Review of research and application of evaporative cooling in preservation of fresh agricultural produce

Extensive review of evaporative coolers for the preservation of fresh agricultural produce in some countries was presented.Most of the designs employ mainly direct evaporative cooling methods which are simple but with lower thermal performance,and can only be used for short term storage of agricultural produce with moderate respiratory rates.Researches into novel technologies in evaporative cooling systems which can improve the cooling performances,such as membrane air treatments,dew point type and heat pipe type heat exchanger in indirect/direct evaporative cooling application,and their feasibilities in agricultural storage are either absent or scarce.Some kinds of materials especially agricultural residues have been used for air water contact in evaporative cooling in different climates,but most of the analyses focused on effect of air flow rate and pad thickness on the cooling effectiveness,and the energy efficiency and evaporation loss of these materials in most cases were not evaluated or presented.The paper highlights the prospects and constraints of commercialization and marketing of evaporative coolers in some developing countries,and the general weakness in researches and the ways forward in new area of research and development are concluded.

Investigation of the structural changes of cocoa bean (with and without seed coat) during convective drying

The influence of seed coat on the behaviour of heterogeneous structure of cocoa bean(frosteros sp.)during convective drying with tempering period was investigated in an isothermal condition.It was found that the removal rate of moisture and air diffusion between the cocoa kernel and seed coat is not the same especially at the temperature of 55℃and initial drying time for all temperatures used.When the drying temperature increased to 70℃and 81℃,the cocoa kernel and the seed coat shrinks simultaneously,indicating that the rate of moisture and air removal from the kernel through the seed coat are the same.Change in sphericity of the bean was more pronounced at the temperature of 55℃for the seeds with seed coat while for all other drying conditions it remains fairly constant after one-hour drying.

Water absorption characteristics of Canarium Schweinfurthii fruits

Water absorption characteristics of two varieties of Canarium Schweinfurthii engl.fruit(Canarium Schweinfurthii engl.long and short)essential for predicting their suitable absorption conditions was investigated at three different temperatures(35,50,65
C).Increase in moisture content of the fruits was measured at one-hour interval until constant values were obtained after five successive intervals of moisture measurements.Loss of soluble constituents,textural and nutritive qualities of the rehydrated products and their thermodynamic behavior were also measured and calculated.The results obtained revealed that saturation time for 35,50 and 65
C of long and short varieties are 14,18 and 40 h and 18,22 and 36 h respectively.Rate of absorption of the fruits differ significantly(p>0.05)with temperature and not with the variety.Water absorption rate of Canarium Schweinfurthii engl.long and short varieties are 2.71 and 2.25 kg/h respectively.The moisture bearing capacity,textural,and nutritive qualities of the reconstituted products showed no significant difference among varieties at different temperatures used.Fruits soaked at 35
C produced reusable residual water,retained their nutritive values and soluble constituent more than other soaking temperatures studied.However,the absorption reaction is endothermic with negative entropy and Gibbs energy values were above zero.Midilli model had the best quality for describing the absorption characteristics of both Canarium Schweifurthii engl.fruits.