Increase Of Total Pressure Drop Research Articles

Three-dimensional methodology to predict reversed flow in primary side of U-tube steam generator

Reversed flow in u-tube steam generator (SG) can result in the reduction of normal flow area and the increase of total pressure drop of SG primary side. The primary coolant flow rate will be lowered when reversed flow takes place, especially under the condition of natural circulation. In the past, the reversed flow phenomena have been observed, while most of the available publications were carried out based on one-dimensional system code or over-simplified single tube model, and very limited work has been done with 3D models. The overall 3D characteristics of flow distribution in the steam generator have not fully revealed. In this work, a fully 3D CFD model combining the porous media and open media were built to study the reversed flow in u-tube SG. The critical mass flow rate for reversed flow was obtained, so does the fraction and location of reversed flow with mass flow rate. The location of reversed flow shifts from short to long tubes at first and then shifts back to short tube with reducing the total mass flow rate.

Single-phase density wave oscillation -A new mechanism of flow instability in inverted U-type steam generator

Flow reversal under low mass flow conditions is harmful to the performance of inverted U-type steam generator (UTSG) and existing research attributes the phenomenon to be flow excursion instability. In this paper, a new mechanism of flow instability that could also induce flow reversal, namely single-phase density wave oscillation (DWO), was analyzed based on numerical methods. As a primary study, the analysis was done in parallel channels consisted of two identical inverted U-type tubes. It was found that for UTSG at low mass flow conditions, the compressibility of single-phase flow would be a key factor to trigger the positive feedback of mass flow-temperature-pressure drop in DWO. Single-phase DWO should result in premature of flow reversal compared to that caused by flow excursion (FE), and analysis showed that it could occur only if the primary side temperature difference and average temperature of UTSG were both large enough, and for large-scale UTSG DWO would disappear due to the increase of total pressure drop. Parameter effects on single-phase DWO in UTSG were also carefully studied and it was found that the trends could be well explained by the variation of system compressibility.

Heat Exchanger Handling MWCNT/Water Nanofluids

Heat exchangers are an essential part in an assortment of mechanical settings, for example, cooling frameworks, force plants, refineries, and in this way ceaseless endeavor are made to expand their heat transfer efficiencies. Optimize design of helical coil heat exchanger by using fins and the Compare pressure & temperature by conventional design. The final outcome of the study increase the total heat transfer rate inside the domain. And increase the pressure drop inside the domain. The water outlet temperature decrease up to 315k and cold outlet temperature increase up to 320 k. and total pressure drop increase with the temperature increases. Finally the CFD data were compared with previous data the total pressure drop increase up to 0.65 bar for case-2.the overall efficiency of the system incites up to 5% to 6%.

Optimizing Design and Analysis on The Helically Coiled Tube Heat Exchanger By Providing Fins

Heat exchangers are an essential part in an assortment of mechanical settings, for example, cooling frameworks, force plants, refineries, and in this way ceaseless endeavor are made to expand their heat transfer efficiencies. Optimize design of helical coil heat exchanger by using fins and the Compare pressure & temperature by conventional design. The final outcome of the study increase the total heat transfer rate inside the domain. And increase the pressure drop inside the domain. The water outlet temperature decrease up to 315k and cold outlet temperature increase up to 320 k. and total pressure drop increase with the temperature increases. Finally the CFD data were compared with previous data the total pressure drop increase up to 0.65 bar for case-2.the overall efficiency of the system incites up to 5% to 6%.

Prediction and Comparison of Shell Condensers With Straight or Helical Channels for Underwater Vehicles

The shell condenser is one of the key components of underwater vehicles. To study its thermal performance and to design a more efficient structure, a computational model is generated to simulate condensation inside straight and helical channels. The model combines empirical correlations and a MATLAB-based iterative algorithm. The vapor quality is used as a sign of the degree of condensation. Three calculation models are compared, and the optimal model is verified by a comparison of simulated results and available experimental data. Several cases are designed to reveal the effects of various inlet conditions and the diameter-over-radius (Dh/R) ratio. The results show that the inlet temperature and mass rate significantly affect the flow and heat transfer in the condensation process, the heat transfer capabilities of the helical channels are much better than that of the straight channel, and both the heat transfer coefficient and total pressure drop increase with the decrease of Dh/R. This study may provide a useful reference for performance prediction and structural design of shell condensers used for underwater vehicles and may provide a relatively universal prediction model for condensation in channels.

