Investigation on Heat Transfer Characteristics in the Test Section With Non-Uniform Heat Flux Distribution Under Natural Circulation

2017 ◽  
Author(s):  
Qiang Wang ◽  
Puzhen Gao ◽  
Xianbing Chen ◽  
Zhongyi Wang ◽  
Ying Huang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Section ◽  
Flux Distribution ◽  
Natural Circulation ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Natural circulation served as an indispensable part of nuclear, attracted much more attentions in recent years. It does not need a pump to provide power. The operating principle of natural circulation caused its complexity in analysis process. It was still a difficult issue to reveal the law of natural circulation accurately. Many experiments and calculations had to be conducted to study the basic physical regulation. This paper concentrated upon the heat transfer characteristics in the test section with two different types of heat flux distribution. The two types of heating flux distribution in the test section were linear and chopped cosine along axial direction. Based on a natural circulation experimental facility, physical models and mathematic models were established. RELAP5 code was used to calculate the thermal hydraulic state of natural circulation loop. The variation of heat transfer coefficient along flow direction was different. It was tightly related to heat flux. Some relevant experiments were conducted in many different conditions and steady sate experimental data were achieved to verified theoretical calculations. Experimental data, such as water temperature, wall temperature and flow rate were recorded when the system is stable. The heat transfer coefficients were calculated according to the experimental data. The factors that affected the heat transfer characteristics of natural circulation were analyzed by comparing the heat transfer coefficient under different conditions. The heat transfer coefficient was calculated according to the empirical correlations as well. After a series of analysis, the results indicated heat transfer coefficient had an obvious difference, which influenced ability of natural circulation. Comparing with experimental data, the evaluation of different empirical correlations was conducted in two test sections. Some empirical correlations turned out to be suitable for the estimation of heat transfer in experiment facility. The increase of heat flux could enhance heat transfer process in the two test section under low pressure. Average heat transfer coefficient increased with the decrease of inlet subcooling degree. The system pressure effected the heat transfer characteristics of natural circulation as well. The increase of mass flux would promote heat transfer while the level was different. RELAP5 had a great agreement with experimental data in single phase flow. Natural circulation ability was influenced by the position of average heat source center, which was slightly different in the research objects. The research would lend strong empirical support to the guideline of experiment and subsequence study in natural circulation.

Heat Transfer Characteristics of CuO-Base Oil Nanofluid Laminar Flow Inside Flattened Tubes Under Constant Heat Flux

2010 ◽  
Author(s):  
P. Razi ◽  
M. A. Akhavan-Behabadi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Constant Heat Flux ◽  
Electrical Heating ◽  
Heat Transfer Characteristics ◽  
Constant Heat ◽  
Base Oil ◽  
Transfer Characteristics

An experimental investigation has been carried out to study the heat transfer characteristics of CuO-Base oil nanofluid flow inside horizontal flattened tubes under constant heat flux. The nanofluid flowing inside the tube is heated by an electrical heating coil wrapped around it. The convective heat transfer coefficients of nanofluids are obtained for laminar fully developed flow inside round and flattened tubes. The effect of different parameters such as Reynolds number, flattened tube internal height, nanoparticles concentration and heat flux on heat transfer coefficient is studied. Observations show that the heat transfer performance is improved as the tube profile is flattened. The heat transfer coefficient is increased by using nanofluid instead of base fluid. Also, it can be concluded that decreasing the internal height of the flattened tubes and increasing the concentration of nanoparticles both contribute to the enhancement of heat transfer coefficient.

Heat Transfer Characteristics of Downward Supercritical Kerosene Flow in Minitubes

2016 ◽  
Author(s):  
Jinpin Lin ◽  
Jingzhi Zhang ◽  
Ekaterina Sokolova ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermophysical Properties ◽  
Flow Direction ◽  
Wall Heat Flux ◽  
Heat Transfer Characteristics ◽  
Operation Condition ◽  
Transfer Characteristics

