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Showing papers on "Subcooling published in 2019"


Journal ArticleDOI
TL;DR: In this paper, an environmental and economical assessment model is developed, in order to evaluate the performances of transcritical CO2 heat pump system with dedicated mechanical subcooling (CO2 HPDMS).

105 citations


Journal ArticleDOI
TL;DR: In this paper, a transcritical CO 2 heat pump (HP) system for residential space heating integrated with direct dedicated mechanical subcooling (DMS) is proposed, and mathematical models are developed to study the...

75 citations


Journal ArticleDOI
20 Nov 2019-Joule
TL;DR: In this paper, a 3D hybrid surface consisting of superhydrophobic (SHB) Si nanowire arrays and hydrophilic microchannels was proposed to enhance the condensation at high subcooling temperatures.

67 citations


Journal ArticleDOI
15 Sep 2019-Fuel
TL;DR: In this paper, an improved, high pressure, stirred automated lag time apparatus (HPS-ALTA) was used to determine gas hydrate nucleation and growth rates from induction time measurements at fixed subcooling.

55 citations


Journal ArticleDOI
TL;DR: In this article, a PVT based solar heat pump system employing VI cycle (PVT-VISHP) was proposed, fabricated and investigated experimentally, and the system's performance was evaluated based on the average ambient temperature of −1.13°C and solar irradiation of 164.1°C.

52 citations


Journal ArticleDOI
TL;DR: In this paper, a high-pressure desalination apparatus was designed and constructed to produce the overflow of hydrates in the inner annulus of a gas bubble column placed inside a dissociation reactor.

51 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented the evolution of a concept of air-source heat pump for simultaneous heating and cooling (HPS) for collective residential buildings, hotels or highly-glazed office buildings.

50 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed the combination of a subcooled energy storage unit with an organic Rankine cycle for improving the electricity efficiency of this compressed air concept, and the proposed hybrid system is thermodynamically analyzed and the exergetic and energetic performances of the system under uniform and fluctuating operation conditions are evaluated.

49 citations


Journal ArticleDOI
01 Jan 2019
TL;DR: In this article, a comparison of different transcritical CO2 refrigeration systems and the determination of the most promising configurations is presented. And the results show that the system with the mechanical subcooling and the two-stage compression system are the most efficient choices with a mean coefficient of performance enhancement at 75.8% and 49.8%, respectively.
Abstract: The refrigeration systems with CO2 seem to be attractive choices for the design of refrigeration systems with small environmental impact. The objective of this work is the comparison of different transcritical CO2 refrigeration systems and the determination of the most promising configurations. A typical system (evaporator, compressor, gas cooler, expansion valve) is the reference system and it is compared with a system with internal heat exchanger, a parallel compression system, a two-stage compression system and a system with mechanical subcooling after the gas collector. The examined systems produce refrigeration at one temperature level and they are examined for various operation scenarios. More specifically, the refrigeration temperature is examined from −35 °C to +5 °C, while the condenser temperature (or the gas cooler outlet temperature) from 35 °C to 50 °C. The analysis is conducted with developed models in Engineering Equation Solver (EES). According to the results, all the examined systems are more efficient than the reference system for all the examined scenarios. The system with the mechanical subcooling and the two-stage compression system are found to be the most efficient choices with a mean coefficient of performance enhancement at 75.8% and 49.8% respectively.

44 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the heat transfer and pressure drop characteristics during flow boiling of deionized water (DI water) in open microchannels and analyzed the effects of operating conditions and channel dimensions.

44 citations


Journal ArticleDOI
01 Jan 2019
TL;DR: In this paper, the authors investigated ten different refrigeration systems with CO2 and compared them with a conventional system with R404A in terms of energy efficiency and energy saving. But, the results showed that the simple booster CO2 system is less efficient than the conventional R404-A system with 15.23% higher yearly electricity consumption.
Abstract: The recent regulation concerning the ban of the hydro-fluorocarbon (HFC) refrigerants has led to the employment of environmentally friendly solutions for refrigeration. Systems that employ CO2 seem to be a viable option which is compatible with the current legislation. The objective of the present work is the investigation of ten different refrigeration systems with CO2 and to compare them with a conventional system with R404A in energetic terms. The analysis is conducted on an annual basis by using the measured energy consumptions and loads for an existing system with R404A. Except for the refrigeration system comparison, a model for the prediction of the hourly refrigeration loads of the existing supermarket is developed using experimental results. This model is applied for the yearly evaluation of the proposed CO2 refrigeration systems. The examined CO2 system configurations include a simple booster system, a system with parallel compression, a system with parallel compression and overfed evaporators in the medium temperature, a system with parallel compression and overfed evaporators in both medium and low temperature, a system similar to the last one with the addition of an intercooler after the low temperature compressors, and all the aforementioned systems with the addition of a mechanical subcooling cycle after the gas cooler. According to the final results, the most promising configuration is the one with parallel compression, overfed evaporators in medium and low temperature, intercooler and mechanical subcooling, which leads to 8.53% yearly electricity savings compared to the conventional R404A system. Moreover, it is important to state that the simple booster CO2 system is found to be less efficient than the conventional R404A system with 15.23% higher yearly electricity consumption.

