CONVECTIVE BOILING HEAT TRANSFER OF WATER IN A CAPILLARY TUBE UNDER A LOW FLOW RATE CONDITION

Equipment ◽  
2006 ◽  
Author(s):  
F. Kaminaga ◽  
S. Baduge ◽  
K. Matsumura
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Boiling Heat Transfer ◽  
Capillary Tube ◽  
Low Flow ◽  
Convective Boiling ◽  
Rate Condition ◽  
Low Flow Rate

scholarly journals Pore-Scale Simulations of Particles Migration and Deposition in Porous Media Using LBM-DEM Coupling Method

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 465
Author(s):  
Yanjie Zhou ◽  
Liping Chen ◽  
Yanfeng Gong ◽  
Shilin Wang
Keyword(s):  
Porous Media ◽  
Critical Velocity ◽  
Flow Rate ◽  
Shear Force ◽  
Particle Deposition ◽  
Moving Boundary ◽  
Low Flow ◽  
Rate Condition ◽  
Groundwater Source ◽  
Low Flow Rate

This paper studies the migration and deposition of suspended particles in porous media. This problem results from the fact that during the operation of a groundwater source heat pump, the recharging process will contribute to the impairment of soil permeability. A coupling lattice Boltzmann method, discrete element method and immersed moving boundary method were used to investigate the migration of particles in porous media. The DKT (Drifting, Kissing, Tumbling) phenomena were employed to validate our program. The coupled effects of concentration, flow rate and pH on the clogging mechanism of the porous media were analyzed. Results show that, due to the repulsive barrier between the particles and porous media, there is a critical velocity. At a low flow rate, the deposition ratio increases with the increase in velocity. Beyond the critical velocity, the deposition ratio decreases when the velocity increases due to higher shear force. Permeability impairment increases with the increase in concentration, especially in the low flow rate condition. Changes in pH mainly affect the repulsive barrier. For a low flow rate, the decrease in repulsive barrier greatly promotes the deposition of particles. Under the condition of favorable deposition, the increase in flow rate reduces the deposition phenomenon. Under the condition of unfavorable deposition, the lower flow rate condition has a lower deposition ratio. The process of particle deposition and the dynamic motion after deposition were observed such as particles gliding over the surface. Accumulated particles in the downstream form bridges and hinder fluid flow. At a high flow rate, strong shear force is more capable of destroying bridges and recovering permeability. Adsorbed particles glide on the surface of the grain and deposit in the downstream. This paper aims to help understanding of the micro-events of particle deposition and the clogging process.

scholarly journals Experimental investigation of convective boiling in mini-channels: Cooling application of the proton exchange membrane fuel cells

2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 223-232 ◽  
Author(s):  
Mounir Boudouh ◽  
Ameur Si ◽  
Hasna Louahlia-Gualous
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Boiling Heat Transfer ◽  
Heat Conduction Problem ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Proton Exchange ◽  
Low Flow ◽  
Convective Boiling ◽  
Maximum Heat

An experimental study of convective boiling heat transfer of water flowing in minichannels at low flow rate is carried out with pure de-ionised water and copper-water nanofluids. A low concentration of copper nanometer-sized particles was used to enhance the boiling heat transfer. The aim is to characterize the surface temperature as well as to estimate the local heat transfer coefficients by using the inverse heat conduction problem IHCP. The inlet water temperature is fixed at 60?C and mass fluxes operated in range of 212-573 kg/m?.s in minichannels of dimensions 500?2000 ?m?. The maximum heat flux investigated in the tests is limited to 7000 W/m?. The results show that the surface temperature and the local heat transfer coefficient are dependent on the axial location and the adding of copper nanoparticles can significantly improve the heat transfer.

