Experimental Evaluation of One,Two, and Three Stage Evaporative Cooling Systems

The thermal performance of four different arrangements of evaporative air coolers have been evaluated experimentally during the hot summer of Kuwait. The systems include one-stage direct evaporative cooling (DEC), one-stage indirect evaporative cooler (IEC) linked to an external cooling tower, two-stage indirect/direct evaporative coolers (IEC/DEC), and three-stage system of evaporative cooling and mechanical vapor compression (IEC/DEC-MVC). Two variables are used to evaluate the system thermal performance, the thermal effectiveness and the energy efficiency ratio (EER). The data show that the IEC/DEC has the highest EER, followed by the DEC, IEC/DEC-MVC, and IEC. The DEC has the lowest effectiveness, succeeded by the DEC/IEC, IEC, and IEC/DEC-MVC. Coupling MVC with IEC/DEC extends the cooling range and can cool the ambient air dry bulb temperature over a range of 40°C to 15°C at any value of ambient air wet bulb temperature. Two experimental correlations have been developed for each one of the tested systems. The first one relates the effectiveness to water to air mass flow ratio (L/G) or Reynolds number (Re), while the second correlation relates the EER with effectiveness and L/G and/or Re. These relationships are very important in designing and optimizing the studied evaporative cooling units.     

Optimal power system stabilizer

Optimal control theory applied to find excitation control signals to stabilize synchronous machines is well developed (Yu et al. 1970). This paper presents a new effective method to design such an optimal power system stabilizer. A new algorithm to solve the algebraic Riccati equation (ARE) is presented. The stabilizing signal was tested on a single-machine infinite-bus system.     

Enthalpy of Denaturation and Surface Functional Properties of Heated Egg White Proteins in the Dry State

The enthalpy of denaturation (ΔH) and surface properties of proteins were related to elucidate the mechanisms of foaming and emulsifying properties by using various heated egg white proteins in the dry state. Foaming and emulsifying properties of all sample proteins were greatly increased with a decrease in the enthalpy of denaturation as determined by differential scanning calorimetry analysis. In plots, foaming and emulsifying properties correlated linearly with ΔH values for various dry-heated egg white proteins. Thus, the enthalpy of denaturation of proteins seemed to be a significant structural factor governing surface functional properties.     

Strategies for insuring subcontracted works

In the UK construction industry there are different strategies used in practice for the insurance of subcontracted work of which two predominate: one is for subcontracted work to be insured by both main contractor and subcontractor (model A) and the other is for only the main contractor to insure the subcontracted work (model B). The extent of use of these approaches is discussed and the rationales for them are presented in the context of research undertaken by questionnaire surveys and structured interviews. The paper provides a background to the requirements for subcontractor insurance found in commonly used forms of contract, including FIDIC. Four possible models of subcontractor insurance are identified and their relationships to the contract provisions in model forms is outlined. Two of the models have little practical relevance to subcontractor insurance and the reasons for this are given. About 75% of the main contractors in the research sample were found to adopt model A for all disciplines, although the reasons given were not entirely consistent. About 15% of the sample adopt model B for all disciplines and the remainder use different models for different disciplines. Again, the rationales for these choices were not found to be robust. The main conclusions are first that the choice of strategy for subcontractor insurance is highly independent of both the discipline and the selected form of subcontract, and second that some commercial decisions in this area may be sub-optimal. There is an unreconciled argument over the immediate commercial advantages claimed by many for model A and the potential for longer term reduction in insurance costs which might arise from the widespread adoption of model B.