Performance prediction of an absorption heat pump for utilization in industry

Recently, an absorption heat pump has been put on the market for industrial utilization. It is a H₂O-LiBr absorption machine which heats up water to 90°C with a cold source at 40°C. The capacity and COP of the machine have been studied by a computer program as a function of cold source temperature and heated fluid temperature. Also, a comparison with a compression heat pump is reported.     

The use of an absorption heat pump by a thermal bathing establishment

An energy saving plant was realized by a thermal bathing establishment. The plant is composed of a three fluid plate heat exchanger and an absorption heat pump between the source preheated water and the discharged one. During the cold winter the establishment is maintained at a temperature of 5°C. The absorption heat pump uses the thermal water as cold source.     

Performance of a Single-Family Heat Pump at Different Working Conditions Using Small Quantity of Propane as Refrigerant

The performance of a domestic heat pump that uses a low quantity of propane as refrigerant has been experimentally investigated. The heat pump consists of two minichannel aluminium heat exchangers, a scroll compressor, and an electronic expansion valve. It was charged with the minimum amount of refrigerant propane required for the stable operation of the heat pump without permitting refrigerant vapor into the expansion valve at incoming heat source fluid temperature to the evaporator of +10°C. The inlet temperature of the heat source fluid passing through the evaporator was varied from +10°C to ?10°C while holding the condensing temperature constant at 35°C, 40°C, 50°C, and 60°C, respectively. The minimum refrigerant charges required at above-tested condensing temperatures were found to decrease when the condensing temperature increased and were recorded as 230 g, 224 g, 215 g, and 205 g, respectively. The results confirm that a heat pump with 5 kW capacity can be designed with less than 200 g charge of refrigerant propane in the system. Due to the high solubility of propane in compressor lubrication oil, the amount of refrigerant which may escape rapidly in case of accident or leakage is less than 150 g.     

New compression heat pump media for medium and high temperature application

The economy and operability of compression heat pump systems is to a great extent influenced by the working fluid. However, the choice of the appropriate medium for a given heat pump application is not straight forward, since a great number of physical and non-physical properties of the presumptive working fluids have to be accounted for.A systematic method of looking for the best medium has been developed. With the help of a commercial flowsheet program a simulation routine of the heat pump cycle has been established. This routine was used to screen all substances in the attached data bank in respect to their applicability as working media. In all, 940 substances have been investigated. From these substances 42 show favourable properties as working fluids for the application in three cases, namely with a temperature of the heat source of 2°C and of the heat sink of 70°C respectively, 60°C source temperature and 120°C at the heat sink and of 90°C source temperature and 150°C at the heat sink.A further investigation of these 42 substances with respect to toxicity and stability left four of them as the ultimate proposal for operable compression heat pump fluids.Besides the actual proposal of new media, the investigation produces a much better understanding of the influence of physical properties on the heat pump performance. From the great number of data, a reliable prediction of the applicability of a given substance as a working fluid, based on the critical data, was deduced.     

Techno-economic viability of upgrading thermal effluents in industries: Application in developing countries

Upgrading industrial thermal effluents using a heat pump is an effective energy conservation measure. Although it is proven and has been in use in industrialized countries, its application is grossly lacking in the developing world.Using technical and economical parameters, this paper investigates the viability of upgrading industrial thermal effluents and hence conserving energy using different types of heat pumps. Eleven different types of systems are formulated using the mathematical models developed for multi-stage vapor compression heat pumps and multi-stage vapor jet compressors and adopting the “Grossman Absorption Model” for the absorption heat transformer. A comparative analysis is performed for upgrading the low temperature industrial thermal effluents by employing various types of heat pumps with presently existing fuel and electricity prices in Thailand. It does not take into account the process details or the heat pump integration details. A case of integrating heat pumps in distillation columns in an industrial plant in Sri Lanka is also investigated. The energy saving potential clearly indicates that heat pumps are techno-economically viable in the industries of developing countries. The absorption heat transformer is very attractive since it utilizes waste heat itself to upgrade the thermal effluent temperature.     

Developments in geothermal energy in Mexico—part forty. The future for geothermal energy in Mexico

In Mexico there are many potential geothermal energy sources with a wide range of temperatures. At present high temperature geothermal energy is used to generate electricity. Considerable experience has been accumulated in the exploitation of geothermal energy. Lower grade geothermal heat could be used to generate electricity with organic Rankine cycle plants. There is little industrial exploitation of lower temperature geothermal resources at present even though in the centre of Mexico areas of geothermal activity coincide with industrial zones. However, this situation could change with the use of suitable heat exchangers and heat pumps, particularly absorption systems to supply process heat with very little pollution.     

