Intermediate Heat Research Articles

Spinning Process of D406A Ultra-High Strength Steel

D406A steel is a medium-carbon low-alloy steel, which has excellent comprehensive mechanical properties. It is widely used in the production of missiles and rocket barrels. In this paper, the spinning forming limit test and the intermediate heat treatment process of ultra-high-strength steel were used to explore the effect of spinning process and heat treatment on the properties of spinning parts. The research results showed that the reduction amount of the material made the material thinning rate approach the limit thinning rate. The final blank wall thickness was reduced from 15 mm to 3.0 mm when the cracking occurred. It was calculated that the material's power spinning limit thinning rate was 80%. The ferrite matrix after spinning showed a streamline distribution characteristic perpendicular to the thinning direction, and the precipitated carbides were uniformly distributed on the surface of the matrix, which had the characteristics of deformation and extension along the streamline. After the heat treatment, the structure of the spinning parts changed continuously. When the structure was quenched and tempered, the martensitic structure can be obtained, and the tempered martensitic structure was smaller. Furthermore a test piece for ultra-high-strength steel spinning technology has been developed, and the solutions discussed for flanging defects in the actual spinning process, and test data for the actual production of ultra-high-strength steel spinning parts accumulated.

Isochoric moisture heating as a tool to control the functionality of soy protein

In this study, we investigated the effect of isochoric moisture heating on the functionalities of simply fractionated soy protein. Soy protein-rich fractions (SPFs) were produced through a simplified wet fractionation process, in which the defatting and intensive washing steps were omitted. After a neutralization step, the protein-rich dispersions were heated up to various temperatures ranging from 60 to 100 °C and subsequently freeze-dried. It was found that the denaturation level, the water holding capacity and the viscosity of SPFs increased as the processing temperature rose, whereas the solubility of SPFs decreased. Additionally, among the different conditions, an intermediate heating temperature of 70 °C resulted in SPFs having a gel network with the highest elasticity. Overall, isochoric moisture heating coupled to simplified fractionation can be used to precisely control the functionality of soy protein ingredients with mild heating conditions. This work provides insights on the production of ingredients with desired functionality for novel soy-based applications like soy meat analogues.

Calculation of the Efficiency of Regenerative Air Heat Exchanger with Intermediate Heat Carrier

The study deals with a new regenerative air heat exchanger with an intermediate heat carrier used in the systems of room ventilation. A physical and mathematical model of the heat transfer process is proposed. The influence of design and operating parameters on the temperature efficiency of the heat exchanger is analyzed. The possibility of a significant increase in its efficiency with a decrease in the packing diameter is shown. As a result of calculations, it was found that with a decrease in the filling height, the maximum temperature efficiency shifted towards a decrease in the air flow rate from its value determined from the equality of water equivalents of liquid and air.

Rankine-vortex model based assessment of CFD methods for simulating the effect of gas entrainment observed in the hot-pool of sodium coold fast breeder reactors

The flow behavior in the hot pool of a compact Sodium Cooled Fast Breeder Reactor (SFR) is investigated in the MICAS facility of the CEA. Computational Fluid Dynamics (CFD) is used to assist the interpretation of the experiments by multi-scale calculations. Special attention is given to the risk of gas entrainment into the reactor core due to the formation of drain-type vortexes at the intermediate heat exchanger intakes. After theoretical considerations based on the Rankine-vortex model, the single effect gas entrainment experiment of Monji is analyzed by different CFD methods. The well-known incapacity of linear RANS models to simulate swirling flow is emphasized and limitations regarding the representation of gas cores by single-phase models are discussed. Then, the flow in the MICAS facility is analyzed by CFD using RANS and LES. The quantitative comparison between experiment and calculation shows that RANS can simulate correctly the global flow patterns in the hot pool. Small-scale drain-type vortexes have not been observed in the RANS calculations. LES can predict the onset of the formation of drain-type vortexes. However, single-phase models cannot simulate stable drain-vortexes.

