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The classical microbubble generator of the venturi nozzle type is still used in a wide range of industries despite its relatively low performance. In this study, for overcoming the relatively low performances and maintaining the existing advantages, the cylindrical venturi type of microbubble generators with screw structures and flared diffusers are proposed using conventional 3D printers. In the experimental facility, flow rates and pressure drop were measured. Using high speed images, the performances were deduced for prepared microbubble generators. Based on experimental data, the effect of screw structures for performances of microbubble generators was identified. Furthermore, the flared diffuser to the diffuser of regular venturi nozzle with constant diverging angle were compared. Additionally, synergies are obtained by the screw structure in the flare diffuser. In conclusion, the performances of the venturi type microbubble generator through optimal designed screw structures by 39.4 % were improved. [ABSTRACT FROM AUTHOR]

The novelty of this work is a new type of stack, namely, the parallel wave stack (PWS). In this paper, we study the performance of an air-based standing wave thermoacoustic refrigerator using the PWS. We use small heat pipes with a heat transfer rate of approximately 30 W as heat exchangers for the system. We investigate the effect of the ratio of stack length (Ls) to the distance between stack center and reflector (Xs) on the performance of the refrigerator parallel wave stacks with a blockage ratio (BR) of 67 %, 71 %, and 74 %, and with Ls/Xs ratios of 0.74, 0.96, and 1.20. We tested and compared these under a cooling load (Qc) of 0.5 W to 2 W and a frequency of 150 Hz. The results show that a BR of 71% with an Ls/Xs ratio of 0.96 provides a minimum cold-side temperature (Tc), and a maximum temperature difference (ΔTm), a maximum coefficient of performance, and a maximum relative coefficient of performance. This new type of stack can provide a higher performance. The structure of the stack is also stronger than others. This stack is an alternative and can be used in a thermoacoustic refrigerator. The results obtained from the present study will be very useful for improving the performance of the thermoacoustic refrigerator in the future. [ABSTRACT FROM AUTHOR]

In this study, we analytically investigate the performances of annular fins with rectangular and hyperbolic profiles under partially wet conditions. We propose four equations for the profiles of enthalpy difference, four equations for heat transfer rates, and four equations for fin efficiency which is a function of interface radius. We then present four equations for evaluating interface radius. Results indicate that the heat transfer rate and efficiency of an annular fin with a rectangular profile is higher than that with a hyperbolic profile. The efficiency under partially wet conditions is between those under fully dry and fully wet conditions. The efficiency of fully dry fins is independent of relative humidity; however, for fully wet and partially wet conditions, efficiencies increase with decreasing relative humidity. At the same relative humidity, heat transfer rate increases with an increasing ratio of outside radius to inside radius. In contrast, fin efficiency decreases. By analytical method, the partially wet annular fin performances are investigated. Partially wet fin efficiency of annular fin of rectangular profile is presented. Partially wet fin efficiency of annular fin of hyperbolic profile is presented. [ABSTRACT FROM AUTHOR]

The thermal conductivity of TiC/water nanofluid is found out at different weight fractions of 0.1%, 0.2% and 0.3% and the results are compared with water (base fluid). It has been shown that the thermal conductivity of TiC/water nanofluid is improved when compared with water. Then, an inexpensive cryogenic treatment is adopted to find the thermal conductivity of cryo-TiC/water nanofluid. It has been found that the cryogenic treatment on TiC nanopowder is further enhancing the thermal conductivity of TiC/water nanofluid. The lattice vibration of the particles is responsible for the improvement of thermal conductivity. [ABSTRACT FROM AUTHOR]

Highlights • Heat transfer and pressure drop of R-134a in dimpled tubes are investigated. • The effects of dimpled depth on the heat transfer and pressure drop are examined. • The heat transfer enhancement factor is up to 1.81 times of smooth tube. • The correlations to predict the Nusselt number and friction factor are proposed. Abstract An experimental investigation is conducted to determine the effect of dimpled depth on the condensation heat transfer coefficient and pressure drop of R-134a flowing inside dimpled tubes. The test condenser is a double tube heat exchanger where the refrigerant flows inside and water flows in the annulus. The inner tube is a 1500 mm long and 8.1 mm inside diameter. The experiments are carried out for one smooth tube and three dimpled tubes having dimpled depth of 0.5, 0.75, and 1.0 mm. For each test tube, several test runs are performed over mass flux range of 300–500 kg/m2s, heat flux range of 10–20 kW/m2, and condensing temperature range of 40–50 °C. The experimental results reveal that the dimpled tube presents the significant heat transfer enhancement and pressure drop penalty. The tube with the highest dimpled depth yields the highest heat transfer enhancement and pressure drop penalty up to 83% and 892% higher than those of the smooth tube, respectively. Additionally, the overall performance of dimpled tube is evaluated in term of efficiency index. The new correlations including the effect of dimpled depth, dimpled pitch, and helical pitch on the Nusselt number and friction factor of R-134a in dimpled tube are developed. [ABSTRACT FROM AUTHOR]

