Comparative experimental investigation of two evacuated tube solar water heaters of different configurations for domestic application of Baghdad- Iraq

Abstract

Evacuated tube solar water heaters have drawbacks that limit their performance against local habits of hot water consumption, like slow water temperature rise and slow response to loading. A method to enhance their performance is using heat pipes as heat transport tools from the solar collectors to the storage water. The present work investigates the enhancement of thermal performance of evacuated tube solar water heaters subjected to (non- standard) load conditions and weather conditions of Baghdad- Iraq. Two identical evacuated tube solar water heaters (both of 120 l capacity and 20 evacuated tube solar collectors) are investigated experimentally. One system works with thermosyphon (natural convection); the other system incorporates 20 wickless heat pipes (closed thermosyphon tubes), of 16 mm diameter and 1750 mm length and are charged with methanol as working fluid at 50% fill charge ratio, as thermal conductors from the solar collectors to the storage tank. A comparison of performance of the two solar systems has been conducted by subjecting them simultaneously to different load conditions namely; no load, intermittent and continuous loading to simulate the hot water consumption habits in the local community. Extra experiments were conducted at sunny days and various weathers at no load to verify the thermal diode effect of heat pipes and the effect of weather conditions on the systems performance. Experimental results reveal an enhancement in overall daily efficiency of the heat pipe system over the thermosyphon system by 22.5% for no load, 42.5% for intermittent loading and 32.4% for continuous loading. The heat pipe system produced higher temperatures and better response at all load conditions and adverse weather conditions that make it more suitable for local domestic application. The thermosyphon system performs suitably with no load and intermittent load at small removal quantities. Results agree with those in the literature.