Experimental and theoretical studies were conducted to investigate the thermal contact resistances (TCRs) between two aluminum rods. One pair of aluminum rods each having a flat rough surface and four pairs of aluminum rods each having a flat convex rough surface were used as specimens. The flat convex rough surface was composed of a contact and a noncontact surface, and the specimens were prepared by changing radius and height of the contact surface. In experiments, after a prescribed pressure was loaded on a pair of the aluminum rods, the top of the upper rod was heated by a film heater while the bottom of the lower rod was cooled using a cooling block. The TCR between the two rods was evaluated from steady-state temperature distributions in the rods. The experimental results of the TCR for the flat rough surfaces were compared with the calculated values by Sanokawa’s equation. Based on a concept of analogy between an electric and a thermal resistance network, two simple equations to evaluate the TCR for the flat convex rough surfaces were derived. These two equations were obtained by dividing the physical model perpendicular (Case I) and parallel (Case II) to the heat flow direction. The simple equation of Case I was moreover modified to consider the influence of the constriction/spreading resistance in the rods, and its validity was confirmed by comparing the calculated values with the experimental results.
Agricultural crop plants, vegetable and flower and ornamental plants, have an optimum growth temperature range that concentrates within 15-25 °C. A seasonal temperature change has strong influence on growing of agricultural products. The soil warming for plant husbandry is one of the effective growth promotion methods for agricultural crop plant in cold season. Generally, the ridge warming is performed by warm water circulation of underground. Moreover, there is another research which observed the growth process of the Welsh onion using an electrically heated wire for soil warming. These studies showed that the soil warming brings growth promotion of agricultural products. But all passed studies are carried out by using the heavy oil or electric power for soil warming as fuel.
The experimental result of previous study was shown that the relationship between heat amount of soil warming for plant husbandry by ground heat and the growth promoting effect in cold season. The growth promoting effect was recognized by the previous experimental study that had been carried out under the very small heat amount soil warming. The underground 2-4m ground heat source that keeps temperature range 15-25 °C through a year was used for soil warming.
This study shows the relationship between growth promoting effect and heat amount of soil cooling in warm season. The growth promoting effect is proved by the Japanese-mustard-spinach cultivation experiment by using both ground and high-bench at the actual ridges. The growth promoting effect, weight, height and number of leaves, is evaluated in 12 or 10 times actual experiment for five years. This paper describes the relationship between growth promoting effect and the heat amount of soil temperature regulation by using copper pipe or water circulation. The new soil cooling system that is suggested by this study is able to cool the ridge at the heat amount range of < 25 MJ/m2, and it brings the growth-promoting rate of 13-22% on cultivation.