Evacuated Tube Heat Pipe Collectors Research Articles

Performance Enhancement and Improvement of Energy Efficiency in Evacuated Tube Heat Pipe Collector with Nanocomposite: A Review

Solar collector tube is used to combine incident energy and convert it into heat energy. Recently several studies have been done on improving the performance of the solar collector. Solar energy is clean energy and does not create pollution. The sun gives more power than we need. Solar collector consists of an absorber unit which transfers the heat energy of the sun to a working fluid. It is easily seen that solar intensity has more effect on the evacuated tube solar collector. In solar applications like distillation of salty water, heating, drying, air conditioning, and air heating, evacuated tube collector gives higher efficiency than flat plate collector. The evacuated tube solar collector technology gives good performance in bad weather conditions than the conventional system because vacuum inside the glass tube allows it to store higher percentage of heat. The challenge in the production of future generation evacuated tube collector technology is the control and management of operating temperature and heat generation. Heat pipe of solar collector controls operating temperature and prevent overheating that common problem in solar heating application. After chemical treatment, the heat pipe will control the freezing and prevent the evacuated tube. Heat transfer equipment is used to transfer the heat from one fluid to another fluid in many industries. The performance of solar collector with heat pipe depends on various factors such as solar radiation, ambient temperature, and flow conditions. With increasing mass flow rate, the heat transfer coefficient of the nanofluids increases. The use of nanofluids with evacuated tube heat pipe solar collector gives more efficiency and increase the output.

A Solar Thermal Application for Mongolian Detached Houses: An Energy, Environmental, and Economic Analysis Based on Dynamic Simulations

Ulaanbaatar (Mongolia) is the coldest capital city in the world with approximately 98% of its heating demand satisfied by means of coal-burning stoves. This leads to enormous air pollutant emissions, with Ulaanbaatar being one of the top five most polluted cities in the world. In this study, an innovative solar hybrid heating system for the Mongolian scenario was used, which was based on the operation of a solar field composed of four series-connected evacuated tube heat pipe collectors, coupled with a thermal energy storage. The solar hybrid heating system was simulated and analyzed using the software TRNSYS. The simulations were designed to satisfy the heating demand of a typical single-family detached house located in Ulaanbaatar and were carried out with and without considering the soiling effects on the solar system operation. The overall performance of the proposed plant was compared with those associated with different fossil fuel-based Mongolian conventional heating systems, in order to assess the potential energy, environmental and economic benefits. The results highlighted that the proposed plant allowed for the obtainment of significant reductions in terms of primary energy consumption (up to 34.6%), global CO2 equivalent emissions (up to 52.3%), and operating costs (up to 49.6%), even if the expected return on the investment could be unacceptable.

Improving the performance of evacuated tube heat pipe collectors using oil and foamed metals

Abstract The objective of this research is to improve the heating capability of evacuated tubes that comprises heat pipes. Thermal oil is inserted in the evacuated tube in order to improve the rate of heat transfer, such that the mode of heat transfer from the inner surface of the evacuated tube to the heat pipe becomes convection via the oil, as well as conduction through the installed fin. The finned surface has been replaced by a foamed-copper. An experimental setup has been developed to study the influence of oil and foamed metals on the performance of evacuated tubes with heat pipes. It has been found that the bulb temperature as well as the heating efficiency of the evacuated tube heat pipe has increased in case of inserting oil in the evacuated tube and replacing the finned surface with foamed copper. Also, the thermal oil acts as a heat storage.

Theoretical and experimental analysis of thermal performance of a solar water heating system with evacuated tube heat pipe collector

This study was carried out to theoretically and experimentally evaluate the performance of a solar water heating system with evacuated tube heat pipe collector. First, a mathematical model was presented according to thermal and exergy analysis to analyze the collector performance and then the given system was constructed and experimentally tested according to a real consumption pattern. The obtained results showed that the optimal number of collector pipes was reported to be 15. Also, a direct association was found between hot water consumption and system performance. The trend of changes for exergetic efficiency is ascending as the time is passed. At the end of the day, this efficiency reaches its maximum level, around 5.4%. The maximum outlet temperature of collector was about 64°C, which occurred between 15:00 and 16:00pm. In the early morning, an auxiliary system was required; however, this support system went off cycle after 14:00pm and the solar cycle alone supplied the required energy. The comparison of theoretical and experimental results was indicative of the capability of the developed model in predicting the performance of heat pipe solar water heater with maximum relative error of 8.4% and the maximum standard error of 1.91%.

