On the Effect of Lubricant on Pool Boiling Heat Transfer Performance

   For typical vapor compression processes, lubricant oil is very essential for lubricating and sealing the sliding parts and the lubricant also takes part in cushioning cylinder valves. However lubricants may migrate to the evaporator to alter the heat transfer characteristics. This is can be made clear from the viscosity and surface tension of lubricant since the viscosity of lubricant oil is about two to three orders higher than that of refrigerant whereas the corresponding surface tension of lubricant is approximately one order higher. Typically, the presence of lubricant may deteriorate heat transfer performance, yet this phenomenon becomes more severe when the lubricant mass fraction is higher. However, some previous literatures had clearly showed that the presence of lubricant oil may favor the heat transfer performance at a low lubricant fraction and the heat transfer performance may peak at a specific oil concentration. In this study, the authors aim at clarifying this phenomenon subject to pool boiling condition. Various parameters affecting the heat transfer coefficient, such as viscosity, surface tension, critical solution temperature and other thermodynamic and transport properties will be examined.    During pool boiling process, the lubricant accumulates on the surface since the refrigerant is preferential to evaporate. Hence, excess lubricant enrichment on the surface results in a thin lubricant excess layer and a thermal boundary layer, which influence the heat transfer performance, either enhancement or degradation. The excess layer may bring about a liquid-solid surface energy reduction which increases site density and reduces the bubble departure diameter, causing enhancement and degradation in heat transfer performance, respectively. However, the effect of the bubble departure diameter normally surpasses the influence of site density. This may be the crucial reason that gives rise to an occurrence of the plateau of heat transfer coefficient and followed by an apparent decline of heat transfer coefficient with a further increase of lubricant concentration.    Moreover, with the preferential evaporation of the refrigerant, a surface tension gradient is formed, which induces the Marangoni effect through which refrigerant/lubricant mixtures is supplied toward the contact line. From the phase equilibrium diagram, the maximum of the Marangoni number may occur at the low lubricant concentration with a maximum temperature difference. Hence, the presence of Marangoni effect may also be the favor the heat transfer accordingly. Also, a small fraction of lubricant will increase a larger viscosity that provide a thicker thermal boundary layer which may activate more site density, and enhances the heat transfer performance. Furthermore, miscibility may also play a crucial factor that affects the pool boiling heat transfer performance. The fluid with a smaller difference between the bulk fluid temperature and critical solution temperature may yield a better heat transfer performance by drawing superheated liquid onto the bubble sides.

The Effect of Refrigeration Lubricant Properties on Nucleate Pool Boiling Heat Transfer Performance

Refrigeration lubricant plays a key role in lubricating and sealing during vapor compression processes. However, it may migrate to the evaporator to influence the heat transfer characteristics, either enhancement or degradation. The aim of this study is to fundamentally understand the effect of lubricant properties and bubble parameters on heat transfer performance. To clarify parameters affecting the heat transfer coefficient, several experiments were conducted on a horizontal flat surface, and pool-boiling phenomenon was recording by high-speed camera. Comparisons of heat transfer measurements for different refrigerant/lubricant mixtures were made, including two different refrigerants (R-134a & R-1234ze) and eight POE lubricants with different miscibility, ISO68 to ISO170 viscosity range. This study shows that improvements over pure refrigerant heat transfer can be obtained for refrigerant /lubricant mixtures with small lubricant mass fraction, high lubricant viscosity, and a low critical solution temperature (CST). The presence of lubricant will decrease the departure bubble diameter and may deteriorate heat transfer performance when the lubricant mass fraction is higher than 3%. A mechanistic explanation was provided for the observed refrigerant/lubricant boiling phenomenon, and we were successfully in creating a new model to quantify the effect of lubricant properties on the heat transfer performance. This model was developed based on cavity boiling theory, interfacial energy calculation between metal-liquid surface, and liquid-bubble interface. According to the model, the presence of lubricant layer on metal surface and surrounding the bubble will significantly alter waiting time of boiling, bubble departure time, activity site density of boiling incipience and superheat on heating surface

(Z)-4-[(Ethyl­amino)(furan-2-yl)methyl­idene]-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one

