THERMAL CONTACT CONDUCTANCE OF A COATED PAPER/METAL INTERFACE

A better understanding of the parameters associated with heating of the coated paper during drying process would permit a more accurate design and control of the process to achieve an improved coated paper quality and printability. Following the application of the coating, the coated paper passes through non-contact dryers (i.e. infrared dryers and impinging hot air dryers). When the coating has coalesced, further drying is achieved with steam-heated, contact dryers. One parameter affecting the heat transfer from a metallic dryer drum to the coated paper is the thermal contact conductance at the interface between the coated paper and the drum. In this paper, the thermal contact conductance of a coated paper/metal interface is determined and compared to that of the uncoated paper. Two types of base stock and one type of coating are considered. The thermal contact conductance values are given as a function of the applied interface pressure.     

Method for the Design of a Contact Dryer-Application to Sludge Treatment in Thin Film Boiling

A method, based on the analysis of heat transfer, is developed for the design of contact dryers in thin film boiling for sludge treatment. An experimental device was built in order to estimate the heat flux density exchanged between a hot metallic plate and the drying sample. This specific device is made of a thick copper plate heated at a temperature above 100°C, on which the sludge is coated. The contact temperature and the heat flux density are estimated using a temperature sensor inside the copper block, and an inverse conduction method (Beck's sequential function specification method). The corresponding drying curve is deduced from an energy balance. Sludge drying was studied on an electrically heated laboratory continuous drum dryer. A simple steady state model of the drum dryer was developed by taking into account the combined effects of internal and external transfers. This model is validated by comparison with drying curves obtained from sampling and simulation. In this case, the relative importance of internal and external heat transfers is highlighted.     

MEASUREMENTS OF THERMAL CONTACT CONDUCTANCE FOR A PAPER/METAL INTERFACE AND EFFECTIVE CONDUCTIVITY OF MACHINE SAMPLES

The thermal contact conductance for a paper/metal interface and the effective thermal conductivity of paper samples were determined using an experimental contact conductance apparatus. The effects of pressure and moisture content on the thermal contact conductance and the effective thermal conductivity were investigated. The samples considered in the experiments consisted of paper machine samples from different sections of the drying section. The results are compared to those of the handsheets prepared in our laboratory.     

A SIMPLE DYNAMIC MODEL FOR SOLID TRANSPORT IN ROTARY DRYERS

The solid particle movement in a rotary drum plays an important role in drying processes. The solid distribution in the drum affects the amount of contact surface between the solid and the gas. The retention time of solids influences the time particles can stay in contact with the gas in order to transfer heat and mass. Any heat and mass transfer model for a solid particle dryer must be able to predict solid flowrate and solid hold-up. There have been several reports in the literature regarding the modelling aspects of solid transport in dryers. If the model is developed for model-based control, it must be simple and yet represent dynamics of the system accurately. This paper addresses solid motion modelling and the effects of different variables involved in solid transport phenomena. Sugar drying process is the case study in this work. A steady state semi-empirical model was modified to predict solid hold-up and flowrate in rotary dryers. This model was incorporated into a heat and mass transfer model ;o predict solid moisture and temperature for inferential and model-based control purposes. Results of several experiments that have been used to investigate dynamics of the system in terms of solid motion and to validate the model are also presented. The approach advocated in this paper is directly applicable to the transport of other solids in rotary drum equipment and can thus be regarded as a generalized model.     

A SIMPLE DYNAMIC MODEL FOR SOLID TRANSPORT IN ROTARY DRYERS

ABSTRACT

The solid particle movement in a rotary drum plays an important role in drying processes. The solid distribution in the drum affects the amount of contact surface between the solid and the gas. The retention time of solids influences the time particles can stay in contact with the gas in order to transfer heat and mass. Any heat and mass transfer model for a solid particle dryer must be able to predict solid flowrate and solid hold-up. There have been several reports in the literature regarding the modelling aspects of solid transport in dryers. If the model is developed for model-based control, it must be simple and yet represent dynamics of the system accurately. This paper addresses solid motion modelling and the effects of different variables involved in solid transport phenomena. Sugar drying process is the case study in this work. A steady state semi-empirical model was modified to predict solid hold-up and flowrate in rotary dryers. This model was incorporated into a heat and mass transfer model ;o predict solid moisture and temperature for inferential and model-based control purposes. Results of several experiments that have been used to investigate dynamics of the system in terms of solid motion and to validate the model are also presented. The approach advocated in this paper is directly applicable to the transport of other solids in rotary drum equipment and can thus be regarded as a generalized model.     

MEASUREMENTS OF THERMAL CONTACT CONDUCTANCE FOR A PAPER/METAL INTERFACE AND EFFECTIVE CONDUCTIVITY OF MACHINE SAMPLES

ABSTRACT

The thermal contact conductance for a paper/metal interface and the effective thermal conductivity of paper samples were determined using an experimental contact conductance apparatus. The effects of pressure and moisture content on the thermal contact conductance and the effective thermal conductivity were investigated. The samples considered in the experiments consisted of paper machine samples from different sections of the drying section. The results are compared to those of the handsheets prepared in our laboratory.     