Performance analysis and comparison of concentrated evacuated tube heat pipe solar collectors

Two profiles of concentrated evacuated tube heat pipe solar collectors made of single-sided and double-sided absorber have been analyzed and compared under control conditions and results presented in this paper. These innovative concentrated evacuated tube heat pipe solar collectors were experimentally tested at a tilt angle of 60° to the horizontal. Using in-door solar simulated experimental conditions temperature response, collection efficiency, heat loss coefficients and energy collection rates as well as the incident angle modifier (IAM) were recorded and compared at five different transverse angles (0–40°) at 10° increments.The use of concentrated single-sided and double-sided absorber evacuated tube heat pipe solar collectors is seen to be feasible for integrating solar thermal energy into buildings for heating demands. The concentrated double-sided absorber evacuated tube heat pipe proves better compared to the concentrated single-sided absorber evacuated tube heat pipe solar collector due to higher outlet temperature with greater temperature differential and improved thermal performance. The integration of this innovative system implies that the number of the evacuated tube heat pipe collectors needed to attain higher temperature is reduced. Furthermore, the size of reflectors and related reflector losses are reduced due to the truncated nature of the reflectors providing a low concentration ratio.

In-door experimental analysis of concentrated and non-concentrated evacuated tube heat pipe collectors for medium temperature applications

The paper presents the performance of an evacuated tube heat pipe solar collector compared to a concentrated evacuated tube single-sided coated heat pipe absorber for medium temperature applications. The aperture areas of the solar collectors were 0.107m2 and 0.2004m2 for the evacuated tube heat pipe and the concentrated evacuated tube single-sided coated heat pipe absorber, respectively. Experiments were conducted at five different transverse angles (0–40°) with a collector title angle of 60° to the horizontal. These solar collectors were tested over a range of operating temperatures and the mean fluid and ambient air temperature differential increase and outlet and inlet fluid temperature differential, energy collection rates and efficiency and the heat loss coefficients of each solar collector was experimentally measured, calculated and compared to each other. The concentrated evacuated tube heat pipe solar collector showed an improvement of 30% and 25.42% in overall average outlet and inlet fluid temperature differential and total daily energy collection, respectively compared to the non-concentrated evacuated tube heat pipe collectors.

Comparative field performance study of concentrator augmented array with two system configurations

The paper describes the system and experimental evaluation of an evacuated tube heat pipe collector array augmented with a novel design internal concentrator having a direct flow absorber and tested in the north–south and east–west align configurations under real outdoor conditions. External and internal concentrators have the potential to supply higher generator inlet temperatures needed for solar driven cooling systems. However, internal concentrator augmented solar collectors can further reduce heat losses and increase output temperatures. It is shown that collector outlet temperatures of 110 °C or more is possible and can be efficiently used to drive solar cooling systems with higher coefficient of performance (COP). The evacuated tube collector array augmented with a novely designed internal concentrator having a direct flow absorber in the north–south alignment was found to be more energy efficient with larger temperature lift and outlet and inlet temperature differential and substantial improvement in thermal performance compared to its east–west align configuration due to shorter connection piping connecting the internal concentrator augmented CPC to the evacuated tube heat pipe collector array.

The potential applications and advantages of powering solar air-conditioning systems using concentrator augmented solar collectors

Non-concentrated evacuated tube heat pipe solar collectors have been reported to show higher fluid temperatures with improved thermal performance in the low to medium temperature range (⩽60°C) due to low heat losses but suffer higher heat losses at the medium to higher temperature range (⩾80°C) which reduces their efficiency compared to concentrated evacuated tube heat pipe solar collectors. To operate as stand-alone systems capable of attaining temperatures in the range of 70–120°C, an innovative concentrator augmented solar collector can be an attractive option. The performance of a combined low-concentrator augmented solar collector in an array of evacuated tube heat pipe solar collectors defined as concentrator augmented evacuated tube heat pipe array (CAETHPA) and an array of evacuated tube heat pipe collectors (ETHPC) were tested and compared and results presented in this paper. The analysis of the experimental data allows concluding that the use of a CAETHPA is a more efficient alternative for integrating renewable energy into buildings with higher fluid temperature response, energy collection and lower heat loss coefficient compared to the use of evacuated tube heat pipe collector array (ETHPA).

Optical evaluation and analysis of an internal low-concentrated evacuated tube heat pipe solar collector for powering solar air-conditioning systems

An optical evaluation and analysis of an internal low-concentrating evacuated tube heat pipe solar collector designed to enhance the collection of solar radiation for medium temperature applications is presented in this paper. The internal low-concentrating evacuated tube heat pipe solar collector was designed with an acceptance angle of 20° given a geometrical concentration ratio of 2.92. The truncation of the upper part of the reflector giving a geometrical concentration ratio of 1.95 was carried and enabled the internal low-concentrating evacuated tube heat pipe collector to be enclosed by a borosilicate glass tube with 100 mm and 93 mm outer and inner diameters, respectively. Ray trace analysis at different transverse angles determines optical efficiencies, related optical losses and flux distribution on the absorber of the internal low-concentrating evacuated tube heat pipe solar collector. A detailed two dimensional ray trace techniques considering only the direct insolation component predicated overall ray’s acceptance of 93.72% and optical efficiency of 79.13% from transverse angles of 0° to 20°.