Evaporator Of Heat Pump Research Articles

An experimental study for drying Pisum sativum on an electric dryer and a heat pump dryer

A study of drying parameters on the drying process of Pisum Sativum bean was carried out. The effects of drying temperature of moisture air from 40°C to 80°C on the drying time and on the drying kinetics were demonstrated not only on conventional electric dryers but also on heat pump dryers. Besides, checking the steady operation of the heat pump dryer was also considered. The results show that, when temperature rises, the shorter time and the faster removal of moisture content can be obtained for both dryer systems. Drying in an electric heater at 80°C took only 1 hour 45 minutes, but the broken skin of pea seeds happened. The comparison of heat pump dryer and electric dryer was presented with the shorter drying time on heat pump than electric dryer as a result of removing water vapor from moisture air at the evaporator of heat pump, it led to the reduction of specific humidity of air entering the drying chamber. And the last impressive result which can be seen is that the drying rate of a heat pump is higher than an electric dryer at the same drying temperatures beside the energy consumption of electric dryer is 2.76 times as much as that of heat pump dryer.

Optimization Analysis of System and Air Distribution for Solar and Heat Pump Multi-energy Complementary Zanthoxylum Drying

Crops have high moisture content and are easily deteriorated, requiring dry storage. However, the drying energy consumption is relatively large and the drying quality of materials is often affected by the uneven distribution of indoor airflow. Author takes Zanthoxylumas for an example and designs two solar and heat pump drying systems in which the heat pump evaporator and the heat pipe are used to recover the waste heat respectively. The energy efficiency is compared and analyzed, the result shows that when the heat evaporator is used to recover the waste heat, the energy efficiency is higher and COP of the heat pump can reach 4.06. Based on the optimized system, the FLUENT software is used to simulate the airflow organization of the two types that supplying below and returning upward, and the side-supplying and side-returning. The results show that the airflow in the drying chamber has better uniformity when using the side-supplying and side-returning, which satisfies the requirements of Zanthoxylum drying.

Feasibility study of exploiting gearbox oil temperature of wind turbine for improving a heat pump water heater in cold areas

Purpose. Feasibility of completely dispensing with solar collectors (SCs) that are used in heat pump (HP) systems for hot water in cold areas. Methodology. Since the temperature of gearbox oil is relatively high, lots of heat can be exploited. Therefore, the recovery of this unutilized heat from gearbox oil temperature of a wind turbine shows a promising solution in improving heat pump (HP) efficiency for hot water especially in cold environment or the district that is located in the north of our planet where the solar energy is very low. This investigation focuses on the feasibility of direct conversion of mechanical energy harvested from the wind speed into thermal energy by exploiting only the friction phenomenon inside the gearbox of the wind turbine by completely dispensing with solar collectors (SCs) that are used in combined solar assisted heat pump (SAHP) because the SCs have various problems, such as large heat loss, low efficiency, freezing and tube-burst, which may limit their applications. Findings. Results show that the wind turbine can provide the power required for HP during the winter season due to high wind speed in Xuzhou city, Jiangsu, China particularly in January. At best, coefficient of performance (COP) may reach 4.08 without SCs, thus the suggested system ensures high COP in addition to decrease in the fuel consumption by 23.25%. Originality. Wind power driven HPs have been suggested in many pervious papers as a sustainable measure to provide heat to a house; however, to improve COP of HP system, we suggest using a wind turbine to directly drive the HP and exploit gearbox oil temperature in an assistant heat exchanger installed after the HP evaporator for providing additional thermal energy to refrigerant R12 and cooling the gearbox oil. Practical value. The coefficient of performance (COP) of HP has reached 4.08 without SCs, so the suggested system demonstrates high COP in addition to the reduced fuel consumption. Approximately 23.25% of energy could be saved using this novel system compared to a fuel water heater for DHW.

Research Status of Defrosting Technology of Air Source Heat Pump

Air source heat pump has the characteristics of high efficiency, energy saving, green and pollution-free, and has been widely used in building energy saving projects. However, the frosting phenomenon of the air source heat pump evaporator during the heating operation in cold areas in winter will reduce the heat production of the system, affect the comfort experience, and even cause the system down or irreversible damage to the heat pump system when the frosting is serious. This paper summarizes the research of domestic and foreign scholars on air source heat pump defrosting, analyzes the existing problems of defrosting technology, and finally looks forward to the future development trend of air source heat pump defrosting research.

