A New Method for the Determination of the Specific Heat Capacity Using Laser-Flash Calorimetry Down to 77K

A new method for evaluation of the specific heat capacity in the temperature regime between 77K and 330K using laser-flash calorimetry is presented. Usually, laser-flash calorimetry is accomplished by performing an additional laser-flash measurement on a reference specimen with a known specific heat capacity and by comparing the maximum rear-side temperatures rises. In this study, the calibration is achieved by comparison of the rear-side temperature rise to specific-heat-capacity data determined by other methods in an adjacent temperature regime. Subsequently, the thus yielded proportional factor is used for the evaluation of the specific heat capacity from laser-flash measurements at temperatures where no specific-heat-capacity data are available. The reliability of this method is shown by performing measurements on a material with known specific heat capacity, aluminum oxide. Furthermore, the specific heat capacity and thermal conductivity of borosilicate crown glass (BK7) was determined experimentally.     

无接触热阻全铝换热器空调系统制冷性能研究

本文用新型无接触热阻全铝换热器对传统家用空调换热器进行了替代设计,利用空气焓值法对使用新型换热器和管片式换热器的家用窗式空调器进行对比试验,优化并测试了毛细管规格和制冷剂充灌量对新型换热器空调系统制冷性能的影响。研究结果表明：新型无接触热阻全铝换热器在换热面积减小37.53%时,制冷量反而提高3.59%,能效比EER提高7%。新型换热器有更强的换热能力,是目前家用空调换热器的理想替代产品。     

比热测试技术进展

物质的热容测试对热分析数据有着重要影响,也是物质本身固有属性的重要表征特性,因此热容的测定得到越来越多人的关注。本文通过介缉连续测试热容法、阶梯测试热容法、液体热容测试法和滴落测试热容法等多种热容测试方法,展示了热容测试技术的发展及改进。     

The heat capacity of cerous magnesium nitrate and some related materials between 0.3 and 4 K

Cerous magnesium nitrate (CMN) is the preeminent electronic paramagnet in use in cryogenic physics for magnetic thermometry and adiabatic cooling. In demagnetization experiments designed to establish the thermodynamic temperature relations for CMN, an inexplicable heat capacity anomaly was found to occur above 20 mK and is shown here to persist to temperatures near 1 K. The anomaly is small but its presence interferes with and may cause errors in the analysis of thermometric data. We have measured the heat capacity of CMN, lanthanum magnesium nitrate (LMN), cerous nitrate hexahydrate, and a saturated aqueous solution of CMN (CMN liquor) in the temperature range 0.3–4 K in an attempt to find the source of the anomaly. The LMN heat capacity shows no anomaly and is used to approximate the lattice heat capacity of CMN. At low temperatures the CMN heat capacity, exclusive of the lattice contribution, is some 2 1/2 times larger than the magnetic heat capacity predicted by other investigations. At high temperatures an exponentially increasing heat capacity due to the first excited electronic level is observed and indicates a splitting which is in accurate agreement with the spectroscopic value. There is evidence that the lattice heat capacity in CMN is about 1% smaller than in LMN, which is probably the result of the crystal-field interaction with the electronic states of the cerous ions. The lattice terms and theT ^–2term of the magnetic heat capacity for cerous nitrate have been determined, the latter being 25 times larger than the predictedT ^–2term in CMN. The CMN liquor measurements indicate that this sample had probably become a glass on cooling. The lattice heat capacity is considerably larger than could be predicted from the separate components and there is no indication of the exponential term which would be observable if appreciable crystalline CMN were present. These measurements help to define the nature of the anomalous heat capacity and remove from consideration some possible explanations, but they do not reveal the cause of the anomaly.     

Capacity-controlled ground source heat pumps in hydronic heating systems

The objective of this study was to investigate the energy-saving potential of using variable-speed capacity control instead of the conventional intermittent operation mode for domestic ground source heat pumps. Variable-speed capacity control is commonly used in air-to-air heat pumps, but not in ground source heat pumps for hydronic heating systems, even though the energy-saving potential may be greater for this application. A theoretical analysis indicates how the energy efficiency is influenced by variable-speed capacity control of the compressor. The analysis shows that, to take full advantage of the capacity control, care should be taken to achieve the correct relationship between refrigerant flow and heat transfer media flows. Intermittent control and variable-speed capacity control were compared by laboratory tests on two capacity-controlled heat pumps and one standard heat pump with a single-speed compressor. Test data were then used for seasonal performance factor (SPF) calculations. The SPF calculations show that despite improved performance at part load the variable-speed controlled heat pump did not improve the annual efficiency compared to the intermittently operated heat pump. This is mainly due to inverter and compressor motor efficiencies and the need for improved efficiency and control of pumps used in the heating and ground collector systems.     

