NOVELTY - The exchanger (10) has circular cross sectioned tubular bodies (12, 14) in which fluids flow, where a bridge (16) thermally links the tubular bodies. Fins extend radially and outwardly from non-shared outer walls, where the exchanger is immersed in an external fluid. A connector is provided in an external circulation system. The bridge is a common wall that is shared by the tubular bodies, and is a solid unit connecting the tubular bodies. The bridge receives a change phase material fluid. The fluids within the tubular bodies are separated from the external fluid by the outer walls.    USE - Modular,multi-mode one-piece heat exchanger for use with a system for recovering solar energy i.e. tracking type parabolic mirror solar heating system, for providing direct thermal exchange between fluids e.g. liquid, solid and gases (all claimed) such as oil, water and glycol, for applications in solar industry and/or in food industry. Uses include but are not limited to space heating applications, refrigeration applications, air conditioning applications, power plant applications, chemical plant applications, petrochemical plant applications, petroleum refinery applications, natural gas processing applications and sewage treatment applications.    ADVANTAGE - The exchanger can be used for a range of applications, and includes two fluids. The exchanger is manufactured in an inexpensive manner, and allows mass production in a range of sizes and lengths. The exchanger has less number of mounting operations. The exchanger is assembled in modules of a multiplicity of series connected in series or parallel so as to increase thermodynamic exchanges.    DETAILED DESCRIPTION - The external fluid is a flowing fluid or a non-flowing fluid or a partly flowing fluid such as liquids, solids and gases. The exchanger is made of extruded aluminum or aluminum alloy. The connector is a XGELTHERM (RTM: not defined) Grade 500 type connector. INDEPENDENT CLAIMS are included the following:    (1) a method for making heat exchanger    (2) a system for recovering solar energy by solar energy concentration.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a heat exchanger    Modular, multi-mode one-piece heat exchanger (10)    Cross sectioned tubular bodies (12, 14)    Bridge (16)