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Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Inadequate cooling of produce after it has been packed into ventilated packaging can result in inconsistent fruit quality. Misalignment of ventilation holes during stacking as well as the use of internal packaging, such as trays, polyliner bags and thrift bags reduces airflow distribution through the packaging. Consequently, the complex needs of maintaining the cold chain of perishable produce and the considerable variations in packaging designs have made it challenging to find an optimal ventilated package and stacking arrangement. The aims of this study were, therefore, to assess the status of ventilated packaging in the South African pome fruit industry, and to characterize the effects of package design and multi-scale packaging components on the resistance to airflow and cooling performance of apples under forced-air cooling conditions. A survey of the pome fruit industry identified over twenty packaging designs which were grouped into eleven unique designs and further categorised into either ‘display’ or ‘telescopic’ designs. Although South African fruit industry standards recommend ventilation areas of at least 5%, the ventilation areas of package designs identified from the survey varied considerably between <1 and 11%. Furthermore, the study showed that use of stacking renders many of the ventilation holes ineffective, due to blockages from adjacent cartons. The contribution of each component of the multi-scale packages used for handling apples was determined by analysis of pressure drop during forced-air cooling. The results showed when utilising a combination of cartons, fruit trays and plastic liner bags, the total pressure drop contribution of the cartons (8%) and fruit trays (3%) was minimal, while the use of plastic liner bags contributed 89%. However, in a carton and thrift bag packaging combination, the thrift bags contributed 66% to the pressure drop while the carton contributed 34%. The cooling results indicated a negative correlation between the total stack ventilation area and the cooling heterogeneity. In addition, the airflow velocity was correlated positively with fruit cooling rate and negatively with total moisture loss. Fruit packed inside polyliner bags had cooling rates four times slower than fruit on trays and three times slower in thrift bags. The use of liner bags blocked the ventilation holes, thereby reducing the airflow velocity. As a result of the longer cooling times in the polyliner bags, fruit remained at higher temperatures for longer periods, resulting in up to three times more moisture loss during forced-air cooling. In addition, a temperature gradient formed due to a progressive increase in air temperature through the stack, thereby resulting in a similar gradient of moisture loss. This research showed that airflow velocity and distribution were the most important factors contributing to the effectiveness of fruit cooling in multi-scale packaging. From a cold chain perspective, future packaging designs should therefore focus on optimising ventilation characteristics and alignment during stacking to ensure adequate airflow. Given the contribution of internal packaging to high resistance to airflow, such packaging components should be used with caution and only when necessary to meet physiological and market requirements. / AFRIKAANSE OPSOMMING: Onvoldoende verkoeling van vars produkte nadat hulle verpak is kan lei tot wisselende vruggehalte. Wanbelyning van ventilasiegate tydens stapeling sowel as die gebruik van interne verpakking soos rakkies (eng. “trays”), poli-etileensakke en drasakkies (eng. “thrift bag”) verminder die lugverspreiding deur die verpakking. Komplekse behoeftes om bederfbare produkte in die koue ketting te behou en die aansienlike verskille in verpakkingsontwerpe het dit 'n uitdaging gemaak om 'n optimale geventileerde verpakking en stapelskikking of -rangskikking te vind. Die doelwitte van hierdie studie was dus om die status van geventileerde verpakking in die Suid-Afrikaanse kernvrugbedryf te asseseer, en die gevolge van die verpakkingsontwerp en multi-skaal verpakkingskomponente op die weerstand teen lugvloei en verkoeling van appels onder geforseerde lugverkoeling te bepaal. ‘n Opname van die kernvrugbedryf het meer as twintig verpakkingsontwerpe geïdentifiseer, wat in elf unieke ontwerpe gegroepeer is en verder getipeer word in ‘vertoon’ en ‘teleskopiese’ kartonontwerpe. Alhoewel die Suid-Afrikaanse vrugindustrie-standaarde ventilasie areas van ten minste 5% aanbeveel, het die ventilasie areas van die verpakkingsontwerpe geïdentifiseer uit die opname aansienlik gewissel tussen <1 en 11%. Verder het die studie getoon dat gebruik van stapeling baie van die ventilasiegate ondoeltreffend laat weens blokkasies veroorsaak deur aangrensende kartonne. Die bydrae van elke komponent van die multi-skaal verpakkingskombinasies gebruik vir die hantering van appels was bepaal deur analise van die afname in lugdruk tydens geforseerde lugverkoelingskondisies. Die resultate het getoon dat wanneer ‘n kombinasie van kartonne, polietileensakke en vrugte plus rakkies gebruik word, die bydrae van die kartonne (8%) en vrugte plus rakkies (3%) tot die totale afname in lugdruk minimaal was, terwyl die gebruik van polietileensakke ‘n 89% bydrae gemaak het. In ‘n karton en drasakkie kombinasie het die drasakkies 66% bygedra tot die afname in lugdruk, terwyl die karton 34% bygedra het. Die verkoelingsresultate het 'n negatiewe korrelasie getoon tussen die totale stapelventilasie-area en die verkoelingsheterogeniteit. Daarbenewens was die lugvloeisnelheid positief gekorreleer met vrugverkoelingstempo en negatief gekorreleer met totale vogverlies. Die verkoelingstydperk