A numerical study of heat transfer enhancement by helically corrugated tubes in the intermediate heat exchanger of a very-high-temperature gas-cooled reactor

We numerically investigate heat transfer enhancement by helically corrugated tubes (HCTs) in the intermediate heat exchanger (IHX) of a very-high-temperature gas-cooled reactor (VHTR). A comparison with heat transfer in a smooth tube shows that HCTs have better heat transfer over the full IHX temperature range. The helical corrugations strengthen the intensity of the turbulence and create rotational flow, which better mixes the fluid and improves the synergy between the velocity field and the temperature gradient field. The effects of tube structural parameters and fluid physical properties on the Nusselt number (Nu), friction factor, and performance evaluation criterion (PEC) were also analyzed. The corrugations have optimal heights for the maximum Nu and PEC. Nu decreases as the corrugation pitch increases, whereas the PEC shows the opposite trend. The best heat transfer enhancement is 1.69 for e/d = 0.03 and p/d = 0.4, and the best overall performance is 1.13 for e/d = 0.01 and p/d = 0.8, both of which are in the high-temperature region.

Nuclear Hydrogen Production: Modeling and Preliminary Optimization of a Helical Tube Heat Exchanger

Hydrogen production is a topical issue in an energy scenario where decarbonization is a priority, especially with reference to the transport sector that has a great weight on global emissions. Starting from this consideration, GIF (Generation-IV International Forum) investigated the possibility to produce hydrogen by nuclear energy. The “classic” strategy is based on the use of nuclear as energy source for the electrolysis; but on the medium-long term, a more sustainable and smart approach could be founded on the use of thermochemical processes (e.g., I-S) that require a direct coupling of a chemical plant to a nuclear reactor. In order to develop this strategy, it is mandatory to design and optimize all the key components involved in this complex plant. In this study, we developed the 3D-CAD and CFD models of the intermediate heat exchanger (IHX) installed in the Japanese HTTR nuclear power plant. This component is extremely important for both the safety of the two plants and the stability of the whole hydrogen production plant. Initially, our model (developed by AutoCAD 3D and implemented in Star CCM+) was validated on the basis of experimental data available in literature; then, an initial optimization of the IHX testing innovative materials, such as Alloy 617 and ODS–MA754, and a different primary coolant (supercritical CO2) was performed.

Design and optimization of the secondary circuit for the WCLL BB option of the EU-DEMO power plant

EU-DEMO will be a DEMOnstration Fusion power plant designed to demonstrate production of grid electricity from fusion at the level of a few hundred MW. The Primary Heat Transfer System (PHTS) transfers heat from the breeding blanket (BB), divertor and vacuum vessel to the secondary Power Conversion System (PCS) responsible for conversion of thermal energy into electricity. Two main BB conceptions, and the relative PHTSs, for EU-DEMO are being developed: the Helium Cooled Pebble Bed (HCPB) BB and the Water Cooled Lithium Lead (WCLL) BB. Two options for each conception are considered: with or without the Intermediate Heat Transfer System (IHTS), containing the Energy Storage System (ESS), between the BB PHTS and PCS. The role of IHTS+ ESS is to ensure continuous smooth thermal energy transfer from the reactor sources to PCS despite the pulsed operation of the DEMO reactor. In the present work we discuss the mature concept of the PCS configuration for the option WCLL BB with the IHTS+ESS (based on the 2018 EU-DEMO reference), which allows almost constant production of electricity during both plasma pulse and dwell phases. The operating parameters of the circuit were optimized to minimize the temperature oscillations ΔT = |Tpulse - Tdwell| in all the circuit components, which occur due to the pulsation of the DEMO cold sources of Divertor and Vacuum Vessel whose HXs are integrated in PCS itself. Operation of the PCS circuit during the pulse and dwell phases was simulated using the GateCycle software, to show the system performance and to enable discussion on the feasibility of the concept.

Investigation of the Correlation between Initial Microstructure and Critical Current Density of Nb-46.5 wt%Ti Superconducting Material

We have investigated the effect of initial microstructures on the change in critical current density (Jc) of Nb-46.5 wt%Ti (NbTi) superconducting material. It is well known that α-Ti phases distributed in NbTi material act as a flux pinning center, resulting in an improvement in critical current density. Therefore, it is crucial to obtain the grain-refined microstructure, which is strongly related with precipitation of uniformly distributed fine α-Ti phases and higher volume faction of α-Ti phases, as α-Ti phases are precipitated at the grain boundaries and triple points during heat treatments. Therefore, in order to characterize the effect of initial microstructure of NbTi on critical current density, different initial microstructures were obtained by applying equal channel angular pressing (ECAP) and hot rolling with different strains. It was revealed experimentally that hot rolling with a higher strain is efficient for obtaining the initial microstructure, which has equiaxed fine grains of β-NbTi with the aid of dynamic recrystallization, and which is helpful for precipitating fine α-Ti phases during intermediate heat treatment. Furthermore, it was confirmed that critical current density can be enhanced by obtaining a smaller α-Ti phase, a higher aspect ratio of α-Ti phase, a higher volume fraction of α-Ti phase and a ribbon-like folded α-Ti phase.

