Improvement of Salt-affected Soils, Part 4: Heat Transfer Coefficient and Thermal Conductivity of Salt-affected Soils

ARTICLE IN PRESS Biosystems Engineering (2007) 96 (4), 593–603 doi:10.1016/j.biosystemseng.2006.12.003 SW—Soil and Water

Improvement of Salt-affected Soils, Part 4: Heat Transfer Coefficient and Thermal Conductivity of Salt-affected Soils G. Guo1; H. Zhang1; K. Araya2; H. Jia3; K. Ohomiya1; J. Matsuda1 1 University of Hokkaido, Sapporo 060-0009, Japan; e-mail: [email protected] Environmental Science Laboratory, Senshu University, Bibai, Hokkaido 079-0197, Japan; e-mail of corresponding author: [email protected] 3 Hejiang Agricultural Research Institute, Jiamusi, Black Dragon, People’s Republic of China; e-mail: [email protected] 2

(Received 7 March 2006; accepted in revised form 5 December 2006; published online 29 January 2007)

A new method was investigated for the improvement of salt-affected soils in regions where a sufficient amount of rainfall occurs in summer and the heat transfer coefficient and thermal conductivity of their soils were discussed. The subsoil is made coarse by soil sintering, and the capillarity from groundwater is cut-off. Thus, the rise to the soil surface of salts which are dissolved in the groundwater is prevented, and even if the groundwater level is high, the evaporation of water from the soil surface is reduced. In this paper, the heat transfer coefficient and thermal conductivity of the salt-affected soils were determined at the sintering temperatures (850–950 1C) in order to obtain basic data for soil sintering. Based on these values, design and construction of a device for soil sintering will be described in a subsequent report. The results show that the heat transfer coefficient to the steel surface was about 40 W m2K1 in the range of 280–320 1C. The heat transfer coefficient of the studied soil surfaces was about 60 W m2K1 in the range of 700–1000 1C regardless of types of soil. The thermal conductivity of pseudogley soil from Japan was about 01 W m1K1 (specimen temperature was about 900 1C, and soil water content was 0% dry basis) when the solid ratio was less than 038, and it was about 03 W m1K1 when the solid ratio was more than 038. The thermal conductivity of solonchak and solonetz from China was 01–03 W m1K1 (specimen temperature was about 900 1C, and soil water content was 0% dry basis) regardless of the types of soil and horizon. The thermal conductivity of the upper layer soils of the solonchak and solonetz did not increase with greater solid ratio because salts contained in them make for a low thermal conductivity. r 2006 IAgrE. All rights reserved Published by Elsevier Ltd

1. Introduction Salt-affected soils are formed in arid or semi-arid areas of the world and are widely distributed. In this paper, two salt-affected soils in the People’s Republic of China are examined, and their heat transfer coefficient and thermal conductivity are discussed in order to obtain basic data for soil sintering for soil improvement. One of the salt-affected soils in China is called whitish oasis soil. It is found on the North of River and Inner Mongolia provinces (about 350 Gm2). As it contains calcium carbonate (CaCO3), it belongs to the saline soil group (solonchak) according to pedological classifica1537-5110/$32.00

tion (Dudal, 1969; Scheffer & Schachtschabel, 1976; Abrol et al., 1988; Cardon & Mortvedt, 2001). The other salt-affected soil in China is called meadow alkali soil, which is common in the Black Dragon and Jilin provinces (about 35 Gm2). As it contains sodium carbonate (Na2CO3), it belongs to the sodic soil group (solonetz) according to pedological. In a previous paper (Guo et al., 2006; Jia et al., 2006), a new method of soil improvement of the salt-affected soils with sufficient rainfall was discussed; a coarse layer was provided below the subsoil. It was demonstrated with indoor soil cylinder experiments that the capillary water from groundwater could be cut-off, thus preventing 593

r 2006 IAgrE. All rights reserved Published by Elsevier Ltd

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Notation Ai As ci cs0 cp D M Ms Msx0 Nu Pr p0 Qa 

