•Experimental results of two multi-twisted-tube gas coolers in a CO2 heat pump water heater were compared.•Heat transfer characteristics of the gas coolers with the number of inner tubes changing ...from 2 to 7 were analyzed.•Several ways to improve the water outlet temperature of gas cooler were discussed.
Multi-twisted-tube type heat exchangers applied in a transcritical CO2 heat pump as gas coolers were investigated. The influence of different numbers of inner tubes on the heat transfer and the pressure drop was discussed by means of experiments and theoretical analysis. The performances of two gas coolers with three and four inner tubes were measured and compared. It is found that heat transfer characteristics of the gas cooler with four inner tubes is better than that with three inner tubes. Based on the theoretical analysis, outlet temperature of water increases with increasing the number of inner tubes at the beginning and the increasing tendency becomes gentle when the number of inner tubes is more than four. But the pressure drop of gas cooler rises greatly with the increment of the number of inner tubes. It is implied from the analysis that the coefficient of performance of CO2 heat pump is not optimum when the outlet temperature of water becomes high by increasing mass flow rate of CO2 and decreasing the mass flow rate of water. In order to get both high COP and high outlet temperature of water, the water side heat transfer coefficient of the gas cooler needs improving.
Objective:
To investigate the effects of glucose-free and glucose-containing dialysates during dialysis in maintenance hemodialysis (MHD) patients by the prospective cross-over study, and detect ...glucose control methods in MHD patients.
Methods:
A total of 66 MHD 18–75 years old patients in our hospital from Nov. 2019 to Mar. 2020 were recruited. All patients underwent HD with 4 hours per time, three times per week. Glucose-free dialysate (glucose-free group) and then 5.55 mmol/L glucose-containing dialysate (glucose-5.55 group) were used alternately in dialysis. The demographics and parameters of pre- and post-dialysis were recorded.
Results:
A total of 60 patients were analyzed, and 28 patients among them had type 2 diabetes. Serum glucose pre and post dialysis were 8.64 ± 4.18 mmol/L versus 5.74 ± 1.82 mmol/L (p < 0.01) in glucose-free dialysate, and 9.31 ± 4.89 mmol/L versus 7.80 ± 2.59 mmol/L (p < 0.01) in glucose-5.55 dialysate. The post-dialysis blood glucose of glucose-free group was lower than glucose-5.55 group (5.74 ± 1.82 vs 7.80 ± 2.59, p < 0.01). About 18 (30.00%) patients in glucose-free group and 1 patient (1.67%) in glucose-5.55 group whose blood glucose was lower than 4.44 mmol/L (p < 0.01). About 29 patients (48.33%) in glucose-free group and 17 patients (28.33%; p = 0.02) in glucose-5.55 group have hunger feeling. Serum sodium level in the glucose-free group was higher than that in Glucose-5.55 group (137.92 ± 1.64 vs 136.70 ± 1.64, p < 0.01). Post-dialysis blood glucose had no significant differences between patients not using diabetes-related medication (13 patients) and patients using diabetes-related medication (15 patients) in glucose-free group (7.13 ± 1.78 mmol/L vs 6.08 ± 2.84 mmol/L, p = 0.23) and glucose-5.55 group (9.22 ± 2.59 mmol/L vs 9.35 ± 2.88 mmol/L, p = 0.90).
Conclusions:
Glucose-free and glucose-5.55 dialysate both decrease the blood glucose post-dialysis. Dialysates containing 5.55 mmol/L glucose can reduce the incidence of hypoglycemia and lower serum sodium, but have no effect on blood pressure during dialysis. Stopping insulin and oral anti-diabetic drugs once before dialysis may not affect the control of blood glucose.
A rechargeable lithium battery, Li//Br, is reported using an aqueous bromide/tribromide redox pair and a coated lithium metal as the positive and negative electrodes, respectively. The positive Br ...sub(2) electrode shows fast redox kinetics and good stability. This battery presents excellent electrochemical performance with an average discharge voltage up to 3.96 V at 1.7 mA cm super(-2), an energy density of 1220 Wh kg super(-1), a power density of 29.7 mW cm super(-2) at a current density of 12.8 mA cm super(-2), and a long cycling life. There is no evidence of voltage decrease after 100 cycles at 35% DOD. It would become a good platform between lithium ion batteries and Li//air batteries since the former shows lower energy density and the latter has some challenging problems that need to be solved prior to practical application. This finding presents another promising choice for electrochemical energy storage systems.
