Secondary Heat Transfer Fluid Research Articles

Optical analysis and design of a novel solar beam down concentrator for indoor cooking

This investigation provides the design and optical analysis of an innovative solar beam-down configuration, which can be a promising passive solution for indoor solar-based cooking, offering an eco-friendly and sustainable approach. The system uses a beam-down parabolic dish concentrator to concentrate the solar radiation onto a ground-mounted receiver module, which has a secondary optical module consisting of a secondary reflector-light pipe system. The receiver module is a well-insulated tank consisting of a receiver in contact with a primary heat transfer fluid. The thermal energy stored in the receiver module is transported via a secondary heat transfer fluid to and from the cooktop via a tube-in-tube arrangement, which induces a thermosyphon effect. A multi-variable optical analysis through an efficient ray tracing methodology has been adopted to identify optimal design values of optical components such as parabolic dish concentrators, secondary reflectors, and light pipe-receiver assemblies. The optimal optical design parameters and their corresponding ray trace analysis results are elaborated. It was found that the designed beam-down parabolic dish concentrator system provides an ideal thermal energy of 10.3 kWh per day at an average DNI of 650 W/m2. Further, this investigation provides a design for a beam-down parabolic dish concentrating system that may be used for efficient and sustainable solar energy solutions.

Hydrogen production by using high-temperature gas-cooled reactors

Nuclear energy is a necessary component of a cheap and abundant total primary energy supply where there are no entries from the combustion of carbon and hydrocarbon fuels. This perspective discusses how high-temperature gas-cooled reactors could be developed targeting the production of electricity through advanced ultra-supercritical (AUSC) Rankine cycles and hydrogen through electrolysis (temperatures of the secondary heat transfer fluid <750 °C) as well as hydrogen through direct thermochemical cycles on top of AUSC electricity production (temperatures of the secondary heat transfer fluid 950 to 1000 °C).

Performance analysis of Parabolic Trough Collector using TRNSYS®-A case study in Indian coastal region

A solar water heating system incorporating parabolic trough collector (PTC) with Phase change material (PCM) is simulated using TRNSYS® software. The simulation is carried out to predict the hot water availability during the peak hot water demands of the morning and evening hours. Lauric acid (LA) is used as the primary heat transfer fluid (HTF) to extract the sun’s energy in PTC whereas, water is used as the secondary heat transfer fluid to extract heat from the primary heat transfer fluid. The study models a medium temperature, concentrating parabolic trough collector without any solar tracking components. TRNSYS® simulation components have been studied completely using Type 1245 parabolic trough collector with Type 533 horizontal storage tank with heat exchangers, which fulfils daily hot water demands of domestic and industrial applications. The storage tank is vertically stratified to regulate the temperature of HTF coming out of the collector. The results showed that LA having a thermal conductivity of 0.975 KJ/hr-mK provides a peak energy gain of 18500 KJ/hr in February and 5000 KJ/hr in July along with a 100°C rise in temperature for the city of Mangalore, India. The weather condition of the city provides an average annual collector efficiency of 26%.

Economic impact of latent heat thermal energy storage systems within direct steam generating solar thermal power plants with parabolic troughs

One possible way to further reduce levelized costs of electricity of concentrated solar thermal energy is to directly use water/steam as the primary heat transfer fluid within a concentrated collector field. This so-called direct steam generation offers the opportunity of higher operating temperatures and better exergy efficiency. A technical challenge of the direct steam generation technology compared to oil-driven power cycles is a competitive storage technology for heat transfer fluids with a phase change. Latent heat thermal energy storages are suitable for storing heat at a constant temperature and can be used for direct steam generation power plants. The calculation of the economic impact of an economically optimized thermal energy storage system, based on a latent heat thermal energy storage system with phase change material, is the main focus of the presented work. To reach that goal, a thermal energy storage system for a direct steam generation power plant with parabolic troughs in the solar field was thermally designed to determine the boundary conditions. This paper discusses the economic impact of the designed thermal energy storage system based on the levelized costs of electricity results, provided via a wide parametric study. A state-of-the-art power cycle with a primary and a secondary heat transfer fluid and a two-tank thermal energy storage is used as a benchmark technology for electricity generation with solar thermal energy. The benchmark and direct steam generation systems are compared to each other, based respectively on their annual electricity yields and their levelized costs of electricity at two different sites. A brief comparison of a passive and an active latent heat storage system is included. Finally, specific target costs for the new direct steam generation thermal energy storage system are determined based on the results of the parametric study.

