Low Temperature Heat Sources Research Articles

Experimental investigation of the thermal performance of a novel concentric tube heat pipe heat exchanger

A novel concentric tube heat pipe exchanger was designed and expected to be utilized in integrated waste heat recovery equipment with higher heat transfer efficiency at lower temperature heat sources. The heat transfer performance of the novel heat pipe heat exchanger using acetone as working fluid was experimentally studied. It is found that the novel heat pipe heat exchanger has good isothermal performance and operation stability. The results showed that when the length of evaporator was 260 mm, the inclination angle was 60°, the flow of cooling water was 0.5 m3/h, the cooling water temperature was 30 °C, the novel heat exchanger delivered a better heat transfer performance. The maximum heat transfer quantity is about 1600 W, and the average thermal resistance is 0.042 °C/W.

Experimental and simulation analysis of low temperature heat sources driven adsorption air conditioning, refrigeration, integrating ammonia, and organic expanding power generation

Adsorption cooling technology is an effective method to use low-temperature heat sources, such as solar energy, waste heat from industry, etc. However, there exists one bottleneck in the adsorption system application, because of its low energy usage efficiency. In this paper, one novel integrated cycle is designed, investigated, and tested. It includes adsorption cooling cycle, ammonia expanding power generation, and organic Rankine cycle. By the performance comparison of 16 different organics, R600 is the most suitable choice for organic Rankine cycle in this system, due to its highest potential exergy and proper working pressure. The system total exergy efficiency can be improved significantly by the two parts of power generation. The results show that when the heating source, cooling water temperature, and evaporation temperature are approximately 120.1°C, 29.6°C, and −5.3°C, the specific cooling power, coefficient of performance, and total exergy efficiency can arrive at 351.4 W/kg, 0.17, and 0.34, respectively.

Thermodynamic and economic analysis and multi-objective optimization of a novel transcritical CO2 Rankine cycle with an ejector driven by low grade heat source

Transcritical CO2 Rankine cycle (T-CO2) is a promising technology for the utilization of low temperature heat source. The low critical temperature of CO2 (about 31 °C) leads to a restriction in the practical application of the cycle, since CO2 could hardly be condensed into liquid using higher temperature heat sink under the environment conditions. In this paper, a novel transcritical CO2 Rankine cycle with an ejector is proposed to solve the condensation problem of CO2 under the higher temperature heat sink. By establishing the mathematical model, a parametric analysis is carried out to examine the effects of five key parameters on thermodynamic and economic performances of the system. A multi-objective optimization is also conducted to obtain the optimum performance of cycle. The results indicate that increasing turbine inlet temperature and ejector back pressure could increase the exergy efficiency. In addition, lower investment cost of the system could be achieved by increasing the turbine back pressure and the valve expansion pressure. Furthermore, according to the Pareto frontier solution of multi-objective optimization, the exergy efficiency could reach a maximum of 19.33% and the investment cost of the system could reach a minimum of 657.9 × 103 USD.

A Thermodynamic Analysis of a New Cycle for Adsorption Heat Pump “Heat from Cold”: Effect of the Working Pair on Cycle Efficiency

A thermodynamic analysis was carried out for a new “Heat from Cold” (HeCol) adsorption cycle for transformation of the ambient heat using the following working pairs: activated carbon ASM-35.4–methanol or composite sorbent LiCl/silica gel–methanol. Unlike the conventional cycle of an adsorption thermal engine where the adsorbent is regenerated at a constant pressure by its heating up to 80–150°C, the adsorbent in the HeCol cycle is regenerated by depressurization, which is performed due to a low ambient temperature. The balances of energy and entropy are calculated at each cycle stage and each element of the transformer under conditions of ideal heat transfer. The performance of the cycle for both pairs is compared. The threshold ambient temperature above which useful heat is not produced has been determined. The threshold values depend only on the absorption potential of methanol. It is demonstrated that useful heat with a high temperature potential of approximately 40°C can be obtained from a natural source of low-potential heat (such as a river, lake, or sea) only at a sufficiently low ambient temperature. The cycle with the composite sorbent LiCl/silica gel–methanol yielded much more useful heat than the cycle with the activated carbon ASM-35.4–methanol due to the features of the characteristic curve for methanol vapor adsorption on the composite sorbent. The amount of useful heat increases with decreasing ambient temperature and increasing temperature of the natural low-temperature heat source. The examined cycle can be used for upgrading the ambient heat temperature potential in countries with a cold climate.