Qab 

Qcup R Re ta tb tc td tg u V Vj Vs Vsolid

sectional area of steel block, 361  103 m2 sectional area of soil heating cup, 908  103 m2 specific heat of steel (300 1C), 045 kJ kg1K1 specific heat of dry soil (900 1C), 06 kJ kg1K1 specific heat of flame (air) at constant pressure, 1189  103 (1000 1C) kJ kg1K1 diameter of burner nozzle, 80  103 m soil mass charged into soil sampler, g soil mass charged into soil heating cup, kg soil or steel mass in unit depth in heating cup, kg Nusselt number Prandtl number absolute atmospheric pressure, 101325  105 Pa input and transferred heat flow rate from flame at point A, W heat flow rate conducted from point A to point B, W radiated heat flow rate of soil heating cup, W gas constant of air, 287 Jkg1 K1 Reynolds number temperature at soil or steel surface, 1C temperature at point B, 1C temperature at point C, 1C temperature at point D, 1C temperature of burner flame (gas), 1C velocity of burner flame, m s1 volume of soil heating cup, 463  104 m3 actual volume of soil, ml volume of soil sampler, 100 ml volume of solid phase in soil sampler, ml

the rise of dissolved salts to the soil surface. It was shown that the salts accumulating in the topsoil were leached out by every rainfall, which then caused the pH values to decrease. In this paper, it was envisaged that the subsoil could be sintered by a burner to produce the coarse layer in the subsoil. This is less costly than largescale public works, where the Ap and B horizon are moved away without soil mixing, to enable gravel to be spread on the area before the soil layers are then returned. Applying the values for the soil specific heat, presented in the preceeding paper (Guo et al., 2007) the heat transfer coefficient and thermal conductivity of their soils at sintering temperatures (850–950 1C) were determined. All these values will be used for the design and construction of a device for a soil sintering machine which will be described in a subsequent report.

x x0 xab ai as0 Dp e ea es la li ls0 m n t Dt rg rbs0 rs0 y

distance from plate end, m unit depth of soil layer, m distance between point A and point B, 001 m mean heat transfer coefficient to steel surface, W m2 K1 mean heat transfer coefficient to dry soil surface, W m2 K1 pressure difference determined by pitot-tube, Pa porosity air porosity solid ratio thermal conductivity of flame (air), 8297  102 (1000 1C) W m1 K1 thermal conductivity of steel, 307 (500 1C) W m1 K1 thermal conductivity of dry soil, W m1 K1 viscosity of flame (air), 5151  105 (1000 1C), Pa s kinematic viscosity of flame (air), 1899  104 (1000 1C), m2 s1 time, s time while soil surface temperature rises from temperature ta1 to temperature ta2, s density of air, kg m3 bulk density of dry soil, kg m3 real density of dry soil, kg m3 soil water content, % d.b. (dry basis)

Subscript 1 2

initial final

2. Experimental details 2.1. Soils in this study Figure 1(a) shows a typical solonchak from a cultivated field in Sangyi, North of River, where no irrigation system is applied. The Ap horizon (pH 89) is a 200 mm layer of humic, brown soil which contains organic matter suitable for plant growth. The Bca horizon (pH 94) is a 300 mm layer of accumulated calcium and whitish soil. The C horizon (pH 97) is the white and brown parent material. The Bca and C horizons are extremely hard, and the soil penetration resistance (cone penetrometer, 301 cone angle and 16 mm base diameter) is more than 5 MPa. Figure 1(b) shows a typical solonetz for a natural pasture field in Daqing City, Black Dragon. There is no irrigation system here, either. The Ana horizon (pH

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595

Fig. 1. Typical salt-affected soils in China; (a) saline soil (solonchak, whitish oasis soil) in the Shangyi county, North of River; Ap horizon, humic soil with organic matter; Bca horizon, whitish, hard and impermeable soil where calcium accumulated; C horizon, hard parent material (b) sodic soil (solonetz, meadow alkali soil) in the Dajing city, Black Dragon; Ana horizon, soil where sodium accumulated; A horizon, humic soil with organic matter; B horizon, soil where A horizon leaches; C horizon, parent material

108) is a thin (50 mm) layer of accumulated Na2CO3 and whitish soil. The A horizon (pH 104) is a 150 mm layer of humic, black and brown soil which contains organic matter. The B horizon (pH 103) is a 200 mm layer of brown soil into which the fine clayey soil particles leach from the A horizon due to rainfall. The C horizon (pH 102) is the brown parent material. Eight types of soil specimens were tested. The Chinese soils in this study were the first (Ap), second (B) and

third (C) horizons of the solonchak [Fig. 1(a)], and the first (Ana), second (A), third (B) and fourth (C) horizons of the solonetz [Fig. 1(b)]. For comparison, pseudogley soil, which is a typical Japanese clay, was also tested. The pseudogley soil is not a salt-affected soil but an acid soil (pH 59). In addition, to determine the radiated heat of the soil heating cup, and to determine the performance of the measuring device, a steel block (S45C, 665 mm in