Modelling an active magnetic refrigeration system: A comparison with different models of incompressible flow through a packed bed

Abstract Active Magnetic Regenerative refrigeration system (AMR) is an environmentally attractive refrigeration alternative to vapour compression plants. A magnetic refrigerator is composed of a regenerator that is a solid packed bed made of a magnetic material and a secondary heat transfer fluid flowing in the porous matrix. The secondary fluid can be a liquid (water or water anti-freezing mixture). Modelling is a particularly cost-effective method for studying, designing and optimizing a magnetic refrigeration system. In this paper a comparison between three different models to simulate the thermo-fluidodynamic behaviour of an AMR cycle is carried out. Each model simulates both the magnetic material and the secondary fluid of an AMR operating in conformity with a Brayton regenerative cycle. In the reported models Gd x Dy 1−x alloys are the constituent materials for the regenerator over the temperature range 260–280 K. The heat transfer medium is a water-glycol mixture (50% by weight).With these models, the refrigeration capacity, the power consumption and consequently the coefficient of performance of the cycle can be predicted.

Heating Performance of Zeotropic Mixture and Temperature Glide Matching with Secondary Fluid

In order to decrease the heat rejection pressure of pure CO2 refrigerating system and meanwhile have sustainable environmentally benefits for working fluild, several natural zeotropic CO2/Propane mixtures are applied to heat pump system to investigate the heating performance. The heat rejection pressure of CO2/Propane mixtures is reduced when the mass fraction of carbon dioxide is decreased. Under the given conditions, there is an optimum range of mass fraction of CO2/Propane of which the mixtures have superior heating coefficient of performance. The temperature glide characteristics of CO2/Propane mixtures at heating mode was also researched to analyze the heat transfer efficiency. Both a sufficient heat exchange area and a good working fluid’s temperature gradient matching with that of the secondary heat transfer fluid contribute to a higher heat transfer efficiency of heat exchanger.

Experimental investigation of a vapor compression heat pump used for cooling and heating applications

The present work aims at evaluating the performance characteristics of a vapor compression heat pump (VCHP) for simultaneous space cooling (summer air conditioning) and hot water supply. In order to achieve this objective, a test facility was developed and experiments were performed over a wide range of evaporator water inlet temperature (14:26 °C) and condenser water inlet temperature (22:34 °C). R134a was used as a primary working fluid whereas water was adopted as a secondary heat transfer fluid at both heat source (evaporator) and heat sink (condenser) of the heat pump. Performance characteristics of the considered heat pump were characterized by outlet water temperatures, water side capacities and coefficient of performance (COP) for various operating modes namely: cooling, heating and simultaneous cooling and heating. Results showed that COP increases with the evaporator water inlet temperature while decreases as the condenser water inlet temperature increases. However, the evaporator water inlet temperature has more effect on the performance characteristics of the heat pump than that of condenser water inlet temperature. Actual COP of cooling mode between 1.9 to 3.1 and that of heating mode from 2.9 to 3.3 were obtained. Actual simultaneous COP between 3.7 and 4.9 was achieved.

Energetic performances of a refrigerating loop using ice slurry

The consideration of environmental constraints in production, transport and distribution of cold energy resulted in reconsidering the practices of installations dimensioning in particular. Their containment led to the development of secondary refrigerants such as ice slurries to store, transport and distribute the cold energy. These heat transfer fluids should have good thermophysical properties, giving high transport capability, high heat transfer ability as well as low pressure drops. The use of ice slurries can lead to lower flow rates and smaller pumping power compared to single phase fluid. The purpose of the presented work is to study the distribution network of indirect cold systems thanks to a model allowing the evaluation of the influence of various parameters on the operating behaviour of the installation. The available domain for the use of secondary heat transfer fluid (whether in their single phase or two phase form) is determined considering the best design from an energetic point of view. Because of the essential role of the fluid distribution between the production site and consumers, we focus our study on pressure drops and pumping power due to the fluid flow in cooling loops. For each investigated case, the minimum consumption power is obtained with the two phases (solid-liquid) heat transfer fluid (ice slurry).

Cooling performance of several CO 2/propane mixtures and glide matching with secondary heat transfer fluid

This paper presents the cooling performance of several CO 2/propane mixtures measured in air-conditioning test rig at several conditions. The discharge pressure of CO 2/propane mixtures is reduced with increasing mole fraction of propane and their reduced values coincide approximately with the circulation concentrations of propane. Since propane is the refrigerant having a higher refrigerating effect and a much lower vapor density than CO 2, adding propane to CO 2 improves the system efficiency and reduces the cooling capacity. The temperature glide effect of CO 2/propane mixtures on the cooling performance was analyzed based on the experimental data. To utilize the temperature glide effect successfully, a sufficient heat exchange area is required, and the temperature gradient of refrigerant must be similar to that of secondary heat transfer fluid. It is better the temperature change of refrigerant can prevent pinching with that of the secondary heat transfer fluid.

