Heat transfer system using solar energy

Abstract

A system for heating a fluid conveyed or contained in a pipe or other process equipment by solar energy is disclosed. The system includes passive and active control methods to control the temperature of the fluid within a selected temperature range. The passive methods use the natural properties of selected materials for the system and the geometry and the orientation of the materials to control the temperature range. The active methods uses one or more than one control mechanism for changing the ratio of energy gain and heat loss at any point in time during a day and between days and across seasons, with these mechanisms including mechanisms to control energy transfer in and heat transfer out of the fluid.

1 . A system for heating a fluid conveyed or contained in a pipe or other process equipment by solar energy includes:
 (a) an aperture for allowing energy transfer from solar radiation to the fluid, the aperture including a layer of a first material on at least a part of the pipe or other process equipment, with the layer of the first material being (i) transparent to solar radiation so that solar radiation can pass through the first material with minimal energy loss and heat the fluid during periods when solar radiation is incident on the pipe or other process equipment and (ii) a thermal insulator to minimise heat loss from the fluid via the first material at all times, and   (b) a layer of a second material on at least a part of the pipe or other process equipment that is not transparent to solar radiation and is a thermal insulator to minimise heat loss from the fluid via the second material at all times.   
     
     
         2 . The system defined in claim I wherein, in a case of process equipment in the form of a cylindrical pipe that has an aperture defined by lengthwise extending sides that extend outwardly, typically radially outwardly, from the pipe, the sides include a reflective surface on the sides of the aperture to reflect solar radiation from the reflective surface into the aperture to increase the heat gain in the fluid in the pipe. 
     
     
         3 . The system defined in  claim 1  includes an optical element such as a reflector that increases the amount of solar radiation that is incident on the aperture to increase the heat gain in the fluid in the pipe or other process equipment. 
     
     
         4 . The system defined in  claim 1  wherein the aperture includes an emissivity control means that reduces the emissivity of the aperture to minimise loss of heat from the pipe of other process equipment by radiation. 
     
     
         5 . The system defined in  claim 6  wherein the emissivity control means includes a low emissivity coating on the pipe of other process equipment. 
     
     
         6 . The system defined in  claim 6  wherein the emissivity control means includes a means that changes the optical characteristics of the aperture to minimise loss of heat from the pipe or other process equipment via the aperture by conduction and/or convection and/or radiation. 
     
     
         7 . The system defined in  claim 6  wherein the emissivity control means includes an air gap between the section of the pipe or other process equipment and the layer of the first material. 
     
     
         8 . The system defined in  claim 6  wherein the emissivity control means includes a material for the first layer that transmits certain wavelengths of solar radiation and prevents or minimises transmission of heat via radiation emitted from the fluid in the process equipment. 
     
     
         9 . The system defined in  claim 10  wherein the material for the first layer is selected to transmit short wavelength radiation through the layer to the pipe of other process equipment and to minimise or prevent transmission of longer wavelength radiation emitted from the pipe or other process equipment. 
     
     
         10 . The system defined in  claim 1  includes locating the aperture in a relatively shielded area, i.e. an area of the process equipment that does not transfer heat to the same extent as other areas of the pipe or other process equipment to minimise heat loss from the pipe or other process equipment. 
     
     
         11 . The system defined in  claim 10  wherein the aperture is positioned in a downwardly-facing section of the pipe of other process equipment so that the layer of the first material is shielded from direct exposure to solar radiation. 
     
     
         12 . The system defined in  claim 11  includes an optical element such as a reflector for increasing the amount of solar radiation that is incident on the aperture. 
     
     
         13 . The system defined in  claim 1  includes means for controlling the temperature of the fluid in the pipe or other process equipment to be at a target temperature or within a selected target temperature rang; and with minimal variations in temperature, during each 24 hour period. 
     
     
         14 . The system defined in  claim 13  wherein the aperture is formed to selectively allow the transmission of solar radiation through the aperture depending on the position of the Sun in relation to the pipe or other process equipment to control the amount of solar radiation that is transmitted to the fluid during different periods of the daylight hours and taking into account seasonal issues, i.e. the different position of the Sun in different seasons. 
     
     
         15 . The system defined in  claim 14  wherein the aperture is formed or arranged to selectively control (i.e. minimise) the transmission of solar radiation through the layer of the first material during the middle of a day when there is a high concentration of solar radiation that is incident on the pipe or other process equipment and hence a higher possibility of overheating the fluid than at other parts of the day or when the pipe is already at the target temperature. 
     
     
         16 . The system defined in  claim 14  wherein the layer of the first material includes a material that comprises a bundle of parallel hollow tubes of transparent or partially transparent material or of a material that has reflective walls that are selectively positioned so that the length dimension of the tubes is aligned with the direction of solar radiation during cold periods (which may be a part or parts of a day or across a number of days or seasonal) so that there is minimum restriction to transmission of solar radiation and, as a consequence, the length dimension of the tubes is not aligned with the direction of solar radiation during hot periods (which may be a part or parts of a day or across a number of days or seasonal) so that there is maximum restriction to transmission of solar radiation during this period. 
     
     
         17 . The system defined in  claim 14  wherein the aperture includes a plurality of louvers that are fixed or selectively adjustable to control the amount of solar radiation that is transmitted through the aperture. 
     
     
         18 . The system defined in  claim 14  includes an optical element such as a reflector that increases the amount of solar radiation that is incident on a given area of the aperture and can be adjusted to vary the amount of reflected solar radiation that is incident on the aperture during the course of the daylight hours. 
     
     
         19 . The system defined in  claim 13  wherein the aperture is formed to be responsive to temperature. 
     
     
         20 . The system defined in  claim 19  wherein the aperture includes a thermochromic layer which reduces the transmission of solar radiation when the temperature of the thermochromic layer reaches a threshold temperature and vice versa. 
     
     
         21 . A pipe or other process equipment and the system for heating a fluid conveyed or contained in the pipe or other process equipment defined in  claim 1 .