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diameter and 50 mm in height) with thermal conductivity of 307 Wm1 K1 [500 1C (Japanese Society of Theromophysical Properties, 1990)] was used. 2.2. Determination of heat transfer coefficient and thermal conductivity The method to determine the thermal conductivity of soils is generally a hot-wire (probe) method (Uei & Fukui, 1966; Noborio et al., 1966; Hayashi & Uei, 1971; Hayashi et al., 1974; Kasubuchi, 1977; Feng et al., 2002). Recently, a ground-source heat pump method is also used (Shonder & Beck, 2000; Hokuden, 2005). Data from these results is used to generate a theoretical analysis of the thermal conductivity of pore-solid fractals such as soils (Mitsuno et al., 1983; Ishida et al., 1983; Kasubuchi, 1984; Bruckler et al., 1987; Fricke et al., 2002; Lehmann et al., 2003; Cote & Konrad, 2005). In addition, the effects of salts such as NaCl on the thermal conductivity have been reported (AbuHamdeh et al., 2000; Nidal et al., 2000; Mochizuki et al., 2002). The thermal conductivity of soils at high temperatures has also been determined but it is similar to that at 90 1C, which is a natural state at times (Tarnawski et al., 2000a, 2000b; Hiraiwa & Kasubuchi, 2000; Momose & Kasubuchi, 2002). However, these methods cannot generally be used at high temperatures such as 900 1C because the probes which give the heatpulse are adversely affected. The measurement of thermal conductivity at about 900 1C was done only for refractory bricks (Uei &

Fukui, 1966; Hayashi & Uei, 1971; Hayashi et al., 1974). Campbell et al. (1994) reported the thermal conductivity of soils at 600 1C predicted from a theoretical equation, based on the results of them measured at 90 1C. To measure the approximate thermal conductivity and heat transfer coefficient of the salt-affected soils, a device was used to heat the soil surface of a soil layer with a burner flame, and the change of temperature in the soil was recorded. This device is similar to the actual prototype soil sintering machine, which will be described in future reports. Figure 2 shows an indoor device to measure heat transfer coefficient and thermal conductivity. Each of eight soil specimens was dried in an oven to decrease the soil water content at 5–10% dry basis (d.b.), and then, it was placed in the soil heating cup (Tarnawski & Leong, 2000). The soil mass Ms in kg was determined by a pan balance (about 065 kg), and using the volume soil heating cup V in m3 (463  104 m3), the soil bulk density rbs0 in kg m3 was calculated. The same soil specimen was put in a soil sampler (Vs ¼ 100 ml), too, and this soil mass M in g was also determined by the pan balancer. Then, the actual volume of soil Vj in ml was determined by an actual volumetric meter (Society of Soil Physics, 1987). The soil water content y in % dry basis (d.b.) was determined by an infrared lay moisture meter (Society of Soil Dynamics, 1990). With these values, the soil real density rs0 in kg m3, porosity e, air porosity ea, and solid ratio es were calculated.

Fig. 2. Device to measure heat transfer coefficient and thermal conductivity of soils, where soil layer is heated by an oil burner

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IMPROVEMENT OF SALT-AFFECTED SOILS

The solid ratio es is defined as

(1)

where Vs is the volume of the soil sampler in ml and Vsolid is the volume of the solid phase in the soil sampler in ml (Jia et al., 2006). An oil burner was mounted above the soil heating cup to heat the soil specimen. An oil burner was used because the soil mass charged into the soil heating cup Ms was about 065 kg and could not be heated by an acetylene burner with such small capacity. Besides, the oil burner will be used for a prototype machine. The distance between the tip of the burner and the soil surface was 02 m because the maximum flame temperature (about 1000 1C) was obtained in this distance as mentioned below. Figure 3 shows the schematic diagram of the soil heating cup which was made of a square steel pipe (inner dimensions are 953 mm by 953 mm and height is 50 mm). The four walls of the square pipe were insulated by rolled asbestos, and another asbestos mat was laid on the bottom. Three thermocouples [chromel (Ni+Cr)almel (Ni+Al+Si+Mn)] were set in the soil layer at the following distances from the soil surface: 10 mm (point B), 20 mm (point C) and 40 mm (point D). At these sites, each soil temperature tb, tc, and td in 1C was determined. The temperature at the soil surface ta in 1C was determined by a radiation thermometer. As the each soil specimen was heated as shown in Fig. 3, seven temperature recordings at each of four points were

p  0  R 273 þ tg

(2)

where p0 is the absolute atmospheric pressure in Pa and R is the gas constant of air in J kg1 K1. The velocity of the burner flame by the pitot-tube is given by Bernoulli’s theory: sffiffiffiffiffiffiffiffiffi 2Dp u¼ (3) rg where Dp is the pressure difference determined by the pitot-tube in Pa.

