Heat Recovery Performance Research Articles

Coupling effect of key parameters of heat recovery components on the HAT cycle performance

Humid Air Turbine (HAT) cycle that uses a water-air mixture as a working fluid has a significant advantage in the distributed generation technologies and combined heat and power. The feature of the HAT cycle is that air humidification is carried out at a variable temperature. This cycle is considered as one of the optimal humidified gas turbine cycles to achieve the energy cascade utilization. However, most studies typically use the method of a single variable to investigate the coupled process of humidification and heat recovery, which limits the further performance improvement of the HAT cycle. Herein, we study the interactions among air humidification, heat recovery and system performance to elaborate the effects of interactive variables on the HAT cycle performance. Considering the complexity of the interaction of water-air ratio, aftercooler effectiveness and recuperator effectiveness, a thorough numerical analysis was carried out from the following perspectives: the thermodynamic correlation between components and systems was investigated by controlling a single parameter; the interaction of multiple variables was performed with identical turbine inlet temperature (TIT) and pressure ratio (PR) conditions; and the coupling relationship between interactive variables with a variation of TIT and PR conditions. A thorough analysis revealed that the variables that significantly impact the HAT cycle efficiency are successively RE, W/A, and AE. The analysis of the coupling effects of interactive variables under different TITs is consistent with the above results. As the PR increases, the W/A and AE have a more significant effect on HAT cycle efficiency and the effect of RE on the HAT cycle efficiency greatly diminishes. The HAT cycle efficiency, specific work output, and heat recovery achieved 43.9%, 556 kJ/kg, 5505.33 kW, where its corresponding TIT, PR, W/A, AE, RE values are 1280 °C, 8, 1.5,0.75, 0.9, respectively. Overall, a thorough analysis of interactive variables is of great significance to fully understand the effect of heat recovery on the efficiency enhancement and specific work output improvement from the thermodynamic perspective.

Numerical evaluation of the effects of asymmetric membrane heat conductivity and moisture adsorption hysteresis on the performance of air-to-air membrane enthalpy exchanger

Effects of tangential heat conduction and moisture adsorption hysteresis of the membrane on the heat recovery performance of cross-flow and counter-flow membrane enthalpy exchangers are investigated numerically. The accuracy of the numerical simulation model is evaluated by predicting an experimental case and a reasonable accuracy is achieved. It is found that the temperature profile at the membrane surface is significantly influenced by the tangential heat conduction in the membrane. The variation of temperature profile at the membrane surface results in variations of the convective heat resistance and the sensible heat effectiveness. Simulation results demonstrate that the sensible heat effectiveness firstly increases and then decreases with the increasing membrane heat conductivity. The optimal membrane heat conductivity is about 0.1 ∼ 1 W m−1 K−1. Two types of the moisture adsorption hysteresis are assumed and expressed by simple expressions. It is found that the moisture adsorption hysteresis decreases the moisture diffusion flux across the membrane and accordingly decreases the latent heat effectiveness obviously for both counter-flow and cross-flow patterns. Current results indicate that membranes with large heat conductivity are not beneficial for sensible heat recovery and membranes with small adsorption hysteresis are beneficial for latent heat recovery.

Experimental and numerical analysis on heat and moisture recovery performance of enthalpy wheel with condensation

The enthalpy wheel has been extensively used in industrial systems for waste heat recovery. Compared with the application in air conditioning systems, the enthalpy wheel in industrial systems works under the conditions with high temperature and high humidity. Condensation inside the enthalpy wheel is common, especially in cold climates, but there is a lack of research on the enthalpy wheel performance under such working conditions. In this paper, experiments of the enthalpy wheel are conducted and the condensation phenomenon is observed. Experimental results show that the condensation ratio can exceed 20%, resulting in a worse moisture recovery performance. Whereas the total heat recovery performance is independent of condensation ratio, and heat recovery efficiency can reach 82%. A mathematical model of the enthalpy wheel is built to simulate the heat and mass transfer process and to describe the parameter distribution. The condensation location inside the enthalpy wheel is predicted. The condensation ratio is strongly related to the inlet air parameters. The rotation speed is a key factor influencing the heat recovery efficiency and the moisture recovery efficiency but has a slight effect on the condensation ratio. This research is expected to be useful for enthalpy wheel applications in industrial systems.