Simulation of a CubeSat with internal heat transfer using Finite Volume Method

Estimating temperature is essential both to design reliable CubeSats and to keep it under maximum operating efficiency. This paper presents the transient thermal simulation of a CubeSat 1U, where the heat transfer by conduction and radiation (external and internal) are solved considering a typical CubeSat mission launched from the International Space Station. The objective is to obtain the temperature field based on the Finite Volume Method (FVM), with inner heat transfer by radiation. The Gebhart method computes the internal heat exchange through successive reflections, and an obstruction model supports the calculation of view factors. Three boundary conditions for the inner side of the CubeSat are tested: without internal heat transfer by radiation, or zero emissivity (ϵ=0.0), with intermediate internal heat transfer by radiation (ϵ=0.5), and maximum internal heat transfer by radiation (ϵ=1.0). The results show a significant impact of the internal heat transfer by radiation in the temperature field of both inner and outer parts of the satellite, and therefore it should not be ignored. Good agreement of transient temperature is found between the FVM and another more straightforward formulation based on the Lumped Method, although the three-dimensional effects are significant and cannot be obtained with such a simplified model.

Conceptual design overview of the ITER WCLL Water Cooling System and supporting thermal-hydraulic analysis

In this paper, the conceptual design of the International Thermonuclear Experimental Reactor (ITER) Water-Cooled Lithium-Lead (WCLL) Test Blanket Module (TBM) Water Cooling System (WCS) from Europe is presented. The system consists of two loops in series. This design feature allows the removal of heat from the TBM box avoiding at the same time the release of radionuclides into the ITER Component Cooling Water System (CCWS), that acts as WCLL Test Blanket System heat sink. For this purpose, the WCS primary loop deals with the direct heat removal from the ITER TBM and the secondary one implements physical separation between the contaminated primary loop coolant and the CCWS. The insertion of an economizer into the primary loop determines the characteristic “eight” shape of the circuit. This choice was done in order to reduce the temperature difference on the intermediate heat exchanger. Hairpin type and steam bubble are the technologies selected for heat exchangers and pressurizers, respectively. Pressure and temperature control systems are foreseen to limit excursions from rated values in normal operational states and abnormal transients.A computational activity was promoted to assess the WCLL-WCS conceptual design, using a modified version of the RELAP5 Mod3.3 system code. A detailed thermal-hydraulic model was developed on the basis of design outcomes. The nodalization scheme includes the TBM, the WCS, a portion of the CCWS and the lithium-lead circuit. The computational campaign involved both the normal operational state and selected abnormal transients. In all the scenarios simulated, the conceptual design has highlighted the capability of operating the system respecting all the thermal-hydraulic requirements. The abnormal transient selected and presented is the loss of flow in the CCWS (loss of heat sink). In these conditions, TBM cooling function has been verified, keeping standard control strategies without any external action.

Features of annealing of alloy steels with mixed structure

It is necessary to obtain initial rolled product with a structure which has high ductility and low hardness for further mechanical processing of alloyed rolled metal products into the ready product. In this case the enterprises carry out a special softening heat treatment to increase the ductility of the metal. The treatment represents the annealing at subcritical temperatures (А1 — 25…40 °С) with long holding. During annealing the structural transformations are running and the formed structure has a granular morphology. To obtain spheroidizing in the steels with a mixed structure (contains at the same time pearlite, bainite or martensite) usually requires a lot of time and energy, because the structural transformations during heat treatment are running with different intensities in different phases. Established by study, that in the steels with a mixed structure during annealing the structural transformations begin from the thermodynamically less stable structures. So, to reduce the mode of the softening heat treatment (annealing) of the investigated steels it is rationally to change the cooling conditions after rolling and to provide the increased quantity of bainite and martensite. For medium-carbon steels alloyed by chromium, molybdenum and vanadium and also for low-carbon steel alloyed by manganese and silicon, an increase of the cooling rate after hot rolling by ~1.5 times allows to obtain more sensitive structure to annealing. So, the structure consists at least 80 % of the bainite, ~15 % of the ferrite and 5 % of the pearlite for chromium-molybdenum steel. The base of the structure contains bainite (~90 %), martensite (~5 %) and ferrite (up to 5 %) for chromium-molybdenum-vanadium steel. For low-carbon silicon-manganese steel an increase of the cooling rate leads to the formation of the structure which contains at least 35 % of the bainite-martensite, ~60 % of the ferrite and 5 % of the pearlite. The structural transformations proceed at the low temperatures and require a shorter duration of the holding in the obtained structures during further annealing. Receiving such structure after rolling, allows to speed up intermediate softening heat treatment, thereby reducing energy costs, and provides high ductility of steel before mechanical processing.