Multi-objective optimisation and fast decision-making method for working fluid selection in organic Rankine cycle with low-temperature waste heat source in industry

In China, the utilisation of low-temperature waste heat (especially at temperatures lower than 100 °C) plays a significant role in increasing the energy-consumption efficiency in the industry. The organic Rankine cycle (ORC) is considered as a promising method to recover the aforementioned part of the waste heat. In the study, six potential candidates, namely R141b, R142b, R245ca, R245fa, R600a, and R601a were screened from 12 dry or adiabatic organic working fluids based on their thermodynamic performances in the ORC. A multi-objective optimisation (MOO) was performed for the thermodynamic performance (exergy efficiency, EXE) and economic performance (levelised energy cost, LEC) by using non-dominated sorting genetic algorithm-II (NSGA-II). The Pareto frontiers were obtained for the six candidates with the algorithm, and each optimal compromise solution was accurately obtained with the fuzzy set theory. Based on the EXE and LEC of the optimal compromise solution, the total cost and power generation efficiency for the six candidates were determined. This was used to obtain an explicit evaluation index in economic performance, namely static investment payback period (SIPP), to identify that the R245ca corresponded to the most cost-effective working fluid with the shortest SIPP. This suggests R245ca was the fastest to cover the investment and cost of the ORC system. Furthermore, a fast decision-making method was introduced to select the optimal working fluid based on the grey relational analysis (GRA) by considering key physical property parameters of the working fluids. The results suggest that any potential working fluid to recover low-temperature waste heat in the ORC can be evaluated by the simplified grey relational degree (SGRD) proposed in the study.

Technical engineering design, thermal experimental and economic simulation analysis of absorption cooling/heating systems in China

In low temperature heat sources driven cooling/heating absorption systems, there are many equipment combinations. Usually, there are contradictions between the equipment efficiency and their economy; for example, the high efficiency- solar collector usually has a high price. So, in this paper, ten absorption cooling/heating systems with different heat sources and different absorption technologies are investigated for technical-economic-thermal analysis. The heat sources are flat plate solar collector, evacuated U-pipe solar collector and middle-temperature high efficiency solar collector and waste heat. The absorption chillers are 1-effect LiBr absorption chiller, 2-effect LiBr absorption chiller, novel 1–2 effect LiBr absorption chiller and novel high efficiency-heat-recovery ammonia water absorption system. The results show that 2-effect absorption chiller with heat source of waste heat is the most optimized choice, which lowest payback period is about 1.9 years. The second choices are the 2-effect LiBr absorption system with novel middle-temperature solar collectors/natural gases and the novel ammonia water absorption system with waste heat sources.

Effects of superheat and internal heat exchanger on thermo-economic performance of organic Rankine cycle based on fluid type and heat sources

The study investigates the comprehensive effects of superheat and internal heat exchanger (IHX) on the thermo-economic performance of organic Rankine cycle (ORC). Exergy efficiency, net power output, and electricity production cost (EPC) are compared based on the working fluid properties and heat sources. The results indicate that under a lower heat source temperature and load, exergy efficiency of IHX-ORC does not always exceed that of simple ORC (S-ORC) when EPC is selected as an objective function, and IHX-ORC exhibits a worse economic performance than S-ORC for all fluids (R161, R1234ze, R152a, cyclopropane, butane, R123, cyclopentane, heptane, and cyclohexane). However, IHX-ORC with dry fluid achieves a better thermo-economic performance than that with wet fluid when the heat source temperature and load increase to a high level. The EPC of IHX-ORC is close to that of S-ORC with the increase in heat source temperature and load, and thus, IHX-ORC exhibits approximately 10–17% higher thermal efficiency and 5–10% higher exergy efficiency than those of S-ORC. With respect to butane and R123, the net power output exhibits approximately 22.5% and 23.5% growth, respectively. In order to evaluate the feasibility of IHX-ORC, a judgement indicator [α > 1.90625 + 0.4258ξ] with respect to six factors is proposed.

