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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Techno-Economic Simulation Results Using dGeo for EGS-Based District Heating in the Northeastern United States

This dataset presents the results of techno-economic simulations performed using the Distributed Geothermal Market Demand Model (dGeo) to evaluate the feasibility of Enhanced Geothermal Systems (EGS)-based district heating in the Northeastern United States. Developed by the National Renewable Energy Laboratory (NREL), dGeo is a geospatially resolved, bottom-up modeling framework designed to explore the deployment potential of geothermal distributed energy resources. The dataset, created as part of the Cornell EGS Ground-Truthing Project, provides census tract-level data that includes inputs and outputs such as thermal demand, road length, energy prices, geothermal system sizing, annual energy contributions from geothermal and natural gas peaking boilers, system capital costs (CAPEX), operation and maintenance costs (OPEX), and the levelized cost of heat (LCOH). Key simulation parameters include geothermal gradients, measured well depths, production temperatures, and district heating piping lengths based on S1400 neighborhood road lengths. The simulations assume a target bottom hole temperature of 80C and the development of new district heating networks in each census tract.

15 GEOTHERMAL ENERGY↗
DOE OSTI2021

Regional suitability of heating tower heat pumps based on technical and economic performance maps

The heating tower heat pump (HTHP) technology is evolving rapidly due to its high performance in summer and frost-free characteristic in winter. However, lacking comprehensive comparisons between the HTHP and conventional methods, such as air-source heat pump (ASHP), and chiller and boiler, greatly limits its applications. To address this problem, this paper carries out technological and economic performance analyses of the three systems in 353 locations over China by the processes of building load calculation, system sizing, annual simulation, performance comparison, and demonstration. Energy saving principle and potential of the HTHP are presented and explained. Based on that, economic performance comparison is conducted by considering the energy conversion efficiency and prices. The results show that the HTHP has advantage over the ASHP in most locations in China. The improvement in annual coefficient of performance (COP) is about 10% to 20%. For the locations in southwest China like Chongqing, the improvement is also less than 10% due to the large regeneration penalization in winter and small difference between dry-bulb and wet-bulb temperature in summer. The annual COP of the HTHP is 10% to 23% higher than that of the chiller and boiler in hot summer and cold winter zone, and cold zone. However, the HTHP shows no advantage over the chiller and boiler in severe cold zone because of the low efficiency of heat pump in winter, neither in hot summer and warm winter zone due to the small heating load. Based on the results, technical and economic performance maps are developed to guide the application of the HTHP in different climate regions.

heating tower heat pump, air-source heat pump, chi↗
DOE OSTI2025

Quantum heat engine based on quantum interferometry: The SU(1,1) Otto cycle

We present a quantum heat engine based on a quantum Otto cycle whose working substance reproduces the same outcomes as an SU ( 1 , 1 ) interference process at the end of each adiabatic transformation. This device takes advantage of the extraordinary quantum metrological features of the SU ( 1 , 1 ) interferometer to better discriminate the sources of uncertainty of relevant observables during each adiabatic stroke of the cycle. In particular, the SU ( 1 , 1 ) adiabatic transformations enable high-precision estimations of the energy extracted from the adiabatic stroke, despite the presence of thermal fluctuations. Applications to circuit QED platforms are also discussed. Published by the American Physical Society 2025