Delamination behavior of lithium-ion battery anodes: Influence of drying temperature during electrode processing

One essential process step during electrode processing for lithium-ion batteries is the drying of the wet particulate electrode coating. The electrode film solidifies during evaporation of the solvent and a porous film is formed. In this study, we focus on the influence of drying temperature on the internal electrode structure of the dry film. Anode slurries that consist of graphite and an aqueous binder system were coated and subsequently dried. To assure defined and controllable drying conditions, a laboratory set-up with a temperature-controlled substrate carrier and an impingement dryer was used. To facilitate a scale-up to continuously passed dryers, the choice of experimental temperatures was based on a calculation of steady-state temperatures that result from gas temperatures that are commonly applied in industrial drying processes. The delamination behavior of the differently dried electrodes was investigated by means of a 90° peel test. The results show a strong dependency of electrode adhesion on drying temperature. A lower adhesion force at higher temperatures hints at a variation in binder content at the interface between the copper substrate and the coating layer. The formation of a consolidation layer at the air-film interface during drying is identified as a possible explanation and a criterion for consolidation layer formation is suggested.     

煤泥干燥新工艺、新装备

论述了当前发展煤泥干燥脱水的意义以及对煤泥进行火力干燥需解决的主要理论问题;介绍了泥质物料干燥新技术新工艺系统的组成及工作原理;目前经过改造设计的滚筒式干燥机已形成规模和系列化,滚筒直径φ1．5-5．2m,处理煤泥量在10-300t／h;在一些选煤厂应用后,取得了良好的经济效益和社会效益。     

Modeling of heat pump tumble dryer energy consumption and drying time

The use of heat pump tumble dryers is nowadays more common because they offer huge energy savings compared to conventional tumble dryers. Earlier studies made on conventional tumble dryers have shown that parameters such as heater power, fan speed, drum speed, weight and initial moisture content of textiles and air leakage have a huge impact on the energy efficiency and drying time. In the present study, a modified commercial heat pump tumble dryer was evaluated for energy consumption and drying time by changing operating parameters including fan speed, drum speed, and mass load. The total energy consumption and drying time were measured and corrected for the initial and final moisture content in the textiles. The experimental results based on 27 drying tests were evaluated to develop linear regression models for energy consumption and drying time, which show a good agreement with the experimental data. The results show that a large mass load, a high drum speed, and a low fan speed give the highest energy efficiency, i.e. the lowest energy consumption per kg of drying load. Larger loads extend the length of the drying cycle while higher fan and drum speeds result in shorter drying time.     

Enhancing the Energy Efficiency of Domestic Dryer by Drying Process Optimization

The domestic tumble dryers are becoming indispensable household appliances and responsible for up to 10% of the total residential energy use in developed countries. However, their energy efficiency is low. In this paper, the development of a multi-sensor computer-controlled prototype platform for fabric drying is described for improving the efficiency of dryers. The prototype platform enables the real-time control and recording of key drying parameters including heater power, air flow velocity, rotating speed of drying drum, and drying cycle time. These parameters are automatically adjusted according to the exhaust air humidity instead of the temperature which is used traditionally. Additionally, a new drying model of dividing the drying process into four stages based on the humidity of the exhaust air has been investigated to further increase the energy saving. The performance of this staged drying model is experimentally evaluated in respect to energy consumption, drying time, and the smoothness of fabric after drying. The results clearly indicate that the staged controlling of heating power input not only decreases energy consumption by 21.5%, but also improves the fabric smoothness by 0.9 grade compared to using a single heating power input for the whole drying process. The research outcome can enable the design and production of new dryers that are more energy efficient and lead to dried clothes that require less ironing, which in turn further reduces energy consumption.     

用于中药浸膏干燥的滚筒干燥机

对滚筒干燥机在罗布麻浸膏干燥上成功应用进行了研究,并与现有中药浸膏干燥机进行了对比分析,探讨了滚筒干燥机在中药浸膏干燥领域应用的可行性。     

INDIRECT THERMAL DRYING OF LIGNITE: DESIGN ASPECTS OF A ROTARY DRYER

An investigation of the thermal drying of lignite has been carried out, by using an indirect heat pilot rotary drum. The process aims at the production of dry lignite and clean steam as part of a gasification procedure. Both flighted and bare drum modes have been employed. Temperature profiles along the dryer length, the amount of evaporation (moisture conversion) and the solids residence time distribution (RTD) were measured. A non-isothermal model was tested under three different regimes of solids flow. Model integration, by taking account of experimental amount of evaporation at dryer exit and temperature profiles along the dryer length, has been utilized in the validation of drying kinetics and heat transfer correlations. Model predictions compare satisfactorily with the operating data of an indirect heat industrial lignite dryer. Overall heat transfer coefficients of the pilot rotary dryer were found to agree well with those reported for direct heat dryers.     

