Heat Source Temperature Research Articles

Experimental investigations on the performance of a thermo-mechanical refrigeration system utilizing ultra-low temperature waste heat sources

Experimental studies that investigate the utilization of ultra-low temperature (between 48 °C and 120 °C) waste heat, which forms 25 % of the global unrecovered waste heat, to drive thermal cooling systems are rare. Thus, this study fills a significant gap in the literature by (i) experimentally evaluating the performance of a new full-scale thermo-mechanical refrigeration (TMR) system at ultra-low temperatures ranging from 50 °C to 85 °C, (ii) characterizing its operation with different commercial refrigerants, and (iii) identifying optimal operating conditions and working fluids for the investigated TMR system. An organic Rankine cycle (ORC), vapor compression cycle (VCC), and expander-compressor unit (ECU) make up the TMR system. To ensure its efficient operation, flexibility, and reliability, a full-scale ECU-based TMR system with a design capacity of 1 kW at a heat source temperature of 85 °C is built and put through a series of tests. Furthermore, the TMR system is tested with different commercial refrigerants (R134a, R410A, R407C) over a wide range of operating conditions of the power loop. The results reveal that the ECU-based TMR system can work with ultra-low temperatures of 65 °C with an energy efficiency of 5.92 % and COP of 2.36, for the ORC and VCC, respectively. At a heat source temperature of 85 °C, a condenser water temperature of 15 °C, and an evaporator water temperature of 33 °C, the energy efficiency of the ORC and COP of the VCC are increased to 9.85 % and 3.99, respectively. For the cooling quality, the TMR system shows a minimum evaporator temperature of −10 °C using R134a in both the power and cooling loop, which is improved to lower than −20 °C by using R407C in the cooling loop. The results presented herein will be beneficial to the development, design, and optimization of refrigeration and power systems that utilize low-temperature waste heat.

Steady-state interconnected cycle modeling and experimental results of a lab-scale ORC

ORC is one of the mature technologies for power generation from low temperature heat sources. In this study, the aim is to develop an accurate ORC model which is validated using reliable steady-state data. For this purpose, tests are carried out at four different heat source temperatures ranging from 80 to 110 °C to obtain data in a repeatable manner. The proposed model considers pressure drop and heat transfer correlations to improve the accuracy of model predictions. Using the refrigerant pump mass flow rate, thermal oil pump volumetric flow rate, cooling water inlet temperature, cooling water volumetric flow rate, the throttle valve outlet set pressure, and refrigerant pump outlet pressure as input, the model predicts the pressure, temperature, and mass flow rate in the cycle. The results show that the steady-state ORC model is significantly accurate, with ±1% deviations in pressure and ±1 °C in temperature, and ±5% in mass flow rate, heat transfer rate and refrigerant pump power predictions. The novel iterative model presented in this study includes pipe losses and significantly improves the simulation accuracy of ORCs with long pipes.

Thermal-economic and sensitivity analysis of different Rankine-based Carnot battery configurations for energy storage

The rapid growth of renewable energy, accompanied by intermittent and instability, has brought great challenges to energy storage technology. Rankine-based Carnot batteries are considered a promising solution to electricity storage in view of their high energy density at a low temperature. Determining the suitable Rankine-based Carnot battery configuration for its development and application requires accurate prediction and comprehensive comparison of the system performance under different conditions. In this paper, three Rankine-based Carnot Battery systems were constructed using a heat pump-organic Rankine cycle. Mathematical models of the aforementioned systems were built to assess and compare their performance from a thermodynamic standpoint. The results showed that the basic heat pump-organic Rankine cycle and reversible heat pump-organic Rankine cycle are better in energy and exergy aspects, where power-to-power-efficiency and exergy efficiency are higher by about 21.4% and 18.7% than that of reversible heat pump-organic Rankine cycle using a dual-function machine, respectively. Compared with basic heat pump-organic Rankine cycle and reversible heat pump-organic Rankine cycle, the levelized cost of storage of reversible heat pump-organic Rankine cycle using a dual-function machine is lower by about 12.3% and 5.4%, respectively. Taking the three criteria together, it seems that the reversible heat pump-organic Rankine cycle is better thermo-economically. The sensitivity analysis revealed that the heat source temperature has a greater impact on the reversible heat pump-organic Rankine cycle using a dual-function machine, and its absolute value of the sensitivity coefficient is 3.

