Amendment to the Montreal Protocol offers an opportunity to improve AC energy efficiency in tandem with the phasedown of high global warming potential (GWP) hydrofluorocarbon (HFC) refrigerants. Based on the most recent information, a literature review, and interviews with manufacturers and industry experts, we find the main barriers to deploying high-efficiency ACs include concerns about market demand and cost, which could be mitigated by appropriately improved design of market-transformation programs such as standards and labeling, incentive, and procurement programs. The main barriers to the low-GWP refrigerant transition include the need for timely revision of safety standards and associated costs for capacity-building activities allowing safe use of low-GWP refrigerants in ACs. Policy action and the market transformation can be accelerated by advancing the refrigerant transition and efficiency improvements in parallel.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Low-GWP Refrigerants Status and Outlook

Refrigeration - including air conditioning (AC) – contributes substantially to the modern life of the 21st century and its economy. The food cold chain, air conditioning, healthcare and energy are examples of sectors for which refrigeration is indispensable. About 5 billion refrigeration systems – of different types and sizes– operate worldwide in different applications [1]. The dominant share of equipment providing refrigeration operate on the vapor-compression-cycle principle and use fluorocarbon refrigerants. Concerns about the environmental safety have become the driving force for refrigerant changes within the last 35 years. The phased-out schedule of stratospheric-ozone-depleting fluids was first formulated by the Montreal Protocol (MP) in 1987 and was made more stringent during the follow-up international meetings [2]. The affected chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants were largely replaced by hydrofluorocarbons (HFCs).The 2016 Kigali Amendment to the MP [3] responses to the concerns about the Earth climate change. The refrigeration and AC sectors are attributed with about 7.8 % of global greenhouse gas emissions [4]. This contribution comes in the form of direct effect, which is related to refrigerant emissions from refrigeration systems (37 %), and in the form of indirect effect, which is related to CO2 emissions from fossil fuel power plants producing electricity to power refrigeration systems (63 %) [4]. The Kigali Amendment aims at reducing the direct effect. The effect a given molecule has on the climate change is quantified in a simplified manner by its Global Warming Potential (GWP), a relative index referencing the effect produced to that of the same mass of carbon dioxide released to the atmosphere. By definition, GWP of carbon dioxide is equal to one.While HFC refrigerants have on average a lower GWP than the CFCs and HCFCs they replaced, they are still potent greenhouse gases (GHGs). The Kigali Amendment phases down the use of HFCs by imposing a schedule for reducing a weighted GWP value to be implemented by a country through the year 2047 (Figure 1). It provides four paths depending on the country location and category assigned in the MP, and also prescribes a method for establishing the baseline consumption used for calculating GWP reductions. For developing countries, it is expected to bring the weighed GWP across all refrigeration applications down to about 300 from the baseline value of about 2000. The implementation of Kigali Amendment aims at reducing the future warming due to HFCs from the range of 0.3 °C to 0.5 °C to less than 0.1 °C [5]. While this reduction may seem to be small, it must be viewed in the context of the 2015 Paris Agreement [6], which calls for holding global warming to well below 2 °C and pursuing to limit global warming to 1.5 °C relative to pre-industrial levels [6]. Considering that average global temperatures reached 1 °C above pre-industrial levels for the first time in 2015 [7], the Earth is already within 1 °C of the “2 °C limit”.The low-GWP requirement narrows the pool of fluids that can be considered for application as a refrigerant [8]. This Informatory Note discusses low-GWP refrigerant options for major applications and presents their selection merits.