Objective:
To evaluate the association between brachial artery blood velocity by color Doppler flow imaging (CDFI) and primary maturation of radio-cephalic autologous arteriovenous fistula (RC-AVF).
...Methods:
Clinical data from patients who underwent end-to-side cephalic-radial anastomosis were collected from December 2015 to December 2020. The anastomosis diameter (mm), blood velocity (cm/s), and brachial artery diameters (mm) 7 cm proximal to the elbow pre- and postoperation were measured by GE LOGIC-E9 ultrasound. The AVF was mature if it could be cannulated successfully and the blood flow was >200 ml/min during dialysis.
Results:
A total of 197 patients were included in our statistical analysis. A total of 163 patients had mature AVFs, and 34 patients had poor maturity (assisted and failed maturation). There were no significant differences in the clinical characteristics, peak systolic velocity (PSV) of the brachial artery, diameter of the radial artery or cephalic vein measured by CDFI preoperatively. The diameter of the brachial artery (5.41 ± 0.77 vs 4.89 ± 0.90, p = 0.00) and the fistula anastomosis (2.79 ± 0.78 vs 2.45 ± 0.85, p = 0.02) and PSV of the brachial artery (123.58 ± 37.11 vs 89.63 ± 28.31, p = 0.00) in the mature group were higher than those in the immature group.
Conclusion:
Brachial artery PSV and increased brachial artery PSV could be used to detect RC-AVF maturation in the early stage.
The friction and heat transfer characteristics of single phase liquid flow through two multi-port extruded (MPE) micro-tubes were investigated by experiments and theoretical analysis. The ...cross-section geometries of two tubes were rectangular (approximate square) and circular, and the hydraulic diameters were 0.715 and 0.86mm respectively. The working fluid was ethanol and its Reynolds number was in the range of 50–2400. The inlet temperature changed from 5 to 45°C and the heat flux ranged from 3 to 9kW/m2. The measurements of pressure drop were performed under isothermal and non-isothermal (constant heat flux) conditions. The effects of different boundary conditions on the simultaneous pressure drop and heat transfer characteristics were studied. The results showed that the Nusselt numbers decrease with the increase of inlet temperature and heat flux. Furthermore, the scaling effects of conjugate heat transfer, entrance effects and temperature dependent viscosity variation on the convective heat transfer are significant. Based on the experimental data, new correlations for the Nusselt numbers were obtained considering the scaling effects for the multi-port tubes.
The flow boiling heat transfer of carbon dioxide with PAG-type lubricating oil entrained from 0% to 5% in horizontal smooth tubes was examined. Experiments were conducted using test tubes with inner ...diameter of 2–6 mm at mass fluxes of 360–1440 kg m−2 s−1 and heat fluxes of 4.5–36 kW m−2. The saturation temperature was 15 °C.
At low oil concentrations of 0.5–1%, the heat transfer coefficient decreased to less than half that under oil-free conditions. The heat transfer coefficient did not decrease further with increasing oil concentration up to 5%. The heat flux positively influenced the heat transfer coefficient in low vapor quality regions, not the high vapor quality regions. The presence of oil caused the mass flux to significantly influence the heat transfer coefficient at a low heat flux till dryout, while no significant influence of the mass flux at a high heat flux was observed. The dryout quality decreased at a large mass flux. The measured pressure drops increased monotonously because of the lubricating oil.
► The heat transfer coefficient decreases sharply at a critical oil concentration. ► Critical oil concentration is 0.5% for a 2-mm tube and 1% for 4- and 6-mm tubes. ► Both the heat flux and mass flux have positive influence on heat transfer coefficient. ► The oil concentration/heat flux does not influence the measured dryout parameters. ► Decreasing the tube diameter significantly increases the heat transfer coefficient.
