Techno-economic analysis of single U-tube and double U-tube heat exchangers in Chongqing area

On the basis of practical projects in Chongqing,the thermal performance of heat exchangers (single U-tube type and double U-tube type) of the ground-source heat pump (GSHP) system in the hot summer was obtained and analyzed. The data obtained from test could match with the result deduced from theoretical calculation. From the test results,the cooling capacity of double U-tube is 1.6 times that of single U-tube. Taking cost per depth per watt Clq as the evaluation standard,Clq of single U-tube is 4.69 RMB$/W,and Clq of double U-tube is 3.14 RMB$/W. The double U-tube heat exchangers usage should be prioritized.

Numerical simulation on heat transfer performance of vertical U-tube with different borehole fill materials

Heat exchange performance of vertical U-tube heat exchanger was studied with two different borehole fill materials and CFD software. Borehole surface temperature and water temperature distribution were simulated on the condition of continuous operation for 8 h in winter with inlet water temperature being 10℃. The results show that there is no obvious difference on heat exchanger performance between the two different borehole fill materials.

Performance enhancement of filled-type solar collector with U-tube

In order to increase the efficiency of solar collector, a methodology is proposed based on the analysis of its influencing factors, such as thermal conductivity of filled layer, structure forms of filled layer and heat loss coefficient. The results of analysis show that the heat transfer between pipes in evacuated tube is one of the most important factors, which can lead to the decrease of the outlet temperature of working fluid. In order to eliminate the negative influence of the heat transfer between pipes, the hollow filled-type evacuated tube with U-tube(HUFET) was developed, and the heat transfer characteristics of HUFET were analyzed by theoretical and experimental studies. The results show that the thermal resistances decrease with the increase of the thermal conductivity of filled layer. When the thermal conductivity is over 10 W/(m·K), the change of thermal resistances is very little.Furthermore, the larger the thermal conductivity of filled layer, the less the rate of the energy transfer between the two pipes to the total energy transfer, which is between the absorber tube and the working fluid. There is a little difference between the efficiencies of HUFET and UFET, with the efficiency of HUFET 2.4% higher than that of UFET. Meanwhile, the validation of the model developed was confirmed by the experiment.

An Analytical Model for the Thermal Assessment of a Vertical Double U-Tube Ground-Coupled Heat Pump System in Steady-State Conditions

An analytical model was built to predict the thermal resistance of a vertical double U-tube ground-coupled heat pump that operates under steady-state conditions.It included a geometry obstruction factor for heat transfer throughout the backfill medium due to the presence of the second loop.The verification of the model was achieved by the implementation of five different borehole configurations and a comparison with other correlations in the available literature.The model considered a U-tube spacing range between(2)and(4)times the U-tube outside diameter producing a geometry configuration factor range of(0.29-0.6).The results of the model were utilized for the assessment of the DX ground heat exchanger coupled heat pump system.For similar geometrical configurations,the borehole thermal resistance experienced a decrease as the geometry factor increased.The single U-tube borehole thermal resistance was higher than that of the double U-tube heat exchanger by(10-27)%for the examined geometry configurations.The borehole thermal resistance at tube spacing of twice the tube diameter was higher than the predicted value at the triple diameter and fell in the range of(18-34)%.

Thermal performance of a single U-tube ground heat exchanger:A parametric study

In this research,the thermal performance of a single U-tube vertical ground heat exchanger is evaluated numerically as a function of the most influential flow parameters,namely,the soil porosity,volumetric heat capacity,and thermal conductivity of the backfill material,inlet volume flow rate,and inlet fluid temperature.The results are discussed in terms of the variations of the heat exchange rate,the effective thermal resistance,and the effectiveness of the ground heat exchanger.They show that the inlet volume flow rate,inlet fluid temperature,and backfill material thermal conductivity have significant effects on the thermal performance of the ground heat exchanger,such that by decreasing the inlet volume flow rate and increasing the backfill material thermal conductivity and inlet fluid temperature,the outlet fluid temperature decreases considerably.On the contrary,the soil porosity and backfill material volumetric heat capacity have negligible effects on the studied ground heat exchanger’s thermal performance.The lowest inlet fluid temperature reaches a the maximum effective thermal resistance of borehole and soil,and consequently the minimum heat transfer rate and effectiveness.Also,multilinear regression analyses are performed to determine the most feasible models able to predict the thermal properties of the single U-tube ground heat exchanger.

