Thermosyphon Heat Pipe Technology

Heat pipes play vital roles in increasing heat transfer performance of many engineering systems such as solar collectors and this leads to an increase in their usage. Investigation on the performance of heat pipes under different operation conditions and inclination angles is required for effective utilization. In this chapter, a general overview on the construction, operation, advantages, and classifications of heat pipes is presented. Particular attention is given to the heat pipe without wick material in the inner diameter (thermosyphon). Intensive discussions are presented on the construction, operations, advantages and applications of thermosyphon heat pipe. The experimental and numerical approaches on the performance evaluation and characterization of thermosyphon are discussed. A detailed procedure on how experimental work is carried out on thermosyphon is discussed including instrumentation and calibration of the devices. Modelling and simulation of the performance of thermosyphon are discussed, including the model set-up procedure. Factors affecting the performance of thermosyphon such as fill ratio, working fluid, heat input, inclination angles, are analysed based on the overall thermal resistance and thermosyphon performance. Current researches on the effects of major factors affecting the operation of thermosyphon are presented, as well as their current development and various applications in engineering systems

Characterisation of metal organic frameworks for adsorption cooling

Silica gel/water adsorption cooling systems suffer from size, performance and cost limitations. Therefore, there is a need for new adsorbent materials that outperform silica gel. Metal organic frameworks (MOFs) are new micro-porous materials that have extraordinary porosity and uniform structure. Due to the lack of published data that characterise MOF/water adsorption, this paper experimentally investigates the adsorption characteristics of HKUST-1 (Cu-BTC (copper benzene-1,3,5-tricarboxylate), C 18H 6Cu 3O 12) and MIL-100 (Fe-BTC (Iron 1,3,5- benzenetricarboxylate), C 9H 3FeO 6) MOFs compared to silica gel RD-2060. The adsorption characteristics of Silica gel RD-2060, HKUST-1 and MIL-100 were determined using an advanced gravimetric dynamic vapour sorption analyser (DVS). Results showed that HKUST-1 performed better than silica gel RD-2060 with an increase of water uptake of 93.2%, which could lead to a considerable increase in refrigerant flow rate, cooling capacity and/or reducing the size of the adsorption system. However, MIL-100 MOF showed reduced water uptake comparable to silica gel RD-2060 for water chilling applications with evaporation at 5 0C. These results highlight the potential of using MOF materials to improve the efficiency of water adsorption cooling systems

Numerical investigation of turbulent flow heat transfer and pressure drop of AL2O3/water nanofluid in helically coiled tubes

Passive convective heat transfer enhancement can be achieved by improving the thermo-physical properties of the working fluid, changing flow geometry or both. This work presents a numerical study to investigate the combined effect of using helical coils and nanofluids on the heat transfer characteristics and pressure losses in turbulent flow regime. The developed computational fluid dynamics models were validated against published experimental data and empirical correlations. Results have shown that combining the effects of alumina (Al2O3) nanoparticles and tube coiling could enhance the heat transfer coefficient by up to 60% compared with that of pure water in straight tube at the same Reynolds number. Also, results showed that the pressure drop in helical coils using Al2O3 nanofluid for volume fraction of 3% was six times that of water in straight tubes (80% of the pressure drop increase is due to nanoparticles addition), while the effect of Reynolds number on the pressure drop penalty factor was found to be insignificant