Dynamic modeling study for a solar evaporator with expansion valve assembly of a transcritical CO2 heat pump

Faria, Ralney; Nunes, Raphael; Koury, R.N.N.; Machado, Luiz

doi:10.1016/j.ijrefrig.2016.01.004

Cited by 34 publications

(17 citation statements)

References 25 publications

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“…The experimental results showed that the hot gas bypass defrosting method could only achieve efficiency as high as 40%. Furthermore, Calabrese et al [122] conducted an experimental study on a CO 2 ASHP installed on a building rooftop to understand the effect of the inlet air temperature at the gas cooler on the heating capacity and COP. The inlet air at the gas cooler was a combination of fresh air supplied from the environment and recirculated air from the HP system.…”

Section: Heat Sourcesmentioning

confidence: 99%

Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

et al. 2019

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Heat pump (HP) is one of the most energy efficient tools for address heating and possibly cooling needs in buildings. Growing environmental concerns over conventional HP refrigerants, chlorofluorocarbons (CFCs), and hydrofluorocarbons (HFCs) have forced legislators and researchers to look for alternatives. As such, carbon dioxide (R744/CO2) has come to light due to its low global warming potential (GWP) and zero ozone depleting characteristics. Even though CO2 is environmentally benign, the performance of CO2 HP has been of concern since its inception. To improve the performance of CO2 HP, research has been playing a pivotal role in developing functional designs of heat exchangers, expansion devices, and compressors to suit the CO2 transcritical cycle. Different CO2 HP cycles coupled with auxiliary components, hybrid systems, and refrigerant mixtures along with advanced control strategies have been applied and tested. This paper presents a complete overview of the most recent developments of transcritical CO2 HPs, their components, and applications.

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Section: Heat Sourcesmentioning

confidence: 99%

Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

et al. 2019

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“…The mathematical modeling of the heat exchanger for water and air fluids is done by considering the mass, energy, and momentum conservation laws simultaneously. The energy conservation law for the air is given by the following equation [43]. The indices j and i represent the control volume position in the heat exchanger composition.…”

Section: Heat Exchanger Modelmentioning

confidence: 99%

“…Table 2 represents technical specification of the proposed model. [46], which was employed in several investigations [43], [47]- [49]. For the proposed heat exchanger, located before the cavern, Fe3O4/water ferrofluid was proposed as the secondary fluid, which absorbs the heat of the air before cavern and stores in an isolation tank.…”

mentioning

confidence: 99%

The influence of magnetic field on heat transfer of magnetic nanofluid in a double pipe heat exchanger proposed in a small-scale CAES system

Malekan

Khosravi

Zhao

2019

Applied Thermal Engineering

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Globally, the integration of renewable energy (which has an intermittent nature) into the power system requires the system operators to improve the system performance to be able to effectively handle the variations of the power production in order to balance the supply and demand. This problem is seen as a major obstacle to the expansion of renewable energy if it is not handled in a suitable way. Efficient electricity storage technology is one of the feasible solutions. The current study proposes Fe3O4/water nanofluid under magnetic field as the secondary fluid in the proposed double pipe heat exchanger before the cavern. The heat of compressed air is absorbed by the secondary fluid and it is stored in an isolation tank. This stored fluid is used to warm up the air that leaves the cavern for expanding in the turbine. The results demonstrated that increasing the mass flow rate of secondary fluid decreases the cavern temperature. Also, the value of convective heat transfer of ferrofluid increases when the volume fraction of nanoparticle as well as magnetic field increases. Furthermore, increasing the volume fraction and magnetic field increases the pressure drop and friction factor of ferrofluid.

