| 1. |
- Bitaraf Haghighi, Ehsan, et al.
(författare)
-
Combined effect of physical properties and convective heat transfer coefficient of nanofluids on their cooling efficiency
- 2015
-
Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933 .- 1879-0178. ; 68, s. 32-42
-
Tidskriftsartikel (refereegranskat)abstract
- The advantages of using Al2O3, TiO2, SiO2 and CeO2 nanofluids as coolants have been investigated by analysing the combined effect of nanoparticles on thermophysical properties and heat transfer coefficient. The thermal conductivity and viscosity of these nanofluids were measured at two leading European universities to ensure the accuracy of the results. The thermal conductivity of nanofluids agreed with the prediction of the Maxwell model within +/- 10% even at elevated temperature of 50 oC indicating that the Brownian motion of nanoparticles does not affect thermal conductivity of nanofluids. The viscosity of nanofluids is well correlated by modified Krieger-Dougherty model providing that the effect of nanoparticles aggregation is taken into account. It was found that at the same Reynolds number the advantage of using a nanofluid increases with increasing nanofluid viscosity which is counterintuitive. At the same pumping power nanofluids do not offer any advantage in terms of cooling efficiency over base fluids since the increase in viscosity outweighs the enhancement of thermal conductivity.
|
|
| 2. |
- Davoodabadi Farahani, Somayeh, et al.
(författare)
-
Effect of PCM and porous media/nanofluid on the thermal efficiency of microchannel heat sinks
- 2021
-
Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933 .- 1879-0178. ; 127
-
Tidskriftsartikel (refereegranskat)abstract
- The present study is a genuine attempt to improve the thermal behavior and hydraulic performance of a conventional microchannel heat sink (MCHS) using porous material, phase change material (PCM) and nanofluid. Three-dimensional microchannels with square, circular and flattened circular geometries are examined numerically by considering the thermal conduction in solid parts. Various factors are examined, including the effect of the number of channels, fluid velocity passing through channels, porous substrate thickness, PCM layer thickness, Darcy number, porosity coefficient, thermal conductivity ratio in the porous material, volume fraction and nanoparticle diameter. According to the findings, for a critical thickness of the porous substrate, the thermal performance is at its minimum. With increasing values of Darcy number, porosity coefficient, nanoparticle diameter and PCM thickness, the thermal performance of MCHS decreases. An MCHS with square geometry displays a better thermal performance compared to the other two geometries. Furthermore, the use of porous material, nanofluid and PCM improves the thermal behavior compared with a conventional microchannel. The thermal performance of MCHS with PCM is approximately 47% and 17% higher than that of a microchannel with the porous substrate and a microchannel incorporating a combination of the porous layer and nanofluid.
|
|
| 3. |
- Falciani, Gabriele, et al.
(författare)
-
Design and testing of a device for the characterization of gas transfer through soap films and measurement protocol based on color matching
- 2023
-
Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier. - 0735-1933 .- 1879-0178. ; 149
-
Tidskriftsartikel (refereegranskat)abstract
- Soap films are interesting for their potential utilization as soft, self-assembled, self-healing and possibly recyclable membranes. The intrinsic possibility of tuning their properties, such as e.g. surface and bulk elasticity or permeability, via tailored chemistry makes them flexible enough for a wide range of physical-chemical applications. Here we introduce a novel device that can serve as a research platform for the detailed experimental characterization of the soap film permeability to gases. The design and manufacturing of the novel platform are discussed, along with a sample characterization protocol based on a color-matching procedure for dioxygen diffusion through typical soap films. The experimental data is compared with the results obtained from a numerical model, specifically developed for the problem, and good agreement is found. In perspective, the proposed platform can serve for the precise characterization of gas transfer properties of soap films made from different surfactant mixtures and in the presence of different gases.
|
|
| 4. |
|
|
| 5. |
- Haghighi, Ehsan Bitaraf, et al.