Journal ArticleDOI
TL;DR: In this article, the solidification behavior of de-ionized (DI) water as the base phase change material (PCM) dispersed with various mass fractions of sodium chloride and D-sorbitol in a spherical encapsulation was investigated.
Abstract: This work aims to investigate the solidification behavior of de-ionized (DI) water as the base phase change material (PCM) dispersed with various mass fractions of sodium chloride and D-sorbitol in a spherical encapsulation. The DSC analysis of water illustrated that subcooling of DI water increases with respect to cooling rate due to inadequate time to complete the crystallization. The solidification experiments were carried out at a bath temperature of −7 °C and DI water undergoes a subcooling of −5.4 °C. However, the subcooling substantially reduced to −2.8 °C for DI water with 0.5 wt. % sodium chloride and 1 wt. % of D-sorbitol. Accelerated mode of charging prevails in all the PCM samples and the innermost 6% of volume got solidified in decelerated mode. The cooling rate is found to decrease with respect to increase in concentration of the dispersants in subcooling region, but at a particular concentration both dispersants provide the enhanced cooling rate for a given driving potential than DI water. It is concluded that reduction of subcooling and partial charging of water based PCMs would be helpful to enhance the energy efficiency of the cool thermal energy storage (CTES) system.

Journal ArticleDOI
TL;DR: In this paper, the authors explore subcooled nucleate flow boiling of FC-72 in a rectangular channel having two opposite heating walls at different mass velocities and wall heat fluxes ranging from 42% to 45% of CHF.

Journal ArticleDOI
Xi Liu1, Ruansong Fu1, Zhiqiang Wang, Li Lin1, Zhixin Sun1, Xuelai Li1 
TL;DR: In this paper, the authors proposed a new configuration of transcritical CO2 refrigeration cycle combined with a thermoelectric subcooler and an ejector (TES+EJE) is proposed.

Journal ArticleDOI
TL;DR: In this article, a superhydrophilic-hydrophobic (SHPi-HPo) network hybrid surface was designed to investigate the condensation heat transfer using stainless steel as substrate material.

Journal ArticleDOI
TL;DR: In this article, the effects of ultrasonic wave propagation in Al2O3 nanofluids under different flow regimes were studied through experiments, and the boiling curves and critical heat flux were obtained with and without ultrasound.

Journal ArticleDOI
TL;DR: In this article, the authors conducted a pool boiling experiment on the hybrid micro/nanostructure surface (NPF50-60) with nano-forest structure fabricated on the top and bottom of micro-pin-fins using the dry etching and plasma repolymerization techniques.

Journal ArticleDOI
Bin Liu1, Jie Liu1, Yonghai Zhang1, Jinjia Wei1, Wenjun Wang1 
TL;DR: In this paper, the pool boiling heat transfer of micro/nano hierarchically structured surfaces, as well as that of a smooth surface in gas dissolved FC-72 (the subcooling is 1 K) was studied.

Journal ArticleDOI
Qi Peng1, Li Jia1, Jian Guo1, Chao Dang1, Yi Ding1, Liaofei Yin1, Qiao Yan1 
TL;DR: In this article, a hierarchically microgrooved superhydrophobic surface was fabricated by the mechanical broaching and chemical etching methods to enhance the condensation heat transfer characteristics.
Abstract: Condensation is of great interest in various heat exchange processes, owing to the elevated heat and mass transfer by phase change. In this work, a hierarchically microgrooved superhydrophobic surface was fabricated by the mechanical broaching and chemical etching methods to enhance the condensation heat transfer. The dynamic behaviors of condensed droplets and condensation heat transfer characteristics were analyzed on such surface. Particularly, there were two droplet jumping modes, the conventional coalescence jumping of small droplets (<100 μm) at small subcooling (ΔT < 5 K) and the forced jumping of large stretched droplets (400–500 μm) in microgrooves at a broad range of subcooling (ΔT < 12 K), simultaneously emerging on the hierarchically microgrooved superhydrophobic surface. The interesting coalescence-induced sweeping behavior independent of gravity is observed at large surface subcooling. The coalescence-induced jumping and sweeping significantly facilitated the renewal of surface. The investigation has showed that a 90% higher heat flux at small subcooling (ΔT < 5 K) and a 66% higher heat flux at large subcooling (5 K < ΔT < 24 K) were reached on the hierarchically microgrooved superhydrophobic surface compared with the plain hydrophobic surface.

