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19 pages, 5446 KiB

Open AccessArticle

Influence of Frost Growth and Migration in Cryogenic Heat Exchanger on Air Refrigerator

by Shanju Yang, Zhan Liu, Bao Fu and Yu Chen

Appl. Sci. 2019, 9(4), 753; https://doi.org/10.3390/app9040753 - 21 Feb 2019

Cited by 4 | Viewed by 3756

Abstract

Frost formation degrades the performance of heat exchangers greatly, thus influencing the cryogenic refrigerator. Different from frost formation on the evaporator surface, the growth and migration of frost layer inside the heat exchanger is of low temperature and humidity. In addition to the [...] Read more.

Frost formation degrades the performance of heat exchangers greatly, thus influencing the cryogenic refrigerator. Different from frost formation on the evaporator surface, the growth and migration of frost layer inside the heat exchanger is of low temperature and humidity. In addition to the constantly changing boundary conditions, the effective prediction is difficult. In the present study, a numerical model was proposed to analyze the frost formation in the cryogenic heat exchanger of a reverse Brayton air refrigerator. Under small amounts of moisture, the growing of frost layer was simulated through the numerical heat and mass transfer by adopting semiempirical correlations. The frost formation model was inserted into the transient model of refrigerator, and numerical calculations were performed on heat and mass transfer rates, and growth and migration of frost layers in forced convection conditions. Experiments were conducted under different air humidity to investigate the frost formation and verify the numerical model. Through the model, the influences of frosting on the refrigerator were evaluated under different moisture contents and running time. It can be used to predict the performance of air refrigerators with low humidity and provide a basis for improving the system operation and efficiency. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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12 pages, 4736 KiB

Open AccessArticle

Adsorption Transformation of Heat: The Applicability in Various Climatic Zones of the Russian Federation

by Alexandra Grekova, Larisa Gordeeva, Alessio Sapienza and Yuri Aristov

Appl. Sci. 2019, 9(1), 139; https://doi.org/10.3390/app9010139 - 3 Jan 2019

Cited by 9 | Viewed by 4918

Abstract

Adsorption heat transformation (AHT) is energy and environment saving technology that allows the effective utilization of renewable and waste heat with low-temperature potential. For the enhancement of AHT efficiency, properties of the working pair “adsorbent–adsorbate” have to be intelligently adapted to the operating [...] Read more.

Adsorption heat transformation (AHT) is energy and environment saving technology that allows the effective utilization of renewable and waste heat with low-temperature potential. For the enhancement of AHT efficiency, properties of the working pair “adsorbent–adsorbate” have to be intelligently adapted to the operating conditions of the specific AHT cycle. In this work, the applicability of ATH technology in the Russian Federation (RF) was analyzed. For various geographic zones of the RF, the proper AHT application (cooling, heating, heat amplification, or storage) was selected depending on the zone climatic conditions. Data on the adsorption equilibrium for more than 40 “adsorbent–adsorbate” pairs collected from the literature were analyzed to select the most suitable pairs for the particular application/zone. Recommendations on AHT applications and the proper working pairs for the considered RF climatic zones are made. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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18 pages, 6342 KiB

Open AccessArticle

A Fast Prediction Model for Heat Transfer of Hot-Wall Heat Exchanger Based on Analytical Solution

by Wenju Hu, Peng Jia, Jinzhe Nie, Yan Gao and Qunli Zhang

Appl. Sci. 2019, 9(1), 72; https://doi.org/10.3390/app9010072 - 25 Dec 2018

Cited by 4 | Viewed by 3586

Abstract

The hot-wall heat exchanger (HWHE) has been widely used in thermal engineering fields such as ceiling radiant heating/cooling, refrigerator condenser, solar heat collection, and high-temperature heat recovery. However, the numerical simulation normally used for heat transfer prediction in HWHE is usually not as [...] Read more.

The hot-wall heat exchanger (HWHE) has been widely used in thermal engineering fields such as ceiling radiant heating/cooling, refrigerator condenser, solar heat collection, and high-temperature heat recovery. However, the numerical simulation normally used for heat transfer prediction in HWHE is usually not as convenient as the analytic solutions in engineering applications. In this paper, a new heat transfer mathematical model of HWHE-based on analytic solutions was developed, which could be much faster to obtain the heat transfer properties of HWHE. The proposed model was validated under four conditions with literature values, which showed that the deviations of heat flux are 2.53%, 0.99%, 2.12%, and 1.96%, indicating its accuracy is satisfied. The model was then used to analyze the thermal property of HWHE. The results show the thermal resistance caused by panel with heat convection and conduction accounts for 96.54% of HWHE thermal resistance, and the thermal resistance caused by heat convection on the surface of panel is 74.43%. The analyzation results also show that adding aluminum foil around pipes could decrease HWHE thermal resistance by 5.11%. Besides, the influence of pipe diameters, pipe distance, pipe heat conductivity, side wall heat conductivity, and convective heat transfer coefficient on the heat transfer performance of HWHE was analyzed. The research in this paper can be used for fast prediction and optimization of heat transfer in HWHE. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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18 pages, 2576 KiB