The heat transfer characteristics of supercritical China RP-3 aviation kerosene flowing downward in a vertical circular tube are numerically investigated. A ten-species surrogate model is used to calculate the thermophysical properties of kerosene and the Re-Normalization Group (RNG) k-ε model with the enhanced wall treatment is adopted to simulate the turbulent flow. The effects of diameter, wall heat flux, and pressure on temperature and heat transfer coefficient are studied. The numerical results show three types of heat transfer deterioration exist along the flow direction. The first deterioration at the tube inlet region is caused by the development of the thermal boundary layer, which exist whatever the operation condition is. The second and third kind of deterioration take place when the inner wall temperature or the bulk fuel temperature approaches the pseudo-critical temperature under a pressure close to the critical value. The heat transfer coefficients increase with decreasing diameter and increasing pressure. The increase of inlet pressure can effectively eliminate the deteriorations because the thermophysical properties change less near the critical point at higher pressure. The decrease of wall heat flux will delay the onsets of the second and third kind of deterioration. The numerical heat transfer coefficient fit well with the empirical correlations.

Study on Flow and Heat Transfer Characteristics of Different States of Water Under Natural Circulation

2014 ◽  
Author(s):  
Zhongyun Ju ◽  
Tao Zhou ◽  
Jingjing Li ◽  
Zejun Xiao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flow ◽  
Supercritical Water ◽  
Natural Circulation ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

Software CFX is used to build a typical natural circulation loop to study flow and heat transfer characteristics of water vapor, the vapor-liquid two-phase and supercritical water under natural circulation. During the process of natural circulation, the variation of parameters, heat transfer coefficient and mass flow is compared. It is found that when formed a natural circulation, the steam has a lower mass flow and heat transfer coefficient, while the two parameters of two-phase and supercritical water are higher. Indicates that the heat transfer capability of steam is weak, the steam cannot transfer heat out opportunely when serious accidents take place. The two-phase water is of high heat transfer coefficient. Supercritical water is of strong exchange capacity, supercritical water under natural circulation is a promising flow pattern.

Flow and Heat Transfer Characteristics of a Natural Circulation Evaporative Cooling System for Electronic Components

2004 ◽  
Vol 126 (3) ◽  
pp. 317-324 ◽  
Author(s):  
Hiroshi Honda ◽  
ZhengGuo Zhang ◽  
Nobuo Takata
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Test Section ◽  
Cooling System ◽  
Natural Circulation ◽  
Electronic Components ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Test Loop

Experiments were conducted to study the flow and heat transfer characteristics of a natural circulation liquid cooling system for electronic components. The test loop consisted of a horizontal test section, a horizontal evaporator, a vertical tube, a horizontal condenser, a rubber bag attached at the exit of the condenser, a downcomer, a mass flow meter, and a liquid subcooler. The loop height H was set at either 250 or 450 mm. FC-72 was filled in the test loop up to some level of loop height and the upper part was filled with air. During the operation of the cooling system, the rubber bag expanded and stored the mixture of generated vapor and air. Thus the inner pressure was maintained at atmospheric pressure. In the test section, a silicon chip with dimensions of 10×10×0.5 mm3 was attached at the bottom surface of a horizontal duct with dimensions of 10×14 mm2. A smooth chip and four chips with square micro-pin-fins with 150 to 300 μm in fin height were tested. The duct height s was set at 10 mm for most of the experiments. The cases of s=1 and 25 mm were also tested for one of the micro-pin-finned chips. For each H, the average flow rate of FC-72 was correlated well as a function of the static pressure difference between the two vertical tubes. All chips showed the boiling curve similar to that for pool boiling except that the critical heat flux was lower for the natural circulation loop. For all chips tested, the maximum allowable heat flux qmax increased monotonically with increasing liquid subcooling ΔTsub. Comparison of the results for s=1, 10 and 25 mm revealed that the highest qmax was obtained with s=10 mm. The values of qmax for s=1 and 25 mm were 36–46% and 87–90% of that for s=10 mm, respectively. The maximum value of qmax=56 W/cm2 was obtained by one of the micro-pin-finned chips at s=10 mm and ΔTsub=35 K.