THERMODYNAMIC ANALYSIS OF BASIC AND REGENERATIVE ORGANIC RANKINE CYCLES USING DRY FLUIDS FROM WASTE HEAT RECOVERY

The organic Rankine cycle (ORC), which generates electric energy using low temperature heat sources, is a promising technology in energy production sector. The ORC, which uses an organic fluid with its lower boiling point and higher vapor pressure than water-steam as a working fluid. The thermal efficiency of an ORC showes the performance of system, depends on system compenents, working fluid and operating conditions. This paper presents an thermodynamics examination of basic ORC and regenerative ORC for waste heat recovery applications using dry organic fluids. R113, R114, R227ea, R245fa and R600a with the boiling points from -16 oC to 48 oC are selected in the analyses. The relationships between the ORC's performance parameters for basic and regenerative technologies and the properties of working fluids are evaluated based on various turbine inlet pressure values. Results show that regenerative ORC has higher thermal efficiency compared with basic ORC. Also, the thermal efficiency increases with the increment of the turbine inlet pressure for both basic ORC and regenerative ORC.

Economic feasibility of booster heat pumps in heat pump-based district heating systems

District heating systems are appropriate infrastructures to supply space heating and domestic hot water from a number of potential sources in future energy systems based on renewable energy. On the other hand, district heating is also facing competition from heating technologies in individual buildings. Lowering the district heating temperatures will improve efficiency and competitiveness of district heating; however, the production of domestic hot water is an impediment to this. This article uses energyPRO to analyse three low-temperature district heating schemes. District heating is supplied from a heat pump using air, seawater or groundwater as heat sources. Domestic hot water is supplied by booster heat pumps using district heating as heat source or through a heat exchanger. The economic benefit of adding booster heat pumps to cover the domestic hot water demands is assessed by modelling the time-varying operation against the electricity market as well as the time-varying coefficient of performance of heat pumps and grid losses. Based on this operation cost reduction assessment, the energy system value of booster heat pumps ranges from 2500 to 6800€ per house depending on the choice of low-temperature heat source for the district heating heat pump as well as economic time-horizon and discount rate.

Evaluating the cost of heat for end users in ultra low temperature district heating networks with booster heat pumps

A promising district heating concept consists of distributing the heat at temperatures below 45 °C and using booster heat pumps at the customers' substations to provide the appropriate temperature needed for space heating and domestic hot water production. As such, thermal networks would be able to abate heat losses and substantially increase the number of recoverable heat sources. At the same time, the supply temperature from the booster heat pumps can be tailored to the building supplied instead of being based on the most critical consumer. This work investigates the performance of booster heat pumps assuming network supply temperatures in the range between 15 °C and 45 °C. The impact of supply and return temperature on the levelized cost of heat for different end users was assessed. The parametric study shows the importance of the nominal network temperature difference in the design phase of the system in order to reach a good trade-off between initial investment and operating costs. The economic analysis shows that the system is already competitive with individual gas boilers provided that a local low-temperature heat source can be recovered with minor marginal costs.

(Invited) Thermoelectric Properties of π-Conjugated Polymers in Ionic-Liquid-Gated Transistors

