Parametric Analysis of a Falling Film Pillow Plate Evaporator
Translated title
Parametrisk Analyse af en falling film pillow plate fordamper
Author
Olsen, Lasse
Term
4. term
Education
Publication year
2021
Submitted on
2021-05-27
Pages
101
Abstract
This project develops a parametric model to analyze heat transfer in a flooded falling film pillow plate evaporator, a plate-based heat exchanger where a thin liquid film flows downward while the refrigerant boils. The modeling first estimates the total thermal resistance by combining three types of heat transfer and accounting for two effects: possible dry-out during evaporation, and changes in boiling heat transfer as a function of refrigerant quality (vapor fraction). The heat exchanger is simulated using the cell method, which divides it into small cells. The model is validated against data from ATHCO (a pillow plate manufacturer) and predicts the overall heat transfer coefficient with an error of about 14%, mostly underpredicting heat transfer. This accuracy is considered acceptable, so a parametric analysis of design and operating conditions is performed. The results show that heat transfer can be improved by increasing area (e.g., greater height), increasing the temperature difference (by raising the inlet temperature or the falling film flow rate), or increasing the flow rates of the refrigerant and/or the falling film. Increasing the refrigerant flow rate is especially beneficial because it reduces the risk of dry-out.
Dette projekt udvikler en parametrisk model til at analysere varmeoverførsel i en flooded falling film pillow plate-fordamper, en pladebaseret varmeveksler hvor en tynd væskefilm løber nedad, mens kølemidlet fordamper. Først beregnes den samlede termiske modstand ved at kombinere tre former for varmeoverførsel og ved at tage højde for to forhold: mulig dry-out (at filmen tørrer ud) under fordampningen og ændringer i kogende varmeoverførsel som funktion af kølemidlets kvalitet (dampfraktion). Varmeveksleren modelleres med cell-metoden, som deler den op i små celler. Modellen valideres mod data fra ATHCO (producent af pillow plates) og forudsiger den samlede varmeovergangskoefficient med en fejl på ca. 14 %, oftest med en undervurdering af varmeoverførslen. Denne nøjagtighed vurderes som acceptabel, og derfor gennemføres en parametrisk analyse af design- og driftsparametre. Resultaterne viser, at varmeoverførslen kan forbedres ved at øge arealet (f.eks. større højde), øge temperaturforskellen (ved at hæve indløbstemperaturen eller flowet af falling film), eller øge flowet af kølemidlet og/eller falling film. At øge kølemidlets flow er særligt gavnligt, fordi det mindsker risikoen for dry-out.
[This apstract has been rewritten with the help of AI based on the project's original abstract]