Radiation thermometer

tg

A tb

• Qab

tc td

B C

40 50

50

Asbestos

rg ¼

Thermocouple

ta • Qcup

The temperature of the burner flame tg in 1C was also determined by the radiation thermometer. A steel rod of 1 mm in diameter was set in the burner flame, and heated up at every 01 m distance from the burner nozzle, and the radiation of the steel rod was determined by the radiation thermometer. The flow velocity of burner flame u in m s1 was determined by putting a pitot-tube into the flame. The density of the flame (air) rg in kg m3 is obtained from the characteristic equation for a perfect gas:

Oil burner

200

Steel plate

2.3. Determination of temperature and velocity of burner flame

10

V solid Vs

20

s ¼

M  Vj   100 þ1 y ¼ Vs

made at 20 s intervals, and from these values, the heat transfer coefficient was calculated. Heating the soil layer was continued until the soil temperature became stable (steady state). Seven more temperature measurements at each four point were recorded, and from these values, the thermal conductivity was calculated.

D

Soil specimen 95.3

Soil cup (square pipe) 



Fig. 3. Schematic diagram of soil heating cup; ta, temperature at soil surface; Qab ; heat conducted from point A to point B; Qcup ; radiated heat of soil heating cup; tb, temperature at point B; tc, temperature at point C; td, temperature at point D; tg, temperature of flame (gas); all dimension in mm

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3. Experimental design 3.1. Determination of heat transfer coefficient to soil surface and steel surface As shown in Fig. 3, the temperature of the soil surface ta1 (about 20 1C initially) was raised by the oil burner to the temperature ta. It is assumed that the temperature of the soil layer of a unit depth x0 in m from the soil surface becomes uniformly ta. The heat given by the flame for dt is used for raising the soil temperature up to dta, and hence, the heat balance is   as0 As tg  ta dt ¼ cs0 M sx0 dta (4) where as0 is the heat transfer coefficient to the soil surface (dry soil) in W m2 K1; As is the sectional area of the heating cup (heated area of the soil surface) in m2; cs0 is the specific heat of dry soil in kJkg1K1 (Guo et al., 2007) and t is time in s. The soil mass unit depth Msx0 is given by M sx0 ¼ x0 As rbs0

(5)

Integrating Eqn (5) leads to solution and when t ¼ 0, the temperature ta ¼ ta1 exists, and after Dt, ta ¼ ta2 , and the solution of Eqn (4) is    cs0 M sx0   ln tg  ta1  ln tg  ta2 as0 ¼ (6) DtAs where: Dt is the time in s while the temperature of the soil surface rises from ta1 to ta2. The mean heat transfer coefficient to dry soils as0 can be obtained from Eqn (6). Besides, if the soil specimen in Fig. 3 is a steel block, the mean heat transfer coefficient to the steel surface ai in W m2 K1 can be also obtained from Eqn (6). The unit depth x0 for soils was determined as 001 m by measuring the actual soil depth which was heated up to 900 1C for 500 s. That for the steel was determined as 0002 m by a theoretical analysis (Koto, 1965) in which the steel surface was heated up to 700 1C for 500 s.

(665 mm in diameter) was set on the surface in order to that the burner flame heated the steel block surface alone. As the steel block was heated, seven temperature recordings at each four point were made at 2 s intervals at each point, and the heat transfer coefficient of the steel surface was calculated. Then, heating continued until the steel temperature became constant (steady state) and then the temperatures ta, tb, tc, and td were determined.The heat flow rate conducted from point A to point B Qab in W is 

Qab ¼ li Ai

ta  tb xab

where li is the thermal conductivity of the steel in W m1 K1, xab is the distance between point A and point B in m, and Ai is the sectional area of the steel block in m2. The input and transferred heat flow rate from the flame at point A Qa in W is    Q a ¼ ai A i t g  t a (8) where ai is the mean heat transfer coefficient to the steel surface. When the temperature becomes stable, the radiated 

heat flow rate Qcup in W of the soil heating cup which leaks from the wall (A–B) to atmosphere in Fig. 3 is 





Qcup ¼ Qa  Qab

(9) 

It is assumed that this radiated heat flow rate Qcup is the same as when the soil is charged alone into the soil heating cup without the steel block. Then, soil whose thermal conductivity ls0 is unknown is placed into the soil heating cup and heated from the soil surface. When temperature levels off, the temperatures ta, tb, tc and td are recorded. 