In this study, a comparison of the convective heat transfer, pressure drop, and performance index characteristics of heat sinks with a miniature circular pin-fin inline arrangement (MCFHS) and a zigzag flow channel with single cross-cut structures (CCZ-HS) is presented. SiO2-water nanofluids with different particle concentrations are used as the coolant. The effects of the heat sink type, particle concentration and fluid flow rate on the thermal and hydraulic performances are evaluated. The testing conditions are performed at the wall heat fluxes of 10 to 60 kW/m2 and at a mass flow rate ranging from 0.18 to 0.6 kg/s. The dimension of heat sinks is equally designed at 28 × 33 mm. The heat transfer area of MCFHS and of CCZ-HS is 1430 and 1238 mm2, respectively. Similarly, the hydraulic diameter of the flow channel of MCFHS and of CCZ-HS is 1.2 and 1.0 mm, respectively. The measured data indicate that the cooling performances of CCZ-HS are about 24-55% greater than that of MCFHS. The effects of the channel diameter and single cross-cut of the flow channel are more dominant than the effects of the fin structure and heat transfer area. [ABSTRACT FROM AUTHOR]

The heat transfer enhancement and pressure loss penalty of condensing refrigerant R-134a in dimpled tubes with different helical and dimpled pitches are experimentally investigated. The test section is a 1500-mm-long tube-in-tube heat exchanger placed horizontally. The inside and outside diameters of the inner tubes are 8.1 and 9.52 mm, respectively. One smooth tube and five dimpled tubes with different helical and dimpled pitches are tested. The experimental runs are done at saturated condensing temperatures ranging from 40 to 50 °C. The mass fluxes and heat fluxes vary from 300 to 500 kg/m 2  s and from 10 to 20 kW/m 2 , respectively. The results show that the dimpled tubes yield higher heat transfer enhancement and pressure drop penalty compared to the smooth tube under the same operating condition. By decreasing helical and dimpled pitches, both the heat transfer coefficient and frictional pressure drop increase significantly. The maximum heat transfer coefficient and frictional pressure drop are achieved through the tube with the lowest helical and dimpled pitches (p = 5.08 mm, z = 3.24 mm) up to 88% and 630% higher than those of the smooth tube, respectively. The new correlations for predicting the Nusselt number and friction factor of R-134a condensing in dimpled tubes with different helical and dimpled pitches are proposed. [ABSTRACT FROM AUTHOR]

This paper presents the condensation heat transfer of R-134a flowing inside a chevron gasketed plate heat exchanger. The study focuses on the effect of surface roughness on the heat transfer coefficient and pressure drop. The stainless steel plate heat exchanger has a total length of 360 mm and total width of 100 mm. The experiment is conducted at a condensation temperature of 40–50 °C, a heat flux of 5–15 kW/m 2 , and refrigerant mass flux of 61–89 kg/m 2 s and plate surface roughness ranging between 0.594 μm and 2.754 μm. Unlike the increase in temperature, the increase in surface roughness and mass flux leads to an increase in the heat transfer coefficient and frictional pressure gradient. The increase in heat flux leads to a slight increase in heat transfer coefficient, but has no effect on the pressure drop. The thermal performance factors are in the range of 0.99–1.22 and 0.92–1.19 for roughnesses of 1.816 and 2.754 µm, respectively. [ABSTRACT FROM AUTHOR]

This research reports the thermal performance and flow characteristics of nanofluid flows in two different types of microchannel heat sink (MCHS) with multiple zigzag flow channel structures experimentally with regard to the continuous zigzag flow channel (CZ-HS) and the single cross-cutting zigzag flow channel (CCZ-HS). SiO 2 nanoparticles with particle loadings of 0.3, 0.6, and 0.8 vol.% and dispersed in deionized water (DI water) are used as the working medium. Both CZ-HS and CCZ-HS are made from copper material. Their dimensions are approximately 28 × 33 mm. Hydraulic diameter and number of flow channels are equally designed as seven 1-mm flow channels, respectively. The heat transfer area of CZ-HS is approximately 1176 mm 2 and that of CCZ-HS is 1238 mm 2 . The effects of single cross-cutting of the flow channel, Reynolds number, and particle concentration on the Nusselt number and pressure drop characteristics are investigated. The experimental data indicate that the nanofluid-cooled heat sink provided larger thermal performance than the heat sink cooled by water of approximately 3–15%. Similarly, the results indicated that the thermal performances of the CCZ-HS are larger than those of the CZ-HS by an average of 2–6%. For the pressure drop, the measured data showed that particle concentration and cross-cutting of the flow channel have a small effect on the pressure-drop data. [ABSTRACT FROM AUTHOR]