非对称纳米通道内流体流动与传热的分子动力学

采用分子动力学方法研究了流体在非对称浸润性粗糙纳米通道内的流动与传热过程,分析了两侧壁面浸润性不对称对流体速度滑移和温度阶跃的影响,以及非对称浸润性组合对流体内部热量传递的影响.研究结果表明,纳米通道主流区域的流体速度在外力作用下呈抛物线分布,但是纳米通道上下壁面浸润性不对称导致速度分布不呈中心对称,同时通道壁面的纳米结构也会限制流体的流动.流体在流动过程中产生黏性耗散,使流体温度升高.增强冷壁面的疏水性对近热壁面区域的流体速度几乎没有影响,滑移速度和滑移长度基本不变,始终为锁定边界,但是会导致近冷壁面区域的流体速度逐渐增大,对应的滑移速度和滑移长度随之增大.此时,近冷壁面区域的流体温度逐渐超过近热壁面区域的流体温度,流体出现反转温度分布,流体内部热流逆向传递.随着两侧壁面浸润性不对称程度增加,流体反转温度分布更加明显.     

The development and investigation of a strongly non-equilibrium model of heat transfer in fluid with allowance for the spatial and temporal non-locality and energy dissipation

The differential equation of heat transfer with allowance for energy dissipation and spatial and temporal nonlocality has been derived by the relaxation of heat flux and temperature gradient in the Fourier law formula for the heat flux at the use of the heat balance equation. An investigation of the numerical solution of the heat-transfer problem at a laminar fluid flow in a plane duct has shown the impossibility of an instantaneous acceptance of the boundary condition of the first kind — the process of its settling at small values of relaxation coefficients takes a finite time interval the duration of which is determined by the thermophysical and relaxation properties of the fluid. At large values of relaxation coefficients, the use of the boundary condition of the first kind is possible only at Fo → ∞. The friction heat consideration leads to the alteration of temperature profiles, which is due to the rise of the intervals of elevated temperatures in the zone of the maximal velocity gradients. With increasing relaxation coefficients, the smoothing of temperature profiles occurs, and at their certain high values, the fluid cooling occurs at a gradientless temperature variation along the transverse spatial variable and, consequently, the temperature proves to be dependent only on time and on longitudinal coordinate.     

Experimental Investigations on Latent Heat Storage Unit using Paraffin Wax as Phase Change Material

Thermal performance of a latent heat storage unit is evaluated experimentally. The latent heat thermal energy storage system analyzed in this work is a shell-and-tube type of heat exchanger using paraffin wax (melting point between 58°C and 60°C) as the phase change material. The temperature distribution in the phase change material is measured with time. The influence of mass flow rate and inlet temperature of the heat transfer fluid on heat fraction is examined for both the melting and solidification processes. The mass flow rate of heat transfer fluid (water) is varied in the range of 0.0167 kg/s to 0.0833 kg/s (1 kg/min to 5 kg/min), and the fluid inlet temperature is varied between 75°C and 85°C. The experimental results indicate that the total melting time of the phase change material increases as the mass flow rate and inlet temperature of heat transfer fluid decrease. The fluid inlet temperature influences the heat fraction considerably as compared to the mass flow rate of heat transfer fluid during the melting process of the phase change material.     

气泡泵在冷态试验下的性能研究

搭建气泡输入式冷态试验系统,以常压饱和水为工质,均匀输入空气形成连续气泡用于模拟气泡泵运行系统,对气泡泵的性能进行研究。其实验结果与在加热状态下气泡泵的性能相比较,综合分析气体输入量(可转换成加热量)、沉浸比等对气泡泵性能的影响,提出产生此结果的原因。     

热漏对换热器(火积)耗散最小化的影响

建立了存在热漏的换热器的传热过程模型.假定热流体与冷流体间的传热以及冷流体与外界环境间的热漏均服从牛顿传热定律,在冷流体净传热量一定的条件下,应用最优控制理论导出了换热过程(火积)耗散最小时热流体温度和冷流体温度的最优构型,并将最优路径分别与热流体温度一定和热流率一定的传统传热策略进行了比较.研究结果对于实际换热器的优化设计和最优运行具有一定的理论指导意义.     

Heat pump design with thermal storage

This paper is concerned with the problems of designing heat pumps using atmospheric air as the external low temperature source of energy with the accumulation of thermal energy in a circuit of working fluid. The optimal dimensioning of heat pump systems with thermal storage by means of the computer simulation minimizes disadvantages occurring in heat pump systems ithout thermal storage.     