Open AccessArticle

Off-Design Modeling and Simulation of Solar Absorption-Subcooled Compression Hybrid Cooling System

by Zeyu Li, Jianting Yu, Erjian Chen and Yue Jing

Appl. Sci. 2018, 8(12), 2612; https://doi.org/10.3390/app8122612 - 13 Dec 2018

Cited by 13 | Viewed by 3115

Abstract

The solar absorption-subcooled compression hybrid cooling system (SASCHCS) is potentially an economical solution for high-rise buildings. The hybrid system is subjected to off-design operation frequently, owing to the changes in solar irradiance and cooling demand. However, a large amount of iterations and difficult [...] Read more.

The solar absorption-subcooled compression hybrid cooling system (SASCHCS) is potentially an economical solution for high-rise buildings. The hybrid system is subjected to off-design operation frequently, owing to the changes in solar irradiance and cooling demand. However, a large amount of iterations and difficult convergence are encountered in the traditional off-design modeling. Hence, our present study contributes to the development of an off-design model that is exact and can be solved conveniently. A novel modeling method based on the combination of an absorption subsystem described by the characteristic equation and a compression subsystem modeled by the lumped parameter method is proposed. A prototype and corresponding experimental system are developed to verify the model. A good agreement between the theoretical result and test data is displayed. The maximum deviation is less than 4%. Subsequently, the performance of the facility for different operating conditions is simulated and analyzed. We found that the subcooling power relies significantly on the compressor speed, i.e., a reduction by 58.6% when the compressor speed reduces by 80%. In addition, a high temperature and low flow rate of cooling water in the compression subsystem is adverse to the performance of the hybrid system. Our study can serve as the foundation for the operational analysis of the solar absorption-subcooled compression hybrid cooling system as well as promote its development. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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20 pages, 2819 KiB

Open AccessArticle

Gear and Runge–Kutta Numerical Discretization Methods in Differential Equations of Adsorption in Adsorption Heat Pump

by Katarzyna Zwarycz-Makles and Dorota Majorkowska-Mech

Appl. Sci. 2018, 8(12), 2437; https://doi.org/10.3390/app8122437 - 1 Dec 2018

Cited by 5 | Viewed by 4698

Abstract

The main aim of this paper was to find the correct method of calculating equations of heat and mass transfer for the adsorption process and to calculate it numerically in reasonable time and with proper accuracy. An adsorption heat pump with a silica [...] Read more.

The main aim of this paper was to find the correct method of calculating equations of heat and mass transfer for the adsorption process and to calculate it numerically in reasonable time and with proper accuracy. An adsorption heat pump with a silica gel adsorbent and water adsorbate is discussed. We developed a mathematical model of temperature and uptake changes in the adsorber/desorber comprising the set of heat and mass balance partial differential equations (PDEs), together with the initial and boundary conditions and solved it by the numerical method of lines (NMOL). Spatial discretization was performed with equally spaced axial nodes and the PDEs were reduced to a set of ordinary differential equations (ODEs). We focused on the comparison of results obtained when the set of heat and mass balance ODEs for an adsorber was solved using: (1) the Runge–Kutta fixed step size fourth-order method (RKfixed), (2) the Runge–Kutta–Fehlberg 4.5th-order method with a variable step size (RK45), and (3) the Gear Backward Differentiation Formulae numerical (Gear BDF) methods. In our experience, all three types of ODE numerical methods (RKfixed, RK45, and Gear BDF) can be applied in simple models to model an adsorber with attention on their limitations. The Gear BDF method usually requires much fewer steps than the RK45 method for almost the same calculating time. RK methods require many more steps to obtain results, and the calculating time depends on accuracy or defined time step. Moreover, one should pay attention to the number of nodes or possible oscillations. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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12 pages, 2203 KiB

Open AccessFeature PaperArticle

Correlation for Condensation Heat Transfer in a 4.0 mm Smooth Tube and Relationship with R1234ze(E), R404A, and R290

by Norihiro Inoue, Masataka Hirose, Daisuke Jige and Junya Ichinose

Appl. Sci. 2018, 8(11), 2267; https://doi.org/10.3390/app8112267 - 16 Nov 2018

Cited by 7 | Viewed by 3698

Abstract

In this study, the condensation heat transfer coefficient and pressure drop characteristics of a 4 mm outside diameter smooth tube, using R32, R152a, R410A, and R1234ze(E) refrigerants, were examined. Condensation heat transfer coefficients and pressure drops were measured at a saturation temperature of [...] Read more.