This article presents two mathematical models for estimating the performances of finned tube heat exchangers with wavy configuration under partly and fully wet surface conditions. The actual dry bulb temperature method is the first one and the other is the method of equivalent dry bulb temperature. For the first one, the actual dry bulb temperature method that was firstly presented by our research team in 2015 is more uncomplicated than the well-known enthalpy potential method and is also easier than the equivalent dry bulb temperature method. Moreover, it has never been applicable to the finned tube heat exchanger. For accuracy, the finned tube heat exchangers are distinguished into teeny segments and every segments are separated by conditions of surface into three groups: partially wet segments, fully wet segments, fully dry segments. This procedure is called the finite circular fin method that was firstly presented by our research in 2007. From the results, the heat and mass transfer characteristics estimated by the method of equivalent dry bulb temperature are greater than those estimated by the method of actual dry bulb temperature. This is the influence of the non-constant terms in both methods. Moreover, the correlations for the conditions of party and fully wet surface are revealed for predicting the heat and mass transfer coefficients of the finned tube heat exchanger with wavy configuration. The users can apply our presented models with the proposed correlation for predicting the heat and mass transfer performances of finned tube heat exchangers with wavy configuration under the conditions of fully and partly wet surface. [ABSTRACT FROM AUTHOR]

This study investigates the heat transfer and pressure drop of R-134a during condensation inside a dimpled tube. The test section is a horizontal counter-flow double-tube heat exchanger with refrigerant flowing in the inner tube and cold water flowing in the annulus. The inner tubes consist of one smooth tube and one dimpled tube, which are made from copper. The length and inner diameter of the test tube are 1500 mm and 8.1 mm, respectively. The test runs are performed at saturation temperatures of 40, 45, and 50 °C, heat fluxes of 10, 15, and 20 kW/m 2 , and mass fluxes of 300, 400, and 500 kg/m 2 s. The effects of heat flux, mass flux, and saturation temperature on the heat transfer coefficient and frictional pressure drop are examined. Comparisons between smooth and dimpled tubes on the heat transfer and frictional pressure drop are also discussed. It is observed that the heat transfer coefficient and frictional pressure drop obtained from a dimpled tube are higher than that of the smooth tube. In addition, as the equivalent Reynolds number increases, the dimpled tube enhances the Nusselt number around 1.3–1.4 times in comparison to the smooth tube. Whereas, when the equivalent Reynolds number decreases, the two-phase friction factor rises around 2.8–4.1 times as compared to the smooth tube. [ABSTRACT FROM AUTHOR]

At present, the global community is aware of the critical limit of the pollution from fossil fuels. Many countries, including Thailand, have explored alternative energy, one of which is solar energy. In particular, the use of solar power for electricity generation is important to reduce imported energy because Thailand’s primary commercial energy imports comprise approximately 50%, of all of Thailand’s energy. The government has supported renewable energy through the long-term 22-year Alternative Energy Development Plan 2015–2036 (AEDP 2015), which aims to boost the production of electricity using renewable energy, especially solar, to 6000 MW by the year 2036. The government has the price incentives for power producers. The result is that the Electricity Generation Authority of Thailand (EGAT), Provincial Electricity Authority (PEA), and Metropolitan Electricity Authority (MEA) have a production capacity of solar-power-generation projects of 1558 MW, and the projects of 1261 MW are under construction. This is 46.98% of the AEDP 2015 target. The major barriers of solar-powered-system development are the high investment cost, uncertain subsidies and lack of thorough policy planning. Those obstructions depend on the government’s strategy. [ABSTRACT FROM AUTHOR]

A two-phase air–water flow experiment was carried out to obtain flow pattern, void fraction, and pressure drop data from a vertical micro-channel, which was a fused silica tube with a diameter of 0.53 mm and a length of 320 mm. The adiabatic two-phase flow behaviors during vertical upward direction were experimentally investigated, and consequently, a buoyancy effect can be detected in this work. A flow visualization study was performed, leading to observation of slug flow, throat–annular flow, churn flow, annular flow, and annular–rivulet flow. The shape of the interfacial surface in the slug flow pattern was deformed during vertical upward flow, which was different from the bullet-shaped gas slug observed in the horizontal channel. The flow visualization results also indicate that the flow pattern map for vertical upward flow is not completely compatible with that for horizontal flow. Image analysis was performed to determine the void fraction, which increases linearly with increasing volumetric quality. The vertical upward flow gave a lower void fraction than the horizontal flow. The frictional pressure drop can be increased when the churn flow is formed in the channel. In addition, vertical upward flow can result in higher pressure drop when compared with the horizontal channel. [ABSTRACT FROM AUTHOR]

The paper reports an experimental investigation into the thermal performance and pressure drop characteristics of nanofluid-cooled heat sinks and then compares the results with the data for water-cooled heat sinks. Heat sinks with miniature circular-fin (MCFHS) and square-fin (MSFHS) structures are used and made from aluminum material with dimensions of 28 × 33 mm. Similarly, SiO 2 nanoparticles dispersed in deionized water with particle concentrations of 0.2%, 0.4%, and 0.6% volume are used as working fluids. The effects of pin fin configuration, particle concentration, and flow rate on the heat transfer performance and flow behaviors are presented. Reynolds numbers based on the hydraulic diameter of each flow channel ranging between 700 and 3700, fluid temperature of 15 °C, and heat flux ranging from 2 and 5 W/cm 2 are tested. Hydraulic diameters based on each flow channel are equally designed at 1.2 mm for both heat sinks. The experimental results indicate that the heat transfer coefficient increased with increasing Reynolds numbers and particle concentrations. The MCFHS gave greater heat transfer performance than that of the MSFHS by about 6–9%. For pressure drop data, the measured data showed that the pin fin configuration and particle concentration had small effects on the pressure drop and pumping power. [ABSTRACT FROM AUTHOR]