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“…The Cheng et al flow pattern based evaporation heat transfer and two phase frictional pressure drop models for have been widely used for simulations of CO2 refrigeration, air-conditioning and heat pump systems by a number of researchers [61][62][63][64][65]. For example, in order to improve the system performance of the CO2 heat pump, it is necessary to develop an optimum design and a control method for the CO2 heat pump water heater.…”

Section: Simulations Of Co2 Thermal Systems Using the Cheng Et Al Momentioning

confidence: 99%

“…It shows good agreement with the experimental results. Faria et al [64] investigated of the behaviour of the solar evaporator and expansion valve assembly of a transcritical CO2 heat pump in transient and steady conditions. The dynamic behaviour of systems using CO2 as a refrigerant is significantly influenced by the dynamics of the heat transfer mechanisms.…”

Section: Simulations Of Co2 Thermal Systems Using the Cheng Et Al Momentioning

confidence: 99%

Flow Boiling Heat Transfer and Two-Phase Flow of Carbon Dioxide: Fundamentals, Mechanistic Models and Applications

Cheng¹

2019

Proceedings of the 4th World Congress on Momentum, Heat and Mass Transfer

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In order to design evaporators for the CO2 thermal systems effectively, it is essential to understand the fundamentals and mechanisms of flow boiling heat transfer, flow patterns and two-phase flow characteristics of CO2 inside horizontal tubes including both the macro-and micro-channels. The proper prediction models for CO2 flow boiling heat transfer should be relevant to the physical mechanisms and corresponding flow patterns. This paper presents a comprehensive review of flow boiling heat transfer and two-phase flow of CO2 characteristics and their prediction methods. First, the review addresses the extensive experimental studies on flow boiling heat transfer and two-phase flow in macro-channels and micro-channels. Then, The studies of CO2 two-phase flow patterns are summarized. Furthermore, the effects of oil on the flow boiling heat transfer and two-phase pressure drops are analyzed. The generalized mechanistic models for flow boiling heat transfer and two-phase pressure drops of CO2 and a new flow pattern map specially for CO2, which cover both macro-and micro-channels developed by Cheng et al. are presented and compared to the experimental data in the literature. It has been proved that the models and flow maps favorably agree with the experimental data. In the application aspect, comparison of simulation results and the experimental data in the real thermal systems are presented.Keywords: Carbon dioxide, flow boiling, two phase flow, flow patterns, heat transfer, flow pattern map, dryout, mechanisms, mechanistic model and applications.ICMFHT Keynote 2-2 that of R22 and NH3. As the effects of good thermophysical properties, favorably evaporation heat transfer and two-phase flow characteristics of CO2, smaller pipe dimensions can be used in its refrigeration systems. The use of CO2 in these refrigeration systems requires the understanding and prediction of convective boiling, two-phase flow patterns and pressure drops at low temperatures for achieving more accurate designs of evaporators and more energy-efficient cycles using CO2.Furthermore, CO2 has favorable thermal performance when used in air-conditioning and heat pump systems as compared to conventional refrigerants. For example, in the CO2 automobile air-conditioning system. for ambient air temperatures, the heat transfer process on the high pressure side of a CO2 cycle is not a condensation process as in conventional systems but a supercritical gas cooling process [3,4,6]. For the evaporation processes in the evaporator, CO2 evaporates at much higher pressure than conventional refrigerant R134a [1,3]. The physical and transport properties of CO2 are quite different from those of conventional refrigerants at the same saturation temperatures. The physical properties have a significant effect on the evaporation processes including the two-phase flow patterns, evaporation heat transfer characteristics and two-phase frictional pressure drops in the compact heat exchangers with micro-channels. Therefore, it is essential to understand the two-phase flow and...

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Dynamic modeling study for a solar evaporator with expansion valve assembly of a transcritical CO2 heat pump

Cited by 34 publications

References 25 publications

Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

The influence of magnetic field on heat transfer of magnetic nanofluid in a double pipe heat exchanger proposed in a small-scale CAES system

Flow Boiling Heat Transfer and Two-Phase Flow of Carbon Dioxide: Fundamentals, Mechanistic Models and Applications

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