EXPERIMENTAL STUDIES ON A NOVEL CHEMICAL HEAT PUMP DRYER USING A GAS-SOLID REACTION

The authors have been studying Chemical Heat Pumps (CHP) from the viewpoints of energy saving and environmental impact. The CHP can store thermal energy in the form of chemical energy by an endothermic reaction, and release it at various temperature levels during heat demand periods by exo/endothermic reactions. The authors have proposed in an earlier study a novel chemical heat pump (CHP) system for environmentally-friendly effective utilization of thermal energy in drying as a chemical heat pump dryer (CHPD). In this exploratory study, we test the effectiveness of operating the proposed CHPDs experimentally. Basic experiments on the CHPDs such as hot dry air production for convective drying are performed on lab-scale CHPD apparatuses using gas-solid reactions in calcium oxide/calcium hydroxide reactant beds. The proposed CHPDs are found to produce hot air by CHP operation for drying. The temperature levels of the produced hot air and the reaction rates/conversions are as good as in the case of hot water supply system using basically same CHP operation. The cold heat for air dehumidification is also found to be generated/recovered by the same CHPD system. The generated heat amounts can be increased by changing the operating conditions although the heat recovery must be enhanced for practical application of CHPDs.     

EXPERIMENTAL STUDIES ON A NOVEL CHEMICAL HEAT PUMP DRYER USING A GAS–SOLID REACTION

The authors have been studying Chemical Heat Pumps (CHP) from the viewpoints of energy saving and environmental impact. The CHP can store thermal energy in the form of chemical energy by an endothermic reaction, and release it at various temperature levels during heat demand periods by exo/endothermic reactions. The authors have proposed in an earlier study a novel chemical heat pump (CHP) system for environmentally-friendly effective utilization of thermal energy in drying as a chemical heat pump dryer (CHPD). In this exploratory study, we test the effectiveness of operating the proposed CHPDs experimentally. Basic experiments on the CHPDs such as hot dry air production for convective drying are performed on lab-scale CHPD apparatuses using gas–solid reactions in calcium oxide/calcium hydroxide reactant beds. The proposed CHPDs are found to produce hot air by CHP operation for drying. The temperature levels of the produced hot air and the reaction rates/conversions are as good as in the case of hot water supply system using basically same CHP operation. The cold heat for air dehumidification is also found to be generated/recovered by the same CHPD system. The generated heat amounts can be increased by changing the operating conditions although the heat recovery must be enhanced for practical application of CHPDs.     

Enhancement of Energy Efficiency of a Chemical Heat Pump-Assisted Convective Dryer

In earlier studies we have shown by simulation and experimental studies that the proposed chemical heat pump (CHP) unit can be used to recover waste heat from dryers and reuse it by storing and releasing heat with upgrading the temperature or by dehumidification. However, the final thermal energy production efficiency of the CHP for drying was found to be low. In this paper we present experimental results to demonstrate the potential for improved heat-recovery/storage and the heat-release/production of hot dry air for batch drying applications using the heat enhancement mode of the CHP. A new laboratory scale experimental CHP dryer system was built utilizing the calcium oxide/calcium hydroxide hydration/dehydration reversible reaction. The aim of this study is to improve the efficiencies of the heat recovery from heat source in the heat-storage step and the hot dry air production in the heat-release step of the CHP for heating up the air to around 100°C. The results of this experimental study utilizing a new reactor design showed that the shallow reactor/heat exchanger could accomplish 94% chemical heat storage and produce 100°C air at better than 75% efficiency for the reaction heat by controlling the preheating condition. The reaction conversion reached 90% in these experiments. The proposed CHP-assisted convective dryer system is found to be energy-efficient over a wide temperature range of industrial interest.     