The performance of a transcritical CO 2 cycle with an internal heat exchanger for hot water heating

The main purpose of this study is to investigate the performance of a transcritical CO 2 cycle with an internal heat exchanger for hot water heating. Performance test and simulation have been carried out for a transcritical CO 2 cycle by varying secondary heat transfer fluid temperatures at evaporator and gas-cooler inlets as well as the discharge pressure. Variations of mass flow rate of refrigerant, compressor power, heating capacity, and co-efficient of performance (COP) with respect to the length of an internal heat exchanger are presented at various operating conditions. Good quantitative agreement between model predictions and experimental results has been found; most parameters have absolute average deviations of less than 4%. As the length of the internal heat exchanger increases, COP is enhanced but heating capacity tends to decrease due to the trade-offs between the effectiveness and pressure drop in the internal heat exchanger.

Performance of a small, low-lift regenerator-based thermoacoustic refrigerator

A regenerator-based thermoacoustic refrigerator [Swift, Gardner, and Backhaus, ‘‘Acoustic recovery of lost power in pulse tube refrigerators,’’ J. Acoust. Soc. Am. 105(2), 711 (1999)] has been constructed. It is capable of moving about 5 W across a 40&amp;lt;th&amp;gt;°C temperature span. The machine operates with air at atmospheric pressure and is driven by an off-the-shelf electro-dynamic loudspeaker capable of producing peak-to-mean pressure ratios up to 12%. The thermal core of this research device contains an exhaust-side shell and tube heat exchanger (with water as the secondary heat transfer fluid), a regenerator made of 88 annular stainless-steel screens, and a constantan wire electrical heater that applies a measurable heat load to the cold side of the regenerator. An annular latex diaphragm is placed over the cold side of the regenerator to stop time-averaged mass flow through the regenerator and insulate the cold side [Gedeon, ‘‘DC Gas Flows in Stirling and Pulse Tube Cryocoolers,’’ in Cryocoolers 9, edited by R. G. Ross (Plenum, New York, 1997)]. Detailed measurements of heat load, temperature span, and exhaust heat flux will be presented and compared to DeltaE. [Work supported by ONR.]

Performance and heat transfer characteristics of hydrocarbon refrigerants in a heat pump system

Performance of a heat pump system using hydrocarbon refrigerants has been investigated experimentally. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in a heat pump system. The heat pump system consists of compressor, condenser, evaporator, and expansion device with auxiliary facilities such as evacuating and charging unit, the secondary heat transfer fluid circulation unit, and several measurement units. Performance of each refrigerant is compared at several compressor speeds and temperature levels of the secondary heat transfer fluid. Coefficient of performance (COP) and cooling/heating capacity of hydrocarbon refrigerants are presented. Experimental results show that some hydrocarbon refrigerants are comparable to R22. Condensation and evaporation heat transfer coefficients of selected refrigerants are obtained from overall conductance measurements for subsections of heat exchangers, and compared with those of R22. It is found that heat transfer is degraded for hydrocarbon refrigerant mixtures due to composition variation with phase change. Empirical correlations to estimate heat transfer coefficients for pure and mixed hydrocarbons are developed, and they show good agreement with experimental data. Some hydrocarbon refrigerants have better performance characteristics than R22.

A study on the performance of multi-stage heat pumps using mixtures

Multi-stage heat pumps composed of a condenser, evaporator, compressor, suction line heat exchanger, and low and/or high stage economizers are studied by computer simulation. Their thermodynamic performance and design options are examined for various working fluids. In the simulation, HCFC22/HCFC142b and HFC134a are studied as an interim and long term alternatives for CFC12 while HFC32/HFC134a and HFC125/HFC134a are studied as long term alternatives for HCFC22. The results indicate that the three-stage super heat pump with appropriate mixtures is up to 27.3% more energy efficient than the conventional single-stage system with pure fluids. While many factors contribute to the performance increase of a super heat pump, the most important factor is found to be the temperature matching between the secondary heat transfer fluid and refrigerant mixture, which is followed by the use of a low stage economizer and suction line heat exchanger. The contribution resulting from the use of a high stage economizer, however, is not significant. With the suction line heat exchanger, the system efficiency increases more with the fluids of larger molar liquid specific heats. From the view point of volumetric capacity and energy efficiency, a 40%HCFC22/60%HCFC142b mixture is proposed as an interim alternative for CFC12 while a 25%HFC32/75%HFC134a mixture is proposed as a long term alternative for HCFC22.