Refrigerant- Lubricant Mixture Properties Influencing Bubble Dynamic Parameters and Heat Transfer Coefficient in Nucleate Pool Boiling

We have been successfully developed a model regarding lubricant effect on individual processes of bubble nucleation, growth and departure period for nucleate pool boiling heat transfer. In this study, three type POE refrigeration lubricants with different refrigerant miscibility (POEA/POEB/POEC), two viscosity grades (ISO68 & 170), three kind of refrigerants (R-134a/R-1234ze/R-134yf), and three different saturated temperatures (10℃/0℃/10℃) are taken into calculation under different heat flux ranging from 10 KW/m2 to 80 KW/m2. Based on this model, a knowledge of chemical structures and physical properties of lubricant and refrigerant is sufficient to get bubble dynamic parameters and predict the boiling performance near metal surface. According to calculating results, several key factors play an important role in pool boiling heat transfer and show drastic influence on bubble parameters and HTC, such as refrigerant type, saturated temperature, heat flux and lubricant concentration. Regarding lubricant chemical structure effect on heat transfer performance, it will be direct related to OCR and following influence on HTC in real evaporator environment. But if keeping same lubricant concentration, different results will appear. Various lubricant structures may provide different volume size, adsorption energy on metal surface and interaction force between refrigerant and lubricant, but these factors sometimes offset each other and lead to only a slight difference in bubble size, contact angle, surface coverage concentration, and HTC. The calculation indicates that the presence of lubricant imposes a negative effect on HTC during waiting period of bubble formation and departure period, but a positive effect on HTC may prevail in bubble growth period. Such two effects compete during the boiling process and could lead increase or impair heat transfer performance at a low lubricant concentration

Prevalence of latent tuberculosis infection in BCG-vaccinated healthcare workers by using an interferon-gamma release assay and the tuberculin skin test in an intermediate tuberculosis burden country

BackgroundThe risk of healthcare workers (HCWs) acquiring tuberculosis (TB) infection is high. We determined the prevalence of latent TB infection (LTBI) in HCWs with a high Bacille Calmette-Guérin (BCG) vaccine coverage in an intermediate TB burden country by using an interferon-gamma release assay [QuantiFERON-TB Gold (QFT-G)] and by using the tuberculin skin test (TST). Risk factors associated with a positive test were determined.MethodsThis prospective cross-sectional study enrolled HCWs from a medical center in Taiwan. Participants were grouped into workers without exposure (Group 1) and workers who self-reported a history of TB exposure (Group 2). All participants completed a questionnaire to collect demographic information and risk factors for acquiring TB. The QFT-G test and the TST were administered and risk factors for a positive test were analyzed.ResultsWe recruited 193 HCWs [149 (77.2%) female workers] with a mean age of 35.6 years. All were BCG-vaccinated. The prevalence of LTBI was 88.8% (based on the TST) and 14.5% (based on the QFT-G test). There was no difference between HCWs with and without known exposure to TB. Agreement between the tests was poor (i.e., the kappa value was less than 0.05). Multivariable logistic regression showed that only the QFT-G test was associated with age (35 years or greater) (adjusted OR, 2.53; p = 0.03).ConclusionBy using the QFT-G test or TST, this study found a similar prevalence of LTBI in HCWs with and without known exposure to TB. This suggests that in intermediate TB burden countries exposure to TB may occur within the hospital and within the community. Compared to the TST, the QFT-G test was correlated better with age, which is a known risk factor for latent TB infection

Ring Characteristics and Compressive Strength of Japanese Cedar Trees Grown Under Different Silvicultural Treatments

The effects of different plantation spacings and thinning treatments on the ring characteristics, compressive strength, and dynamic modulus of elasticity (DMOE) of Japanese cedar (Cryptomeria japonica) trees were investigated. The results revealed that young trees of more-closely spaced plantations (3000 trees/ha) had higher wood density and compressive strength than those of more-widely spaced plantations (2200 trees/ha). Different (first and second) thinning treatments of the 2 initial spacings had little effect on ring characteristics or compressive strength. Overall, the average ring characteristics, compressive strength, and DMOE of 35-yr-old Japanese cedar at different plantation spacings and thinning treatments showed no statistically significant differences. The results suggest that using these silvicultural treatments with a longer rotation age will have no detrimental effects on the wood density, compressive strength, or DMOE

Transactive Memory System, Job Competence and Individual Performance

The purpose of this paper is to understand important variables that impact individual performance within a team. This will enhance knowledge management within a team context and facilitate competence development of individuals. This research proposes and examines a multi-level model which elaborates how transactive memory system and job competence (i.e., technology competence and teamwork competence) affect individual performance. An empirical study was conducted with 19 teams of television news reporters, with 211 valid survey responses. Hierarchical linear modeling was applied to analyze the data. The result indicated that transactive memory system and technology competence helped to improve a reporter’s job performance. Furthermore, the relationships were fully mediated by teamwork competence. Our findings thus suggest teamwork competence is the core. Neither technology competence nor transactive memory system will necessarily translate directly into enhanced individual performance. Therefore, for organizational investment on transactive memory system and digital technologies to take effect, management should help develop the employee’s teamwork competence

On Online Engagement: Does the Leadership Style Matter?