Cold and heat tolerances of hybrids for restoration of the endangered Juglans cinerea L

• Key message Hybrids had overall intermediate cold and heat tolerances compared to their progenitors, Juglans cinerea and Juglans ailantifolia . Differences in hybrids were small compared to J. cinerea though, indicating that when considering extreme temperature tolerances, hybrids might be usesd in some restoration circumstances. However, hybrids might exceed their cold tolerance in especially cold areas, such as J. cinerea’s northern range limits. • Context Hybridization could incorporate traits for surviving detrimental global changes. Juglans cinerea, an endangered North American tree species, can hybridize with non-native Juglans ailantifolia Carr. Evidence indicates their hybrids could hold resistance to the fungal disease threatening J. cinerea. Consequently, the hybrids are being evaluated for restoration use, but to be effective, they must survive in J. cinerea’s distribution. An ecophysiological evaluation could contribute to predicting potential hybrid utilization areas. • Aims To provide a relative comparison of the cold and heat tolerances among J. cinerea provenances and between J. cinerea, J. ailantifolia, and their hybrids. • Methods In the cold test, twigs were subjected to five freeze treatments and resulting damage was estimated using electrolyte leakage. In the heat test, leaflets were subjected to six hot water bath treatments and damage was estimated using chlorophyll fluorescence. • Results Within J. cinerea, trees from colder areas exhibited less cold damage than those from warmer areas. Differences in heat damage did not occur among hardiness zones. Juglans cinerea exhibited greatest cold tolerance, J. ailantifolia exhibited greatest heat tolerance, and hybrids were intermediate. • Conclusion Differences in the cold and heat tolerances of J. cinerea and its hybrids were overall minimal, although greater in cold tolerance.

Optimization of heat transfer processes in the circuit of a nuclear power plant in order to increase it

The urgency of the work is due to the depletion of traditional fuel reserves and increasing the load on the biosphere because of emissions from burning coal, oil and gas. The solution of these problems are the development of nuclear energy. The advantages of nuclear energy are analyzed, namely: high calorific value of nuclear fuel, better economic indicators, less environmental pollution. The purpose of this work is to optimize the heat transfer processes in the secondary circuit of a nuclear power plant. It is proposed to take the second circuit of the third power unit of the Rivne nuclear power plant as the object of research. The need for knowledge of heat transfer processes and hydrodynamics is determined by the fact that nuclear reactors are energy-intensive thermal machines, in which these processes are manifested in a rather complex form. Therefore, measures to optimize heat transfer processes in the thermal circuit of the second circuit of the NPP in order to increase energy performance are considered. In order to remove from the system the hardness salts that settle on the walls of the equipment and impair the heat transfer processes, a reagent has been selected to bind the hardness salts. he addition of the PuroTech113 reagent to the working circuit of the secondary circuit made it possible to free the system from the deposition of hardness salts in it, as this reagent "binds" free calcium and magnesium ions. In turn, scale is no longer deposited on the walls of the heat exchange equipment, which allows to fully transferring the required amount of heat. Recalculation of the thermal balance showed that the efficiency of the unit is increased by 3%.The efficiency coefficient of the heat exchanger was chosen as the criterion of optimality. The efficiency of the heat exchanger in the general case is a function of the mode parameters, the scheme of mutual movement of heat carriers and features of hydrodynamics and heat transfer of real heat exchangers. The problem of optimizing the movement of heat carriers in intermediate heat exchangers is solved in paper.