Ferreri, Alessandro (ORCID:0000000185459205)↗
DOE OSTI2020

Subcloud and Cloud-Base Latent Heat Fluxes during Shallow Cumulus Convection

Doppler and Raman lidar observations of vertical velocity and water vapor mixing ratio are used to probe the physics and statistics of subcloud and cloud-base latent heat fluxes during cumulus convection at the ARM Southern Great Plains (SGP) site in Oklahoma, United States. The statistical results show that latent heat fluxes increase with height from the surface up to ~0.8 Z i (where Z i is the convective boundary layer depth) and then decrease to ~0 at Z i . Peak fluxes aloft exceeding 500 W m −2 are associated with periods of increased cumulus cloud cover and stronger jumps in the mean humidity profile. These entrainment fluxes are much larger than the surface fluxes, indicating substantial drying over the 0–0.8 Z i layer accompanied by moistening aloft as the CBL deepens over the diurnal cycle. We also show that the boundary layer humidity budget is approximately closed by computing the flux divergence across the 0–0.8 Z i layer. Composite subcloud velocity and water vapor anomalies show that clouds are linked to coherent updraft and moisture plumes. The moisture anomaly is Gaussian, most pronounced above 0.8 Z i and systematically wider than the velocity anomaly, which has a narrow central updraft flanked by downdrafts. This size and shape disparity results in downdrafts characterized by a high water vapor mixing ratio and thus a broad joint probability density function (JPDF) of velocity and mixing ratio in the upper CBL. We also show that cloud-base latent heat fluxes can be both positive and negative and that the instantaneous positive fluxes can be very large (~10 000 W m −2 ). However, since cloud fraction tends to be small, the net impact of these fluxes remains modest.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Ammonia-based chemisorption heat pumps for cold-climate heating applications: A comprehensive review

This paper reviews the state of the art of chemisorption heat pumps that use ammonia as the refrigerant for cold-climate heating applications. In such a system, ammonia vapor is adsorbed by the solid salt through reversible chemisorption reactions, and the thermal effect of the reaction and ammonia phase change is used to extract heat from a cold environment and supply heat to a warm environment. With the high latent heat and low boiling point of ammonia as a low-temperature refrigerant and the high sorption capacity of ammonia-based chemisorption reactions, chemisorption heat pumps have the potential to produce high-efficiency heating, particularly for cold climates. This review first briefly introduces the basics of ammonia-based chemisorption heat pump systems. Then, the latest development of sorbent materials, including ammoniate salts and heat-conductive porous matrix materials, are summarized with the focus on low-temperature heating conditions. The design of system components, as well as cycle configurations, in the literature are summarized. This review concludes with highlights of recent developments on these topics and suggestions of areas for further research.

42 ENGINEERING↗
DOE OSTI2020

Analysis and Evaluation of Thermally Annealed Pyrolytic Graphite Heat Spreader for Power Modules

Next generation power modules demand increased heat extraction capability along with reduced weight and volume. In this paper, thermally annealed pyrolytic graphite (TPG) is analyzed and compared with conventional materials used in power modules for thermal management. Fundamental properties of TPG are explained and compared with commonly used materials in power module heat spreaders and substrates. The encapsulated TPG based heat spreader is manufactured and compared with bulk copper in simulation and experimental based analysis. The results show that encapsulated TPG based heat spreader achieves more than 50% reduction in thermal resistance along with 48% reduction in weight in the heat spreader layer.

Gurpinar, Emre↗
DOE OSTI2026

Virtual refrigerant charge sensor for variable-speed heat pumps based on feature selection

The refrigerant charge level in heat pump systems significantly impacts their energy efficiency. Virtual refrigerant charge (VRC) sensing technology has been comprehensively investigated and well-established due to its lower cost compared to physical sensors. However, the previous VRC research often relied on expert judgment and physical reasoning for their variable selection, which can potentially select redundant (or highly correlated) or insignificant features, and it is also primarily focused on single-speed systems. To address these challenges, this study proposes a VRC algorithm for variable-speed heat pumps that selects features through a rigorous feature selection method in combination with physical insights. We also propose a piecewise linear model structure segmented by subcooling temperature to accurately predict charge levels, particularly when subcooling temperatures are substantially low. The proposed algorithm was evaluated using experimental data of a residential R410A heat pump, and the performance was compared with two baseline VRC algorithms. The results are: (1) The proposed algorithm outperforms for the case with subcooling temperature less than 1 °C. (2) The proposed algorithm achieves a tested mean absolute percentage error (MAPE) of 4.23%, and improves the overall accuracy for cooling conditions by approximately 60%, compared with the two baseline algorithms. (3) The proposed algorithm uses two fewer features and improves the accuracy for undercharge cooling conditions by 68.0%, compared with baseline algorithm 2. These improvements enhance prediction accuracy and prevent overfitting, providing a more reliable refrigerant charge level prediction and helping improve the heat pump energy efficiency.

Liang, Chenjiyu↗
DOE OSTI2021

Cycle-to-cycle variability in spark-assisted compression ignition engines near optimal mean combustion phasing

Stoichiometric spark-assisted compression ignition (SACI) combustion with exhaust gas recirculation (EGR) dilution has demonstrated higher part-load thermal efficiencies compared to spark-ignited engines, while maintaining ultra-low tailpipe emissions. However, SACI is often characterized by high cyclic variability in heat release or torque output, which poses a challenge to its implementation in light-duty vehicles. This paper presents an experimental investigation of cyclic variability in stoichiometric SACI combustion under EGR-dilute conditions, while maintaining mean combustion phasing (θ 50 ) near optimal timing for thermal efficiency. The present work focuses on SACI conditions where the flame-based heat release fraction is between approximately 10% and 40% of the overall heat release, and therefore contributes significantly to the combustion process. For the SACI conditions examined, the variability in θ 50 was driven by variability in autoignition timing, which in turn correlated with the start of measurable heat release (θ 02 ). High variability in θ 50 caused unstable work output due to very late combustion with poor or no end-gas autoignition. The use of a high ignition energy dual-coil offset ignition system had negligible impact in reducing θ 50 variability. Analysis of experimental data from close to 1000 operating conditions showed that the magnitude of θ 50 variability correlates with the flame-based heat release fraction ([Formula: see text]), for a large range of intake pressures, spark timings and exhaust gas recirculation levels. For the SACI conditions examined, combustion phasing variability was largely determined by flame-based combustion and particularly the initial flame formation (θ IGN-02 ), and minimally by the end-gas autoignition heat release. The analysis also demonstrated that θ 50 variability is amplified as the contribution of the flame to the overall heat release increases.

Engineering↗
DOE OSTI2021

A fast reduced model for a shell-and-tube based latent heat thermal energy storage heat exchanger and its application for cost optimal design by nonlinear programming

Numerical simulation of latent heat thermal energy storage (LHTES) systems plays a fundamental role in studying the physical process and guiding the engineering design. Discretization of the PDEs describing the nonlinear solidification/melting process of phase change materials (PCMs) leads to a large-scale complex dynamics system, where the system behavior depends on a set of parameters. In a design setting, repeated model evaluations are required over the set of parameters results in significant computational burden. In this paper, an explicit analytic solution was built for the propagation of the solidification front in a cylindrical coordinate. The analytic solution approach is further employed to develop a low computational reduced model (RM) as a module for a shell-and-tube based LHTES heat exchanger. The levelized Cost of Energy (LCOE) is used as a design metric and the RM model is used to apply system-level constraints in the nonlinear programming formulation that facilitates efficient global optimal design of the PCM properties, flow conditions and tube geometries. The use of LCOE as the design metric prevents over design of the heat transfer rate and also establishes a fair ground for evaluation of different thermal storage technologies and their integrated applications with other systems. Optimal results showed that a higher effectiveness results in a higher LCOE; the velocity of the HTF and the length of the channel are highly correlated with each other; both larger PCM latent energy and conductivity result in lower LCOE.

25 ENERGY STORAGE↗
DOE OSTI2025

Design, fabrication, simulation, and testing of additively manufactured lattice-based copper heat sinks

Here, this study investigates the potential advantages of lattice structure-based bound metal material extrusion (MEX) 3D printing for fabricating high-performance copper heat sinks. Copper powder-filled polymer filaments, with a copper content of > 90 wt.%, were developed specifically for the bound metal MEX 3D printing process. Three types of structures—planar, strut, and surface lattices—were 3D printed to facilitate efficient heat transfer pathways within the heat sinks. Subsequent post-processing steps, including polymer removal and sintering, were performed to achieve dense copper parts. Hot isostatic pressing was further employed to enhance the sintered density from 93 to 98%. Finite element analysis (FEA) simulations were conducted to assess the heat transfer efficiency of the designs, and heat transfer experiments were performed using a custom setup to validate the simulation results. Additionally, this research explores the use of extended hold times during pre-sintering and a reduced atmosphere to enhance the %IACS values (electrical conductivity) and thermal performance of the bound metal MEX 3D printed copper heat sinks. The investigation combines experimental analysis, including simulations and heat transfer experiments, to gain insights into the structure-material property relationships and optimize the thermal performance of the printed heat sinks.