Thermal energy havesting from low-temperature heat sources, such as human body, is a promissing method to feed energy to vast number of micro-devices and sensors in Internet of Things (IoT) technologies. Thermoelectric generator, used for this purpose, can directly convert heat into electric power through Seebeck effect. In recent years, organic semiconductor materials, such as π-conjugated polymers, have been attracting much attention as a potential candidate for light-weight, flexible, and low-toxic thermoelectric generators. However, thermoelectric performance of polymer-based devices are still low compared to that of inorganic materials, although various novel polymers exhibitting high mobilities have been synthesized so far. The possible reason for this is the absence of both the suitable doping method and the fundamental understanding of thermoelectric properties in these polymer materials. In general, the power factor (P) of a thermoelectric device is described as a product of the electrical conductivity (σ) and Seebeck coefficient (S) as P=S2σ, whereas these two quantities tend to show opposite behavior upon carrier doping. Thus, it is indispensable to clarify the accurate relationship between σ and S in doped films in order to obtain a guideline to improve P. In semicrystalline polymers such as PBTTT (Fig. 1(a)), an empirical relation of S∝σ -1/4 (P∝σ 1/2) has been reported in a wide range of σ by using chemical doping, although no physical background for this relation has been clarified [1]. However, different σ-S relation has also been pointed out recently based on the data analyses of various reports including the same data set in ref. 1 [2]. Such difference seems to arise from the different doping conditions in chemical doping. In this presentation, we report our recent challenge to determine the accurate σ-S relation in various high-mobility polymer materials by using an electrolyte-gated thin-film transistor (TFT) structure, which enables a continuous electrochemical doping on the same device up to high carrier densities. Fig. 1(b) shows a schematic illustration of the TFT device and measurement setup [3]. We adopted an ionic liquid as the electrolyte, which was drop-casted on the polymer thin film fabricated on the glass substrate. A temperature gradient was given by a couple of Peltier devices and the induced voltage (ΔV) and temperature difference (ΔT) between source (S) and drain (D) electrodes were measured to obtain seebeck coefficient (S=ΔV/ΔT) under various gate voltages (V g). The electrical conductivity was simultaneously measured at each V g. Fig. 1(c) shows an example of σ-S and σ-P relations upon electrochemical doping obtained for two PBTTT devices. We observe highly reproducible data for these devices. In the low conductivity region (σ<100 S/cm), the empirical relation of S∝σ -1/4 is clearly confirmed, whereas the deviation from this relation becomes evident in the high conductivity region (σ>100 S/cm). The maximum of P appears around the boundary of low and high conductivity regions. In the high conductivity region, the σ-S relation seems to approach S∝σ -1, typical to the Mott’s relation expected for metals. This behavior is consistent with the semiconductor-metal transition of PBTTT occuring at highly-doped regions, which is observed from the temperature dependence of the conductivity as well as the electron spin resonance (ESR) measurements. Similar σ-S relation was commonly observed in a wide range of polymers such as donor-acceptor (DA) type copolymers. The maximum value of P can be enhanced by the surface treatment of the substrate by self-assembled monolayers or by aligning the polymer main chain, presumably due to the increase of the mobility, although the S∝σ -1/4 relation is unchanged in the low conductivity regions. The above σ-S relation insensitive to the mobility is indicative of the contribution of domain boundaries in thermoelectric properties. [1] A. M. Glaudell et al., Adv. Energy Mater. 5, 1401072 (2015). [2] S. D. Kang et al., Nat. Mater. 16, 252 (2017). [3] J. Pu et al., Phys. Rev. B. 94, 014312 (2016). Figure 1

Energetic and exergetic assessment of a two-stage Organic Rankine Cycle with reactivity controlled compression ignition engine as a low temperature heat source

The waste heat from exhaust gases and cooling water of Reactivity Controlled Compression Ignition are used to launch a two-stage Organic Rankine Cycle. Considering the chemical kinetic mechanism, a Computational Fluid Dynamic model is presented to simulate the gasoline-diesel fueled RCCI engine. In addition, the performance of ORC is simulated by applying the Engineering Equation Solver software. By linking these two codes, a detailed Computational Fluid Dynamic-thermo analysis is carried out for the proposed heat recovery system and also the potential effects of some decision parameters on the performances of the combined Reactivity Controlled Compression Ignition – Organic Rankine Cycle system are studied in detail. The obtained results show that coupling Organic Rankine Cycle to the engine, improves Fuel Conversion Efficiency, break specific of Oxides of Nitrogen and Carbon Monoxide emissions as well as exergy efficiency to compare with sole engine operation state. According to the parametric analysis, can be seen that the temperature and pinch point differences of the evaporators, expanders’ efficiencies as well as the temperatures and mass flow rates of the engine exhausted gases and cooling water should be taken as the effective parameters to evaluate the proposed system in terms of the first and second laws of thermodynamic. Moreover, a comparative study is performed between Reactivity Controlled Compression Ignition engine and a conventional diesel engine as the heat source of the heat recovery system. Results indicate that the energy and exergy efficiencies of Reactivity Controlled Compression Ignition – Organic Rankine Cycle system are higher than diesel – ORC under the same operations load, although, using a diesel engine has a greater influence on the net output power of the attached cycle, regardless of the engines’ power.

Design and Experimental Study of a 5-kW Organic Rankine Cycle with Axial-Flow Turbine for Low-Temperature Heat Recovery

AbstractThe microscale organic Rankine cycle (ORC) system is considered a promising technology to recover thermal energy from widely distributed low-temperature heat sources. By using HFC-R225fa as...

