Joule-Thompson Effect

6 Key excerpts on "Joule-Thompson Effect"

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  eBook - ePub

  Chemical Thermodynamics for Process Simulation

  • Jürgen Gmehling, Michael Kleiber, Bärbel Kolbe, Jürgen Rarey(Authors)
  • 2019(Publication Date)
  • Wiley-VCH

    (Publisher)

  Considering that no heat exchange takes place and that differences in velocity and height at the end of the control volume are negligible for the energy balance, the First Law can be formulated as 14.2 Figure 14.1 Illustration of the flow in an orifice of a pipe. Nevertheless, a change in temperature can occur. Behind the orifice, vortices are formed, and two effects compete: the flow involving friction of the vortices causes a temperature rise, and the pressure loss causes a lowering of the temperature, as energy is necessary to overcome the attractive forces between the molecules. 1 The Joule–Thomson coefficient (∂T / ∂P) h determines which of these two effects dominates. It can be evaluated as follows. The total differential of the specific enthalpy is 14.3 With (∂h / ∂T) P = c P, one gets 14.4 which is the differential Joule–Thomson coefficient. In Appendix C, the following relation is derived: 14.5 Combining Eqs. 14.4 and 14.5, the Joule–Thomson coefficient becomes 14.6 For ideal gases, the Joule–Thomson coefficient is 14.7 and there is no temperature change by the Joule–Thomson effect. The sign of the Joule–Thomson coefficient in Eq. 14.6 depends on the temperature. At the inversion temperature, (∂T / ∂P) h = 0. Below the inversion temperature, the temperature of the gas is lowered by throttling (Joule–Thomson effect). For air, the inversion temperature is T inv = 760 K. For hydrogen (T inv ≈ 200 K) and helium (T inv ≈ 40 K), it is considerably lower. The Joule–Thomson effect is used for liquefaction of these three gases with the Linde process; because of the low inversion temperatures of hydrogen and helium, a precooling with liquefied air or liquefied hydrogen, respectively, is necessary

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  Refrigeration Process, Cooling Technology and Thermodynamic Cycles (Concepts and Applications)

  • (Author)
  • 2014(Publication Date)
  • Learning Press

    (Publisher)

  Joule heating, the heat that is generated whenever a voltage is applied across a resistive material, is somewhat related, though it is not generally termed a thermoelectric effect (and it is usually regarded as being a loss mechanism due to non-ideality in ther-moelectric devices). The Peltier–Seebeck and Thomson effects can in principle be thermodynamically reversible, whereas Joule heating is not. Seebeck effect The Seebeck effect is the conversion of temperature differences directly into electricity. Seebeck discovered that a compass needle would be deflected when a closed loop was formed of two metals joined in two places with a temperature difference between the junctions. This is because the metals respond differently to the temperature difference, which creates a current loop, which produces a magnetic field. Seebeck, however, at this time did not recognize there was an electric current involved, so he called the phenomenon the thermomagnetic effect, thinking that the two metals became mag-netically polarized by the temperature gradient. The Danish physicist Hans Christian Ørsted played a vital role in explaining and conceiving the term thermoelectricity. The effect is that a voltage, the thermoelectric EMF, is created in the presence of a temperature difference between two different metals or semiconductors. This causes a continuous current in the conductors if they form a complete loop. The voltage created is of the order of several microvolts per kelvin difference. One such combination, copper-constantan, has a Seebeck coefficient of 41 microvolts per kelvin at room temperature. In the circuit:

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  eBook - ePub

  Process Systems and Materials for CO2 Capture

  Modelling, Design, Control and Integration

  • Athanasios I. Papadopoulos, Panos Seferlis, Athanasios I. Papadopoulos, Panos Seferlis(Authors)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  The ability of mathematical modeling to characterize membrane permeation processes has encouraged various modeling efforts employing different numerical solutions that are incorporated within commercial process simulators to be adapted in industrial applications [1–5]. This incorporation allows any combinations of membrane with other readily available unit operations within the industrial process simulator (e.g. compressor and heat exchanger) to study the entire process flow as a whole [6, 7]. Most importantly, it enables membrane systems with recycling to be simulated because stages of modules arranged in parallel or series without recycle streams constitute a single‐stage membrane process, whereby the extent to which a feed gas mixture can be separated to cater for varying design configurations is limited [8]. Therefore, in actual industrial design, cascades of membrane modules with recycle streams are typically adopted to achieve a higher degree of separation, which presents a research gap for further research work in process simulators to fully utilize the inherent recycling techniques [8]. In addition, process simulation also allows the convenient adaptation of its intrinsic capabilities for prediction of physical and thermodynamic properties, which are highly essential for the optimization of process economics [1]. A detailed analysis devoted to the methodology adapted to characterize membrane separation in process simulators has been outlined in our previous work [8].