Ajjarapu, Kameswara Pavan Kumar [Oak Ridge Nationa↗
DOE OSTI2021

Design Optimization of A-Type Heat Exchangers based on High Performance, Non-Round Tubes

Air-to-refrigerant heat exchangers (HXs) have been the topic of considerable research as they are the fundamental heat transfer components of HVAC&R systems. For residential and commercial applications, indoor heat exchangers are often in A-type configurations to reduce air-conditioner system footprint while still delivering the required cooling or heating. Classical HX design practices typically assume a uniform frontal air velocity profile to facilitate the use of conventional tube-fin airside heat transfer and pressure drop correlations for performance prediction. However, it is well-reported throughout the literature that A-type HXs experience significant airflow maldistribution which can severely degrade HX performance. Additionally, recent advancements in simulation software such as Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA) and optimization algorithms have led researchers to consider primary heat transfer surface optimization to achieve highly compact HXs which do not require fins. In this paper, an A-type HX which utilizes shape-optimized non-round tubes is optimized for minimum duct size and airside pressure drop. This is achieved through coupling of an experimentally validated finite volume HX model with automated 2D CFD simulations of airflow through the HX for airside thermal-hydraulic performance evaluation. Preliminary results show that the optimal designs deliver similar capacity while achieving 20% reductions in airside pressure drop and duct cross-section area. Additionally, the optimal design apex angles in this study were similar to those from previous A-Type HX optimization studies for conventional tube-fin HX geometries, suggesting that the apex angle for optimal A-Type configuration performance may be independent of tube geometry.

42 ENGINEERING↗
DOE OSTI2025

Experimental investigation on phase change material–based finned tube heat exchanger for thermal energy storage and building envelope thermal management

Phase change materials (PCMs) are attractive solutions for thermal energy storage (TES) applications by absorbing and releasing large amounts of latent heat during solid–liquid phase transitions. However, their relatively low thermal conductivity requires novel heat exchanger–based solutions to improve the power density and overall energy storage efficiency of the TES system. This work presents the design and experimental results of a finned tube heat exchanger to store collected natural thermal energy from a building envelope in a latent-based TES and to release it later for building heating/cooling applications. We experimentally evaluate the finned tube heat exchanger and evaluate the performance of TES in reducing building heating and cooling loads over 3–4 h of desired time of operation (e.g., peak load). The optimized design allows for maximum energy density by minimizing the heat exchanger volume, and the system is evaluated experimentally using commercially available heat exchanger materials and an organic PCM. Here, the experimental results reveal that the TES system is able to charge and discharge stored latent energy within 3–4 h, matching peak building electricity demand duration under an average fluid flow rate of 0.136 kg/s and temperature difference of 5.55 °C. Importantly, such optimized designs illuminate a path toward TES designs that are low-cost, scalable, and optimized for thermal energy and power availability under the desired time of operation.

25 ENERGY STORAGE↗
DOE OSTI2023

A hybrid method to evaluate the life cycle climate performance of heat pumps

Heat pumps have a significant impact on the climate, and numerous studies exist discussing the environmental impact of heat pumps quantitatively. Life Cycle Climate Performance (LCCP) is a widely accepted metric and can evaluate the carbon footprint of heat pumps from cradle to grave. LCCP calculation typically requires inputs like annual energy consumption, the material used, refrigerant type, and charge level, which are usually the intermediate or final results from heat pump simulation tools. Thus, a platform linking the heat pump simulation software, local weather conditions, and LCCP evaluation tool can simplify the heat pump design process, especially for complicated systems. This paper presents an LCCP evaluation tool accessing the outputs from the DOE Heat Pump Design Model and the building loads and temperature bin data from AHRI standard 210/240. As for case studies, this paper investigates the LCCP values and life cycle electricity costs (LCEC) of a given cooling-based heat pump with R410A in five typical US cities. In conclusion, this cooling-based heat pump has the highest LCCP value at Chicago and lowest LCCP value at Seattle. In contrast, the heat pump has the highest LCEC at Seattle and the lowest LCEC at Miami. As a future work, a more comprehensive carbon emission and cost analysis of heat pump systems will be conducted through all major cities around the world.

