Eiji Hihara

Mechanism of absorption enhancement by surfactant

Abstract In absorption refrigeration technology, it is well known that the water vapor absorption into the lithium bromide (LiBr) aqueous solution is enhanced by the addition of surfactant. The Marangoni effect plays a role but its mechanism is not clearly understood yet. In the present study, the existence of instability due to Marangoni effect was investigated using the linear stability analysis, based on the salting out effect. Then the vapor absorption augmentation was estimated by the numerical simulation of cellular convection. Both theoretical results qualitatively agree well with the experimental ones.

Effect of surfactant on falling film absorption

Abstract Absorption of vapour into a falling film of absorbent solution is frequently used for absorption heat pumps and chemical processes. For an improvement in absorption rate, a small amount of surfactant is added to the solution. In the present research, processes of heat and mass transfer are experimentally investigated for the case of water vapour absorption into aqueous solutions of lithium bromide flowing on a flat plate. Variables considered are flow rate of inlet solution, concentration of additive and inclination angle of the plate. The use of 2-ethyl-1-hexanol as an additive results in a four- to five-fold enhancement in absorption rate. The occurrence of surface disturbances does not have a direct relation to the solubility limit of the additive. A qualitative discussion of additives in the role of inducing surface disturbances is presented.

Boiling Heat Transfer of Carbon Dioxide in Horizontal Tubes

In this study, boiling heat transfer coefficients of carbon dioxide in horizontally located smooth tubes were experimentally investigated. The inner diameter of heat transfer tubes was 1, 2, 4, and 6 mm. Experiments were conducted at evaporating temperature of 5 and 15 °C, heat fluxes from 4.5 to 36 kW/m2 , and mass fluxes from 360 to 1440 kg/m2 s. The heat transfer coefficients in the pre-dryout region and post-dryout region were investigated, as well as the dryout quality. Due to the small viscosity and surface tension of CO2 , the dryout occurs at a small quality from 0.4 to 0.7. The inception quality decreases with the increase of mass flux, and is affected by the heat flux and tube diameter; the effects of heat flux on the heat transfer coefficient are much significant in the pre-dryout region, which is related with the activation of nucleate boiling. On the contrary, the effects of mass flux are relatively low due to the low two-phase density ratio near the critical point. In addition, this tendency becomes more significant when the small tube is tested; In the post-dryout region, mass velocity is the dominating factor on heat transfer coefficient. At small mass flux, the heat transfer coefficient decreases with the increase of quality, while at large mass flux such as 1440kg/m2 s, the heat transfer coefficient turns to increasing with the quality. By increasing the evaporating temperature, the pre-dryout heat transfer coefficient increases, while the dryout inception quality and post-dryout heat transfer coefficient are not affected greatly by the evaporating temperature.Copyright

A new absorption refrigeration cycle using solar energy

Abstract A new type of absorption refrigeration cycle that is co-driven both by solar energy and electricity was evaluated. The principle of a heat transformer was applied to the absorption refrigeration system to increase its efficiency. In this paper, a thermodynamic model describing the performance of the new cycle was developed and a computer program was written to evaluate its performance. The COP, condenser heat load, the theoretical minimum evaporating temperature and refrigeration capacity for a typical daily load of the system were calculated and compared with those of traditional absorption refrigeration systems. The results show that the new cycle not only overcomes some shortcomings of the traditional absorption cycle with unsteady energy input from a variable source such as solar energy, but also increases the system’s coefficient of performance.

Generation of micro gas bubbles of uniform diameter in an ultrasonic field

Consecutive images of the fragmentation of capillary waves in an ultrasonic field were obtained using a high-speed video camera through a microscope at a frame rate of 500000 frames per second. The images showed that micro bubbles of uniform diameter from 4 to 15

Boiling heat transfer of a ternary refrigerant mixture inside a horizontal smooth tube

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Prediction of air coil performance under partially wet and totally wet cooling conditions using equivalent dry-bulb temperature method

m were generated at a constant periodic rate when a small amount of gas was introduced (via a needle) into a highly viscous liquid whose kinematic viscosity was between 5 and 100 mm

A unified formula for calculating body surface area of humans and animals

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Water adsorption–desorption isotherms of two-dimensional hexagonal mesoporous silica around freezing point

. Conditions for stable generation of micro bubbles of uniform diameter were also studied by changing the inner diameter of the needle between 0.08 and 0.34 mm, excitation frequency of around 18.77 and 42.15 kHz, kinematic viscosity of liquid between 5 and 100 mm

Acceleration patterns in the lower and upper trunk during running

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