Improving drying performance of tumble dryer

Determination of moisture level of textile products has a great importance in processes such as textile production, textile dyeing and textile drying. Measuring the textile moisture level is a critical parameter for tumble dryers. The tumble dryer was started to produce in 1840. Since the early 2000s, it has entered a white-goods market in Turkey. In the winter season, laundry is not hung out. Also new buildings do not have balconies, so the drying machine is necessary for house. Tumble dryers perform the drying process of laundry that washed in the washing machine. One of the critical issues in tumble dryer is the detection of laundry moisture level. Dryers provide homogeneous drying when they can detect the moisture level. It can also improve energy efficiency by optimizing the drying time of tumble dryer. There are two types tumble dryer in white-goods market. One is a heat pump tumble dryer and the other is a resistance heater tumble dryer. In resistance heater, the air temperature is raised to 90 ° C and sent into the drum. The laundry is dried with the hot air. Tumble dryers with resistance heater work with timers. There is no sensor system to detect the moisture level of the laundry. Only the temperature inside the drum is controlled using the temperature sensor. The user adjusts the timer before the drying cycle, which is done with time adjustment without measuring moisture level of laundry. The low time input by the user causes the laundry to not be homogeneously dried. Over-setting of timers causes the clothes to overheat after drying. It damages the laundry. In tumble dryers with heat pump, air is heated to 55 ° C and sent into the drum. In the heat pump tumble dryers, conductivity is measured by the conductivity plates and the laundry moisture level is calculated by the measured conductivity value. The conductivity plates are fixed in the machine in the stationary area at the front of the drum. Although this method works better than the resistance heater dryer, the humidity level of all the laundry cannot be detected because the measurement is made from a fixed point. In addition, conductivity plates cannot be measured at points where the laundry conductivity is low at the end of the drying cycle. Low conductivity raises the laundry resistance above the level that the conductivity plates can measure. When the resistance value exceeds the level that the conductivity plates can measure, the dryer uses a timer according to the selected drying program and finishes the drying cycle with timer. At the end of the drying cycle, the completion of the drying cycle with the timer, as resistance heater dryers, causes homogeneous drying problems. In this study, a measurement system was developed to solve the problem of sensitive moisture level detection in textile products. With the developed measuring system, high resistance measurements at low voltage levels are made precisely. With the same sensor design, low resistance values and high resistance values can be measured accurately and precisely. Two calibration circuits are used to accurately measure low and high resistance levels in the developed measurement system. When the drying cycle starts, humid cloths have resistance values of about 70kΩ-150kΩ. At the beginning of the cycle low resistance levels are measured. The calibration circuit is software-switched for low resistances. so that a precise measurement can be made. When the resistance value measured on the laundry reaches 7MΩ, the accuracy of the measuring system decreases and the resistance values can not be accurately measured. When the resistance value reaches 7MΩ, the measurement circuit is switched by software. The calibration circuit is switched to high resistance measurement. At high resistance levels, the current level through the measurement circuit reaches very low values, so the circuit is affected by noise. Filter circuits were used in the calibration circuit to prevent this noise. In addition, high resistance values occur at the end of the drying cycle because the moisture level of laundry reaches very low levels. Reading the resistance values with an ADC port is causing trouble. The input impedances of the ADC ports in microprocessors are considered to be infinite in theory. In practice, the ADC inputs of the processors have 100 MΩ input impedances. When the resistance level on the laundry reaches high values, it acts as a voltage divider circuit together with the ADC port. The calibration circuit and the ADC ports are isolated by an opamp buffer circuit. Thus, both low and high resistance levels can be accurately measured. In order to use the developed measuring system in the dryer, a special mobile sensor device has been designed. The mobile sensor device was used to detect the moisture level of the laundry by being thrown into the drum together with the laundry. The moisture level of all fabrics has been made measurable by the ability to make high resistance measurements and to move within the drum with the laundry. Drying experiments were carried out with the developed sensor system. The moisture level of the laundry was measured until drying cycle ended and dryness detection was performed with the sensor system. Thus, it is presented as a solution to the problem of measuring the moisture level in dryers. Although the dryer cannot accurately measure 10% or less dryness level with the existing sensor structure, it is possible to make precise measurements with the new designed sensor system and algorithms.