APPLICATION OF ENERGY AND EXERGY ANALYSIS TO INVESTIGATE THE OPERATION OF AN AIR HANDLING UNIT WITH HEAT PUMP

With the growth of energy-efficient building sector, ventilation systems are becoming increasingly important not only of fresh air supply but also in terms of energy consumption. The aim of this paper is to describe and analyse the operation of an air handling unit (AHU) with a heat pump using energy and exergy analyses under the variable environmental temperature (from –30 °C to 10 °C). The application of selected methods is illustrated in a case study of an AHU using environmental temperatures of Vilnius city during heating season (from the beginning of October to the end of April). An analytical method for determining distribution of the environmental (outdoor air) temperature is used. Energy and exergy analyses showed periods when the highest amounts of energy and exergy were consumed and the greatest exergy losses occurred. This allowed to reveal the component of the system with the highest exergy losses – the heat pump evaporator. Therefore, further research is needed for its design and application. At the end of the article, the seasonal indicators of the AHU with heat pump operation were calculated: coefficient of performance and exergy efficiency. The presented research procedure could be applied to the analysis of other energy systems and processes in them.

Thermal performance assessment of an evaporative condenser-based combined heat pump and humidification-dehumidification desalination system

A new design for heat pump integrated humidification-dehumidification (HDH-HP) desalination cycles was proposed in the current experimental study. An evaporative condenser was designed and fabricated instead of a separate humidifier, heater, and air/water-cooled condensers find in previous HDH-HP systems. Meanwhile, the air dehumidification process in this work directly occurred inside the heat pump evaporator. The effect of several operating parameters such as ambient wet-bulb temperature, spraying saline water and airflow rates, compressor speed, superheat, and evaporator saturation temperature control modes of the electronic expansion valve (EEV) on freshwater production and GOR were studied. Analyzing the experimental results indicated that the system productivity and GOR reached 1.08 kg/h and 2.00, respectively. Higher freshwater produced at decreased airflow rates and increased ambient wet-bulb temperatures, spraying water flow rate and compressor speeds. Moreover, it was observed that the system performance enhances at higher adjusted evaporator saturated temperatures and lower superheats in the EEV controller. The experimental data for cooling capacity, compressor power, and current consumption was in agreement with polynomials provided by the compressor manufacturer. Additionally, the cost of generated freshwater was obtained as 0.019 $/L.

PVT and ETC Coupling for Annual Heating and Cooling by Absorption Heat Pumps

Until recently, solar assisted heat pumps have used solar collectors as a cold source. Solar collectors provide, when possible, direct heat, otherwise they offer temperature levels to the heat pump evaporator higher than the outside air. At the same time, solar thermal cooling exploits the solar collectors and the absorption chiller only in hot months. Photovoltaic/Thermal (PVT) modules have been available on the market in recent years for solar cogeneration, but their utilization can be problematic due to PhotoVoltaic (PV) cell damage in cases where there is no heating request. This paper considers the possibility of coupling evacuated tube collectors and photovoltaic/thermal modules to drive an absorption heat pump-based plant operating as an absorption chiller in the summertime. The cold source is the solar energy and the ground, which is recharged by the solar thermal and photovoltaic/thermal collectors and by the cooling of the absorber-condenser in mid-seasons and summer. This study analyzes the system behavior in yearly operation and evaluates the role of suitable storage tanks in two different climates, varying the size of the two solar fields and the generator tank. In the best plant configuration, a primary energy ratio of 26.6 in colder climates with cloudy skies and 20 in hotter climates with clearer skies is obtained.

