Machine and deep learning driven models for the design of heat exchangers with micro-finned tubes

The design of micro-finned tube heat exchangers is a complex task due to intricate geometry, heat transfer goals, material selection, and manufacturing challenges. Nowadays, mathematical models provide valuable insights, aid in optimization, and allow us to explore various design parameters efficiently. However, existing empirical models often fall short in facilitating an optimal design because of their limited accuracy, sensitivity to assumption, and context dependency. In this scenario, the use of Machine and Deep Learning (ML and DL) methods can enhance accuracy, manage nonlinearity, adjust to varying conditions, decrease dependence on assumptions, automatically extract pertinent features, and provide scalability. Indeed, ML and DL techniques can derive valuable insights from datasets, contributing to a comprehensive understanding. By means of multiple ML and DL methods, this paper addresses the challenge of estimating key parameters in micro-finned tube heat exchangers such as the heat transfer coefficient (HTC) and frictional pressure drop (FPD). The methods have been trained and tested using an experimental dataset consisting of over a thousand data points associated with flow condensation, involving various tube geometries. In this context, the Artificial Neural Network (ANN) demonstrates superior performance in accurately estimating parameters with MAEs in the range below 4.5% for both HTC and FPD. Finally, recognizing the importance of comprehending the internal mechanisms of the black-box ANN model, the paper explores its interpretability aspects.

Experimental investigation on boiling heat transfer and pressure drop of R245fa in a horizontal micro-fin tube

An experimental investigation on the boiling heat transfer and frictional pressure drop of R245fa in a 7 mm horizontal micro-fin tube was performed.The results show that in terms of flow boiling heat transfer characteristics,boiling heat transfer coefficient(HTC)increases with mass velocity of R245fa,while it decreases with the increment of saturation temperature and heat flux.With the increase of vapor quality,HTC has a maximum and the corresponding vapor quality is about 0.4,which varies with the operating conditions.When vapor quality is larger than the transition point,HTC can be promoted more remarkably at higher mass velocity or lower saturation temperature.Among the four selected correlations,KANDLIKAR correlation matches with 91.6%of experimental data within the deviation range of±25%,and the absolute mean deviation is 11.2%.Also,in terms of frictional pressure drop characteristics of flow boiling,the results of this study show that frictional pressure drop increases with mass velocity and heat flux of R245fa,while it decreases with the increment of saturation temperature.MULLER-STEINHAGEN-HECK correlation shows the best prediction accuracy for frictional pressure drop among the four widely used correlations.It covers 84.1%of experimental data within the deviation range of±20%,and the absolute mean deviation is 10.1%.

Characteristics and Formation Mechanism for Stainless Steel Fiber with Periodic Micro-fins

Metal fibers have been widely used in many industrial applications due to their unique advantages. In certain applications, such as catalyst supports or orthopedic implants, a rough surface or tiny outshoots on the surface of metal fibers to increase surface area are needed. However, it has not been concerned about the surface morphologies of metal fiber in the current research of metal fiber manufacturing. In this paper, a special multi-tooth tool composed of a row of triangular tiny teeth is designed. The entire cutting layer of multi-tooth tool bifurcates into several thin cutting layers due to tiny teeth involved in cutting. As a result, several stainless steel fibers with periodic micro-fins are produced simultaneously. Morphology of periodic micro-fins is found to be diverse and can be classified into three categories： unilateral plane, unilateral tapering and bilateral. There are two forming mechanisms for the micro-fins. One is that periodic burrs remained on the free side of cutting layer of a tiny tooth create micro-fins of stainless steel fiber produced by the next neighboring tiny tooth; the other is that the connections between two fibers stuck together come to be micro-fins if the two fibers are finally detached. Influence of cutting conditions on formation of micro-fins is investigated. Experimental results show that cutting depth has no significant effect on micro-fin formation, high cutting speed is conducive to micro-fin formation, and feed should be between 0.12 mm/r and 0.2 mm/r to reliably obtain stainless steel fiber with micro-fins. This research presents a new pattern of stainless steel fiber characterized by periodic micro-fins formed on the edge of fiber and its manufacturing method.

Convective Boiling of Near-Azeotropic Refrigerant R410A in the Horizontal Micro-fin Tube

Using near-azeotropic refrigerant R410A as the working fluid, the experimental studies on the horizontal micro-fin tubes were conducted. Several factors affecting heat transfer coefficients were analyzed, and the characteristics of flow boiling of the refrigerant in the horizontal micro-fin tubes were discussed. The local heat transfer coefficients increase with mass flux, heat flux and quality. And the heat transfer enhancement factor of those testing tubes is about 1.6 to 2.2.