Abstract 295: Importance of the Rate of Platelet Activation by Thrombin for Regulating the Size of Thrombi Formed Under Low Blood Flow Velocity Conditions

2016 ◽  
Vol 119 (suppl_1) ◽  
Author(s):  
Shinichi Goto ◽  
Kengo Ayabe ◽  
Youth Kawamura ◽  
Noriko Tamura ◽  
Shinya Goto
Keyword(s):  
Blood Flow ◽  
Flow Velocity ◽  
Platelet Activation ◽  
Flow Rate ◽  
Blood Flow Rate ◽  
Low Flow ◽  
Coagulation Cascade ◽  
Computer Simulation Model ◽  
Rate Condition ◽  
Low Flow Rate

Background: Platelets, coagulation cascade including thrombin and fibrin, and fibrinolysis by plasmin along with blood flow are known to play regulatory roles in thrombogenesis. However, quantitative and interactive contribution of these factors are not fully understood. Method: We developed a computer simulation model of thrombi at sites of vessel injury by implementing quantitative parameters of blood flow, platelet, coagulation cascade and fibrinolysis. In this model, we defined thrombi as the area where the amount of activated platelet become 80% or more of the global platelet count of 3.0х10 5 /mm 3 upon vessel damage We have measured the 3-dimensional size of thrombi as defined in various conditions with various parameters of flow velocity, rate of platelet activation by thrombin, rate of thrombin production on the surface of activated platelets, rate of fibrinolysis and rate of plasmin production. Results: Rate of platelet activation by thrombin had the largest influence on the size of thrombi under low flow rate condition of 0.5 (cm/sec) (Fig1 A). When blood flow rate increased to 2.0 (cm/sec), the absolute importance of this parameter decreased (Fig1 B). Conclusion: Our results show that the rate of platelet activation by thrombin, which are signaled with PAR-1 receptor in human, has a marked effect on the size of thrombi in low flow rate condition suggesting the benefit of blocking this receptor in low blood flow condition such as venous thrombosis.

Cooling Characteristics of Ultrafine Cryoprobe Utilizing Convective Boiling Heat Transfer in Microchannel

2010 ◽  
Author(s):  
Junnosuke Okajima ◽  
Shigenao Maruyama ◽  
Hiroki Takeda ◽  
Atsuki Komiya ◽  
Sangkwon Jeong
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Cooling System ◽  
Capillary Tube ◽  
Phase Flow ◽  
Two Phase ◽  
Convective Boiling

This paper describes a novel cooling system to be applied in cryosurgery. An ultrafine cryoprobe has been developed to treat small lesions which cannot be treated by conventional cryoprobes. The main problem of the ultrafine cryoprobe is the reduction of the heat transfer rate by the small flow rate due to the large pressure drop in a microchannel and the large ratio of the surface area to the volume. In order to overcome these problems, we utilized boiling heat transfer in a microchannel as the heat transfer mechanism in the ultrafine cryoprobe. The objectives of this paper are to develop an ultrafine cryoprobe and evaluate its cooling characteristics. The ultrafine cryoprobe has a co-axial double tube structure which consists of inner and outer stainless steel tubes. The outer and inner diameters of the outer tube are 0.55mm and 0.3mm, respectively. The outer and inner diameters of the inner tube are 0.15mm and 0.07mm, respectively. The inner tube serves as a capillary tube to change the refrigerant from liquid state to two-phase flow. Furthermore, two-phase flow passes through the annular passage between the inner and out tube. The hydraulic diameter of the annular passage is 0.15mm. Furthermore, HFC-23 (Boiling point is −82.1°C at 1atm) is used as the refrigerants. The temperature of the ultrafine cryoprobe was measured. The lowest temperatures were −45°C in the insulated condition and −35°C in the agar at 37°C (which simulates in vivo condition). Furthermore, the frozen region which is generated around the ultrafine cryoprobe was measured 5mm from the tip of cryoprobe at 120s, and resulted to be 3mm in diameter. Moreover, the change of the refrigerant state is calculated by using the energy conservation equation and the empirical correlations of two-phase pressure drop and boiling heat transfer. As a result, the refrigerant state in the ultrafine cryoprobe depends on the external heat flux. Finally, the required geometry of the ultrafine cryoprobe to make high cooling performance is evaluated.

Sign in / Sign up

Export Citation Format

Share Document