Investigation on thermal-hydraulic performance of outdoor heat exchanger in air sources heat pump

A plethora of findings exists on the decreasing heat transfer performance of ASHP under frosting condition. This study investigates, using field and laboratory experiments, the frosting behavior and heat transfer performance of fin-tube exchangers. Findings from our initial observation revealed the severity of frosting phenomenon during winter in hot summer and cold winter zone of China; for avoiding the lower COP, defrosting period of ASHP was not longer than 60 min. The results showed that the basic tube surface temperature decreases with running time and remains stable after 70 min, and an adverse pressure drop ensued. The findings, thereby suggests a 70 min defrosting period in ASHP. Comparing jH/fH and COP between exchangers revealed an improved performance of plain fin-tube exchanger over that of louver fin-tube exchanger in all the test conditions. Therefore, under frosting condition, plain fin-tube heat exchanger provides a superior thermal-hydraulic performance over louver fin-tube heat exchanger. Findings from this study will help designers and facility managers in taking a more informed decision when selecting heat exchanger types for ASHP

Compact/micro heat exchangers – Their role in heat pumping equipment

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Compact and micro-heat exchangers have many advantages over their larger counterparts, particularly when used to handle clean fluid streams, either single- or two-phase. Probably the most exciting feature of such heat exchangers is their ability to operate with close approach temperatures, leading to high effectiveness. This can be particularly beneficial when the exchangers are used in power-producing or power-consuming systems, where the improved heat exchanger effectiveness can be immediately realised in higher power outputs or reduced power consumption. In the case of heat pumping equipment – the most common examples being air-water or air-air vapour compression cycle heat pumps for domestic heating – this manifests itself in an increased Coefficient of Performance (COP) that reduces CO2 emissions due to a lower energy input needed to drive the compressor. This paper discusses some of the work carried out in five countries, Austria, Japan, Sweden, USA and the UK, within the IEA Heat Pump Implementing Agreement Annex 33 to identify the heat exchangers that can most benefit heat pump cycles, with a strong emphasis on micro-channel heat transfer. It also presents data on other research relevant to the subject, with an emphasis on the ‘micro’ size range

Single-phase laminar flow heat transfer from confined electron beam enhanced surfaces

An experimental investigation of the thermal-hydraulic characteristics for single-phase flow through three electron beam enhanced structures was conducted with water at mass flow rates from 0.005 kg/s to 0.045 kg/s. The structures featured copper heat transfer surfaces, approximately 28 mm wide and 32 mm long in the flow direction, with complex three-dimensional (3D) electron beam manufactured pyramid-like structures. The channel height varied depending on the height of the protrusions and the tip clearance was maintained at 0.1-0.3 mm. The average protrusion densities for the three samples S1, S2, and S3 were 13, 11, and 25 per cm2 with protrusion heights of 2.5, 2.8, and 1.6 mm, respectively. The data gathered were compared to those for a smooth channel surface operating under similar conditions. The results show an increase up to approximately three times for the average Nusselt number compared with the smooth surface. This is attributed to the surface irregularities of the enhanced surfaces, which not only increase the heat transfer area but also improve mixing, disturb the thermal and velocity boundary layers, and reduce thermal resistance. The increase in heat transfer with the enhanced surfaces was accompanied by an increase of pressure drop, which has to be considered in design.The authors would like to acknowledge Dr Anita Buxton and Dr Bruce Dance of TWI for their contribution to this project and also EPSRC and TSB for funding the EngD programme and sponsoring the ASTIA collaborative research project that helped to develop the Electron Beam enhanced surfaces respectively

On-chip micro-evaporation: Experimental evaluation of liquid pumping and vapor compression cooling systems

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Thermal designers of data centers and server manufacturers are showing a great concern regarding the cooling of new generation data centers, which are more compact and dissipate more power than is currently possible to cool by conventional air conditioning systems. With very large data centers exceeding 100 000 servers, some consume more than 50 MW [1] of electrical energy to operate, energy which is directly converted to heat and then simply wasted as it is dissipated into the atmosphere. A potentially significantly better solution would be to make use of on-chip two-phase cooling [2], which, besides improving the cooling performance at the chip level, also adds the capability to reuse the waste heat in a convenient manner, since higher evaporating and condensing temperatures of the two-phase cooling system (from 60-95°C) are possible with such a new green cooling technology. In the present project, two such two-phase cooling cycles using micro-evaporation technology were experimentally evaluated with specific attention being paid to energy consumption, overall exergetic efficiency and controllability. The main difference between the two cooling cycles is the driver, where both a mini-compressor and a gear pump were considered. The former has the advantage due to its appeal of energy recovery since its exergy potential is higher and the waste heat is exported at a higher temperature for reuse.This study is supported by: the Swiss Commission for Technology and Innovation (CTI) contract number 6862.2; the LTCM laboratory; IBM Zürich Research Laboratory (Switzerland) and Embraco (Brazil)

