低温工艺热流体的分级冷却及控制研究

针对常规冷却方式和ORC发电冷却方式的缺陷,提出了低温工艺热流体的分级冷却系统;以某煤制油过程中的低温热流体工况为研究对象,计算了分级冷却系统的能耗情况,并与常规冷却方式和ORC发电冷却方式的能耗进行了对比,结果表明:分级冷却系统在工艺热流体冷却过程中,相比常规冷却方式,不仅不消耗额外的电能和水资源,反而产生发电收益,并且其发电功率远大于发电冷却方式的发电功率;最后,提出了低温工艺热流体分级冷却系统的控制方法。     

粉体流冷却器应用于重质纯碱冷却工艺——加拿大BULKFLOW公司粉体流冷却器助力纯碱冷却工艺

节能降耗一直是化工生产的主题，节能降耗不仅仅是降低生产成本，同时也是改善生产环境的重要保证。纯碱工业的传统冷却工艺是采用流化床风冷，单位冷却能耗居高不下，同时粉尘损耗也影响着周围环境。本文将介绍解决这个问题的方案。     

工艺冷却用蒸发器的选择

在设计工艺冷却过程中,充分了解不同形式的工艺冷却用蒸发器,才能选择最适合工艺条件的换热器。本文对制冷工艺用的3种常用蒸发器的使用范围、结构设计以及使用中的注意事项等进行归纳总结,为制冷工艺设计人员、化工工艺设计人员等提供一些参考。     

粉体流冷却器应用于重质纯碱冷却工艺——加拿大BULKFLOW公司粉体流冷却器助力纯碱冷却工艺

节能降耗一直是化工生产的主题，节能降耗不仅仅是降低生产成本，同时也是改善生产环境的重要保证。纯碱工业的传统冷却工艺是采用流化床风冷，单位冷却能耗居高不下，同时粉尘损耗也影响着周围环境。本文将介绍解决这个问题的方案。[编者按]     

一种新型差动位移变换器

本通过对三段式差动电感变换器轴向磁场分布的研究,找出了其非线性的根本原因,并针对这个问题提出一种新颖的差动式电感变换器的结构形式。实验测试证明,这种结构的变换器的线性范围较同样长度尺寸的传统三段式变换器宽,且灵敏度高、漂移小,精度能够达到要求,同时其结构和绕线工艺也较传统的三段式位移变换器简单,便于工厂进行大批量的生产。     

离心式压缩机电机冷却系统设计及仿真

阐述几种离心式压缩机电机冷却方式,提出一种新型螺旋形冷却回路。对螺旋形冷却回路的损耗情况进行仿真分析,提出螺旋形冷却回路电机开设定子铁芯液态制冷剂流道的方案以降低转子带液的机械损耗。整机试验结果表明,开设定子铁芯液态制冷剂流道可以显著降低转子带液机械损耗,压缩机组能效提升约2%。     

猪肉快速冷却制冷系统设计要点

快速冷却工艺对猪肉品质有着至关重要的影响,但是在实际使用过程中存在制冷效果不理想、结霜严重、耗电量大等问题。根据工程设计经验,提出关于猪肉快速冷却制冷系统工艺参数、冷负荷计算、冷风机布置、送风方式设计和融霜系统设计等问题的解决方案。     

关于热鲜肉冷却工艺设计的几点想法

通过对目前热鲜肉两段冷却工艺设计及使用过程中存在问题的分析，针对性的提出对该工艺设计的一些思路和想法。     

变压器节能技术的发展及趋势

配电变压器的损耗主要包括空载损耗和负载损耗。降低变压器损耗一般通过两种途径,一种是使用更多的材料来降低损耗;另一种是采用新的技术和工艺来降低损耗。后一种是在变压器结构、材料、工艺和设计上采用新的技术,在不增加产品体积和重量的条件下,达到降低损耗的目的,这将是今后我国变压器节能技术发展的唯一道路。本文分别回顾变压器铁芯和绕组技术发     

设计中的三段式

指出了三段式是形式美学法则中节奏法则的特殊情况,用大量的实例说明了三段式在平面及产品等设计中已经得到了广泛应用.从审美心理学的角度分析了三段式受到设计师和大众推崇的深层次原因,探讨了三段式在平面和产品造型设计中的运用方法和技巧.     