Performance of U-tube Solar Water Heaters Facing Different Directions

System performance of solar water heaters depends upon collector and storage tank designs, solar radiation intensity and ambient temperature, amongst others. Evacuated glass tube collectors with U-tubes inside are less prone to leakages than the all-glass or the heat pipe types. U-tube solar water heaters suspended on walls and balconies could help overcome present day roof space restriction and increasing apartment-style housing. As such, their performance would depend upon its orientation when mounted in a vertical position. This paper reports the results of outdoor tests conducted on natural convection U-tube solar water heaters oriented towards different directions. Long and short term test procedures were employed to allow us to compare their performances as if they were tested simultaneously side-by-side.

亨通光电成功研发A-Dry^(TM)全干式光缆及U-Tube^(TM)超细气吹微缆

近日,亨通光电成功研发A-Dry^（TM）全干式光缆及U-TubeTM超细气吹微缆,既可满足海外电信市场不同层次的网络建设需求,又可为国内电信市场提供多样化的产品选择,进一步推进公司＂从本土企业向国际化企业、从生产型企业向研发生产型企业、从产品供应商向系统集成服务商转型＂的战略转型,为实现＂打造行业领军企业,加快推进国际化进程＂的战略目标提供强力支撑,进一步提升亨通光电在行业中的技术研发领先地位。

Flow Regimes in Bubble Columns with and without Internals: A Review

Hydrodynamics characterization in terms offlow regime behavior is a crucial task to enhance the design of bubble column reactors and scaling up related methodologies.This review presents recent studies on the typicalflow regimes established in bubble columns.Some effort is also provided to introduce relevant definitions pertaining to thisfield,namely,that of“void fraction”and related(local,chordal,cross-sectional and volumetric)variants.Experimental studies involving different parameters that affect design and operating conditions are also discussed in detail.In the second part of the review,the attention is shifted to cases with internals of various types(perfo-rated plates,baffles,vibrating helical springs,mixers,and heat exchanger tubes)immersed in the bubble columns.It is shown that the presence of these elements has a limited influence on the global column hydrodynamics.However,they can make the homogeneousflow regime more stable in terms of transition gas velocity and transi-tion holdup value.The last section is used to highlight gaps which have not beenfilled yet and future directions of investigation.

A novel distributed solar refrigeration system based on evacuated U-tube solar collector and elastocaloric refrigerator

Refrigeration challenges in regions with electricity shortages significantly decrease the quality of life for residents. In response to the prevalent refrigeration challenges in power-deficient areas, a novel distributed solar refrigeration system, comprising an evacuated U-tube solar collector and elastocaloric refrigerator, is theoretically introduced. Theoretical formulations for the energy efficiency and cooling power of the solar refrigeration system are presented to facilitate predictive assessments of the performance properties. Under typical conditions, the energy efficiency and cooling power of the solar refrigeration system are,respectively, 4.84% and 200.15 W. Subsequently, an extensive parameter study is conducted to comprehensively uncover key performance influencers and identify avenues for improvement. In addition, local sensitivity analyses identify that the length ratio is the top influential parameter, while the heat transfer fluid flow rate is the least sensitivity. A pragmatic case study,conducted with the weather data of Ningbo City, China, serves to empirically predict the performance of the hybrid system within the constraints of practical circumstances.

Simultaneous Optimization of Synthesis and Scheduling of Cleaning in Flexible Heat Exchanger Networks

A novel methodology is presented for simultaneously optimizing synthesis and cleaning schedule of flexible heat exchanger network(HEN)by genetic/simulated annealing algorithms(GA/SA).Through taking into account the effect of fouling process on optimal network topology,a preliminary network structure possessing two-fold oversynthesis is obtained by means of pseudo-temperature enthalpy(T-H)diagram approach prior to simultaneous optimization.Thus,the computational complexity of this problem classified as NP(Non-deterministic Polynomial)-complete can be significantly reduced.The promising matches resulting from preliminary synthesis stage are further optimized in parallel with their heat exchange areas and cleaning schedule.In addition,a novel continu- ous time representation is introduced to subdivide the given time horizon into several variable-size intervals according to operating periods of heat exchangers,and then flexible HEN synthesis can be implemented in dynamic manner.A numerical example is provided to demonstrate that the presented strategy is feasible to decrease the total annual cost(TAC)and further improve network flexibility,but even more important,it may be applied to solve large-scale flexible HEN synthesis problems.