Heat capacity of fcc calcium

The lattice entropy derived from the measured heat capacity at intermediate and high temperatures is analyzed to yield a weakly temperature dependent entropy Debye temperature. An unusual temperature dependence of this quantity may be a sign of error in the heat capacity data. When this analysis is applied to heat capacity data recommended by Hultgren et al. (1973) for 20 nontransition metals, the result for fcc Ca stands out as anomalous. We have reconsidered heat capacity data of fcc Ca and find that measurements by Eastman et al. (1924), which were given little weight by Hultgren et al., are consistent with a normal behavior of the entropy Debye temperature up to 450 K.     

变温热源不可逆布雷顿制冷循环制冷率和制冷系数优化

用有限时间热力学方法分析变温热源不可逆简单布雷顿制冷循环的特性,分别以制冷率和制冷系数为优化目标,优化了循环中换热器的热导分配以及工质和热源间的热容率匹配,并采用数值计算分析了压比、换热器总热导、压缩机和膨胀机效率、工质热容率等参数对最优制冷率和制冷系数的影响特点.所得结果对工程制冷系统设计有一定的指导意义.     

空调室外换热器分布式流路设计与实验验证

空调室外换热器通常使用流路数目均一的流路,使空调器无法在不同的制冷剂流动特性下均具有最佳的换热状态。本文提出了一种室外换热器的分布式流路方案,以提升空调器的全年换热性能。首先根据制冷剂在换热器内的沿程流动特性提出流路数目随制冷剂干度增大而增大的分布式流路方案;然后通过换热器仿真软件分析分布式流路的换热特性和阻力特性;最后通过实验验证了分布式流路对空调器性能的提升效果。结果表明,与采用固定流路的空调室外换热器相比,采用分布式流路的空调系统的全年性能系数APF提高了1. 8%～5. 8%;室外换热器的额定制热量、低温制热量、超低温制热量分别约提高了4. 3%、7. 5%、5. 9%。     

Heat Capacity of 1D Molecular Chains

The heat capacity of 1D chains of nitrogen and methane molecules (adsorbed in the outer grooves of bundles of closed-cap single-walled carbon nanotubes) has been studied in the temperature ranges 2–40 and 2–60 K, respectively. The temperature dependence of the heat capacity of 1D chains of nitrogen molecules below 3 K is close to a linear. It was found that the rotational heat capacity of methane molecules is a significant part of the total heat capacity of the chains throughout the whole investigated temperature range, whereas in the case of nitrogen, the librations are significant only above 15 K. The dependence of the heat capacity for methane below 10 K indicates the presence of a Schottky anomaly caused by the tunneling between the lowest energy levels of the \(\hbox {CH}_{4}\) molecule rotational spectra. Characteristic features observed in the temperature dependence of the heat capacity of 1D methane crystals are also discussed.     

Special features of the heat capacity of detonation nanocrystalline diamond

The heat capacity of detonation nanocrystalline diamond has been studied by adiabatic calorimetry in the 60–300 K temperature range. It has been found that the heat capacity of commercial samples of nanodiamond exceeds that of bulk diamond by more than 30%. It has been shown that this excess is only partially caused by the impurities and for an impurity-free nanodiamond it is more than 15%. It has been proposed to explain this feature of the heat capacity by a contribution of surface carbon atoms into a low energy density of diamond phonon states. Based on the experimentally obtained temperature dependences of the heat capacity, the standard values of the enthalpy, entropy, and reduced Gibbs free energy of commercial and impurity-free nanodiamond have been calculated.     

空调器用换热器的换热量衰减率测试方法

为了快速评估空调器用换热器长期运行后的换热量衰减情况,本文提出一套通过测试换热器加速积尘前后的换热量来预测其换热量衰减率的测试方法。该测试方法中,采用负反馈模式精确调节换热器迎风面的粉尘浓度,能够在加速积尘时间内维持换热器迎风面粉尘浓度的稳定性;通过对加速积尘循环空间与换热量测试风道进行一体化设计,能够在不需要移机时实现加速积尘与换热量测试之间的切换。在入口空气温度为45℃、流速为1. 5 m/s,入口水温为21℃、流速为0. 5 m/s的工况下对该测试方法的可靠性和一致性进行了验证,结果表明:换热器迎风面粉尘浓度能够稳定维持在目标浓度120 mg/m3,波动范围在±20%内;对4种具有不同结构的换热器样件进行了多次换热量衰减率测试,其换热量衰减率相对偏差均在±10%之内,表明该测试方法具有较好的一致性。     

Measurement of low temperature heat capacity of metals under pressure

An alternating heat flow method is used to measure the heat capacity of metals at low temperatures under hydrostatic compression. The phase shift method is developed for taking account of the losses in the medium. The method was tested by measuring the heat capacity of Sn at pressures up to 10 k bar. The errors of measurements are ～3%.     

电动客车用余热回收型热泵的换热器优化及性能实验研究

本文针对热泵空调系统在冬季低温工况下制热能力衰减问题,通过换热器设计优化,研发出基于喷射补气的余热回收型热泵空调系统,并进行了性能实验研究.结果表明:研制的准二级压缩电动客车热泵空调系统在低温条件下具有较好的制热性能.在环境温度为-20℃,车内温度为20℃,余热量为1.8 kW的制热工况下,相比于无余热回收工况,系统制...     

