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SCIENCE CHINA Technological Sciences, Volume 61 , Issue 2 : 219-231(2018) https://doi.org/10.1007/s11431-017-9121-6

Experimental study on the new type of electrical storage heater based on flat micro-heat pipe arrays

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  • ReceivedJun 25, 2017
  • AcceptedAug 16, 2017
  • PublishedSep 13, 2017

Abstract

A new type of electrical storage heater that utilizes latent heat storage and flat micro-heat pipe arrays (FMHPAs) was developed. The thermal characteristics of the heater were tested through experimentation. The structure and operating principle of the storage heater were expounded. Three rows of FMHPAs were applied (three rows with five assemblies each) with a mass of 28 kg of phase change material (PCM) in the heat storage tank. Electric power was supplied to the PCM in the range of 0.2‒2.04 kW, and air was used as heat transfer fluid, with the volume flow rate ranging from 40‒120 m3/h. The inlet temperature was in the range of 15‒24°C. The effects of heating power, air volume flow rate, and inlet temperature were investigated. The electrical storage heater exhibited efficiencies of 97% and 87% with 1.98 and 1.30 kW of power during charging and discharging, respectively. Application of the proposed storage heater can transfer electricity from peak periods to off-peak periods, and the excess energy generated by wind farms can be stored as heat and released when needed. Good economic and environmental benefits can be obtained.


Funded by

Scientific Research Project of Beijing Educational Committee(004000546315527)

National Key Technology Research and Development Program of the Ministry of Science and Technology of China(2012BAA13B02)

Graduate Science and Technology Foundation of Beijing University of Technology(ykj201600060)


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  • Figure 1

    (Color online) Structure of the storage heater and heat transfer unit.

  • Figure 2

    (Color online) Structure and operating principle of the FMHPA components.

  • Figure 3

    (Color online) Experimental system diagram.

  • Figure 4

    (Color online) Measuring point arrangement diagram.

  • Figure 5

    (Color online) Temperature curve along the Z direction of the No. 8 FMHPA assembly versus time in the charging and discharging processes.

  • Figure 6

    (Color online) Temperature curves along the X direction of Nos. 6‒10 FMHPA assemblies at different times in the charging process (a) and versus time in the discharging process (b).

  • Figure 7

    (Color online) Temperature curve along the Y direction of the No. 8 FMHPA assembly versus time in the charging and discharging process.

  • Figure 8

    (Color online) Electrical energy and average temperature of PCM versus time in the charging process.

  • Figure 9

    (Color online) Energy proportion in the charging process.

  • Figure 10

    (Color online) Curve of average temperature of PCM at different heating powers versus time.

  • Figure 11

    (Color online) Curve of charging completion time and charging efficiency at different heating powers.

  • Figure 12

    (Color online) Curve of inlet and outlet temperatures, extraction power and average temperature of PCM versus time.

  • Figure 13

    (Color online) Energy proportion in the discharging process.

  • Figure 14

    (Color online) Curve of average temperature of PCM at different volume flow rates of HTF versus time.

  • Figure 15

    (Color online) Curve of extraction power at different volume flow rates of HTF versus time.

  • Figure 16

    (Color online) Curve of average temperature of PCM at different inlet temperatures of HTF versus time.

  • Figure 17

    (Color online) Curve of extraction power at different inlet temperatures of HTF versus time.

  • Table 1   Thermal-physical properties of #52 commercial paraffin wax

    Parameters

    Units

    Value

    Phase transition temperature

    °C

    52

    Latent heat of phase change

    kJ/kg

    153.4

    Specific heat capacity

    kJ/(kg·K)

    2.83

    Thermal conductivity

    W/m·K

    0.11

    Solid-state density

    g/cm3

    1.05

    Liquid-state density

    g/cm3

    0.80

  • Table 2   Experimental conditions during discharging process

    Experiment

    Inlet temperature (°C)

    Air volume flow (m3/h)

    Constant temperature test

    15

    40

    60

    80

    100

    120

    Constant flow test

    15

    80

    18

    21

    24

  • Table 3   Model specifications and accuracy of the testing instrument

    Testing instrument

    Model specification

    Accuracy

    Data collector

    Agilent 34970A

    Thermocouple

    WRNK-191

    ±0.75%|t|°C

    Thermal resistance

    Pt100 WZPF-293

    0.15 + 0.2%|t|°C

    Flowmeter

    TSI-8371

    ±2%

    Electricity meter

    W350

    ±1%

  • Table 4   Uncertainty error of the calculated parameter

    Parameter

    Maximum

    Unit

    Uncertainty

    Ec/d (Pc/d)

    7.05 (1.98)

    MJ (kW)

    ±3.61%

    η c

    96.97

    %

    ±4.13%

    Ee (Pe)

    6.27 (1.41)

    MJ (kW)

    ±2.29%

    η e

    86.84

    %

    ±4.22%

  • Table 5   Comparison of the pollutant emissions of electrical storage heating and coal stove heating

    Heating method

    Gas

    CO2 (kg)

    SO2 (kg)

    NOx (kg)

    Coal stove heating

    4.45 × 1010

    1.44 × 108

    1.26 × 108

    Electrical storage heating

    0

    0

    0

    Emission reductions

    4.45 × 1010

    1.44 × 108

    1.26 × 108

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