RAMI analyses for the primary heat transfer systems of breeding blankets and the related balance of plant of DEMO reactor

Two models are currently taken as reference for the breeding blanket (BB) of DEMO, the Helium Cooled Pebble Bed (HCPB) and the Water Cooled Lithium Lead (WCLL). For both the models two Balance of Plant (BOP) configurations are currently investigated. They are all based on four independent primary heat transfer systems (PHTSs). The largest PHTS is devoted to remove the BB thermal power, two PHTSs for the divertor (DIV) and one for the vacuum vessel (VV) heat removals. Both DIV loops and VV loop transfer their thermal power directly to the power conversion system (PCS). The two BOP configurations are investigated to cope with the pulsed operation of the reactor. The first configuration consists of an “indirect coupling” of the BB PHTS to the PCS by an Intermediate Heat Transfer System placed in between them. The second configuration consists in a “direct-coupling” of the BB PHTS to the PCS.Reliability, availability, maintainability and inspectability (RAMI) analyses for the four PHTS and PCS configurations are presented in this paper. The Failure Mode, Effect Analysis (FMEA) and the Reliability Block Diagram (RBD) methodologies have been used to perform the studies. As main result can be highlighted that even the low reliability of the systems to operate without failure and the large number of requests of corrective maintenance, all the systems are in compliance with an operational availability target of 30 %.

Cascaded Multicore Vapor Chambers for Intrapackage Spreading of High-Power, Heterogeneous Heat Loads

A cascaded multicore vapor chamber (CMVC) is designed for dissipating heat from high-flux hotspots simultaneously with a high-total-power background. Current thermal management strategies rely on spreading high local heat fluxes by conduction in the lid of electronics packages. Embedding vapor chambers (VCs) within the lid is an attractive option to directly address intrapackage hotspots. We investigate the design of intralid VCs, for a generic device having a total heat load of 476 W having a background heat flux of 0.75 W/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with hotspots of 8 W/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> over a 1-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area. A conventional VC design, having a single vapor core, will require a thick evaporator wick to avoid the capillary limit for large total power. The necessity for a thick wick then imposes a large thermal conduction resistance when the VC is exposed to high heat flux hotspots. The proposed CMVC architecture aims to address this limitation. The cascaded architecture comprises a bottom-tier VC having an array of multiple small vapor cores for spreading heat from the small hotspots. These small vapor cores have short paths of liquid return to the evaporator, such that they can handle their footprint heat load while using thin wicks, resulting in a low hotspot thermal resistance. Furthermore, local dampening of the hotspots by the bottom tier then reduces the thermal conduction resistance across the necessarily thick wick in the top tier. Hence, the cascaded architecture has the potential to significantly reduce the overall thermal resistance, relative to a single tier. To substantiate this design rationale, experiments are performed to illustrate that the resistance of a commercial VC can be significantly reduced by interfacing the heat source with an intermediate heat spreader. Reduced-order models are then used to understand the effect of the wick properties (porosity and particle size) and geometric parameters on the thermal performance of the CMVC for the representative power map. The optimal CMVC design offers a thermal resistance (0.66 K/W) that is significantly lower compared to a conventional single-core VC (1.76 K/W) owing to a reduction in the conduction resistances across the internal wicks. That parametric optimization results demonstrate that the thermal resistance of the CMVC is more sensitive to the wick porosity compared to the particle diameter. Furthermore, there exists a wide range of wick properties and vapor core sizes for which near-optimum thermal performance can be attained, which is particularly attractive from the standpoint of flexibility in design and manufacturing.

Enhanced process for energy efficient extraction of 1,3-butadiene from a crude C4 cut

1,3-butadiene is an essential platform chemical for producing rubberlike polymers, which is extracted from C4 hydrocarbons that are produced through steam cracking. The current state-of-the-art technology is the BASF process that uses thermally coupled extractive distillation (ED) followed by two distillation columns. However, the process requires high temperature heat input, thus high cost hot utility and reduces the possibility for process heat integration.To solve these issues, this study proposes novel enhancements: the ED part is modified with intermediate heating and the classic columns are replaced with a heat pump assisted dividing wall column (DWC). Rigorous simulations were carried out in Aspen Plus for a typical ED process. The intermediate reboiler system is designed to maximize the possible process heat recovery. The results show that the heat pump assisted DWC is able to reduce the energy intensity of the classic distillation section of the BASF process by 54.8% and reduces the total annual costs by 29.9%. Additionally, the intermediate reboiler reduces the energy intensity of the ED section by 8.3% while also reducing the CAPEX of the system due to the need for a smaller recycle compressor. In combination, these modifications are able to achieve up to a 21% reduction in the energy intensity of the overall process, with a payback time of 1 year.