Simulation research of a dual-loop booster heat pump system on district heating under ultra-low temperature

ULTDH (ultra-low temperature district heating) system improves the shortcoming of significant loss of heating network in traditional district heating systems. This work proposes a dual-loop booster heat pump for ULTDH to improve the heating capacity and COP. The system is modeled by MATLAB, and the water temperature between the two loops is solved by the NSGA-II algorithm (Non-dominated Sorting Genetic Algorithm-II algorithm). The simulation results show that when the heat source temperature changes from 20 °C to 40 °C, the COP and heating capacity of the dual-loop system increase by 43.79% and 90.30%, respectively, which are higher than those of the single-loop system. When the temperature difference between the inlet and outlet of the evaporator is increased, the heating capacity of the dual-loop system is still 7.31–33.47% higher than that of the single-loop system. When the hot water supply temperature is 60 °C, the COP of the dual-loop system is 3.34, which is 23.70% higher than that of the single-loop system. During the whole heating period in Beijing, the dual-loop system can save 17.67 % of the electric energy than the single-loop system. The dual-loop system shows excellent advantages in heating capacity and COP.

DETERMINATION OF OPTIMUM FLUID FOR DIFFERENT HEAT SOURCE TEMPERATURES BASED ON MULTI-OBJECTIVE FUNCTIONS IN THE ORGANIC RANKİNE CYCLE

In this study, the optimum fluid was determined by using Non-dominated Sorting Genetic Algorithm-II (NSGA-II) within the scope of Organic Rankine Cycles (ORC) low temperature applications. Heat source temperatures are taken as 90, 100 and 110 °C. Fluid optimization was performed by comparing the performance of 8 fluids from 4 different categories under different criteria (dry-R601 and R601a, isentropic-R141b and R123, wet-R152a and R134a, new generations-R1234yf and R1234ze). Objective functions have been established under the parameters of Energy, Exergy, Economy and Environment (4E). In ORC systems, every organic fluid has certain advantages and disadvantages. It is seen that the studies on organic fluid selection meet a single goal from the system performance parameters. However, it has been observed that the turbine power performance is not at the desired level due to the required evaporator capacity of the fluid, which performs well in terms of thermal efficiency in ORC systems. Therefore, it is necessary to determine the percentage of organic fluid that can be used by optimizing it under different objective functions. In this study, the optimum fluid was determined for ORCs operating under 90, 100 and 110 °C heat source temperatures by evaluating different objective functions together.

Best thermoelectric efficiency of ever-explored materials

A thermoelectric device is a heat engine that directly converts heat into electricity. Many materials with a high figure of merit have been discovered in the anticipation of a high thermoelectric efficiency. However, there has been a lack of investigations on efficiency-based material evaluation, and little is known about the achievable limit of thermoelectric efficiency. Here, we report the highest thermoelectric efficiency using 12,645 published materials. The 97,841,810 thermoelectric efficiencies are calculated using 808,610 device configurations under various heat-source temperatures ( ) when the cold-side temperature is 300K, solving one-dimensional thermoelectric integral equations with temperature-dependent thermoelectric properties. For infinite-cascade devices, a thermoelectric efficiency larger than 33% (≈⅓) is achievable when exceeds 1400K. For single-stage devices, the best efficiency of 17.1% (≈1/6) is possible when is 860K. Leg segmentation can overcome this limit, delivering a very high efficiency of 24% (≈1/4) when is 1100K.

Numerical Analysis of Flow Boiling Characteristics of a Single Channel Heat Sink Subjected to Multiple Heat Sources

High-power electronic devices with multiple heat sources often require temperature uniformity and to operate within their functional temperature range for optimal performance. Micro-channel cooling could satisfy the heat dissipation requirements, but it may cause temperature non-uniformity. In this paper, simulations are performed for different geometric parameters of the channel and the position of the heat source. The results show that a flattened channel can effectively reduce the heat source temperature, broadening the straight channel can reduce the flow resistance and enhance heat transfer, while widening the channel at the bend may lead to local dryness. Meanwhile, a thermal model is established to analyze the influence of the position of the heat source. The results also show that with the increase in the curved channel radius, the phenomenon of vapor–liquid separation becomes more obvious, the pressure drop decreases, but the heat transfer effect worsens.