van vrugte in die poli-etileensakke was vier keer langer as die rakkie met vrugte kombinasie en drie keer langer in die drasakkies. Die poli-etileensakke het die ventilasiegate versper en dus die lugvloeisnelheid verlaag. Weens die langer verkoelingstye in die poli-etileensakke was vrugte veel langer aan hoër temperature blootgestel, wat uiteindelik gelei het tot drie keer meer massaverlies gedurende geforseerde lugverkoeling. Daarby het ‘n temperatuurgradiënt gevorm as gevolg van ‘n progressiewe verhoging in lugtemperatuur deur die stapel wat gelei het tot ‘n gelykstaande gradiënt van vogverlies. Hierdie navorsing het getoon dat die lugvloeisnelheid en -verspreiding die belangrikste faktore was wat die doeltreffendheid van vrugverkoeling in multi-skaal verpakking geaffekteer het. Uit 'n koelketting perspektief moet die toekomstige verpakkingsontwerpe dus fokus op die optimalisering van ventilasie eienskappe en belyning (eng. “alignment”) tydens stapeling om voldoende lugvloei te verseker. Gegewe die bydrae van die interne verpakking tot hoë weerstand teen lugvloei, moet sulke verpakkingskomponente met omsigtigheid gebruik word en slegs wanneer dit nodig is om aan markvereistes te voldoen.

Content removed due to copyright restrictions: Smale, N.J. Tanner D.J., Amos N.D., Cleland D.J. (2003). Airflow properties of packaged horticultural produce - a practical study. Acta Horticulturae, (599), 443-450 / Horticultural exports are of economic significance to New Zealand. Only through providing consistently high quality products to distant markets can New Zealand hope to command a premium price. New Zealand's two major horticultural exports, apples and kiwifruit, are transported to foreign markets by sea; either in refrigerated holds on-board cargo vessels or in refrigerated containers. Long transit times mean that conditions in these systems must be carefully controlled to ensure high quality product arrives at market. Effective distribution of air is a key consideration in transport systems. A mathematical model to describe the flow of air in marine transport systems was developed. The model was based on a resistance network framework, relying on simplification of the complex geometry within the refrigerated space to a discrete number of flow paths and points of convergence and divergence. Correlations quantifying the flow resistance of each channel were required. Some of these correlations were already available, and some were developed specifically for this purpose. A general method for predicting the flow resistance of enclosed conduits based on the Darcy-Weisbach, laminar and Colebrook equations was found to be sufficiently accurate for use. The flow resistance of horizontally vented horticultural packages was quantified and the cause of the flow resistance investigated. Entrance and exit effects were found to be significant, and a relationship between vent size and flow resistance was developed. Air interchange between a vented carton and the general refrigerated space was shown to be a significant mode of heat transfer. The effect of vent design on the rate of air interchange was found to be complex. Quantitative relationships between vent characteristics and rates of air interchange could not be developed; however, some general observations were made. Vent size, aspect ratio and alignment were all found to affect the rate of interchange. An existing method for determining in-package fluid velocities was refined to improve the accuracy of data and reduce the measurement time. A low-cost method for measuring airflows in transport systems was also developed utilising thermistors. These thermistor anemometers were used to monitor velocities in four shipments of fresh produce from New Zealand. Three of the four vessels monitored showed large variation in the circulation rate in the period between evaporator defrosts due to frosting. In some cases, frosting was severe enough to cause loss of delivery air temperature control. Management of defrosts was identified as an area of improvement in refrigerated hold management. Validation of the model developed was performed using four systems: a laboratory scale test-rig, a 40' container and two of the surveyed refrigerated holds. Airflow predictions were used with a heat transfer model to predict in-package temperatures. Comparison of measured and predicted flows and in-package temperatures showed good agreement given uncertainty of geometry and input data. The implications of altering a number of operational and design variables in both containers and refrigerated holds were investigated using the developed models. Increased circulation rates were found to increase cooling rates and reduce temperature variability in both types of systems; however, the magnitude of the benefit decreased with increasing circulation rate. Removal of the floor gratings and the use of pallet bases as an air distribution channel was found to increase temperature variability in both types of systems. The magnitude of the increase was small in a 40' container but substantial in a refrigerated hold. The correlations and models developed in this thesis provide useful tools to analyse and optimise the design and operation of refrigerated marine transport systems.

Thesis (MComm)--Stellenbosch University, 1986. / ENGLISH ABSTRACT: This section of the researchproject examines the needs of the consumer in the Western Cape, with regard to the packaging of fresh produce. Information was obtained by means of questionnaires and analysed by a computer: the chi-square was used to determine statisfactical significance. It was found that the consumer prefers .prepacked fresh produce with the proviso that the product remains visible, for instance the guaze type bag / AFRIKAANSE OPSOMMING: sien item vir volteks.