(författare)
-
Accurate basis of comparison for convective heat transfer in nanofluids
- 2014
-
Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933 .- 1879-0178. ; 52, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal conductivity and viscosity of alumina (Al2O3), zirconia (ZrO2), and titania (TiO2) nanofluids (NFs) were measured at 20°C. All the NF systems were water based and contained 9wt.% solid particles. Additionally, the heat transfer coefficients for these NFs were measured in a straight tube of 1.5m length and 3.7mm inner diameter. Based on the results, it can be stated that classical correlations, such as Shah and Gnielinski, for laminar and turbulent flow respectively, can be employed to predict convective heat transfer coefficients in NFs, if the accurate thermophysical properties are used in the calculations. Convective heat transfer coefficients for NFs were also compared with those of the base fluids using two different bases for the comparison, with contradictory results: while compared at equal Reynolds number, the heat transfer coefficients increased by 8-51%, whereas compared at equal pumping power the heat transfer coefficients decreased by 17-63%. As NFs have higher viscosity than the base fluids, equal Reynolds number requires higher volumetric flow, hence higher pumping power for the NFs. It is therefore strongly suggested that heat transfer results should be compared at equal pumping power and not at equal Reynolds number.
|
|
| 6. |
- Hussain, Shafqat, et al.
(författare)
-
Mixed bioconvection flow of Ag-MgO/water in the presence of oxytactic bacteria and inclined periodic magnetic field
- 2022
-
Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier. - 0735-1933 .- 1879-0178. ; 134
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a numerical investigation on mixed bioconvection flow of silver(Ag)-magnesium oxide(MgO)-water hybrid nanofluid in a trapezoidal porous cavity under the effect of inclined periodic magnetic field is carried out. Brinkman-Forchheimer-extended Darcy model for the porous medium is adopted. Galerkin weighted residual finite element method is implemented to simulate the governing steady dimensionless equations. The resulting discrete nonlinear algebraic systems are treated using the adaptive Newton's method. The fluid flow, heat and mass transfer behavior are examined in variation of parameters as Hartmann number (Ha = 0-100), angle of periodic magnetic field (theta = 0 circle- 90 circle), period of periodic magnetic field (? = 0.1-1), bioconvection Rayleigh number (Rb = 10-100), Richardson number (Ri = 0.1-5), Lewis number (Le = 1-10) and Peclet number (Pe = 0.1-1). The rise in Hartmann number has a weakening effect on both transfer of heat and mass. When theta = 0 circle, convective heat and mass transfer is the smallest at ? = 1 where the most reduction in the average Nusselt and Sherwood numbers is 9.14% and 6.98% as ? is raised from 0.1 to 1, respectively, and occurs at Ha = 100. The significant decrement in the average Nusselt number is 42.57% at Ha = 75 and in the Sherwood number is 10.4% at Ha = 50 when theta is changed from 0 circle to 90 circle.
|
|
| 7. |
- Liu, Qingming, et al.
(författare)
-
Bubble interaction of annular flow in micro-channel boiling
- 2019
-
Ingår i: International Communications in Heat and Mass Transfer. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0735-1933 .- 1879-0178. ; 101, s. 76-81
-
Tidskriftsartikel (refereegranskat)abstract
- The development of heat transfer models of micro-channel boiling relies on understanding of all individual flow regimes as well as interactions and transitions between them. The presented paper performs a detailed study on the interactions between annular flow and its trailing bubbles in a cylindrical micro-channel with a diameter of 0.4 mm. Inlet mass flux is 400 kg/(m(2).s) and constant wall heat flux is 80 and 160 kW/m(2), respectively. The growth rate of the bubble and the flow regime transition are validated against published experimental data. Comparisons of the results between transition flow and single annular flow show that the transition processes enhance bubble evaporation. A new phenomenon is observed: extreme high local heat transfer rates are observed under certain conditions. A detailed investigation of the thin film region unveil that this enhancement is a consequence of the interface distortion caused by the presence of the trailing bubble. This bubble interface deformation depends primarily on a few factors including wall heat flux, surface tension, trailing bubble.
|
|
| 8. |
- Liu, Qingming, et al.
