Effect of hydrophobic coating on inside wall of pipe on adhesion/fixation of crystal on the surface was investigated to inhibit the pipe blockage of erythritol slurry flow. In the experiment, the pipe, through which erythritol slurry flowed, was cooled from outside, and the fixed crystals inside the wall were observed. Transparent acrylic pipe was used, and 2 types of hydrophobic coating were tested. As a result, the relationship between flow velocity and heat flux when fixation of crystal occurs in the coating pipes was almost same with bared pipe. This means the fixation of crystals cannot be inhibited by those types of coatings. However it was found that the mass of crystals fixed in the pipe can be reduced in the pipes of hydrophobic coating, when the erythritol slurry flow forms heterogeneous flow or homogeneous flow.

In this study, natural convection characteristics of a suspension having fine dispersoid in a rectangular vessel with vertical heating/cooling walls were studied numerically. The suspension was treated as single-phase Newtonian fluid and phase change of dispersoid was modelled by using solid fraction which represents the ratio solid phase dispersoid. By comparing the experimental results with the simulation results, it was confirmed that formation of multiple temperature layer can be modelled using the solid fraction although the heat transfer characteristics did not show reasonable agreement. Moreover, the simulation results indicated that the formation of multiple temperature layer was attributed to the formation of solid fraction distribution inside the suspension.

The effects of n-Decane (DCA) and n-Octane (OCT) on the crystallization of n-Hexadecane (HD) were investigated to systematically assess the effect of lipid component interactions on lipid supercooling. We plotted the crystal nucleation temperature against the equilibrium freezing point for the HD-DCA and HD-OCT systems and found a first-order correlation. However, slope evaluation revealed that HD did not supercool as much as the aqueous solution system. n-Alkanes are nonpolar and form weaker molecular interactions than aqueous solutions, possibly contributing to their low supercooling temperature. Supercooling progressed more in the HD-DCA than in the HDOCT system, demonstrating that the degree of supercooling is dependent on the lipid component interactions.

Heating system of EV consumes electric energy for travel and shortens mileage per charge. An electric heater has a simple structure, but its efficiency is low with its cop less than 1. A heat pump system, on the other hand, is more efficient and its heating energy utilization efficiency is higher. However, it has some problems to solve. One of them is frost formation on the heat exchanger surface, and this lowers the heat exchange performance. In the case of the heat pump system for buildings, defrosting operation temporarily stops heating and air blower at outdoor heat exchanger to melt the frost. However, as for EV heat pump system, air blow at heat exchanger cannot be stopped while the vehicle is running. So it keeps operating with frost formation on outdoor heat exchanger. In this paper we study the change of the heating efficiency and the performance under the condition of frost formation.

In this study, a frost layer was fabricated for 60 minutes by reproducing the temperature and humidity environment of the outdoor heat exchanger during heating operation of the air conditioner, and its effective thermal conductivities and densities were measured every 15 minutes. The environmental conditions at the time of the experiment were as follows: the air temperature at 1.3 to 1.8 ℃, the absolute humidity at 0.0033 to 0.0036 kg/kg(DA), the wind velocity near the substrate at 2.0 to 2.3 m/s and the cooling surface temperature at -17.7 to -17.2 ℃. The thermal conductivities was measured by 3ω method, and the growth process of the frost layer was observed by a digital microscope. The thermal conductivities and densities of the frost layer increased with an increasing elapsed time, the thermal conductivities was in the range of 0.05 to 0.14 W/ (m·K), and the densities was in the range of 55 to 115 kg/m³. The increasing rate of frost layer formation was remarkable in the formation time of 15 to 30 min, and was gradual after the formation time of 30 min. In addition, the thermal conductivities increased with an increasing density.

In this study, the effect of the surface properties on the microstructure of the ice crystal in the frost layer is investigated by using the X-ray micro CT. The frost formation process begins with the condensation of water vapor on the cold surface as the supercooled liquid water droplets. After freezing the droplets, the columnar crystals appear from the top of the ice droplets, and the frost layer is formed. The surface properties of the cooling surface affect the droplet shapes of the dropwise condensation on the initial stage of frost formation. In this study, the frost layer is formed on the silicon substrate with different contact angles of less than 15 deg. or 96.2 deg. On the hydrophobic surface, the relatively small ice droplets are formed on the silicon substrate, and the plate type ice crystals cover on the ice droplets. The local frost density became small at the upper part of the plate type ice crystals.

Frost formation on heat exchangers has been matter in years at refrigeration and air-conditioning domain, because it becomes a factor for decreasing heat exchange efficiency and increasing resistance of flow, and so defrosting is absolutely necessary. Therefore mechanical defrosting without melting is proposed for improving COP, and reducing the mechanical adhesion of frost crystal on cooling surface is major problem. In this study, we proposed the M-shaped microfabricated cooling surface for reducing the mechanical adhesion on cooling surface. We investigate the effect of M-shaped surface on the formation and growth of frost crystal by CFD simulation and observation of cooling surface. Then, we confirm superiority of M-shaped about effect on reducing the cooling surface where frost forms and constriction of bridging gaps in frost crystals.

Frosting is a phenomenon in which both heat and mass transfers take place simultaneously, and it is also a transient one in that frost crystals are formed and then grow from the cooling surface to form a frost layer on the surface. With a systematic understanding of the phenomenon, a reduction in energy consumption in low temperature devices can be achieved through the prevention and control of the problematic frost formation and growth in heat exchangers of such devices. The present study carries out a fundamental research on the method of reducing the frost deposition in the region I (-40.1°C ≤ t_w<0°C , t_w : cooling surface temperature). As a result, we obtained the possibility of reducing the frost deposition.

Frost formation on the air side of an air-refrigerant heat exchanger operating under low temperature conditions results in an increase in thermal resistance and an increase in pressure drop. We have focused on the removal of water vapor in the air causing frost layer by adsorbent. In this study, an adsorbent-coated fin-and-tube heat exchanger under a continuous frosting-condition such as the outdoor unit of air-conditioner has been evaluated experimentally. The effect of inlet air velocity on heat transfer characteristics and mass transfer characteristics with frost formation of the test heat exchanger was investigated. The result showed that the frost layer thickness of the test fin surface was zero for about 10 minutes after the start of the experiment in the case of 1.0 m/s. It was found that the adsorbent has an effect on the frost formation suppression.