Experimental investigation and optimization of total energy consumption in humidification-dehumidification system

In this paper, the electricity consumption model and pressure drop model of humidification-dehumidification (HDH) system is developed. An experimental study is carried out to investigate the effects of operating parameters on the pressure drop of HDH system. The pressure drops in humidifier, dehumidifier and the total pressure drop increase with the increase of air and solution mass flow rate. The values of undetermined coefficient in the pressure drop model are obtained based on the experimental data. Meanwhile, the validation of the pressure drop model is varied though experiment. On this basis, the optimization model for minimum specific total energy consumption (STEC) is proposed. The optimization results show that the value of optimized STEC increase with the increase of evaporation rate requirements. The value of air mass flow rate (mg) should be as small as possible. The adjustment of solution mass flow rate (ml) and solution inlet temperature in humidifier (Tlhi) is a priority. The minimum value of optimized STEC is 822.676 kJ/kg.

Experimental investigation of the flow and heat transfer of magnetic nanofluid in a vertical tube in the presence of magnetic quadrupole field

In this paper, the effects of applying magnetic field on hydrodynamics and heat transfer of Fe3O4/water magnetic nanofluid flowing inside a vertical tube have been studied experimentally. The applied magnetic field was resulted from quadrupole magnets located at different axial positions along the tube length. The variations of the local heat transfer coefficient and also the pressure drop of the ferrofluid flow along the length of the tube by applying the magnetic quadrupole field have been investigated for different Reynolds numbers.The obtained experimental results show maximum enhancements of 23.4%, 37.9% and 48.9% in the local heat transfer coefficient for the magnetic nanofluid with 2 vol% Fe3O4 in the presence of the quadrupole magnets located at three different axial installation positions for the Reynolds number of 580 and the relative increase in total pressure drop by applying the magnetic field is about 1% for Re=580. The increase of the heat transfer coefficient is due to the radial magnetic force toward the heated wall generated by magnetic quadrupole field acting over the ferrofluid flowing inside the tube so that the velocity of the ferrofluid in the vicinity of the heated wall is increased. It is also observed that the enhancement of heat transfer coefficient by applying magnetic quadrupole is decreased with increasing the Reynolds number.

Analyze of laminar flow and boiling heat transfer characteristics of R134a in the horizontal micro-channel under low temperature condition

A numerical investigation has been carried out to examine the characteristics of laminar flow and boiling heat transfer of R134a in horizontal micro-channel with hydraulic diameter of 1mm. Three-dimensional equations considering conjugate heat transfer, viscous heating and temperature-dependent properties are solved for the fluid flow and heat transfer by ANSYS FLUENT. The influence of refrigerant mass velocity, heat flux density and gasification rate on boiling heat transfer was studied. Results show that under the low temperature condition, the total pressure drop increase with the heat flux along the tube, which caused the saturation temperature of refrigerant decrease, and evaporate strengthen, therefore, the total temperature increase at first and then slow down, the heat flux is mainly used in phase-change in this stage. It also can be found that the greater mass flow rate is more advantageous to evaporation.

Design and optimization of baffled fluid distributor for realizing target flow distribution in a tubular solar receiver

This paper presents an original study on the design and optimization of baffled fluid distributor for the realization of optimal fluid flow distribution in a tubular solar receiver. The basic idea is to install a perforated baffle in the inlet fluid distributor and to optimize the configuration of orifices on the baffle so as to approach the target flow distribution among downstream parallel tubes. A pressurized-air solar receiver comprising of 45 parallel tubes is used for study, with copper or Inconel 600 used as the filling material.Results show that the final fluid flow distributions realized by the geometrically optimized baffles are in good agreement with the target curves. The peak temperature of the receiver wall can be minimized accordingly with moderate increase in total pressure drop of the receiver system. It is shown that the insertion of a geometrically optimized baffle is generally a practical solution with various features: capable of realizing non-uniform target distribution; small pressure drop increase; compact geometry; flexible and adaptive; easy fabrication with a reasonable cost, etc.