In this study, the condensation heat transfer coefficient and pressure drop characteristics of a 4 mm outside diameter smooth tube, using R32, R152a, R410A, and R1234ze(E) refrigerants, were examined. Condensation heat transfer coefficients and pressure drops were measured at a saturation temperature of 35 °C, in the region of mass velocities from 100 to 400 kg m⁻²s⁻¹. The frictional pressure drop, and the condensation heat transfer from the new measurements, using R1234ze(E) as a refrigerant, were compared with those of R32, R152a, and R410A, in the smooth tube. Experimental values of condensation heat transfer coefficient of smooth tube were also compared to the predicted values obtained using the previously established correlations. The previous correlation from Cavallini et al., for the condensation heat transfer coefficient of small-diameter smooth tube, was estimated to be within ±30%. However, the general correlation, which can be easily predicted, for condensation heat transfer inside small-diameter smooth tubes, was suggested, and the relationship of the general correlation was compared with data for R1234ze(E) obtained by us, and R404A and R290 obtained by other researchers. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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21 pages, 12763 KiB

Open AccessArticle

Water Extraction from Air by Refrigeration—Experimental Results from an Integrated System Application

by Lucia Cattani, Anna Magrini and Paolo Cattani

Appl. Sci. 2018, 8(11), 2262; https://doi.org/10.3390/app8112262 - 16 Nov 2018

Cited by 24 | Viewed by 6017

Abstract

Water is an indispensable resource for life. Several technologies have been studied and used in the past to extract water from the ground, the air or the sea. The technologies vary depending on community needs and resources. In developed countries, air conditioning systems [...] Read more.

Water is an indispensable resource for life. Several technologies have been studied and used in the past to extract water from the ground, the air or the sea. The technologies vary depending on community needs and resources. In developed countries, air conditioning systems are widespread, and the use of condensed water from air conditioning systems is of potential interest. In hot and dry climates, in arid regions where refrigeration processes represent a basic need for indoor comfort, advantages of an integrated design of HVAC (Heating, Ventilation and Air Conditioning) systems optimized for water production rather than for air treatment could be evaluated. In the current work, a real application, which embodies savings of both energy and drinking water, is presented. It represents an evolution of a previously studied integrated system to simultaneously provide air conditioning and water to a hotel. The main target of this system is to meet drinking water requirements and, secondly, to provide domestic water heating and primary air for a non-conditioned zone. Main features of the integrated system are outlined, the needs of the hotel are described, and calculations of water and energy savings are presented. Moreover, a simulation tool was developed with the aim to evaluate possible water savings in a one-year period and to improve the efficiency of the system. A method to verify the effectiveness of the integrated system is also described. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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18 pages, 8377 KiB

Open AccessArticle

Field Experiments to Evaluate Thermal Performance of Energy Slabs with Different Installation Conditions

by Seokjae Lee, Sangwoo Park, Minkyu Kang and Hangseok Choi

Appl. Sci. 2018, 8(11), 2214; https://doi.org/10.3390/app8112214 - 10 Nov 2018

Cited by 12 | Viewed by 2989

Abstract

The energy slab is a novel type of horizontal Ground Heat Exchanger (GHEX), where heat exchange pipes are encased in building slab structures. The thermal performance of energy slabs is usually inferior to the conventional closed-loop vertical GHEX because its installation depth is [...] Read more.

The energy slab is a novel type of horizontal Ground Heat Exchanger (GHEX), where heat exchange pipes are encased in building slab structures. The thermal performance of energy slabs is usually inferior to the conventional closed-loop vertical GHEX because its installation depth is relatively shallow and therefore affected by ambient air temperature. In this paper, heat exchange pipes were made of not only conventional high-density polyethylene (HDPE), but also stainless steel (STS), which is expected to enhance the thermal performance of the energy slabs. In addition to a floor slab, a side wall slab was also used as a component of energy slabs to maximize the use of geothermal energy that can be generated from the underground space. Moreover, a thermal insulation layer in the energy slabs was considered in order to reduce thermal interference induced by ambient air temperature. Consequently, two different field-scale energy slabs (i.e., floor-type and wall-type energy slabs) were constructed in a test bed, and two types of heat exchange pipes (i.e., STS pipe and HDPE pipes) were installed in each energy slab. A series of thermal response tests (TRTs) and thermal performance tests (TPTs) were conducted to evaluate the heat exchange performance of the constructed energy slabs. Use of the STS heat exchange pipe enhanced the thermal performance of energy slabs. Additionally, the wall-type energy slab had a similar thermal performance to the floor-type energy slab, which infers the applicability of the additional use of the wall-type energy slab. Note that if an energy slab is not thermally cut off from the building’s interior space with the aid of thermal insulation layers, heat exchange within the energy slabs should be significantly influenced by fluctuations in ambient temperature. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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24 pages, 5372 KiB

Open AccessArticle

Integration of the Experimental Results of a Parabolic Trough Collector (PTC) Solar Plant to an Absorption Air-Conditioning System

by Yuridiana Rocio Galindo Luna, Wilfrido Rivera Gómez Franco, Ulises Dehesa Carrasco, Rosenberg Javier Romero Domínguez and José Camilo Jiménez García

Appl. Sci. 2018, 8(11), 2163; https://doi.org/10.3390/app8112163 - 5 Nov 2018

Cited by 11 | Viewed by 3311

Abstract

The present study reports the experimental results of a parabolic trough collector field and an absorption cooling system with a nominal capacity of 5 kW, which operates with the ammonia-lithium nitrate mixture. The parabolic trough collectors’ field consists of 15 collectors that are [...] Read more.

