Y.J. Dai

Use of liquid desiccant cooling to improve the performance of vapor compression air conditioning

A hybrid air conditioning system, which consists of sections of desiccant dehumidification, evaporative cooling and vapor compression air conditioning, has been established in this paper. Experimental investigation demonstrates that cooling production and COP of the new hybrid system can be increased significantly, if they are compared with those of vapor compression system (VCS) alone. Assuming that the outlet temperature and humidity of the system are constant, psychrometric analysis at ARI conditions has been conducted under three different cases. The benefits are represented by lower electricity consumption of the compressor, higher COP of the system, less flow rate of condensation air, and reduced size of VCS, etc. The reason that the hybrid system is superior in performance to conventional systems lies in that desiccant dehumidification and evaporative cooling changes the inlet states of the air entering into VCS. Furthermore, the effects of dehumidification and evaporative cooling are analyzed in the paper.

A simulation study of heat and mass transfer in a honeycombed rotary desiccant dehumidifier

A one-dimensional coupled heat and mass transfer model, which is expected for use in designing and manufacturing of a honeycombed rotary desiccant wheel, is presented in this paper. The mathematical model has been validated using a real desiccant wheel, and the calculation results are in reasonable agreement with the experimental data. Based on this model, the temperature and humidity profiles in the wheel during both the dehumidification and the regeneration processes are analyzed and verified by experimental data. The numerical results indicate that in the regeneration process a hump curve of air humidity ratio along the channel exists all the time. In the regeneration process the hump of air humidity ratio moves from the duct entrance to the duct exit and increases gradually until the hump reaches the duct exit, where the hump will drop subsequently. The effects of velocity of regeneration air Vreg inlet temperature of regeneration air Treg and velocity of process air Vad on the hump moving speed are investigated. To improve the performance of desiccant wheel, it is essential to accelerate the hump moving from the duct entrance to the duct exit as soon as possible.

Case study of solar chimney power plants in Northwestern regions of China

A solar chimney power plant, which is expected to provide electric power for remote villages in northwestern China, has been analyzed in this paper. Three counties in Ning Xia Hui Autonomous region, namely, Yinchuan, Pingluo, and Helan, where solar radiation is better than other regions of China, were selected as pilot locations to construct solar power plant. The solar power plant chimney, in which the height and diameter of the chimney are 200 m and 10 m, respectively, and the diameter of the solar collector cover is 500 m, is able to produce 110~190 kW electric power on a monthly average all year. Some parameters, such as chimney height, diameter of the solar collector, ambient temperature, solar irradiance and the efficiency of wind turbine, etc. which influence the performance of power generation, are also analyzed.

Experimental investigation of a solar desalination unit with humidification and dehumidification

A solar desalination unit with humidification and dehumidification is presented. Experiments on the unit were conducted. It was found that the performance of the system was strongly dependent on the temperature of inlet salt water to the humidifier, the mass flow rate of salt water, and the mass flow rate of the process air. There existed an optimum rotation speed for the fan corresponding to an optimum mass flow rate of air with respect to both thermal efficiency and water production. The unit worked perfectly and the thermal efficiency was above 80%. Other low-grade heat resources such as waste heat can also be utilized to drive the desalination process. It was expected that the unit would be of great potential for use in desalination in arid areas and isolated islands.

Parameter analysis to improve rotary desiccant dehumidification using a mathematical model

Waves analysis using psychrometric chart, a method aiming to evaluate the rotary desiccant dehumidification, is presented in this paper. The continuity and energy conservation equations for the transient coupled heat and mass transfer are established and solved using a finite differential model. The locus of points of outlet air states along the rotational direction may be plotted as two wave fronts and one breakthrough point for both dehumidification and regeneration processes. Thermal wave, concentration wave, and middle zone point are explained in terms of the different characteristics of their own. The rules to improve the performance of dehumidification according to the wave shape are proposed and some important parameters, such as heat capacity, adsorption heat, rotation speed, regeneration temperature, thickness of the desiccant matrix and the desiccant isothermal shape, are discussed in detail using psychrometric chart. It is demonstrated that the chart method is feasible and rapid in evaluating the performance of the rotary dehumidifier.

