Performance assessment of hybrid desiccant cooling system at various climates
In our work, operation of hybrid desiccant cooling system (HDCS) has been investigated based on experimental studies. Different climates have been created by changing the temperature and humidity of HDCS inlet air, using an electrical heater and a centrifuge humidifier. Input energies, temperature of various points, and their relative humidity have been measured at the created climates. Coefficient of performance (COP), thermal coefficient of performance, and electrical coefficient of performance (ECOP) of the HDCS have been calculated. As a reference situation, vapor compression system (VCS) was examined at the same condition as HDCS. Results show that COP of HDCS in comparison with VCS decreased about 36% and 28% in hot-dry and hot-humid climates, respectively, which is due to the thermal energy consumption in HDCS. In contrast its ECOP increased, which means that by using HDCS some electrical energy would be saved. Defining operating cost index (OCI) parameter, operation costs of VCS and HDCS have been compared. Analyzing the OCI results shows that in HDCS, although decreasing the electricity consumption results in more usage of natural gas, these systems are economical especially in those countries with low natural gas prices.
A review of the mathematical models for predicting rotary desiccant wheel
In the solid desiccant wheel air-conditioning system, the performance of the desiccant wheel is critical to the capability, size and cost of the whole system. Constructing mathematical model is an effective method for analyzing the performance of the rotary wheel as well as the system. The model can also be used to guide system operation, interpret experimental results and assist in system design and optimization. The overall objective of this paper is to provide a review of various efforts that researchers have made to mathematically model the coupled heat and mass transfer process occurring within the wheel. The paper first briefly describes desiccant wheel including fundamental principle, heat and mass transfer mechanism and the method of model establishment. Then various models consisting of ideal assumptions, governing equations, auxiliary conditions, solution methods and main results are presented. The models can be classified into two main categories: (1) gas-side resistance (GSR) model; (2) gas and solid-side resistance (GSSR) model which can be further subdivided into pseudo-gas-side (PGS) model, gas and solid-side (GSS) model and parabolic concentration profile (PCP) model. It shows that GSSR models are higher in precision and more complex compared with GSR models. In addition, the simplified empirical models based on measured data are briefly discussed. This review is useful for understanding the evolution process and status quo of the mathematical model and highlighting the key aspects of model improvement such as taking account of pressure loss or air leakage.
DESIGN CONCEPT OF THE SOIL IMPROVEMENT FOR ROAD CONSTRUCION ON SOFT CLAY
This paper presents an innovative use of soil-cement mixing method using jet grouting technique to improve the bearing capacity of subbase foundation for road construction in Thailand. The construction sequences and the basic design example of jet grouting for embankment works on soft clay are also given in this paper. The design concept and method of analysis of jet grouting work using finite element technique, results of finite element analysis, the installation adopted and effectiveness of soil improvement system are given and discussed. It was found that the total settlement is reduced by the jet grouting. A case history at Pak Phanang Diversion Dam project, Nakornsrithamarat, Thailand is presented describing the engineering design and construction aspects of a successful project, which demonstrated the advantage of soil-cement mixing method over conventional pile driving for this site.