The present study reports the experimental results of a parabolic trough collector field and an absorption cooling system with a nominal capacity of 5 kW, which operates with the ammonia-lithium nitrate mixture. The parabolic trough collectors’ field consists of 15 collectors that are made of aluminum plate in the reflector surface and cooper in the absorber tube, with a total area of 38.4 m². The absorption cooling system consists of 5 plate heat exchangers working as the main components. Parametric analyses were carried out to evaluate the performance of both systems under different operating conditions, in independent way. The results showed that the solar collectors’ field can provide up to 6.5 kW of useful heat to the absorption cooling system at temperatures up to 105 °C with thermal efficiencies up to 19.8% and exergy efficiencies up to 14.93, while the cooling system operated at generation temperatures from 85–95 °C and condensation temperatures between 20 and 28 °C, achieving external coefficients of performance up to 0.56, cooling temperatures as low as 6 °C, and exergy efficiencies up to 0.13. The highest value for the solar coefficient of performance reached 0.07. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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18 pages, 4847 KiB

Open AccessFeature PaperArticle

Experimental Study of Condensation Heat Transfer and Pressure Drop inside a Small Diameter Microfin and Smooth Tube at Low Mass Flux Condition

by M. Khairul Bashar, Keisuke Nakamura, Keishi Kariya and Akio Miyara

Appl. Sci. 2018, 8(11), 2146; https://doi.org/10.3390/app8112146 - 2 Nov 2018

Cited by 22 | Viewed by 4621

Abstract

This study was made to investigate the condensation local heat transfer and adiabatic pressure drop of R134a inside a 2.5 mm outside diameter smooth and microfin tube at low mass flux condition. Data were measured for mass fluxes from 50 to 300 kg [...] Read more.

This study was made to investigate the condensation local heat transfer and adiabatic pressure drop of R134a inside a 2.5 mm outside diameter smooth and microfin tube at low mass flux condition. Data were measured for mass fluxes from 50 to 300 kg m⁻²s⁻¹, vapor qualities from 0 to 1 and saturation temperatures from 20 to 30 °C. The effects of mass flux, vapor quality, saturation temperature, microfin and diameter of test tube were analyzed. The pressure drop of the microfin tube was about 1.5 times higher than that of the smooth tube at mass flux 50 kg m⁻²s⁻¹. The heat transfer coefficient of the microfin tube was about 2–5 times higher than that of the smooth tube at mass flux 100 kg m⁻²s⁻¹. Experimental results were also compared with typical correlations. For the microfin tube, however, all the existing correlations do not adequately predict the present data. Poor predictions may be attributed to the lack of the small diameter microfin tube with low mass flux data in their database. Hence, it is essential to develop a condensation and pressure drop correlation for the small diameter microfin tube at low mass flux condition. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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15 pages, 5234 KiB

Open AccessArticle

Performance Characteristics of a Seawater Ice-Making Device Using a Scraped Surface Double Tube Evaporator

by Hyun-Kyung Lee, Kwang-Hwan Choi, Jung-In Yoon, Choon-Geun Moon, Min-Ju Jeon, Joon-Hyuk Lee, Kwang-Seok Lee and Chang-Hyo Son

Appl. Sci. 2018, 8(11), 2063; https://doi.org/10.3390/app8112063 - 25 Oct 2018

Cited by 5 | Viewed by 3667

Abstract

In this study, to investigate the performance characteristics of a seawater ice-making device, using a scraped surface double tube evaporator, experiments were conducted under various operating conditions, including inlet temperature and flow rate of seawater, evaporating temperature, and scraper rotation speed. The main [...] Read more.

In this study, to investigate the performance characteristics of a seawater ice-making device, using a scraped surface double tube evaporator, experiments were conducted under various operating conditions, including inlet temperature and flow rate of seawater, evaporating temperature, and scraper rotation speed. The main results are summarized as follows: (1) The section where stable ice making is possible, is determined by the inlet temperature and the flow rate range of seawater. By controlling the flow rate of seawater, the ice packing factor (IPF) of the device can be adjusted from 0.3 to 14.7%. (2) The IPF increases in cases where the evaporating temperature decreases linearly, until −13 °C. As the temperature of refrigerant that flows into the evaporator changes, the IPF is changed. Consideration is required for these connections. (3) The IPF increases when speeding up the scraper. The minimum rotating speed of the scraper was 350 rpm in these experiments. Optimum operating conditions for the seawater ice slurry maker are established through experiments. These results will be considered as important data for designing a slurry type seawater ice-making device. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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21 pages, 5219 KiB

