| 1. |
- Ali, Rashid, et al.
(författare)
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Experimental Investigation of Two-phase Pressure Drop in a Microchannel
- 2011
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 32:13/14, s. 1126-1138
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Tidskriftsartikel (refereegranskat)abstract
- Experimental results of two-phase pressure drop in a horizontal circular microchannel are reported in this paper. A test tube was made of fused silica having an internal diameter of 781 mu m with a total length of 261 mm and a heated length of 191 mm. The outer surface of the test tube was coated with an electrically conductive thin layer of ITO (indium tin oxide) for direct heating of the test section. Refrigerants R134a and R245fa were used as the working fluids, and mass flux during the experiments was varied between 100 and 650 kg/m(2)-s. Experiments were performed at two different system pressures corresponding to saturation temperatures of 25 degrees C and 30 degrees C for R134a and at three different system pressures corresponding to saturation temperatures of 30 degrees C, 35 degrees C, and 40 degrees C for R245fa. Two-phase frictional pressure drop characteristics with variation of mass flux, vapor fraction, saturation temperature, and heat flux were explored in detail. Finally, the prediction capability of some well-known correlations available in the literature, some developed for macrochannels and others especially developed for microchannels, was assessed.
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| 2. |
- Anwar, Zahid, et al.
(författare)
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Flow Boiling Heat Transfer and Dryout Characteristics of R600a in a Vertical Minichannel
- 2015
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 36:14-15, s. 1230-1240
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Tidskriftsartikel (refereegranskat)abstract
- Refrigerant-related environmental concerns forced legislative bodies to phase out some types of refrigerants, namely, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) and in the near future European legislation will be affecting hydrofluorocarbons (HFCs) as well. Natural refrigerants such as hydrocarbons can thus be expected to be more common as refrigerants in the future. Experimental findings on flow boiling heat transfer and dryout characteristics of isobutane (R600a) in a uniformly heated, vertical, stainless-steel test section (1.60mm inside diameter and 245mm heated length) are reported in this article. The experiments were conducted at two saturation pressures corresponding to the temperatures of 27 and 32 degrees C, with five mass fluxes in the range 50-350kg/m(2)-s and at outlet vapor qualities up to dryout conditions. Analysis showed that heat transfer was primarily controlled by the applied heat flux with insignificant effect of mass flux and vapor quality. The dryout heat flux increased with increasing mass flux; however, no significant effect of varying saturation temperature was observed. The experimental results (for heat transfer and dryout) were compared with different macro and microscale correlations from the literature.
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| 3. |
- Asadi, Masoud, et al.
(författare)
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Constructal Optimization of Louver Fin Channels Subjected to Heat Transfer Rate Maximization and Pressure Loss Minimization
- 2018
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 39:5, s. 436-448
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Tidskriftsartikel (refereegranskat)abstract
- To obtain better fluid mixing and higher heat transfer rate in the low Reynolds number regime, various types of fins have been employed for electronic cooling applications. However, previous works showed that there are no remarkable differences in the thermal performance of a straight-plate and a channel with louvered-fins when the Reynolds number is low or moderate. In this paper, the Constructal law is applied to optimize the geometry of a channel with louvered-fins, where the objective is to maximize the total heat transfer rate and minimize the pressure loss. The selected domain has three degrees of freedom; the louver angle ratio, the louver pitch ratio, and the inlet louver length to outlet louver length ratio. The results showed that the effect of louver on the louver pitch ratio and the inlet louver length to outlet louver length ratio. There is a minimum value for the louver pitch ratio and below this value the vortices upstream of the turnaround louver block the distance between louvers and so decreases the flow efficiency. A comparison between results and previous experimental studies indicated that the channel optimized by constructal law is considerably superior compared to the standard channel in low Reynolds number regime.
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| 4. |
- Azimian, AR, et al.