The heat flow rate Qab from point A to point B in the soil is 

Qab ¼ ls0 As 3.2. Determination of radiated heat of soil heating cup and thermal conductivity of soils

(7)

ta  tb xab

(10)

The heat flow rate transferred at point A from the flame 

Qa is Firstly, to determine the heat radiation to the atmosphere of the soil heating cup in Fig. 3 and to determine the performance of the measuring device, a round steel block (S45C, 665 mm in diameter and 50 mm in height) was set at the centre of the soil heating cup, and the clearance space between the steel block and the square pipe was filled by the pseudogley soil. In the steel block also, another three thermocouples were mounted same as shown in Fig. 3. The temperature at the surface of the steel block was also measured by the radiation thermometer. A steel plate cover which had a round hall

   Qa ¼ as0 As tg  ta

(11)

The difference between Eqn (10) and Eqn (11) is equal 

to the radiated heat Qcup of Eqn (9) and so

   as0 As tg  ta  Qcup xab ls0 ¼ As ðta  tb Þ

(12)

The thermal conductivity of the soil ls0 can be obtained from Eqn (12).

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3.3. Theoretical heat transfer coefficient One theoretical analysis of the heat transfer coefficient is flat plate theory (Koto, 1965), and it is given as Nu ¼

as0 x 00296 Re08 Pr ¼ la 1 þ 211 Re01 ðPr  1Þ

(13)

where Nu is Nusselt number; Pr is Prandtl number; x is the distance from the plate end in m and la is the thermal conductivity of the flame (air) in W m1 K1. The Reynolds number Re is given by ux (14) Re ¼ n where n is the kinematic viscosity of the flame (air) in m2 s1. Prandtl number Pr is obtained as cp m Pr ¼ (15) la where cp is the specific heat of the flame (air) at constant pressure in kJ kg1 K1, and m is the viscosity of the flame (air) in Pa s. Another theoretical analysis is jet-flow theory (Japanese Society of Mechanical Engineers, 1986), and it is represented as Nu ¼ 094Pr04 Re05

(16)

In this case, Reynolds number Re is uD (17) n where D is the diameter of the burner nozzle in m. The Nusselt number in this case is Re ¼

Nu ¼

as0 D la

Heat transfer coefficient i, Wm–2K–1

IMPROVEMENT OF SALT-AFFECTED SOILS

100 80 60 40 20 0 280

290 300 310 Temperature of steel surface t, °C

320

Fig. 4. Heat transfer coefficient to steel surface as a function of temperature of steel surface; , jet flow theory; flat plate theory; measured values Table 1 Specification of burner flame (air) at 1000 1C, burner, soil heating cup, soil and steel Parameters Kinematic viscosity n m2 s1 Specific heat at constant pressure cp, J kg1 K1 Viscosity m, Pa s Thermal conductivity l, W m1 K1 Atmospheric pressure p0, Pa Gas constant R, N m kg1 K1 Distance x, m Diameter of burner nozzle D, m Sectional area of soil heating cup As, m2 Sectional area of steel block Ai, m2 Specific heat of steel (300 1C) ci, kJ kg1 K1 Specific heat of dry soil (900 1C) cs0, kJ kg1 K1

Value 1899  104 1189  103 5151  105 8297  102 101325  105 287 575  103 800  103 908  103 360  103 045 06

(18)

4. Results and discussion 4.1. Heat transfer coefficient to steel surface and soil surface Figure 4 shows the measured heat transfer coefficient to the steel surface ai which was calculated from Eqn (6) with the temperatures at each point in the steel block and the values in Table 1. The mean heat transfer coefficient ai is about 40 W m2 K1. Figure 5 shows the measured heat transfer coefficient to the soil surface as0. The value cs0 of specific heat of soils at 900 1C determined in the previous report (Guo et al., 2007) was used (Table 1). In the range of 700–1000 1C, the values of the heat transfer coefficient of all soils were the same. Representative values of the pseudogley soil and the Ap soil of the solonchak are

shown. The mean heat transfer coefficient as0 is about 60 W m2 K1. When the soil was charged into the soil heating cup, the soil was packed tightly into it, and so, the size of soil clods became almost identical. Hence, the soil surface conditions of any soil were alike. The heat transfer coefficient to the steel surface is smaller than that to the soil surface, because of the difference in surface roughness. The roughness of the soil surface is greater than that of the steel surface, and when the flame hits the soil surface, many eddy currents are produced, so, the value of the heat transfer coefficient to the soil surface increases.