Open AccessArticle

Numerical Analysis for Performance Evaluation of a Multi-Functional CO₂ Heat Pump Water Heating System

by Ryohei Yokoyama, Masashi Ohkura, Takuya Nakamata and Tetsuya Wakui

Appl. Sci. 2018, 8(10), 1829; https://doi.org/10.3390/app8101829 - 5 Oct 2018

Cited by 3 | Viewed by 3840

Abstract

In recent years, CO₂ heat pump water heating systems have been developed, and their performances have been enhanced while their functions have been expanded. In a multi-functional system, used for both hot water supply and bath heating, hot water retrieved from the [...] Read more.

In recent years, CO₂ heat pump water heating systems have been developed, and their performances have been enhanced while their functions have been expanded. In a multi-functional system, used for both hot water supply and bath heating, hot water retrieved from the top of a storage tank is returned to its bottom or side after heat exchange for bath heating, which destroys the stratified temperature distribution in the storage tank and degrades the system performance. In this paper, the performance of a multi-functional CO₂ heat pump water heating system has been evaluated by numerical simulation. A system model was created by combining component models for a CO₂ heat pump, mixing valves, a storage tank, a heat exchanger, and a bathtub. Partly, perfect mixing by hot water return was assumed in the component model for the storage tank, and its validity was verified through experiments. A performance analysis has been conducted under daily repeated hot water and bath heating demands, and the system performance was evaluated at a periodically steady state. As a result, the system efficiency and the volume of unused hot water in the multi-functional system decreased by 4.9% and 16.3%, respectively, as compared to those in the uni-functional system, when hot water returned to the bottom of the storage tank. When the position for hot water return is heightened, the system efficiency becomes higher than that in the uni-functional system, while the volume of unused hot water decreases furthermore. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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17 pages, 7728 KiB

Open AccessArticle

A Study on the Improvement Effect and Field Applicability of the Deep Soft Ground by Ground Heating Method

by Mincheol Park

Appl. Sci. 2018, 8(6), 852; https://doi.org/10.3390/app8060852 - 23 May 2018

Cited by 3 | Viewed by 3781

Abstract

The soft ground in coastal areas should be treated when it needs to be used for the sustainably developed of urban or industrial complex constructions. The ground heating method for soft ground improvement was applied in Eastern Europe in the 1960s, but it [...] Read more.

The soft ground in coastal areas should be treated when it needs to be used for the sustainably developed of urban or industrial complex constructions. The ground heating method for soft ground improvement was applied in Eastern Europe in the 1960s, but it was not widely used due to economic and environmental problems. The author developed a device for improving soft ground using an electric heating pipe. This paper investigates the improvement effect and field application of deep soft ground by the ground heating method using the electric heating pipe. Ground heating increases the temperature of the deep soft ground and increases the tip resistance of the static electronic piezo-cone penetration test. Additionally, the pressure of the pore water decreases because the pore water is evaporated due to the ground heating. As a result of the experiment, it was verified that there was an improvement in the effect of deep soft ground by the ground heating method. With ground heating for 96 h, the tip resistance was increased by 61% at a point 0.35 m horizontally away from the electric heat pipe, 22% at 0.97 m, and 2% at 1.31 m. As a result of the field test, it was found that there were no problems in the power supply of the diesel generator and the control panel. It was easy to install the electric heating pipes in the deep soft ground. However, due to boring, the ground was disturbed and water vapor was discharged through this gap. To minimize the discharge of water vapor, it is necessary to drive the electric heating pipe. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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17 pages, 3578 KiB

Open AccessArticle

Exergy Analysis of Serpentine Thermosyphon Solar Water Heater

by Muhammad Faisal Hasan, Md. Sayeed Ur Rahim Mahadi, Takahiko Miyazaki, Shigeru Koyama and Kyaw Thu

Appl. Sci. 2018, 8(3), 391; https://doi.org/10.3390/app8030391 - 7 Mar 2018

Cited by 11 | Viewed by 6913

Abstract

The performance of a solar hot water system is assessed for heat pump and domestic heating applications. Thermodynamic analysis on a serpentine-type thermosyphon flat-plate solar heater is conducted using the Second Law of thermodynamics. Exergetic optimization is first performed to determine the parameters [...] Read more.