Analysis of magnetic treatment of production fluid with high content of asphalt-resin-paraffin deposits

Purpose. Justification of magnetic field application in order to prevent formation of asphalt-resin-paraffin deposits (ARPD) in oil and gas equipment, and consider some current views on the state of ARPD problem in oilfield equipment and possible methods for its solution using magnetic treatment. Methods. Analysis and generalization of the research results of production fluid magnetic treatment using COMSOL Multiphysics software. Findings. The technology of magnetic fields application in prevention of asphalt-resin-paraffin deposits is introduced in the article. The obtained results of production fluid magnetic treatment make it possible to use it in oil wells equipped with pumping units, as well as in free flow production method or in wells operated by electric-centrifugal pump, and in oil pipelines. Originality. The use of high energy magnets based on rare earth materials can reduce asphalt-resin-paraffin deposits in oil equipment. Practical implications. The proposed magnetic treatment creates opportunities for field exploitation at the later stages of development which are characterized by a high content of asphaltenes, resins and paraffins. The results of production fluid magnetic treatment have proved the efficiency of this technology, which has doubled a turnaround time.Мета. Обґрунтувати використання магнітного поля для запобігання асфальтосмолистопарафінових відкладень на нафтогазовому обладнанні, а також розглянути сучасні погляди на стан проблеми асфальтосмолистопарафінових відкладень на нафтопромисловому обладнанні та можливі методи її вирішення за допомогою магнітної обробки. Методика. Аналіз та узагальнення результатів комплексу досліджень магнітної обробки свердловинної продукції за допомогою використання програми COMSOL Multiphysics. Результати. Запропоновано технологію використання магнітного поля для запобігання асфальтосмолистопарафінових відкладень. Отримані результати використання магнітної обробки свердловинної продукції дають можливість використовувати її у нафтопромисловій практиці як у свердловинах, які обладнанні штанговими свердловинними насосними установками, так і при експлуатації свердловин фонтанним способом або свердловин, що експлуатуються електровідцентровими насосами, а також на нафтопроводах. Наукова новизна. Використання високоенергетичних магнітів на основі рідкоземельних матеріалів, дозволяє зменшити асфальтосмолистопарафінові відклади на нафтовому обладнанні. Практична значимість. Запропонована магнітна обробка свердловинної продукції створює важливі передумови експлуатації родовищ, які знаходяться на пізніх стадії розробки та характеризуються великим вмістом асфальтенів, смол та парафінів. Результати проведення магнітної обробки свердловинної продукції довели ефективність використання даної обробки, що призвело до збільшення міжремонтного періоду у два рази.Цель. Обосновать использование магнитного поля для предотвращения асфальтосмолистопарафиновых отложений на нефтегазовом оборудовании, а также рассмотреть современные взгляды на состояние проблемы асфальтосмолистопарафинових отложений на нефтепромысловом оборудовании и возможные методы ее решения с помощью магнитной обработки. Методика. Анализ и обобщение результатов комплекса исследований магнитной обработки скважинной продукции с помощью использования программы COMSOL Multiphysics. Результаты. Предложена технология использования магнитного поля для предотвращения асфальтосмолистопарафиновых отложений. Полученные результаты использования магнитной обработки скважинной продукции, дают возможность использовать ее в нефтепромысловой практике как в скважинах, оборудованных штанговыми скважинными насосными установками, так и при эксплуатации скважин фонтанным способом или скважин, эксплуатируемых электроценторобежными насосами, а также на нефтепроводах. Научная новизна. Использование высокоэнергетических магнитов на основе редкоземельных материалов позволяет уменьшить асфальтосмолистопарафиновые отложения на нефтяном оборудовании. Практическая значимость. Предложенная магнитная обработка скважинной продукции создает важные предпосылки эксплуатации месторождений, которые находятся на поздней стадии разработки и характеризуются большим содержанием асфальтенов, смол и парафинов. Результаты проведения магнитной обработки скважинной продукции доказали эффективность использования данной обработки, что привело к увеличению межремонтного периода в два раза.The present study would have been impossible without support from Poltava National Technical Yuri Kondratyuk University administration. We express our sincere gratitude for the opportunity to conduct tests in modern Laboratory of Oil and Gas Technologies