  Nonetheless, it has been shown that the majority of the simulation models have adopted the common assumption of isothermal operation throughout the membrane [9–13]. In real membrane gas separation, the expansion of residue gas from the higher to the lower pressure side of the permeate stream is often accompanied by a thermodynamic change, which means that the isothermal assumption is invalid. The phenomenon associated with temperature alterations when the feed gas passes through the membrane, which resembles an adiabatic expansion valve, is regarded as the Joule–Thomson (JT) effect. In this circumstance, the gas enthalpy remains constant but the pressure and specific volume change when the gas expands from the high to the low pressure end [14]. Implications of the JT effect are especially pronounced in feed gas with a high contaminant content and under high pressure, which may cause condensation across the membrane and ultimately contribute to fouling. In addition, the JT effect is also important to characterize the separation performance since the membrane permeance is dependent upon the temperature [5].

  A limited number of studies have been devoted to the elucidation of the JT effect for membrane separation. Rautenbach and Dahm [15] adopted constant JT coefficients to study the temperature drop distribution of CO2 /CH4 binary mixtures in a one‐dimensional crossflow mass transfer membrane. Gorrisen [16] continued to evoke the heat effect in a crossflow membrane permeator for binary gas mixtures through adaptation of JT coefficients that are dependent upon the gas concentrations and heat capacities. Cornelissen [17] also contributed to the study of the heat effect on gas permeation, which is exclusively applicable to spiral wound membranes. Coker et al. [14] developed a one‐dimensional mathematical model confined to the countercurrent hollow fiber membrane module that permits the consideration of non‐isothermal thermodynamic conditions attributed to gas expansion across the membrane and its effect to membrane permeability performance. Scholz et al. [18] linked non‐ideal effects, including the JT effect confined to a binary mixture in gas permeation modeling, which has been further interfaced in the Aspen Custom Modeler, but they have not presented the effect of variable permeance due to a change in temperature on the performance of their gas separation system. In recent work, we developed a crossflow hollow fiber membrane model considering temperature and pressure dependence of membrane permeability for CO2 /CH4

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  Thermal Design

  Heat Sinks, Thermoelectrics, Heat Pipes, Compact Heat Exchangers, and Solar Cells

  • HoSung Lee(Author)
  • 2022(Publication Date)
  • Wiley

    (Publisher)

  There is another form of heat, called Joule heating (I 2 R), which is irreversible and is always generated as current flows in a wire. The Thomson heat is reversible between heat and electricity. 5.1 Introduction 339 5.1.5 Thomson (or Kelvin) Relationships The interrelationships between the three thermoelectric effects are important in order to understand the basic phenomena. In 1854, Thomson [2] studied the relationships thermodynamically and provided two relationships as shown in Eqs. (5.4) and (5.5) by applying the first and second laws of thermodynamics with the assumption that the reversible and irreversible processes in thermoelectricity are separable. The necessity for the assumption remained an objection to the theory until the advent of the new thermodynamics. The Thomson effect is relatively small compared to the Peltier effect, but it plays an important role in deducing the Thomson relationships. These relationships were later completely confirmed by experiments. 𝜋 AB = 𝛼 AB T (5.4) 𝜏 AB = T d𝛼 AB dT (5.5) Equation (5.4) leads to the very useful Peltier cooling as ̇ Q Peltier = 𝛼 AB TI (5.6) where T is the temperature at a junction between two different materials and the dot above the heat Q indicates the amount of heat transported per unit time. 5.1.6 The Figure of Merit The performance of thermoelectric devices is measured by the figure of merit (Z), with units 1/K: Z = 𝛼 2 𝜌k = 𝛼 2 𝜎 k (5.7) where 𝛼 = Seebeck coefficient, μV/K; 𝜌 = electrical resistivity, Ωcm σ = 1/ρ = electrical conductivity, (Ωcm) −1 k = thermal conductivity, W/mK The dimensionless figure of merit is defined by ZT , where T is the absolute temperature. There is no fundamental limit on ZT , but for decades it was limited to values around ZT ≈1 in existing devices. The greater the value of ZT is, the greater the energy conversion efficiency of the material. The quantity of 𝛼 2 𝜎 is defined as the power factor.