Condensation Heat Transfer Characteristics of R134A on Smooth or Finned Horizontal Tube

2005 ◽  
Author(s):  
M. Fatouh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Condensation Heat Transfer ◽  
Heat Transfer Characteristics ◽  
Finned Tubes ◽  
Overall Heat Transfer Coefficient ◽  
Transfer Characteristics

The present work aimed at determining the condensation heat transfer characteristics of R134a on single horizontal smooth and finned tubes under different parameters. These are saturated temperature (36°C and 43°C), inlet coolant temperature (25°C and 30°C) and coolant mass flow rate (100: 800 kg/h) for smooth and finned tubes. In the case of finned tubes, the pitch to height ratio varies from 0.5 to 3.08. Experimental condensation heat transfer characteristics for R134a and R12 on a smooth tube are compared. Experimental results confirmed that the heat flux and the overall heat transfer coefficient for R134a increase when coolant mass flow rate, saturation temperature and fin height increase or as both coolant inlet temperature and fin height decrease. The influence of fin pitch, on condensation heat flux and overall heat transfer, is lower than that of fin height. However, the heat flux and the overall heat transfer coefficient for R134a are correlated with the investigated parameters. Finally, the comparison between R12 and R134a revealed that the condensation heat transfer characteristics for R134a are better than those of R12.

scholarly journals Numerical Investigation on the Influence of Surface Flow Direction on the Heat Transfer Characteristics in a Granite Single Fracture

2021 ◽  
Vol 11 (2) ◽  
pp. 751
Author(s):  
Xuefeng Gao ◽  
Yanjun Zhang ◽  
Zhongjun Hu ◽  
Yibin Huang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Flow Direction ◽  
Heat Extraction ◽  
Geothermal System ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Heat Transfer Capacity

As fluid passes through the fracture of an enhanced geothermal system, the flow direction exhibits distinct angular relationships with the geometric profile of the rough fracture. This will inevitably affect the heat transfer characteristics in the fracture. Therefore, we established a hydro-thermal coupling model to study the influence of the fluid flow direction on the heat transfer characteristics of granite single fractures and the accuracy of the numerical model was verified by experiments. Results demonstrate a strong correlation between the distribution of the local heat transfer coefficient and the fracture morphology. A change in the flow direction is likely to alter the transfer coefficient value and does not affect the distribution characteristics along the flow path. Increasing injection flow rate has an enhanced effect. Although the heat transfer capacity in the fractured increases with the flow rate, a sharp decline in the heat extraction rate and the total heat transfer coefficient is also observed. Furthermore, the model with the smooth fracture surface in the flow direction exhibits a higher heat transfer capacity compared to that of the fracture model with varying roughness. This is attributed to the presence of fluid deflection and dominant channels.

A Fundamental View of the Flow Boiling Heat Transfer Characteristics of Nano-Refrigerants

2012 ◽  
Author(s):  
Lorenzo Cremaschi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Phase ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow Boiling Heat Transfer

Driven by higher energy efficiency targets and industrial needs of process intensification and miniaturization, nanofluids have been proposed in energy conversion, power generation, chemical, electronic cooling, biological, and environmental systems. In space conditioning and in cooling systems for high power density electronics, vapor compression cycles provide cooling. The working fluid is a refrigerant and oil mixture. A small amount of lubricating oil is needed to lubricate and to seal the sliding parts of the compressors. In heat exchangers the oil in excess penalizes the heat transfer and increases the flow losses: both effects are highly undesired but yet unavoidable. This paper studies the heat transfer characteristics of nanorefrigerants, a new class of nanofluids defined as refrigerant and lubricant mixtures in which nano-size particles are dispersed in the high-viscosity liquid phase. The heat transfer coefficient is strongly governed by the viscous film excess layer that resides at the wall surface. In the state-of-the-art knowledge, while nanoparticles in the refrigerant and lubricant mixtures were recently experimentally studied and yielded convective in-tube flow boiling heat transfer enhancements by as much as 101%, the interactions of nanoparticles with the mixture still pose several open questions. The model developed in this work suggested that the nanoparticles in this excess layer generate a micro-convective mass flux transverse to the flow direction that augments the thermal energy transport within the oil film in addition to the macroscopic heat conduction and fluid convection effects. The nanoparticles motion in the shearing-induced and non-uniform shear rate field is added to the motion of the nanoparticles due to their own Brownian diffusion. The augmentation of the liquid phase thermal conductivity was predicted by the developed model but alone it did not fully explain the intensification on the two-phase flow boiling heat transfer coefficient reported in previous work in the literature. Thus, additional nano- and micro-scale heat transfer intensification mechanisms were proposed.

