Thermal analysis of a plastic helical coil heat exchanger for a domestic water storage tank

In the present study, the heat transfer coefficients of helically coiled corrugated plastic tube heat exchanger inside of the solar boiler vessel were investigated experimentally. The metal coil of the conventional solar boiler for domestic usage was replaced by a plastic tube and the results were compared with the numerical simulation and the technical documentation of the initial solar boiler. All the required parameters like inlet and outlet temperatures of tubeside and stratified temperatures, flow rate of fluids, etc. were measured using appropriate instruments. The test runs were performed for different temperatures inside the tank ranging from 30-60°C and different flow rates from which the heat transfer coefficients were calculated

Determining heat losses in a reheat furnace : a case study

In a previous study of an actual reheat furnace with a capacity of 45 ton/h, it was found that a staggering 20% of the input energy was unaccounted for in the heat balance. It was hypothesized that this missing energy was lost to the environment as heat losses. In this work, the main losses are identified and quantified. First, the heat transfer through the wall of the furnace was determined. For this, an extensive measurement campaign was performed. Based on the measured wall temperatures and emissivity values, the heat transfer from the walls for the operating conditions at the time of the measurements was estimated. The heat rejected through the walls amounts to approximately one fifth of the total heat loss. Secondly, when the furnace door is opened, a relatively large flow rate of hot gas leaves the furnace, and a net heat loss occurs due to the radiative heat exchange between the furnace interior and the environment. As the aforementioned heat losses are very difficult to measure, a simplified theoretical model was made based on physical principles. The corresponding results indicate that the opening of the furnace accounts for a large part of the remaining heat loss

Do voltage-gated Kv1.1 and inward rectifier Kir2.1 potassium channels form heteromultimers?

AbstractPossible heteromultimer formation between Kv- and Kir-type K+ channels was investigated, in connection with the known functional diversity of K+ channels in vivo. Voltage-clamp experiments were performed on Xenopus oocytes, either injected with concatenated Kir2.1-Kv1.1 mRNA, or co-injected with Kv1.1 and Kir2.1 mRNA. K+ currents could be approximated by the algebraic sum of the 2 K+ current types alone. The tandem construct did not show functional expression, although it could be detected by Western blotting. We conclude that Kv1.1 and Kir2.1 α-subunit proteins fail to assemble and do not contribute functional diversity to K+ channels

Steady state modeling of a fire tube boiler

Manufacturers increasingly strive to customize fire tube boiler designs to specific needs. A comprehensive thermal design model is therefore necessary. In this article a steady state thermal model based on the plug flow furnace model and the ε- NTU method is presented. The model includes the turn boxes which other authors neglect. The steady state model furthermore allows optimizing the boiler designs. It is used to analyze the gas temperature along the flow length. Secondly, the article compares a plug flow furnace model, the ε- NTU method with and without radiation. The ε- NTU with radiation allows decreasing the number of control volumes while retaining accuracy. Additionally the effect of the turn boxes is investigated.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers

Endovascular Repair of Inflammatory Abdominal Aortic Aneurysms with Special Reference to Concomitant Ureteric Obstruction

AbstractObjectives: to study the technical feasibility and results of endovascular treatment of inflammatory abdominal aortic aneurysms (AAA).Design: prospective study.Material and methods: seven patients underwent endovascular repair of an inflammatory AAA. Five patients (8 ureters) were treated with ureteric stents CT scans were obtained one year.Results: the early technical success rate was 100%. Four ureters remained entrapped at one year. Partial regression of periaortic fibrosis was documented in three patients, while four patients showed no regression.Conclusion: endovascular reconstruction of inflammatory abdominal aneurysms is technically feasible. Further study is warranted with regard to the evolution of the periaortic fibrosis and the possible benefits for patients with concomitant hydronephrosis

Dynamic and steady state performance model of fire tube boilers with different turn boxes

The market for fire tube boilers is increasingly demanding custom designs from the manufacturers. For these new designs, a comprehensive thermal model is needed. In this article, both a steady state and dynamic thermal model is developed based on the plug flow furnace model with general experimental correlations. The steady state model allows optimizing (i.e. safely downsizing) boiler designs. This model has been verified with measurement reports. The dynamic model is used to estimate the peak load capability of a boiler. In the presented case, the fire tube boiler can produce up to 2.5 times the nominal steam flow rate for a period of 10 min. Special attention has been paid to the turn boxes and their specific placement, which other models in literature neglect. The efficiency penalty of a non-submerged turn box can reach up to 12% but can be reduced significantly by insulation. Turn boxes also affect peak load capability. If the total length of the boiler is constant, submerging the turn box has a positive effect on the peak load capability. This effect is mostly attributed to the increased water volume. Finally, the article includes a comparison between the plug flow furnace model the ε-NTU method and the ε-NTU method with inclusion of radiation to model the tube passes. The ε-NTU method with inclusion of radiation allows to significantly reduce the necessary number of control volumes without reduction in the model accuracy

Plastic helical coil heat exchanger as an alternative for a domestic water storage tank

A reduction in weight and cost of a domestic hot water storage vessels is an interesting case for the industry, that can be reached by an alternative material of the helical coil heat exchanger inside them. The goal of the present study was to design a fully polymer solar boiler demonstrator and to explore its thermal performance in the low pressure and low temperature conditions. The metal coil of the conventional solar boiler for domestic usage was replaced by a plastic tube and the heat transfer behavior of helically coiled smooth plastic tube heat exchanger was investigated experimentally. The heat exchanger is placed in the middle of the tank in two parallel coils that fill almost whole height of the vessel in order to achieve maximal surface area. The water inside the tank was heated by circulating in closed loop with heater to achieve constant initial temperature across the whole volume of the vessel. When reached, the heating was stopped and a cold water of the tap temperature started to flow inside the polymeric tube. All the required parameters like inlet and outlet temperatures of tube-side and stratified temperatures in fifteen different points, flow rate of fluids and pressure drop were measured using appropriate instruments. The test runs were performed for different initial temperatures inside the tank ranging from 30-60°C from which the overall heat transfer coefficient and thermal resistances were calculated. The validity of obtained results was compared with the numerical simulation and the experimental results on the initial metallic tube.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers