Chemical heat pump using heat of reversible catalytic reactions

One of the most important objects of research in the field of energy conservation is development of a high temperature heat pump for the industrial sector. In this framework this paper introduces a new concept of heat pump, which is a hybrid between a compressor and chemical heat pump, where instead of the latent heat of liquids, the proposed system uses the heat of gaseous catalytic reversible reactions (type A → B + C). This paper proposes a simple scheme with a mathematical model for the calculation of the parameters necessary to qualify the behaviour of the Heat Reaction Chemical Heat Pump (HRCHP). The Coefficient of Performance (COP) is calculated as a function of the temperature of the heat source, the temperature to which the pump upgrades the heat and the conversion of the chemical reaction. A more optimized scheme is prospected.     

Water-to-water heat transfer in tube–tube heat exchanger: Experimental and analytical study

Tube–tube heat exchanger (TTHE) is a low cost, vented double wall heat exchanger which increases reliability by avoiding mixing of fluids exchanging heat. It can be potentially used for heat recovery from engine cooling circuit, oil cooling, desuperheating in refrigeration and air conditioning, dairy, and pharmaceutical industry, chemical industry, refinery, etc. These tube–tube heat exchangers are successfully demonstrated for superheat recovery water heating applications, condenser and evaporator in heat pumps, lube oil cooler for shipboard gas turbines, milk chilling and pasteurizing application. This paper presents an experimental study on various layouts of TTHE for water-to-water heat transfer. The theoretical and experimental results on this type of heat exchanger configuration could not be located in literature. Overall heat transfer coefficient and pumping power were experimentally determined for a fixed tube length and surface area of serpentine layouts with different number of bends and results are compared with straight tube TTHE. In the case investigated, serpentine layout TTHE with seven bends has shown optimum performance, with overall heat transfer coefficient 17% higher than straight tube TTHE. Two out of five serpentine layout TTHE have shown poor heat transfer performance than straight tube TTHE. The experimental results also indicate that there is a definite optimum for a number of bends in serpentine layout TTHE. An analytical model for prediction of thermo-hydraulic performance of straight layout has been developed and validated experimentally.     

Transient response of plate heat exchangers considering effect of flow maldistribution

Plate heat exchangers have been playing important role in the power and process industries in the recent past. Hence, it is important to develop simulation strategies for plate heat exchangers accurately. This analysis represents the dynamic behaviour of the single pass plate heat exchangers, considering flow maldistribution from port to channel. In addition to maldistribution the fluid axial dispersion is used to characterise the back mixing and other deviations from plug flow. Due to unequal distribution of the fluid, the velocity of the fluid varies from channel to channel and hence the heat transfer coefficient variation is also taken into consideration. Solutions to the governing equations have been obtained using the method of Laplace transform followed by numerical inversion from frequency domain. The results are presented on the effects of flow maldistribution and conventional heat exchanger parameters on the temperature transients of both U-type and Z-type configurations. It is found that the effect of flow maldistribution is significant and it deteriorates the thermal performance as well as the characteristic features of the dynamic response of the heat exchanger. In contrast to the previous studies, here the axial dispersion describes the inchannel back mixing alone, not maldistribution, which is physically more appropriate. Present method is an efficient and consistent way of describing maldistribution and back mixing effects on the transient response of plate heat exchangers using an analytical method without performing intensive computation by complete numerical simulation.     

Numerical studies on heat transfer characteristics of graphite–water microfluid in a coiled agitated vessel

Agitation is one of the widely used chemical engineering operations involving both simultaneous heat transfers and reaction. In this study, an effort has been made to simulate experimentally studied heat transfer behavior of microfluid in an agitated vessel. Simulated Nusselt numbers were compared with experimental values and found to be in good agreement with experimental values within ±10% deviation. Simulated temperature contours clearly depicted the temperature of cooling water increases gradually along the length of helical coil from the inlet to outlet. Radial mixing was found to be more in disk turbine agitator than the propeller agitator which lead to higher heat transfer rate in disk turbine agitator confirming the experimental observation.     

Identification of zeolites for heat transformer,chemical heat pump and cooling systems

Among the gas-solid adsorption processes the zeolite water adsorption seems to be very interesting for use in thermodynamic systems such as chemical heat pump, heat transformer and cooling systems. This work evaluates theoretically the best type of zeolite for use in each system on the basis of the adsorption data of zeolites using prefixed operative conditions. Results obtained indicate that thermodynamically a given zeolite type achieves better results than the others for each of the abovementioned systems. Methodology and criterion of comparison used can be applied to other gas-solid processes aiming at realizing chemical heat pump, heat transformer and cooling systems.     

Study on forced convective heat transfer of non-newtonian nanofluids

This paper is concerned with the forced convective heat transfer of dilute liquid suspensions of nanoparticles (nanofluids) flowing through a straight pipe under laminar conditions. Stable nanofluids are formulated by using the high shear mixing and ultrasonication methods. They are then characterised for their size, surface charge, thermal and rheological properties and tested for their convective heat transfer behaviour. Mathematical modelling is performed to simulate the convective heat transfer of nanofluids using a single phase flow model and considering nanofluids as both Newtonian and non-Newtonian fluid. Both experiments and mathematical modelling show that nanofluids can substantially enhance the convective heat transfer. Analyses of the results suggest that the non-Newtonian character of nanofluids influences the overall enhancement, especially for nanofluids with an obvious non-Newtonian character.     

Application of a chemical heat pump to a cogeneration system

The feasibility of a proposed system that combines a magnesium oxide/water chemical heat pump and a diesel engine as a cogeneration system is discussed based on experimental results. The combined system is intended to utilize the waste heat discharge from the engine by means of the chemical heat pump and to level the heat supply load of the engine, allowing enhanced energy utilization. The thermal performance of the chemical heat pump in the cogeneration system is estimated based on the results of a packed‐bed experiment. The estimation indicates that by storing the waste heat from the engine during low demand periods, the cogeneration system can produce more than several times the standard thermal output of the diesel engine during peak demand periods. Copyright © 2001 John Wiley & Sons, Ltd.     

A feasibility study of improved heat recovery and excess heat export at a Swedish chemical complex site

New ambitious targets for reduced greenhouse gas emissions and increased energy efficiency in industry and in the stationary energy sector provide incentives for industrial plants to investigate opportunities for substantially increasing recovery and use of excess heat from their operations. This work investigates the economic feasibility of recovering industrial excess heat at a Swedish chemical complex site for increased site internal heat recovery or export to a regional district heating (DH) network. The work is based on investment cost data estimated in previous work by the authors. A site‐wide heat collection and distribution system based on circulating hot water was envisioned, which is also connected to a regional DH network. With the help of multiobjective optimization, the optimal heat contributions from the individual plant sites were identified that minimize the total system cost for a large range of options involving different quantities of internally recovered heat and heat export to the DH system. A payback period analysis was conducted together with a risk assessment to take into account uncertainty regarding utility steam production cost and heat sale price. The results of the study indicate that a payback period of around 3 years can be achieved for a number of cases in which 30% to 50% of the total excess heat produced by the site plants is recovered. Although it seems more profitable to recover heat at the site rather than exporting heat to the DH system only, profitability appears to be maximized by hybrid solutions that allow a share of the excess heat to be sold to the DH system and some heat to be recovered at the site simultaneously.     

Temperatures and the condensate heat resistance in dropwise condensation of multicomponent mixtures with inert gases

The temperature variations occurring in dropwise condensation at condenser plates of a compact, polymer heat exchanger are studied using instantaneous infrared temperature field recordings. An averaging procedure in time and an assessment of extreme values is proposed and carried out. With the results, the heat resistance of the condensate is quantified. It is found that mixing and convection in the condensate, caused by coalescence and drainage of drops, reduces the condensate heat resistance by a factor 4 as compared with purely conductive heat transfer. This reduction is comparable, both in nature and in magnitude, to the effect of enhanced mixing due to turbulence in the liquid film of filmwise condensation. A second condensable species has been added to the gas mixture in order to study the contribution of Marangoni convection due to concentration gradients to the condensate heat transfer resistance. No contribution is found.     

高位进气转静系旋转盘流动与换热的数值模拟

采用扩展混合长度湍流模型和S IM PLE算法,用共轭数值计算的方法模拟航空发动机涡轮盘冷却系统的高位进气、径向出流转静系旋转盘腔模型的流场和温度场,分析了其盘面平均努塞尔数N uav随旋转雷诺数R eω和流量系数Cw的变化。结果表明,随着转速和冷气流量的提高换热得以增强,但在本次计算范围内提高转速对换热的增强幅度小于提高冷气流量对换热的增强幅度。     

The heat transfer and pressure loss characteristics of a heat exchanger for recovering latent heat (the heat transfer and pressure loss characteristics of the heat exchanger with wing fin)

In recent years the requirement for reduction of energy consumption has been increasing to solve the problems of global warming and the shortage of petroleum resources. A latent heat recovery type heat exchanger is one of the effective methods of improving thermal efficiency by recovering latent heat. This paper described the heat transfer and pressure loss characteristics of a latent heat recovery type heat exchanger having a wing fin (fin pitch: 4 mm, fin length: 65 mm). These were clarified by measuring the exchange heat quantity, the pressure loss of heat exchanger, and the heat transfer coefficient between outer fin surface and gas. The effects of condensate behavior in the fins on heat transfer and pressure loss characteristics were clarified. Furthermore, the equations for predicting the heat transfer coefficient and pressure loss which are necessary in the design of the heat exchanger were proposed. ©2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(4): 215–229, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20154     

Optimization of magnesium hydroxide composite material mixed with expanded graphite and calcium chloride for chemical heat pumps

A composite chemical heat storage material (EMC) comprising a mixture of expanded graphite (EG), magnesium hydroxide (Mg(OH)₂), and calcium chloride (CaCl₂) was developed as a magnesium oxide/water chemical heat pump reactant. The optimization of a mixing weight ratio between the Mg(OH)₂ content of EMC and EMC itself was discussed from the viewpoints of both heat storage capacity and reactivity by considering the reaction rate constants from a kinetic analysis. It was confirmed that the dehydration reactivity of EMC increased as the mixing weight ratio decreased; however, the heat capacity of the EMC unit mass decreased. A multiplied factor consisting of the multiplied value dehydration rate constant and mixing weight ratio was introduced. It was suggested that a weight ratio of approximately 0.80 was the optimized value when the mixing molar ratio between CaCl₂ and Mg(OH)₂ was 0.10. Dehydration of EMC with an optimized mixing weight ratio and dehydration of pure Mg(OH)₂ were conducted under various temperatures to compare the reaction rate constants of each material. From this study, it was demonstrated that EMC performed better on dehydration than pure Mg(OH)₂.     

Use of high performance plate heat exchangers in chemical and process industries

At present, plate heat exchangers constantly open up new application fields in the chemical, process, and allied industries due to their numerous advantages. The channel flow between individual plates is characterized by high turbulence induced at low flow velocities. Heat transfer coefficients are generally higher in plate heat exchangers than in conventional shell-and-tube heat exchangers. According to the nature of the process, physical properties of the media, and allowable pressure drops, plates with a variety of patterns are available to adapt the equipment optimally to the specific process conditions. For handling aggressive media the module welded plate heat exchanger was developed. The laser welded modular design keeps the inherent advantages of plate type heat exchanger. It can be disassembled and mechanically cleaned outside the modules. The capacity can also be subsequently modified by changing the number of plates, or the plate patterns can be altered as it can be with the gasketed units. Typical applications of module welded plate heat exchangers in the chemical industry are acid coolers, thermal oil coolers, or condensers for hydrocarbon mixtures.     

Acetaldehyde/ethyl-alcohol reaction for a medium-level heat transport system

An acetaldehyde/ethyl-alcohol reversible hydrogenation and dehydrogenation reaction is proposed for a medium-level heat transport system. Under atmospheric pressure the dehydrogenation converts heat at a temperature of 350–400°C to chemical energy. At another location chemical energy may be converted back, by the hydrogenation, to thermal energy at 200–250°C For both reactions, the same silica-supported copper catalysts, particularly of ion-exchange type, have high activities and selectivities. A small amount of ethyl acetate is produced. However, the reaction producing ethyl acetate is also exothermic, so that the acetate only slightly decreases the amount of heat to be transported with this system.     

Heat-spreading analysis of a heat sink base embedded with a heat pipe

A simplified model predicting the heat transfer performance of a heat sink base with a high thermal conductivity was developed. Numerical analysis was performed using the commercial software FLUENT. The investigation indicates that for heat sink bases with a high effective thermal conductivity, such as the base embedded with a typical heat pipe, the entire heat sink can be modeled as a flat plate with a uniform temperature and an effective convection heat transfer coefficient. This simplified model can be used to determine the heat transfer performance of a heat sink embedded with a typical heat pipe or vapor chamber.     

Second law analysis and heat transfer in a cross-flow heat exchanger with a new winglet-type vortex generator

In this paper a second law analysis of a cross-flow heat exchanger (HX) is studied in the presence of a balance between the entropy generation due to heat transfer and fluid friction. The entropy generation in a cross-flow HX with a new winglet-type convergent–divergent longitudinal vortex generator (CDLVG) is investigated. Optimization of HX channel geometry and effect of design parameters regarding the overall system performance are presented. For the HX flow lengths and CDLVGs the optimization model was developed on the basis of the entropy generation minimization (EGM). It was found that increasing the cross-flow fluid velocity enhances the heat transfer rate and reduces the heat transfer irreversibility. The test results demonstrate that the CDLVGs are potential candidate procedure to improve the disorderly mixing in channel flows of the cross-flow type HX for large values of the Reynolds number.     

多污染热源置换通风的应用与节能

简述了多污染热源置换通风的原理、特性及其与混合通风的比较 ,列举了工程应用实例 ,并对其节能效果进行了分析讨论 ,指出多污染热源置换通风是一种值得推广的通风方式     

化学吸附制冷系统吸附床强化传热的实验研究

对化学吸附制冷系统吸附的强化传热传质方法进行了实验研究，针对化学吸附在脱附和吸附方面与物理吸特的不同特点，提出了几种强化传热的方案，通过实验加以比较,得出优化的发生器吸附床结构。     

Numerical simulation of stacked microchannel heat sink with mixing-enhanced passive structure

The paper is focused on the investigation of numerical simulation of stacked two-layer microchannel heat sink with enhanced mixing passive microstructure. In contrast to the smooth microchannel studies in the literature, the microchannel with embedded passive microstructure is chosen. The computational fluid dynamics (CFD) will be used to simulate the flow and heat transfer in a stacked two-layer microchannels with multiple MEMS easy-processing passive microstructures. To simulate the conjugated heat transfer among the heatsink and fluid, the three-dimensional conjugated model is used to solve this problem. The important parameters (e.g. the ratio of embedded structure height to microchannel height and fluid property) are investigated. The ratio of embedded structure height to microchannel height is changed from 0.13 to 0.26. The microchannel Reynolds number is fixed at 14.8. The stacked microchannel with passive structures has better performance than the smooth microchannels.     

Direct heat transfer considerations for improving energy efficiency in pulp and paper Kraft mills

The success of any process improvement study depends on the quality of the available data and the way in which the plant-specific characteristics are incorporated in the applied conceptual models; in the context of process integration studies these issues are directly related to the rules followed during the data extraction stage. Improving energy efficiency in a pulp and paper Kraft mill requires the identification of the most promising heat recovery network retrofit projects. In a retrofit analysis using pinch technology/process integration methods, only the process streams associated to the existing heat exchangers and some outlet streams (such as wastewater/effluent streams and vents) with high potential for heat recovery are usually included, while the energy exchanged through non-isothermal stream mixing (NIM) or direct heat transfer (DHT) is often assumed fixed and is not considered in the analysis. Relaxing this assumption requires extracting more data to represent the DHT design configuration that exists in the plant. However, different data extraction options can be considered to represent the DHT configuration depending on the associated process/operation constraints. This work describes a systematic procedure to extract and analyse the impacts of DHT on the overall energy efficiency of a Kraft process with a specific focus on mixing along the pulp line and in water tanks.