Secretory Expression of an Alkaline Alginate Lyase With Heat Recovery Property in Yarrowia lipolytica

Alginate lyase possesses wide application prospects for the degradation of brown algae and preparation of alginate oligosaccharides, and its degradation products display a variety of biological activities. Although many enzymes of this type have been reported, alginate lyases with unique properties are still relatively rare. In the present work, an alginate lyase abbreviated as Alyw203 has been cloned from Vibrio sp. W2 and expressed in food-grade Yarrowia lipolytica. The Alyw203 gene consists of an open reading frame (ORF) of 1,566 bp containing 521 amino acids, of which the first 17 amino acids are considered signal peptides, corresponding to secretory features. The peak activity of the current enzyme appears at 45°C with a molecular weight of approximately 57.0 kDa. Interestingly, Alyw203 exhibits unique heat recovery performance, returning above 90% of its initial activity in the subsequent incubation for 20 min at 10°C, which is conducive to the recovery of current enzymes at low-temperature conditions. Meanwhile, the highest activity is obtained under alkaline conditions of pH 10.0, showing outstanding pH stability. Additionally, as an alginate lyase independent of NaCl and resistant to metal ions, Alyw203 is highly active in various ionic environments. Moreover, the hydrolyzates of present enzymes are mainly concentrated in the oligosaccharides of DP1–DP2, displaying perfect product specificity. The alkali suitability, heat recovery performance, and high oligosaccharide yield of Alyw203 make it a potential candidate for industrial production of the monosaccharide and disaccharide.

Energy performance analysis and optimization of a coupled adsorption and absorption cascade refrigeration system

An energy cascade utilization system is an advanced technology that recoveries waste heat energy efficiently. However, research on cascade systems by utilizing waste hot water with 60–100 °C is still considerably lacking in the literature. Specifically, this paper investigates the waste heat recovery performance of a multistage coupled absorption chiller (ABC)-adsorption chiller (ADC) cascade system. The proposed ABC-ADC cascade system is capable of producing potable water and three streams of chilled water under different temperature settings. Firstly, the experimental analysis is judiciously carried out on a four-bed two-evaporator ADC subsystem prototype. Key results reveal that the ADC’s maximum specific daily water production is 10.5 m3/day/ton. Subsequently, the ABC-ADC cascade system’s performance is experimentally analysed and optimized. The achievable maximum cooling coefficient of performance (COPc) is obtained to be 0.55. Additionally, a general method is proposed to optimize the subsystem’s cooling capacity combination of the ABC-ADC cascade system in search of an optimal COPc. The results indicate that the optimized COPc can further be enhanced by around 20%. The performance efficiency of an optimized ABC-ADC cascade system incorporating a microturbine system is then investigated. Compared to the experimental ABC-ADC cascade system, the optimized system’ total coefficient of performance is demonstrated to improve by 18%. The primary energy saving ratio is also promoted from 9.8% to 18%. Moreover, 68.92% of the gas turbine’s dissipated energy is able to be recovered by the optimized ABC-ADC system. As far as application is concerned, this cascade system has been demonstrated to be superior to standalone heat-driven chillers with great commercial potential for implementation in industries where low-grade waste heat is readily available.