Experimental Convective Heat Transfer With Nanofluids

2008 ◽  
Author(s):  
S. Kabelac ◽  
K. B. Anoop
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Turbulent Regime ◽  
Heat Transfer Characteristics ◽  
Forced Convective Heat Transfer ◽  
Transfer Characteristics

Nanofluids are colloidal suspensions with nano-sized particles (<100nm) dispersed in a base fluid. From literature it is seen that these fluids exhibit better heat transfer characteristics. In our present work, thermal conductivity and the forced convective heat transfer coefficient of an alumina-water nanofluid is investigated. Thermal conductivity is measured by a steady state method using a Guarded Hot Plate apparatus customized for liquids. Forced convective heat transfer characteristics are evaluated with help of a test loop under constant heat flux condition. Controlled experiments under turbulent flow regime are carried out using two particle concentrations (0.5vol% and 1vol %). Experimental results show that, thermal conductivity of nanofluids increases with concentration, but the heat transfer coefficient in the turbulent regime does not exhibit any remarkable increase above measurement uncertainty.

Numerical Investigation of Heat and Mass Flux Effects on Heat Transfer Characteristics of Supercritical Water in an Upward Flow Vertical Tube

2014 ◽  
Vol 592-594 ◽  
pp. 1667-1671
Author(s):  
T. Vinoth ◽  
K. Karuppasamy ◽  
D. Santhosh Kumar ◽  
R. Dhanuskodi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Supercritical Water ◽  
Mass Flux ◽  
Vertical Tube ◽  
Upward Flow ◽  
Heat Transfer Characteristics ◽  
Ansys Fluent ◽  
Transfer Characteristics

In the present work, the heat transfer characteristics of supercritical pressure water are numerically investigated in an upward flow vertical smooth tube. The numerical simulations are carried out by using Ansys-Fluent solver. The objective of the present work is to investigate the effect of heat flux and mass flux on heat transfer characteristics in supercritical water. In order to perform numerical simulation, experimental data of Mokryet al.[2] is considered. Various simulations were carried out for the inlet parameters of temperature 350°C, pressure 240bar; heat flux values ranging from 190 to 884kW/m2and mass flux values ranging from 498 to 1499kg/m2s. Based on the available parameters of heat flux and mass flux, they are segregated as groups with heat flux to mass flux ratios of 0.39 and 0.67. According to computational data, the heat transfer enhancement and heat transfer deterioration phenomenon of supercritical water were analyzed and based on the comparison with experimental data; their occurrence and mechanism were addressed.

An Empirical Study on Heat Transfer Characteristics of CuO/Base Oil Nanofluid Flow in a Tube With Coiled Wire Inserts

2010 ◽  
Author(s):  
M. A. Akhavan-Behabadi ◽  
M. Saeedinia ◽  
S. M. Hashemi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Constant Heat Flux ◽  
Wire Diameter ◽  
Heat Transfer Characteristics ◽  
Nanofluid Flow ◽  
Base Oil ◽  
The Heat Transfer Coefficient

In the present study, an experimental investigation has been carried out to study the heat transfer characteristics of CuO/Base oil nanofluid flow inside horizontal oiled wire inserted tubes (roughed tubes) under constant heat flux. The nanofluids with CuO nanoparticles weight fraction ranging from 0 to 2% are prepared. The oiled wires with different wire wire diameteres and different oil pitches are used as inserts inside a horizontal plain copper tube. The nanofluid flowing inside the tube is heated by electrical heating coil wrapped around it. The convective heat transfer characteristis of the prepared nanofluids are measured during laminar fully developed flow inside horizontal plain and roughed tubes under constant heat flux. The effect of different parameters such as mass velocity, wire wire diameter, oil pith, nanofluid particles concentration and heat flux on heat transfer coefficient is studied. The heat transfer coefficient is increased when a roughed tube is used instead of a plain tube. Moreover, at the same flow conditions, by increasing of wire wire diameter and decreasing of oil pitch, the heat transfer performance is improved. Observations also show that by using nanofluid instead of base fluid, the heat transfer coefficient increases and this increase grows at higher nanoparticles concentrations. As a result, it an be concluded that increasing of wire wire diameter, decreasing of oil pitch and increasing the concentration of nanoparticle, contribute to the enhancement of heat transfer coefficient.

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