Flow boiling visualization and heat transfer in metal-foam-filled mini tubes - Part I: Flow pattern map and experimental data

Bamorovat Abadi, G.,Moon, C.,Kim, K.C. Pergamon Press ; Elsevier Science Ltd 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.98 No.-

High-porosity open-cell metal foams are well known to enhance the heat transfer mechanism in rectangular or circular channels. Their high surface area to volume ratio makes them a great candidate for manufacturing high-performance small-scale heat exchangers. This two-part experimental study investigated the two-phase flow boiling inside a circular copper mini tube. In Part I, the flow pattern was visualized by high-speed imaging in glass tubes. Flow pattern maps, the heat transfer coefficient, and pressure drop are presented for mean vapor quality of 0.1-0.7, heat flux of 20-40kW/m<SUP>2</SUP>, and mass flux of 400-700kg/m<SUP>2</SUP>s. The experiments were also performed without the metal foam in the mini tube for comparison to the original data. In this range of experimental conditions, the metal foam increased the heat transfer coefficient up to 3.2 times. Also, as expected, the metal foams adversely affected the pressure drop inside the tubes.

Flow boiling visualization and heat transfer in metal-foam-filled mini tubes - Part II: Developing predictive methods for heat transfer coefficient and pressure drop

Bamorovat Abadi, G.,Moon, C.,Kim, K.C. Pergamon Press ; Elsevier Science Ltd 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.98 No.-

High-porosity metal foams are proposed for insertion into heat exchanger channels to enhance the heat transfer mechanism in evaporators that are mainly used in organic Rankine cycle applications. This two-part experimental study investigates the two-phase flow inside a circular copper mini tube. Part I visualized the flow pattern and presented flow pattern maps, heat transfer coefficient data, and pressure drop data. Part II compares experimental data to recent correlations developed for metal-foam-filled mini tubes. The experimental conditions of the present study fall outside the valid range of the correlations, so none of them can predict the heat transfer coefficient or pressure drop accurately. Therefore, both the heat transfer coefficient and pressure drop are correlated using new approaches based on previous works and the present experimental data. Good agreement is observed between the experimental data and the new correlations in these experimental conditions.

Experimental heat transfer and pressure drop in a metal-foam-filled tube heat exchanger

Bamorovat Abadi, G.,Kim, K.C. Elsevier 2017 Experimental thermal and fluid science Vol.82 No.-

<P>Heat transfer in small tubes is of particular interest in the heat exchanger industry for manufacturing shell-and-tube or concentric-tube heat exchangers. Metal-foam-filled tubes enhance the heat transfer mechanism by providing a high surface-area-to-volume ratio. This experimental study investigates the heat transfer and pressure drop in such tubes. Single-phase experiments were performed using copper tubes with an inner diameter of 4 mm and filled with copper metal foam. R245fa refrigerant was used as the working fluid with mass flux ranging from 200 to 1000 kg/m(2) s. The heat transfer coefficient and pressure drop data are reported and compared to a tube without metal foam. The experimental data are also compared to well-known correlations from the literature. Most of the correlations are unable to capture any data point since they were developed for much bigger channels. New correlations are proposed to predict the heat transfer coefficient and pressure drop in such small tubes with metal foam inside. (C) 2016 Elsevier Inc. All rights reserved.</P>

Thermal performance of a 10-kW phase-change plate heat exchanger with metal foam filled channels

Bamorovat Abadi, Gholamreza,Kim, Dae Yeon,Yoon, Sang Youl,Kim, Kyung Chun Elsevier 2016 Applied thermal engineering Vol.99 No.-