Three-zone numerical modeling method for predicting system-level waste heat recovery performance of thermoelectric generator with various electrical array configurations

In this study, an experimentally validated numerical model is formulated to accurately predict the energy harvesting performance of a thermoelectric generator (TEG) by reflecting the underlying physics of the thermoelectric energy conversion phenomena. The most advantageous feature of the modeling method employed herein is its high reliability because the system-level performance is predicted based on module-level power generation characteristics. A further benefit that the proposed physics-based model affords is that the effect of electrical array configurations (i.e., the particular manner by which the thermoelectric modules (TEMs) are electrically connected) on the waste heat recovery performance of the TEG can be accurately predicted. For this purpose, a three-zone modeling method, wherein each TEM is modeled into heat sink, heat generation, and heat conduction zones, is proposed. Moreover, user-defined functions are embedded into the numerical model to correlate the temperature fields obtained from the transport of momentum and energy with the Seebeck effect and Joule heating that appear as the thermoelectric output power and heat sink/heat generation near the TEM surface. The accuracy and reliability of the numerical model are validated by the experimental results of temperature and output power using a TEG prototype whose configurations and dimensions are identical to those of the proposed numerical model. Further comparisons between the numerical results obtained using eight different electrical array configurations and the corresponding experimental results ensure the robustness of the modeling method and numerical model formulated in this study. Finally, two correlations are derived as a function of the number of electrical array branches to predict the output voltage and current of a TEG whose branches consist of an identical number of TEMs for minimizing unexpected power losses.

Performance analysis of ceramic membrane tube modules for water and heat recovery in coal-fired power plants

Ceramic membrane separation technology is a promising method for water and heat recovery from exhaust flue gas in thermal power plants. Matching among function, load and structure of membrane modules is critical to design and operation of such recovery processes. In this paper, an analytical model based on membrane separation mechanism is proposed to evaluate the water and heat recovery performance in a ceramic membrane module. A series of calculation considering both structural parameters and load conditions in a power plant is conducted. Results show that under the conditions of different flue gas temperature and water vapor volume fraction, the membrane module has three working modes corresponding to different condensation processes. For flue gas with high temperature and low humidity, the temperature rise of cooling water can reach up to 40 °C when the mass flow rate ratio of cooling water to flue gas is less than 50%. For flue gas with low temperature and high humidity, low cooling water temperature could promote water recovery process. Keeping the mass flow rate ratio higher than 200% can maintain the water recovery rate not less than 60%. The optimal water and heat recovery rate is obtained by optimizing the size and structure of the membrane module within limited volume. This study provides a basis for structure optimization and operation regulation of ceramic membrane modules for water and heat recovery purpose.

Experimental and numerical studies on novel airfoil fins heat exchanger in flue gas heat recovery system

• The novel airfoil fins heat exchanger was studied experimentally and numerically. • The novel airfoil fins channel has the best thermal–hydraulic performance. • The enhancement mechanism could be explained with field synergy principle. • Thermal-hydraulic correlations of novel airfoil heat exchanger were proposed. To improve the performance of waste heat recovery, a novel airfoil fins heat exchanger was applied to flue gas waste heat recovery. Two groups of experimental conditions were installed to test the heat effectiveness of the novel airfoil fins heat exchanger. The results showed that the heat effectiveness of the novel airfoil fins heat exchanger could reach more than 96%, which is higher than the conventional heat exchanger. The thermal–hydraulic performances of the novel airfoil channel, NACA 0020 airfoil channel and zigzag channel were investigated with the first and second laws of thermodynamics, which showed that the novel airfoil channel has the best comprehensive thermal–hydraulic performance among the three channels. The correlations of Nusselt number and friction factor of the novel airfoil fins heat exchanger were proposed for flue gas, whose maximum deviations were within ±5.0% and ±7.1%, respectively. The present work could provide guidance for the application of the novel airfoil fins heat exchanger in waste heat recovery.