A Gd‐Film Thermomagnetic Generator in Resonant Self‐Actuation Mode

AbstractThermomagnetic generation is a promising technology for conversion of low‐grade waste heat into electricity. Key requirements for the development of efficient thermomagnetic generators (TMGs) are tailored thermomagnetic materials as well as innovative designs enabling fast heat transfer. Recently, film‐based thermomagnetic generators are developed that operate in the mode of resonant self‐actuation enabling high frequency and stroke of a movable cantilever and, thus, efficient conversion of thermal energy into electrical energy. Here, the performance of a Gadolinium (Gd)‐film‐based TMG that is optimized for resonant self‐actuation near room temperature is reported. The Gd‐film TMG exhibits large oscillation frequencies up to 106 Hz and large strokes up to 2 mm corresponding to 38% of the oscillating cantilever's length. This performance occurs in a sharply bound range of ambient temperatures with an upper limit near the film's ferromagnetic to paramagnetic transition temperature Tc of 20 °C and of heat source temperatures ranging between 40 and 75 °C. The maximum power per footprint is 23.8 µWcm−2, at which the Gd film undergoes a temperature change of only 0.9 °C at ≈10 °C above Tc.

Case study: Design of an absorption refrigeration system for milk preservation in Jalisco, Mexico

This article presents a case study focused on designing a refrigeration system for milk storage in a town of Jalisco, Mexico. An absorption refrigeration unit is proposed, activated with a geothermal heat source from an existing well. An economic analysis of the proposal and its comparison with a conventional system and a solar system is presented. The proposed system must provide refrigeration to the warehouse (cold room) with a cooling load of 5 kW, with a geothermal heat source temperature of 80 °C for the single effect system and 163 °C for the double effect system. For the design of the warehouse, the thermal loads were obtained through ceilings and walls, by lighting, infiltration, and by occupation, through the EnergyPlus software. The results show values of monthly thermal loads ranging between 0.94 and 1.1 kW. The single-effect system achieved a COP of 0.85 costing approximately $13,083, while the double-effect system reached a COP of 1.38 with a cost of $18,144.

Techno-economic evaluation of industrial heat pump applications in US pulp and paper, textile, and automotive industries

Industrial process heat decarbonization through electrification could contribute significantly to climate change mitigation efforts. In the US industry, thermal processes accounted for more than two-thirds of the total final energy demand in 2021. Cross-cutting electrification technologies like industrial heat pumps are suitable for the process heat supply to several industrial unit operations in a sustainable way while also improving overall energy efficiency. This study employs a bottom-up approach to investigate the techno-enviro-economic potentials of deploying high-temperature and steam-generating heat pumps in US textile, pulp and paper, and automotive sectors in different timeframes. The results show that the annual technical potential energy and CO2 savings by electrifying heat supply are 310 PJ (or 36% of the projected energy demand) and 28 MtCO2 (or 71% of the projected CO2 emissions) in 2050 respectively, however, these incur additional costs in each sector (ranging between 5 and 18 $/GJ). The required heating capacity of industrial heat pumps is estimated at 15 GW, which translates roughly into a market of over 6000 heat pump units and an investment volume of $7 billion in the studied processes. Although there may be individual cost-effective opportunities for electrifying heat supply in specific industrial sites, the overall costs are estimated to be high in the three industrial sectors due to the large disparity between electricity and natural gas prices and low heat source temperatures. To overcome the identified techno-economic barriers, comprehensive action plans for different stakeholders are also given. This study provides novel insights that should inform policymakers’ and executives’ decisions about the electrification of the current and future US industrial heat supply in relevant industrial sectors.

Thermodynamic Analysis and Optimization of the Micro-CCHP System with a Biomass Heat Source

In this article, new multiple-production systems based on the micro-combined cooling, heating and power (CCHP) cycle with biomass heat sources are presented. In this proposed system, absorption refrigeration cycle subsystems and a water softener system have been used to increase the efficiency of the basic cycle and reduce waste. Comprehensive thermodynamic modeling was carried out on the proposed system. The validation of subsystems and the optimization of the system via the genetic algorithm method was carried out using Engineering Equation Solver (EES) software. The results show that among the components of the system, the dehumidifier has the highest exergy destruction. The effect of the parameters of evaporator temperature 1, ammonia concentration, absorber temperature, heater temperature difference, generator 1 pressure and heat source temperature on the performance of the system was determined. Based on the parametric study, as the temperature of evaporator 1 increases, the energy efficiency of the system increases. The maximum values of the energy efficiency and exergy of the whole system in the range of heat source temperatures between 740 and 750 K are equal to 74.2% and 47.7%. The energy and exergy efficiencies of the system in the basic mode are equal to 70.68% and 44.32%, respectively, and in the optimization mode with the MOOD mode, they are 87.91 and 49.3, respectively.