4.2. Temperature and velocity of burner flame Figure 6 shows the measured temperatures of the burner flame tg. The flame temperature was 800 1C at the nozzle port and about 1000 1C at 02 m from the nozzle,

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Velocity u, ms–1

Heat transfer coefficient  s 0, Wm–2K–1

G. GUO ET AL.

80 60 40 20 0 700

800 900 Temperature of steel surface t, °C

25 20 15 10 5 0

0

1000

Fig. 5. Heat transfer coefficient to soil surface as a function of temperature of soil surface; , pseudogley soil; , Ap soil of the solonchak; , jet flow theory; flat plate theory

0.2

0.4 0.6 0.8 1 Distance from burner nozzle, m

1.2

Fig. 7. Velocity of burner flame as a function of distance from nozzle

1200 1000 800 600 400 200 0

Heat flow rate Q, W

Flame temperature tg, °C

60

0

0.1

0.2 0.3 0.4 Distance from nozzle, m

0.5

Fig. 6. Temperature of burner flame as a function of distance from nozzle

and then, it sharply decreased with distance. The flame temperature becomes maximum at 02 m because the air which is taken in from the wall of burner cylinder has an optimum mixing with fuel at this point. Figure 7 shows the velocity of the burner flame measured by the pitot-tube and calculated from Eqn (3). The velocities are at the centre of the flame. The velocity of the burner flame was 18 m s1 at 02 m from the nozzle. 4.3. Theoretical heat transfer coefficient The burner flame is a mixture of CO2 and air, but if it is assumed that the flame consists of air alone, the specifications of air (Table 1) can be used. The sizes of the burner nozzle and the soil heating cup are also shown in Table 1. With the flame temperature (1000 1C) in Fig. 6, the flame velocity (18 m s1) in Fig. 7 and the values in Table 1, the heat transfer coefficient of the flat plate theory of Eqn (13) and that of the jet-flow theory of Eqn (16) were calculated and shown in Figures 4 and 5. The heat transfer coefficient of the flat plate theory is 419 Wm2K1, and that of the jet-flow theory is 752 W m2 K1. The value by the jet-flow theory is a little greater than that by the flat plate theory but both theoretical values of the heat transfer coefficient coincide well with the measured value.

50 40 30 20 10 0 640

645 650 655 Temperature at steel surface ta, °C

660

Fig. 8. Radiated heat flow rate of soil heating cup as a function of temperature at steel surface; , input transferred heat flow   rate Qa ; , conducted heat flow rate (point A-B) Qab ; ,  radiated heat flow rate (point A–B) Qcup

4.4. Radiated heat of soil heating cup  The radiated heat flow rate of the soil heating cup Qcup of Eqn (9) was calculated and shown in Fig. 8. In the range of 640–660 1C, the heat flow rate transferred  from the flame to the steel surface at point A Qa is about 50 W regardless of the temperature of the steel surface. The heat flow rate conducted from point A to point B  Qab in Fig. 3 is about 43 W. Hence, the radiated heat flow rate of the soil heating cup Qcup is about 7 W regardless of the temperature. Hereafter, when the thermal conductivity of soils ls0 of Eqn (12) is  calculated, Qcup ¼ 7 is used.

4.5. Thermal conductivity of soils Figure 9 shows the thermal conductivity ls0 of the pseudogley soil from Japan caluculated from Eqn (12). In Fig. 9, the soil temperature was about 950 1C at the soil surface (point A in Fig. 3), and about 850 1C in the soil (point B) and so, the mean soil temperature was about 900 1C. In this case, there is no water among the soil particles because of the high temperature. Hence, the heat conducts through only one route, i.e. soil

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0.35

0.4 Solid ratio s

0.45

0.5

Fig. 9. Thermal conductivity of the pseudogley soil at 850–950 1C as a function of solid ratio

particle–soil particle (Maeda et al., 1983). With a greater solid ratio, the route of soil particle–soil particle increases, and the thermal conductivity ls0 also increases. The thermal conductivity of the pseudogley soil ls0 is about 01 W m1 K1 when the solid ratio is less than 038 and about 03 W m1 K1 when the solid ratio is more than 038. These values are a little smaller than the values of 029–044 W m1 K1 of a clay loam (20 1C, soil water content 10% d.b.) reported by Abu-Hamdeh et al., (2000) and the values of 025–060 W m1 K1 of a clay (20 1C, soil water content 17% d.b.) reported by Nidal et al., (2000). This is because when there is water among the soil particles, so another route of heat conduction exists (soil particle–water–soil particle) and the thermal conductivity subsequently increases. Also, at high temperature such as 900 1C, the materials contained in the soil changed, that is Hashimoto & Hamano (1975) reported that kaolinite (Al2O32SiO22H2O), which is the main parent material of soils, loses its constitutent water and changes into metakaoline (Al2O32SiO2) at 600 1C. When the sintering temperature is 800–1000 1C, this metakaoline turns into transitional mullite [2(Al2O3SiO2)], and when the sintering temperature is 1300–1400 1C, the transitional mullite transforms into mullite (3Al2O32SiO2). Figure 10 shows the thermal conductivity of the solonchak soils from China, and Figure 11 shows that of the solonetz soil from China. The thermal conductivity of all soils ls0 is 01–03 W m1 K1. The thermal conductivity of the Ap and Bca soils of the upper layers of the solonchak does not increase with greater solid ratio. Similarly, the thermal conductivity of the Ana and A soils of the upper layers of the solonetz does not increase with greater solid ratio. This is because the greater amount of salts in the upper layer (the solonchak contains CaCO3 and the solonetz contains Na2CO3 ) create a low thermal conductivity (Abu-Hamdeh et al., 2000; Nidal et al., 2000).