A Diffusion Model for a Drum Dryer Subjected to Conduction, Convection, and Radiant Heat Input

Drum dryers are commonly used for production of a flaky dry powder from thick suspensions. This article presents results of a simple diffusion-based model to predict the drying performance of a pilot-scale twin-drum dryer. Numerical results are compared with experimental data obtained for a biological sludge whose initial moisture content varied from 1.0 to 2.3 kg/kg db. The agreement of model predictions with the pilot-scale experimental data is favorable. Effects of film thickness, drum rotational speed, external air flow velocity, and its humidity are examined parametrically. Sludge film thickness is identified as the most critical operating parameter to control the final moisture content and productivity of the dryer. The validated model is used to predict performance of a drum dryer subjected to heat input by convection and radiation along with conduction through the drum wall. It is shown that dryer output can be enhanced significantly by increasing the film thickness and applying radiant heating in the initial period of drying. A simple mathematical model of this type can be used for the purpose of design and analysis as well as scale-up of industrial drum dryers based on simple laboratory-scale experiments.     

一种衣物空气低温烘干循环系统的设计及分析

基于机械热泵除湿原理,同时结合洗衣机衣物烘干温度的要求,设计出一种衣物空气低温烘干循环系统。借助EES软件对该系统建立系统模型,通过理论模拟分析研究其热力学性能,并对影响其热力性能的关键操作参量影响进行分析。研究结果表明,在保证冷凝量均为1.02 kg/h的情况下,该设计系统的单位能耗除湿速率（moisture extraction rate,MER）为0.5018 kW?h/kg,较常规电加热热风烘干系统降低了16.5%;COP为0.79,较常规烘干系统提高了16.5%。此外,相比较常规电加热热风烘干系统方案烘干温度90 ℃,该方案设计的滚筒操作温度仅为57.68 ℃,有效地拓展了可烘干衣物的范围。     

OPTIMUM AIR DRYING STRATEGY FOR DEHUMIDIFIER TIMBER DRYERS

This paper presents an economic model for analyzing the cost behavior of dehumidifier timber drying process. Various costs, including those of air drying, are identified and quantified. Reasonable assumptions are made to simplify the calculation process. For species of both softwoods and hardwoods, the optimum air drying strategies are investigated based on two scenarios of existing commercial dehumifier dryers and well-run high performance dehumidifier dryers. This paper finds that when the timber maximum air drying degrade rate is less than 5%, air drying adds significant value to the operation of dehumidifier dryers. This benefit accelerates with the extent of air drying. With the use of high performance dehumidifier dryers, the importance of air drying tends to decrease. The cost of air drying is very sensitive to both the assumed interest rate and timber maximum air drying degrade rate.     

OPTIMUM AIR DRYING STRATEGY FOR DEHUMIDIFIER TIMBER DRYERS

This paper presents an economic model for analyzing the cost behavior of dehumidifier timber drying process. Various costs, including those of air drying, are identified and quantified. Reasonable assumptions are made to simplify the calculation process. For species of both softwoods and hardwoods, the optimum air drying strategies are investigated based on two scenarios of existing commercial dehumifier dryers and well-run high performance dehumidifier dryers. This paper finds that when the timber maximum air drying degrade rate is less than 5%, air drying adds significant value to the operation of dehumidifier dryers. This benefit accelerates with the extent of air drying. With the use of high performance dehumidifier dryers, the importance of air drying tends to decrease. The cost of air drying is very sensitive to both the assumed interest rate and timber maximum air drying degrade rate.     

INDIRECT THERMAL DRYING OF LIGNITE: DESIGN ASPECTS OF A ROTARY DRYER

ABSTRACT

An investigation of the thermal drying of lignite has been carried out, by using an indirect heat pilot rotary drum. The process aims at the production of dry lignite and clean steam as part of a gasification procedure. Both flighted and bare drum modes have been employed. Temperature profiles along the dryer length, the amount of evaporation (moisture conversion) and the solids residence time distribution (RTD) were measured. A non-isothermal model was tested under three different regimes of solids flow. Model integration, by taking account of experimental amount of evaporation at dryer exit and temperature profiles along the dryer length, has been utilized in the validation of drying kinetics and heat transfer correlations. Model predictions compare satisfactorily with the operating data of an indirect heat industrial lignite dryer. Overall heat transfer coefficients of the pilot rotary dryer were found to agree well with those reported for direct heat dryers.     

聚合物涂膜干燥研究进展

评述了人们对于聚合物涂膜形成过程及干燥机理的认识 ,并以涂膜干燥过程的模拟、涂膜缺陷的形成、扩散系数的测定及估算等方面的研究进展为依据 ,讨论了聚合物涂膜干燥过程中需要进一步研究和开发的领域