3-7.Three types of drying 2.Drying of the surface attached water

Even if it tells “dryness” to a mouthful, there are three kinds of dry work.

They are dryness of surface water of adhesion, dryness of the coating film, and internal dryness of material.
Since the preceding sections has explained the internal dryness, this section explains the surface dryness.

The drying time of surface adhesion water is determined by supply of evaporative latent heat.

The saturated vapor pressure of water and latent heat of evaporation

Temp.	Pressure	latent heat
℃	mmHg	kcal/kg	kJ/g
0	4.6	597.1	2.502
1	4.9	596.6	2.500
2	5.3	596.0	2.498
3	5.7	595.4	2.495
4	6.1	594.9	2.493
5	6.5	594.3	2.491
6	7.0	593.8	2.488
7	7.5	593.2	2.486
8	8.0	592.6	2.483
9	8.6	592.1	2.481
10	9.2	591.5	2.478
11	9.8	590.9	2.475
12	10.5	590.4	2.473
13	11.2	589.8	2.471
14	12.0	589.3	2.469
15	12.8	588.7	2.466
16	13.6	588.1	2.464
17	14.5	587.5	2.461
18	15.5	587.0	2.459
19	16.5	586.4	2.456
20	17.5	585.9	2.454
21	18.6	585.3	2.452
22	19.8	584.8	2.450
23	21.1	584.2	2.447
24	22.4	583.6	2.445
25	23.8	583.1	2.443
26	25.2	582.5	2.440
27	26.7	581.9	2.438
28	28.3	581.4	2.436
29	30.0	580.8	2.433
30	31.8	580.2	2.431
31	33.7	579.7	2.428
32	35.7	579.1	2.426
33	37.7	578.5	2.423
34	39.9	578.0	2.421
35	42.2	577.4	2.419
36	44.6	576.8	2.416
37	47.1	576.2	2.414
38	49.7	575.7	2.412
39	52.4	575.1	2.409
40	55.3	574.5	2.407
41	58.3	574.0	2.405
42	61.5	573.4	2.402
43	64.8	572.8	2.400
44	68.3	572.2	2.397
45	71.9	571.7	2.395
46	75.7	571.1	2.392
47	79.6	570.5	2.390
48	83.7	570.0	2.388
49	88.0	569.4	2.385
50	92.5	568.8	2.383
51	97.2	568.2	2.380
52	102.1	567.6	2.378
53	107.2	567.1	2.376
54	112.5	566.5	2.373
55	118.1	565.9	2.371
56	123.9	565.3	2.368
57	129.9	564.7	2.366
58	136.1	564.1	2.363
59	142.7	563.6	2.361
60	149.4	563.0	2.359
61	156.5	562.4	2.356
62	163.8	561.8	2.354
63	171.5	561.2	2.351
64	179.4	560.6	2.349
65	187.6	560.0	2.346
66	196.2	559.5	2.344
67	205.0	558.9	2.341
68	214.3	558.3	2.339
69	223.8	557.7	2.336
70	233.8	557.1	2.334
71	244.1	556.5	2.331
72	254.7	555.9	2.329
73	265.8	555.3	2.326
74	277.3	554.7	2.324
75	289.2	554.1	2.321
76	301.5	553.5	2.319
77	314.2	552.9	2.316
78	327.4	552.3	2.314
79	341.1	551.7	2.311
80	355.3	551.1	2.309
81	369.9	550.5	2.306
82	385.0	549.9	2.304
83	400.7	549.3	2.301
84	416.9	548.7	2.299
85	433.6	548.1	2.296
86	450.9	547.5	2.294
87	468.7	546.9	2.291
88	487.2	546.2	2.288
89	506.2	545.6	2.286
90	525.9	545.0	2.283
91	546.2	544.4	2.281
92	567.1	543.8	2.278
93	588.7	543.2	2.276
94	611.0	542.6	2.273
95	634.0	541.9	2.270
96	657.7	541.4	2.268
97	682.1	540.7	2.265
98	707.3	540.1	2.263
99	733.3	539.4	2.260
100	760.0	538.8	2.257
101	787.0	538.1	2.254
102	815.2	537.4	2.251
103	844.2	536.8	2.249
104	874.5	536.2	2.246
105	906.1	535.6	2.244
106	938.4	535.0	2.241
107	971.6	534.3	2.239
108	1003.7	533.7	2.236
109	1040.0	533.0	2.233
110	1074.6	532.4	2.231

The quantity of heat which heated material becomes a constant drying period, while waterdrop is on the surface, since it is consumed as vapor-ized latent heat.

Although it can heated to the temperature which can untill withstand the material, as shown in the following table, there is only a difference of 10% to 100 ℃ from 0 ℃.

It seems that there is little necessity of raising material temperature by force.

<<Evaporation heat of the water 1g >>

Temp.℃	0℃	20℃	40℃	60℃	80℃	100℃
latent heat	2502J	2454J	2407J	2359J	2309J	2257J

The adhering water has been adhered by the interfacial tension on the material surface.

The vapor pressure of water adhering is equal to the saturated vapor pressure, and since the evaporation temperature of water is proportional to pressure, if low pressure and a vacuum are used, low-temperature drying will be made.