Experiment of complex flow in full size horizontal wells with perforated completion

Abstract A full size perforated casing of 139.7 mm in external diameter was adopted to simulate the horizontal wellbore. The influences of perforation parameters and injection rate on the pressure drop in horizontal wells were investigated by experiments. The results show that: (1) With the increase of perforation density, perforation diameter and perforation phase, both the frictional pressure drop and the total pressure drop increase and the mixture pressure drop decreases. (2) When the mainstream Reynolds number at the perforated casing exit remains constant, with the increase of injection rate, the total pressure drop and mixing pressure drop increase. When the injection rate is less than the critical injection rate (0.05%–0.10% under the study conditions), the mixing pressure drop is less than 0. When the injection rate is greater than the critical injection rate, the mixing pressure drop is greater than 0. The acceleration pressure drop can be neglected when the injection rate is less than 0.10%, otherwise the acceleration pressure drop rises significantly with the increase of injection rate. (3) With the increase of injection rate, the proportion of frictional pressure drop to total pressure drop decreases while that of acceleration pressure drop to total pressure drop increases. When the injection rate is less than 1.00%, the proportion of mixing pressure drop to total pressure drop tends to rise with the increase of injection rate. When the injection rate is greater than 1.00%, the proportion of mixing pressure drop to total pressure drop almost remains unchanged.

Genetic Algorithm Optimization for Primary Surfaces Recuperator of Microturbine

In recent years, the genetic algorithm (GA) technique has gotten much attention in solving real-world problems. This technique has a strong ability for global searching and optimization based on various objectives for their optimal parameters. The technique may be applied to complicated heat exchangers and is particularly useful for new types. It is important to optimize the heat exchanger, for minimum volume/weight, to save fabrication cost or for improved effectiveness to save energy consumption, under the requirement of allowable pressure drop; simultaneously it is mandatory to optimize geometry parameters of heating plate from technical and economic standpoints. In this paper, GA is used to optimize the cross wavy primary surface (CWPS) and cross corrugated primary surface (CCPS) geometry characteristic of recuperator in a 100kW microturbine, in order to get more compactness and minimum volume and weight. Two kinds of fitness assignment methods are considered. Furthermore, GA parameters are set optimally to yield smoother and faster fitness convergence. The comparison shows the superiority of GA and confirms its potential to solve the objective problem. When the rectangular recuperator core size and corrugated geometries are evaluated, in the CWPS the weight of the recuperator decreases by 12% or more; the coefficient of compactness increases by up to 19%, with an increase of total pressure drop by 0.84% compared to the original design data; and the total pressure drop versus the operating pressure is controlled to be less than 3%. In the CCPS area compactness is increased to 70% of the initial data by decreasing pitch and relatively high height of the passage, the weight decreases by 17–36%, depending on the inclination angle (θ). Comparatively the CCPS shows superior performance for use in compact recuperators in the future. The GA technique chooses from a variety of geometry characters, optimizes them and picks out the one which provides the closest fit to the recuperator for microturbine.

Case Study on the Practical Use of Wettable Filters in the Removal of Submicron Particles

Chemical and metallurgical industries frequently generate submicron wet/dry sticky particles. Conventional wet scrubbers, usually Venturi scrubbers, are used in such industries with varying degrees of success. These scrubbers may be capable of removing larger particles, but become inefficient when particle size drops below the one-micron level. The main idea of this project was to utilize a wettable filtration system after the scrubber to achieve a high removal efficiency with a relatively low increase in total pressure drop. The use of wettable filtration allows an equilibrium liquid film to develop on each of the filter fibres (Agranovski et al. [1]). This liquid film than acts as the primary filtration zone, removing particles before they reach the filter's surface. The filtered contaminants are then removed from the fibre by a continuous influx of fresh water preventing blockages to the system. The new filtration systems can be incorporated into existing air pollution control systems by utilizing a space inside hollow liquid/air separators commonly used for the baffling of droplets after wet scrubbers. The new wettable filtration system installed at a strip galvanizing plant achieved removal efficiencies of approximately 98.6 % for the total particle loading with a minimal increase in pressure drop.

On the examination of recycle on heat (and mass) transfer in concentric tubes

AbstractThe effect of recycle on heat (and mass) transfer in concentric circular tubes has been investigated by finite difference methods. Theoretical results show that recycle can enhance the heat transfer rate for large Graetz numbers compared with that in an open tube (without an inner tube inserted and without recycle). Competition between a preheating effect and a residence‐time effect can be used to explain the heat transfer behavior. The heat transfer rate can be further augmented, with nearly no increase in total pressure drop, by employing flow pattern B instead of flow pattern A.