三排变片距翅片盘管换热器结霜特性实验研究

为改善空气源热泵室外翅片盘管换热器在低环境温度下沿空气流动方向结霜不均匀、首排结霜量较大进而导致热泵除霜间隔较短、制热能力下降等问题,对不同翅片片距组合的变片距翅片盘管换热器在低环温工况下运行及结霜的情况进行实验研究。结果表明：变片距翅片盘管换热器在低环温条件下可有效延长迎风面管排发生结霜堵塞的时间、对于结霜生长速度和结霜质量也有抑制作用。变片距翅片盘管换热器在结霜中后期阶段换热功率更高,在合理的翅片间距组合下,变片距翅片盘管换热器可以在不损失过多换热功率的情况下延长换热器迎风面管排结霜堵塞的时间,如样品4的平均换热功率比样品1低6.02%,而除霜间隔延长了37 min。     

水环热泵辅助热源容量在部分负荷率下的试验研究

针对水环热泵空调系统辅助热源容量选取问题,在部分负荷率对水环热泵系统能耗影响分析的基础上,选取天津地区具体工程实例,分别对辅助热源容量为35 kW,38.5 kW和42 kW三种方案进行100%,80%,60%,40%和20%五档部分负荷率的工程进行测试,并采用部分负荷率无因次能耗分析方法对空调主设备、辅助热源以及系统能耗进行分析。分析结果表明：水环热泵空调系统能耗随部分负荷率变化具有非线性的变化特征,其畸变工况点出现在80%～100%负荷段;针对此建筑,辅助热源容量按建筑热负荷55%（即38.5 kW）选取是最佳方案。     

中温固体比热容测量基准的研究进展

中温固体比热容测量基准装置是保证比热容、相变温度、相变焓等量值溯源的核心。装置主要采用绝热量热方法,实现量值结果溯源至SI单位。介绍了比热容装置的研究意义与测量原理,分析了其在该领域的研究状况,在此基础上提出了我国中温固体比热容测量基准装置的新方案和总体设计。     

A study of the heat capacity of coated metal materials by the laser flash method

Results of laser-flash measurements of the specific heat capacity of samples of metallic materials (12Kh18N9T stainless steel, VZhM-4 nickel superalloy) coated with heat-resistant silicate enamel in a temperature range of 20–1300°C are described. In this temperature range, the coating is characterized by a high emissivity factor with a constant magnitude of 0.9. Analysis of the measurement results for the specific heat capacity of the steel samples and comparison of these results with the reference data and the most reliable literature data reveal that a decrease in the apparent specific heat capacity in a temperature range of 850–1100°C is attributed to an exothermic heat effect. The deviation of the measurement results from the reference data is no more than 3%. New data on the heat capacity of the VZhM-4 nickel alloy are derived. The temperature dependences of the apparent (with allowance for the heat effect of dissolution of the γ' phase) and true specific heat capacities are described. The discrepancy between the calculated and measured values does not exceed 2%.     

Explaining the heat capacity of wood constituents by molecular vibrations

The heat capacity of wood and its constituents is important for the correct evaluation of many of their thermodynamic properties, including heat exchange involved in sorption of water. In this study, the dry state heat capacity of cellulose, hemicelluloses and lignin are mathematically described by fundamental physical theories relating heat capacity with molecular vibrations. Based on knowledge about chemical structure and molecular vibrations derived from infrared and Raman spectroscopy, heat capacities are calculated and compared with experimental data from literature for a range of bio- and wood polymers in the temperature range 5–370 K. A very close correspondence between experimental and calculated results is observed, illustrating the possibility of linking macroscopic thermodynamic properties with their physical nano-scale origin.     

低温空气源热泵技术的应用

介绍带经济器的低温空气源热泵技术,通过对低温空气源热泵机组与普通空气源热泵机组的制冷量、制热量和能效比等参数进行测试及对比,探讨低温空气源热泵技术的应用优势。试验结果表明:与普通机组相比,低温机组在名义制冷和名义制热工况下冷热量和能效均有所提升;在-10~-15℃的环境中,普通机组制热量严重衰减使其不适用于此温度区间,低温机组制热量虽然也在减少,但其COP仍可达2.0,且排气温度相对较低;在-15~-20℃超低温环境中,低温机组仍可稳定运行,且能效比在2.0左右。     

大规模弃风储热供暖协调计算方法

国家鼓励清洁供暖,电采暖是清洁供暖的重要组成部分。但常规用电成本高,如果利用弃风电,不仅消纳弃风电,还能降低电供暖成本。文中以一个实际电网为例,通过研究弃风总量、储热能力和供暖能力,提出了弃风储热供暖协调调度策略。对一个拥有大规模弃风电量、大规模储热的电网具有实际意义。