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Drying introduction

Introduction of the drying process

Drying is the most important operation and adds to the cost of production. Drying of the textile is done in two stages i.e either the intermediate or finishing stages. 

Technologists are motivated to investigate energy-saving techniques and alternative non-conventional sources as a result of the decreasing energy resources and the rising expense of fuel. 

Technologists need to explore energy saving without harming environmental sources.

I.e.- eco-friendly as well as an economical solution for energy utilization.

Drying machine
Drying machine


Drying of textile is the removal of water from wet fabric by evaporation process due to the application of heat.

Drying occurs through the vaporization of water by supplying heat to the wet fabric. 

We can supply heat to textile materials in various ways like heating with contact rollers, heating in the air and by radiation also hence, based on ways of heat supply following are the methods of heat application. 

I.e - Heat may be supplied by : 

(A) Conduction or contact (drying cylinders)

(B) Convection (centre, tumble dryer),

(C) Radiation (infrared, microwave or radiofrequency electromagnetic field).

 

Importance of drying

  • The wet fabric is directly taken for printing or dyeing then due to the presence of water inside it it is difficult for the dye to penetrate inside the fabric. 
  • Print paste viscosity will decrease which results in a faint printing effect.
  • Due to the presence of water the interstitial spaces between fibres are blocked which will not allow either dye or chemicals to penetrate inside and result in faulty printing or dyeing.
  • Due to moisture inside the fabric, further processing will be difficult so drying is an important operation.
  • If drying is not done, problems in further processing will be the result.
  • For the evaporation of water, we require more steam because the specific heat of water is 1 kcal/kg °C as well to heat dry air inside the centre we require more energy.

Basic terms:

(1) Sensible heat: Heat that causes a change in temperature 

(2) Latent heat: Heat that causes a change in phase without temperature change. i.e heat supply to boiling water to convert into water vapour

(3) Specific heat: Quantity of heat required to raise the temperature of unit mass by unit degree Celsius.

Heat energy vs temperature for drying
Heat energy vs temperature for drying


Water has a specific heat of 1 kcal/kg °C, so to boil 1 kg of water at 30 °C, 70 kcal of energy are needed as sensible heat; in contrast, 540 kcal/kg are needed as latent heat of vaporisation to convert the phase from liquid to vapour.

Additionally, a large volume of hot air will be pumped as an air-drying medium.

Air is a poor heat exchange medium because of its low specific heat of 0.24 kcal/kg.C.

As a result, overall drying requires a lot of energy.

 

Recognizing this process houses made progress on three principle objectives:

i. To eliminate or minimize intermediate drying operations

ii. To reduce the amount of water to be evaporated

iii. To cut the cost of drying by implementing efficient measures

All these measures are to minimize wastage or to conserve energy.


Question 

  1. What is the drying process?
  2. Why Drying is important? What if drying is not done
  3. Which terms are useful for drying process understanding? explain those.


Continue read,

Part 1 Drying introduction 

Part 2 Role of Moisture in the drying process

Part 3 Drying method - Conduction and Radiation

Part 4 Drying method - Convection


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