This paper is a continuation of the authors’ previous work. Theoretical and experimental studies of the heat transfer characteristics of a helical-coiled, crimped, spiral, finned-tube heat exchanger in dry surface conditions are presented. The test section is a helical-coiled, finned-tube heat exchanger. The coil unit is composed of four concentric helical-coiled tubes of different diameters. All tubes are constructed by bending straight copper tube into seven layers of helical coil. Aluminum crimped spiral fins, with an outer diameter of 28.25 mm and a thickness of 0.5 mm, are connected around the tube. Hot water is used as a working fluid for the tube side, while ambient air is used for the shell side. The test runs are done at air mass flow rates ranging between 0.04 and 0.13 kg/s. The water mass flow rates are between 0.2 and 0.4 kg/s. The water temperatures are between 40 and 50°C. A mathematical model is developed and the simulation results show reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]

This paper defines and discusses two important types of citations, self-citation and mandatory citation, in engineering journals. Citation can be classified in three categories: optional; semi-mandatory; and mandatory. There are some negative and positive impacts for the authors' paper and journals' reputation if mandatory citation of a paper or set of papers is requested. These effects can be different based on the recommended papers for citing in the new research. Mandatory citation has various types discussed in this paper. Self-citation and its reasons and impacts are also discussed in the present study. [ABSTRACT FROM AUTHOR]

Experimental data regarding heat transfer coefficient and pressure drop of water flow inside a plate heat exchanger with a rough surface is investigated and compared with that obtained from a smooth surface. Three commercial stainless steel corrugated plates with symmetrical chevron angle of 25° are used. The water flow inside the plate heat exchanger is arranged for a single pass and counter flow. The test runs are performed at Reynolds numbers ranging between 1300 and 3200 and plate surface roughness ranging between 0.936 μm and 3.312 μm. The experimental results show that increase in surface roughness yields an increase in heat transfer coefficient between 4.46% and 17.95% and an increase in pressure drop between 3.90% and 19.24% with respect to a smooth surface. The correlations for predicting the Nusselt number and friction factor of water flow inside a plate heat exchanger with a rough surface are proposed. [ABSTRACT FROM AUTHOR]

In this paper, flow patterns and heat transfer characteristics of R134a refrigerant during flow boiling in a single rectangular micro-channel with 0.68 mm hydraulic diameter are investigated. In this experiment, heat transfer coefficients were studied at a heat flux range of 7.63–49.46 kW/m 2 , mass flux range of 600–1400 kg/m 2 s, and saturation temperature range of 23–31 °C. Results show that there are six different flow patterns occurring during boiling of R134a refrigerants: bubbly flow, bubbly-slug flow, slug flow, throat-annular flow, churn flow, and annular flow. It is also found that flow pattern has a significant relation to heat transfer coefficients. In low heat flux range, variation of mass flux has no significant effect on the heat transfer coefficient. It corresponds to the nucleate boiling heat transfer mechanism in which its flow patterns are bubbly flow, bubbly-slug flow, slug flow, throat-annular flow, and churn flow. The heat transfer coefficient at higher saturation temperatures is greater than that of lower saturation temperatures. In high heat flux ranges, the heat transfer coefficient increases with increasing mass flux. It corresponds to the convective boiling heat transfer mechanism in which its flow pattern is annular flow. Increase of saturation temperature causes the heat transfer coefficient to decrease. At very high saturation temperature, a partial dry-out occurs that results in a lower heat transfer coefficient. [ABSTRACT FROM AUTHOR]

This study presents the experimental thermal and hydraulic performance of heat sink with miniature circular pin fin structure using two different types of nanofluid as coolant. ZnO and SiO 2 nanoparticles dispersed in DI water with particle volume fraction of 0.2, 0.4 and 0.6 vol.% are tested and compared with the data for water. A heat sink with inline arrangement of circular pins is designed and made from aluminum material. The height, diameter, pitch, and number of pins are 1.2, 1.2, 2.4 mm and 143, respectively. Uniform heat flux at the bottom of the heat sink is performed. The present work is conducted at fluid temperature of 15 °C. The mass flow rate ranged from 0.65 to 3.32 kg/min and the heat flux ranged between 20 and 48 kW/m 2 . The effects of particle type, particle concentration, and mass flow rate on the thermal and hydraulic performances are reported. The measured data show that the heat transfer performance of the nanofluid-cooled heat sink is higher than that of the water-cooled heat sink. Comparison between ZnO and SiO 2 nanofluids, higher heat transfer performance for ZnO–water nanofluids is observed by about 3–9%. For hydraulic performance, the results show that the addition of nanoparticles in the base fluid have a small effect on the pumping power. Finally, new heat transfer and pressure drop correlations are proposed to predict the Nusselt number and pressure drop of nanofluids flow in heat sinks with pin fin configuration. [ABSTRACT FROM AUTHOR]

