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Abstract
This paper contains an analysis of the process carried out in a heating system for the treatment of aqueous kaolin suspension in order to identify the causes of cyclical, relatively frequent loss of system functionality. The analysis showed that the main cause of the short usability time of the installation is the inappropriateness of the heat exchangers' construction for the implemented technology, while the physical and chemical parameters and the rheological properties of kaolin suspensions are of secondary importance. It is proposed to replace the plate heat exchangers used in the installation with heat pipe exchangers of special construction. The results of laboratory and experimental tests of a heat pipe exchanger designed specifically for the described application are presented. An empirical comparison of the effectiveness of the proposed heat exchanger with a double pipe exchanger was performed by conducting tests in the process conditions of genuine installations and using the method of ϵ–NTU for efficiency calculations.
NOMENCLATURE
| A | = | heat transfer area of double pipe heat exchanger, m2 |
| C | = | concentration,% m/m (percent by mass) |
| cp | = | specific heat at constant pressure, J kg−1 K−1 |
| D | = | internal pipe diameter, m |
| Dz | = | external pipe diameter, m |
| F | = | heat transfer area of heat pipe heat exchanger, m2 |
| K | = | fluid consistency index, Pa sn |
| K' | = | apparent fluid consistency index, Pa sn' |
| L | = | length of exchanger, m |
| = | mass flow rate, kg s−1 | |
| n | = | flow behavior index, dimensionless |
| n' | = | apparent flow behavior index, dimensionless |
| NTU | = | number of transfer units, dimensionless |
| = | heat transfer rate (heat “duty”), W | |
| R | = | correlation coefficient, dimensionless |
| R2 | = | determination coefficient, dimensionless |
| ReMR | = | Metzner and Reed Reynolds number, dimensionless |
| TM | = | methanol temperature, K |
| T | = | temperature, K |
| U | = | overall heat transfer coefficient, W m−2 K−1 |
| = | volumetric flow rate, m3 s−1 | |
| v | = | linear velocity, m s−1 |
| W | = | heat capacity rate, W K−1 |
Greek Symbols
| α | = | significance coefficient, dimensionless |
| ΔTm | = | logarithmic average temperature difference, K |
| δ | = | pipe wall thickness, m |
| ϵ | = | thermal efficiency of heat exchanger, dimensionless |
| ηh | = | temperature efficiency of the hot fluid, dimensionless |
| ρ | = | density, kg m−3 |
Subscripts
| c | = | cold fluid (heat-receiving fluid) |
| con | = | condensation zone |
| DP | = | double pipe |
| ev | = | evaporation zone |
| h | = | hot fluid (heat-releasing fluid) |
| HP | = | heat pipe |
| p | = | pasteurization |
| s | = | suspension |
Superscripts
| in | = | inlet |
| out | = | outlet |
Additional information
Notes on contributors
Halina Marczak
Halina Marczak is an assistant professor in the Department of Safety, Process Engineering, and Ecology in Lublin University of Technology, Lublin, Poland. She received her Ph.D. in mechanics and machinery construction from the Lublin University of Technology, Lublin, Poland. She is currently working on enhanced heat transfer in heat exchangers.
Lech Hys
Lech Hys is an assistant professor in the Department of Safety, Process Engineering, and Ecology in Lublin University of Technology, Lublin, Poland. He received his Ph.D. in mechanics and machinery construction from the Lublin University of Technology, Lublin, Poland. He is currently working on enhanced heat transfer in heat exchangers.