Characterization of botryococcus sp. and identification of carbohydrates metabolic related enzymes toward lipid production

The advancement of microalgal biofuels is faced with challenges among which is low strain performance in lipid production. Alternatively, the carbohydrate production in microalgal cells could be manipulated to increase the lipid content thereby maximizing the overall biofuel production. This work is aimed at determining metabolic pathway and enzymes involved in carbohydrate metabolism of Botryococcus sp. The B. sp. from Taman Negara Johor Endau Rompin was isolated and identified. Some relevant intracellular metabolites were extracted and quantified through HPLC and GC-MS analysis while extracellular metabolites excreted into the Bold basal medium were also analysed and identified through GC-MS. Enzymes involved in carbohydrate metabolism leading to lipid production in B. sp. under natural conditions were also identified through one-dimensional gel electrophoresis followed by proteomic mass spectrometry (LC-MS) and database searching. Finally, the carbohydrate to lipid metabolic pathway of B. sp. cultivated under natural conditions was determined. The total carbohydrate content was found to be 23 % per milligram biomass dry weight with monomeric sugars galactose, glucose, mannose, and arabinose. Total protein estimated for the microalgae B. sp. is 16.22 % and the lipid content was found to be 60.69 %. The extracellular metabolites constitute majorly cyclohydrocarbons, nitrogenated hydrocarbons, siloxanes, phenols and phenol derivatives. A glycolytic enzyme ‘Enolase ’which can generate phosphoenolpyruvate (PEP) and then convert it into pyruvate was identified in this study. Enolase which helps in high lipid metabolism was found in the cytoplasm and was used to construct the alternative pathway. Enolase was found to export fixed carbon (3PGA) to the cytoplasm, hence providing a shorter route to lipid production than the normal process via the plastid leading to the production of more lipid in Botryococcus

Design sensitivity analysis of a plate-finned air-cooled condenser for waste heat recovery ORCs

The study is related to the design sensitivity analysis of a plate-finned tube bundle V-shaped air-cooled condenser design problem for a range of representative low-temperature waste heat recovery Organic Rankine Cycle (ORC) cases. An iterative design model is implemented which reveals the thermodynamic and geometric design error margins that occur when different in-tube prediction methods are used. 19 condensation heat transfer correlations are used simultaneously within arrays of geometric and thermodynamic variables. Through attained 19 different convective coefficients, a design sensitivity on the calculated overall heat transfer coefficient, total transferred heat, degree of subcooling, required tube and fin material amount, air- and refrigerant-side pressure drops is reported

Two-phase heat transfer in small passages and microfinned surfaces - Fundamentals and applications

Micro channels and internally finned tubes are increasingly being utilized in the evaporators and condensers of refrigeration systems. The adoption of such geometries in the development of micro-cooling systems is first discussed in this paper. Recent work on flow boiling heat transfer and condensation in small to micro passages as well as on microfinned surfaces is then presented. The complex effect of diameter size on flow boiling patterns and heat transfer and correlations currently available in literature are summarized. Condensation in microfinned tubes and microchannels is then discussed

Phase Change Material Evolution in Thermal Energy Storage Systems for the Building Sector, with a Focus on Ground-Coupled Heat Pumps

The building sector is responsible for a third of the global energy consumption and a quarter of greenhouse gas emissions. Phase change materials (PCMs) have shown high potential for latent thermal energy storage (LTES) through their integration in building materials, with the aim of enhancing the efficient use of energy. Although research on PCMs began decades ago, this technology is still far from being widespread. This work analyses the main contributions to the employment of PCMs in the building sector, to better understand the motivations behind the restricted employment of PCM-based LTES technologies. The main research and review studies are critically discussed, focusing on: strategies used to regulate indoor thermal conditions, the variation of mechanical properties in PCMs-based mortars and cements, and applications with ground-coupled heat pumps. The employment of materials obtained from wastes and natural sources was also taken in account as a possible key to developing composite materials with good performance and sustainability at the same time. As a result, the integration of PCMs in LTES is still in its early stages, but reveals high potential for employment in the building sector, thanks to the continuous design improvement and optimization driven by high-performance materials and a new way of coupling with tailored envelopes