The performance of a solar hot water system is assessed for heat pump and domestic heating applications. Thermodynamic analysis on a serpentine-type thermosyphon flat-plate solar heater is conducted using the Second Law of thermodynamics. Exergetic optimization is first performed to determine the parameters for the maximum exergy efficiency using MATLAB optimization toolbox. Geometric parameters (collector surface area, dimensions, and pipe diameter), optical parameters (transmittance absorptance product), ambient temperature, solar irradiation and operating parameters (mass flow rate, fluid temperature, and overall heat transfer (loss) coefficient) are accounted for in the optimization scheme. The exergy efficiency at optimum condition is found to be 3.72%. The results are validated using experimental data and found to be in good agreement. The analysis is further extended to the influence of various operating parameters on the exergetic efficiency. It is observed that optical and thermal exergy losses contribute almost 20%, whereas approximately 77% exergy destruction is contributed by the thermal energy conversion. Exergy destruction due to pressure drop is found negligible. The result of this analysis can be used for designing and optimization of domestic heat pump system and hot water application. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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17 pages, 6884 KiB

Open AccessArticle

Conversion of a Direct to an Indirect Refrigeration System at Medium Temperature Using R-134a and R-507A: An Energy Impact Analysis

by Rodrigo Llopis, Daniel Sánchez, Ramón Cabello, Jesús Catalán-Gil and Laura Nebot-Andrés

Appl. Sci. 2018, 8(2), 247; https://doi.org/10.3390/app8020247 - 6 Feb 2018

Cited by 7 | Viewed by 6762

Abstract

This work presents the experimental evaluation of energy consumption and refrigerant charge reduction when a commercial direct expansion refrigeration system is converted into an indirect system. The evaluation (with R-134a and R-507A) used a commercial cabinet with doors for medium temperature and a [...] Read more.

This work presents the experimental evaluation of energy consumption and refrigerant charge reduction when a commercial direct expansion refrigeration system is converted into an indirect system. The evaluation (with R-134a and R-507A) used a commercial cabinet with doors for medium temperature and a single-stage refrigeration cycle using a semi-hermetic compressor and electronic expansion valve; 24-h energy consumption tests were performed at laboratory conditions for each refrigerant and configuration at three heat rejection levels (23.3, 32.8 and 43.6 °C), maintaining an average product temperature inside the cabinet of 2 °C. The work analyses the impact of the conversion on temperature and pressure indicators, as well as, in the energy performance of each element. For R-134a the refrigerant charge was reduced in a 42.9%, but the energy consumption rose by 22.0%–22.8%; for R-507A the charge reduction was of 32.8% with an increase in energy consumption of between 27.7% and 38.7%. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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14 pages, 2885 KiB

Open AccessFeature PaperArticle

Impact of Blockage Ratio on Thermal Performance of Delta-Winglet Vortex Generators

by Indri Yaningsih, Agung Tri Wijayanta, Takahiko Miyazaki and Shigeru Koyama

Appl. Sci. 2018, 8(2), 181; https://doi.org/10.3390/app8020181 - 26 Jan 2018

Cited by 18 | Viewed by 4683

Abstract

The impact of double-sided delta-winglet tape (DWTs) inserts on convective heat transfer and friction behaviors in a tube was experimentally investigated. Three DWTs with ratios of winglet-height (b) to inner tube diameter (d_i) called blockage ratio (R [...] Read more.

The impact of double-sided delta-winglet tape (DWTs) inserts on convective heat transfer and friction behaviors in a tube was experimentally investigated. Three DWTs with ratios of winglet-height (b) to inner tube diameter (d_i) called blockage ratio (R_b) of 0.28, 0.35 and 0.42 were tested and their performance was compared to that of a longitudinal strip and plain tube under similar test flow conditions. Experiments were conducted over a wide range of flow rates, 3.35 × 10⁻⁵–8.33 × 10⁻⁵ m³/s, which correspond to 5500 ≤ Reynolds number (Re) ≤ 14,500 in the 14.3 mm i.d. tube. The results revealed that using DWTs dramatically increased the Nusselt number (Nu) by as much as 364.3% and the friction factor (f) by 15.5 times compared with those of a plain tube. Thermal performance (η) increased with a corresponding increase in R_b. The highest thermal performance (η) obtained was 1.4. Showing a notable improvement on the thermal performance of the system, DWTs are proposed as a favorable insert device. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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1120 KiB

Open AccessArticle

Dynamic Performance Analysis for an Absorption Chiller under Different Working Conditions

by Jian Wang, Sheng Shang, Xianting Li, Baolong Wang, Wei Wu and Wenxing Shi

Appl. Sci. 2017, 7(8), 797; https://doi.org/10.3390/app7080797 - 5 Aug 2017

Cited by 16 | Viewed by 5619

Abstract

Due to the merits of energy saving and environmental protection, the absorption chiller (AC) has attracted a lot of attention, and previous studies only concentrated on the dynamic response of the AC under a single working condition. However, the working conditions are usually [...] Read more.