A tabulated sizing method for the early stage design of geothermal energy piles including thermal storage

Geothermal systems are often employed for both the heating and cooling of sustainable constructions. Energy piles (U-shaped heat exchangers inserted into the foundation piles) are widely included in these installations, whose performance is usually estimated by means of complex, time-consuming simulations already at an early design stage.Here we propose a simple methodology, where a hand calculation tool provides the condenser yield per pile meter, ground area yield and demand covered by the heat pump by specifying only building heat load and geometric characteristics of the energy piles field. Our tool is tested by assuming 20 years of operation in a hall-type commercial building in a cold climate. A validated IDA-ICE parametric study couples the heat pump evaporator operation with heat transfer processes between energy piles and soil. Various system configurations are considered and thermal storage in the soil is included.We find that the expected yield is not directly proportional to pile separation, while a smaller extraction power is favoured. Thermal storage in the soil is also confirmed to be critical. Besides our specific quantitative results, our practical guideline is qualitatively general and can be extended to any given building type and climate.

Numerical investigations of solar-assisted hybrid desiccant evaporative cooling system for hot and humid climate

This article presents numerical investigations of the solar-assisted hybrid desiccant evaporative cooling system integrated with standard air collectors for applications under the hot and humid climatic conditions of Kuwait city. The objective is to introduce the energy-efficient and carbon-free solar-assisted hybrid desiccant evaporative cooling system to alleviate the principal problems of electricity consumption and carbon emissions resulting from the use of the conventional vapor-compression cooling systems. In the normal building, during cooling load operation, the solar-assisted hybrid desiccant evaporative cooling system can cope with the cooling load particularly sensible by evaporative cooling and latent through desiccant dehumidification. The outcomes of this work indicate that solar-assisted hybrid desiccant evaporative cooling device integrated with air collectors is capable of providing average coefficient of performance of 0.85 and has the potential to provide cooling with energy saving when compared with conventional vapor-compression refrigeration systems. It was concluded that under the intense outdoor environmental conditions (ambient air at greater than 45°C and 60% relative humidity), the delivered supply air from the evaporative cooling was nearly at 27°C and 65% relative humidity. To solve this problem, the system was assisted with conventional cooling coil (evaporator of heat pump) to supply air at comfortable conditions in the conditioned space.

Development of an intensive microwave-thermal treatment technology for heterogenic environments

The study suggests a technology of intensive, energy-efficient microwave-thermal mass transfer during washing and drying of agricultural and industrial products in a non-resonant microwave chamber with a uniform heating field. The chamber is equipped with a vacuum pump and an ultrasonic generator and is functionally connected to the evaporator and condenser of the heat pump. The traveling wave mode in the microwave chamber and intense evaporation are facilitated by the microwave field energy concentrator in the volume of the environment and the absorbing ferrite coating, which converts the ballast energy of the field into thermal energy on a perforated partition for products. This helps to reduce the significant cost of time and energy in the case of washing and drying heterogenic environments.The article substantiates the direction of developing the physicotechnical foundations of microwave-thermal treatment of environments with the aim of washing products using ultrasonic and microwave generators in a vacuum chamber to intensify the process. The authors show the necessity of developing the theory and practice of manufacturing and using radio-absorbing materials converting field energy to thermal energy. A coordinated integration of the upgraded microwave and additional convection drying technologies is proposed for the purpose to harmonize economical, intensive and environmentally friendly mass transfer of moisture during drying of the processed environment. It was found that the achievement and use of a synergistic effect, namely the energy efficiency of the process of complete drying in the middle of the chamber, contributes to the intensive evaporation of moisture from products in a uniform electromagnetic field in the chamber and the current dehumidification of moist air by the heat pump evaporator. Dry air is supplied into the microwave chamber after it is heated by the heat pump condenser. This contributes to a significantly more effective washing and drying of products. The application of this circuit solution and the optimal parameters of the regime in practice make it possible to solve the contradictory problem of increasing the efficiency and environmental friendliness of the processes in everyday life as well as in agricultural and industrial production.