SIMULATION OF HYDRATION/DEHYDRATION OF CaO/Ca(OH)2 CHEMICAL HEAT PUMP REACTOR FOR COLD/HOT HEAT GENERATION

ABSTRACT

A chemical heat pump (CHP) utilizes reversible reactions involving significant endothermic and exothermic heats of reaction in order to develop a heat pump effect by storing and releasing energy while transforming it from chemical to thermal energy and vice versa. In this paper, we present a mathematical model and its numerical solution for the heat and mass transport phenomena occurring in the reactant particle bed of the CHP for heat storage and cold/hot heat generation based on the CaO/Ca(OH)₂ reversible hydration/dehydration reaction

Transient conservation equations of mass and energy transport including chemical kinetics are solved numerically subject to appropriate boundary and initial conditions to examine the influence of the mass transfer resistance on the overall performance of this CHP configuration. These results are presented and discussed with the aim of enhancing the CHP performance in next generation reactor designs.     

超细CuO粉体用于异丙苯氧化反应的研究

近年来，苯酚市场需求增长速率较快，提高苯酚的生产技术及生产能力并降低成本势在必行。以Cu(NO₃)₂·3H₂O和NaOH为原料，采用固相研磨混合法在室温下制备了超细CuO，采用X射线衍射（XRD）和扫描电镜（SEM）对合成CuO的结构和形貌进行了表征分析，并与分析纯的CuO相比较。将超细CuO用于空气氧化异丙苯制过氧化氢异丙苯（CHP）的反应。常压下，考察了反应温度和催化剂用量等条件对CHP浓度的影响，100 mL异丙苯加入1 g催化剂，90 ℃反应12 h后，CHP累积浓度达27%左右，符合工业生产要求。催化剂回收后经简单再生处理可重复使用。     

Gaseous Carbon Dioxide as the Heat and Mass Transfer Medium in Drying

Using available correlations for heat transfer, a comparative analysis of drying rates in CO₂ and in air was performed for several basic types of dryers. Higher heat transfer rates were found for dryers with active hydrodynamics, which translates into shorter drying time for materials dried in the first drying period. These results were validated by experiments on drying wheat kernels fluidized by air and by CO₂. Shorter drying times by about 20% were confirmed for CO₂, which offers energy savings of about 3% of the heat input to the dryer. Additional energy savings of 4% of the heat load can be expected for drying at temperatures below 100°C because of the lower wet-bulb temperature for CO₂ than that for air. The potential for CO₂ abatement was evaluated based on a case study for drying of distillers' spent grain.     

Simulation and Experiment of a Cogeneration System Based on Proton Exchange Membrane Fuel Cell

This project designs and simulates a cogeneration system of proton exchange membrane fuel cell using Matlab/Simulink software and Thermolib heat module components. The system not only satisfies the need for electric power, but also provides heat recovery for future uses, thus increasing energy transfer efficiency. PEM fuel cell‐based cogeneration system is introduced, including the hydrogen supply subsystem, air supply subsystem, load control subsystem, real‐time monitoring block, and heat recovery subsystem. The complete fuel cell‐based cogeneration system is constructed by assembling the fuel cell stack, fuel, coolant flow rate control system, and all the subsystems. In addition to the fuel cell experiment, influencing factors on the fuel cell‐based system, such as the fuel inhale rate, coolant flow rate, system temperature, fuel humidification, thermal efficiency, electrical efficiency, and combined heat and power (CHP) system efficiency, are analyzed and charted regarding different loads. In this system, with the power at 3 kW, the CHP efficiency reaches 64%. The CHP efficiency is 76.6% with the load power at 4 kW. When the power is at 5 kW, the thermal efficiency reaches 36.9% and the CHP efficiency reaches 82.9%.     

MODELLING OF HEAT TRANSFER IN HOT PRESSING AND IMPULSE DRYING OF PAPER

A modelling and simulation study regarding the heat transfer in hot pressing as well as in impulse drying of paper has been performed. The study is focused on modelling the heat transfer from a hot surface to a moist paper sheet and the heat transfer inside the paper sheet. The model is based on solving the equation for unsteady heat transfer by conduction. The model was compared with experimental data from a heated laboratory platen press and data from the experimental paper machine EuroFEX at the Swedish Pulp and Paper Research Institute (STFI) in Stockholm. The results in this study showed that a rather simple heat transfer model could be used to simulate the heat transfer in cases in which the temperature was moderate and the applied pressure did not exceed 0.5 MPa. It was also concluded that a paper could be regarded as a semi-infinite body for basis weights above 110 g/m², considering the assumptions used in the model. It was also shown that a laboratory press could simulate heat transfer in hot pressing and impulse drying with a high degree of accuracy.     

