Showing papers on "Subcooling published in 2013"
TL;DR: In this paper, the effect of nanoparticle loading on the thermal conductivity of PCM/nanoparticle composite was investigated in a square enclosure with a constant heat flux on one side, while the other sides are thermally insulated.
166 citations
TL;DR: In this article, the effect of nano-enhanced phase change materials (NePCM) inside an annular cavity formed between two circular cylinders is investigated experimentally and numerically, where the inner cylindrical tube is subjected to a constant heat flux, while the outer shell is thermally insulated.
159 citations
TL;DR: In this article, the effect of dispersing nanoparticles in the base phase change material (PCM) on the melting heat transfer characteristics in the enclosure was examined for the relevant parameters in the following ranges: the mass particle fraction of nanoparticles, ω p ǫ = 0, 5, 10 ¼ ; the Rayleigh number, Ra f Â= 1.71 Ã 1.67 Ã 10 6 −5 ; the Stefan number, Ste f ´= 0.037 Â 0.108; and the subcooling parameter, Sb
153 citations
TL;DR: In this article, the effect of Weber number on spreading of droplets of three different liquids namely water, isopropyl alcohol and acetone was studied using a high speed camera.
120 citations
TL;DR: In this article, the solidification behavior of water-based nanofluid phase change material encapsulated in a spherical container was presented. And the authors predicted that there is a possible energy saving potential of approximately 6-9% in the thermal energy storage (CTES) system using the NFPCMs.
Abstract: This present study presents the solidification behavior of water based nanofluid phase change material encapsulated in a spherical container. The nanofluid phase change material (NFPCM) was prepared by dispersing the multi wall carbon nanotubes (MWCNT) with volume fractions of 0.15%, 0.3%, 0.45%, and 0.6% in de-ionized (DI) water as the base phase change material. The solidification experiments were conducted with DI water and the NFPCM and maximum reductions of 14% and 20.1% were observed in the solidification time with the NFPCMs at surrounding bath temperature of −9 °C and −12 °C respectively. The presence of MWCNT also acted as nucleating agent that caused appreciable reduction in the subcooling. The enhanced thermal transport properties of the NFPCM are very useful to operate the cool thermal energy storage (CTES) system at higher operating temperature of the secondary refrigerant. It is predicted that there is a possible energy saving potential of approximately 6–9% in the CTES using the NFPCMs.
119 citations
TL;DR: In this paper, a thermodynamic model for cascaded vapor compression-absorption system (CVCAS) has been developed which consists of a vapor compression refrigeration system (VCRS) coupled with single effect vapor absorption refrigeration (VARS) Based on first and second laws, a comparative performance analysis of CVCAS and an independent VCRS has been carried out for a design capacity of 6667kW.
108 citations
TL;DR: In this article, an experimental investigation has been conducted to evaluate the steam heat removal capacity with non-condensable gases (e.g. air, helium) over a vertical tube external surface.
96 citations
TL;DR: In this paper, an experimental investigation of the optimal heat rejection pressure for a transcritical CO 2 heat pump water heater is presented, and it is found that the optimal PSR varies with gas-cooler outlet refrigeration temperature at different ambient temperatures.
95 citations
TL;DR: In this article, a population balance approach is used, where bubbles are generated at the wall with a certain size that subsequently evolve due to both condensation/evaporation and coalescence/breakup processes.
87 citations
TL;DR: In this paper, the authors measured the initial thickness of a single methane hydrate bubble in water at 274.0, 276.0 and 278.0 K. The results showed that the initial hydrate film thickness decreases from tens of micrometers to about 10 µm with the subcooling increased from 0.5 K to about 3 K.
