Transactions of the ASAE Vol. 46(2): 423–432 E 2003 American Society of Agricultural Engineers ISSN 0001–2351 423 HEAT AND MOISTURE TRANSFER AND QUALITY CHANGES IN CONTAINERIZED ALFALFA CUBES DURING TRANSPORT S. Sokhansanj, H. Khoshtaghaza, G. J. Schoenau, E. A. Arinze, L. G. Tabil ABSTRACT. Most of the alfalfa cubes produced in North America are exported to the Pacific Rim countries. The alfalfa cubes may be exposed in transit to ambient conditions varying in temperature from below freezing to above 40°C and in relative humidity up to 100%. Heat balance equations based on bulk thermal diffusion and natural convection were developed. The governing partial differential equations were used to develop a numerical computer solution model. The temperatures of the headspace above the cubes and the container ceiling were required for prediction of cube temperatures. The model predictions agreed well with measured data during shipment of the cubes. Moisture transfer within the cube pile in the container was modeled with the assumption of no moisture transfer with the outside air (i.e., completely sealed condition). However, the calculated humidity ratio in the headspace was lower than the measured humidity ratio. It was therefore concluded that the source of the extra moisture inside the container was due to moist air from outside leaking into the container. The calculated spoilage potential agreed with the observation of mold on the cube. This model can be used to predict the onset of mold growth during transit. Keywords. Alfalfa, Container, Forage, Forage cubes, Heat transfer, Moisture transfer, Overseas shipping, Transportation. lfalfa cubes are produced from dehydrated or sun–dried alfalfa, which is chopped and pressed in a special pellet mill. A typical cube (fig. 1) is about 32 × 32 mm in cross–section and 40 to 100 mm in length. The cube has a specific density and a bulk density of about 0.85 and 0.47 Mg/m 3 , respectively. Canada and the U.S. are the major producers of alfalfa cubes; Japan is a major importer. In Canada, cubes are usually containerized (placed in large and sealed containers suitable for truck, train, or ship transport). The cube containers are shipped by rail to west coast ports in British Columbia, where they are transferred onto ocean–going vessels. The duration of the shipment from the processing plants in Canada to various destinations in the Pacific Rim countries varies from 14 to over 60 days. In contrast to bulk handling of alfalfa pellets, which are smaller in size, containerized alfalfa cubes do not undergo severe physical handling. However, cubes are a perishable commodity and may spoil by mold development in transit due to exposure to heat and moisture. Alfalfa cubes readily absorb moisture from a humid environment, and quickly become soft, weak, and moldy. Article was submitted for review in December 1998; approved for publication by the Food & Process Engineering Institute Division of ASAE in March 1999. The authors are Shahab Sokhansanj, ASAE Member Engineer, Professor, Department of Agricultural and Bioresource Engineering, University of Saskatchewan, Saskatoon, Canada; Hadi Khoshtaghaza, Assistant Professor, Department of Agricultural Engineering, University of Tarbiat Moddarres, Tehran, Iran; and Greg J. Schoenau, Professor, Department of Mechanical Engineering, Edwin A. Arinze, Research Scientist/Professor, Department of Mechanical Engineering, and Lope G. Tabil, Assistant Professor, Department of Agricultural and Bioresource Engineering, University of Saskatchewan, Saskatoon, Canada. Corresponding author: Shahab Sokhansanj, 245 East 17th St., North Vancouver, BC, Canada V7L 2V8; phone: 604–904–4272; e–mail: sokhansanjs@shaw.ca. Figure 1. Regular–size alfalfa cubes (30 mm × 30 mm × 40 mm long). Alfalfa cubes are highly valued for use in cattle and horse feed rations. However, buyers in Japan and other markets in the Far East demand a top–quality product with an attractive green color. Moldy cubes are downgraded or rejected outright at the port of destination. Preserving the green color of the cubes is important because the green color is associated with freshness and high–quality nutrients content. Mathematical modeling of heat and moisture transfer in perishable commodities during shipment is scarce in the literature. The available information addresses principally the storage of agricultural crops in non–insulated buildings. Yaciuk et al. (1975) and Smith and Sokhansanj (1989) showed that the effect of natural convection on the tempera- ture distribution in stored grain is minimal, and that the thermal environment in a freestanding grain bin can be modeled sufficiently accurately with the conduction equa- tion alone. Nguyen (1987) and Beukema et al. (1983) showed that the circulation of air in bulk grain is due to strong convection flows in the headspace of the container. Casada and Young (1994a) developed a model to predict heat and A