Sustainability and Growth of Islamic Micro-Finance： A Case Study ofAnjuman Islahul Muslemeen Based in Bhopal India

Micro-finance is providing financial services to poor people, who traditionally lack access to banking and related services. In India, the population of Muslims is about 180 million and the majority of them live below poverty line. The regions where poor Muslims are in majority are marked as negative for providing loans by the banks. Study on interest-free （Islamic） micro-finance for implementation in a country like India can be very helpful in eradicating poverty and developing micro-enterprises together with sustainable development of poor and country as a whole. The primary aim of Islamic teachings （economics） is social justice to all irrespective of caste, creed, race, colour, and religion. Due to this reason, interest （riba） is prohibited not only in Islam but also in Christianity. This paper studies an Islamic micro-finance institution （Anjuman Islahul Muslemeen） situated in Bhopal （Madhya Pradesh）, India. The institution was registered in 1918 by a group of Muslims to help the poor. Today, about 98 years have passed by and all group members have changed but the organization is still growing with the aim of the well-being of poor people, not only Muslims but non-Muslims as well and is serving the humanity.

Enhancement of pentlandite surface magnetism and implications for its separation from serpentine via magnetic separation

The magnetism of pentlandite surface was enhanced through the selective precipitation of micro-fine magnetite fractions on pentlandite surfaces. This was achieved through adjustment of slurry pH and addition of surfactants. The results showed that at pH 8.8 with the addition of 100 g/t sodium hexametaphosphate, 4.5 L/t oleic acid, and 4.5 L/t kerosene, significant amount of fine magnetite particles adhered to the pentlandite surface, while trace amount of coating was found on serpentine surfaces. Thus, the magnetism of pentlandite was enhanced and pentlandite was well separated from serpentine by magnetic separation under the magnetic field intensity of 200 kA/m. Scanning electron microscopy （SEM） and zeta potential measurement were performed to characterize changes of mineral surface properties. Calculations of the extended Derjaguin-Landau-Verwey-Ocerbeek （EDLVO） theory indicated that, in the presence of surfactants the total interaction energy between magnetite and pentlandite became stronger than that between magnetite and serpentine. This enabled the selective adhesion of magnetite particles to pentlandite surfaces, thereby enhancing its magnetism.

Process mineralogy of copper-nickel sulphide flotation by a cyclonic-static micro-bubble flotation column

In our study we investigated a refractory copper-nickel sulfide ore separation by using a cyclonic-static micro-bubble flotation column (FCSMC). The process mineralogy of the main products was studied. Using a scanning electron microscope-energy dispersive system (SEM-EDS) and an X-ray spectrometer the mineral category and content of samples were analyzed. By using a mineral liberation analyzer (MLA) the mineral liberation characteristics were revealed. It is shown that in roughing feed the monomers liberation degree of nickel pyrite and chalcopyrite take up 84.11% and 88.82%, respectively. In tailings, the lost nickel pyrite and chalcopyrite are mainly monomers. Therefore, strengthening the micro-fine particle recovery capacity is the key to increase recovery.

Marketing and Financial Aspects With Microcredit and Turkey Sample

The main targets set for economic growth in the World Bank＇s 1990 report is to provide a permanent and sustainable poverty eradication strategies on the development. Used for this purpose today, the most effective strategy comes at the beginning of micro-credit system. Microcredit, in particular in the area of the individuals, and its opportunities to increase the credit to the users of the production process and ensure active participation in the society starting from the women＇s economic initiatives, but it cannot be considered as a micro-economic factors in the economy to facilitate an effective financial mechanism. Many studies in the literature have revealed that women＇s contribution to family income of households in poverty has created an important support. In addition, micro-credit system encourages women to create their own jobs, as the GNP （Gross National Product） of the countries contribution to increase employment opportunities. There are opinions arguing that, making use of the contact with communities in the potential female workforce satisfactory for women to create job opportunities to gain income is able to provide initial capital to the existing banking system, because in many countries＇ negative socio-cultural conditions, competing with men is much difficult. Micro-credit system, in the respect of changing countries socio-cultural and socio-economic structures is an important contribution. Microfinance occurred in recent years by rapid developments in Turkey since 2000, progress has been very professional. Our work in the field of micro-finance started operations in 2002, the Evaluation of Women＇s Work Association of Business Economics and the Grameen Bank realized Maya model adapted for Waste Prevention Foundation of Turkey should apply micro-finance. Micro-finance practices in the world and Turkey also compared practices. Turkey＇s application of micro-finance in banks＇ credit policies that support marketing activities related to marketing and sales strategies was examined by size. Also, emerging areas in Turkey, especially in the south-east region, the application of micro-finance loans contributed to the development of this geographical area were assessed. Studies of marketing and financial aspects of micro-finance were examined, the economic dimension of these practices by the country＇s social, cultural, political development has also been found to contribute significantly.

