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Convective and evaporative heat transfer coefficients during drying of ivy gourd under natural and forced convection solar dryer

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Abstract

In the present work, a study on convective heat, mass transfer coefficients and evaporative heat transfer coefficient of the thin layer drying process of ivy gourd is performed. The experiment was conducted in three drying modes such as natural, forced convection solar dryer and open sun drying. The hourly data for the rate of moisture removal, sample temperature, relative humidity inside and outside the solar and ambient air temperature for complete drying have been recorded. The drying air temperature varied from 55, 65, 70 and 75 °C, and the air velocity was 1, 1.5 and 2 m/s. All the drying experiments had shown a falling rate period. The data obtained from experimentation have been used to evaluate the experimental constant values of C and n by simple regression analysis. Based on the values of “C” and “n”, convective and evaporative heat transfer coefficients for ivy gourd were determined. The average convective heat and mass transfer coefficients varied between 2.64 and 8.30 W/m2 °C and 0.0025 to 0.0076 m/s for temperature ranges, at the different air velocities, respectively. The average evaporative heat transfer coefficient for ivy gourd varied from 181.89 to 421.84 W/m2 °C. It was observed that convective and evaporative heat transfer coefficients increase with the increase in drying air temperature. The rate of increment of evaporative heat transfer coefficient is higher than the convective heat transfer coefficient. The intensity of heat and mass transfer during solar drying depends on the drying air temperature and velocity.

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Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Abbreviations

\(MR\) :

Moisture ratio of a sample (Eq. 1)

\(Y\left(t\right)\) :

Moisture ratio at the time [h] (Eq. 1)

\({Y}_{2}\) :

Equilibrium moisture (Eq. 1)

\({Y}_{1}\) :

Initial moisture content [g/g] (Eq. 1)

\(Nu\) :

Nusselt number (Eq. 2)

\(C\) :

Experimental constant (Tables 2 and 3)

\(Re\) :

Reynolds number (Eq. 3a)

\(Pr\) :

Prandtl number (Eq. 3a)

\({K}_{v}\) :

Thermal conductivity of air [W/m2 °C] (Eq. 3a)

\(X\) :

Characteristics dimension [m] (Eq. 3a)

\({h}_{c}\) :

Convective heat transfer coefficient [W/m2 °C] (Eq. 3a)

\({h}_{c, avg}\) :

Average convective heat transfer coefficient [W/m2 °C]

\({h}_{m}\) :

Convective mass transfer coefficient [m/s] (Tables 2 and 3)

\({h}_{m, avg}\) :

Average convective mass transfer coefficient [m/s] (Tables 2 and 3)

\({h}_{e}\) :

Evaporative heat transfer coefficient [W/m2 °C] (Eq. 9)

\({h}_{e, avg}\) :

Average evaporative heat transfer coefficient [W/m2 °C] (Tables 2 and 3)

\(n\) :

Experimental constant (Tables 2 and 3)

\({Q}_{e}\) :

Rate of heat utilized to evaporate moisture [J/m2 s] (Eq. 4)

\(P\left(T\right)\) :

Partial vapour pressure at the temperature [N/m2] (Eq. 14)

\({T}_{c}\) :

Temperature of sample surface [°C] (Eq. 9)

\({T}_{e}\) :

Temperature just above sample surface [°C]

\({A}_{m}\) :

Mesh area [m2] (Eq. 6)

\({m}_{ev}\) :

Moisture evaporated [kg] (Eq. 8)

\({C}_{v}\) :

Specific heat of air [J/kg °C] (Eq. 10)

\(\gamma\) :

Relative humidity [%] (Eq. 6)

\(\lambda\) :

Latent heat of vaporization [J/kg] (Eq. 6)

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Authors and Affiliations

  1. Department of Aerospace Engineering, SJC Institute of Technology, Chikkaballapur, Karnataka, 562101, India

    Elavarasan Elangovan

  2. Department of Mechanical Engineering, National Institute of Technology Puducherry, Karaikal, U.T of Puducherry, India

    Sendhil Kumar Natarajan

Authors
  1. Elavarasan Elangovan
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  2. Sendhil Kumar Natarajan
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Contributions

Elavarasan Elangovan: data curation, conceptualization, investigation, formal analysis, writing original draft preparation.

Sendhil Kumar Natarajan: resources, validation, project administration, writing—review and editing, supervision, conceptualization.

Corresponding author

Correspondence to Sendhil Kumar Natarajan.

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The authors declare no competing interests.

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Elangovan, E., Natarajan, S.K. Convective and evaporative heat transfer coefficients during drying of ivy gourd under natural and forced convection solar dryer. Environ Sci Pollut Res 30, 10469–10483 (2023). https://doi.org/10.1007/s11356-022-22865-5

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  • DOI: https://doi.org/10.1007/s11356-022-22865-5

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