Improving heat transfer and water recovery performance in high‐moisture flue gas condensation using silicon carbide membranes

Desulfurated flue gas in coal-fired power plants contains profuse water vapor and latent heat, the recovery of which is crucial. Herein, a novel use of silicon carbide (SiC) membranes to construct a transport membrane condenser (TMC) for simultaneous water and waste heat recovery from high-moisture flue gas is reported. The performances of water and heat recovery were systematically compared between typical dense heat exchange materials (304 stainless steel and perfluoroalkoxy [PFA]) and porous ceramic membranes (Al2O3 membrane and SiC membrane). Porous ceramic membranes showed higher heat transfer performance than dense materials, suggesting a non-negligible mass transfer effect on heat transfer. Compared with the Al2O3 membrane, the SiC membrane exhibited better water and heat recovery performance because of its superior thermal conductivity. Using the SiC membrane as the heat exchange material, a water flux of 11.3-44.4 kg·m−2·h−1 and a water recovery efficiency of 46.5%-76.9% were achieved. The thermal resistance from the gas boundary layer dominated the heat transfer process in SiC membrane condensers as the thermal resistances from the membrane and condensate film were markedly reduced. This study forms a basis for future investigations on heat transfer enhancement of membrane condensers used for industrial moisture recovery.

Experimental investigation on heat recovery from flue gas using falling film method

The discharge of the flue gas is rich in water vapor and its latent heat, which leads to the main heat and moisture loss for the natural gas. In this article, based on the falling film spray technology, a new test rig was set up to test the heat and moisture recovery performance from flue gas. The effects of water–air ratio and inlet air temperature on the heat transfer effectiveness were examined in a systematic manner. Four case studies, i.e. empty tower, conical baffles staggered arranged in the tower, falling film plates and baffle plates fixed on the falling film plate were designed for the current system. Experimental results showed that: (i) increasing the water–air ratio or decreasing the inlet air temperature can improve the heat transfer effectiveness; (ii) the case with conical baffles shows the highest heat transfer effectiveness. In comparison with the falling film plates, the arranged baffle plates on the falling film plate can further improve the heat transfer effectiveness; (iii) for the cases with falling plates, the heat transfer effectiveness increases with the increase of the number of the falling film plates. The maximum heat transfer effectiveness is obtained at 5 falling film plates; (iv) for the case with conical baffles, increasing the floor of the conical baffles can improve the heat transfer effectiveness. In the range of the present work, the larger central angle of the spiracle is beneficial to increase the heat transfer effectiveness. For the optimal case in the range of the present work, the heat transfer effectiveness is 41.0% higher than that for the empty tower.

Continuous automated ventilation heat recovery efficiency performance assessment using building monitoring system

The performance of ventilation heat recovery has high impact to the total energy consumption of modern buildings and its sub-optimal performance results in a remarkable energy penalty. There are several issues, which can significantly affect the heat recovery efficiency such as the inaccuracy of sensors, errors in control systems, mechanical defects and incorrect setting of the system. In addition, the direct comparison of the designed and measured heat recovery efficiency is not necessarily meaningful due to varying boundary conditions e.g. mass flow rates. The main focus of this paper is to develop and demonstrate a simple automated method for monitoring the heat recovery efficiency of ventilation units using building monitoring system (BMS). As the supply and extract air mass flows and temperatures may differ from the calculated initial design parameters, the proposed solution is to analyse the heat recovery efficiency using the number of transfer unit (NTU) method. With this method the efficiency is always calculated by the limiting mass flow, meaning that the warm exhaust air can not transfer more energy to the cold supply air than it is able to contain. As a result, the NTU method gives us the possibility to continuously compare the result to the temperature efficiency declared by the producer of the unit. The developed method demonstrated that the application of NTU method enables identifying sub-optimal performance of ventilation heat recovery, which would not have been revealed by direct comparison of temperature efficiencies. In some cases, low measured temperature efficiency was associated with problems not connected to the heat recovery heat exchanger. The method also enabled to estimate the additional heating costs due to the decreased heat recovery efficiency.

