P. S. Doherty

Development of a prototype low-temperature Rankine cycle electricity generation system

This paper describes the development of a small-scale system designed to generate electricity from low temperature heat (e.g., solar energy). The system operates on the Rankine cycle and uses n-pentane as the working fluid. A prototype system has been designed, constructed and tested. It is capable of delivering 1.5 kW of electricity with a thermal efficiency of 4.3%. Laboratory test results and a cost estimate for the prototype unit are presented in the paper.

Development of a solar-powered passive ejector cooling system

This paper describes the development of an ejector refrigeration system that is powered by solar thermal energy. The cooling system contains no active parts and is therefore deemed passive. Water is used as the refrigerant though other natural refrigerants could be used for lower temperature operation. A prototype system was built with a nominal cooling capacity of 7 kW. This system was laboratory tested and then installed in an existing office in Loughborough, UK. The system has operated with a COP of up to 0.3 at this location. The system is also able to provide up to 20 kW of heating to the building during the winter.

A combined heat and power system for buildings driven by solar energy and gas

A novel hybrid solar/gas system intended to provide cooling/heating and electricity generation for buildings was developed. The system is based on the combination of an ejector heat pump cycle with a Rankine cycle. It is driven by solar energy and supplemented by a gas burner. The system also uses an environmentally friendly refrigerant to have minimal impact on the environment. Results of system computer modelling, prototype tests and economic analysis are reported. The system was judged to be viable and reliable. Technical improvements still have to be achieved to improve system economics.

Application of CFD to closed-wet cooling towers

Computational fluid dynamics (CFD) is applied to predicting the performance of closed-wet cooling towers (CWCTs) for chilled ceilings according to the cooling capacity and pressure loss. The prediction involves the two-phase flow of gas and water droplets. The predicted thermal performance is compared with experimental measurement for a large industrial CWCT and a small prototype cooling tower. CFD is then applied to the design of a new cooling tower for field testing. The accuracy of CFD modelling of the pressure loss for fluid flow over the heat exchanger is assessed for a range of flow velocities applied in CWCTs. The predicted pressure loss for single-phase flow of air over the heat exchanger is in good agreement with the empirical equation for tube bundles. CFD can be used to assess the effect of flow interference on the fluid distribution and pressure loss of single- and multi-phase flow over the heat exchanger.

Thermal performance of a novel air conditioning system using a liquid desiccant

A new air conditioning system using a liquid desiccant and needle impeller rotors has been modelled. Experimental data obtained for different components, i.e., evaporators and absorber, were used in the model. System performance was quantified through the definition of thermal coefficient of performance. Simulation results show the effect of different system parameters: ambient temperature, ambient humidity and heat exchanger efficiency.

Performance testing of different types of liquid flat plate collectors

This paper presents the results obtained from laboratory testing of four liquid flat plate collectors. The collectors tested include a wavy fin collector, two flat plate heat pipe collectors, and a clip fin solar collector. The clip fin solar collector was tested, so as to compare this simple and inexpensive type of collector against the more costly wavy fin collector and the flat plate heat pipe collector. Using a similar basis of comparison, efficiency values have been formulated in order to compare the performance of the solar collectors. The experimental results show the clip fin solar collector to be promising, with experimental efficiencies approaching 86 per cent. Copyright

Theoretical and Experimental Investigation of a Novel Hybrid Heat-Pipe Solar Collector

Abstract This article describes a novel flat plate heat-pipe solar collector, namely, the hybrid heat-pipe solar collector. An analytical model has been developed to calculate the collector efficiency as well as simulate the heat transfer processes occurring in the collector. The effects of heat pipes/absorber, top cover, flue gas channel geometry, and flue gas temperature and flow rate, on the collector efficiency were investigated based on three modes of operation, i.e., solar only operation, solar/exhaust gas combined, and solar, exhaust gas and boiler combined. Experimental testing of the collector was also carried out for each of these modes of operation under real climatic conditions. The results were used to estimate the efficiency of the collector and determine the relation between the efficiency and general external parameter. The modeling and experimental results were compared and a correlation factor was used to modify the theoretical predictions. It was found that the efficiency of the collector was increased by about 20–30% compared to a conventional flat-plate heat pipe solar collector.

Thermal performance of a closed wet cooling tower for chilled ceilings: measurement and CFD simulation

A closed wet cooling tower, adapted for use with chilled ceilings in buildings, was tested experimentally. The thermal efficiency of the cooling tower was measured for different air flow rates, water flow rates, spray flow rates and wet bulb air temperatures. CFD was also used to predict the thermal performance of the cooling tower. Good agreement was obtained between CFD prediction and experimental measurement. Copyright

Investigation of the flow in an impulse micro turbine using numerical CFD predictions and laboratory testing

SYNOPSIS A 12-blade, 45° pitched-blade impulse micro turbine was used to generate electricity by operating with selected working fluids, namely, water, n-pentane, methanol and R141b. The turbine geometry was fixed during the investigation but the flow area of the working fluid was varied in order to determine its effect on performance. A number of inlet and outlet conditions were assumed and CFD numerical prediction was carried out using the FLUENT code. The simulation results allowed the percentage of un-blocked flow area to be determined for different working fluids and different inlet/outlet conditions, and the optimum working fluid and operation conditions to be found. An experimental trial was carried out using n-pentane as the working fluid at an inlet pressure of 5.14 bar(a) and an outlet pressure of 1.15 bar(a), in order to demonstrate the thermal and power characteristics of the micro turbine. CFD modelling predictions were validated by comparison with the experimental results.

Flue gas sorption heat recovery : experimental test and modelling results

An investigation of sorption fluids to recover latent and sensible heat from flue gas exhaust using the process of dehumidification has been carried out. Lithium bromide, potassium formate and lithium chloride were identified as suitable working fluids. The study also included the construction and testing of a small-scale experimental system. A detailed parametric model was developed, enabling different gaseous fuels to be investigated and the associated flue gas energy loss and potential heat recovery to be estimated. Results from the studies indicate a potential fuel saving of between 5 and 8% above that of a standard condensing boiler. An analysis of the likely environmental and economic impacts of systems based on sorption heat recovery was carried out.