CO2-空气微通道蒸发器两相区熵产分析

微通道已成为换热器研究领域的热点,以CO₂微通道蒸发器为研究对象,建立了CO₂微通道蒸发器两相区内、外侧均有相变的熵产模型,通过建立的CO₂微通道蒸发器二维分布参数模型求解系统熵产数.分析CO₂与空气侧质量流率、空气入口温度及CO₂蒸发温度对系统熵产数的影响.结果表明:CO₂质量流率对系统熵产数影响很小;系统熵产数主要由CO₂与空气两侧温差传热引起;系统熵产数随空气入口温度的增大而增大,随CO₂的蒸发温度的增大而减小;随着空气质量流率的增大,系统熵产数增大,且蒸发温度越高,空气质量流率对系统熵产数的影响越大.     

Chemical and adsorption heat pumps: Cycle efficiency and boundary temperatures

The efficiency of an ideal three-temperature (3T) cycle of a chemical heat pump (CHP) is considered. For a reversible CHP 3T cycle, the maximal efficiency can be determined using the ratio of the heat of evaporation of the working fluid and the heat of the chemical reaction or using the boundary temperatures of the cycle. The boundary temperatures of the reversible CHP cycle are not independent variables relative to each other. As they are related by the Clausius-Clapeyron equation for the equilibrium of the pure fluid and by the van’t Hoff equation for the chemical reaction, the choice of one of these temperatures completely determines the two others. Comparison of the efficiencies of the CHP cycle and the cycle of an adsorption heat pump (AHP) shows that the CHP efficiency can theoretically reach the Carnot-cycle efficiency whereas the AHP efficiency is always less than the Carnot-cycle efficiency because of the generation of entropy due to the transfer of heat to (from) the adsorber at a finite temperature difference. The minimal temperature of the external heat source needed for the operation of the CHP (AHP) cycle, the minimal evaporator temperature, and the maximal condenser temperature are calculated. These temperatures are determined for CHP (AHP) applications such as heating, air conditioning, ice production, and deep freezing in different climatic zones. Original Russian Text ? Yu.I. Aristov, 2008, published in Teoreticheskie Osnovy Khimicheskoi Tekhnologii, 2008, Vol. 42, No. 6, pp. 676–685.     

Saving fuel consumption and reducing pollution emissions for industrial furnace

The furnace efficiency can be maintained or improved slightly by lowering the excess air ratio and raising the air preheat temperature in the heat furnace. The results obtained with a plant-size industrial furnace show that when the excess air oxygen concentration is reduced from 4% to 3%, the furnace efficiency is raised by 0.6%. However, raising the temperature of the pre-heated air will cause a higher furnace temperature and a faster flowing speed of the air in the furnace. Thus, the heat in the radiation zone of the furnace can be evenly transmitted to shorten the time for the fuel to reach the igniting point, and reduce the heat loss from the hot air stream. This will reduce the emission of CO₂ and NO_x. If the temperature of the pre-heated air is raised from 200 °C to 240 °C, about 2.3 × 10⁶ m³ of natural gas can be saved annually to reduce 3.1 × 10³ t of CO₂ and 14.3% of nitrogen oxide emissions. Such operational adjustments of the furnace using the recovered FG will save energy, reduce CO₂ emission and alleviate the adverse impact to environment.     

水平矩形散热片的流动特性及传热性能

水平矩形散热片的流动特性及传热性能沈文生陈烈强（华南理工大学，广州５１０６４１）梁振华梁天培（香港理工大学）关键词散热片速度分布传热系数１前言作为强化传热元件之一的散热片因制造方便、结构简单及传热效率高而广泛地应用于许多工程系统，例如电子设备、热电设...     

