預(yù)熱是大多數(shù)物料烘干前需要做的第一步，因?yàn)橥ǔＧ闆r下，熱泵烘干的溫度要求是高于環(huán)境溫度的，特別是在氣溫低的時(shí)候或者北方地區(qū)，預(yù)熱顯得更加重要。預(yù)熱階段由于烘干房初始溫度較低，物料水分蒸發(fā)較少，因此濕度相對(duì)較低，一般只加熱不進(jìn)行排濕，以保證物料迅速升溫達(dá)到物料內(nèi)外溫度平衡，空氣濕度越大、熱焓值越高、導(dǎo)熱效果越好。
Preheating is the first step before drying most materials, because
usually, the temperature of heat pump drying is higher than the ambient
temperature, especially in low temperature or northern areas, preheating
is more important. In the preheating stage, due to the low initial
temperature of the drying room and less evaporation of material
moisture, the humidity is relatively low. Generally, only heating is
used without moisture removal, so as to ensure that the materials can be
heated rapidly to achieve the internal and external temperature balance
of materials. The greater the air humidity, the higher the enthalpy
value, and the better the heat conduction effect.
預(yù)熱時(shí)間長(zhǎng)短需要根據(jù)定網(wǎng)站建設(shè) 伺服液位儀 防撞墻模具 唐山護(hù)欄 遮陽網(wǎng) 風(fēng)電基礎(chǔ)模具料屬性、物料數(shù)量和環(huán)境溫度來確定，一般為兩到三個(gè)小時(shí)即可，預(yù)熱溫度通常不能太高，最好稍微低于物料烘干的本身溫度要求，如果溫度太高可能導(dǎo)致物料外觀和顏色的變化以及營(yíng)養(yǎng)成分的流失，比如碎裂、變黑等等。
The preheating time shall be determined according to the material
properties, material quantity and ambient temperature, generally two to
three hours. The preheating temperature shall not be too high, and it is
better to be slightly lower than the temperature required for drying
the material. If the temperature is too high, it may lead to changes in
the appearance and color of the material and the loss of nutrients, such
as fragmentation, blackening, etc.