Macroporous ceramic membrane condenser for water and heat recovery from flue gas

In this work, we experimentally study a macroporous ceramic membrane condenser (MCMC) with an average pore size of 3 µm for water and heat recovery from flue gas. Firstly, the heat and mass transfer mechanisms of MCMC are analyzed. The membrane surface is only wetted and no condensate accumulation, suggesting that the condensation rate is the key factor affecting the water recovery performance. Moreover, the thermal resistance in MCMC is concentrated at gas side, and the conductive resistance of the membrane occupies only about 1% of total resistance. The results also show that the experimental Sherwood numbers are larger than the correlated Sherwood numbers obtained by heat and mass transfer analogy. It may be caused by the hydrophilic properties of the membrane surface. Finally, the effects of operating conditions on water and heat recovery performance are investigated. The CMCM shows excellent performance in recovering water and heat, and the gas flow rate and gas/cooling water temperature have significant effect on recovered water/heat flux. In the future, we will further explore the coupled heat and mass transfer process and clear up the cause of the mass transfer enhancement.

Experimental investigation of optimal location of flow straightener from the aspects of power output and pressure drop characteristics of a thermoelectric generator

This study addresses the combined effects of the location and porosity of a flow straightener on the waste heat recovery performance of a thermoelectric generator (TEG). An exhaust gas channel was built for the flexible placement of a flow straightener with varying porosity in the range of 0.121–0.516 at five different locations. Customized thermoelectric modules were placed between the exhaust gas channel and two coolant channels for waste heat recovery. A diesel engine releases the exhaust gas flow into the exhaust gas channel of the TEG placed in the middle of the tail pipe. Experimental results showed that a TEG design in which a flow straightener is positioned near the inlet of the TEG needs to be avoided because of a low power output to pressure loss ratio. The net power output, energy conversion efficiency, and pressure drop characteristics were enhanced as the location of flow straightener moved rearward of the TEG. A friction factor correlation was also proposed for predicting pressure drop characteristics of TEGs equipped with a flow straightener to improve their practicality in industry and engineering fields.

Modeling and optimization of hydrophobic surfaces for a two-phase closed thermosyphon

Promoting dropwise condensation on condensers has the potential to significantly improve cooling and heat recovery performance of two-phase closed thermosyphons (TPCTs). If it is well designed, the dropwise condensation can provide an order of magnitude higher heat transfer coefficient than filmwise condensation of conventional metal condensers. The thermal design of an ideal dropwise condensing surface is so important in the rationale for the advantage of dropwise condensation in the TPCTs. However, the effect of the hydrophobic promoter thickness on the thermal characteristics of the TPCT and its optimal value are still unclear. Here, we develop a unified model framework for the TPCT with the dropwise condenser and investigate how much the dropwise condensation can improve the thermal performance of the TPCT. As the hydrophobic promoter for the TPCT, we proposed a nanoscopically smooth Teflon-based hydrophobic coating on theoretical insights, experimentally evaluated its condensation heat transfer, and then developed its dropwise model with high accuracy by combining a recent dropwise model with the optimized parameters. Subsequently, the developed model was unified with the TPCT model to investigate the thermal characteristics of the TPCT system and the effect of the promoter thickness. The model results show that the Teflon-coated condenser with a thin thickness (≤ 10 nm) can significantly reduce the overall thermal resistance of the TPCT by up to 4.5 times compared to filmwise condensation. However, an increase in film thickness limited the performance enhancement of the TPCT due to the dominant thermal resistance through the film. By considering both the durability and the thermal resistance of the TPCT, we suggested the optimal Teflon film thickness as approximately 60 nm. This work provides physical insights and guidelines to obtain ideal TPCTs combined with dropwise condensers.