DEVELOPMENT AND EVALUATION OF A PLANAR HEAT PIPE FOR COOLING ELECTRONIC SYSTEMS

A planar heat pipe (;rectangular cross section) was designed, built and tested using flexible electrical rubber heaters to provide the necessary heat. The device was constructed from 0.043” (0.1092 cm) copper sheet, with three layers of 100-mesh copper screen as a capillary wick. The dimensions of the planar heat pipe were 6 inches ( 15.24 cm) by 12 inches (30.48 cm) by 3/4 inches (1.905 cm). Water was used as the working fluid. Steady state, and in once case, transient responses, were investigated. External axial temperature profiles for different applied powers and operating temperatures were measured. Operation of the device was stable and repeatable within a temperature range of 30^° to 95^°C; no temperature or pressure fluctuations were noted.

The optimum amount of working fluid for a typical situation was obtained experimentally. Effects of air and amount of working fluid inside the planar heat pipe were investigated. The optimum amount of working fluid which was obtained experimentally was used throughout the remaining tests in this research. Effects of gravity, a wide range of operating temperature, Reynolds number at constant input power, and Reynolds number at constant operating temperature were investigated. The maximum heat transfer rate of the planar heat pipe was obtained experimentally and compared to it is theoretical value. Good agreement was obtained between the two values.     

Microstructure-Mechanical Property Relationships in Hot Isostatically Pressed Alumina and Zirconia-Toughened Alumina

The rates of densification and the mechanical properties of pure Al₂O₃ and ZrO₂-toughened Al₂O₃ (ZTA) have been investigated as a function of the temperatures and time schedules used for hot isostatic pressing (HIP) as a postsintering heat treatment for samples which had already been pressureless sintered in air at 1460°C for 45 min. ZTA hot isostatically presed at 1400°C had a finer grain size and a narrower grain size distribution than ZTA hot isostatically pressed at 1600°C. At both HIP conditions, the density which could be obtained was almost the maximum theoretical density. The amount of grinding-induced and fracture-induced monoclinic ZrO₂ formed as a result of the tetragonal → monoclinic martensitic transformation in ZTA was higher in the samples hot isostatically pressed at 1400°C. ZTA hot isostatically pressed at 1600°C and 100 MPa had fewer flaws and higher strengths than ZTA hot isostatically pressed at 1400°C for the same time, with a gradual improvement in mechanical properties with increasing HIP time at each of these two temperatures. The best mechanical properties were obtained from ZTA hot isostatically pressed at 100 MPa and 1600°C for 1 h: these specimens had a four-point bend strength of 940 ± 15 MPa at room temperature and 540 ± 15 MPa at 1000°C and an indentation fracture toughness at room temperature of 9.4 ± 0.2 MPa·m^1/2.     

Studies on Dehydration of Sapota (Achras zapota)

Sapota (Achras zapota) is a tropical fruit found in several parts of India. It is one of the most popular fruits besides mango, custard apple, and several others. Once ripe, it needs to be consumed within a couple of days due to the highly perishable nature of this exquisite fruit variety. The best way to increase the shelf-life is through the process of dehydration of peeled sapota. In the present study, the convective air drying of sapota pulp was carried out and compared with low-temperature drying techniques such as heat pump-assisted drying and freeze drying. The sapota paste was dried in a convective dryer to study the effect of operating parameters such as air temperature and air velocity. In addition, the effect of additives such as oat and wheat fibers and the paste thickness on drying was also studied. The critical analysis of dehydrated sapota was carried out in terms of water activity, sugar content, color, and rehydration ratio. The drying data were analyzed using Page's model and Newton's model on the basis of root mean square error (RMSE), reduced χ square (χ²) and correlation coefficient (R²).     

SPRAY DRYING DYNAMIC MODELING WITH A MECHANISTIC MODEL

In this work we suggest the dynamic modeling of a spray dryer considered as a series of well-stirred dryers. That is, a series of dryers in which the output variables are equal to the state variables. The state equations were obtained from the heat and water mass balances in product and air. Additionally, heat and water mass balances in interface jointly with water equilibrium relation between product and air were considered. A pilot spray dryer was modeled assuming one, two, five and 20 well stirred steps. Low-fat milk with 10-20% of solids was dried at different inlet air temperatures (120-160°C), air flow rate of 0.19 kg dry air s^-1 and different feed rates (1.4 - 4.2 × 10^-4 kg dry solids s^-1). Stationary result showed that the model predicts the experimental air outlet temperature, at different inlet conditions with a maximum deviation of 6°C. The dynamic simulation reproduce the experimental one with moderate accuracy. Experimental dynamic showed that the pilot plant spray dryer has a well-stirred process behavior. The model represents a method for estimate outlet product moisture as function of the outlet air temperature. This has application for automatic control because there is not an easy way to measure on-line measure the outlet product moisture content.     