A solar-air hybrid source heat pump for space heating and domestic hot water

Traditional solar collectors (SCs) cannot effectively use solar energy of varying intensity, and air source heat pumps cannot supply heat steadily during defrosting conditions. Accordingly, a solar-air hybrid source heat pump (HSHP) system is proposed to solve these problems. A SC was indirectly connected to a heat pump evaporator and water tank for a user at the same time, to allow direct heating when the solar energy is abundant and to supply heat to the heat pump. Multiple air heat exchangers were also connected indirectly to the heat pump. When one of these is in defrosting mode, the others can still work to guarantee a continuous heat output. The structure and operation strategies are introduced, and a numerical model is established to evaluate the performance of the solar-air HSHP. The performance was also compared with a traditional SC plus an air source heat pump (SC + ASHP). The results show that: (1) the heat provided by the solar-air source heat pump mode is 15%, 11%, and 12% of the total heat production in Chengdu, Beijing, and Shenyang, respectively, which indicates that weak solar radiation can also be used effectively; (2) the energy for defrosting using a solar-air HSHP is only between 30% and 36% of that when using a SC + ASHP system, and between 16% and 35% of that in the ASHP system, which indicates a large energy savings potential of the system in defrosting conditions; and (3) the seasonal performance factor (SPF) during a heating season is 3.61, 3.27, and 2.45 in Chengdu, Beijing, and Shenyang, respectively, and it can reach up to 6.92 in Lhasa due to sufficient solar energy resources.

Multi-criteria investigation of a pumped thermal electricity storage (PTES) system with thermal integration and sensible heat storage

In the present paper a multicriteria analysis of a Rankine Pumped Thermal Electricity Storage (PTES) system with low-grade thermal energy integration is performed. The system is composed by an ORC for the discharging phase and a high-temperature heat pump for the charging phase. As previously demonstrated, the low-grade thermal energy can be provided at the heat pump evaporator to boost the PTES performances. As it regards the multi-criteria analysis, a tradeoff is required when electric-to-electric energy ratio ηrt, total exergy exploitation efficiency ψut and energy density ρen, are maximized concurrently. By means of multi-objective optimization, theoretical performances of the system are derived in two different layouts, which are differentiated by the presence, or not, of internal regeneration in charge and discharge subsystems. Results showed that regeneration can be very effective, as it relaxes the tradeoff between the objectives, thus yielding better global performances. Pareto fronts are built and explored to characterize the PTES system. Configurations of interest are proposed, and PTES performances are compared with other storage technologies. Theoretical results showed that, by exploiting thermal energy at temperature lower than 80 °C, ηrt≈0.55 and ρen≈15 kWh/m3 can be concurrently achieved. This can be done at the cost of an inefficient exploitation of the thermal source, as ψut≈0.05. If higher total exergy utilization efficiency is required, storage density can still be maintained high, but ηrt must drop down to 0.4.

Performance analysis of solar assisted heat pump coupled with build-in PCM heat storage based on PV/T panel

PV/T (photovoltaic/thermal) technology is a combination of PV module (photovoltaic utilization) and collector (photothermal utilization), which can improve the comprehensive utilization efficiency of solar energy and has a broad application prospect. In this paper, PV/T module is coupled with heat pump evaporator to form a direct-expansion solar PV/T heat pump which is suitable for heat application in high latitude area. To achieve stable residential heating, a solar PV/T heat pump system coupled with build-in PCM (phase change material) heat storage is therefore proposed and simulated. Meanwhile, the mathematical model of solar PV/T heat pump coupled with build-in PCM heat storage system is established and verified. The simulation results show that the temperature of underfloor heating which using build-in PCM heat storage can reach 22–31 °C after 39 h when the circulating water is 40 °C. Moreover, the heating COP (Coefficient of Performance) increases with the increase of solar radiation, ambient temperature and area of PV/T collector, and decrease of wind speed, respectively. A 20 m2 PV/T panel module can output 21.4% of the electricity to power grid when the solar radiation intensity is 600 W/m2 and meet the heat demand of a 100 m2 room while maintain the operation of the system. Meanwhile, the heating COP can reach 5.79 which is 70% higher than the conventional air conditioning system and the electrical, thermal, overall efficiencies are 17.77%, 55.76% and 75.49%, respectively.