In the present paper, the thermal conductivity of hybrid nanofluids is experimentally investigated. The studied nanofluid was produced using a two-step method by dispersing Cu and TiO 2 nanoparticles with average diameter of 70 and 40 nm in a binary mixture of water/EG (60:40). The properties of this nanofluid were measured in various solid concentrations (0.1, 0.2, 0.4, 0.8, 1, 1.5, and 2%) and temperatures ranging from 30 to 60 °C. Next, two new correlations for predicting the thermal conductivity of studied hybrid nanofluids, in terms of solid concentration and temperature, are proposed that use an artificial neural network (ANN) and are based on experimental data. The results indicate that these two new models have great ability to predict thermal conductivity and show excellent agreement with the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we aim to discuss the fake journals and their advertisement and publication techniques. These types of journals mostly start and continue their activities by using the name of some indexed journals and establishing fake websites. The fake journals and publishers, while asking the authors for a significant amount of money for publishing their papers, have no peer-review process, publish the papers without any revision on the fake sites, and put the scientific reputation and prestige of the researchers in jeopardy. In the rest of the paper, we present some viable techniques in order for researchers and students to identify these journals. [ABSTRACT FROM AUTHOR]

Hydropower is currently the world׳s largest renewable energy source and plays an important role in the worldwide generation of electricity. Thailand has plenty of water resources that can be used to generate electricity. However, the appropriate development of hydropower coupled with proper utilization of available water resources in Thailand should be undertaken in the future. By the end of September 2013, the on-grid capacity of hydropower in Thailand reached 3497 MW, or about 11% of the whole productivity system. The existing potential of hydropower in Thailand was at 15,155 MW or about 4 times the capacity at the time. In addition, the 25 river areas of the country could allow for small-scale hydropower plants with a total potential of no less than 1500 MW. In 2021, the Ministry of Energy anticipates that Thailand will be able to increase electricity generation from alternative and renewable energy sources to 9201 MW, with 1608 MW being generated by hydropower. The present study has been carried out to review the water resources, current situation, and potential of hydropower in Thailand. Future development plans for promoting hydropower have also been presented. [ABSTRACT FROM AUTHOR]

Cooling systems are needed for electronic devices in order to operate efficiently. Whereas the size of the equipment has decreased to the micro scale, research on the heat transfer characteristics in a microchannel heat sink is needed. In this work, we suggest that the segmented air–water flow can enhance the heat transfer rate in a microchannel heat sink as compared to using single-phase water cooling. The experiment was conducted with two-phase air–water flow in a single rectangular microchannel with a hydraulic diameter of 267 μm. The test section was made from copper. For a clear understanding, two-phase flow pattern, pressure drop, and heat transfer characteristics in the low Reynolds number of air–water flow were identified. The results show that segmented, throat-annular, throat-annular/liquid, and annular flow were observed within the test section. A flow pattern map was created and compared with the previous maps. The pressure drop can be predicted by the homogeneous flow model and the Friedel correlation separated flow model. The Nusselt number of segmented flow increases up to 1.2 times over the single-phase flow. [ABSTRACT FROM AUTHOR]

A heat sink is a kind of heat exchanger used as a cooling system for electronic components due to simplicity, low cost, and a reliable manufacturing process. The heat sink can be divided by plate and pin fin shapes. In the past decade, several published articles have focused on studying the effects of fin shapes and arrays of heat sinks on flow characteristics and thermal performance with forced convection. However, only a few publications have focused on the flow directions (parallel and impingement flows) and flow behaviors (bypass and non-bypass flows) through the heat sink, which are necessary for fin and overall cooling system design. The purpose of this article is to summarize the publications with respect to experimental research on the fluid flow directions and behaviors through heat sinks as well as offering guidelines for future research. [ABSTRACT FROM AUTHOR]

Abstract: This paper is a continuation of the authors’ previous work on the condensation of R134a flowing inside a multiport minichannel (Sakamatapan et al., 2013) [22]. The pressure drop’s characteristics during condensation were investigated in an experiment for R134a flowing inside a multiport minichannel. The pressure drop characteristics were observed under mass flux range of 345–685kg/m2, heat flux of 15–25kW/m2, and saturation temperature of 35–45°C. Two types of multiport minichannels having 14 channels, one with a 1.1mm hydraulic diameter and another with 8 channels with a 1.2mm hydraulic diameter, were designed as a counter flow tube in a tube heat exchanger. The results showed that the total pressure drop is dominated by the frictional pressure drop. The frictional pressure gradient increased with the augmentation of mass flux and vapor quality, but the increase of the saturation temperature and channel size play an important role in the decrease of frictional pressure gradient. On the other hand, the heat flux had an insignificant effect on the frictional pressure gradient. Moreover, the miniscale correlations were conducted to predict the frictional pressure gradient, and it was found that only the multiport minichannel correlations gave a reasonable result. A new two-phase friction factor correlation was proposed using the equivalent Reynolds number concept to predict the frictional pressure gradient during condensation. [Copyright &y& Elsevier]