In the crystal of the title compound, C17H17N3O2, the mol­ecules exist in the keto–enamine form. The pyrazole ring is oriented at 10.59 (4) and 57.98 (5)° to the phenyl and furyl rings, respectively, and the dihedral angle between phenyl and furyl rings is 73.30 (11)°. An intra­molecular N—H⋯O hydrogen bond occurs between imino and carbonyl groups. In the crystal, weak C—H⋯O hydrogen bonds link the mol­ecules into supra­molecular chains along the b axis

Quantum electric-dipole liquid on a triangular lattice

Geometric frustrations and quantum mechanical fluctuations may prohibit the formation of long-range ordering even at the lowest temperature, and therefore liquid-like ground states could be expected. A good example is the quantum spin liquid in frustrated magnets that represents an exotic phase of matter and is attracting enormous interests. Geometric frustrations and quantum fluctuations can happen beyond magnetic systems. Here we propose that quantum electric-dipole liquids, analogs to quantum spin liquids, could emerge in frustrated dielectrics where antiferroelectrically coupled small electric dipoles reside on a triangular lattice. The quantum paraelectric hexaferrite BaFe12O19, in which small electric dipoles originated from the off-center displacement of Fe3+ in the FeO5 bipyramids constitute a two-dimensional triangular lattice, represents a promising candidate to generate the anticipated electric-dipole liquid. We present a series of experimental evidences, including dielectric permittivity, heat capacity, and thermal conductivity measured down to 66 mK, to reveal the existence of a nontrivial ground state in BaFe12O19, characterized by itinerant low-energy excitations with a small gap, to which we interpret as an exotic liquid-like quantum phase. The quantum electric-dipole liquids in frustrated dielectrics open up a fresh playground for fundamental physics and may find applications in quantum information and computation as well.Comment: 13 pages, 6 figure

Pleural Effusion after Percutaneous Radiofrequency Ablation for Hepatic Malignancies

AbstractBackground and AimsRadiofrequency ablation (RFA) can play an important role in the treatment of primary or metastatic liver tumors. Currently, percutaneous RFA is generally regarded as a safe, effective, and minimally invasive procedure. This study aimed to evaluate the presence and course of pleural effusion after monopolar RFA.MethodsFrom October 2008 to July 2013, a total of 54 patients (28 male and 26 female, mean age 65.2) treated with monopolar RFA were included in our study. 47 patients were diagnosed with hepatocellular carcinoma, 4 patients with hepatic metastasis, and 3 patients had other diagnoses. There were a total of 115 sessions of treatment and 199 liver tumors to be treated (1.73 ± 1.02 tumors treated per session). The tumor size ranged from 0.8 cm to 5.0 cm (mean 2.31 cm, standard deviation 1.04 cm). Thereafter, a follow-up ultrasound was performed within 24 hours subsequent to ablation to evaluate the presence of pleural effusion. The degree of pleural effusion was assessed by chest X-ray.ResultsFifteen (13.0%) treatment sessions in 14 patients showed right-sided pleural effusion after ablations. One patient had a large amount of effusion, while other patients manifested a minimal to small amount of effusion. There were 5 patients that experienced delayed resolution of pleural effusion; one patient (0.87%) had a minimal amount of pleural effusion even after one month. Overall, there was no pneumothorax, or periprocedural morality. Age, gender, tumor numbers, tumor sizes, and complete ablation of target tumors were similar among groups presenting with or without pleural effusion. Tumor locations associated with S78 segments abutting the diaphragm or right lobe of the liver were not associated with development of pleural effusion. Only the duration of ablation time had a marginal trend toward significance (p = 0.051).ConclusionsThe transient appearance of right-sided pleural effusion after percutaneous RFA for hepatic malignancies was not infrequent. However, refractory pleural effusion was rare

Application of Traditional Chinese Medical Herbs in Prevention and Treatment of Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is a common viral pathogen of the lower respiratory tract, which, in the absence of effective management, causes millions of cases of severe illness per year. Many of these infections develop into fatal pneumonia. In a review of English and Chinese medical literature, recent traditional Chinese medical herb- (TCMH-) based progress in the area of prevention and treatment was identified, and the potential anti-RSV compounds, herbs, and formulas were explored. Traditional Chinese medical herbs have a positive effect on inhibiting viral attachment, inhibiting viral internalization, syncytial formation, alleviation of airway inflammation, and stimulation of interferon secretion and immune system; however, the anti-RSV mechanisms of TCMHs are complicated, which should be further investigated