Cogeneration system based on large temperature difference heat transfer with stepwise utilization

Organic Rankine cycle (ORC) plays a critical role in systems such as waste heat recovery, cogeneration, renewable energy generation and energy storage. No matter which field ORC is applied in, the evaporator side of ORC has an extremely poor utilization of the thermal energy from heat source, resulting in the outlet temperature of hot side fluid being much higher than the inlet temperature of cold side fluid. In order to fully capitalize on the thermal energy, this study introduces the two-stage absorption heat exchanger (AHE) and integrates it into ORC to obtain an original high-efficiency cogeneration system (AHEORC-CHP), which is parametrically analyzed by constructing and operating thermo-economic model in terms of the expansion pressure ratio and working fluid of ORC, the type and flow rate of heat source, and the inlet temperature of generator in AHE. Due to the existence of pinch point temperature difference, conventional ORC design can only reduce the outlet temperature of the heat source with an inlet temperature of 130 °C to about 70 °C under the condition of ideal heat transfer. The AHEORC-CHP configuration proposed in this work can achieve a significant reduction in the final outlet temperature of waste heat source (as low as 24.69 °C) and realize heat exchange with large temperature difference and efficient utilization of the heat source. Besides, the thermoelectric efficiency and temperature effectiveness can reach 90.9% and 1.2 respectively, while the profit ratio of investment rises to 8.46. Further improving the performance of AHEORC-CHP system requires optimizing the design of the pressure in absorption heat pump (AHP) cycle as well as the concentration and flow rate of LiBr-H2O solution. This study can provide a simulation pathway for the application of two-stage AHE in ORC, and likewise for future experimental investigations.

Energy and exergy analysis of a liquid desiccant heat and mass transfer loop with natural convection: The effect of heat sink and heat source temperature

Desiccant systems, as a promising air conditioning technology have opened new aspects as a replacement for vapor compression systems. The liquid desiccant energy exchanger system with natural convection flow is proposed here; the system is a loop with two hollow fiber membrane air-desiccant exchanger of shell-and-tube type that works as the humidifier and regenerator. The LiCl aqueous solution as desiccant directed over the fibers and the air is inside the fibers; the water stream flows outside the modules to provide the required heat exchange. The heat sink and source as merged subparts of the exchangers have a major influence on system performance. The system is examined from the energetic and exergetic viewpoints at different heat sink and heat source temperatures. Keeping the fixed air flow rate and using the standard air properties, the cold and hot water temperatures of 15–25 °C and 50–70 were employed and the effectiveness coefficients including the latent, sensible and total and 2nd law efficiency evaluated. It was shown that the values of NTU and Cr* depend on each other and attenuating effect of NTU reduction is higher than enhancing effect of Cr* increase on effectiveness values. The prominent factor on exergy performance which hinders the effect of the other parameters is the solution flow rate. Also, the highest and lowest values of 2 nd law efficiency are 81% and 5% which are for temperature pairs of (52, 20) and (65,25), respectively.

Fabrication and Characterization of Acicular Micro-Textured Copper Sheet Device for Low-Temperature Heat Radiation

An acicular microtextured sheet was developed as a heat radiation device from the high-temperature source to the cooling medium in the infrared (IR) spectrum. The copper surface was modified by acicular micro-texturing to place a semi-regular micro-/nano-cone structure onto it. FT-IR (Fourier transformation IR) spectroscopy was utilized to measure the transmittance diagram in near-IR to far-IR wavelengths. The wavelength (λ) of 6.7 μm, where the highest absorbance valley was detected in the diagram, was equivalent to the doubled size of the micro-cone average height, with Have = 3.3 μm; λ ~ 2 × Have. The electromagnetic waves in the far-IR wavelength were emitted by acicular micro-textured metallic sheets. The heat radiation transfer experiment was performed to describe this low-temperature heat radiation behavior. No temperature rise was detected on the black-colored polycarbonate (BC-PC) plate away from the bare copper sheet without textures, located on the high-temperature source. The temperature increased by 4 K on the BC-PC plate using the acicular textured copper sheet device. The emitter temperature also decreased significantly by 50 K or 50% of the heat source temperature.

