NOMOGRAMS FOR DETERMINING THE THERMO-PHYSICAL PROPERTIES OF FRUIT JUICES
Abstract
Accurate thermophysical property data are indispensable for heat-transfer calculations, equipment sizing, and reliable control of thermal treatments in juice processing. Yet these properties depend jointly on temperature and soluble-solids content and can vary by cultivar, creating a gap between laboratory tabulations and day-to-day engineering needs. This study quantifies those dependencies for directly pressed apple juices from the Golden Rangers and Simirenko cultivars and introduces compact nomograms that enable rapid, instrument-free estimation of key properties during design and operation. Experimental measurements covered density (kg·m⁻³), kinematic viscosity (mm²·s⁻¹), thermal conductivity (W·m⁻¹·K⁻¹), and specific heat capacity (kJ·kg⁻¹·K⁻¹) across 20–90 °C and soluble-solids levels of 12–15%. The soluble-solids content in the tested juices was 12.7–14.3%, corresponding to 11.5–13 °Brix, consistent with single-strength apple juice. Nomograms were constructed from the experimental surfaces using separable temperature–solids mappings to ensure linear, parallel scales for temperature, solids, and the target property, providing accurate read-off within the measured domain. The data show that, within the studied range, higher soluble-solids content produces an average 3.2% rise in density. At 20 °C, kinematic viscosity was 1.45 mm²·s⁻¹ for Golden Rangers and 1.38 mm²·s⁻¹ for Simirenko; heating from 20 to 90 °C reduced viscosity by up to a factor of 3.1. Increasing soluble solids from 12% to 15% decreased thermal conductivity by up to 3.2%, whereas raising temperature from 20 to 90 °C increased specific heat capacity by about 3.7% (≈3% overall at 12.7–14.3% solids). Across compositions, specific heat varied by roughly 3–5% relative to the solids fraction. Practically, the nomograms allow engineers to (i) interpolate properties quickly for energy and duty calculations, (ii) compute Reynolds and Prandtl numbers for heat-exchanger design and verification, and (iii) evaluate how moderate shifts in °Brix or operating temperature affect residence time and thermal load during pasteurization (notably in tubular exchangers). The tools are intended for use within the measured bounds (20–90 °C; 12–15% solids); extension to broader °Brix ranges and additional fruit matrices represents a natural avenue for future work.