Shen, Bo↗
DOE OSTI2021

Options For Large-Scale Installation of Individual Heat Substations Based on International Best Practices

The purpose of this report is to provide recommendations for actions Ukraine could take to implement large-scale installation of IHSs as part of comprehensive district heating reform. The report discusses the importance of IHS in the district heating sector, then presents several case studies of approaches that European countries have taken to facilitate large-scale IHS installation in multi-apartment buildings. These case studies focus on the ownership and financing of IHS, as there are different models for how this can be done (the DH company can make the investments and recover the costs through the tariff, or building residents can make the investments themselves). They also include details on the approval process and technical specifications, as these can add additional barriers and time to the installation process.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2023

Heat Transfer of an Integrated Counterflow Ceramic Heat Exchanger

The ceramic-based heat exchanger is one of the leading contenders for high-efficiency concentrating solar power plants using a molten salt heat transfer fluid and a supercritical carbon dioxide Brayton power cycle operating at temperatures above 700 °C due to the excellent resistance of ceramics to corrosion, oxidation, erosion, creep, and fouling. In the present study, the thermal performance of a ceramic silicon carbide prototype heat exchanger, with semi-elliptical heat transfer channels, integrated header channels, and a counterflow configuration fabricated by using binder jetting additive manufacturing, was experimentally investigated. Experimental heat transfer tests of the prototype were conducted at high temperatures and under various test fluid flow rates and inlet temperatures. The experimental heat transfer rates compared favorably with simulation predictions.

Yu, Wenhua (ORCID:0000000219457014)↗
DOE OSTI2025

Impacts of irrigation expansion on moist-heat stress based on IRRMIP results

Irrigation rapidly expanded during the 20 th century, affecting climate via water, energy, and biogeochemical changes. Previous assessments of these effects predominantly relied on a single Earth System Model, and therefore suffered from structural model uncertainties. Here we quantify the impacts of historical irrigation expansion on climate by analysing simulation results from six Earth system models participating in the Irrigation Model Intercomparison Project (IRRMIP). Results show that irrigation expansion causes a rapid increase in irrigation water withdrawal, which leads to less frequent 2-meter air temperature heat extremes across heavily irrigated areas (≥4 times less likely). However, due to the irrigation-induced increase in air humidity, the cooling effect of irrigation expansion on moist-heat stress is less pronounced or even reversed, depending on the heat stress metric. In summary, this study indicates that irrigation deployment is not an efficient adaptation measure to escalating human heat stress under climate change, calling for carefully dealing with the increased exposure of local people to moist-heat stress.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Review of the potential and challenges of MOF-based adsorption heat pumps for sustainable cooling and heating in the buildings

Heat pumps are regarded as the most suitable means to meet the future demand of heating and cooling in the building, as they require small input of electrical energy and output high thermal energy. Vapor compression heat pump (VCHP) and transcritical-CO 2 heat pump are the two major heat pump technologies currently dominating the market. However, VCHP system suffers from its fugitive emission of hydrofluorocarbon (HFC) refrigerants, and transcritical-CO 2 system requires high operating pressure (typically 9–13 MPa). For low-to-medium temperature heating and cooling applications thermally driven adsorption heat pump (AHP) provides a better alternative to VCHP and transcritical-CO 2 system as AHP uses natural refrigerants and operates at a much lower pressure. But currently available AHP technology has the limitation of low coefficient of performance (COP). Advances in synthesizing metal-organic frameworks (MOF) with high gas adsorption capacity have created an opportunity to address the problem of low COP of current AHP technology. Here, this article reviews the progress made in the past decade in utilizing MOF and conventional adsorbents with different working fluids in AHP technology and compares their performance. The article also summarizes the key challenges for the MOF-based AHP technology and provides the authors’ perspective to address these challenges.

30 DIRECT ENERGY CONVERSION↗