Study on heat transfer characteristics of cement-based honeycomb structures based on infrared imaging

The honeycomb structure may become the most potential material for constructing low-carbon and energy-saving buildings due to its excellent mechanical and thermal properties. The aim of this study was to investigate the temperature field evolution and heat transfer mechanism of cement-based honeycomb structures (CHSs) based on infrared thermal imaging technology. And the effects of heat source temperature and cavity bulk density on the temperatures of CHS were investigated. The results show that the heat transfer of CHS develops from an unsteady state to a steady state, and its thermal diffusion effect weakens layer by layer upward through the honeycomb cavities. The CHS temperatures increase linearly with increasing heat source temperature, but the temperature increase of the cavity wall is significantly higher than that of the air in the cavity. When the heat source temperatures increase from 40 to 85 °C, the temperature differences between the cavity wall and the air in the cavity increase in the range of 4.67–12.50 °C. The temperatures of the CHSs show a decreasing trend with increasing cavity volumes, and the air temperature reduction in the cavity is about 1.90–2.19 times that of the cavity wall. Moreover, it is found that the cavity wall temperature is mainly controlled by the heat source. In contrast, the air temperature in the cavity is influenced by both the heat source and the cavity volume. Ultimately, we speculate that increasing the thermal resistance of the cavity wall and the cavity volume is beneficial to improve the thermal insulation performance of the CHS.

Geothermal trigeneration systems with Organic Rankine Cycles: Evaluation of different plant configurations considering part load behaviour

Due to the increasing importance of cooling applications, geothermal trigeneration systems might be of high interest in the future. This work aims at evaluating different plant layouts against the background of more advanced plant configurations and part load behaviour. Five different plant configurations are analysed for geothermal heat source temperatures between 110 and 150 °C. The highest net power output is achieved by an advanced serial-parallel configuration (ASPC), but in case of high heating and cooling demand, a standard serial-parallel configuration is more favourable. For the considered base demand scenario of 130 °C, the ASPC results in an annual net power generation of 20.94 GWh, which is 6.9% higher than the second favourable configuration. The application of a recuperator within the ORC system has a significant impact on the serial concepts, but only marginally increases the power output of the parallel layouts. Comparing two exergetic efficiencies highlights that the assumed definition can result in a different ranking of the plant layouts. Considering the exergy that is transferred from the brine to the trigeneration system reveals the highest exergetic efficiency for a serial configuration, while the focus on the available exergy flow reveals the highest efficiency for the ASPC layout. Considering a brine temperature of 130 °C results in a maximal achievable second law efficiency of 34.1% if evaluating the available exergy flow. The evaluation of the pay-back period reveals that the ASPC results in the shortest pay-back period of 13.8 years.

Numerical investigation on particle removal and energy consumption of supplied and recirculated ventilation for industrial workshop

In the weld back-cleaning process, many high-concentration pollutants are produced, which can lead to health problems after prolonged exposure. In this study, a novel recirculating stratified ventilation system is proposed that combines supply and recirculating ventilation. It reduces indoor particulate concentration and exhausts air volume based on the air gouging process in a casting workshop. The influences of the supplied and recirculated air velocities on the particle removal efficiency and energy consumption were investigated and compared with those of a traditional exhaust system. The computational fluid dynamics-discrete phase model coupling method was adopted. First, the feasibility of the model was verified using previously published experimental data. The concentration of the unsteady particles was then simulated with different supplied and recirculated air velocities in the ventilation system. The particles were dispersed owing to the influence of the heat-source temperature. With an increasing supplied air velocity and constant recirculated air velocity, the average particle concentration was decreased. The results show that the particle removal efficiency can be improved by approximately 100%, and 90% of the energy can be saved to achieve the same removal efficiency as a traditional ceiling exhaust system.