Journal ArticleDOI
TL;DR: In this article, an experimental study was carried out to investigate the heat transfer, pressure drop and flow instability characteristics associated with the flow pattern of deionized water during two-phase boiling in a silicon-based manifold microchannel heat sink coated with silicon nanowires compared to a plain-wall device.

Journal ArticleDOI
Guodong Xia1, Yuanzheng Lv1, Lixin Cheng1, D.D. Ma1, Y.T. Jia1 
TL;DR: In this article, both experiments and dynamics simulation of the continuous two-phase instable boiling in multiple parallel microchannels were systematically conducted and the measured flow boiling heat transfer coefficients and two phase frictional pressure drops were analyzed according to the observed flow phenomena and mechanisms.

Journal ArticleDOI
TL;DR: In this paper, the impact of the polysaccharides on the hydrate microstructure was investigated using powder X-ray diffraction and Raman spectroscopy, and the authors found that the polymers exhibited good biodegradability and increased the maximum subcooling of hydrate formation.

Journal ArticleDOI
15 Dec 2019-Energy
TL;DR: In this article, the thermal performance of a two-stage compression transcritical CO2 refrigeration system with R290 mechanical subcooling unit was evaluated under the optimal sub-cooling temperature and compressor discharge pressure.

Journal ArticleDOI
TL;DR: In this article, an experimental investigation of subcooled flow boiling in the rectangular microchannel with hydraulic diameter of 0.94 mm (5.01′mm)×′0.52”mm) for different orientations on hydrophilic and super-hydrophilic surfaces is conducted utilizing deionized water as the working fluid.

Journal ArticleDOI
J. Zhang1, Hou Yu1, Mingkun Wang1, Y.W. Wu1, Wen Xi Tian1, S.Z. Qiu1, Guanghui Su1 
TL;DR: In this article, the characteristics of two-phase critical flow through short slits (L/d) were investigated and correlations were developed for the flow rate through short-slits, showing a reasonable accuracy in predicting test data both in this study and from literature.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the energy efficiency of a dedicated and integrated mechanical subcooling system in CO2 booster systems for supermarket applications through the use of thermodynamic models close to reality.
Abstract: Energy improvements offered by dedicated and integrated mechanical subcooling systems in CO2 booster systems for supermarket applications are analyzed here through the use of thermodynamic models close to reality. Using a reference supermarket with 41 kW and 140 kW thermal loads at low and medium temperature, respectively, and considering as state-of-the-art system the CO2 booster with parallel compressor and flash gas by-pass, it has been concluded that both systems allow to reduce energy consumption. However, its operation is highly dependent on environmental conditions. The dedicated mechanical subcooling system offers annual energy reductions for tempered places from 1.5% to 2.9%, for warm between 2.9% and 3.4% and for hot from 3.0% to 5.1%. The integrated subcooling system obtains reductions between 3.1% and 4.0% for cold regions, from 1.4% to 2.9% for tempered, from 2.9% to 3.4% for warm and from 1.3% to 2.4% for hot regions.

Journal ArticleDOI
Bin Liu1, Jie Liu1, Jie Zhou1, Bo Yuan1, Yonghai Zhang1, Jinjia Wei1, Wenjun Wang1 
TL;DR: In this article, the authors presented the pool boiling heat transfer of gas dissolved FC-72 on micro/nanostructured surfaces, named LS30, LS70, LS100, LS200, LS400 and LS800.

Journal ArticleDOI
Yang Luo1, Junye Li1, Kan Zhou1, Jingzhi Zhang2, Wei Li1 
TL;DR: In this article, a computational fluid dynamics (CFD) approach including subcooled two-phase flow boiling process and conjugate heat transfer effect is performed using a MMC unit cell model.

Journal ArticleDOI
TL;DR: In this paper, a real-time non-intrusive technique, namely rainbow schlieren deflectometry has been employed to simultaneously map the full bubble cycle and temperature gradients field near the heated surface as well as around the bubble.

Journal ArticleDOI
TL;DR: In this article, the authors performed 10 pure steam experiments in the range of steam mass flux 5-80 kg/m2) and water temperature 19-96 ǫ°C and found that steam condensation behave, fluid oscillation and pressure oscillation are recorded and analyzed.