Due to the merits of energy saving and environmental protection, the absorption chiller (AC) has attracted a lot of attention, and previous studies only concentrated on the dynamic response of the AC under a single working condition. However, the working conditions are usually variable, and the dynamic performance under different working conditions is beneficial for the adjustment of AC and the control of the whole system, of which the stabilization can be affected by the AC transient process. Therefore, the steady and dynamic models of a single-effect H₂O-LiBr absorption chiller are built up, the thermal inertia and fluid storage are also taken into consideration. And the dynamic performance analyses of the AC are completed under different external parameters. Furthermore, a whole system using AC in a process plant is analyzed. As a conclusion, the time required to reach a new steady-state (relaxation time) increases when the step change of the generator inlet temperature becomes large, the cooling water inlet temperature rises, or the evaporator inlet temperature decreases. In addition, the control strategy considering the AC dynamic performance is favorable to the operation of the whole system. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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546 KiB

Open AccessArticle

Numerical Calculation of the Performance of a Thermoacoustic System with Engine and Cooler Stacks in a Looped Tube

by Irna Farikhah and Yuki Ueda

Appl. Sci. 2017, 7(7), 672; https://doi.org/10.3390/app7070672 - 30 Jun 2017

Cited by 14 | Viewed by 6690

Abstract

The performance of a thermoacoustic system that is composed of a looped tube, an engine stack, a cooler stack, and four heat exchangers, is numerically investigated. Each stack has narrow flow channels, is sandwiched by two heat exchangers, and is located in the [...] Read more.

The performance of a thermoacoustic system that is composed of a looped tube, an engine stack, a cooler stack, and four heat exchangers, is numerically investigated. Each stack has narrow flow channels, is sandwiched by two heat exchangers, and is located in the looped tube. In order to provide a design guide, the performance of the system is numerically calculated by changing the following three parameters: the radius of the flow channels in the engine stack, the radius of the flow channels in the cooler stack, and the relative position of the cooler stack. It was found that when the three parameters are optimized, the efficiency of the engine stack reaches 75% of Carnot’s efficiency and the coefficient of the performance (COP) of the cooler stack is 53% of Carnot’s COP, whereas 33% of the acoustic power generated by the engine stack is utilized in the cooler stack. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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3364 KiB

Open AccessArticle

Optimal Design of an Air-to-Air Heat Exchanger with Cross-Corrugated Triangular Ducts by Using a Particle Swarm Optimization Algorithm

by Caihang Liang, Xiaoman Tong, Tengyue Lei, Zhenxing Li and Guoshan Wu

Appl. Sci. 2017, 7(6), 554; https://doi.org/10.3390/app7060554 - 26 May 2017

Cited by 25 | Viewed by 7138

Abstract

Air-to-air heat exchangers with cross-corrugated triangular ducts are widely used in various industrial fields to recover waste heat. The geometric parameters of the heat exchangers greatly affect the performance and total annual cost of these systems. In this study, the effectiveness-number of transfer [...] Read more.

Air-to-air heat exchangers with cross-corrugated triangular ducts are widely used in various industrial fields to recover waste heat. The geometric parameters of the heat exchangers greatly affect the performance and total annual cost of these systems. In this study, the effectiveness-number of transfer units (ε-NTU) method was utilized to develop the thermal mathematical model, which was verified by comparing it with previous research. The configuration parameters of the heat exchanger were optimized in this study. The particle swarm optimization (PSO) algorithm was applied using both single and multi-objective algorithm. The colburn factor (j factor), friction factor (f factor), and comprehensive thermal hydraulic performance index (JF factor) were considered as objective functions to be optimized using a single objective and multi-objective algorithm. Then, the entropy generation rate and total annual cost were optimized by using a multi-objective PSO algorithm. In addition, to identify the influential geometric parameters, a global sensitivity analysis was performed. The sensitivity analysis showed that the apex angle θ, channel height H, and heat exchanger height L_h influenced the performance and annual total cost of these systems. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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4015 KiB

Open AccessArticle

Using Thermal Shock to Inhibit Biofilm Formation in the Treated Sewage Source Heat Pump Systems

by Siyuan Chang, Jinchun Chen and Lin Shi

Appl. Sci. 2017, 7(4), 343; https://doi.org/10.3390/app7040343 - 30 Mar 2017

Cited by 9 | Viewed by 6749

Abstract

Treated sewage source heat pump systems can reuse the waste energy in the treated sewage. However, biofilms in the heat exchangers decrease the system efficiency. This work investigates the feasibility of thermal shock at accessible temperatures in heat exchangers for biofilm inhibition. Bacillus [...] Read more.