(författare)
-
On the dynamics and heat transfer of bubble train in micro-channel flow boiling
- 2017
-
Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier. - 0735-1933 .- 1879-0178. ; 87, s. 198-203
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics and heat transfer characteristics of flow boiling bubble train moving in a micro channel is studied numerically. The coupled level set and volume of fluid (CLSVOF) is utilized to track interface and a non-equilibrium phase change model is applied to calculate the interface temperature as well as heat flux jump. The working fluid is R134a and the wall material is aluminum. The fluid enters the channel with a constant mass flux (335 kg/m(2)*s), and the boundary wall is heated with constant heat flux (14 kW/m(2)). The growth of bubbles and the transition of flow regime are compared to an experimental visualization. Moreover, the bubble evaporation rate and wall heat transfer coefficient have been examined, respectively. Local heat transfer is significantly enhanced by evaporation occurring vicinity of interface of the bubbles. The local wall temperature is found to be dependent on the thickness of the liquid film between the bubble train and the wall.
|
|
| 9. |
- Liu, Qingming, et al.
(författare)
-
WITHDRAWN: Numerical study of the interactions and merge of multiple bubbles during convective boiling in micro channels
- 2017
-
Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier. - 0735-1933 .- 1879-0178. ; 80, s. 10-17
-
Tidskriftsartikel (refereegranskat)abstract
- Multi bubbles interaction and merger in a micro-channel flow boiling has been numerically studied. Effects of mass flux (56, 112, 200, and 335 kg/m2 ∗ s), wall heat flux (5, 10, and 15 kW/m2) and saturated temperature (300.15 and 303.15 K) are investigated. The coupled level set and volume of fluid (CLSVOF) method and non-equilibrium phase model are implemented to capture the two-phase interface, and the lateral merger process. It is found that the whole transition process can be divided to three sub-stages: sliding, merger, and post-merger. The evaporation rate is much higher in the first two stages due to the boundary layer effects in. Both the mass flux and heat flux affect bubble growth. Specifically, the bubble growth rate increase with the increase of heat flux, or the decrease of mass flux.
|
|
| 10. |
- Mehrabi, M., et al.
(författare)
-
Modeling of condensation heat transfer coefficients and flow regimes in flattened channels
- 2021
-
Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier. - 0735-1933 .- 1879-0178. ; 126
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, an adaptive neuro-fuzzy inference system (ANFIS) with fuzzy C-means clustering (FCM) structure identification is proposed to model condensation heat transfer and flow regimes in flattened smooth tubes with different aspect ratios. The FCM-ANFIS model was trained by using experimental data points for six effective chosen parameters of saturation temperature, heat flux, mass flux, aspect ratio and hydraulic diameter of the flattened tube, and vapor quality. Three flow regimes of annular flow, stratified, and intermittent flow were linked to the effective parameters based on the experimental data. Two models were proposed to predict the condensation heat transfer coefficient and the flow regime of R134a and R410a in flattened smooth tubes. Three statistical criteria were used to ascertain the accurateness of the models compared to the experimental results. It is found that while among benchmarked cases, the proposed model for the condensation heat transfer coefficient performs well, the best result with the lowest error (MAE = 0.029, RMSE = 0.036 and MRE = 2.83%) is when T-sat = 45 degrees C, q ‘’ = 10 kW/m(2), G = 100 kg/m(2). s, beta = 6 and D-h = 2.3 mm. On the other hand, in the worst-performing case when the errors are MAE = 0.239, RMSE = 0.239 and MRE = 13.36%, the predicted results are still in the uncertainty range of the experimental result when T-sat = 45 degrees C, q ‘’ = 5 kW/m(2), G = 200 kg/m(2). s, beta = 6 and D-h = 2.3 mm.
|
|