<P><B>Abstract</B></P> <P>Compact-sized organic Rankine cycle (ORC) power generators call for small-scale heat exchangers to work with them. Since the heat transfer area plays a direct role in the performance of heat exchangers, micro-cellular structures such as metal foams are proposed to increase the heat duty of heat exchangers by increasing the surface area while maintaining their small size. In this experimental study, the performance of a 10-kW heat exchanger with channels filled with copper metal foam was investigated. A hot water loop was designed for heat input. The cold side of the heat exchanger works with R245fa as the working fluid. Single-phase and two-phase experiments were performed with different mass fluxes ranging from 180 to 600 kg/m<SUP>2</SUP>s. The effect of the pores per inch (PPI), working pressure, and different arrangements of metal foams was also investigated. Although the metal foam increases the pressure drop in the channel, it increases the recovered waste heat from the heat source and overall heat transfer coefficient of the heat exchanger by up to 2.3 times compared to a conventional heat exchanger without metal foams.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thermal performance of a metal foam filled heat exchanger has been studied. </LI> <LI> The effect of pressure, metal foam configuration and PPI value is reported. </LI> <LI> 20 PPI metal foam proved to have the best performance. </LI> <LI> With 20 PPI metal foam the overall HTC increased by 2.3 times. </LI> <LI> ORC evaporator size can be reduced by using proper metal foam. </LI> </UL> </P>

Enhancement of phase-change evaporators with zeotropic refrigerant mixture using metal foams

Bamorovat Abadi, Gholamreza,Kim, Kyung Chun Elsevier 2017 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.106 No.-

<P><B>Abstract</B></P> <P>Almost all thermal systems use some kind of heat exchanger. In many cases, evaporators are needed for systems such as organic Rankine cycle (ORC) systems. Evaporators contribute to a big portion of the capital cost, and their price is directly related to their size or transfer area. Highly porous open-cell metal foams are being considered to improve performance while keeping the size of heat exchangers small. This study experimentally investigates the degradation of the heat transfer coefficient of zeotropic mixtures during phase change in a plate heat exchanger with metal-foam-filled channels. The working fluids were pure R245fa and a zeotropic mixture of R245fa/R134a (0.6/0.4 molar ratio). The results show that the metal foams significantly increase the recovered heat, overall heat transfer coefficient, and effectiveness of the heat exchanger for mass flux ranging from 90 to 290kg/m<SUP>2</SUP>s, but at the expense of increasing the pressure drop. The same improvement was observed for the mixture of refrigerants. The degraded heat transfer coefficient of the mixture compared to the pure refrigerants was recovered by the introduction of metal foams to the system. New correlations are proposed to predict the two-phase heat transfer coefficient of both pure R245fa and the refrigerant mixture in metal foam evaporators.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Zeotropic mixture in a metal foam heat exchanger has been studied experimentally. </LI> <LI> R245fa and mixture of R245fa/R134a (0.6/0.4) were investigated. </LI> <LI> Heat transfer enhancement was observed for both types of refrigerants. </LI> <LI> 20 PPI metal foam proved to have the best performance in all cases. </LI> <LI> New correlations were proposed for two-phase flow parameters. </LI> </UL> </P>

Investigation of organic Rankine cycles with zeotropic mixtures as a working fluid: Advantages and issues

Bamorovat Abadi, Gholamreza,Kim, Kyung Chun Elsevier 2017 RENEWABLE & SUSTAINABLE ENERGY REVIEWS Vol.73 No.-

<P><B>Abstract</B></P> <P>Global warming has been a major concern, and the amount of CO<SUB>2</SUB> released to the atmosphere keeps increasing due to overuse of the earth's fossil fuel reserves. Overpopulation and lack of comprehensive energy management add to the problem. New and renewable energy sources are still expensive or in the conceptual phase. The organic Rankine cycle (ORC) seems to be a viable option to address these issues by reusing waste and low-grade heat that would otherwise be released into the environment. Many ORC power plants are already in commercial use. Since the introduction of the basic ORC (BORC), there have been many revolutionary ideas to optimize the performance of power generators, but they have not been experimentally tested extensively. This study focuses on zeotropic refrigerant mixtures made of two or three refrigerants instead of a single working fluid. The main advantages of this system are increased exergy efficiency and decreased irreversibility in the evaporator and condenser, where the isothermal phase change of pure refrigerant would not match the temperature profile of the heat source and heat sink. Published experimental studies on this topic are extremely rare. This study discusses almost all the articles on this subject, the proposed mixtures, and the conclusions.</P>

