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.

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.

Heat Transfer Characteristics of Gaseous Flows in Micro-Channels With Negative Heat Flux

2006 ◽  
Author(s):  
Chungpyo Hong ◽  
Yutaka Asako
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Constant Heat Flux ◽  
Channel Height ◽  
Gas Temperature ◽  
Heat Transfer Characteristics ◽  
Constant Heat ◽  
Transfer Characteristics ◽  
Micro Channels ◽  
Gaseous Flows

Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in micro-channels with CHF (constant heat flux) whose value is negative. The combined effect of viscous dissipation and compressibility is also investigated. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The computations are performed for channels with constant heat flux with range from −104 to −102 Wm−2. The channel height ranges from 10 to 100 μm and the aspect ratio of the channel height and length is 200. The stagnation pressure varies from 120 to 500 kPa. The outlet pressure is fixed at the atmosphere. The wall and bulk temperatures in micro-channels are compared with those of the case of positive heat flux and also compared with those of the incompressible flow in a conventional sized channel. In the case of negative heat flux, temperature profiles normalized by heat flux have different trends in the case of positive heat flux, when flow is fast. A gas temperature falls down due to the energy conversion. A correlation for the prediction of the wall temperature of the gaseous flow in the micro-channel is proposed.

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.

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 Gaseous Slip Flow in Concentric Micro Annular Tubes

2009 ◽  
Author(s):  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Koichi Suzuki
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Incompressible Flow ◽  
Slip Flow ◽  
Outer Wall ◽  
Constant Heat Flux ◽  
Heat Transfer Characteristics ◽  
Constant Heat ◽  
Transfer Characteristics ◽  
Adiabatic Case

A concentric micro annular passage is a basic and important micro-geometry of micro-fluidic-systems from simple heat exchanger to the most complicated nuclear reactors. Therefore, heat transfer characteristics of gaseous flows in concentric micro annular tubes with constant heat flux whose value was positive or negative were numerically investigated. The slip velocity, temperature jump and shear stress work were considered on the slip boundary. The numerical methodology was based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The computations were performed for two thermal cases. This is, the heat flux was constant at the inner wall and outer wall was adiabatic (Case 1) and the heat flux was constant at the outer wall and the inner wall was adiabatic (Case 2). Each constant heat flux of 104 Wm−2 for the positive value and −104 Wm−2 for the negative value was chosen. The outer tube radius ranged from 20 to 150 μm with the radius ratio 0.02, 0.05, 0.1, 0.25 and 0.5 and the ratio of length to hydraulic diameter was 100. The stagnation pressure was chosen in such a way that the exit Mach number ranges from 0.1 to 0.7. The outlet pressure was fixed at the atmospheric pressure. The heat transfer characteristics in concentric micro annular tubes were obtained. The wall and bulk temperatures with positive heat flux are compared with those of negative heat flux cases and also compared with those of the simultaneously developing incompressible flow. The results show that the compressible slip flow Nusselt number is different from that of incompressible flow. And, the temperatures normalized by heat flux have different trends whether heat flux value is positive or negative. A correlation for the prediction of the heat transfer characteristics of gas slip flow in concentric micro annular tubes is proposed.

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