(författare)
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Generation of steam tables using artificial neural networks
- 2004
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 1521-0537 .- 0145-7632. ; 25:2, s. 41-51
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Tidskriftsartikel (refereegranskat)abstract
- The industrial formulations for the thermodynamic properties of water/steam, which are approximations of the scientific one, are intended to be used in applications where computational speed is of importance, such as in power plant modelling and control. The traditional methods for implementing these tables in software imply either the use of polynomial algorithms, which demand long iteration times, or look-up tables, which require a large memory capacity. On the other hand, there is a group of useful tools, called Artificial Neural Networks (ANNs), that have been successfully applied for pattern recognition and function approximation tasks in, for instance, the areas of medicine, engineering, and economics. This paper aims to show the potential of ANNs for generating the water/steam tables. ANNs enable the production of user-friendly software, which furthermore increases the computational speed while sustaining good accuracy. This new approach avoids the limitations of the traditional methods and can be advantageously implemented in heat and mass balance programs to speed up calculations. Promising results obtained with this technique are highlighted in the present paper, demonstrating the reliability of using ANNs in lieu of polynomials algorithms and look-up tables.
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| 5. |
- Belov, Ilja, et al.
(författare)
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Simulation and Experimental Methodology for Virtual Prototyping of Annealed Industrial Coils
- 2023
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Ingår i: Heat Transfer Engineering. - : Taylor & Francis. - 0145-7632 .- 1521-0537. ; 44:4, s. 353-367
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Tidskriftsartikel (refereegranskat)abstract
- The finite element three-dimensional transient model of the annealing process, including conductive and convective heat transfer in an aluminum (Al) coil was developed, implemented, and validated. It combines winding force dependent effective radial thermal conductivity model and the novel convective heat transfer modeling methodology. Experimental validation of the finite element model was performed for two industrial coils having different dimensions, strip thickness and crowning depth. The general agreement between the predicted and measured temperatures for most of the probes was better than 10% at the target material temperature. A series of measurements were configured and performed to supply both the input and validation data for the simulations. The effect of the additional wetted area on the convective heat transfer at the coil base was quantified. The guidelines on the virtual prototyping of the Al coil annealing process were provided, which can be of interest for the process designers.
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| 6. |
- Bobbili, Prabhakara Rao, et al.
(författare)
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Pressure Drop in Multi-Parallel Channels of Corrugated Plate Steam Condensers
- 2009
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 1521-0537 .- 0145-7632. ; 30:13, s. 1024-1032
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Konferensbidrag (refereegranskat)abstract
- An experimental investigation has been carried out to find the pressure difference of the process of steam condensation across the port to channel in plate heat exchangers. In the present study, low corrugation angle (30 degrees) plates have been used for different number of channels, namely, 10 and 80. The process steam entered at 1 bar with a small degree of superheat. Water has been used as the cold fluid. The pressure probes are inserted through the plate gasket into both the inlet and exit ports of the channel. The pressure drop of the process steam has been measured and recorded at the first, middle, and last channels at different flow and exit conditions for each plate package of the heat exchanger. Also, the overall pressure drop has been measured at different conditions at the outlet of the process steam, i.e., full and partial condensation. The pressure drop measurements have indicated that there is a considerable variation in pressure drop from the first channel to the last channel due to flow maldistribution. The experimental data has been analyzed to show how the flow maldistribution affects the pressure drop of a plate condenser.
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| 7. |
- Cao, Zhen, et al.