The news industry is facing tremendous changes. Integrating digital technologies into news practices has become the key to survival. Social media engagement editors are one of such innovations to respond to the challenge. Engagement editors are required to facilitate the functions of marketing, editing, content production, and data analysis. They thus play the role of boundary-spanner within and beyond the organizational boundaries. However, there are few studies to explore issues associated with the management of social media engagement editors. This research examines whether and how the leadership style (i.e., transformational and passive leadership style) influences engagement editors’ job performance. We collected 122 valid responses, and used the SmartPLS 3 and SPSS 19.0 to analyze the data. Our findings indicate that performance of engagement editors is influenced by the leadership style; moreover, job autonomy mediates the positive effect of transformational leadership on engagement editors’ job performance. Implications for the management of social media engagement editors are discussed

Preparation of Monodisperse Iron Oxide Nanoparticles via the Synthesis and Decomposition of Iron Fatty Acid Complexes

Iron fatty acid complexes (IFACs) are prepared via the dissolution of porous hematite powder in hot unsaturated fatty acid. The IFACs are then decomposed in five different organic solvents under reflux conditions in the presence of the respective fatty acid. The XRD analysis results indicate that the resulting NPs comprise a mixture of wustite, magnetite, and maghemite phases. The solvents with a higher boiling point prompt the formation of larger NPs containing wustite as the major component, while those with a lower boiling point produce smaller NPs with maghemite as the major component. In addition, it is shown that unstable NPs with a mixed wustite–magnetite composition can be oxidized to pure maghemite by extending the reaction time or using an oxidizing agent

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

Primary Urothelial Carcinoma of the Ureter: 11-Year Experience in Taipei Veterans General Hospital

BackgroundUrothelial carcinoma of the upper urinary tract is relatively rare, occurring in 5% of all urothelial tumors. Ureteral urothelial carcinoma is even less common than that of the renal pelvis, accounting for about 25% of all upper urinary tract tumors. The aim of this study was to evaluate the clinical behavior, survival, recurrence and prognostic information of primary ureteral urothelial carcinoma from our 11 years of experience at the Taipei Veterans General Hospital.MethodsWe retrospectively reviewed 111 patients with ureteral urothelial carcinoma who had been treated in our hospital between January 1993 and December 2003. Tumor staging was according to the 2002 AJCC TNM classification and stage groupings. Patients with stage 0a and stage 0is were categorized as stage 0a/is, and patients with pathologic T stage pTa and pTis were categorized as pTa/is for statistical analysis. The Kaplan-Meier method was used for survival analysis.ResultsThere were 69 males and 42 females, with a mean age of 70.5 ± 9.4 years at diagnosis. Of the 111 patients, 5 presented with stage 0a/is, 38 with stage I, 23 with stage II, 21 with stage III, and 24 with stage IV. Nephroureterectomy with bladder cuff excision was performed in 78 patients, 12 patients received segmental resection of the ureter, 4 received ureteroscopic laser coagulation, and 17 underwent chemotherapy or radiotherapy or both. Tumors were located on the left side in 53 patients, on the right in 53, and bilaterally in 5. The most frequent initial presenting symptom was gross hematuria (65%). The mean postoperative follow-up period was 49.3 months. Disease recurrence in the nephroureterectomy group occurred in 36 patients (46.2%), with 17 (21.8%) at the urinary bladder, 2 (2.6%) at the retroperitoneum, 1 (1.3%) at the contralateral ureter, 6 (7.7%) with distant metastases to the lung, bone, distant lymph nodes or liver, and 10 (12.8%) at multiple sites. The 5-year cancer-specific survival rate was 100% for pTa/is, 95.2% for pT1, 69.4% for pT2, and 43.8% for pT3. All 3 pT4 cases died of cancer in a median of 12 months. Significant prognostic factors for cancer-specific survival by univariate analysis were pT (p = 0.00001), stage (p = 0.00001), type of treatment (p = 0.00001) and grade (p = 0.0001). On multivariate analysis, only stage (p = 0.0001) and grade (p = 0.014) were significant for cancer-specific and overall survival. Stage (p = 0.0001), pT (p =0.0001) and grade (p = 0.026) were also significant prognostic factors of recurrence in multivariate analysis.ConclusionOur experience showed that patients with pTa/is and pT1 tumors treated with radical surgery have excellent prognoses. Tumor stage and grade are the only significant prognostic factors for both cancer-specific and overall survival