Investigation of Mechanical Effects on Heat Pump Evaporator to Accelerate Water Drainage

Investigation of Mechanical Effects on Heat Pump Evaporator to Accelerate Water Drainage

Condensation frosting on meter-scale superhydrophobic and superhydrophilic heat exchangers

Frost formation on heat transfer equipment such as air-source heat pump evaporators can result in drastic efficiency penalties. The performance reduction is a result of the insulating nature of ice and the increased fan power required to pump air through the constricted channels between frosted fins. Furthermore, the need to defrost adds appreciable energy use to the system. In this study, we develop a nanoengineered coating process that can be scalably applied to meter-scale, fully-assembled, aluminum heat exchangers. We demonstrate the coating on a decimeter-scale copper-tube aluminum-fin commercial heat exchanger having a 25 × 15 cm face area, and 9 corrugated fins per inch. The frosting characteristics on the unaltered heat exchanger are compared to identical components with superhydrophobic and superhydrophilic coatings for a range of inlet coolant temperatures (−5 to −10 °C) and ambient humidities (30 to 50%). The results show that a superhydrophobic heat exchanger can decrease frost accumulation, maintain heat transfer rates above half of the maximum capacity three times longer, reduce the required defrosting time and energy by 50%, and reduce the amount of water retained by 75% when compared to its uncoated and superhydrophilic counterparts.

Simulating and experimental research on a low-concentrating PV/T triple-generation system

A low-concentrating photovoltaic/thermal triple-generation system for heating, cooling and electricity is proposed in this study. The main components of the system are the low-concentrating PV/T module, high-temperature water source heat pump, lithium bromide absorption chiller and capillary net radiant ceiling. The annual system performance and the optimal capacity configuration of each component are stimulated by Transient System Simulation Program software. In addition, the outdoor experiments are carried out on the roof of a building in Changping, Beijing. In winter, the hot water produced by the low-concentrating PV/T module enters the heat pump evaporator for further heating, then through the pipes and enters the capillary net for building heating. In summer, the hot water enters an absorption lithium bromide chiller. The chilled water from the chiller enters the capillary net and lowers the room temperature. The experiments are conducted under different radiation conditions. The main parameters of the system are recorded. The results show that, under the low concentration condition, the system produces hot water of 45 °C–90 °C; meanwhile, the efficiency of PV cells stabilized approximately 10%. The lithium bromide absorption chiller operates stably, with the COP above 0.5. The low-concentrating PV/T triple-generation system provides a new idea for the comprehensive utilization of solar energy and energy cascade utilization.

The water heat pump operation under frost conditions on the evaporator surface

The conditions and characteristics of ice formation on the pipe surface of a heat pump evaporator which depends on water ( at a temperature lower than 280 K) as a low-grade energy source are investigated experimentally. Under the operating conditions of this heat pump, the ice thicknesses and temperatures values at freon pipe wall and for water in the evaporator are registered. The results allowed us to make a conclusion of the possibility to use a water source heat pump in practical applications under the conditions of partial ice coverage for the evaporator surface to heat up water in a condenser to 313 K. It is established from experiments that with the decrease in water initial temperature in the evaporator by 6 degrees, the maximum value of formed ice thickness on the evaporator surface is increased by 30 %. The dependence of Nusselt number on the natural convection characteristics undergoing phase change is established.

Performance analysis of combined cooling heating and power (CCHP) exhaust waste heat coupled air source heat pump system

To achieve the deep recovery of exhaust waste heat, a combined cooling heating and power (CCHP) dynamic exhaust low temperature waste heat coupled air source heat pump system is proposed in this paper. Aspen Plus software was used to simulate the system and analyze the effects of the recyclable waste heat of the system, the coefficient of performance (COP) of the heat pump and the impact of the primary energy utilization rate. The results showed that under the design condition, the exhaust waste heat of CCHP system was 1.22 kW, the recyclable waste heat of heat pump system was up to 1.07 kW, the exhaust waste heat recovery rate was 87.7%. The COP was up to 4.66, increased 39.5%. The primary energy utilization efficiency was increased by 3.9%. It solves the problem of heat pump evaporator frosting and poor performance of low temperature in cold regions. This study provides an important reference for the combined and efficient application of CCHP systems and heat pump units.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ ПРОЦЕССОВ ТЕПЛОПЕРЕНОСА ПРИ РАБОТЕ ТЕПЛОНАСОСНЫХ СИСТЕМ ИСПОЛЬЗОВАНИЯ ГЕОТЕРМАЛЬНОЙ ЭНЕРГИИ