Experimental Studies of Heat Transfer Characteristics and Properties of the Cross-Flow Pipe Flow Melt Lead

The process of heat transfer in a HLMC cross-flow around heat-transfer tubes is not yet thoroughly studied. Therefore, it is of great interest to carry out experimental studies for determining the heat transfer characteristics in a lead coolant cross-flow around tubes. It is also interesting to explore the velocity and temperature fields in a HLMC flow. To achieve this goal, experts of the NNSTU performed the work aimed at the experimental determination of the temperature and velocity fields in high-temperature lead coolant cross-flows around a tube bundle. The experimental studies were carried out in a specially designed high-temperature liquid-metal facility. The experimental facility is a combination of two high-temperature liquid-metal setups, i.e., FT-2 with a lead coolant and FT-1 with a lead-bismuth coolant, united by an experimental site. The experimental site is a model of the steam generator of the BREST-300 reactor facility. The heat-transfer surface is an in-line tube bank of a diameter of 17 × 3.5 mm, which is made of 10H9NSMFB ferritic-martensitic steel. The temperature of the heat-transfer surface is measured with thermocouples of a diameter of 1 mm being installed in the walls of heat-transfer tubes. The velocity and temperature fields in a high-temperature HLMC flow are measured with special sensors installed in the flow cross section between the rows of heat-transfer tubes. The characteristics of heat transfer and velocity fields in a lead coolant flow were studied in different directions of the coolant flow: The vertical (“top-down” and “bottom-up”) and the horizontal ones. The studies were conducted under the following operating conditions: The temperature of lead was t = 450°C - 5000°C, the thermodynamic activity of oxygen was a = 10-5 - 100, and the lead flow through the experimental site was Q = 3 - 6 m3/h, which corresponds to coolant velocities of V = 0.4 - 0.8 m/s. Comprehensive experimental studies of the characteristics of heat transfer in a lead coolant cross-flow around tubes have been carried out for the first time and the dependences for a controlled and regulated content of the thermodynamically active oxygen impurity and sediments of impurities have been obtained. The effect of the oxygen impurity content in the coolant and characteristics of protective oxide coatings on the temperature and velocity fields in a lead coolant flow is revealed. This is because the presence of oxygen in the coolant and oxide coatings on the surface, which restrict the liquid-metal flow, leads to a change in the characteristics of the wall-adjacent region. The obtained experimental data on the distribution of the velocity and temperature fields in a HLMC flow permit studying the heat-transfer processes and, on this basis, creating program codes for engineering calculations of HLMC flows around heat-transfer surfaces.

Temperature distribution of the incompletely mixed fluid flowing in the tubes and the unmixed fluid crossing over the tubes

A new model is established to describe heat exchanging of the incompletely mixed fluid flowing in the tubes and the unmixed fluid crossing out of the tubes in the heat-exchangers especially in air cooler. In the model, a new method of analyzing volume is proposed to develop the temperature distribution equations of the two fluids --tw（x） and ta（X,,7＂）. With tw（x） and ta （x, ,7）, the curves of the temperature distribution of the two fluids can be obtained. Also tw（x） and ta（x,n） can be used to calculate parameters of structure of an air cooler and to improve performances of it.

Application of fuzzy neural network to the nuclear power plant in process fault diagnosis

The fuzzy logic and neural networks are combined in this paper, setting upthe fuzzy neural network (FNN ) ; meanwhile, the distinct differences and connections between thefuzzy logic and neural network are compared. Furthermore, the algorithm and structure of the FNN areintroduced. In order to diagnose the faults of nuclear power plant, the FNN is applied to thenuclear power planl, and the intelligence fault diagnostic system of the nuclear power plant isbuilt based on the FNN . The fault symptoms and the possibility of the inverted U-tube breakaccident of steam generator are discussed. In order to test the system' s validity, the invertedU-tube break accident of steam generator is used as an example and many simulation experiments areperformed. The test result shows that the FNN can identify the fault.

Simulation of Gas-Liquid Mixture Movement through a Pipeline on the Seabed, Taking into Account the Heat Exchange Process

In the paper, a dynamical model of gas-liquid mixture motion through a pipeline with regard to change of rheological properties that occur as a result of heat-exchange process, is constructed, and the solutions of the obtained connected differential equations are given. Analytic expression allowing to determine pressure change along the length of a pipeline, is obtained.