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Beside staple crops, the fruits and vegetables subsector contribute significantly to domestic and export markets. Yet, this subsector faces a number of challenges that limits its full growth potential. Through 383 randomly selected farmers' interviews in selected districts, the study revealed profound information on the vegetable value chain. Findings show that, there is fair participation of men (58%) and women (42%) in vegetable production. Majority of farmers were between 19 and 49 years old (70%), attained primary education (80%) and had more than 5 years in commercial vegetable production (71.8%). Further, 79.4% of farmers had less than 1 ha of vegetable farmland. Farmers cultivate a wide range of nutritious and commercially valued vegetables including broccoli (50.7%), cauliflower (37.3%), white cabbage (34.7%), crisphead lettuce (24.5%), Chinese cabbage (20.6%), zucchini (20.1%), carrot (18.5%), tomato (14.4%), purple cabbage (10.2%), beetroot (9.4%), African nightshade (8.4%), leaf lettuce (7.6%), green/snap bean (6.8%), snow/sugar-snap pea (5%), leeks (5%), spinach (4.2%), green pepper (4.2%), herbs (parsley, fennel and dill) (4.2%) and celery (2.9%). However, sustainable marketing of fresh vegetables is a challenge leading to most farmers opting to wholesale their produce at the farm gate (70.5%) instead of the marketplace, with the price often being set by the wholesale buyers (78.1%). With the exception of gender, household size, and farming experience; a farmer's location and primary education level had a slightly statistically significant (p = 0.044) influence on opting to use farmgate as the point of sales. The unpredictable market (100%), costly and low-quality inputs (36.4%), pests and diseases (35.2%), and shortage of cold storage facilities (22.9%) were claimed to hamper vegetable production and the producers. In general, vegetables subsector can grow significantly in Tanzania due to the availability of irrigated nutrient-rich land, favorable climate and productive workforce. Thus, good farming practices, marketing and cold chain facilities have the potential to reduce postharvest losses and help realize national sustainable development goals. Key words: Fresh vegetables, postharvest practices, marketing, constraints, cold chains, INTRODUCTION The agricultural sector contributes significantly to the national economy of Tanzania. The sector contributed 26.9% of the National GDP during the year 2020, whereby 15.4% of GDP contribution was [...]

This work conducted an experimental investigation of a small-scale organic Rankine cycle (ORC) system at designed operating and control conditions for low-grade thermal energy recovery application. In the ORC system, R245fa was selected as working fluid while a turboexpander (turbine) with a high speed and permanent magnet synchronous electricity generator was installed to produce electric power and two-plate type heat exchangers were designed as an evaporator and condenser. The effects of condenser cooling water temperatures and R245fa superheat at the turbine inlet on the system performance were measured and analyzed. Practically, to ensure safe operation of the ORC expander, the R245fa superheat at the expander inlet is controlled to remain constant. The experimental results showed that at constant heat source parameters (temperature and flow rate), the turboexpander power output and cycle efficiency increased with lower cooling water temperatures. Under the specified test condition ranges, the maximum turboexpander power generation could achieve 5.405 kW when the cooling water temperature and the pressure ratio were set at 23.0 °C and 7.3 respectively. On the other hand, at certain cooling water temperatures, the superheat at the expander inlet exerted a negative impact on the turboexpander and system performances when the evaporating pressure was kept constant. Ultimately, the superheat was found to be an important control parameter to ensure efficient and safe system operation. [ABSTRACT FROM AUTHOR]

Globally, there is no shortage of low-grade waste and renewable heat sources that can be converted into electricity and useful heat using applicable thermodynamic power cycles and appropriate working fluids. As a natural working fluid, CO 2 is a promising candidate for application in low-grade power generation systems but require optimised design and evaluation. Since CO 2 working fluid has a low critical temperature (31.1̊C) and high critical pressure (73.8 bar), a CO 2 low-grade power generation system will most likely undergo supercritical Rankine (T-CO 2 ) cycles. A T-CO 2 system normally consists of a CO 2 supercritical gas heater, expander, recuperator, condenser and liquid pump with the CO 2 gas heater being a crucial component in determining system thermal and exergy efficiencies. In this paper, the models of a thermal oil-CO 2 plate gas heater has been developed and validated with measurements of a 5 kW e T-CO 2 system test rig. The model is then integrated with other system component models to establish the system model. The system model can be used to evaluate and compare system performances at different operating conditions, including variable CO 2 gas heater pressures and heat sink parameters, thereby optimising system operations. [ABSTRACT FROM AUTHOR]

Abstract: A modern supermarket energy control system has a concurrent need for electricity, space heating or cooling, and food refrigeration. The power supply to the supermarket is primarily from the national grid, where losses in efficiency are due to the processes of energy conversion and transmission. Combined heat and power (CHP) offers the potential to locally produce electrical power and heating which could save energy and reduce CO2 emissions in the long run. During the summer months, as the space heating requirement in a supermarket is relatively small, the energy efficiency of a CHP installation can be improved by using excess thermal energy to drive a sorption refrigeration system to provide space cooling or refrigeration. This process is also known as tri-generation. In recent years, the use of CO2 as a refrigerant in supermarkets has received considerable attention due to its negligible contribution to direct greenhouse gas emissions and excellent thermophysical and heat transfer properties. Consequently, the application of a tri-generation system in a supermarket with CO2 refrigeration merits further investigation. In this paper, to evaluate the performance of a tri-generation system in the supermarket, a previously tested 80kWe microturbine device was applied into an operational supermarket to generate power and provide space heating and cooling through exhaust heat. The performance evaluation and comparison for this tri-generation application is based on the prediction from an integrated model of supermarket energy control, cascade CO2 refrigeration and tri-generation systems. The results from this simulation demonstrate the feasibility of a tri-generation system in the supermarket and pave the way for further consideration towards designs in future. [Copyright &y& Elsevier]