Performance Characteristics of a Drying Heat Pump Using Superheated Steam

ABSTRACT

A complete mathematicalhumerical model is proposed, in order to simulate the performance characteristics of a novel concept of a drying heat pump based on the theory of minimum energy cyclcs. The drying heat pump involvcs vapour condensation in a Lava1 nozzle. removal of the liquid phase in a supersonic separator as well as compression of the working medium. which is superheared vapour.     

Performance Characteristics of a Drying Heat Pump Using Superheated Steam

A complete mathematicalhumerical model is proposed, in order to simulate the performance characteristics of a novel concept of a drying heat pump based on the theory of minimum energy cyclcs. The drying heat pump involvcs vapour condensation in a Lava1 nozzle. removal of the liquid phase in a supersonic separator as well as compression of the working medium. which is superheared vapour.     

Drum Drying of Black Liquor Using Superheated Steam Impinging Jets

ABSTRACT

A novel drum dryer for black liquor utilizing multiple impinging jets of superheated steam was designed and built to evaluate the performance characteristics and effects of various operating parameters thereon. Appropriate ranges of parameters such as steam jet temperature and velocity were examined experimentally lo quantify the optimal operating conditions for the formation of black liquor film on the drum surface as well as the drying kinetics.     

Some Considerations In Simulation Of Superheated Steam Drying Of Softwood Lumber

ABSTRACT

A mathematical model for high-temperature drying of softwood lumber with moist air has been modified and extended to simulate wood drying with superheated steam. In the simulation, differences between the two types of drying are considered, these include: external heat and mass transfer processes and calculation of equilibrium moisture content. The external mass transfer coefficient in the perheated steam drying was found to be much higher than that in the moist air drying, however, the heat ransfer coefficients for these two cases were of the same order. The predicted drying curves and wood temperatures from the superheated steam drying model were compared with experimental data and there was close agreement. Further studies will apply the model to development of commercial drying schedules for wood drying with superheated steam.     

A Comparative Study of Pork Drying Using Superheated Steam and Hot Air

Drying with superheated steam and hot air were comparatively studied for pork. Transport, physical, and chemical properties, i.e., effective diffusivity, color, microstructure, and rehydration ability, were investigated. The experimental results have shown that the decrease of pork moisture content in an early drying time was more rapid in superheated steam than in hot air and appeared to be lower in a latter time. The pork surface as examined by SEM was noticeably different for the samples dried by superheated steam and hot air. The fewer pores at the surface of superheated steam-dried pork caused a slower water penetration into the interior during rehydration, in addition to the lower drying rate. The color of the product from superheated steam was a relatively more intense brown than that obtained from hot air as presented by a lower L? value and a higher a? value.     

A Comparative Study of Pork Drying Using Superheated Steam and Hot Air

Drying with superheated steam and hot air were comparatively studied for pork. Transport, physical, and chemical properties, i.e., effective diffusivity, color, microstructure, and rehydration ability, were investigated. The experimental results have shown that the decrease of pork moisture content in an early drying time was more rapid in superheated steam than in hot air and appeared to be lower in a latter time. The pork surface as examined by SEM was noticeably different for the samples dried by superheated steam and hot air. The fewer pores at the surface of superheated steam-dried pork caused a slower water penetration into the interior during rehydration, in addition to the lower drying rate. The color of the product from superheated steam was a relatively more intense brown than that obtained from hot air as presented by a lower L* value and a higher a* value.     

External Heat Transfer in Moist Air and Superheated Steam for Softwood Drying

In kiln drying of softwood timber, external heat and moisture mass transfer coefficients are important in defining boundary temperature and moisture content at the wood surface. In addition, superheated steam drying of wood is a promising technology but this has not been widely accepted commercially, partially due to the lack of understanding of the drying phenomena occurred during drying. In this work, experimental investigation was performed to quantify the heat transfer between wood surface and surrounding moist air or superheated steam. In the experiment, saturated radiata pine sapwood samples were dried using dry-bulb/wet-bulb temperatures of 60℃/50℃, 90℃/60℃, 120℃/71℃, 140℃/90℃, 160℃/90℃, 140℃/100℃ and 160℃/100℃. The last two schedules were for superheated steam drying as the wet-bulb temperature was set at 100℃. The circulation velocity over the board surface was controlled at 4.2m·s-1. Two additional runs (90℃/60℃) using air velocities of 2.4m·s-1 and 4.8m·s-1 were performed t     

Computational Study of Impingement Jet Drying of Seeds Using Superheated Steam Based on Kinetic Theory of Granular Flow

A Eulerian model including the kinetic theory of granular flow (KTGF) and mass transfer in the period of saturated wet surface has been developed to simulate continuous drying of particulate solids using superheated steam in a radial impingement jet system. When applying this type of drying processes, the preliminary results obtained show good predictive ability of the Eulerian modeling based on KTGF. It is concluded that the present study and other works of modeling can be used to study the dynamics and control of this drying process and thus would facilitate the equipment design and scaling.     