(författare)
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Pool Boiling of NOVEC-649 on Microparticle-Coated and Nanoparticle-Coated Surfaces
- 2021
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 42:19-20, s. 1732-1747
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Tidskriftsartikel (refereegranskat)abstract
- In this study, microparticle coatings and nanoparticle coatings were fabricated on copper surfaces by an electrochemical deposition method and an electrophoretic deposition method, respectively. Pool boiling of NOVEC-649 was experimentally studied on the coated surfaces, concerning heat transfer, bubble dynamics, and critical heat fluxes. Compared with a smooth surface, heat transfer coefficients and critical heat flux (CHF) were improved, achieving a maximum heat transfer enhancement of 460% on the nanoparticle-coated surface and a maximum CHF enhancement of 60% on the microparticle-coated surface. Based on high speed visualizations, bubble departure diameters were measured and compared with several correlations, and then the heat transfer was analyzed by a mechanistic model, considering natural convection, transient heat conduction and microlayer evaporation. The mechanistic model demonstrated a good ability to predict the present results. In addition, wickability, representing a liquid supplement ability, was measured, indicating that the wickability enhancement was probably responsible for the CHF improvement.
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| 8. |
- Choque Campero, Luis Antonio, et al.
(författare)
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A Case Study of the Development Experience of Using a Prototype Stirling Engine in A Novel Bioenergy Driven Co-Generation Plant in Bolivia
- 2023
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 45:3, s. 289-296
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Tidskriftsartikel (refereegranskat)abstract
- The necessity for green technology to generate power in rural regions is becoming more widely recognized. Stirling engines have attracted a lot of interest in recent years due to their relative ease of maintenance and simple design. Practical experience from the operation and maintenance of the Stirling engine Genoa-01 in Bolivia is the subject of this case study. The project uses a trial-and-error approach to maintain the engine in order to find relevant lessons that may be used in training of power plant personnel based in locations with limited technical resources. Analysis of the information gathered during the study identified the main challenges to overcome for small, decentralized power technologies as supply chain of spare parts, technical capacities, and promotion of the technology.
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| 9. |
- Etemad, Sassan, et al.
(författare)
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Hydraulic and Thermal Simulations of a Cross-Corrugated Plate Heat Exchanger Unitary Cell
- 2016
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 1521-0537 .- 0145-7632. ; 37:5, s. 475-486
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Tidskriftsartikel (refereegranskat)abstract
- Simulations have been carried out by means of computational fluid dynamics for turbulent convective heat transfer in a cross-corrugated plate pattern heat exchanger unitary cell at a Reynolds number of 4930. Chen's high-Reynolds-number k-E model, the Reynolds stress model (RSM), Suga's low-Reynolds-number k-E model, and the V2F model were used. The predicted hydraulic and thermal behaviors using these models have been compared and explained. The simulations showed that the interaction between the upper flow and lower flow in the cell creates a shear zone at their interface with a rotating motion and as a consequence the heat transfer is enhanced. This phenomenon was captured best by the V2F model, which predicted the highest Nusselt number and friction factor. Chen's k-E model provided results similar to the RSM. The fact that the RSM was instable and required more computational power makes it less interesting for further use in similar studies. It was also found rewarding to generate multiblock all-hexahedral grids to resolve the existing thermal and hydraulic phenomena in the domain.
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| 10. |
- Feng, Zhaozan, et al.
(författare)
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Effects of Surfactant on Flow Boiling Heat Transfer of Ethylene Glycol/Water Mixtures in a Minitube
- 2016
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 37:13-14, s. 1126-1135
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated effects of surfactant sodium dodecylbenzene sulfonate (SDBS) on flow boiling heat transfer of ethylene glycol/water mixtures in a vertical minitube. Experiments were performed using solutions containing 300 ppm by weight of surfactant and the results were compared with those of pure mixture. Local heat transfer coefficient was measured and found to be dependent on the mass quality. Although the surfactant intensifies the vaporization process, it doesn't necessarily enhance the heat transfer coefficient. Heat transfer coefficients were compared at two different mass fluxes, and the results might be explained based on the local flow pattern and the heat transfer mechanism. After a critical quality, higher quality tends to deteriorate heat transfer due to intermittent dryout, and therefore adding a surfactant to generate more vapor may be of negative effect on the flow boiling heat transfer in a minitube, which is contrary to the experience of enhancing nucleate pool boiling heat transfer with trace surfactants.
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