相变微胶囊悬浮液喷淋换热特性实验研究

根据相变微胶囊储存和释放潜热的特殊性质,分别使用相变微胶囊悬浮液（MPCMS）和纯水作为喷淋介质,搭建了一个小型喷淋塔装置,其中相变微胶囊的芯材为正二十二烷(C₂₂H₄₆)。实验设定了五个喷淋温度(35、40、44、47、51℃)、三个空气流量(0.011、0.018、0.025 m³/s)和两种直径(SMD=80、240 μm)的大、小液滴作为实验变量,探究了上述两种介质与空气之间的换热特性。实验结果表明：相变微胶囊的过冷会影响换热过程。常温常湿条件下,对于小液滴,当空气流量为0.018、0.025 m³/s时,喷淋温度为44、47℃的MPCMS比相同温度下的纯水更能促进换热;当空气流量为0.011 m³/s时,喷淋温度为44℃的MPCMS比相同温度下的纯水更能促进换热。对于大液滴,在三种空气流量下,喷淋温度为44℃的MPCMS比相同温度下的纯水作为喷淋介质时换热效果更好。     

Energy,Thermal, and Economic Analysis of Air Heat Pumps for Hot Water

Operation tests of an air heat pump used for domestic hot water (DHW) heating were performed. The influence of the supply air temperature in the evaporator cycle and the variable heat load of the condenser on the heating power of the heat pump and the coefficient of performance (COP) was evaluated and discussed. In order to ensure conditions for efficient compressor operation, it is advisable to gradate the heat load of the heat pump using a circulating pump with smooth capacity regulation. The economic analysis demonstrates that the usage of air heat pumps for DHW in comparison with installations equipped with solar collectors provides no measurable economic benefits.     

相变微胶囊悬浮液喷淋换热特性实验研究

根据相变微胶囊储存和释放潜热的特殊性质,分别使用相变微胶囊悬浮液（MPCMS）和纯水作为喷淋介质,搭建了一个小型喷淋塔装置,其中相变微胶囊的芯材为正二十二烷(C₂₂H₄₆)。实验设定了五个喷淋温度(35、40、44、47、51℃)、三个空气流量(0.011、0.018、0.025 m³/s)和两种直径(SMD=80、240 μm)的大、小液滴作为实验变量,探究了上述两种介质与空气之间的换热特性。实验结果表明：相变微胶囊的过冷会影响换热过程。常温常湿条件下,对于小液滴,当空气流量为0.018、0.025 m³/s时,喷淋温度为44、47℃的MPCMS比相同温度下的纯水更能促进换热;当空气流量为0.011 m³/s时,喷淋温度为44℃的MPCMS比相同温度下的纯水更能促进换热。对于大液滴,在三种空气流量下,喷淋温度为44℃的MPCMS比相同温度下的纯水作为喷淋介质时换热效果更好。     

Direct heat and mass transfer in structured packings

Direct heat transfer is an important method in the exchange of heat between two countercurrent process streams within a column. The process can be simulated using either the theoretical stage or the rate based concept. With both concepts, a reliable heat transfer coefficient is needed. Additionally, the rate of the heat transfer coefficient is influenced by the simultaneous mass transfer.

A number of application-dependent methods to estimate the heat transfer coefficient have been developed, mainly for random packings. It is the purpose of this paper to extend this work to structured packings.

A number of experiments with air/water have been performed in a column of 300 mm inner diameter with Mellapak 250.Y, 250.X and 125.X at ambient conditions. A second group of measurements were done using an oil/air system where only sensible heat was transferred.

Based on these experimental results a method was developed to predict the heat transfer coefficient for structured packings. The method is applied to examples of industrial importance, like a gas quench, a gas saturator and a pump-around zone in an atmospheric tower.