Fluid Convection Models for Low-Temperature Grinding and Effect of Fluid Warming

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Lei Zhang ◽  
W. Brian Rowe
Keyword(s):  
Low Temperature ◽  
Convection Heat Transfer ◽  
Wheel Speed ◽  
Convection Heat Transfer Coefficient ◽  
Mineral Oils ◽  
Basic Assumptions ◽  
Fluid Convection ◽  
Heat Dispersion ◽  
Fluid Cooling ◽  
Experimental Values

Abstract The paper considers fluid convection in low-temperature grinding. Fluid cooling often predominates over all other forms of heat dispersion in the grinding zone particularly in low-temperature grinding. Experimental values of convection heat transfer coefficient (CHTC) up to and in excess of 200,000 W/m2K have been found by various researchers both for water-based emulsions and in one case for mineral oils employed in high wheel-speed grinding. Several convection models have been developed in recent years for the prediction of CHTCs in low-temperature grinding. This paper reviews advances in convection modeling and reconsiders the basic assumptions implied. A proposal is made for improved estimation for highly churned flow assuming a degree of fluid warming. Predicted coefficients are compared with measured values.

Estimation of the convection heat transfer coefficient of coolant within the grinding zone

2003 ◽  
Vol 217 (3) ◽  
pp. 397-407 ◽  
Author(s):  
T Jin ◽  
D J Stephenson ◽  
W B Rowe
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Film Thickness ◽  
Convection Heat Transfer ◽  
Wheel Speed ◽  
Convection Coefficient ◽  
Convection Heat ◽  
Convection Heat Transfer Coefficient ◽  
Creep Feed ◽  
Fluid Film Thickness

The convection heat transfer coefficient of the coolant within the grinding zone has been estimated using hydrodynamic and thermal modelling. The convection coefficient within the grinding zone can be very high, much higher than the values previously reported. The value is determined by the grinding wheel speed and the fluid film thickness within the contact zone. The film thickness in turn can be determined by wheel speed, porosity, grain size, coolant type and flowrate, nozzle size, etc. For deep grinding conditions [creep feed and high-efficiency deep grinding (HEDG)], the upper bound value of fluid film thickness can be easily achieved by a high coolant supply pressure and flowrate. Predicted values of the convection coefficient from hydrodynamic and thermal modelling show good agreement with experimental estimations obtained by matching measured and theoretical grinding temperatures for a wide range of grinding regimes when using a water-based grinding fluid. This includes HEDG and creep feed grinding for large contact lengths and conventional shallow cut grinding for short contact lengths.

Enhancement of RF Ablation by Combined Use of Ultra-Low Temperature Fluid Cooling and Magnetic Nanoparticles

2010 ◽  
Author(s):  
Zhong-Shan Deng ◽  
Jing Liu
Keyword(s):  
Magnetic Nanoparticles ◽  
Low Temperature ◽  
Bioheat Transfer ◽  
Rf Ablation ◽  
High Electrical Conductivity ◽  
Thermal Coagulation ◽  
Cooling Method ◽  
Tumor Tissues ◽  
Combined Use ◽  
Fluid Cooling

Magnetic nanoparticles with high electrical conductivity have been proved to be effective in enhancing the efficacy of RF ablation. However, the possible carbonization of tissues is an unfavorable factor in achieving greater dimensions of necrosis, because carbonized tissue is a poor conductor, increases impedance and limits propagation area of RF energy. To prevent potential carbonization of tissues surrounding to the heating part of RF electrodes during RF ablation, a new method using ultra-low temperature fluid was proposed for cooling RF electrodes and tissues in the vicinity of RF electrodes in this study. To test its feasibility, the corresponding bioheat transfer process during RF ablation simultaneously applying this cooling method and magnetic nanoparticles was studied through numerical simulations. The results indicate that the cooling method by ultra-low temperature fluid can prevent carbonization of tissues resulted by local high temperature, significantly enlarge the effective heating area and thus actualize highly efficient thermal coagulation to tumor tissues during RF ablation with adjuvant use of magnetic nanoparticles.

scholarly journals Experimental and Theoretical Investigation of the Natural Convection Heat Transfer Coefficient in Phase Change Material (PCM) Based Fin-and-Tube Heat Exchanger

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 716
Author(s):  
Saulius Pakalka ◽  
Kęstutis Valančius ◽  
Giedrė Streckienė
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Energy Storage ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Convection Heat Transfer Coefficient

Latent heat thermal energy storage systems allow storing large amounts of energy in relatively small volumes. Phase change materials (PCMs) are used as a latent heat storage medium. However, low thermal conductivity of most PCMs results in long melting (charging) and solidification (discharging) processes. This study focuses on the PCM melting process in a fin-and-tube type copper heat exchanger. The aim of this study is to define analytically natural convection heat transfer coefficient and compare the results with experimental data. The study shows how the local heat transfer coefficient changes in different areas of the heat exchanger and how it is affected by the choice of characteristic length and boundary conditions. It has been determined that applying the calculation method of the natural convection occurring in the channel leads to results that are closer to the experiment. Using this method, the average values of the heat transfer coefficient (have) during the entire charging process was obtained 68 W/m2K, compared to the experimental result have = 61 W/m2K. This is beneficial in the predesign stage of PCM-based thermal energy storage units.