Thermal-hydraulic performance of a PCHE with sodium and sCO2 as working fluids

The Printed Circuit Heat Exchanger (PCHE) is one of the most attractive options for heat exchanger in compact facilities due to the high area concentration and superior heat transfer efficiency. A PCHE with sodium and supercritical carbon dioxide (sCO2) as working media is used as the intermediate heat exchangers in sodium-cooled fast reactor to reduce facility size and mitigate the consequences of sodium-water reaction by replacing steam with sCO2. The thermal-hydraulic performance of PCHE was analyzed by CFD with SST k-ω and Abid low Reynolds k-ε turbulence models for sCO2 and sodium domains, respectively. Besides, a segregated coupling strategy for the conjugate heat transfer was proposed based on the CORBA interface. The overall and localized heat transfer coefficient and friction factor were obtained and compared with empirical correlations. The mass flux and inlet temperature have significant impacts on the local thermal and hydraulic characteristics.

Estimation of heat transfer coefficient for intermediate fluid stream in triple concentric tube heat exchanger

The design of triple concentric tube heat exchanger (TCTHE) requires heat transfer coefficient (HTC) values for all three fluid streams as input parameters. The fluid through intermediate tube transfers heat to other fluids simultaneously. The present study applies a concept of thermal resistance network and quadratic equation is developed for computing HTC of intermediate fluid for TCTHE under adiabatic condition. ‘Oil ISO VG 22’ is taken as intermediate fluid and is cooled by using water as inner and outer cooling fluid in the present work. The HTCs of inner and outer cooling fluids are calculated from the well-established empirical correlations available in the literature. CAD modelling is done using Catia V5 and simulation is carried out using STAR CCM+ CFD software. The results of the method are compared with those obtained from mathematical models in the literature as well as results from CFD analysis are validated.

Calculation of electric energy savings and simulation of tank operation with variable extraction of steam and liquid phases of propane-butane mixtures

Currently, when consumers use various categories of propane-butane mixtures of liquefied petroleum gas as the main or backup energy carrier, natural and artificial regasification systems based on electric or direct fire evaporators with intermediate heat transfer agent or solid-state intermediate heat transfer agent of various evaporation capacity, which operate depending on the design in various evaporation modes, are widely used. An important element for reducing energy consumption in the artificial liquefied petroleum gas regasification systems is the switching of tank to the combined regasification mode. The combined cycle provides two main periods of tank operation: the initial period with natural regasification of liquefied gas in the day tank, ground tube evaporator, and the subsequent period with artificial regasification of the propane-butane mixture in the evaporator with an intermediate heat transfer agent. For the purpose of theoretical justification of the proposed cycle, a mathematical model of combined regasification of liquefied petroleum gases was developed, which comprehensively takes into account the main periods of tank operation: with natural regasification mode in the day tank, ground heat exchanger and artificial regasification mode in the evaporator. The results of the conducted research show that the implementation of the combined regasification cycle in the liquefied gas supply can significantly reduce the energy costs of its evaporation, increases the energy efficiency of liquefied petroleum gas supply systems and provides an average annual savings of 33.7% in electric energy for regasification.

A Review on Thermal Design of Liquid Droplet Radiator System

Liquid Droplet Radiator (LDR) system is regarded as a quite promising waste heat rejection system for aerospace engineering. A comprehensive review on the state-of-the-art of LDR system was carried out. The thermal design considerations of crucial components such as working fluid, droplet generator and collector, intermediate heat exchanger, circulating pump and return pipe were reviewed. The state-of-the-art of existing mathematical models of radiation and evaporation characteristics of droplet layer from literatures were summarized. Furthermore, thermal designs of three LDR systems were completed. The weight and required planform area between the rectangular and triangular LDR systems were respectively compared and the evaporation models for calculating the mass loss were evaluated. Based on the review, some prospective studies of LDR system were put forward in this paper.