Shenyi Wu

Innovations in vapour-absorption cycles

During the past decade, there has been unprecedented research interest in vapour-absorption cycle refrigeration and heat pumping driven by the need to reduce CO2 emissions related to process and comfort cooling. This paper reviews some recent innovations in vapour absorption-cycle technology, with particular emphasis on the cycle design and fluid selection. The operation and design of innovative cycles are described as well as the latest research in working fluids.

A novel absorption-recompression refrigeration cycle

Abstract This paper reports on a novel ejector boosted single–effect absorption-recompression refrigeration cycle. In this cycle, a steam generator, ejector and a concentrator replace the high and low pressure generators (concentrators) used in conventional double-effect absorption cycle machines, to re-concentrate the absorbent solution. The ejector here acts like a heat-pump to enhance the concentration process by increasing the flow of leaving vapour and by increasing the quantity of heat input at the concentrator. The paper provides a qualitative and quantitative description of the novel cycle and discusses design choices that lead to optimum matching of the absorbent concentrator and ejector. The important role the ejector plays in this novel refrigeration cycle is discussed and some experimental data are presented. An experimental lithium bromide refrigerator based on this cycle is described.

An experimental investigation of steam ejectors for applications in jet-pump refrigerators powered by low-grade heat

Abstract The jet-pump refrigerator cycle offers a low-capital-cost solution for utilizing low-grade waste heat in the production of cooling for buildings and process refrigeration. The heart of the jet-pump refrigerator is an ejector, the performance of which strongly determines the thermal efficiency of the cycle. This paper describes and evaluates the results of an experimental investigation into the operation of ejectors primarily for use in jet-pump refrigerators. The construction of a steam-steam ejector test facility and experimental method are described. Experimental results are provided concerning the effects of primary nozzle exit position within the mixing-entrainment section, primary nozzle exit and diffuser throat areas. The causes and effects of flow instability under conditions of high secondary pressure ratio are also discussed and methods of increasing the critical condenser pressure are identified and rated in order of effect.

A theoretical study of an innovative ejector powered absorption–recompression cycle refrigerator

Abstract This paper describes a novel cycle which uses a steam ejector to enhance the concentration process by compressing the vapour from the lithium bromide solution to a state that it can be used to re-heat the solution from which it came. The energy efficiency and the performance characteristics of the novel cycle are theoretically investigated in this paper. The theoretical results show that the coefficient of performance ( COP ) of the novel cycle is better than the conventional single-effect absorption cycle. The characteristics of the cycle performance show its promise in using high temperature heat source at low cost.

Experimental proof-of-concept testing of an innovative heat-powered vapour recompression-absorption refrigerator cycle

Abstract This paper describes and evaluates the results of an experimental study in relation to the performance of an innovative vapour recompression–absorption refrigerator cycle. This novel refrigerator incorporates a steam jet-pump cycle which acts as an internal heat pump which upgrades otherwise wasted heat from the solution concentrator and uses it to assist in the desorption process. The cycle is described in detail, a description of the experimental, proof-of-concept, refrigerator is given and experimental results are evaluated.

Heat energy storage and cooling in buildings

Abstract: This chapter introduces the technology of heat storage and cooling and its applications in buildings. It discusses the psychrometrics and air conditioning which are relevant to the thermal energy storage for building thermal comfort applications. The discussion then goes on to three heat storage methods, namely, the sensible, the latent and the chemical heat storage technologies and the issues that are related to the performance of the thermal energy storage. It also presents some of the latest developments in thermal energy storage for energy-saving building thermal comfort applications.

A valve operated absorption refrigerator

Abstract This paper presents a lithium bromide absorption refrigerator that does not use a mechanical pump for solution circulation. In this refrigerator, the solution circulation is achieved by making use of pressure in the generator. To achieve this, the generator is designed to carry out two functions namely desorption and circulation alternatively, which is served by two operational valves. A mathematic model for the solution circulation is developed to predict the refrigerator’s performance. Results from the model shows that this refrigerator can give a similar COP to that from single-effect refrigerators with mechanical pump circulation. This paper also discusses some structural effects to the refrigerator’s performance based on the mathematic model.

Low-pressure ejectors: Prediction of performance by computational fluid dynamics

Computational fluid dynamics (CFD) is applied to predict the performance of low-pressure ejectors. Its accuracy is compared with predetermined experimental results. This Note shows that low-pressure ejectors depend strongly on geometry. CFD can predict their performance good accurately whether there is good positive entrainment or back pressure resulting in negative entrainment. It is concluded that CFD is a useful tool for designing low-pressure ejectors.

Mathematical and Experimental Investigation of Water Migration in Plant Xylem

Plant can take water from soil up to several metres high. However, the mechanism of how water rises against gravity is still controversially discussed despite a few mechanisms have been proposed. Also, there still lacks of a critical transportation model because of the diversity and complex xylem structure of plants.This paper mainly focuses on the water transport process within xylem and a mathematical model is presented. With a simplified micro channel from xylem structure and the calculation using the model of water migration in xylem, this paper identified the relationship between various forces and water migration velocity. The velocity of water migration within the plant stem is considered as detail as possible using all major forces involved, and a full mathmetical model is proposed to calculate and predict the velocity of water migration in plants.Using details of a specific plant, the velocity of water migration in the plant can be calculated, and then compared to the experimental result from Magnetic Resonance Imaging (MRI). The two results match perfectly to each other, indicating the accuracy of the mathematical model, thus the mathematical model should have brighter future in further applications.