Investigating the effect of nanoparticles diameter on turbulent flow and heat transfer properties of non-Newtonian carboxymethyl cellulose/CuO fluid in a microtube

2019 ◽  
Vol 29 (5) ◽  
pp. 1699-1723 ◽  
Author(s):  
Ali Rahimi Gheynani ◽  
Omid Ali Akbari ◽  
Majid Zarringhalam ◽  
Gholamreza Ahmadi Sheikh Shabani ◽  
Abdulwahab A. Alnaqi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Electronic Devices ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Vlsi Circuits ◽  
Convection Heat Transfer Coefficient ◽  
Content Type ◽  
Competing Interests

Purpose Although many studies have been conducted on the nanofluid flow in microtubes, this paper, for the first time, aims to investigate the effects of nanoparticle diameter and concentration on the velocity and temperature fields of turbulent non-Newtonian Carboxymethylcellulose (CMC)/copper oxide (CuO) nanofluid in a three-dimensional microtube. Modeling has been done using low- and high-Reynolds turbulent models. CMC/CuO was modeled using power law non-Newtonian model. The authors obtained interesting results, which can be helpful for engineers and researchers that work on cooling of electronic devices such as LED, VLSI circuits and MEMS, as well as similar devices. Design/methodology/approach Present numerical simulation was performed with finite volume method. For obtaining higher accuracy in the numerical solving procedure, second-order upwind discretization and SIMPLEC algorithm were used. For all Reynolds numbers and volume fractions, a maximum residual of 10−6 is considered for saving computer memory usage and the time for the numerical solving procedure. Findings In constant Reynolds number and by decreasing the diameter of nanoparticles, the convection heat transfer coefficient increases. In Reynolds numbers of 2,500, 4,500 and 6,000, using nanoparticles with the diameter of 25 nm compared with 50 nm causes 0.34 per cent enhancement of convection heat transfer coefficient and Nusselt number. Also, in Reynolds number of 2,500, by increasing the concentration of nanoparticles with the diameter of 25 nm from 0.5 to 1 per cent, the average Nusselt number increases by almost 0.1 per cent. Similarly, In Reynolds numbers of 4,500 and 6,000, the average Nusselt number increases by 1.8 per cent. Research limitations/implications The numerical simulation was carried out for three nanoparticle diameters of 25, 50 and 100 nm with three Reynolds numbers of 2,500, 4,500 and 6,000. Constant heat flux is on the channel, and the inlet fluid becomes heated and exists from it. Practical implications The authors obtained interesting results, which can be helpful for engineers and researchers that work on cooling of electronic devices such as LED, VLSI circuits and MEMS, as well as similar devices. Originality/value This manuscript is an original work, has not been published and is not under consideration for publication elsewhere. About the competing interests, the authors declare that they have no competing interests.

Experimental Study on Natural Convection Heat Transfer Outside Tube Bundle in Space Under Low Temperature Difference

2020 ◽  
Author(s):  
Junxiu Xu ◽  
Ming Ding ◽  
Changqi Yan ◽  
Guangming Fan
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Low Temperature ◽  
Tube Bundle ◽  
Convection Heat Transfer ◽  
Heat Removal ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Reactor Pool ◽  
Residual Heat

Abstract The Passive Residual Heat Removal System (PRHRS) is very important for the safety of the heating reactor after shutdown. PRHRS is a natural circulation system driven by density difference, therefore, the heat transfer performance of the Passive Residual Heat Removal Heat Exchanger (PRHR HX) has a great impact to the heat transfer efficiency of PRHRS. However, the most research object of PRHR HX is the C-shape heat exchanger at present, which located in In-containment Refueling Water Storage Tank (IRWST). This heat exchanger is mainly used for the PRHRS of nuclear power plants. In the swimming pool-type low-temperature heating reactor (SPLTHR), the PRHR HX is placed in the reactor pool, which the pressure and temperature of the reactor pool are relatively low, and the outside heat transfer mode of tube bundle is mainly natural convection heat transfer. In this study, a miniaturized single-phase pool water cooling system was built to investigate the natural convective heat transfer coefficient of the heat exchanger under the large space and low temperature conditions. The experimental data had been compared with several correlations. The results show that the predicted value of Yang correlation is the closest to the experimental data, which the maximum deviation is about 11%.

Convective Heat Transfer Enhancement With Nanofluids: The Effect of Temperature-Variable Thermal Conductivity

2010 ◽  
Author(s):  
Sezer O¨zerinc¸ ◽  
Almıla G. Yazıcıog˘lu ◽  
Sadık Kakac¸
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Thermal Dispersion ◽  
Convection Heat ◽  
Transfer Enhancement ◽  
Experimental Values

A nanofluid is defined as the suspension of nanoparticles in a base liquid. Studies in the last decade have shown that significant amount of thermal conductivity and heat transfer enhancement can be obtained by using nanofluids. In the first part of this study, classical forced convection heat transfer correlations developed for pure fluids are used to predict the experimental values of heat transfer enhancement of nanofluids. It is seen that the experimental values of heat transfer enhancement exceed the enhancement predictions of the classical correlations. On the other hand, a recent correlation based on the thermal dispersion phenomenon created by the random motion of nanoparticles predicts the experimental data well. In the second part of the study, in order to further examine the validity of the thermal dispersion approach, a numerical analysis of forced convection heat transfer of Al2O3/water nanofluid inside a circular tube in the laminar flow regime is performed by utilizing single phase assumption. A thermal dispersion model is applied to the problem and variation of thermal conductivity with temperature and variation of thermal dispersion with local axial velocity are taken into account. The agreement of the numerical results with experimental data might be considered as an indication of the validity of the approach.

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