Hybrid Drying of Rubberwood Using Superheated Steam and Hot Air in a Pilot-Scale

A pilot-scale rubberwood dryer was constructed and injected with superheated steam and hot air to study the effect of the hybrid system on the drying rate and mechanical properties of the wood. A total of 300 pieces of rubberwood boards, each with dimensions of 1000 mm long × 76.2 mm wide × 25.4 mm thick, were stacked in 1.0 m × 1.0 m × 1.7 m (1.7 m³) pallet. The stack was impinged with alternating cycles of superheated steam and hot air. The time required for conventional drying was 168 hours, but the drying time for the hybrid system was only 64 hours, resulting in a 62% reduction.

After being dried, the rubberwood boards were mechanically tested for static bending, compression strength, hardness, and shear strengths. From the mechanical tests, the hybrid drying system using superheated steam and hot air had no significant effect on the mean shear strength parallel-to-grain; however; the mean compression strength parallel-to-grain was reduced by 24.2% and the mean MOR by 21.4%. Nonetheless, the mean MOE was increased by 30.4% and the mean of hardness by 16.4%.     

Energy Analysis on Use of Air and Superheated Steam as Drying Media

ABSTRACT

The physical properties of air and superheated steam were analysed in a range of temperature applied in paper and paperboard drying processes. On the basis of tests carried out on a pilot stand the values of energy indices for air and steam drying processes are compared. With the drying media temperature as T_m = 300°C, nozzle velocity v= 60m/s and using the Huang and Mujumdar model as well as relationships given by Chance a compartive analysis of the results has been carried out Variation of several indices in the range of temperatures 100-600°C and various nozzle velocities was studied.     

Low-Temperature Drying Using a Versatile Heat Pump Dehumidifier

A drying system incorporating a commercial 2.3 kW heat pump dehumidifier was designed and constructed. The HPD was equipped with an external water-cooled condenser that rejected excess heat out of the system. The design of the system allowed for conducting drying with recirculation of air as well as use of electrical heaters. In an open mode, the drying could be carried out simultaneously with room dehumidification and water heating in the secondary condenser. Drying experiments were conducted with apple and comparisons were made between HPD assisted drying (partial and complete) and hot air drying (at 45 and 65°C). The HPD dried fruit exhibited better rehydration properties than the hot air dried samples. Water activity of the HPD dried samples was noticeably lower than that of the hot air dried samples at the same water content, indicating that the residual moisture was probably held under higher tension in the former. In terms of energy consumption, the process of HPD assisted drying is more expensive as much of the energy input is rejected at the secondary condenser as excess heat.     

气体分馏装置的操作调优

本文以某气体分馏装置为例,通过严格的流程模拟,分析了产品质量、回流比和塔压等操作参数对总经济效益的影响。     

Superheated Steam Drying of a Single Particle in an Impinging Stream Dryer

ABSTRACT

Impinging stream contactors provide a novel configuration for drying and/or chemical reactions of particulates, pastes or suspensions which can be dispersed in a flowing gas stream. Essentially they consist of one or more highly turbulent “impingement” zones formed by collision of two opposing jets (OJ) in a confied channel or duct. The objective of this paper is to present computational fluid dynamic predictions for two-dimensional turbulent opposing jets over a range of nozzle-to-nozzle separations and jet Reynolds numbers for the simulation of single particle drying in these systems using superheated steam. A number of different turbulence models were tested ( e.g. high Reynolds, Lam-Bremhorst, Launder and Sharma models etc.). Predictions are performed in two distinct parts. In the first part a power law, finite volume method based on the “SIMPLEC” algorithm is used to solve the momentum and energy conservation equations for air in OJ systems in order to gain insight into their     