Abstract: The initial thickness of methane hydrate film was directly measured by suspending a single methane bubble in water at 274.0, 276.0, and 278.0 K. The results show that the initial hydrate film thickness decreases from tens of micrometers to about 10 µm with the subcooling increased from 0.5 K to about 3 K. When subcooling is higher than 1.0 K, all initial film thickness data measured under different temperatures vary inversely with the subcooling. Notable three-dimensional growths of hydrate crystals of different sizes and shapes at film front and emergence of new crystal were clearly observed at lower subcooling that resulting in the rougher surface of hydrate film and uncertainty of initial thickness measurement under lower subcooling. The hydrate film growth was dominated by film growth in thickness, not by lateral growth at low subcooling. The growth in thickness of hydrate shell covering one whole bubble surface was also investigated. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2145–2154, 2013
78 citations
TL;DR: Using the improved double distribution function (DDF) thermal Lattice Boltzmann method (LBM), dropwise condensation of dry saturated vapor at a cold spot on vertical hydrophobic flat plates under gravity effects are simulated numerically for the first time as discussed by the authors.
TL;DR: In this article, the subcooled flow boiling heat transfer coefficient of pure n-heptane and distilled water at different operating conditions have been experimentally measured and compared, and it was shown that water is better cooling fluid in comparison with n-hexane.
TL;DR: In this article, the authors investigated the influence of heat flux, flow velocity, degree of subcooling, and concentration of mixture on heat transfer coefficient in both the convection and nucleate boiling regimes.
TL;DR: In this article, an experimental investigation of bubble dynamics and the effect on flow boiling instabilities and heat transfer in a multiple-microchannel heat sink is presented and discussed, and the results demonstrate that the bubble growth rate in microchannels is different from that in macroscale channels.
TL;DR: In this paper, an enthalpy-based lattice Boltzmann method with a double distribution function (DDF) model is implemented to trace phase change front in a cylindrical-horizontal annul.
TL;DR: In this paper, an experimental investigation into the effects, in terms of energy, of employing a dedicated mechanical subcooling cycle with a residential 1.5-ton simple vapor compression refrigeration system is presented.
TL;DR: In this paper, the effects of various operating parameters on cycle performances are studied, and the effect of the thermoelectric subcooler on the performance of transcritical CO2 refrigeration cycle is investigated.
Abstract: SUMMARY
Use of thermoelectric subcooler is one of the techniques to improve the performance of transcritical CO2 cycle Thermodynamic analyses and optimizations of transcritical CO2 refrigeration cycle with thermoelectric subcooler are presented in this paper Further, the effects of various operating parameters on cycle performances are studied It is possible to optimize current supply, discharge pressure, and CO2 subcooling simultaneously based on maximum cooling COP for thermoelectrically enhanced transcritical CO2 refrigeration cycle to get best performance Results show that thermoelectric current supply, COP improvement, and discharge pressure reduction increase with increase in cycle temperature lift, with maximum values of 11 A, 256%, and 154%, respectively, for studied ranges Use of thermoelectric subcooler in CO2 refrigeration system not only improves the cooling COP, also reduces the system high-side pressure, compressor pressure ratio, and compressor discharge temperature, and enhances the volumetric cooling capacity Component-wise irreversibility distribution shows similar trend with basic CO2 cycle, although values are lower leading to higher second law efficiency Cooling capacity may be enhanced by increasing the current supply for the same thermoelectric configuration with penalty of COP Study reveals that thermoelectrically enhanced CO2 refrigeration cycle yields significant performance improvement especially for higher-cycle temperature lift Copyright © 2011 John Wiley & Sons, Ltd
TL;DR: Based on the newly developed phase-change Lattice Boltzmann method (LBM), the problem of steady laminar film condensation on a hydrophilic vertical flat plate at a subcooled temperature is simulated in this article.
TL;DR: In this paper, the effects of operating temperature, effectiveness of heat exchangers and choice of working fluid on the system were studied and it is evident from the studies that the cycle performance (COP) improves with increasing generator and evaporator temperatures, but reduces with increasing the absorber and condenser temperatures.
Abstract: Presently out of the total energy consumption, a large share of energy is being used by refrigeration and air conditioning equipments. The present study is based on literature review on the refrigeration systems, currently used refrigerant–absorbent pairs and also on different sources of energy. The basis of this study is to know about the user friendly softwares used for the simulation techniques and also on the scope of different alternative forms of energy as a source to generator. The effects of operating temperature, effectiveness of heat exchangers and choice of working fluid on the systems were studied. It is evident from the studies that the cycle performance (COP) improves with increasing generator and evaporator temperatures, but reduces with increasing the absorber and condenser temperatures. The use of heat exchangers improves the overall performance of the system, especially solution heat exchanger (SHE). It is also evident that solar energy obtained in the range of about 100 °C is having good potential to supply sufficient energy to the generator for absorption–refrigeration cycles.