Thermoelectric generator for high temperature geothermal anomalies: Experimental development and field operation

In the current climate and energy context, it is important to develop technologies that permit increase the use of renewable sources such as geothermal energy. Enhancing the use of this renewable source is particularly important in some places, due to its availability and the enormous dependence on fossil fuels, as is the case of the Canary Islands. This work proposes the use of thermoelectric generators with heat exchangers working by phase change to transform the heat from the shallow high temperature geothermal anomalies on the island of Lanzarote directly into electricity, since the use of conventional geothermal power plants would not be possible because they would damage the protected environment. To bring this proposal to reality, this work has succeeded in developing and field-installing a geothermal thermoelectric generator that operates without moving parts thanks to its phase-change heat exchangers. This robust generator do not require maintenance nor auxiliary consumption, and produces a minimal environmental impact, it is noiseless, and the use of water as working fluid makes it completely harmless.The developed device consists of a thermosyphon as hot side heat exchanger, thermoelectric modules and cold side heat exchangers also based in phase change. Tests were carried out in the laboratory at various heat source temperatures and varying the number of thermoelectric modules. It was determined that installing more modules decreases the efficiency per module (from 4.83% with 4 modules to 4.59% with 8 modules at a temperature difference between sources of 235 °C), but for the number of modules tested the total power increases, so the field installation was carried out with 8 modules. After the good results in the laboratory, it was satisfactorily installed at Timanfaya National Park (Lanzarote, Spain) in a borehole with gases at 465 °C. This generator presents a maximum output power of 36 W (4.5 W per module), and is generating 286.94 kWh per year, demonstrating the great potential of the developed thermoelectric generators to build a larger-scale renewable installation.

Efficiency analysis and operating condition optimization of solid oxide electrolysis system coupled with different external heat sources

Coupling external heat sources effectively reduces energy consumption and improves the efficiency of the solid oxide electrolysis (SOEC) system. While an in-depth analysis of the SOEC systems in different coupling scenarios is still needed. According to the internal heat demand and the temperature of external heat sources, three coupling scenarios are defined in this study, i.e., no heat source coupling (Scenario 1), coupled low-temperature heat source (Scenario 2), and coupled high-temperature heat source (Scenario 3). Firstly, the influence of critical parameters on system efficiency is analyzed from two perspectives, including specific system loss and specific energy consumption. The results present that efficiency η1 mainly increases with the rise of steam utilization. Efficiency η2 is not significantly affected by the parameters and is primarily positively correlated with the fuel electrode steam concentration. Efficiency η3 is negatively related to steam utilization, fuel electrode steam concentration, and fuel electrode flow rate, while positively to stack operating temperature. Meanwhile, for Scenarios 1 and 2, the exothermic state of the stack module should be avoided. Furthermore, the system performance maps and stack operating windows in the three scenarios are obtained by changing multiple operating parameters simultaneously and setting constraints. For Scenarios 1 and 2, high system efficiency, high hydrogen production, and long lifetime cannot be achieved simultaneously, so operating parameters need to be selected at a compromise. For scenario 3, high fuel electrode flow rate and low steam utilization can basically meet the above requirements. Both high stack operating temperature and high fuel electrode steam concentration can improve hydrogen production, while the former is mainly beneficial to efficiency η3, and the latter can improve the three efficiencies. The results obtained can be used not only to choose the optimal working conditions of various external heat sources but also to guide the online control and load regulation during system operation.

A thermal management strategy for electronic devices based on copper double skin inspired hydrogel

A passive cooling material was proposed by combining the advantages of an interpenetrating polymer network and copper powder. The experimental thermal conductivity of copper based composite hydrogel was enhanced to 0.71 W/(m·K). At the same time, MD simulations showed a thermal conductivity of approximately 0.84 W/(m·K), which primarily caused by the increased overlap between hydrogel components. Due to the improvement of the thermal conductivity, the heat flux of copper based composite hydrogel increased to 977 W/m2 at a constant heat source temperature of 65 °C and the total heat dissipation increased by 104.4%. The thermal management tests showed copper based composite hydrogel could reach 35 °C, while the copper based composite hydrogel could reach 50 °C. The obtained copper based PNIPAM/Alginate-Ca2+ hydrogel exhibited a synergistic property enhancement of high thermal conductivity, stability in shape and decreased aggregation of the copper nanoparticles, which should provide a new strategy for thermal management.