Heat transfer rates in hot shell, cold tube inclined baffled small shell, and tube heat exchanger using CFD and experimental approach

The work presented is an effort to realize the changes occurring for convective coefficients of heat transfer in STHX fitted with inclined baffles. Effort has been undertaken using Fluent, a commercially available CFD code ona CAD model of small STHX with inclined baffles with cold liquid flowing into the tubes and hot liquid flowing in the shell. Four sets of CFD analysis have been carried out. The hot liquid flow rate through shell compartments varied from 0.2 kg/sec to 0.8 kg/sec in steps of 0.2 kg/sec, while keeping the cold liquid flow condition in tube at 0.4 kg/sec constant. Heat transfer rates, compartment temperatures, and overall heat transfer coefficients, for cold liquid and hot liquid, were studied. The results given by the software using CFD approach were appreciable and comparatively in agreement with the results available by the experimental work, which was undertaken for the same set of inlet pressure conditions, liquid flow rates, and inlet temperatures of liquid for both hot and cold liquids. The experimental output results were also used to validate the results given by the CFD software. The results from the CFD analysis were further used to conclude the effect of baffle inclination on heat duty. The process thus followed also helped realize the effects of baffle inclination on convective heat transfer coefficient of the liquid flow through the shell in an inclined baffle shell and tube heat exchanger. The temperature plots for both cold and hot liquid were also generated for understanding the compartmental temperature distributions inclusive of the inlet and outlet compartments. The heat duty for a heat exchanger has been found to increase with the increase in baffle inclinations from zero degree to 20 degrees. Likewise, the convective heat transfer coefficients have also been found to increase with the increase in baffle inclinations.

The Circulatory Effects of Increased Hydrostatic Pressure Due to Immersion and Submersion

Increased hydrostatic pressure as experienced during immersion and submersion has effects on the circulation. The main effect is counteracting of gravity by buoyancy, which results in reduced extravasation of fluid. Immersion in a cold liquid leads to peripheral vasoconstriction, which centralizes the circulation. Additionally, a pressure difference usually exists between the lungs and the rest of the body, promoting pulmonary edema. However, hydrostatic pressure does not exert an external compressing force that counteracts extravasation, since the increased pressure is transmitted equally throughout all tissues immersed at the same level. Moreover, the vertical gradient of hydrostatic pressure down an immersed body part does not act as a resistance to blood flow. The occurrence of cardiovascular collapse when an immersed person is rescued from the water is not explained by removal of hydrostatic squeeze, but by sudden reinstitution of the effect of gravity in a cold and vasoplegic subject.

Two types of fog shapes above a cold evaporating liquid

When liquid nitrogen is poured into a mug, a mist forms above. This article explores the influence of air humidity on the cloud and the formation of these boundaries in a controlled environment. We have identified that both homogeneous and heterogeneous nucleations occur during their formation. We highlight two types of ice clouds that differ only in the level of air humidity. Indeed, there is a critical humidity level at which one goes from a banded cloud to another without lower limit, extending to the cold liquid. We argue that this critical humidity level is related to the nitrogen flux.

COMPRESSOR PUMP UNIT FOR CO2 LIQUIDATION AND SUPPLY IT FOR CARBAMIDE SYNTHESIS

Carbon dioxide, as well as ammonia, are widely used in large-scale chemistry for the production of urea. Currently, the most common technology for producing carmabide is according to which liquid NH3 is pumped into the synthesis column by a pump at a pressure of 15 MPa, and gaseous CO2 is supplied by a compressor with the same pressure as ammonia. Gaseous CO2 is compressed in a multi-stage compressor to a pressure of 15 MPa before it enters the urea synthesis unit, in which it reacts with ammonia. The specific energy consumption for compressing carbon dioxide in a compressor unit is 0.13 kWh/kg. Reducing energy for producing CO2 and also urea can be achieved when it is possible to supply carbon dioxide in liquid form under a pressure of 15 MPa to the urea synthesis column. The analysis showed that to solve this problem it is necessary to implement two processes: compression to 1.8–3.0 MPa, and then cooling and liquefaction of gaseous CO2 due to the cold of liquid ammonia. Liquefied CO2 can then be pumped to the urea column. In order to introduce carbamide into production, a new carbon dioxide compressor and pumping unit has been created. The installation scheme for compressing CO2 to a pressure of 15 MPa and its subsequent supply to the production of urea is given. A cold liquid ammonia stream with an initial temperature of –30 °C is used as a source of cold in the installation. The performance and power consumption of the compressor unit depend on the compression pressure of CO2. After the CO2 is compressed to 1.8 MPa, it is possible to cool 2.3 t/h of carbon dioxide with cold liquid ammonia and then direct it to the synthesis of urea using a pump under a pressure of 15 MPa. The specific energy consumption in the installation will be 0.1 kWh/kg. When CO2 is compressed up to 3 MPa, the plant capacity is 8.78 t/h, and the unit costs are 0,108 kWh/kg. Urea production in this case may increase from 1400 to 1680 t/day. Ref. 5, Fig. 3, Tab. 3.

P1379Fluoroscopy requirement reduction using an esophageal cooling protocol during left atrial ablation

Background Ablation of the left atrium with radiofrequency (RF) energy is associated with some risks to the esophagus. Cooling the esophagus has been used as one approach to reducing esophageal injury, most commonly with direct instillation of cold liquid via gastric tube placed in the esophagus. A new esophageal cooling device avoids the risks of free liquid instillation by using a closed-loop system, and avoids the need for frequent repositioning or stopping of the procedure often required when utilizing luminal esophageal temperature (LET) monitoring. This in turn may reduce fluoroscopy requirements for the procedure. Purpose Measure the difference in fluoroscopy time required during RF ablation using an esophageal cooling device protocol, and compare this to standard LET monitoring using single or multi-sensor temperature probes. Methods We obtained total fluoroscopy time per patient from records of RF ablation procedures performed by a two operators over a 12 month period. We compared fluoroscopy times between patients treated with an esophageal cooling device to control patients who were treated with LET monitoring using either single-sensor or multi-sensor temperature probes. Results Fluoroscopy times were available for a total of 179 patients treated with an esophageal cooling device, and 118 patients treated with LET monitoring over the 12 month study period. Mean fluoroscopy time for patients treated with esophageal cooling was 4.0 minutes (SD 4.9 minutes) with a median of 2.0 minutes (IQR 1.3 to 3.8 minutes). Mean fluoroscopy time for patients undergoing LET monitoring was 5.5 minutes (SD 5.7 minutes) with a median of 3.0 minutes (IQR 1.9 to 8.4 minutes). This difference represents a 27% reduction in mean fluoroscopy time, and a 33% reduction in median fluoroscopy time in the esophageal cooling group (p<.001, Mann-Whitney U test). Conclusions Fluoroscopy requirements were reduced by 27% with an esophageal cooling device when compared to standard LET monitoring.