Preparation of poly(vinyl alcohol)–silicone based hybrid membranes for the pervaporation separation of water–acetic acid mixtures

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis followed by condensation. The obtained membranes were characterized by Fourier transform infrared spectroscopy, wide-angle x-ray diffraction and differential scanning calorimetry. A remarkable decrease in degree of swelling was observed with increasing TEOS content in membranes and is attributed to the formation of hydrogen bonding and covalent bonds in the membrane matrix. The pervaporation performance of these membranes for the separation of water–acetic acid mixtures was investigated in terms of feed concentration and the content of TEOS used as cross-linking agent. The membrane containing 1 : 2 mass ratio of PVA and TEOS gave the highest separation selectivity of 1116 with a flux of 3.33 × 10^?2kg/m²h at 30°C for 10 mass% of water in the feed. Except for membrane M-1, the observed values of water flux are close to the values of total flux in the investigated composition range, signifying that the developed membranes are highly water selective. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters have been estimated. The resulting activation energy values obtained, showing that water permeation is lower than that of acetic acid, suggest that the membranes have higher separation efficiency. The activation energy values calculated for total permeation and water permeation are close to each other for all the membranes except membrane M-1, signifying that coupled-transport is minimal because of the higher selective nature of membranes. The negative heat of sorption values (ΔH _s) for water in all the membranes suggests a Langmuir mode of sorption.     

The energy equation of a sphere in an unsteady and nonuniform temperature field

The equation for the unsteady heat transfer from a sphere in a viscous/conducting fluid at finite Biot numbers is developed. This process has two characteristic times, one for the diffusion of heat inside the sphere and the other for the diffusion of heat in the external fluid. The solution of the governing equations proves that a general analytical solution may be obtained in the Laplace domain, but not in the time domain. This is due to the complexity of the heat transfer process and the two time scales involved. Asymptotic analytical solutions may be obtained at short and long times. It is observed that the complete form of the energy equation of a small sphere, even at zero Peclet numbers (creeping flow condition) is very complex. Several history terms appear in the energy equation. These emanate from temperature gradients diffused in the two media since the commencement of the heat transfer process.     

非共沸混合工质自复叠热泵循环试验研究

单级压缩式热泵冷凝温度与蒸发温度之差一般为40~50℃,非共沸混合工质自复叠循环具有工作温差大的优点,将其应用于热泵循环,则可产生较大的供热温差。该文通过搭建一个空气源自复叠热泵实验台,利用NIST公司的制冷剂物性数据库Refprop7,绘制出了混合工质的温度-浓度图。经过实验,分析了自复叠热泵循环工作温差的影响因素,得出了自复叠热泵气液分离器简单分离对增大工作温差的作用有限,增加工质的相对挥发度也不能显著改善热泵的运行性能等结论。并进一步得出了增设分凝设施可显著增大工作温差的结论。     

利用液氮冷能的小型天然气液化流程

为了简化小型天然气液化流程中的制冷装置,增加产品的收益率,设计了一种利用液氮冷能且带精馏的天然气液化流程,在得到液化天然气(LNG)的同时得到液化石油气(LPG)。采用HYSYS软件对流程进行模拟,选取P-R方程计算天然气气液相平衡特性,以生产单位质量的LNG耗功最小为目标函数进行优化,得到了关键节点参数,主要分析了塔内工作状况和换热器管路的热负荷分布情况。结果表明:塔的操作压力对产品纯度影响很大,换热器过大的温差和负荷造成了主要的火用损失,LNG回收率大于90%。     

Working fluids for heat transformers

A large amount of thermal energy, in the temperature range of 50–90°C, released to the atmosphere by many commercial installations such as agrofeed, paper mills, dairies and process industries, can be upgraded making possible its use in various forms. Many attempts have benn made in most industrial sectors to recovery this energy by heat pumps, organic Rankine cycles and heat transformers. Among various possibilities, heat transformers present an attractive solution as low level heat can be transformed into a higher temperature with minimum consumption of external energy. Further transformers do not require high maintenance and operating cost.The theoretical performance characteristics of single stage heat transformers using various promising binary mixtures as working fluids have been discussed in this paper. The coefficient of performance, energy efficiencies and mass circulation ratio have been analysed as a function of heat delivery temperature. The comparison of working fluids has also been discussed.     

地源热泵的应用对环境的影响分析

地源热泵被认为是一种高效、节能、环保、有利于可持续发展的技术,它被认为是21世纪最有效的空调技术。然而地源热泵的大量使用也带来了一系列的环境问题。分别针对地表水源热泵、地下水源热泵以及土壤源热泵的使用对环境的影响进行了深入分析,并对可能的解决方案进行了讨论。     

液化天然气CCHP系统的乙烯-丙烷级联动力循环及工艺模拟

文中提出了一种适用于LNG冷热电联产系统的两级乙烯-丙烷级联朗肯动力循环,并采用HYSYS软件对这一级联动力循环进行了工艺模拟,LNG的流量为219kg/h时,共可以产生电力14.06W,并向空调供冷50.24kW.与不采用冷量回收的装置相比,总的能量利用率从83.22％提高到了85.17％.这说明级联式动力循环通过梯...     

Derived thermodynamic design data for heat pump systems operating on R744

Theoretical Rankine coefficients of performance and the compression ratios have been presented for heat pump systems operating on R503. These values are listed in tabular form for temperature lifts of 10–55°C and condensing temperatures of 7–30°C in one degree increments. A composite plot has been drawn to illustrate the feasible operating range of R744 heat pump systems.