Airflow measurement techniques for the improvement of forced-air cooling, refrigeration and drying operations

Abstract

Flowrate and distribution of air is a critical design factor in the cooling, refrigeration and drying of horticultural food products. These operations rely on a constant supply of air distributed throughout bulk arrangements of the produce. Local distribution of the air is critical to optimizing the design and efficiency of these processes. Identification of the key parameters affecting the airflow distribution has been done either experimentally (using intrusive point-wise or bulk measurement techniques) or numerically. The detailed information provided by the use of computational fluid dynamic models has facilitated unique opportunities to investigate alternative system designs, without the need for expensive and time consuming experiments. This study provides a review of the techniques available to measure airflow (thermal and rotatory vane anemometry, pressure differential devices, tracer gases, LDA and PIV). Their advantages and disadvantages (accuracy, resolution, application range, cost, and ease of use) as well as their application in the validation of numerical models are reviewed. The novel and scientifically based design guidelines developed by a better understanding of the airflow behaviour within the system for each of the operations under study are also presented.

Review on low‐temperature heat pump drying applications in food industry: Cooling with dehumidification drying method

“…In cooling, refrigeration and drying horticultural products distribution and flow rate of the air are the critical factors to be concerned (O'Sullivan et al, 2014). When the room air/atmospheric air moves over evaporator coil its DB temperature reduces and simultaneously moisture is also removed since the air is cooled below its dew point temperature.…”

“…Carbon dioxide (R744) is a commonly used natural refrigerant applied in food processing due to its eco‐friendliness, volumetric capacity, heat transfer properties, and heating capability at higher temperatures (Jangam & Mujumdar, 2011; Kim, Pettersen, & Bullard, 2004; Sarkar, Bhattacharyya, & Ramgopal, 2004). In cooling, refrigeration and drying horticultural products distribution and flow rate of the air are the critical factors to be concerned (O'Sullivan et al, 2014). When the room air/atmospheric air moves over evaporator coil its DB temperature reduces and simultaneously moisture is also removed since the air is cooled below its dew point temperature.…”

The cold chain in New Zealand – A review

“…The Centre for Postharvest and Refrigeration Research at Massey University has a strong tradition of conducting research with New Zealand's fruit export industries, and strengthening the cool chain of these industries. Foci of this research are associated with design of packaging to assist cooling and temperature control of fresh produce, (Defraeye et al, 2015;East et al, 2013b;Olatunji et al, 2016;O'Sullivan et al, 2013;O'Sullivan et al, 2016;O'Sullivan et al, 2017;, development of new methods to measure and cool chain systems (East et al, 2009;O'Sullivan et al, 2014;Redding et al, 2016;Huang et al, 2017;Olatunji et al, 2017), measurement of real world cool chain scenarios (East et al, 2003a;Bollen et al, 2015;O'Sullivan, 2016;Shim et al, 2016;Tanner and Paniagua et al, 2014;East et al, 2013a;East et al, 2013c;Paniagua et al, 2012;Zhao et al, 2015) culminating in the development of mathematical models to predict fruit quality based on supply chain temperature information (Hertog et al, 2016;East et al, 2016;East, 2011).…”

Measuring Device for Air Speed in Macroporous Media and Its Application Inside Apple Storage Bins

“…Laguerre et al [ 13 ] measured the air velocity with hot wire anemometers in the homogenized airflow in a supply air duct and in the air curtain of a display cabinet for cooling food packages in retail. Hot wire anemometers are not suitable for complex situations with high fluctuations [ 13 ] or airflow measurements inside packages or bulks because of the size of the probes up to 0.5 m length [ 14 ]. Alvarez and Flick [ 15 ] and Delele et al [ 16 ] studied air velocity and turbulence distribution inside vented bins for agricultural products with hot wire anemometer measurements.…”

“…To investigate airflow profiles more accurate techniques are available as laser Doppler anemometry (LDA) and particle image velocimetry (PIV). These methods allow determination of air velocity in the free space by analyzing tracer particle displacement [ 14 ] at defined measuring points (LDA) or in a field (PIV). Moureh et al [ 18 ] used LDA for measurement of airflow in a reduced-scale model of a truck for food transport.…”