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  Bringing Thermoelectricity into Reality

  • Patricia Aranguren(Author)
  • 2018(Publication Date)
  • IntechOpen

    (Publisher)

  [31] Callen HB. Thermodynamics and an Introduction to Thermostatistics. John Wiley and Sons, Inc; 1985 [32] Laird. Available from: https://www.lairdtech.com/product-categories/thermal-management/ thermoelectric-modules [33] Rowe DM. CRC Handbook of Thermoelectrics. CRC Press; 1995 Bringing Thermoelectricity into Reality 288 Chapter 14 Thermoelectric Cooling: The Thomson Effect in Hybrid Two-Stage Thermoelectric Cooler Systems with Different Leg Geometric Shapes Pablo Eduardo Ruiz-Ortega, Miguel Angel Olivares-Robles and Amado F. Garcia Ruiz Additional information is available at the end of the chapter http://dx.doi.org/10.5772/intechopen.75440 Abstract This chapter aims to analyse the performance of hybrid two-stage thermoelectric cooler systems [two-stage thermoelectric cooling devices (TEC)], which are composed of differ-ent thermoelectric materials in each stage with different leg geometric shapes. If we consider a temperature gradient inside a two-stage TEC, then, besides Joule heat, also Thomson heat has to be taken into account. We discuss the out-of-equilibrium thermody-namics equations of a one-dimensional model to provide the performance expressions that govern the system. TEC system performance is analysed in function of the Thomson coefficients ratio of both stages. We describe a recent geometric optimization procedure that includes leg geometry parameters such as ratio of cross-sectional area and length of legs for each stage of the two-stage TEC. Keywords: ideal equation (IE), Thomson effect, two-stage micro-cooler, Peltier effect 1. Introduction Thermoelectric cooling devices are based on the Peltier effect to convert electrical energy into a temperature gradient.

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  Thermoelectric Materials and Devices

  • Lidong Chen, Ruiheng Liu, Xui Shi(Authors)
  • 2020(Publication Date)
  • Elsevier

    (Publisher)

  C H A P T E R 1 General principles of thermoelectric technology 1.1 Introduction The first thermoelectric effect, namely the Seebeck effect, was discov-ered in 1821, which describes the electromotive force generated by the temperature difference. In the following thirty years or more, Peltier effect and Thomson effect were successively discovered. These effects are the three main physical effects in thermoelectric technology that describe the direct conversion between thermal and electrical energies [1 3] . Although the discoveries of both Seebeck and Peltier effects were made using a circuit composed of two different conductors and the effects were only observed at the junctions between dissimilar conduc-tors, they are actually the bulk properties of the materials involved, not the interfacial phenomena. Solid state physics developed in the follow-ing century reveals that all the three thermoelectric effects originate from the energy difference of carriers in different materials and/or in the different parts of materials under different temperatures. Thomson built the relationship among the three effects, and devel-oped the basic thermodynamic theories for thermoelectric effects [3] . Thomson’s work showed that a circuit composed of two conductors with positive and negative Seebeck coefficients (usually called the ther-mocouple) is a type of heat engine. Such heat engine can generate elec-trical power by virtue of the temperature difference, or pump heat to realize refrigeration. However, since the reversible thermoelectric effects are always accompanied by the irreversible Joule heat and heat conduc-tion, its energy conversion efficiency is principally low. Thermoelectric effects have been widely used for temperature calibrations as thermo-couples, but they had no practical application as heat engine, and there 1 Thermoelectric Materials and Devices DOI: https://doi.org/10.1016/B978-0-12-818413-4.00001-6 Copyright © 2021 China Science Publishing & Media Ltd.

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