Experimental study on single-phase heat transfer and pressure drop of refrigerants in a plate heat exchanger with metal-foam-filled channels

Bamorovat Abadi, Gholamreza,Moon, Chanhee,Kim, Kyung Chun Elsevier 2016 Applied thermal engineering Vol.102 No.-

<P><B>Abstract</B></P> <P>Metal-foam-filled channels are proposed to increase the heat transfer area between hot and cold flows in plate heat exchangers. This experimental study focuses on the single-phase heat transfer mechanism of R245fa refrigerant in a metal-foam-filled plate heat exchanger instead of more commonly used air or water in single-phase experiments. The refrigerant-side heat-transfer coefficient and pressure-drop data are reported. Different metal foams with various pore densities of values of 20, 30, and 60pore per inch (PPI) were examined. Cases were studied with uniform PPI and with two different PPI along the flow direction. A complete heat exchanger test section with an overall volume of 0.001m<SUP>3</SUP> that is able to generate 1–2kW heat duty in this range of experimental conditions is manufactured. The result shows that inserting 60-PPI metal foam increases the refrigerant-side heat transfer coefficient by up to 5.1 times compared to the plate heat exchanger without the metal foam insert. As expected, the pressure drop penalty is huge. The 60-PPI metal foam had the greatest pressure drop, which was 5.7 times that of an empty-channel heat exchanger.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heat exchanger with metal-foam-filled channels is manufactured. </LI> <LI> Single-phase experiments are performed. </LI> <LI> The effect of metal foam configuration and pore density is analyzed. </LI> <LI> With 60PPI metal foam the overall HTC increased by 5.1 times. </LI> <LI> With 60PPI metal foam the pressure drop increased by 5.7 times. </LI> </UL> </P>

Flow Boiling Visualization of Mixture of R134a and R245fa in a Vertical Circular Tube

Gholamerza Bamorovat Abadi,Kyung Chun Kim 한국가시화정보학회 2015 한국가시화정보학회 학술발표대회 논문집 Vol.2015 No.5

Flow Boiling Visualization of R245fa in a 3 mm Circular Horizontal Tube

Gholamreza Bamorovat Abadi,Kyung Chun Kim 한국가시화정보학회 2015 한국가시화정보학회 학술발표대회 논문집 Vol.2015 No.12

Experimental study of the effect of brazed compact metal-foam evaporator in an organic Rankine cycle performance: Toward a compact ORC

Nematollahi, Omid,Abadi, Gholamreza Bamorovat,Kim, Dae Yeon,Kim, Kyung Chun Elsevier 2018 Energy conversion and management Vol.173 No.-

<P><B>Abstract</B></P> <P>Compact-sized organic Rankine cycle (ORC) power generators require small-scale heat exchangers to achieve high power density. The objective of this study is to investigate the effect of a Brazed Metal-foam Plate Heat Exchanger (BMPHE) in an Organic Rankine Cycle (ORC) performance parameters. This evaporator is one of the first industrial full BMPHE which is composed by Nickle-foam with 25 PPI (pore per inch). In addition, a series of the experiments have been done using conventional Brazed Plate Heat Exchanger (BPHE) to make a comprehensive comparison for both cycles. Two parameters of power density and pressure gradient are introduced to make a clear comparison in addition to ORC performance parameters. Experimental data are presented for a 1-kW scroll expander and heat source temperatures between 80 and 120 °C. The results show that although the compact evaporator (BMPHE) increases the pressure drop by factors of 1.4–2.6, the overall performance of the ORC is not adversely affected, and the power density is increased by a factor of 2.5 in maximum.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel application of compact Brazed Metal-foam Plate Heat Exchanger is presented. </LI> <LI> The introduced heat exchanger is tested in an organic Rankine cycle to emphasize the size effect. </LI> <LI> The power density and pressure gradient is used for the comparison. </LI> <LI> The power density is increased by a factor of 2.5 in maximum. </LI> </UL> </P>