Thermal conductivity of dry soil s0, Wm–1K–1

1 0.8 0.6 0.4 0.2 0 0.3

1 0.8 0.6 0.4 0.2 0 0.3

0.35

0.4 Solid ratio s

0.45

0.5

Fig. 10. Thermal conductivity of the solonchak at 850–950 1C as a function of solid ratio; , Ap soil; , Bca soil; , C soil

Thermal conductivity of dry soil s0, Wm–1K–1

Thermal conductivity of dry soil s0, Wm–1K–1

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1 0.8 0.6 0.4 0.2 0 0.3

0.35

0.4 Solid ratio s

0.45

0.5

Fig. 11. Thermal conductivity of solonetz at 850–9501C as a function of solid ratio; , Ana soil; , A soil; , B soil; , C soil

5. Conclusions The subsoil is made coarse by soil sintering, and the capillarity from groundwater is cut-off. Thus, the rise to the soil surface of salts which are dissolved in the groundwater is prevented. To obtain basic data for soil sintering, heat transfer coefficient and thermal conductivity of the salt-affected soils were determined at the sintering temperatures (850–950 1C). Based on these values, a device of soil sintering will be designed and built in a subsequent report. (1) The heat transfer coefficient to the steel surface was about 40 W m2 K1 in the range of 280–320 1C. (2) The heat transfer coefficient of soil surfaces studied here was about 60 Wm2 K1 in the range of 700–1000 1C regardless of the kinds of soils and horizons. (3) The thermal conductivity of the pseudogley soil from Japan was about 01 Wm1 K1 (specimen temperature was about 900 1C, and soil water content was 0% dry basis) when the solid ratio was less than 038 and about 03 W m1 K1 when the solid ratio was more than 038.

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(4) The thermal conductivity of the solonchak and solonetz from China was 01–03 W m1 K1 (specimen temperature was about 900 1C, and soil water content was 0% dry basis) regardless of the kinds of soils and horizons. The thermal conductivity of the upper layers soils of the solonchak and solonetz did not increase with greater solid ratio because salts in the upper layer produce a low thermal conductivity.

References Abrol I P; Yadav J S P; Massoud F I (1988). Salt-affected soils and their management. Soil Resources, Management and Conservation Service, Land and Water Development Division, Food and Agriculture Organization of United Nations, p 5, 9, 14 Abu-Hamdeh N H; Reeder R C; Khdair A I; Al-Jalil H F (2000). Thermal conductivity of disturbed soils under laboratory conditions. Transactions of the ASAE, 43(4), 855–860 Bruckler L; Renault P; Aries F (1987). Laboratory estimation of apparent soil thermal conductivity using a numerical approach. Soil Science, 143(6), 387–397 Campbell G S; Jungbauer J D; Bidlake W R; Hungedford R D (1994). Predicting the effect of temperature on soil thermal conductivity. Soil Science, 158(5), 307–313 Cardon G E; Mortvedt J J (2001). Salt-affected Soils. Colorado State University Cooperative Extension, No. O.503, 1–4 Cote J; Konrad J M (2005). A generalized thermal conductivity model for soils and construction materials. Canadian Geotechnical Journal, 42(2), 443–458 Dudal R (1969). About the legend of the FAO/UNESCO soil map of the world. Technical Work-Planning Conference, National Cooperative Soil Survey, Charleston, SC, January 1969 Feng M; Fredlund D G; Shuai F (2002). A laboratory study of the hysteresis of a thermal conductivity soil suction sensor. Journal of Geotechnical Testing, 25(3), 1–12 Fricke B A; Misra A; Becker B R; Stewart W E (2002). Soil Thermal Conductivity: Effects of Saturation and Dry Density, pp. 1–13. University of Missouri-Kansas City Guo G; Araya K; Jia H; Zhang Z; Ohomiya K; Matsuda (2006). Improvement of salt-affected soils, Part 1: interception of capillarity. Biosystems Engineering, 94(1), 139–150 doi:10.1016/j.biosystemseng.2006.11.007 Guo G; Zhang H; Araya K; Jia H; Ohomiya K; Matsuda J (2007). Improvement of salt-affected soils, part 3: specific heat of salt-affected soils. Biosystems Engineering Hayashi K; Uei I (1971). Rapid determination of thermal conductivity of refractory by hot-wire method (2nd report). Refractory, 23, 496–501 Hayashi K; Fukui M; Uei I (1974). New development of an apparatus for thermal conductivity measurement of refractory bricks by hot-wire method. Yogyo Kyokaishi, 82(1), 21–28 Hashimoto K; Hamano K (1975). Ceramics, p 17, 167, 217, 220, 233. Kyoritsu Press, Tokyo Hiraiwa Y; Kasubuchi T (2000). Temperature dependence of thermal conductivity of soil over a wide range of temperature (5–75 1C). European Journal of Soil Science, 51(2), 211–218