Актуальность. Использование теплонасосных установок для отопления вместо традиционных систем, которые получают энергию в процессе сжигания различных видов топлива, имеет ряд экологических и экономических преимуществ. Тепловые насосы могут получать энергию из воздуха, грунта и воды. Их сферы применения разнообразны: горячее водоснабжение и кондиционирование помещений, нагрев и охлаждение воды для различных нужд, сушки/осушения воздуха, производства пара, испарения, дистилляции. При применении природных водоёмов (озёра, пруды, водохранилища) в качестве низкопотенциального источника энергии теплонасосных установок на поверхности трубки испарителя образуется лёд. Важно рассматривать закономерности и характеристики процессов теплообмена между водой и трубкой испарителя при образовании льда на её поверхности. Цель: математическое моделирование нестационарного конвективного теплообмена между водой и трубками испарителя теплонасосных установок в условиях формирования льда на их поверхности. Объект: теплообменник испарителя теплового насоса, погружённый в воду. Методы: численное решение задач конвективного теплообмена в условиях фазового перехода воды методом конечных элементов в среде COMSOL. Результаты. Установлены закономерности нестационарного конвективного теплопереноса вблизи трубок испарителя водяного теплового насоса с температурой, при которой образуется лёд на их поверхности. Показана необходимость учета влияния термогравитационной конвекции в воде на тепловой поток и процесс образования льда на поверхности трубки испарителя теплонасосной установки. Получены зависимости числа Нуссельта от характеристики конвективного теплообмена в воде (чисел Рэлея, Фурье и Стефана). Выявлено, что перепад температур в воде вблизи трубки увеличивался при уменьшении глубины её расположения относительно поверхности водного источника при показателях температур воды выше 277 К. При температурах воды ниже 277 К тепловой поток достигал максимального значения у поверхности трубки, которая находилась глубже.

ОСОБЕННОСТИ ИСПОЛЬЗОВАНИЯ ГЕОТЕРМАЛЬНОЙ ЭНЕРГИИ С ПРИМЕНЕНИЕМ ТЕПЛОНАСОСНЫХ УСТАНОВОК В УСЛОВИЯХ НИЗКИХ ТЕМПЕРАТУР ВОЗДУХА

Актуальность. Использование низкопотенциальной энергии водоемов с помощью теплонасосных установок в условиях низких температур окружающей среды – воздуха (период времени «осень–зима–весна»), характерных для большей части территории России, связано с возможным обмерзанием трубок испарителя теплонасосных установок, что приводит к изменению режима его работы. Анализ основных закономерностей процессов работы теплообменного оборудования, а также оценка энергоэффективности теплонасосных установок в условиях образования слоя льда на рабочих поверхностях испарителя до настоящего времени не проводились. Цель: экспериментальное изучение основных закономерностей процессов образования льда на рабочих поверхностях трубок испарителя теплонасосных установок, погруженных в воду с температурой, соответствующей условиям осеннего, зимнего и весеннего периодов года для большинства природных водоемов, расположенных в РФ, а также анализ основных характеристик работы ТНУ в таких условиях. Объект: парокомпрессионный тепловой насос, работающий в условиях образования слоя льда на рабочих поверхностях трубок испарителя, помещённых в резервуар с водой, температура которой ниже 280 К. Методы. Значения температур в характерных точках поверхности трубки теплообменника-испарителя и воды, находящейся в этой области, измерялись 15 хромель-алюмелевыми термопреобразователями (ХА термопары), подключенными через АЦП к компьютеру, и регистрировались в реальном времени. На основании полученных данных проводился расчет коэффициента преобразования теплонасосной установки по известной методике. Результаты. Выделен эффект образования льда, толщиной до 10 мм, на поверхности трубок испарителя при температурах воды ниже 280 К и времени работы установки до 8000 сек. Установлено, что этот слой существенно снижает интенсивность передачи теплоты в зону испарения хладагента. Эффективность работы теплонасосной установки при этом снижается до минимума. По результатам выполненных экспериментов сделан вывод о возможности работы теплонасосных установок при частичном покрытии трубки испарителя льдом. Сформулирована гипотеза о механизме процессов теплопереноса и фазовых превращений, протекающих вблизи трубок теплоносителя теплонасосной установки, при температурах воды менее 286 К. Результаты выполненных исследований являются базой для обоснования условий эффективного применения теплонасосных установок в регионах с низкими температурами воздуха в период осени, зимы и весны.