State-space model for transient behavior of transport membrane condenser

In this paper, a state-space model of a transport membrane condenser (TMC) based on a lumped heat and mass transfer model is developed and verified experimentally. The simulated results are in well agreement with the experimental data. Based on the state-space model, the transient relationships between the input parameters (inlet flue gas temperature and humidity ratio, inlet water temperature, flue gas and water flow rates), output parameters (outlet flue gas temperature and humidity ratio, outlet water temperature) and performance parameters (heat and water recovery fluxes, recovery efficiency) of the TMC are obtained and analyzed. It can be found that the perturbation of the flue gas flow rate has a larger effect on the heat and water recovery performances compared to that of the inlet flue gas humidity ratio. The performance parameters change by less than 1% with the inlet flue gas temperature step increasing from 50°C to 53°C. The inlet water parameters have significant effects on the performances. With the inlet water temperature step increasing from 15°C to 16°C, there is a hysteresis time in the response of the outlet water temperature. The comparative analysis based on the state-space model with a simply and rapid solution process can be used to determine the major input variables affecting the performances. The results are useful for the dynamic control of the TMC to obtain required stable performances.

CO2 capture cost saving through waste heat recovery using transport membrane condenser in different solvent-based carbon capture processes

In this study, the waste heat from the hot stripping gas was recovered by adopting the transport membrane condenser (TMC) in the monoethanolamine (MEA)-, diethanolamine (DEA)-, piperazine (PZ)- and potassium glycinate (PG)-based rich-split modified carbon capture processes. A 220-h test showed that TMC can exhibit a good stability on the waste heat recovery performance. The PZ-based TMC-modified rich-split process (i.e., PZ-case) achieved a highest waste heat recovery performance, followed by the PG-case, MEA-case and DEA-case. A strong linear relationship between the heat and water fluxes was observed during the waste heat recovery. Three scenarios were considered for comparing the CO2 capture cost savings of 4 cases. When the TMC area was fixed meaning the same additional investment of rich-split modification, PZ-case gained the highest CO2 capture cost saving ($6.40/t-CO2), followed by PG-, MEA- and DEA-case. When a fixed waste heat recovery performance of 600 kJ/kg-CO2 was required for obtaining the same revenue after rich-split modification, PZ- and PG-case obtained the same CO2 capture cost saving of $4.22/t-CO2. Moreover, when the reboiler duty reduction potential was aimed at 15%, PG-case achieved the maximum CO2 capture cost saving ($4.56/t-CO2).

Advanced exergo-economic schemes and optimization for medium–low grade waste heat recovery of marine dual-fuel engine integrated with accumulator

Facing the multiple pressures of energy reserves decline, ecological environment deterioration and transportation industry prosperity, in order to enhance the marine performance, improve the enterprises economic benefits, and achieve the purpose of energy conservation and emission reduction, the revolution of green and efficient waste heat recovery technology is imperative. Therefore, the exergy-based configuration design of marine cascade waste heat recovery system is proposed, including supercritical Brayton cycle, organic Rankine cycle, organic flash cycle, organic trilateral cycle and absorption refrigeration cycle. Firstly, the mathematical models of three cycle-configurations are established based on thermodynamic equations, and the authority of simulation results is preliminarily verified. Then, the relationship between working-fluid, matching mode and operation parameters with cycle-configuration performance is analyzed in turn. After the multi-objective optimization, the thermodynamic performance and economic benefits of the cycle-configuration are comprehensively evaluated. Finally, the positive influence of the accumulator on the refrigeration system is explored. The numerical results prove that the proposed cycle-configuration has significant thermodynamic performance and economic benefits, reflects the good performance of energy saving and emission reduction, and can eliminate the negative impact of latent heat fluctuation on the refrigeration system. It provides a feasible idea for researchers and manufacturers who are committed to comprehensively improve the performance of cascade waste heat recovery, and fills the research gap in the latest investigation.