Mineralogical characterization and comprehensive utilization of micro-fine tantalum–niobium ores from Songzi

The mineralogical characteristics of tantalumniobium ores from Songzi were investigated using mineral liberation analyzer （MLA） and chemical analysis. In particular, the chemical composition, phase composition, particle size, and dissemination characteristics of the ores were studied in detail. Results show that Ta2O5 and Nb2O5 have grades of 0.013 % and 0.011%, respectively. The main valuable minerals in the ores are tantalite, col- umbite, tantalum-niobite, and microlite, and the gangue minerals associated with tantalum-niobium minerals mainly include quartz, kaolinite, illite, feldspar, and mica among others. The minerals are embedded in a complex manner. Tantalum-niobium minerals with most particle sizes of -0.040 mm are disseminated in minerals, such as mica, illite, quartz, and partially intergrown with topaz and zircon, where they could not be easily liberated. Thus, the ores are classified as low-grade, micro-fine, and refractory tantalum-niobium ores. Based on this consideration, the process of classification-gravity concentration-magnetic separation-middlings regrinding and gravity concentration are finally determined and satisfactory indices are obtained. Two rough concentrates are produced： Concentrate I has Ta2O5 and Nb2O5 grades of 7.0292 % and 3.546 %, respectively, as well as recovery of 49.42 % and 35.46 %. By comparison, Concentrate Ⅱ has Ta2O5 and Nb2O5 grades of 7.0292 % and 3.546 %, respectively, as well as recovery of 49.42 % and 35.46 %.

Heat transfer characteristics in micro-fin tube equipped with double twisted tapes: Effect of twisted tape and micro-fin tube arrangements

An experimental study was carried out to investigate the influence of double twisted-tape inserts （DTs） in micro-fin tubes （MFs） on heat transfer, friction factor and thermal performance factor characteristics of the compound devices in the following configurations： （1） twisted tapes acted in the same direction （for co-swirl） while MF and twisted tapes acted in the same （parallel） direction （MF-CoDTs：P）, （2） twisted tapes acted in the same direction （for co-swirl） while micro-fin tube and twisted tapes acted in opposite directions （MF-CoDTs：O） and （3） twisted tapes acted in opposite directions for counter swirl （MF-CDTs）. The MF alone and the MF equipped with a single twisted tape in parallel/opposite arrangement were also considered for comparison. The experiments were conducted for the flows with the Reynolds numbers between 5 650 and 17 000, under uniform heat flux condition. The experimental results indicate that MF-CDTs induce stronger swirl/turbulence flow, resulting in higher heat transfer rate, friction factor and thermal performance factor than other combined devices. The thermal performance factors associated with the use of MF-CDTs were found to be higher than those associated with the uses of MF-CoDTs：P, MF-CoDTs：O and MF alone up to 9.3%, 6.5% and 56.4%, respectively. The empirical correlations developed using the present experimental data for the Nusselt number, friction factor and thermal performance factor are also reported.

Control of favorable lithology on Jinlongshan micro-fine disseminated gold deposits, southern Qinling Mountains

Jinlongshan gold orebelt, a newly discovered one in sedimentary rock region in southern Qinling Mountains, is mainly located in upper Devonian and lower Carboniferous calcareous siltstone and argillic silty limestone of later Paleozoic era. Typical disseminated gold mineralization occurred in calcareous siltstone, which is major host rock and mainly composed of silt (SiO2 mostly varies from 38% to 73%) and calcite (CaO mostly varies from 10% to 25%). Pyrite created by living beings in Nanyangshan formation may be poor in gold. Faults and favorable layers jointly control disseminated gold mineralization. The significance of this opinion is very great for gold exploration.

A general model for flow boiling heat transfer in microfin tubes based on a new neural network architecture

A new neural network architecture,namely DimNet,was designed for correlating dimensionless quantities with power-law-like relations.Unlike common neural networks that are usually used as“black-boxes”,DimNet is interpretable as it can be converted to an explicit algebraic piecewise power-law-like function.With DimNet,a data-driven,empirical model was developed to predict the pre-dryout heat transfer coefficient of flow boiling within microfin tubes.The model was trained on a database with 7349 experimental data points for 16 refrigerants,and then optimized by comparing different sets of dominant dimensionless quantities and by adjusting the network configuration.The model exhibits an overall mean-absolute-error of 13.8%and no systematic variation with respect to the salient parameters for most conditions.Besides being statistically accurate,the model captures parametric trends of the heat transfer coefficient.The excellent prediction performance of the model was attributed to the DimNet’s ability to automatically classify the data into optimal regions and simultaneously correlate the data of each region.Therefore,the DimNet architecture is inherently suitable for modeling complex heat transfer and flow problems where multiple distinct physical regimes exist,especially for problems where a power-law-like input–output relation is desired such as convective heat transfer.