Treated sewage source heat pump systems can reuse the waste energy in the treated sewage. However, biofilms in the heat exchangers decrease the system efficiency. This work investigates the feasibility of thermal shock at accessible temperatures in heat exchangers for biofilm inhibition. Bacillus subtilis biofilms were formed on coupons and in a miniaturized plate heat exchanger. Thermal shocks at different temperatures (50–80 °C) for different exposure times (1–60 min) were used to treat the biofilms. The results showed that thermal shock had a significant bactericidal and biofilm inhibition effect, and the effect was enhanced as the temperature and the exposure time increased. Data fitting of the biomass showed that temperature had a more significant influence on the biofilm inhibition effect than exposure time. The results of the heat exchanging experiments showed that high temperature thermal shock could significantly mitigate the heat transfer deterioration caused by the biofilms, indicating that thermal shock could be used as a viable biofilm inhibition approach for heat exchangers. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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3659 KiB

Open AccessArticle

The Effects of Wet Compression by the Electronic Expansion Valve Opening on the Performance of a Heat Pump System

by Kyoungjin Seong, Daehui Lee and Jinho Lee

Appl. Sci. 2017, 7(3), 248; https://doi.org/10.3390/app7030248 - 3 Mar 2017

Cited by 9 | Viewed by 5983

Abstract

In this study, by controlling the Electronic Expansion Valve opening, the influence of wet compression on a heat pump system was experimentally investigated in different heating conditions. The results demonstrate that the discharge temperature decreased and the mass flow rate increased, due to [...] Read more.

In this study, by controlling the Electronic Expansion Valve opening, the influence of wet compression on a heat pump system was experimentally investigated in different heating conditions. The results demonstrate that the discharge temperature decreased and the mass flow rate increased, due to quality of the rising liquid droplets. It was also found that the heating capacity and power input of wet compression increased more than that of dry compression, with a superheat of 10 °C. The maximum COP (Coefficient of Performance) exists at a specific quality of ca. 0.94 to 0.90, as the power input in the region of wet compression is proportionally larger than the increase in the heating capacity, according to the decreasing quality. When the Entering Water Temperature of the Outdoor Heat Exchanger was 10 °C, 5 °C, and 0 °C, the COP increased by a maximum of ca. 12.4%, 10.6%, and 10.2%, respectively, in comparison to the superheat of 10 °C. In addition, the superheat at the discharge line is proposed as a proper controlling parameter to adjust the quality at the suction line, by varying the opening of the expansion valve during wet compression. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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2548 KiB

Open AccessArticle

Simulation of Hybrid Photovoltaic Solar Assisted Loop Heat Pipe/Heat Pump System

by Nannan Dai, Xinyi Xu, Shuhong Li and Zheng Zhang

Appl. Sci. 2017, 7(2), 197; https://doi.org/10.3390/app7020197 - 16 Feb 2017

Cited by 26 | Viewed by 6711

Abstract

A hybrid photovoltaic solar assisted loop heat pipe/heat pump (PV-SALHP/HP) water heater system has been developed and numerically studied. The system is the combination of loop heat pipe (LHP) mode and heat pump (HP) mode, and the two modes can be run separately [...] Read more.

A hybrid photovoltaic solar assisted loop heat pipe/heat pump (PV-SALHP/HP) water heater system has been developed and numerically studied. The system is the combination of loop heat pipe (LHP) mode and heat pump (HP) mode, and the two modes can be run separately or compositely according to the weather conditions. The performances of independent heat pump (HP) mode and hybrid loop heat pipe/heat pump (LHP/HP) mode were simulated and compared. Simulation results showed that on typical sunny days in spring or autumn, using LHP/HP mode could save 40.6% power consumption than HP mode. In addition, the optimal switchover from LHP mode to HP mode was analyzed in different weather conditions for energy saving and the all-year round operating performances of the system were also simulated. The simulation results showed that hybrid LHP/HP mode should be utilized to save electricity on sunny days from March to November and the system can rely on LHP mode alone without any power consumption in July and August. When solar radiation and ambient temperature are low in winter, HP mode should be used Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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Review

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24 pages, 11742 KiB

Open AccessFeature PaperReview

Critical Review on the Developments and Future Aspects of Adsorption Heat Pumps for Automobile Air Conditioning

by Shinnosuke Maeda, Kyaw Thu, Tomohiro Maruyama and Takahiko Miyazaki

Appl. Sci. 2018, 8(11), 2061; https://doi.org/10.3390/app8112061 - 25 Oct 2018

Cited by 16 | Viewed by 4863

Abstract

Emission and heat rejection from automobiles are largely responsible for urban environmental issues. Adsorption systems driven by engine waste heat exhibit huge potential to meet the demand for cabin thermal comfort while improving fuel economy. However, the mechanical vapour compression (MVC) systems are [...] Read more.

Emission and heat rejection from automobiles are largely responsible for urban environmental issues. Adsorption systems driven by engine waste heat exhibit huge potential to meet the demand for cabin thermal comfort while improving fuel economy. However, the mechanical vapour compression (MVC) systems are still the undisputed champions in automobile air conditioning. This paper provides a critical review on the development and progress of adsorption heat pumps specifically for automobile air conditioning. In doing so, some of the progress and development in land-based adsorption chillers (heat pump), which are not realistically relevant to automobile adsorption systems, are explicitly excluded. Matching the energy density, durability, and reliability of the MVC systems remain major hurdles. The importance of improving the energy density based on the overall system weight or volume, real-world tests under various driving modes and durability aspects are discussed. Full article

(This article belongs to the Special Issue Sciences in Heat Pump and Refrigeration)

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