Abstract: Thailand generates electricity from many sources, including natural gas, coal/lignite, fuel oil, diesel, and renewable energies, such as wind, hydroelectricity, and solar power. In 2012, the main electrical energy sources in Thailand were natural gas (63.8%) and coal/lignite (27.7%). Due to fuel price spikes and global warming, several countries are now more interested in studying and developing sources of renewable energy. Wind energy – an unlimited and environmentally friendly form of natural energy – has attracted increasing levels of investment, particularly in China, which derives more of its electricity from wind energy generation than any other country in the world. Thailand has also developed and promoted the use of wind turbines to generate electricity. In 2012, Thailand generated about 111.7MW of electricity from wind energy. By 2021, the Thai government's goals are to increase the use of alternative electric energy to about 25% of fossil fuel use and to achieve 1800MW of electricity output from wind energy. This article will present a critical review of the current status of wind energy in Thailand, including future plans for using wind energy in place of fossil fuels – oil, natural gas, and coal – to generate electricity. [Copyright &y& Elsevier]

Highlights: [•] Effect of the free rotation of a swirl device is investigated. [•] Five swirl generators are installed equally distant along the test section. [•] Data of fixed turbine and freely rotating turbine are compared. [•] The performance for rotating turbine is 6.3% higher than that for fixed turbine. [•] The tube with RTSG inserts gave the lowest pressure drop. [Copyright &y& Elsevier]

Abstract: Since early civilization, humans have required energy. Energy grows increasingly important with globalization. The search for energy sets nuclear power as the highest priority for generating electricity. The need to delay global warming initiated a nuclear power plant using a nuclear reactor as its source of thermal energy to generate pollution-free electrical currents. Many countries see the important advantages of nuclear power plants, and Thailand plans nuclear power plant projects (NPP) to be built by the Electricity Generating Authority of Thailand (EGAT). These projects have improved, and the latest Power Development Plan 2010–2030 (PDP 2010) states that by 2023, Thailand will build nuclear power plants with electrical productivity of about 4000MW. The plants will generate commercial electricity for domestic consumption with plans to increase productivity in preparation for Thailand's economic growth and its participation in the ASEAN Economic Community (AEC). These efforts stem from investments in domestic and international industrial businesses in order to impress foreign countries with Thailand's energy security policy. However, the Thai people are concerned with the impacts of nuclear power plants. The people of Thailand require societal awareness in the construction of these plants. [Copyright &y& Elsevier]

In this study, efficiencies for partially wetted fins for the uniform cross section spine, con-ical spine, concave parabolic spine, and convex parabolic spine are presented using an analytical method. Depending on the set of boundary conditions, there are two methods for deriving the efficiencies of partially wet fins for each spine. The eight equations for fin efficiencies were investigated. Fin efficiency is a function of the length of the dry portion. Thus, the equations for calculating the length of the dry portion are also presented. The findings indicate that a larger cross-sectional fin results in a higher conduction heat transfer rate. Contrarily, the fin efficiency is lower. This is different from the longitudinal fin, for which the trend lines of heat transfer rate and fin efficiency are the same. This converse relationship is due to the effect of the ratio of the cross-sectional area to the suiface area. Moreover, partially wet fin efficiencies decrease with increased relative hu-midity. For convenience, the approximate equation for efficiencies for partially wet fins, which is derived from the equations for fully wet and fully dry fin efficiencies, is also pre-sented. [ABSTRACT FROM AUTHOR]

A numerical simulation for calculating the flashing flow characteristics of refrigerants inside short-tube orifices is presented. The refrigerant flow behaviors along short-tube orifices are separated into three sections: subcooled liquid region, metastable liquid region, and two-phase region. Annular two-phase flow pattern is developed from the mass, energy, and momentum equation. The present simulation is corroborated by comparison with the experimental data. The selection charts are also presented to estimate the refrigerant mass flow rate along short-tube orifices in practical applications. [ABSTRACT FROM AUTHOR]

Abstract: Heat transfer enhancement and flow behaviors in horizontal circular tubes installed with five rotating turbine-type swirl generators (RTSG) are presented experimentally. This type of RTSG is an innovative design that has not been seen in the previous research. Deionized water is used as a working fluid and flows through the test section under turbulent flow conditions. A smooth, stainless steel tube 9.2mm in ID, 0.4mm in thickness, and 2.3m in length is used as the test section. RTSG made from aluminum, with a twisted angle of 60° and a length of 2cm, are located at 0.46m equally distant along the test section. When fluid flows through the RTSG, continuously free rotations are observed, and swirl flow after RTSG is created. A DC power supply is used to supply heat load to the test section. Compared with a common, plain tube (without rotating swirl devices), the experimental results indicate that the local heat transfer coefficient of the tube with RTSG inserts is higher than that of the common, plain tube, and they increase when the working fluid flows through the RTSG. Similarly, the wall temperatures of the tube with RTSG inserts are lower than those of the common tube. However, the pressure drop of the tube fitted with RTSG is significantly greater than that of the common, plain tube. [Copyright &y& Elsevier]