Superheated Steam Drying of a Single Particle in an Impinging Stream Dryer

Impinging stream contactors provide a novel configuration for drying and/or chemical reactions of particulates, pastes or suspensions which can be dispersed in a flowing gas stream. Essentially they consist of one or more highly turbulent “impingement” zones formed by collision of two opposing jets (OJ) in a confied channel or duct. The objective of this paper is to present computational fluid dynamic predictions for two-dimensional turbulent opposing jets over a range of nozzle-to-nozzle separations and jet Reynolds numbers for the simulation of single particle drying in these systems using superheated steam. A number of different turbulence models were tested ( e.g. high Reynolds, Lam-Bremhorst, Launder and Sharma models etc.). Predictions are performed in two distinct parts. In the first part a power law, finite volume method based on the “SIMPLEC” algorithm is used to solve the momentum and energy conservation equations for air in OJ systems in order to gain insight into their     

落叶松太阳能热泵干燥特性研究

本文介绍了一种木材太阳能热泵干燥装置及其三种不同的运行方式,并以落叶松为试材,通过两组对比实验,分析干燥介质与干燥箱内的温度变化以及木材含水率变化之间的关系。结果表明太阳能水源热泵联合干燥的优化比传统干燥节能约76．7％,太阳能水源热泵联合干燥比传统干燥节能约66．2％,优化模式比只用太阳能水源热泵联合干燥木材时耗能更低,且干燥质量更好。     

在惰性气体环境中热泵干燥食品

在传统的食品干燥技术中,干燥介质是空气,干燥能力由变化的温度控制。通常,干燥过程在高温下进行,空气中氧的存在影响食品的营养物质。想要在低温条件下提高干燥能力,可以通过热泵来改善干燥环境。热泵是闭环系统,冷凝器产生的热控制干燥温度,蒸发器除去干燥室的水分,干燥介质在低温低湿下运行。由于整个系统在闭路下操作,为了去除空气中氧对食品的影响,采用氮气、二氧化碳等惰性气体代替空气作为干燥介质。本文主要研究：采用氮气、二氧化碳和空气干燥一些热敏性水果,如番石榴和木瓜,探讨对食品营养物质和颜色的影响,并与冷冻干燥、真空干燥的结果进行对比。     

Drying Of Vanilla Pods Using A Greenhouse Effect Solar Dryer

ABSTRACT

This paper describes the basic design of the GHE solar dryer and evaluates the performance of the dryer when used to dry vanilla pods. From laboratory test results it was indicated that the average drying time for vanilla pods was between 49 to 53, 5 hrs, for the case of heating augmentation using coal briquette stoves. The total amount of coal briquettes used to produce drying air temperature between 33 C to 65 C and RH of about 34% during day time was 61 kg equivalent to 6.1 kW heating rate and the average electric energy usage of 36.5 kWh, respectively. Quality test results indicated that the dried products were of grade IA of the export quality standard with vaniline content of 2.36%.     

Grape Drying in a Pilot Plant With a Heat Pump

ABSTRACT

We describe a pilot-scale drying plant comprising a closed-circuit, hot-air convection chamber with a heat pump. In this plant, food and forest products can be drled with lower energy consumption and over a wider range of air, speeds, temperatures and relative humidities than in conventional driers. Also the dryinq conditions can be controlled independently of external conditions. Under several different sets of drying conditions, we determined the kinetics of dryinq of grapes that had been variously pretreated. The effects of drying conditions and the pretreatment on the drying time and the appearance of the dried product were evaluated. The drying kinetics can be described by a diffusion model.     

A Comparative Study of Low-Pressure Superheated Steam and Vacuum Drying of a Heat-Sensitive Material

Abstract

Using carrot cubes as a model heat-sensitive material, experimental investigations were conducted to examine the drying kinetics and various quality parameters of the dried product undergoing both low-pressure superheated steam and vacuum drying. Effects of operating parameters such as pressure and temperature on the drying characteristics as well as quality attributes, i.e., volume, shrinkage, apparent density, color, and rehydration behavior, of the dried product underwent the two drying processes were also evaluated and compared. Although low-pressure steam drying required longer dwell time to achieve the same final moisture content than vacuum drying, some of the quality attributes were superior to those obtained in vacuum drying.     

A Comparative Study of Low-Pressure Superheated Steam and Vacuum Drying of a Heat-Sensitive Material

Using carrot cubes as a model heat-sensitive material, experimental investigations were conducted to examine the drying kinetics and various quality parameters of the dried product undergoing both low-pressure superheated steam and vacuum drying. Effects of operating parameters such as pressure and temperature on the drying characteristics as well as quality attributes, i.e., volume, shrinkage, apparent density, color, and rehydration behavior, of the dried product underwent the two drying processes were also evaluated and compared. Although low-pressure steam drying required longer dwell time to achieve the same final moisture content than vacuum drying, some of the quality attributes were superior to those obtained in vacuum drying.