Experimental study of the two-phase flow distribution in helical-structured vertical headers.

A vertical header is a crucial component of a microchannel heat exchanger that facilitates the distribution of the two phases of the refrigerant into horizontally aligned channels. Ensuring an even distribution of the refrigerant into the channels is imperative for achieving the designed optimal performance. Previous studies have indicated that the distribution characteristics of the vertical header are contingent upon the mass flow rate and geometric properties of the header. This study aims to investigate the distribution characteristics of two-phase flow resulting from structural modifications in the header, specifically by implementing a vertical header with a helical structure. Hence, an experimental device simulating a microchannel heat exchanger found in a commercial air conditioning system was employed. The distribution characteristics of the vertically oriented header with a helical structure were measured by varying the inlet conditions (mass flow rate: 50-100 kg h-1; vapor quality: 0.1-0.2). The measured distribution characteristics were compared with those obtained from a conventional straight vertical header possessing the same cross-sectional properties. The experimental findings demonstrated that the helical structure induced a distinctive flow pattern and facilitated the mixing of the two phases. Furthermore, this helical structure exhibited reduced inertial forces compared to the simple vertical header, leading to improved distribution performance.

Optimizing Calibration for a Capacitance-Based Void Fraction Sensor with Asymmetric Electrodes under Horizontal Flow in a Smoothed Circular Macro-Tube.

In this study, a technique that uses a capacitance sensor with an asymmetric electrode to measure the void fraction of a refrigerant was developed. It is known that the void fraction and flow pattern affect the measured capacitance. Therefore, the relationship between the void fraction and capacitance is not linear; hence, a calibration method for obtaining accurate measurements is necessary. A calibration method was designed in this study based on repeated capacitance measurements and the bimodal temporal distribution to calibrate the atypical and repetitive flow patterns of slug flow and its transition to the intermittent flow regime. The calibration method also considers the weighted-average relation for the gradual transition of the intermittent to annular flow pattern according to the change from low to high quality. The proposed method was experimentally analyzed under the conditions of R32 refrigerant, a tube inner diameter of 7.1 mm, saturation temperature of 25 °C, mass flux of 100-400 kg m-2 s-1, and vapor quality of 0.025-0.900, and it was validated using a quick-closing valve (QCV) system under identical conditions. A relative error of 2.99% was obtained for the entire system, indicating good agreement between the proposed and QCV-based methods.

Feasibility of Novel Rear-Side Mirage Deflection Method for Thermal Conductivity Measurements.

Among the noncontact measurement technologies used to acquire thermal property information, those that use the photothermal effect are attracting attention. However, it is difficult to perform measurements for new materials with different optical and thermal properties, owing to limitations of existing thermal conductivity measurement methods using the photothermal effect. To address this problem, this study aimed to develop a rear-side mirage deflection method capable of measuring thermal conductivity regardless of the material characteristics based on the photothermal effect. A thin copper film (of 20 µm thickness) was formed on the surfaces of the target materials so that measurements could not be affected by the characteristics of the target materials. In addition, phase delay signals were acquired from the rear sides of the target materials to exclude the influence of the pump beam, which is a problem in existing thermal conductivity measurement methods that use the photothermal effect. To verify the feasibility of the proposed measurement technique, thermal conductivity was measured for copper, aluminum, and stainless steel samples with a 250 µm thickness. The results were compared with literature values and showed good agreement with relative errors equal to or less than 0.2%.

Numerical Study on Effective Conditions for the Induction of Apoptotic Temperatures for Various Tumor Aspect Ratios Using a Single Continuous-Wave Laser in Photothermal Therapy Using Gold Nanorods.

Photothermal therapy can serve as an alternative to classic surgery in the treatment of patients with cancer. However, using photothermal therapy can result in local overheating and damage to normal tissues. Therefore, it is important to determine effective heating conditions based on heat transfer. In this study, we analyzed laser-tissue interactions in gold nanoparticle (GNP)-enhanced photothermal therapy based on the theory of heat transfer. The thermal behavior inside tissues during photothermal therapy was analyzed using numerical analysis. The apoptosis ratio was defined by deriving the area having a temperature distribution between 43 °C and 50 °C, which is required for inducing apoptosis. Thermal damage, caused by local heating, was defined using the thermal hazard value. Using this approach, we confirmed that apoptosis can be predicted with respect to tumor size (aspect ratio) and heating conditions (laser intensity and radius) in photothermal therapy with a continuous-wave laser. Finally, we determined the effective apoptosis ratio and thermal hazard value of normal tissue according to tumor size and heating conditions, thereby establishing conditions for inducing maximal levels of cell apoptosis with minimal damage to normal tissue. The optimization conditions proposed in this study can be a gentle and effective treatment option for photothermal therapy.