A computational fluid dynamic model of the heat and moisture transfer during beef chilling

The unsteady heat and mass transfer process during beef carcass chilling was modelled for a three-dimensional beef carcass geometry. A three-step method was used to simulate the simultaneous heat and mass transfer process in order to reduce the computational time. In the first step, a steady state simulation of the flow field was conducted. In the second step, the local heat and mass transfer coefficients were calculated. Finally, the third step consists of the simultaneous heat and mass transfer process simulation on the meat carcass only. A separate 1-D grid was used to calculate the moisture diffusion in the meat. The simulation of a 20-h chilling run takes 5 days on a 2.5 GHz Pentium 4 computer. The model allows calculating and predicting the heat load, temperatures, weight loss and water activity. Local variations in the heat and mass transfer coefficients, temperature and water activity were found around the beef carcass. The CFD model gives temperature predictions that agree with experimental data better than any previous model. The weight loss tends to be over-predicted probably due to neglecting the resistance caused by the fat cover.     

The primary chilling of poultry carcasses—a review

This paper reviews the published scientific studies that have been carried out on the chilling of poultry carcasses. The prime purpose of chilling is to limit the growth of both pathogenic and food spoilage microorganisms. There are a wide range of publications that show that, in general, the numbers of both types of microorganism, on the surface of poultry carcasses, is reduced during the chilling process. Immersion or spin chilling is not used in the production of ‘fresh’ chilled poultry in Europe, ‘dry’ air chilling being the preferred chilling method. Many people believe that there is some clear microbiologically based reason behind the selection of air chilling. However, the published data do not appear to support this belief, and if anything point to a microbial advantage of immersion systems. The rate of chilling has some influence on the taste, texture and appearance of poultry meat. Very rapid chilling can result in tougher chicken meat, while very slow chilling can produce pale soft exudative (PSE) muscle. However, in both cases the effect is not as marked as with red meat. No comprehensive published data has been found on the effect of a range of chilling systems, chilling conditions, carcass weight and shape on the rate of chilling, weight loss and heat loss. Without such data it is impossible to optimise the design of a poultry chilling system.     

Predicting the dynamic product heat load and weight loss during beef chilling using a multi-region finite difference approach

A model for predicting the dynamic product heat load and weight loss during beef chilling has been developed using the finite difference method, in which the irregular beef geometry is approximated by a combination of seven cylinders and slabs. The model was tested against data from 55 industrial beef chilling trials covering a wide range of carcass size, fatness and chilling conditions. The predicted heat removed during the first 2 h in the model was on average 12.6% higher than the experimental value. The predicted weight loss after 20 h was on average 0.0194 kg (0.00046%) higher than the experimental value. Improvements in accuracy would probably have arisen if slaughter floor and chiller conditions had been more accurately known. The model allows for time-variable chiller conditions, making it widely applicable to meat industrv applications.     

A multi-layered two-dimensional finite element model to calculate dynamic product heat load and weight loss during beef chilling

A model for predicting the dynamic product heat load and weight loss during beef chilling has been developed using finite element analysis. The beef geometry is approximated by 13 sections, each represented by a two-dimensional finite element grid using triangular elements. Longitudinal heat conduction was neglected. The model was tested against data from 55 industrial beef chilling trials covering a wide range of carcass size, fat cover and chilling conditions. The heat removal during the first 2 h predicted by the model was on average 5.6% higher than the experimental value. The average percentage error in the predicted weight loss after 20 h was 2.3%.     

Process design data for prok chilling

In 1993 legislation is being enacted throughout the European Community (EC) that will require the maximum temperature of pork carcasses to be below 7°C before cutting or transportation. Results from a survey of UK abattoirs are summarized to highlight the problems and inadequacies of current commercial chilling systems. Design data are presented for conventional pork-chilling systems, which detail the effects of air temperature, air velocity and carcass weight on chilling times. Four novel or modified chilling systems are discussed: ultra-rapid chilling with air at −30°C; immersion chilling in brine at 0°C; ice-bank chilling in humid air at 2°C; and spray chilling in two stages, at 10°C for 2 h followed by 4°C for 21 h. The potential of such systems for the acceleration of chilling rates and for substantial weight savings is identified.     