Abstract: An experimental investigation on the thermal cooling of vapor chamber for cooling computer processing unit of the personal computer is performed. Two different configurations of the vapor chambers with de-ionized water as working fluid are tested under the real operating conditions of PCs. Parametric studies including different aspect ratios, fill ratios, and operating conditions of PC on the CPU temperature are considered. It was found that the vapor chamber cooling technique has significant effect on the thermal cooling of CPU. Average CPU temperatures obtained from the vapor chamber cooling system are 4.1%, 6.89% lower than those from the conventional cooling system for no load and 90% operating loads, respectively. In additional, this cooling system requires 6.89%, 10.53% lower energy consumption for no load and 90% operating loads, respectively. The results of this study are of technological importance for the efficient design of cooling systems of the personal computers or electronic devices to enhance cooling performance. [Copyright &y& Elsevier]

Abstract: New correlations of the two-phase multiplier and heat transfer coefficient of R134a during evaporation in a multiport minichannel at low mass flux are proposed. The experimental results were obtained from a test using a counter-flow tube-in-tube heat exchanger with refrigerant flowing in the inner tube and hot water in the gap between the outer and inner tubes. Test section is composed of the extruded multiport aluminium inner tube with an internal hydraulic diameter of 1.2mm and an acrylic outer tube with an internal hydraulic diameter of 25.4mm. The experiments were performed at heat fluxes between 10 and 35kW/m2, and a refrigerant mass flux between 45 and 155kg/(m2 s). Some physical parameters that influenced the frictional pressure drop and heat transfer coefficient are examined and discussed in detail. The pressure drop and heat transfer coefficient results are also compared with existing correlations. Finally, new correlations for predicting the frictional pressure drop and heat transfer coefficient at low mass fluxes are proposed. [Copyright &y& Elsevier]

This paper presents the seasonal climatology of currents and elevations in the Gulf of Thailand (GoT) derived from a numerical three-dimensional ocean model. A numerical three-dimensional ocean model, based on the Princeton Ocean Model (POM), with rectangular coordinates in horizontal and vertical sigma coordinates was implemented for the GoT, situated between 6 to 14N latitude and 99 to 105E longitude. The Gulf is a relatively shallow body of water with a maximum depth of 83 m and an average depth of 45 m. It was driven at the surface by monthly mean sea surface temperature, salinity and wind stress climatology. In this paper, the simulations of current circulations and sea surface elevations for each season are presented, where the winter, summer, rainy season, and end of the rainy season in Thailand are represented by the months January, May, July, and October, respectively. The simulations in the upper GoT are also described. The results show clockwise circulations during summer and rainy seasons of Thailand. They occur in the central GoT. Two experiments were designed to investigate the effects of freshwater runoff. The freshwater runoff is shown to be the important factor for generating current circulation in the upper GoT at the end of the rainy seasons. The current speed is weakened when the runoff is removed. The sea surface elevations also decrease when the freshwater runoff is removed, especially in October, where it is reduced by about 50 %. [ABSTRACT FROM AUTHOR]

Abstract: The manufacturers of air conditioners need a precise method for calculating the critical flow rate of refrigerant through the short-tube orifice, and they must select the proper size of short-tube orifice at given operating conditions in order to achieve optimum system performance. The present study divides the research into two main groups: studies conducted under the semi-empirical model and those conducted under the theoretical model. The former model has been developed based on the single-phase orifice equation with the correction factor. The latter model applies the proper governing equations, including conservation of mass, momentum, and energy, to determine the refrigerant flow mechanism inside the short-tube orifice. Because these equations are rather difficult to solve, only a few studies have been conducted. This paper describes the details of the numerical modelling of refrigerant flow characteristics through the short-tube orifice reported in previous publications as well as the guideline for future research. [Copyright &y& Elsevier]

Abstract: Nanofluids are a suspension of particles with ultrafine size in a conventional base fluid that increases the heat transfer performance of the original base fluid. They show higher thermal performance than base fluids especially in terms of the thermal conductivity and heat transfer coefficient. During the last decade, many studies have been carried out on the heat transfer and flow characteristics of nanofluids, both experimentally and theoretically. The purpose of this article is to propose a dispersion model for predicting the heat transfer coefficient of nanofluids under laminar flow conditions. TiO2 nanoparticles dispersed in water with various volume fractions and flowing in a horizontal straight tube under constant wall heat flux were used. In addition, the predicted values were compared with the experimental data from He et al. . In the present study, the results show that the proposed model can be used to predict the heat transfer behaviour of nanofluids with reasonable accuracy. Moreover, the results also indicate that the predicted values of the heat transfer coefficient obtained from the present model differ from those obtained by using the Li and Xuan equation by about 3.5% at a particle volume fraction of 2.0%. [Copyright &y& Elsevier]