Yana Motta, Samuel↗
DOE OSTI2018

Low-GWP HVAC System with Ultra-small Centrifugal Compression

Mechanical Solutions, Incorporated (MSI) was awarded a contract from the United States Department of Energy under Contract DE-EE0007042 to advance the potential of vapor compression utilizing an advanced high speed centrifugal compressor with an advanced heat exchanger design. The design was mandated to maintain high efficiency while utilizing a low GWP refrigerant. The specific goal of this program was to develop an advanced 5 ton air conditioning system. The target of the air conditioner is residential and commercial. To accomplish these goals, MSI teamed with Lennox International, a leading air conditioning manufacturer. MSI would design, oversee manufacturing, assemble, and test the compressor, while Lennox designed the heat exchanger and tested the overall air conditioner. Lennox initiated the project with a detailed cycle analysis that examined systems and refrigerants. At various break points, MSI performed a preliminary compressor design to identify realizable targets. Initially, the refrigerant that was targeted was R1234ze(E), but this was subsequently rejected over concerns of flammability. R515a was ultimately accepted as a qualified fluid based upon its GWP and flammability rating. MSI performed a complete design of the centrifugal compressor based upon the cycle system design and analysis. The design was based upon advanced aerodynamics utilizing transient Computational Fluid Dynamics (CFD), as well as mechanical and rotordynamic analysis. A detailed materials investigation was conducted to ensure mechanical integrity and refrigerant compatibility. To achieve the high rotational speed required by the compressor (105,300 rpm), foil bearings were designed by MSI, as was a high speed motor to provide the required torque for the compressor. All elements of the design complied with Design for Manufacturing and Assembly (DFMA) principles. The compressor was manufactured in components, utilizing specializing subcontractors throughout the country. The components were assembled into an operational compressor in MSI’s Albany facility, where it was tested in the MSI refrigeration test loop. The compressor achieved 90% of its maximum speed during testing at MSI. The interaction between the inverter and the high speed motor was the reason that full speed could not be attained. The compressor operated smoothly and quietly at all speeds, with the bearings performing as expected. The compressor was then shipped to Lennox’s facilities in Texas, where it was tested in the entire air conditioning system. Lennox was able to achieve 95% of the maximum rotational speed. They employed the same inverter as MSI. Lennox compiled the results of the testing and based upon the results, a go forward plan has been developed to correct the issues with the inverter, as well as redesign some parts that proved to be a challenge during the program. The consensus of the team is that a fully functional air conditioning system can be developed to achieve all of the goals identified in this program.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2016

Low GWP Refrigerants Modelling Study for a Room Air Conditioner Having Microchannel Heat Exchangers

Microchannel heat exchangers (MHX) have found great successes in residential and commercial air conditioning applications, being compact heat exchangers, to reduce refrigerant charge and material cost. This investigation aims to extend the application of MHXs in split, room air conditioners (RAC), per fundamental heat exchanger and system modelling. For this paper, microchannel condenser and evaporator models were developed, using a segment-to-segment modelling approach. The microchannel heat exchanger models were integrated to a system design model. The system model is able to predict the performance indices, such as cooling capacity, efficiency, sensible heat ratio, etc. Using the calibrated system and heat exchanger models, we evaluated numerous low GWP (global warming potential) refrigerants. The predicted system performance indices, e.g. cooling efficiency, compressor discharge temperature, and required compressor displacement volume etc., are compared. Suitable replacements for R22 and R-410A for the room air conditioner application are recommended.

Low GWP↗
DOE OSTI2015

A comparative study on the environmental impact of supermarket refrigeration systems using low GWP refrigerants

Supermarket refrigeration systems have high environmental impact due to their large refrigerant charge and high leak rates. Consequently, the interest in using low GWP refrigerants such as carbon dioxide (CO 2 ) and new refrigerant blends is increasing. In this study, an open-source Life Cycle Climate Performance (LCCP) framework is presented and used to compare the environmental impact of four supermarket refrigeration systems: a transcritical CO 2 booster system, a cascade CO 2 /N-40 system, a combined secondary circuit with central DX N-40/L-40 system, and a baseline multiplex direct expansion system utilizing R-404A and N-40. The study is performed for different climates within the USA using EnergyPlus to simulate the systems' hourly performance. Finally, further analyses are presented such as parametric, sensitivity, and uncertainty analyses to study the impact of different system parameters on the LCCP.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Potential emission savings from refrigeration and air conditioning systems by using low GWP refrigerants

Refrigeration and air conditioning systems have high, negative environmental impacts due to refrigerant charge leaks from the system and their corresponding high global warming potential. Thus, many efforts are in progress to obtain suitable low GWP alternative refrigerants and more environmentally friendly systems for the future. In addition, the system’s life cycle climate performance (LCCP) is a widespread metric proposed for the evaluation of the system’s environmental impact.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Residential Split Heat Pump Using Low GWP Refrigerants

Conventional refrigerants, e.g. R-410A have high global warming potentials (GWP) > 1800. They are being phased out to protect the environment. The candidates to replace R-410A include R-32, R-452B, R-454B and R-466A for heat pump applications. These candidates are intended for drop-in replacement, i.e. having minimum modifications on existing systems. The paper investigates the low GWP refrigerants drop-in application via system simulations using a well-regarded, hardware-based heat pump model. A baseline heat pump having all fin-and-tube heat exchangers and a two-speed compressor was used. Cross-comparisons were made under rated conditions of ambient temperatures, compressor speeds, indoor air flow rates, respectively for cooling and heating operations. The seasonal performance indices, i.e. SEER and HSPF are presented.