Effects of temperature, light, and pH on the stability of fucoxanthin in an oil-in-water emulsion.

The effects of temperature, light, and pH on the stability of fucoxanthin in an oil-in-water emulsion were investigated with analyzing the kinetics and thermodynamics of fucoxanthin degradation. In the absence of light and air at pH 4.6, increasing the temperature from 25 to 60 °C significantly promoted fucoxanthin degradation. Total and all-trans fucoxanthin demonstrated an energetically unfavorable, non-spontaneous degradation with an Arrhenius temperature dependence. Increasing the light intensity up to 2000 lx at 25 °C and pH 4.6 caused a sharp degradation of total, all-trans, 13-cis, and 13'-cis fucoxanthin, but promoted the formation of the 9'-cis isomer. In the absence of light and air at 25 °C, decreasing the pH to 1.2 caused significant fucoxanthin degradation, whereas increasing the pH to 7.4 retarded the degradation. The property with the greatest influence on fucoxanthin stability was pH, followed by temperature and then light. Total and all-trans fucoxanthin followed first-order degradation kinetics.

Deciphering the interactions of fish gelatine and hyaluronic acid in aqueous solutions.

The interactions of fish gelatine (FG) with hyaluronic acid (HA) are studied in an aqueous environment at 25°C by turbidimetric titration, confocal scanning laser microscopy, dynamic light scattering, zeta potentiometry, spectrophotometry with methylene blue, and construction of state diagrams. FG forms soluble complexes with HA above a boundary pH (pHφ1), where both biopolymers are net-negatively charged, but develop insoluble complexes as liquid-state complex coacervates below pHφ1, where the two biopolymers are oppositely charged. The insoluble complexes are continuously aggregated with further acid titration, followed by immediate visible phase-separation when another boundary pH (pHp) is reached. The complex formation is mainly driven by electrostatic attractions rather than hydrogen bonding or hydrophobic interactions. The complex formation is promoted by increasing FG-to-HA weight ratio or total biopolymer concentration, or at a low ionic strength, but significantly suppressed in the presence of high ionic strength.

Optimization of Manufacturing Conditions for Improving Storage Stability of Coffee-Supplemented Milk Beverage Using Response Surface Methodology.

This study aimed at optimizing the manufacturing conditions of a milk beverage supplemented with coffee, and monitoring its physicochemical and sensory properties during storage. Raw milk, skim milk powder, coffee extract, and emulsifiers were used to manufacture the beverage. Two sucrose fatty acid esters, F110 and F160, were identified as suitable emulsifiers. The optimum conditions for the beverage manufacture, which can satisfy two conditions at the same time, determined by response surface methodology (RSM), were 5,000 rpm primary homogenization speed and 0.207% sucrose fatty acid emulsifier addition. The particle size and zeta-potential of the beverage under the optimum condition were 190.1 nm and - 25.94±0.06 mV, respectively. In comparison study between F110 added group (GF110) and F160 added group (GF160) during storage, all samples maintained its pH around 6.6 to 6.7, and there was no significant difference (p<0.05). In addition, GF110 showed significantly higher zeta-potential than GF160 (p<0.05). The particle size of GF110 and GF160 were approximately 190.1 and 223.1 nm, respectively at initial. However, size distribution of the GF160 tended to increase during storage. Moreover, increase of the particle size in GF160 was observed in microphotographs of it during storage. The L* values gradually decreased within all groups, whereas the a* and b* values did not show significant variations (p<0.05). Compared with GF160, bitterness, floating cream, and rancid flavor were more pronounced in the GF110. Based on the result obtained from the present study, it appears that the sucrose fatty acid ester F110 is more suitable emulsifier when it comes to manufacturing this beverage than the F160, and also contributes to extending product shelf-life.

Elucidation of aqueous interactions between fish gelatin and sodium alginate.

The interactions between fish gelatin (FG) and sodium alginate (AL) in aqueous solutions were investigated at 25°C by turbidimetric acid titration, zeta potentiometry, dynamic light scattering, methylene blue spectrophotometry, confocal microscopy, and three types of state diagram. FG formed solid-state insoluble complexes, i.e., precipitates, with AL, mainly by electrostatic attractions; the complex formation was significantly influenced by pH, FG-to-AL weight ratio, total biopolymer concentration (CT), and ionic strength. The insoluble complexes formed below a boundary pH (pHφ1) underwent continuous aggregation during acid titration, until immediate visible precipitation occurred at another boundary pH (pHp). The formation and aggregation of insoluble complexes were facilitated by increasing CT or adding small amounts of NaCl, but were greatly suppressed in the presence of high NaCl concentration. The insoluble complexes were formed reversibly depending on pH and transformed to a coupled gel network after 24h incubation, depending on pH, CT, and ionic strength.