Date of Award

5-1978

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Chemical Engineering

First Advisor

John N. Beard Jr.

Second Advisor

N. A. Bechwith

Third Advisor

P. C. Hamlne

Abstract

Tenter frame fabric dryers are one of the largest energy consumers in the textile industry. Since many of the drying characteristics of fabric are not well known, undetected changes in dryer operation often result in deleterious effects on the quality of the finished fabric. In order to minimize these effects, the dryers are often operated very conservatively, and this results in increased energy consumption. Optimal dryer operation can reduce energy consumption and increase productivity, but the present method of determining dryer operating conditions by trail-and-error is both time consuming and expensive. The purpose of this investigation was to develop analytical techinques which can be used to study the drying characteristics of fabrics in a laboratory dryer. The information gained could then be used in conjunction with a mathematical model of the drying process to determin optimal dryer operating conditions. Sample preparation techinques were developed whereby a large number of fabric sample could be prepared with reproducible initial moisture contents. This was necessary to obtain uniform fabric moisture data as a function of drying time in the laboratory dryer. By using the developed procedure, fabric samples were prepared with reproducible initial moisture contents of 1.2 ± 0.2 pounds of water per poud of dry cloth. A technique was developed for obtaining fabric temperatures as a function of drying time with a radiation thermometer. The radiation thermometer proved to be a reliable and accurate means of obtaining fabric temperatures from samples as they dried. A mathematical model of a tenter frame dryer, consisting of three ordinary differential equations, was used to describe the drying process. The model was curve-fitted to experimental fabric temperature data which produced values of three experimental parameters. Ideally, the parameters should be independent of temperature and humidity and functions only of dryer configuration and type of fabric being dried. The results of this study indicated that the experimental model parameters appeared to be temperature independent for temperatures between 150 and 260 °F and humidities between 0.0120 and 0.0140 pounds of water per pound of dry air, but humidity dependent for humidities above 0.020 pounds of water per pound of dry air. While the model had been shown previously to predicte fabric temperature profiles in tenter frame dryers, one of the purposes of this study was to show that the model would accurately predict the moisture and temperature profiles of drying fabric in the laboratory dyer. The results indicated that the mathematical model required a modification of the drying rate equation to accurately predict fabric moisture data obtained as a function of drying time in the laboratory dryer. Since the dryer air humidity is an important parameter in the mathematical model, a new procedure had to be developed using psychomatric methods, whereby low air humidities could be measured at high dryer temperatures. The psychormetric method developed gave accurate and reproducible humidity measurements for humidities as low as 0.0120 pounds of water per pound of dry air and temperature as high as 366 °F. The drying compartment of an electrically heated laboratory dryer was modified for this study in order to stimulate the drying characteristics of fabric observed in industrial tenter frame dryers. A cart was designed and fabricated which enabled the fabric samples to be rapidly inserted and removed from the dryer.

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