TL;DR: In this article, the authors investigate the sensible and subcooling phenomena during the outward cylindrical solidification of the phase change material stored on the annulus side, along with 8 longitudinal uniformly spaced copper fins of different heights.
TL;DR: In this article, an absorption-compression hybrid refrigeration cycle has been studied on the basis of available data of working pair 1, 1,1,2-tetrafluoroethane (R134a) and dimethylformamide (DMF).
TL;DR: In this article, an experimental evaluation of a heat-sink based on flow boiling of R134a inside micro-scale channels was performed, and the average heat transfer coefficient increases when the mass velocity increases.
TL;DR: In this article, the authors measured gas hydrate formation for gas mixtures of methane and propane at pressures up to 11.3 MPa using a high-pressure automated lag time apparatus (HP-ALTA).
Abstract: Induction time distributions for gas hydrate formation were measured for gas mixtures of methane + propane at pressures up to 11.3 MPa using a high-pressure automated lag time apparatus (HP-ALTA). Measurements were made at subcooling temperatures between 4.3 and 13.5 K and, while isothermal induction times between 0 and 15,000 s were observed, the median isothermal induction times for the distributions ranged from 100 to 4000 s. A hyperbolic relationship between median induction time and subcooling was used to correlate the data. A graphical interpretation is presented that relates the two types of data that can be acquired by using the HP-ALTA in one of two modes to study hydrate formation: induction time distributions at constant subcooling and formation temperature distributions observed during linear cooling ramps. The equivalence of these two modes provides a robust method for studying the variation of formation phenomena in different hydrate systems. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2640–2646, 2013
TL;DR: In this article, an experimental study of bubble absorption in a plate heat exchanger using ammonium/lithium nitrate and ammonia/(Lithium Nitrate+water) mixtures has been carried out at operating conditions of air-cooled absorption systems driven by low temperature heat sources.
TL;DR: In this article, the convective heat transfer coefficient for a nanofluid in subcooled flow boiling is investigated numerically using two phase mixture model and a good agreement is realized.
TL;DR: A comprehensive literature review on the fundamental issues of critical heat flux (CHF) during flow boiling and nucleate pool boiling in micro-scale channels and confined spaces is presented in this article.
Abstract: This article presents a comprehensive literature review on the fundamental issues of critical heat flux (CHF) during flow boiling and nucleate pool boiling in microscale channels and confined spaces. First, distinction between macro- and micro-scale channels is discussed. Then the CHF mechanisms are discussed. Next, experimental and theoretical studies of subcooled flow boiling CHF in microscale channels together with the prediction methods are reviewed and analyzed. Following this, experimental and theoretical studies on saturated flow boiling CHF together with the prediction methods are summarized and discussed. Furthermore, experimental and theoretical studies on nucleate pool boiling CHF in confined spaces together with the relevant prediction methods are reviewed as well. So far, limited studies on CHF microscale channels and confined spaces are available in the literature. There are numerous discrepancies in the existing studies on CHF results, mechanisms, and prediction methods. Furthermore, there ...
TL;DR: In this article, the authors measured the wetted area fraction in sub-cooled pool boiling of water at atmospheric pressure using the DEPIcT (DEtection of Phase by Infrared Thermography) technique, which exploits the contrast in infrared light emissions between wet and dry areas on the surface of an IR-transparent heater to visualize the instantaneous distribution of the liquid and gas phases in contact with the heater surface.
TL;DR: In this paper, a novel high-efficient absorption refrigeration cycle regarded as an improved single-effect/double-lift configuration is proposed, which uses an evaporator/absorber (E/A) to promote the coefficient of performance and reduce the irreversible loss.
TL;DR: In this paper, the authors measured the heat transfer coefficient and pressure drop in a horizontal tube under low pressure and low flow (LPLF) conditions of subcooled boiling, and derived the correlation for single phase diabatic pressure drop ratio (diabatic to adiabatic) as a function of viscosity ratio (wall temperature to fluid temperature).