Hokuden (2005). Heat pump system of ground-souce heat. Technical Report of Hokkaido Electric Power Company Vol. 1, 1–2 Ishida T; Mitsuno T; Maruyama T (1983). Heat condition of soil under the condition of relatively low water content. Transactions of the Japanese Society of Agricultural Civil Engineers, 103, 28–34 Japanese Society of Mechanical Engineers (1986). JSME Data Book, Heat Transfer, 4th edn, p 66, 111. Maruzen Press, Tokyo Japanese Society of Thermophysical Properties (1990). Thermophysical Properties Handbook, p 21, 30, 189. Yokendo Press, Tokyo Jia H; Zhang H; Araya K; Guo G; Zhang Z; Ohomiya K; Matsuda J (2006). Improvement of salt-affected soils, part 2: interception of capillarity by soil sintering. Biosystems Engineering, 94(2), 263–273, doi:10.1016/j.biosystemseng. 2006.01.013 Kasubuchi T (1977). Twin transient-state cylindrical-probe method for the determination of the thermal conductivity of soil. Soil Science, 124(5), 255–258 Kasubuchi T (1984). Heat conduction model of saturated soil and estimation of thermal conductivity of soil solid phase. Soil Science, 138(3), 240–247 Koto Y (1965). Conductivity of Heat, p 39, 121. Yokendo Press, Tokyo Lehmann P; Staehli M; Papritz A; Gygi A; Fluehler H (2003). A fractal approach to model soil structure and to calculate thermal conductivity of soils. Transport in Porous Media, 52(3), 313–332 Maeda T; Soma K; Ikehata K (1983). Thermal properties related to water retention of organic-volcanic soils. Transactions of the Japanese Society of Agricultural Civil Engineers, 103, 13–20 Mitsuno T; Ishida T; Maruyama T (1983). Model for soil heat condition under a three-phase condition and calculation of soil heat conductivity. Transactions of the Japanese Society of Agricultural Civil Engineers, 103, 35–43 Mochizuki H; Mizoguchi M; Miyazaki T (2002). Modeling of saline soil thermal conductivity. Thermophysics Properties, 23, 123–125 Momose T; Kasubuchi T (2002). Effect of reduced air pressure on soil thermal conductivity over a wide range of water content and temperature. European Journal of Soil Science, 53(4), 599–606 Nidal H; Abu-hamdeh N H; Reeder R C (2000). Soil thermal conductivity: effects of density, moisture, salt concentration, and organic matter. Soil Science Society American Journal, 64, 1285–1290 Noborio K; Mclnnes J; Heilman J L (1966). Measurements of soil water content, heat capacity, and thermal conductivity with a single TDA probe. Soil Science, 161(1), 22–28 Scheffer F; Schachtschabel P (1976). Lehrbuch der Bodenkunde (Handbook of Pedology), pp 407–411. Ferdinand Enke Verlag, Stuttgart Society of Soil Physics (1987). Soil Physical Properties, pp 49–53. Yokendo Press, Tokyo Society of Soil Dynamics (1990). Soil Tests, pp 29–33. Yokendo Press, Tokyo Shonder J A; Beck J V (2000). A new method to determine the thermal properties of soil formation from in situ field tests. Journal of Oak Ridge National Laboratory, 27, 1–5

ARTICLE IN PRESS IMPROVEMENT OF SALT-AFFECTED SOILS

Tarnawski V R; Leong W H (2000). Thermal conductivity of soils at very low moisture content and moderate temperatures. Transport in Porous Media, 41(2), 137–147 Tarnawski V R; Gori F; Wagner B; Buchan G D (2000a). Modeling approaches to predicting thermal conductivity of soils at high temperatures. International Journal of Energy Research, 24(5), 403–423

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Tarnawski V R; Leong W H; Bristow K L (2000b). Developing a temperature-dependent Kersten function for soil thermal conductivity. International Journal of Energy Research, 24(15), 1335–1350 Uei I; Fukui M (1966). Rapid determination of thermal conductivity of refractory by hot-wire method (1st report). Refractory, 18(8), 352–360