A water-cooled concentric gas cooler model was developed to examine the negative effects of the presence of polyalkylene glycol (PAG)–type lubricating oil on convective heat transfer. The model was ...used to analyze the gas cooler performance in detail at different oil concentrations, tube diameters, operation pressures, mass flow rates, and inlet temperatures on the water side. The results show that the entrained lubricating oil had a dominant negative effect on gas coolers with a diameter of less than 2 mm. For CO2 heat pump/refrigeration systems equipped with water-cooled micro- or mini-channel gas coolers, the lubricating oil retained in the heat exchanger should be minimized. The negative effects of the lubricating oil are dominant for a wide range of operation pressures. However, the deterioration in thermal performance becomes more apparent as the pressure approaches the critical pressure value. Proper determination of the coolant fluid mass flow rate increases the thermal effectiveness of the gas cooler for a wide range of water inlet temperatures, but the reduced heat transfer performance is more pronounced at higher mass flow rates.
•A water-cooled CO2 gas cooler model was developed and validated to consider the effects of lubricating oil.•The negative effects of lubricating oil are more significant for gas coolers with small diameters (Dh ≤ 2 mm).•Lubricating oil reduces the thermal performance more as the operation pressure approaches the critical pressure.•High thermal effectiveness can be achieved at a proper water flow rate, but lubricating oil clearly has a negative effect.
Apoptosis of lung structural cells contributes to the process of lung damage and remodeling in chronic obstructive pulmonary disease (COPD). Our previous studies demonstrated that exogenous hydrogen ...sulfide (H
S) can reduce the lung tissue pathology score, anti-inflammation and anti-oxidation effects in COPD, but the effect of H
S in regulating cigarette smoke (CS) induced bronchial epithelial cell apoptosis and the underlying mechanisms are not clear.
To investigate the effect of H
S on CS induced endoplasmic reticulum stress (ERS) and bronchial epithelial cell apoptosis.
Male Sprague-Dawley rats randomly divided into four groups for treatment: control, CS, NaHS + CS, and propargylglycine (PPG) + CS. The rats in the CS group were exposed to CS generated from 20 commercial unfiltered cigarettes for 4 h/day, 7 days/week for 4 months. Since the beginning of the third month, freshly prepared NaHS (14 μmol/kg) and PPG (37.5 mg/kg) were intraperitoneally administered 30 min before CS-exposure in the NaHS and PPG groups. 16HBE cells were pretreated with Taurine (10 mM), 5 mmol/L 4-phenylbutyric acid (4-PBA) or NaHS (100, 200, and 400 μM) for 30 min, and then cells were exposed to 40 μmol/L nicotine for 72 h. ERS markers (GRP94, GRP78) and ERS-mediated apoptosis markers 4-C/EBP homologous protein (CHOP), caspase-3 and caspase-12 were assessed in rat lung tissues and human bronchial epithelial cells. The apoptotic bronchial epithelial cells were detected by Hoechst staining
and TUNEL staining
.
In CS exposed rats, peritoneal injection of NaHS significantly inhibited CS induced overexpression ERS-mediated apoptosis markers and upregulation of apoptotic rate in rat lungs, and inhibiting the endogenous H2S production by peritoneal injection of PPG exacerbated these effects. In the nicotine-exposed bronchial epithelial cells, appropriate concentration of NaHS and ERS inhibitors taurine and 4-PBA inhibited nicotine-induced upregulation of apoptotic rate and overexpression of ERS-mediated apoptosis markers.
H
S inhibited lung tissue damage by attenuating CS induced ERS in rat lung and exogenous H
S attenuated nicotine induced ERS-mediated apoptosis in bronchial epithelial cells.
Improving the efficiency of trans-critical CO2 heat pump systems becomes one of the investigative focuses of the development of refrigeration technologies. The use of expander can improve the ...efficiency of trans-critical CO2 cycles, and make it near to that of traditional refrigeration systems. On the basis of the previously developed single-cylinder rolling piston expander, a new two-rolling piston expander is designed and produced. The design process and its working principles are introduced, and a trans-critical CO2 water–water heat pump system is used to test its efficiency. Results of the tests show that under working conditions the rotating speed of the expander ranges from 850 to 1000 rpm, and its efficiency ranges from 28% to 33%. Analysis of the problems that appeared in the expander is made to further improve its efficiency.
•Design considerations of CO2 two-rolling piston expander.•Analysis of working processes in CO2 two-rolling piston expander.•Analysis of pressure changes in two cylinders.•Main parameters and prototype of CO2 two-rolling piston expander.•Experiments show that the expander operates steadily almost without noise, revealing the design of the prototype is feasible.
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