Abstract: A short-tube orifice is a kind of an expansion device. The advantages of a short-tube orifice are simplicity, low cost, and low starting torque of the compressor as the pressures across the short-tube orifice equalise during the off-cycle. The two-phase flow mechanisms of refrigerant inside the short-tube orifice are very complicated although its physical configurations are simple. During the past decade, investigations of the mass flow rate of various refrigerants inside short-tube orifices, which is useful for selecting the proper size in practical applications, have been reported by many researchers. However, few researchers focused on the flow pattern, choked flow, and metastable flow phenomena inside short-tube orifices, which are necessary for a clear understanding of the flow behaviour and developing suitable calculation techniques. The aim of this paper is to summarise the evolution of the experimental research on refrigerant flow characteristics inside short-tube orifices to provide guidelines for future research. [Copyright &y& Elsevier]

This article describes experimental investigations of the heat transfer coefficient and pressure drop of R-134a flowing inside internally grooved tubes. The test tubes are one smooth tube and four grooved tubes. All test tubes are made from type 304 stainless steel, have an inner diameter of 7.1 mm, are 2,000 mm long and are installed horizontally. The test section is uniformly heated by a DC power supply to create evaporation conditions. The groove depth of all grooved tubes is fixed at 0.2 mm. The experimental conditions are conducted at saturation temperatures of 20, 25 and 30°C, heat fluxes of 5, 10 and 15 kW/m, and mass fluxes of 300, 500 and 700 kg/m s. The effects of groove pitch, mass flux, heat flux, and saturation temperature on heat transfer coefficient and frictional pressure drop are discussed. The results illustrate that the grooved tubes have a significant effect on the heat transfer coefficient and frictional pressure drop augmentations. [ABSTRACT FROM AUTHOR]

Abstract: This article presents the condensation heat transfer and flow characteristics of R-134a flowing through corrugated tubes experimentally. The test section is a horizontal counter-flow concentric tube-in-tube heat exchanger 2000mm in length. A smooth copper tube and corrugated copper tubes having inner diameters of 8.7mm are used as an inner tube. The outer tube is made from smooth copper tube having an inner diameter of 21.2mm. The corrugation pitches used in this study are 5.08, 6.35, and 8.46mm. Similarly, the corrugation depths are 1, 1.25, and 1.5mm, respectively. The test conditions are performed at saturation temperatures of 40–50°C, heat fluxes of 5–10kW/m2, mass fluxes of 200–700kg/m2 s, and equivalent Reynolds numbers of 30000–120000. The Nusselt number and two-phase friction factor obtained from the corrugated tubes are significantly higher than those obtained from the smooth tube. Finally, new correlations are developed based on the present experimental data for predicting the Nusselt number and two-phase friction factor for corrugated tubes. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical investigation of the flow characteristics of helical capillary tubes compared with straight capillary tubes. The homogenous two-phase flow model developed is based on the conservation of mass, energy, and momentum of the fluids in the capillary tube. This model is validated by comparing it with the experimental data of both straight and helical capillary tubes. Comparisons of the predicted results between the straight and helical capillary tubes are presented, together with the experimental results for straight capillary tubes obtained by previous researchers. The results show that the refrigerant flowing through the straight capillary tube provides a slightly lower pressure drop than that in the helical capillary tube, which resulted in a total tube length that was longer by about 20%. In addition, for the same tube length, the mass flow rate in the helical capillary tube with a coil diameter of 40mm is 9% less than that in the straight tube. Finally, the results obtained from the present model show reasonable agreement with the experimental data of helical capillary tubes and can also be applied to predict the flow characteristics of straight capillary tubes by changing to straight tube friction factors, for which Churchill''s equation was used in the present study. [Copyright &y& Elsevier]

Abstract: Adiabatic two-phase air–water flow is experimentally studied in this work. Two channels, made of fused silica, with different diameters of 0.53 and 0.15mm are used as test sections. The void fraction data for both tubes are obtained by image analysis. For the larger channel, the void fraction is found to be a linear relationship with the volumetric quality. In the case of the smaller one, however, the non-linear void fraction is obtained. The measured frictional pressure drop data are compared with the predictions regarding the homogeneous flow assumption. Several well-known two-phase viscosity models are subsequently evaluated for applicability to micro-channels. [Copyright &y& Elsevier]

Abstract: This paper is a continuation of the author’s previous work. New experimental data on the occurrence of choked flow phenomenon and mass flow rate of HFC-134a inside short-tube orifices under choked flow condition are presented. Short-tube orifices diameters ranging from 0.406mm to 0.686mm with lengths ranging from 1mm to 3mm which can be applied to a miniature vapour-compression refrigeration system are examined. The experimental results indicated that the occurrence of choked flow phenomena inside short-tube orifices is different from that obtained from short-tube orifice diameters of greater than 1mm, which are typically used in air-conditioner. The beginning of choked flow is dependent on the downstream pressure, degree of subcooling, and length-to-diameter ratio. Under choked flow condition, the mass flow rate is greatly varied with the short-tube orifice dimension, but it is slightly affected by the operating conditions. A correlation of mass flow rate through short-tube orifices is proposed in terms of the dimensionless parameters. The predicted results show good agreement with experimental data with a mean deviation of 4.69%. [Copyright &y& Elsevier]