Measuring the convective heat transfer coefficient while chilling carcasses

The importance of the heat transfer coefficient when chilling carcasses justifies its re-examination and work to its magnitude and variation. While the air velocity at the surface of carcass (with its rather irregular configuration) is an elusive quantity, the author demonstrates that the measurement of the transfer coefficient and its variation should be based on the rate of air flow over unit mass of carcass and on the rate of weight loss through evaporation.     

Analyse expérimentale et modélisation des cinétiques de température et de perte de poids de carcasses de lapin pendant la réfrigérationExperimental analysis and modelling of temperature and weight loss kinetics of rabbit carcasses during chilling

This study deals with the chilling of rabbit carcasses with constant or time-variable air properties, this latter situation being closer to industrial chilling conditions. The experiments have been carried out with carcasses with weights in the range of 0.8–2.0 kg (1) in constant chilling conditions, 55 trials using six carcasses each, covering the following range: air velocity 0.3–2 m s⁻¹, air temperature −3 to 10°C, relative humidity 70–90%, and (2) nine trials, each using two carcasses, have been performed with time-variable air velocity, between 0.5 and 2.0 m s⁻¹, or time-variable air temperature, between −5 and +5°C. The analysis of the kinetics was based on the slopes of the curves of the dimensionless temperature logarithm versus time. The influence of the carcass weight and of the air properties was assessed. A hidden variability of the cooling conditions was evidenced and explained by water evaporation. A model, based on analytical solutions relative to an infinite cylinder, was adapted to take into account the variation of the chilling conditions. A shape factor and an equivalent surface area have been fitted from the experiments performed with constant chilling condition. The calculated results were compared with the measurements for both constant and time-variable chilling conditions. The average difference between calculated and measured temperature kinetics was in any case lower than 1°C. The weight loss, calculated as a percentage of the initial weight, was predicted with an accuracy of 0.1%. The relative errors in chilling times were lower than 9%.     

Cooling curves for the preliminary design of beef chillers

A multilayer two-dimensional model of beef carcass chilling using CFD-generated heat transfer coefficients was used to calculate the parameters of leg and shoulder cooling curves, assuming an exponential cooling model. A central composite experiment was designed to systematically vary air velocity, side weight and fat thickness. Comparison with experimental data suggests that the predicted characteristic time for the leg, and hence the cooling time to a given temperature, should be multiplied by a correction factor 1.07. The effects of airflow direction and of radiation heat transfer have been quantified. A correlation was proposed to estimate leg centre temperature from shoulder temperature. The shortcut formulae and methods presented here will be useful in the design and troubleshooting of industrial beef chillers. They could also be used in Monte Carlo simulations where a large number of samples are considered, to take into account random variations in product characteristics and operating conditions.     

Fast and slow beeg chilling in a commercial chiller and the effect of operational factors on weight loss

Slow beef chilling to avoid cold shortening (trial 1) was compared with rapid chilling to achieve a quick turnover and low weight loss (trial 2) in a commercial chiller designed to operate under either specification. Both specifications achieved their main aims. In trial 1 no part of the loin fell below 10°C within 10 h post mortem. Deep leg temperatures were between 14.5 and 21°C at 24 h post mortem compared with 9.5–14.8°C in trial 2. The percentage weight loss from fully chilled sides was predicted to be 0.84% less in trial 2 than trial 1. Operational factors, such as the time between death and hot weight, were found to have at least as important an effect on weight loss as the technical specification of the chiller.     

猪白条肉二阶段快速冷却中一些问题的探讨

本文主要讨论猪白条肉在二阶段快速冷却中基本参数的确定，及相关建筑，制冷工艺设计中需注意的问题。以使食品加工更规范，满足广大人民的需求，同时尽可能节能减排，使企业持续发展。