抄録
In order to research the heat balance of the fruit, the author carried out the observations of fruit temperature(apple and egg plant), air temperature, wind velocity and solar, sky radiation from July to October in 1956.
The temperature of fruit situated near the ground were measured with copper-constantan junction at several positions of upper surface, 1.5cm depth from the upper surface, center, lower surf ace and 1.5cm depth from the lower surface, and recored by oscillo-graph.
The heat balance at fruit surface in unit time was showed by following formula;
F=I-R-A (1)
F: heat stored in the fruit,
I: absorbed incoming radiation from the sun,
R: outgoing flux of long wave radiation from the fruit,
A: flux of energy from the fruit surface as sensible heat, all the above being expressed in cal/fruit.
Assuming the average fruit temperature to be t1 and t2 at times T1 and T2, respectively, the heat stored in the fruit (F) is calculated;
F(T2-T1)=4/3πr3×cw(t2-t1) (2)
where r and cw are radius and heat capacity of fruit, respectively.
The absorbed incoming radiation from the sun (I) is represented by;
I=(1-α)(πr2×D+4πr2×S) (3)
where D and S are solar radiation and sky radiation, respectively, and α is the albedo of the fruit surface.
The outgoing flux of long wave radiation from the fruit (R) is found;
R=r+2/r+1βα2π[σTf14-σTα4(a+b√e)] (4)
where r, β and a are vapor pressure (mmHg) near the ground, emissivity (absorptivity) of fruit and radius of fruit, respectively, and e, Tf1 and Ta are the vapor pressure (mb) near the ground, absolute temperature of upper fruit surface and air.
The flux of energy from the fruit surface as sensible heat (A) is calculated from the formula (1).
From the formulae (1), (2) (3) and (4) the heat balance of the fruit at various periods was calculated and showed in Tab. 2.
It is recognized that proportions of heat stored in the fruit (F), flux of energy from the fruit surface as sensible heat (A) and outgoing long wave radiation (R) to radiation from the sun (I) are showed to be 3-7%, 82-90% amd 6-12%, respectively, in the day time.
In the night, the fruit received the heat from the air by Austausch (A) as air temperature was higher than fruit surface temperature, and lost by the long wave radiation (R) from the surface.
Then, fruit lost the heat by the amount corresponding to the difference between R and A.
The heat transfer coefficients from the fruit surface in calm condition are showed in Tab. 3, and the difference between them in stable and unstable is clearly recognized.
The temperature distribution in the fruit is showed in Fig. 1., and the large difference between upper surface temperature and lower surface temperature is recognized.