Experimental investigation on a thermoelectric refrigerator driven by solar cells

Experimental investigation and relevant analysis on a solar cell driven, thermoelectric refrigerator has been conducted. To make the device portable, daytime use and nighttime use of the refrigerator are treated in different ways. Solar cells are applied to power the refrigerator in the day. Storage battery, assisted by an a.c. rectifier, is used to provide electric energy in the night and in cloudy or rainy days. Experiment results demonstrate that the unit can maintain the temperature in the refrigerator at 5–10 °C, and have a COP about 0.3. It is expected that the refrigerator would be potential for cold storage of vaccine, foodstuffs and drink in remote area, or outdoor applications where electric power supply is absent.

Parametric analysis to improve the performance of a solar desalination unit with humidification and dehumidification

Abstract A solar desalination unit with humidification and dehumidification, characterized by reusing some of somewhat concentrated saline water after evaporation, recovering condensation heat, and forced air flow, was expected to produce more fresh water. A mathematical model of the unit is presented. The model was experimentally validated for numerical simulation. Parametric analysis was conducted in order to optimize the unit performance. The effect of some of the operating conditions such as flow rates, temperatures of feed water, air and cooling water, etc., was studied in detail. The daily solar productivity corresponding to unit square meter of collector area is about 6 kg/m 2 /d with 20 MJ solar energy input a day under given conditions. The unit has proven to be an efficient device to utilize solar energy for obtaining fresh water from saline water.

Study of a solar powered solid adsorption–desiccant cooling system used for grain storage

A hybrid solar cooling system, which combines the technologies of rotary desiccant dehumidification and solid adsorption refrigeration, has been proposed for cooling grain. The key components of the system are a rotary desiccant wheel and a solar adsorption collector. The former is used for dehumidification and the later acts as both an adsorption unit and a solar collector. The heating load from sunshine can thus be reduced to a greater extent since the solar adsorption collector is placed on the roof of the grain depot. Compared with the solid adsorption refrigeration system alone, the new hybrid system performs better. Under typical conditions, the coefficient of performance of the system is >0.4 and the outlet temperature is <20°C. It is believed that the system can be used widely in the regions with abundant solar resources due to such advantages as environmental protection, energy saving and low operation costs. Additionally, some parameters, for example, ambient conditions, the effectiveness of the heat exchanger and evaporative cooler, mass air-flow rate, etc., which affect system performance, are also analyzed.

Experimental Study on a Hybrid Desiccant Dehumidification and Air Conditioning System

This paper presents the experimental tests on hybrid desiccant dehumidification and air conditioning systems. Experimental tests are carried out with LiC1 desiccant at typical operative ranges for air conditioning applications, particularly for high humid regions like Hong Kong. Results are reported in terms of coefficient of performance (COP) based on primary energy usage and electrical energy usage, respectively. Experiments have demonstrated consistent reduction in humidity ratio satisfying the sensible as well as latent load through a respective subsystem and thereby resulting in a higher COP based on primary energy usage. Also, results show that the regeneration temperature as well as process air flow rate have a significant role on the system performance. It is found that the hybrid system can achieve a higher part load performance, and hence can assure of its effective operation all year around in hot humid regions.

Dissociative Disorders Among Chinese Inpatients Diagnosed with Schizophrenia

The purpose of this study was to assess the prevalence of dissociative disorders in a sample of Chinese psychiatric inpatients. Participants in the study were 569 consecutively admitted inpatients at Shanghai Mental Health Center, China, of whom 84.9% had a clinical diagnosis of schizophrenia based on the Chinese Classification and Diagnostic Criteria of Mental Disorders, Version 3. All participants completed a self-report measure of dissociation (the Dissociative Experiences Scale), and none had a prior diagnosis of a dissociative disorder. A total of 96 randomly selected participants were interviewed with a structured interview (the Dissociative Disorders Interview Schedule) and a clinical interview. These 96 patients did not differ significantly from the 473 patients who were not interviewed on any demographic measures or who did not complete the self-report dissociation measure. A total of 28 patients (15.3%, after weighting of the data) received a clinical diagnosis of a dissociative disorder based on Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.) criteria. Dissociative identity disorder was diagnosed in 2 patients (0.53%, after weighting). Compared to the patients without a dissociative disorder, patients with dissociative disorders were significantly more likely to report childhood abuse (57.1% vs. 22.1%), but the 2 groups did not differ significantly on any demographic measures. Dissociative disorders were readily identified in an inpatient psychiatric population in China.