Shen, Bo↗
DOE OSTI2023

Experimental investigation on nucleate boiling heat transfer of low GWP refrigerants over metal-foam enhanced tube bundles

The objective of this work is to develop an enhanced tube bundle to improve the nucleate boiling heat transfer for the application of flooded evaporators. The enhanced tube bundle was made by deploying metal foam around the outer surface of aluminum tubes, which provide higher heat transfer area and nucleation site density. The pool boiling experiments for horizontal tube bundles were conducted in a pressure vessel at difference heat fluxes. The heat transfer performance of bare aluminum tube bundle was compared against the metal-foam enhanced tube bundle using low GWP refrigerant, R-1234yf. The experimental results showed that the heat transfer coefficient of the metal-foam enhanced tube bundle was at least two times higher than that of the bare tube bundle, and the enhancement ratio depended on the heat flux condition.

Yang, Cheng-Min↗
DOE OSTI2024

Thermal-hydraulic Performance of Emerging Low GWP Refrigerant Mixture under Flow Boiling in Brazed Plate Heat Exchangers

The hydrofluorocarbon (HFC) refrigerants used in the current refrigeration systems are facing a phase-down due to their higher greenhouse effect resulting in global warming, and thus HVAC&R industry has undergone a transition to low Global Warming Potential (GWP) refrigerants. Refrigerant mixtures are attractive alternatives since their composition can be tailored to comply with environmental regulations while preserving favorable thermophysical properties. However, the new low-GWP zeotropic mixture refrigerants have two or more components with different saturation temperatures at the same pressure level, known as temperature glide, which can cause the degradation of the overall heat transfer performance. The brazed plate heat exchangers (BPHX) provide excellent heat transfer performance due to a compact design and are used in several air-conditioning and refrigeration applications. In this study, flow boiling heat transfer and the associated pressure drop of the refrigerant mixture in a vertical BPHX were experimentally investigated. The single-phase water-to-water experiments were conducted in the tested heat exchanger with a counter-flow configuration. The flow boiling experiments charged with R-134a and R-454C were then performed in a pumped refrigerant loop to evaluate its thermal-hydraulic performance. Furthermore, parametric studies of various heat fluxes, mass fluxes, vapor qualities, and saturation temperatures were also conducted.

Yang, Cheng-Min↗
DOE OSTI2023

Canister valve and actuator deposition in metered dose inhalers formulated with low-GWP propellants

A challenge in pressurised metered-dose inhaler (pMDI) formulation design is management of adhesion of the drug to the canister wall, valve and actuator internal components and surfaces. Wall-material interactions differ between transparent vials used for visual inspection and metal canister pMDI systems. This is of particular concern for low greenhouse warming potential (GWP) formulations where propellant chemistry and solubility with many drugs are not well understood. In this study, we demonstrate a novel application of X-ray fluorescence spectroscopy using synchrotron radiation to assay the contents of surrogate solution and suspension pMDI formulations of potassium iodide and barium sulphate in propellants HFA134a, HFA152a and HFO1234ze(E) using aluminium canisters and standard components. Preliminary results indicate that through unit life drug distribution in the canister valve closure region and actuator can vary significantly with new propellants. For solution formulations HFO1234ze(E) propellant shows the greatest increase in local deposition inside the canister valve closure region as compared to HFA134a and HFA152a, with correspondingly reduced actuator deposition. This is likely driven by chemistry changes. For suspension formulations HFA152a shows the greatest differences, due to its low specific gravity. These changes must be taken into consideration in the development of products utilising low-GWP propellants.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Evaluation and development of flow condensation correlations using the data from low GWP refrigerants in an axial micro-fin aluminum tube

To mitigate global warming, the world is transitioning to refrigerants with low global warming potential (GWP). Supporting this shift requires a model that can accurately predict the heat transfer and pressure drop of new refrigerants, crucial for designing efficient heat exchangers. Existing models, however, are largely based on currently deployed refrigerants and primarily developed for unexpanded micro-fin tubes with spiral angles of 6° to 30°. Their applicability to new refrigerants, especially in expanded micro-fin tubes, is uncertain. This study assesses the performance of four well-known condensation models for six emerging refrigerants—R-32, R-454B, R-454C, R-455A, R-1234yf, and R-1234ze(E)—against experimental data. Initially, the Han and Lee (2005) model shows the best prediction accuracy with a mean absolute deviation (MAD) of 22.1 %. To enhance the accuracy of heat transfer models for new refrigerants and geometries with large temperature glides, two approaches are proposed. Here, the first approach applies a simple correction factor, reducing the MAD of the Cavallini et al. (2009) model from 68.2 % to 15.4 %. The second approach uses the variable metric method for minimization, fitting new constants to the data. This optimization results in the Kedzierski and Goncalves (1997) model achieving the highest accuracy, with a MAD of 13.1 %. For pressure drop models, the Cavallini et al. (1997) model is the most accurate with a MAD of 6.4 %, followed by the Haraguchi et al. (1993) model with a MAD of 9.4 %. Due to its simplicity, the Haraguchi et al. (1993) model is a practical option for predicting frictional pressure drop.

Axial micro-fin tubes↗