Advances in multifunctional balanced ventilation technology for dwellings and arising challenge to quantify energy efficiency and renewable generation contributions using international test standards

This paper evaluates the ability of EN16573:2017 to isolate and quantify the energy efficiency and renewable generation contributions of multifunctional balanced ventilation systems. These systems integrate an air-source heat pump with heat recovery ventilation and two similar, yet physically different configurations (C1 and C2) are assessed. Heat pump operation does not influence heat recovery performance for widely used configuration C1 but does influence for novel configuration C2. This study shows that while EN16573:2017 can isolate the energy efficiency (heat recovery exchanger) and renewable generation (heat pump) contributions for configuration C1, it fails when applied to configuration C2. Measurements undertaken using EN16573:2017 on configuration C2 revealed an overall coefficient of performance of 5.07, split 51% heat exchanger with heat pump off (phase 1), and 49% heat pump (phase 2 minus phase 1). If this result were obtained for configuration C1 the respective contributions would be 51% energy efficiency and 49% renewable generation. While these contributions cannot be resolved using EN16573:2017 for configuration C2, it can be achieved using two additional measurement planes in the incoming airstream. These showed an 88%:12% contribution from the heat exchanger and heat pump, respectively. While accurate, this result under-estimates the true heat pump contribution, as its positive impact on the heat exchanger efficiency boosts its contribution from 51% (phase 1) to 88% (phase 2). This paper acknowledges that heat pump operation leverages a 37% increase in heat exchanger performance and proposes a that the respective contributions of the heat exchanger and heat pump should be 42%:58%.

Experimental study on the condensing heat recovery performance of air source heat pump

Energy recycling and sustainable development problem is imminent and condensing heat recovery technology in air source heat pump has received considerable development and application in recent years. In this article the experimental method is used to mainly explore the performance of four kinds of condensing heat recovery system (e.g. the static type, circulation, paraffin, copper foam/paraffin) in full and partial condensing heat recovery mode. The results show that in the full condensing heat recovery mode, four systems can obtain relatively high performance, but the systems’ performance rapidly decays with time and can't provide enough cooling capacity and hot water production due to the short running time. In partial condensing heat recovery mode, the four systems’ shows better system efficiency compared with the systems without condensing heat recovery. And the circulation system performance increases significantly, which comprehensive efficiency coefficient can reach 5.67 and the average system heat recovery rate is 44.0%. The two phase change heat storage system run steadily and the adding of foam metal copper to paraffin not only enhance the performance of the system but also improve the stability of the system operation.

Heat transfer and recovery performance enhancement of metal and superconducting tapes under high current pulses for improving fault current-limiting behavior of HTS transformers

High-temperature superconducting (HTS) transformer windings operate subcooled at atmospheric pressure to temperatures as low as 65 K, with minimal power dissipation from AC loss in normal operation. During short circuits, HTS transformers are subjected to transient heating by currents as large as 10 times the rated current for durations of up to 2 s. After isolating the fault, HTS transformers are required to cool back down to their base temperature while carrying the operating current. HTS transformer conductors are insulated, typically with wrapped self-adhesive polyimide tape, and windings consist of close-packed conductors wound on composite formers.In this paper, the heat transfer, transient thermal response, and recovery performance of brass-laminated coated conductor HTS wire as well as metallic conductors in liquid nitrogen (LN2) were measured at a range of temperatures from 77 K to 64 K and pressures from atmospheric to 0.14 bar in heating and cooling situations. Measurements were made on bare tapes, and on tapes wrapped with polyimide insulation tape and aramid paper as well as polymer-coated tapes with a range of coating thicknesses. Heat transfer from tapes mounted with one face in contact with a glass-epoxy composite cylindrical former was measured for comparison with free-standing tapes. Using conductors with solid polymer coatings of optimized thickness immersed in subcooled LN2 results in the highest heat transfer and fast recovery following heating to 300 K by a high current pulse. Compared to a bare tape in LN2 at ambient pressure at 77 K, the heat transfer in a coated tape in 65 K subcooled LN2 can be very significantly enhanced by up to a factor of 15, and recovery can be seven times faster.