Thermodynamic analysis of a novel sodium hydroxide-water solution absorption refrigeration, heating and power system for low-temperature heat sources

A novel sodium hydroxide-water solution absorption refrigeration, heating and organic Rankine cycle power system is proposed for low-temperature heat source utilization. The sodium hydroxide-water solution absorption refrigeration is employed as top cycle which directly absorbs heat from low-temperature heat source. While R218 organic Rankine cycle and heating subsystem are adopted to produce power and heating as designed in bottom cycles. Under the considered condition, model results indicate that refrigeration, heating and electricity efficiency are 0.8244, 0.4019 and 0.03437 with the capacity of 945.2, 460.8 and 39.41 kW, respectively. Energy and exergy efficiency of refrigeration, heating and electricity are also theoretically analyzed with various condensation temperature, evaporation temperature, turbine inlet pressure, split ratio and mass fraction of rich sodium hydroxide solution. Sensitivity of parameters to system performance is also analyzed and results indicate that energy and exergy efficiency are remarkably influenced by operating parameters. A comparison between the proposed system and three independent electrical refrigeration, heating and power systems shows that the proposed system has superior performance and the maximum primary energy saving ratio can reach approximately 0.4889. In conclusion, with the multi-productions of refrigeration, heating and electricity, the proposed polygeneration system provides a more rational and effective energy utilization from a single low temperature heat source at suitable level.

Comparison of absorption refrigeration cycles for efficient air-cooled solar cooling

Absorption chiller is a widely used technology owing to its capability to utilize low grade thermal energy including solar thermal energy and waste heat. Yet, most solar absorption cooling systems need cooling tower to dissipate heat rejection into ambient. The use of cooling tower increases both the initial investment and water consumption, which can be improved by air-cooled solar absorption cooling system. In this paper, to give the best absorption cycle options under different conditions, five absorption refrigeration cycles suitable for air-cooled solar cooling including three double lift absorption cycles and two semi-GAX (Generator-Absorber heat eXchange) absorption cycles were compared. Steady-state simulation is carried out. Efficiencies of these cycles were calculated with LiBr-water and water-ammonia working pairs in the scenario of air-cooled solar cooling. Heat source temperatures of 75–100 °C from non-concentrating solar collector and air temperatures of 20–40 °C were considered. Both air-conditioning condition with evaporation temperature of 5 °C and sub-zero condition with −10 °C were discussed. It is found that mass-coupled semi-GAX absorption cycle with ammonia-water is suitable for air-conditioning with higher heat source temperatures, mass-coupled double lift absorption cycle with water-LiBr is suitable for air-conditioning with lower heat source temperature and mass-coupled double lift absorption cycle with ammonia-water is suitable for sub-zero conditions.

Experimental and Theoretical Analysis of the Goswami Cycle Operating at Low Temperature Heat Sources

The Goswami cycle is a cycle that combines an ammonia–water vapor absorption cycle and a Rankine cycle for cooling and mechanical power purposes by using thermal heat sources such as solar energy or geothermal steam. In this paper, a theoretical investigation was conducted to determine the performance outputs of the cycle, namely, net mechanical power, cooling, effective first law efficiency and exergy efficiency, for a boiler and an absorber temperature of 85 °C and 35 °C, respectively, and different boiler pressures and ammonia-water concentrations. In addition, an experimental investigation was carried out to verify the predicted trends of theoretical analysis and evaluate the performance of a modified scroll expander. The theoretical analysis showed that maximum effective first law and exergy efficiencies were 7.2% and 45%, respectively. The experimental tests showed that the scroll expander reached a 30–40% of efficiency when boiler temperature was 85 °C and rectifier temperature was 55 °C. Finally, it was obtained that superheated inlet conditions improved the efficiency of the modified expander.

Synthesis of recent Swedish district heating research

In Sweden, district heating meets currently above half of the heat demands in buildings. District heating research in Sweden has a long tradition dating back to 1975. The latest research program period included 34 projects and was executed between 2013 and 2017. In this paper, a synthesis is performed on the Swedish research frontier by assessing these recent research projects. The three study purposes was to provide an overview over the executed projects, to identify new research questions, and to identify future challenges to the Swedish district heating industry. The assessment was based on six defined key areas, such as demand, resources, system frameworks, technology, cold supply, and international perspective. The subsequent content analysis was performed from three perspectives: the perspective of energy system transition, the customer perspective, and the sustainability perspective. Final conclusions include the three future challenges for the Swedish district heating industry. These are future strategies to communicate the value of district heating, vision for district heating beyond the transition to fossil free supply, and technology development for efficient use of low temperature heat sources.

Performance Comparison of a Vapor-Adsorption Cycle-Based Gas Turbine Inlet Air Cooling System for Different Refrigerants

Presently, to enhance the thermal efficiency of a gas turbine power plant, turbine inlet air cooling (TIAC) is the widely used technique. The conventional refrigeration methods like vapor compression refrigeration and evaporative cooling need electric power, hence absorption and adsorption refrigeration systems are attractive options as they can be powered using the waste heat energy of the exhaust gases. Adsorption system has advantages over absorption system like scalability, requirement of lower heat source temperature, absence of corrosion and crystallization. This paper focuses on the thermodynamic analysis of waste heat powered adsorption chiller used for the cooling of intake air to enhance the net power output of the gas turbine power plant. This paper also presents a comparative analysis of the vapor-adsorption cycle-based TIAC system for four different refrigerants viz. HFC-134a, carbon dioxide, ethanol and ammonia with the motive of finding a substitute refrigerant for HFC-134a which has a high global warming potential (GWP). The adsorption chiller is mathematically modeled in MATLAB with activated carbon as the adsorbent and each one of carbon dioxide, ethanol and ammonia as the adsorbate. The variation of the coefficient of performance (COP) and specific cooling effect (SCE) with varying adsorption temperatures is presented for each pair. The net power output and primary energy rate (PER) improvement of the gas turbine power plant at different ambient temperatures are also discussed. It is observed that ammonia can improve the power plant performance significantly better compared to the other three refrigerants at ambient temperatures less than 40[Formula: see text]C.

Process development and thermodynamic analysis of a novel power generation plant driven by geothermal energy with liquefied natural gas as its heat sink

ORC and Kalina cycles can produce power from low-temperature heat sources. There is, also, a great potential in Liquid Natural Gas gasification units to generate power derived from cold energy within these streams. This work proposes a new power generation plant to convert the trapped energies of geothermal hot water and Liquid Natural Gas streams to useful power. The combined power plant consists of 7 units, which each unit includes three discrete cycles of Kalina and two Organic Rankine power generation cycles to produce power from its heat sources. Geothermal hot water is supplied at 163 °C and pressure of 7 bar with a mass-flow of 39 kg/s from a geothermal well, and moreover, natural gas is supplied at −162 °C and pressure of 10 bar with a mass-flow of 8 kg/s to each unit of the power plant as a cold source. Energy and exergy analyses have been employed to evaluate the performance of the proposed plant. The energy analysis shows that each unit of the proposed plant could produce 1924 kW net power and the energy efficiency of each unit is 13.25%. On the other hand, the exergy analysis reveals that the exergy efficiency of each unit of the proposed plant is 26.13%, while each unit could recover 57% exergy of the LNG stream. Considering the results of the energy and exergy analyses along with sensitivity analysis, the system is amended to maximize the exergy efficiency, which after implementing modifications, the exergy efficiency of the system increases to 32.15%. Also, the net power output of each unit increases to 2485 kW after modifications.

Four different configurations of a 5 kW class shell-and-tube methane steam reformer with a low-temperature heat source

The methane steam reforming reaction is an extremely high endothermic reaction that needs a high temperature heat source. Various fuel cell hybrid systems have been developed to improve the thermal efficiency of the entire system. This paper presents a low temperature steam reformer for those hybrid systems to maximize the utilization of energy from a low temperature waste heat source. In this study, the steam reformer has a shell and tube configuration that is divided into the following zones: the inlet heat exchanging zone, the reforming zone and the exit heat exchanging zone. Four different configurations for methane steam reformers are developed to examine the effect of heat transfer on the methane conversion performance of the low temperature steam reformer. The experimental results show that the overall heat transfer area is a critical parameter in achieving a high methane conversion rate. When the heat transfer area increases about 30%, the results showed elevated dry mole fractions of hydrogen about 3% with about 30 °C rise of reformer outlet temperature.